摘要:

Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) Structure and conformation of tri-O-acetyl-D-glucal dimer in solid state and in solution Andreas H. Franz,a Viktor V. Zhdankin,b Vyacheslav V. Samoshin,a Michael J. Minch,a Victor G. Young, Jr.c and Paul H. Gross*a a Department of Chemistry, University of the Pacific, Stockton, California 95211, USA. E-mail: afranz_bus@yahoo.com; vsamoshi@vms1.cc.uop.edu b Department of Chemistry, Duluth Campus, The University of Minnesota, Duluth, Minnesota 55812, USA.E-mail: vzhdanki@d.umn.edu c X-Ray Crystallographic Laboratory, Minneapolis, Minnesota 55455, USA X-Ray crystallography and 1H NMR spectroscopy indicate that the conformations of both rings A and B and the relative orientation of the rings in the C-linked disaccharide 1,3,4,6-tetra-O-acetyl-2-C-(4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro-hex-2- enopyranosyl)-2-deoxy-b-D-glucopyranose in solution are virtually identical to the crystalline structure.Due to increasing importance of C-disaccharides as mimics of natural O-disaccharides, we became interested in the chemistry of compounds with only one C–C bond between monosaccharide units.1 The first example of this type, reported by R.J. Ferrier and N. Prasad,2 was crystalline dimerisation product 1,3,4,6- tetra-O-acetyl-2-C-[4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro-hex- 2-enopyranosyl]-2-deoxy-b-D-glucopyranose 2, obtained in 10% yield upon the treatment of 3,4,6-tri-O-acetyl-D-glucal 1 with boron trifluoride in benzene (Scheme 1).† The structural assignment of 2 was based2 upon 1H NMR (100 MHz) coupling constants from cyclohexene systems3 and 2,3-dideoxy-2-eno-D-pyranoses4,5 with 5H0 conformation.Those spectra are now not state of the art because of non-first-order effects, poor resolution and overlap of signals. The reliability of chemical reasoning and deriving of the structure from optical rotation data2 is also questionable.6 Through the TOCSY and ROESY 1H NMR investigation of a saturated C-disaccharide prepared by hydrogenation of 2, Wessel and Englert6 have indirectly confirmed the original structural assignment for 2.2 Steel et al.7 reported the NOE confirmation of a structure for a major product obtained in AcClO4-induced dimerisation of 1.However they postulated a different anomeric form with an axial acetoxy group at C(1).7 In order to obtain a direct proof for the structure of 2 and to verify the NMR criteria for C-disaccharides of this type,1 we have performed an X-ray crystal structure analysis and 1H NMR measurements for compound 2.The conformational assignment for saturated ring A in 2 (Figure 1) is rather straightforward. The large spin–spin coupling constants H(1)A–H(2)A, H(2)A–H(3)A, H(3)A–H(4)A and H(4)A– H(5)A (Table 1) point to the trans-diaxial orientation of these pairs of protons, and, consequently, to the equatorial position of all substituents. The anomeric configuration is, therefore, b-D-gluco.For the conformational assignment of unsaturated ring B, Ferrier and Prasad2 used the three-bond vicinal and four-bond allylic–vinylic coupling constants in cyclohexene and † Compound 2 was synthesised according to a procedure proposed by Ferrier and Prasad2 and modified by us1 (Scheme 1) and separated from the mixture of products by flash chromatography on silica gel (ethyl acetate–hexane).The assignment of signals was made based upon COSY, NOESY and HETCOR experiments (Varian Mercury spectrometer, 300 MHz).dihydropyran systems:2,3–5 the vicinal coupling 3J ~ 2 Hz and the allylic coupling 4J –2.5 Hz for the quasi-axial allylic proton, and the vicinal coupling 3J ~ 5 Hz and the allylic coupling 4J –0.3 Hz for the quasi-equatorial proton. The values for conformationally biased 4-tert-butyl-5,6-dihydro-4H-pyran (2.2 Hz for vicinal and 2.0 Hz for allylic coupling of quasi-axial proton) obtained later8 are consistent with these estimations.The coupling constants were believed to be appreciably smaller for H(1)B due to the electronegativity of the endocyclic oxygen.2 Therefore, H(1)B, showing splittings of 1.2 and 2.0 Hz, was concluded to be quasi-axial, and H(4)B with splittings of 0.3 and 5.2 Hz, quasi-equatorial.2 The small coupling constant between H(4)B and H(5)B of 1.7 Hz supports a gauche orientation of these protons and, consequently, a trans-diaxial position of the 4Bacetoxy and 5B-acetoxymethyl groups.2 Thus, the NMR data are in accordance with the structure of 2 (Figure 1).Our measurements of signal splitting in 1H NMR spectra gave similar values for three- and four-bond couplings (Table 1), that support the suggested structure, provided the structural NMR criteria are valid for dihydropyran rings. The CDCl3 solution data are consistent with those previously published.3 The average position of the two ring planes in 2 may be considered nearly perpendicular based upon the small coupling constant between H(2)A and H(1)B.The value 3JH(2)A,H(1)B 1.2– 1.8 Hz points to a torsion angle of approximately 52–56° or 111–114° according to the Altona–Haasnoot equation9 (for a review of different versions of the Karplus equation see ref. 10). Interestingly, the conformational equilibrium for both rings appears to be strongly biased. The absence of a solvent dependence for intracyclic coupling constants (Table 1) also supports this idea. It is reasonable to assume that alternative conformations of the rings do not contribute to any detectable extent to the measured coupling constants.‡ An NOE between H(2)A and H(2)B, but no NOE at H(2)B when H(1)A was irradiated (the mixing time 300 ms), supports the overall conformation of 2 (Figure 1).‡ In case of the anomeric dimer7 the alternative conformation of ring B with a quasi-axial ring A, and a trans-diequatorial position of the 4Bacetoxy and 5B-acetoxymethyl groups was suggested based on the NOE data.O AcO AcO OAc O OAc OAc O OAc OAc OAc OAc BF3·Et2O 1 2 Scheme 1 O OAc OAc O OAc OAc OAc OAc B 2 5 4 6a 6b 4 2 3 1 6a 6b A 1 Figure 1 Structural assignment of compound 2 based upon 1H NMR data (Table 1). 5 3Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) Note that the reference values used for coupling constants in 2,3-dideoxy-2-eno-D-pyranoses4,5 are actually valid for a 5H0- conformation.For compound 2, however, a 5H0-conformation, as discussed above, could possess significantly different NMR coupling constants. Hence, an additional proof of this structure is still needed, which can be obtained by X-ray crystal structure analysis. In this work, the molecular structure of compound 2 has been established unambiguously by X-ray crystallographic data§ (Figure 2).Analysis of the data shows that there is virtually no difference between the solution and crystal conformations of both rings in compound 2. The proton coupling constants correspond satisfactorily to the endocyclic torsion angles in the crystal structure (cf. Figures 1 and 2).Also, the relative orientation of the rings does not change dramatically in solution. We determined the H(1)B–C(1)B–C(2)A–H(2)A torsion angle to be +58° in the solid state (MM2 estimation12 based on X-ray data). It agrees well with our torsion angle of approximately +52–56° obtained by the Altona–Haasnoot equation. Moreover, the orientation of the 5B-acetoxymethyl group with respect to ring B in solution corresponds perfectly to the solid state geometry.The value 3JH(5)B,H(6a)B 9.9–10.5 Hz points to the predominantly antiperiplanar orientation of these protons (cf. Figures 1 and 2). The solid state conformation of the 5A-acetoxymethyl group (Figure 2) is also preferred in CDCl3 § X-ray diffraction analysis. Crystals of compound 2 as thin long colourless needles were grown from methanol.Crystal data for 2 were collected at 173 K with MoKa-radiation on a Siemens SMART Platform CCD diffractometer: C24H32O14, M = 544.50, orthorhombic crystals, space group P212121, a = 5.6647(4), b = 13.4269(9), c = 34.744(2) Å with a = b = g = 90º, V = 2642.6(3) Å3, Z = 4, Dcalc = 1.369 g cm–3. The space group P212121 was determined based upon systematic absence of reflections and intensity statistics.11 The structure of compound 2 was solved by a direct method.All non-hydrogen atoms were refined with anisotropic displacement parameters; the hydrogen atom coordinates were refined isotropically. Based upon the starting material, the absolute configuration of 2 is D. R = 0.0812 for 2613 independent observed reflections [I > 2s(I)], wR2 = 0.1598.Atomic coordinates, bond lengths, bond angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC). For details, see ‘Notice to Authors’, Mendeleev Commun., Issue 1, 1999. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/41. aOverlapped. Table 1 Coupling constants and chemical shifts for 2 in various solvents (Varian Mercury spectrometer, 300 MHz). 3J CDCl3 [2H6]acetone [2H5]pyridine [2H6]DMSO d/ppm 3J/Hz d/ppm 3J/Hz d/ppm 3J/Hz d/ppm 3J/Hz H(1)A 1A–2A 5.85 9.0 5.73 9.0 6.32 9.0 5.82 9.0 H(2)A 2A–1A 2.14 9.0 2.09 9.6 2.45 9.0 2.30 9.6 2A–3A 11.1 11.1 10.5 10.5 2A–1B 1.8 1.8 1.2 0.9 H(3)A 3A–2A 5.38 11.1 5.26 11.4 5.83 10.8 5.30 11.1 3A–4A 9.3 9.0 9.0 9.3 H(4)A 4A–3A 4.93 9.9 4.77 9.3 5.37 9.6 4.81 9.9 4A–5A 9.9 9.3 9.6 9.9 H(5)A 5A–4A 3.74 10.2 ~3.9 –a 4.11 10.2 –a –a 5A–6A 3.6 –a 4.2 –a 5A–6bA 2.1 1.5 2.1 –a H(6a)A 6aA–5A 4.28 4.2 4.13 6.0 4.56 4.2 –a –a 6aA–6bA 12.3 13.0 12.3 –a H(6b)A 6bA–5A 3.99 1.8 3.84 2.1 4.31 2.4 –a –a 6bA–6aA 12.6 12.0 12.3 –a H(1)B 1B–2B 4.25 <1 4.23 1.8 ~4.4 –a –a –a 1B–3B <1 <1 –a –a 1B–2A 2.1 1.8 1.2 –a H(2)B 2B–1B 5.95 <1 6.00 1.8 6.07 1.2 –a –a 2B–3B 10.5 10.5 10.5 –a 2B–4B 1.5 <1 <1 –a H(3)B 3B–1B ~5.8 –a 5.76 2.4 5.93 2.4 –a –a 3B–2B –a 9.9 10.5 –a 3B–4B 4.8 5.4 5.7 –a H(4)B 4B–2B 4.71 <1 4.66 1.2 4.98 <1 –a –a 4B–3B 5.4 6.0 5.4 –a 4B–5B <1 1.2 0.9 –a H(5)B 5B–4B 4.14 <1 3.99 1.8 –a –a –a –a 5B–6aB 9.9 10.5 –a –a 5B–6bB 3.6 3.9 –a –a H(6a)B 6aB–5B 4.43 9.6 4.30 9.6 4.66 9.9 4.31 9.9 6aB–6bB 12.0 12.0 12.0 12.3 H(6b)B 6bB–5B 3.72 3.6 3.75 3.6 3.98 3.6 3.89 3.6 6bB–6aB 12.0 12.0 12.3 12.3 C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) C(13) C(14) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) O(9) C(2) C(1) C(3) C(4) C(5) C(6) O(1) C(7) O(2) C(8) O(3) C(9) O(4) O(5) C(10) Figure 2 Molecular structure of compound 2.Selected torsion angles (º): O(1)B–C(1)B–C(2)A–C(1)A –66.6(6), O(1)B–C(1)B–C(2)A–C(3)A 55.8(6), C(2)B–C(1)B–C(2)A–C(1)A 56.8(6), C(2)B–C(1)B–C(2)A–C(3)A 179.2(4). B AMendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) and pyridine. The small coupling constants 3JH(5)A,H(6a)A @ 4 Hz and 3JH(5)A,H(6b)A @ 2 Hz (Table 1) are indicative of the C(5)A– H(5)A bond bisecting the H(6a)A–C(6)A–H(6b)A angle (Figure 1).The data of X-ray crystal structure analysis and NMR measurements confirm the structure of compound 2 as found by Ferrier et al.2 The conformation was determined to be fairly rigid. The all-equatorial conformation of ring A is totally predominant for obvious reasons. The A moiety of molecule 2, as a very bulky substituent, strongly prefers the quasi-equatorial position, and forces 4B-acetoxy and 5B-acetoxymethyl groups to adopt an unusual diaxial conformation.Our conclusion was also supported by molecular mechanics calculations (MM212). The conformation under consideration is also fixed by multiple intramolecular dipole–dipole and van der Waals attractions (note the parallel orientation of the substituents in Figure 2, which has been reproduced by molecular mechanics).Intermolecular interactions of the same character probably contribute to the stabilisation of this conformation in the crystal state: all molecules are arranged in pairs by an attraction between the anti-parallel chains C(8)–C(10) (Figure 2). The results of this work also allow us to suggest a set of approximate ‘standard’ coupling constants for use in the structural analysis of 2,3-dideoxy-2-enopyranose systems with the a-erythro configuration in the unusual 5H0-conformation (Figure 3).References 1 Glycals II: A. H. Franz and P. H. Gross, Carbohydr. Lett., 1997, 2, 371. 2 R. J. Ferrier and N. Prasad, J. Chem. Soc. (C), 1969, 581. 3 E. W. Garbisch, Jr., J. Am. Chem. Soc., 1964, 5561. 4 R. U. Lemieux, E. Fraga and K. A. Watanabe, Can. J. Chem., 1968, 46, 61. 5 E. F. L. J. Anet, Carbohydr. Res., 1965, 348. 6 H. P. Wessel and G. Englert, J. Carbohydr. Chem., 1995, 14, 179. 7 A. L. J. Byerley, A. M. Kenwright and P. G. Steel, Tetrahedron Lett., 1996, 37, 9093. 8 A. DeBoer, Org. Magn. Reson., 1973, 5, 7. 9 C. A. G. Haasnot, F. A. A. M. De Leeuw and C. Altona, Tetrahedron Lett., 1980, 2783. 10 M. J. Minch, Concepts in Magnetic Resonance, 1994, 6, 41. 11 SHELXTL-Plus V 5.0, Siemens Industrial Automation, Inc., Madison, WI. 12 CAChe 3.5, CAChe Scientific, Inc., 1992. 2 O 1 R' 4 RO 5 OR 6b 6a 3 3JH1,H2 0–2 Hz 4JH1,H3 0–2.5 Hz 3JH4,H3 4.8–5.7 Hz 4JH4,H2 0–1.5 Hz Figure 3 Refined coupling constants for 5H0-conformation of 2,3-dideoxy- 2-enopyranose system. Received: Cambridge, 21st October 1998 Moscow, 10th November 1998; Com. 8/08179D

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) Synthesis of neoglycoconjugate dendrimers Dmitry E. Tsvetkov,a Pavel E. Cheshev,b Alexander B. Tuzikov,c Galina V. Pazynina,c Nicolai V. Bovin,c Robert Riebend and Nikolay E. Nifant’ev*a a N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow, Russian Federation. Fax: +7 095 135 8784; e-mail: nen@ioc.ac.ru b Higher Chemical College, Russian Academy of Sciences, 125819 Moscow, Russian Federation c M.M. Shemyakin–Yu. A. Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117871 Moscow, Russian Federation d Department of Cardiology, Bern University Hospital, CH-3010 Bern, Switzerland A series of polydentate dendritic neoglycoconjugates which contain 4, 8, 16, and 32 B-disaccharide ligands were designed as probes to assess the influence of inter-ligand distances on binding to anti-B-disaccharide immunoglobulins.Interactions of natural proteins and glycoconjugates which contain clustered oligosaccharide ligands play an important role in cell recognition processes.1 The affinity of carbohydrate ligands to proteins depends on spatial organisation of clusters and particularly on the distance between oligosaccharide ligands.2 These characteristics depend on the properties of the carrier molecule used for the preparation of neoglycoconjugates.To date, mainly linear polymers are used as carriers of carbohydrate ligands.1 However, linear polymer-matrix-based conjugates as probes have some disadvantages which are related to the uncertainty and unpredictability of the attachment of ligands within the carrier chain.These problems can be solved by substitution of linear polymeric matrices by dendritic ones (dendrimers), which are highly ordered compounds with a hyper-branched structure with branching sites on each monomeric unit.3 Dendrimers from symmetrical monomeric units are structures of special interest, because they can form polymeric molecules which have a spherical shape and a dense surface.4 Properties of dendrimers can be tuned by changing structure, geometry, size of monomeric units and initiator core.First examples of the preparation of dendritic neoglycoconjugates were published earlier.5–11 In this paper we describe the synthesis of dendritic neoglycoconjugates which contain 4, 8, 16, and 32 B-disaccharide [Bdi; a-D-Gal(1®3)b-D-Gal] ligands.Such glycodendrimers were designed as probes to assess the influence of inter-ligand distances on binding to anti-Bdi immunoglobulins which cause graft rejection in pig to human xenotransplantation.12 For the preparation of conjugates we used polyaminoamide (PAMAM) dendrimers as carriers of carbohydrate ligands. PAMAM carriers were selected due to their availability, high solubility in organic and aqueous phases and low toxicity.13 Synthesis of PAMAM dendrimers 2b–5b was performed according to Tomalia14 with the use of hexamethylene-diamine as the initial core (Scheme 1).Elongation and branching of dendritic chains was achieved by a sequence of stepwise reiterative reactions which included alkylation with methyl acrylate (5 equiv.CH2=CHCOOMe, MeOH, room temperature, 18 h) and amidation by an excess of ethylenediamine (5 equiv. NH2CH2CH2NH2, MeOH, room temperature, 48 h). Purification of aminoesters 2a–5a (Scheme 2) was performed by column chromatography on Kieselgel 60 (Merck) in ethanol, and aminoamides 2b–5b were purified by chromatography on TSK HW-40F gel in a 0.5% aqueous NH3 solution.All compounds were obtained as amorphous colourless solids. Structural assessment of PAMAM matrices was performed using 1H and 13C NMR including 2D 1H–1H and 1H–13C correlation spectroscopy and APT experiments. NMR spectra were recorded on a DRX-500 Bruker instrument; characteristic NMR data are presented in Tables 1 and 2.The completeness of elongation of side chains during iterative elongation steps was confirmed by integration of the signals of groups a + b, d + h and g (Table 1) in the spectra of polyamines 2b–5b. Signals in the NMR spectra of PAMAM derivatives depended on the pH values of solutions. Major changes in the 1H NMR spectra of PAMAM matrices were observed for the signals of fragments with amino groups due to their ability to form ions (Table 1).On the contrary, major changes of chemical shifts in 13C NMR spectra of the same compounds were observed for CH2 groups connected to carboxyamide fragments. Signals of the hexamethylenediamine core were pronounced in the spectra of tetra- and octaamines 2b and 3b. In the case of 16-dentate conjugate 3b, we detected these signals only at pH 1, and they were invisible at all pH values in the spectra of 32-mer 4b.Broadening and low intensity of some signals in the NMR spectra of dendrimers corresponded to published data.15–17 Table 1 1H and 13C NMR shifts for groups in aminoamide matrices 2b–5b (D2O, d/ppm). Group pH 1 pH 10 1H 13C 1H 13C a + b 1.25–1.35 23.8 1.35–1.45 26.4 1.60–1.70 26.3 1.55–1.65 27.6 c 2.65–2.85 52.6 2.45–2.60 53.3–54.0 d 3.53–3.57 34.5–35.5 3.30–3.43 49.8–50.2 e 3.23–3.32 52.0–53.0 2.60–2.80 33.1–33.7 f 3.40–3.52 49.8–52.0 2.65–3.00 41.5–42.0 g 2.65–2.85 29.4–29.9 2.45–2.60 51.5–53.0 h 3.03–3.10 39.3–40.2 3.30–3.43 38.0–39.5 i 3.40–3.52 37.2–38.3 2.65–3.00 40.2–40.8 CH2CH2CH2N CNHCH2 CH2N CH2CH2CNHCH2CH2NH2 O a b c d e f g h i O Scheme 1 (i) Branching and (ii) elongation of dendritic chain.Reagents and conditions: i, 5 equiv. CH2 =CHCOOMe, MeOH, room temperature, 18 h; ii, 5 equiv. (CH2NH2)2 , MeOH, room temperature, 48 h. H2N NH2 N N MeOOC MeOOC COOMe COOMe N N C C C C O NH NH2 O NH NH2 O O HN HN H2N H2N i iiMendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) Spacer-containing Bdi-derivative 7 was used as a carbohydrate ligand for preparation of dendritic neoglycoconjugate targets. This compound was obtained in 75% yield by selective N-acylation of 3-aminopropyl glycoside 618 with a 5 mol excess of bis(p-nitrophenyl) adipate (Scheme 3).The structure of compound 7 was confirmed by the data of 1H and 13C NMR spectra, which contained the complete series of expected signals.Conjugation of hexamethylenediamine and aminoamide matrices 2b–5b with spacer-containing Bdi-derivative 7 (reaction iii in Scheme 2) was performed in DMF (room temperature, 18 h), resulting in bidentate conjugate 1 and glycodendrimers 2c–5c in 51–86% yields. These amorphous colourless compounds were purified by column chromatography on the gel TSK HW-55F by elution with a 0.5% aqueous NH3 solution.Scheme 2 Synthesis of dendritic PAMAM and neoglycoconjugates. Reagents and conditions: i, 5 equiv. CH2=CHCOOMe, MeOH, room temperature, 18 h; ii, 5 equiv. (CH2NH2)2, MeOH, room temperature, 48 h; iii, 7, DMF, room temperature, 18 h. H2N NH2 [(CH2)3NHC(O)(CH2)4C(O)NH(CH2)3OBdi]2 iii i N N O R O R 2a R = OMe (82%) 2b R = NH(CH2)2NH2 (67%) 2c R = NH(CH2)2NH(O)C(CH2)4C(O)NH(CH2)3OBdi (51%) ii iii i O R O R N O NH O NH N R R N R R 2 3a R = (CH2)2COOMe (62%) 3b R = (CH2)2C(O)NH(CH2)2NH2 (74%) 3c R = (CH2)2C(O)NH(CH2)2NH(O)C(CH2)4C(O)NH(CH2)3OBdi (86%) ii iii N O NH O NH N N NH O N NH O N R R R R NH O N R R NH O N R R 4a R = (CH2)2COOMe (64%) 4b R = (CH2)2C(O)NH(CH2)2NH2 (73%) 4c R = (CH2)2C(O)NH(CH2)2NH(O)C(CH2)4C(O)NH(CH2)3OBdi (77%) ii iii i 2 N O NH O NH N N NH O N NH O N NH O N NH O N i O NH N R R O NH N R R O NH N R R O NH N R R NH O N R R NH O N R R 2 5a R = (CH2)2COOMe (58%) 5b R = (CH2)2C(O)NH(CH2)2NH2 (73%) 5c R = (CH2)2C(O)NH(CH2)2NH(O)C(CH2)4C(O)NH(CH2)3OBdi (66%) ii iii 1 (76%) NH NH O O N R R N R RMendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) We also investigated the possibility of glycodendrimer preparation using an alternative procedure based on the application of activated esters of dendrimeric matrices which were terminated with activated carboxyl groups.This way was less effective because the hydrolysis of PAMAM aminoesters (e.g. of compound 2a) and subsequent transesterification with CF3C(O)OSu/Py or CF3C(O)ONp/Py was accompanied by destruction processes and thus gave complex mixtures of products. The structural assessment of dendritic neoglycoconjugates was performed by 1H and 13C NMR as in the cases of parent PAMAM matrices.NMR spectra contained expected series of signals for the matrix part and spacer-containing B-disaccharide fragments (Table 2). The completeness of conjugation of terminal amino groups in PAMAM matrices with carbohydrate ligands was confirmed by the integration of signals for groups c and d in the matrix part and groups h, g and j in the spacer-containing ligand fragments (see scheme in Table 2) in the 1H NMR spectra of glycodendrimers 2c–5c.Chemical shifts of some signals in NMR spectra of glycoconjugates 2c–5c and particularly of CH2 groups in NHCH2- CH2N(CH2CH2CONH)2 fragments (but not methylenes in spacer of Bdi-ligands) were pH-dependent (Table 2).It is remarkable that the signals of carbon NCH2CH2CO were well resolved at pH 10, but were broadened at pH 5.5 and were not observed in the spectra at pH 3. 1H and 13C NMR signals of Bdi-parts in the spectra of glycoconjugates were pH-independent and consistent with the data reported earlier18 for parent amino-propyl glycoside 6.Investigation of the ability of dendrimers to bind to human xenoantibodies (IgG) was performed as described in refs. 19 and 20. Binding of the antibodies to a xenoantigen applied to immunological plates was inhibited with glycodendrimers 1,2c–5c and two reference substances: monomeric Bdi and a conjugate of the Bdi-ligand with polyacrylamide (Bdi–PAA) with a known high activity.18 The inhibitory activities of di-, tetra- and octameric glycoconjugates 1,2c and 3c were similar to those of the monomeric Bdi-ligand (IC50 ~ 500 mM); 16- and 32-dentate glycodendrimers had higher activities (IC50 ~ 60 mM and ~ 40 mM, respectively), but lower than that of Bdi–PAA (IC50 ~ 9 mM).For strong binding to antibodies, inter-ligand distances of the glycoconjugates should be comparable to the distance between antigen binding sites of an IgG immunoglobulin that has a value of 80–120 Å.21 In such a case, co-operative blockage of multiple binding sites can occur.The results of moleculardynamics simulations (15 ps, in vacuo, HyperChem 4.5) showed that, in the case of 16-mer 4c and 32-mer 5c, the inter-ligand distance reached the desirable values.Smaller activities of 4c and 5c as compared to that of Bdi–PAA may be due to the absence of an optimal topology in 4c and 5c for multiple and co-operative interaction with immunoglobulin. One can assume that an increased activity can be reached with larger dendrimers. To prove this assumption, we are currently performing a new synthesis of larger glycodendrimers, whose shape and size may elicit a higher inhibiting activity.In conclusion, we report a convenient way for the preparation of glycodendrimers with specified inter-ligand distances, which can be used as a tool for probing the interaction of carbohydrate receptors with antibodies and clustered lectins. This work was supported by INTAS (grant no. 94-4606), President of the Russian Federation (grant no. 96-15-96991) and the Russian Foundation for Basic Research (grant no. 97-03-33037a). References 1 D. Zanini and R. Roy, in Carbohydrate Mimics: Concepts and Methods, ed. Y. Chapleur, Chemie, Weinheim, 1998. 2 M. Mammen, Seok-Ki Choi and G. M. Whitesides, Angew. Chem., Int. Ed. Engl., 1998, 37, 2754. 3 G. R. Newkome, C. N. Moorefeld and F. Vögtle, Dendritic Molecules, Chemie, Weinheim, 1996. 4 D. Tomalia, A. Naylor and W. Goddard, Angew. Chem., Int. Ed. Engl., 1990, 29, 138. 5 K. Aoi, K. Itoh and M. Okada, Macromolecules, 1995, 28, 5391. 6 T. K. Lindhorst and C. Kieburg, Angew. Chem., Int. Ed. Engl., 1996, 35, 1953. 7 D. Page and R. Roy, Bioconj. Chem., 1997, 8, 114. aNMR signals of the B-disaccharide ligands are narrow lines, pH independent, and remain equal for all generations of glycodendrimers. 1H NMR (D2O) d: 5.19 (d, H1a, 2J 4 Hz), 3.91 (d, H2a), 4.0 (dd, H3a), 4.06 (br. d, H4a), 4.23 (br. t, H5a), 3.78 (m, H6,6'a), 4.48 (d, H1b, 2J 8 Hz), 3.87 (d, H2b), 3.80 (m, H3b), 4.20 (br. d, H4b), 3.68 (m, H5b), 3.78 (m, H6,6'b), 3.36 (m, 2H, CH2NH), 2.77 (m, 2H, NHCOCH2), 1.89 (m, 2H, OCH2CH2), 1.55–1.65 (m, 4H, CH2CH2CH2CH2). 13C NMR (D2O) d: 171.8 (CO), 171.1 (CO), 103.1 (C1a), 69.6 (C2a), 78.8 (C3a), 64.3 (C4a), 74.58 (C5a), 60.3 (C6a), 96.2 (C1b), 66.5 (C2b), 68.8 (C3b), 68.4 (C4b), 70.8 (C5b), 60.2 (C6b), 35.8 (CH2N), 35.0 (CH2COO), 33.2 (NHCOCH2), 29.4 (CH2), 24.6 and 23.8 (CH2CH2CH2CH2).Table 2 1H and 13C NMR shifts for matrices, spacer groups and B-disaccharidea ligands in glycoconjugates 2c–5c (D2O, d/ppm).Group pH 3 pH 5.5 pH 10 1H 13C 1H 13C 1H 13C a 3.12–3.20 37.20 3.18–3.35 37.20 3.35–3.47 36.32 b 3.58–3.63 48.64 2.53–2.80 50.90 2.61–2.67 50.80 c 3.41–3.47 51.60 2.72–2.98 49.74 2.68–2.76 49.99 d 2.68–2.75 n/d 2.32–2.52 33.0–34.0 2.39–2.47 33.27 e + f 3.12–3.20 39.68, 39.08 3.18–3.35 39.62, 39.37 3.30–3.47 39.44, 39.28 g 2.10–2.14 36.16 2.15–2.27 36.32 2.22–2.30 36.19 h 1.42–1.47 25.62, 25.56 1.48–1.62 25.72, 25.68 1.55–1.65 25.59 i 3.12–3.20 37.20 3.18–3.35 37.20 3.35–3.47 37.16 j 1.76 29.21 1.81 29.34 1.70–1.80 29.21 k 3.81 69.01 3.92 69.10 3.95 68.45 CNHCH2CH2N O CH2CH2CNHCH2CH2NHCCH2CH2CH2CH2CNHCH2CH2CH2OBdi O O O a b c d e f g h i k j h g Scheme 3 Synthesis of activated spacer-containing Bdi-derivative 7.O HO OH HO HO O O HO OH OH O NH2 6 (Bdi-OCH2CH2CH2NH2) 5 equiv.(CH2CH2COONp)2 DMSO/DMF, 75% O HO OH HO HO O O HO OH OH O NH 7 (Bdi-OCH2CH2CH2NHCOCH2CH2CH2CH2COONp) O ONp OMendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) 8 T. K. Lindhorst, C. Kieburg and U. Krallmann-Wenzel, Glycoconj. J., 1998, 15, 605. 9 D. Zanini and R. Roy, J. Org. Chem., 1996, 61, 7348. 10 D. Zanini and R. Roy, J.Am. Chem. Soc., 1997, 119, 2088. 11 P. R. Ashton, S. E. Boyd, C. L. Brown, N. Jayaraman, S. A. Nepogodiev and J. F. Stoddart, Chem. Eur. J., 1996, 2, 1115. 12 L. C. Paul, in Xenotransplantation, eds. D. C. C. Cooper, E. Kemp, K. Reemtsma and D. J. G. White, Springer, Heidelberg, 1991, p. 47. 13 R. Duncan and N. Malik, Proc. Int. Symp. Control. Rel. Bioact. Mater., 1996, 23, 105. 14 D. Tomalia, H. Baker and J. Dewald, Macromolecules, 1986, 19, 2466. 15 G. R. Newkome, C. D. Weis, C. N. Moorefield, G. R. Baker, B. J. Childs and J. Epperson, Angew. Chem., Int. Ed. Engl., 1998, 37, 307. 16 I. Gitsov and J. M. J. Frechet, Macromolecules, 1993, 26, 6536. 17 I. Gitsov and J. M. J. Frechet, J. Am. Chem. Soc., 1996, 118, 3785. 18 E. Yu. Korchagina and N. V. Bovin, Bioorg. Khim., 1992, 18, 283 (Russ. J. Bioorg. Chem., 1992, 18, 153). 19 R. Rieben, E. von Allmen, E. Y. Korchagina, U. E. Nydegger, F. A. Neethling, M. Kujundzic, E. Koren, N. V. Bovin and D. K. C. Cooper, Xenotransplantation, 1995, 2, 98. 20 E. Koren, F. A. Neethling, M. Koscec, M. Kujundzic, S. V. Richards, Y. Ye, R. Oriol and D. K. C. Cooper, 2nd International Congress on Xenotransplantation, Transplant Proc. 26:1166, 1994. 21 M. Marquart, J. Deisenhofer, R. Huber and W. Palm, J. Mol. Biol., 1980, 141, 369. [Brookhaven Protein Data Bank, 2ig2 entry]. Received: 4th November 1998; Com. 8/08870E

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) Influence of anions on the kinetics of hydrogen/sodium ion exchange in a crystalline acid zirconium phosphate Vitalii Yu. Kotov,a Irina A. Steninaa and Andrei B. Yaroslavtsev*b a Higher Chemical College, Russian Academy of Sciences, 125047 Moscow, Russian Federation b N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 117907 Moscow, Russian Federation.Fax: +7 095 954 1279 The rates of ion exchange in an acid zirconium phosphate in the presence of different sodium salts solutions and the diffusion coefficients were found to increase in the sequences I– < Br–< Cl– and ClO4 – < NO3 – < SO4 2– ; this phenomenon was explained by different mechanisms of defect formation.The rate-controlling step for the majority of solid-state reactions is the diffusion of cations through the product layer.1 The ionic diffusion within the bulk also plays a decisive role in various ion-exchange reactions. These reactions are most reliable because it is very easy to control changes in the reagent concentrations in the liquid phase. Recently, a method for determination of diffusion coefficients was proposed on the basis of studying the kinetics of ion exchange.2 It was found using this method that the diffusion coefficients of cations in the products of acid zirconium phosphate (a-ZrP) exchange [Na2Zr(PO4)2·3H2O] significantly depend on the pH values of the solution in contact.It was concluded that proton defect migration is a rate-controlling step.3 Anions present in solution can also take part in defect formation at the crystal surface and so affect the kinetics of ion exchange.Crystalline acid zirconium phosphate was synthesised by the well-known procedure.4 The substance was washed with water, treated in an ultrasonic bath to degrade agglomerates and then sieved. The fraction of 0.125–0.25 mm was used for the kinetic investigation.Potentiometric titration was made with an ‘Elchim’ pH meter. Zr(HPO4)2·H2O was equilibrated with 0.4 M NaCl, NaBr, NaI, NaClO4, NaNO3 and 0.2 M Na2SO4 solutions at 302±1 K. Portions of a 0.1 M NaOH solution were added step by step, and pH was measured every 3 s. After equilibrium was reached, the next portion of the alkali was added. The solution was intensely stirred during the experiment.The exchange in a-ZrP takes place by the migration of solid– solid interfaces between the two phases Zr(HPO4)2·H2O and NaHZr(PO4)2·5H2O or NaHZr(PO4)2·5H2O and Na2Zr(PO4)2 ·3H2O.5 Thus, the ion exchange at different steps can be described by the following equations: 8 7 6 5 4 3 0 100 200 300 400 500 600 t/s pH Cl Br I 6.5 6.0 5.0 4.0 3.0 0 100 200 300 400 500 t/s pH 5.5 4.5 3.5 2.5 NO3 SO4 ClO4 Cl Br I NO3 SO4 ClO4 11 10 9 8 7 6 5 0 100 200 300 400 500 600 700 800 900 pH t/s 11 10 9 8 7 6 5 0 100 200 300 400 500 600 700 800 pH t/s (a) (b) (c) (d) Figure 1 pH as a function of time: (a) and (b) I stage, the degree of exchange 58–77%, (c) and (d) II stage, the degree of exchange 17–36%; (a) and (c) in presence of NaCl, NaBr and NaI solutions, (b) and (d) in the presence of NaClO4, NaNO3 and Na2SO4 solutions.Zr(HPO4)2·H2O + Na+ + 5H2O NaHZr(PO4)2·5H2O + H3O+ NaHZr(PO4)2·5H2O + Na+ Na2Zr(PO4)2·3H2O + H3O+ +H2O (1) (2)Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) The typical time dependence of pH values for the process examined is shown in Figure 1.At the beginning of the first step of exchange, the pH values sharply decreased and rapidly attained a plateau [Figures 1(a) and (b)]. For the first stage (conversion <50%), the pH–time plot exhibits an inflection point at pH values close to that for the equilibrium point of the second stage [Figure 1(c)]. This phenomenon is due to the formation of a nonequilibrium disubstituted phase [Na2Zr(PO4)2 ·3H2O] at higher pH values.The low diffusion coefficients in this phase lead to inhibition of the overall process. The presence of this phase was found by X-ray diffraction.3 The further decrease in pH can occur only after redistribution of sodium ions and protons within particles according to the reaction The kinetic curves obtained for the first stage of the exchange in the presence of an Na2SO4 solution differ from the others [Figure 1(a) and (b)].After addition of NaOH, the pH values remain almost unchanged. This phenomenon is explained by low activity coefficients of hydrogen ions in the Na2SO4 solution, because the majority of protons was consumed by association with SO4 2– anions. The calculated amount of HSO4 – ions is much greater than that of the hydroxide ions added at the first stage of exchange. The monoexchanged phase is formed almost completely after equilibrium was reached with the Na2SO4 solution.Thus, the addition of the alkali leads only to neutralisation of acids in solution. This fact is responsible for small pH variation and short equilibration time during the first stage of exchange. In all cases, the nature of the anion does not affect the thermodynamics of exchange. The apparent diffusion coefficients as functions of the pH of solutions were calculated according to the equation suggested in ref. 2. Because of the formation of the nonequilibrium disubstituted phase, only a narrow range of pH is available for the correct determination of the diffusion coefficients of cations for the first stage [Figure 2(a) and (b)].At the second stage of exchange, the calculated diffusion coefficient is described by a more complex function of pH [Figure 2(c) and (d)]. The strong dependence of log D on pH and the independence of sodium ion concentration proves that the diffusion of proton defects in the ion-exchanger body is a rate-controlling step. The log D– pH curve can be divided into three almost linear portions corresponding to three different mechanisms of defect formation.The slopes of these curves are determined by the number of OH– anions, which is necessary for the formation of one defect in solids (a). For example, in the pH range 9–11, defects can be formed according to the equation: where the subscript H denotes the ion position in the crystal lattice, i denotes inerstitials, V denotes vacancies, and the superscripts • and ' denote the positive and negative charges of defects in the solid, respectively. Only a dynamic processes of single defect formation without charge compensation at the surface can correspond to the a = 1 or –1 values: Thus, the main types of proton defects in a-ZrP are vacancies (7 < pH < 11) and interstitials (5 < pH < 7).Note that the calculated diffusion coefficient depends on the nature of anions in solution. Its values increase in the sequences: I– < Br–< Cl–, ClO4 – < < NO3 – < SO4 2– [Figure 2(c) and (d)]. The most significant change in its magnitude occurs on going from sulfate to nitrate. This Cl Br I ClO4 NO3 SO4 Cl Br I ClO4 NO3 SO4 (a) (b) (c) (d) log D/cm2 s–1 pH –7.5 –8.0 –8.5 –9.0 –9.5 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 log D/cm2 s–1 pH –5.0 –6.0 –7.0 –8.0 –9.- 2.6 2.7 2.8 –10.0 log D/cm2 s–1 pH –9.0 –9.5 –10.0 –10.5 –11.0 6 7 8 9 10 11 –11.5 –12.0 –12.5 log D/cm2 s–1 pH –9.0 –10.0 –11.0 6 7 8 9 10 –12.0 Figure 2 Apparent diffusion coefficient as a function of pH: (a) and (b) I stage, the degree of exchange 19–38%, (c) and (d) II stage, the degree of exchange 17–36%; (a) and (c) in the presence of NaCl, NaBr and NaI, (b) and (d) in the presence of NaClO4, NaNO3 and Na2SO4 solutions. Zr(HPO4)2·H2O +Na2Zr(PO4)2·3H2O + 6H2O 2NaHZr(PO4)2·5H2O (3) HH + Na+ aq + OH– aq Na•i + V'H + H2O (a = 0.5) (4) 7 < pH < 9 HH + OH– aq V'H + H2O (a = 1.0) 5 < pH < 7 H+ aq H•i (a = –1.0) (5) (6)Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) fact can be explained only by the participation of anions in defect formation. Anions are unlikely movable through the lattice because of their large ionic radii. They can only take part in the defect formation at the surface. However, the defect concentration continuously changes in going from the ionite/ solution boundary toward the solid phase I/ solid phase II boundary because of diffusion.Thus, the total proton defect concentration in the sample and the average diffusion coefficient are determined by processes that take place at the crystal surface. Indeed, the surface density of the negative charges of anions decreases in the SO4 2–– NO3 – –ClO4 – and Cl––Br––I– sequences.The above sequence is determined by a decrease in the sorption ability of anions at the surface of double sodium zirconium phosphate. According to the data obtained, the additional defect formation in base solutions can be expressed by the equation where X is an anion, the subscripts PO4 and H denote the ion positions in the solid lattice. This equation describes the phosphate ions/X exchange on the particle surface.The formation of proton vacancies leads to charge compensation. For the solutions containing SO4 2– ions, this process is most pronounced, and, according to another charge of the anion, this equation transforms to Thus, the slope of log D–pH plots is the smallest in this case [Figure 2(c) and (d)]. At lower pH, the sorption of protons occurs at the interstitials on the crystal surface [equation (6)].In acid solutions, it becomes easy because of anion sorption on the surface, which decreases the positive charge. The higher the sorption ability of anions, the greater the concentration of proton defects and the higher the diffusion coefficient. The influence of the nature of anions on the kinetics of ion exchange decreases with increasing pH.This is due to high concentrations of OH– ions. In this range, their concentration becomes comparable to the concentration of the other anion in solution, and competitive processes take place. The presence of a trace concentration of Na2HPO4 in NaCl solutions increases the diffusion coefficient also due to the large sorption ability of the anion [Figure 3].This effect is more profound for the first stage [Figure 3(a)]. At the second stage, the sodium zirconium double phosphate remained in contact with the alkaline solution for a longer time, and hydrolysis can occur. As a result, the amount of phosphate ions added to the solution becomes comparable to that released in the hydrolysis. Thus, this effect becomes negligible [Figure 3(b)].Thus, the data obtained suggest that the kinetics of cation exchange can be affected by the nature of anions present in solution. An increase in the sorption ability of anions leads to an increase in the diffusion coefficients of cations in the double sodium zirconium phosphate hydrate due to defect formation. This work was supported by the Russian Foundation for Basic Research (grant no. 97-03-33736). References 1 S.A.Rise, Diffusion-Limited Reactions, Elsevier, Amsterdam, 1985. 2 A. B. Yaroslavtsev, Solid State Ionics, 1997, 97, 281. 3 V. Yu. Kotov, I. A. Stenina and A. B. Yaroslavtsev, Zh. Neorg. Khim., 1998, 43, 1786 (Russ. J. Inorg. Chem., 1998, 43, 1658). 4 G. Alberti and E. Torracca, J. Inorg. Nucl. Chem., 1968, 30, 317. 5 G. Alberti, Acc. Chem. Res., 1978, 11, 163. Cl Cl + 10–5 PO4 Cl + 10–4 PO4 (a) (b) –7.0 –7.5 –8.0 –8.5 –9.0 2.4 2.5 2.6 2.7 2.8 log D/cm2 s–1 pH Cl Cl + 10–5 PO4 Cl + 10–4 PO4 –9.5 –10.0 –10.5 –12.0 –13.0 6 7 8 9 10 log D/cm2 s–1 pH –12.5 –11.0 –11.5 11 Figure 3 Apparent diffusion coefficient as a function of pH in the presence of a 0.4 M NaCl solution with trace amounts of 0, 10–5 and 10–4 M Na2HPO4 solutions: (a) I stage, the degree of exchange 0–19%, (b) II stage, the degree of exchange 36–55%. OH– aq + X– aq + (PO4)PO4 + 2HH HPO4 2– aq + X•• PO4+ 2V'H + H2O (a= 0.33) (7) SO4 2– aq + (PO4)PO4 + HH HPO4 2– aq + (SO• 4)PO4 + V'H (a = 0) (8) Received: Moscow, 5th October 1998 Cambridge, 26th November 1998; Com. 8/07925K

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) Synthesis of bis(2-tetrahydropyranyl)methanes — new potential precursors for cyclic polyethers† Vyacheslav V. Samoshin,* Dmitriy E. Gremyachinskiy and Paul H. Gross* Department of Chemistry, University of the Pacific, Stockton, California 95211, USA. Fax: +1 209 946 2607; e-mail: vsamoshi@vms1.cc.uop.edu The TiCl4- or SnCl4-promoted cyclization of homoallylic alcohols with malonaldehyde bis(dimethylacetal) affords bis(2-tetrahydropyranyl) methane derivatives, which are potential precursors of C-(1®1)-disaccharides and other cyclic polyethers.Lewis acid promoted cyclization of homoallylic alcohols with aldehydes or their acetals was suggested for the preparation of 2,6-disubstituted tetrahydropyran derivatives.1 Later we developed the cyclization of this type for preparing synthetic intermediates for aminomethyl C-glycosides.2 Here we report the first one-step synthesis of structures containing two of these rings — bis(2-tetrahydropyranyl)methane derivatives 3 and 4, which may serve as convenient precursors for various C-(1®1)- disaccharides and as building blocks for the total synthesis of natural products such as polyether antibiotics and toxins.By TiCl4- or SnCl4-promoted cyclization of homoallylic alcohols 1 with malonaldehyde bis(dimethylacetal) 2 in the molar ratio 2:1, compounds 3 and 4 were prepared as a mixture of diastereomers, which was separated by flash chromatography.‡ The signals in well-resolved 1H NMR spectra of compounds DL-3, meso-3 and DL-4 (300 MHz, CDCl3) were assigned using the COSY and homonuclear decoupling technique.§ The large spin–spin coupling constants H(2)–H(3), H(3)–H(4), H(4)–H(5) and H(5)–H(6) proved the trans-diaxial orientation of these pairs of protons and, consequently, the thermodynamically most stable equatorial position of all substituents in these stereoisomers.The assignment of stereoisomers was also based on 1H NMR data.The identity of signals of the methylene bridge protons Ha pointed to the molecular C2 symmetry for the racemic mixtures of compounds D,L-3 or D,L-4. The methylene bridge protons Ha and Hb of the second stereoisomer 3 showed different signals thus proving the meso-configuration. Interestingly, DL-3 has a strong fresh odour, while meso-3 practically does not smell.Compounds 3 and 4 potentially can be functionalised in different ways2 providing an approach to various useful products, e.g., C-(1®1)-disaccharides. References 1 (a) R. C. Winstead, T. H. Simpson, G. A. Lock, M. D. Schiavelli and D. W. Thompson, J. Org. Chem., 1986, 51, 275; (b) N. A. Nikolic, E. Gonda, C. P. Desmond Longford, N. T. Lane and D. W.Thompson, J. Org. Chem., 1989, 54, 2748; (c) Z. Y. Wei, J. S. Li, D. Wang and T. H. Chan, Tetrahedron Lett., 1987, 28, 3441; (d) Z. Y. Wei, J. S. Li and T. H. Chan, J. Org. Chem., 1989, 54, 5768; (e) L. Coppi, A. Ricci and M. Taddei, J. Org. Chem., 1988, 53, 911; (f) L. Marko and D. J. Bayston, Tetrahedron, 1994, 50, 7141. 2 (a) P. H. Gross, Carbohydr. Polym., 1998, 37, 215; (b) M.Valdayo, D. Ngyen and P. H. Gross, Abstracts of 207th ACS National Meeting, San Diego, USA, 1994, CARB 4; (c) P. H. Gross, M. Suarez-Contreras, M. Valdayo, D. E. Gremyachinskiy and V. V. Samoshin, Abstracts of 215th ACS National Meeting, Dallas, USA, 1998, CARB 36. 3 R. J. Collins, B. Ellis, S. B. Hansen, H. S. Mackenzie, R. J. Moualim, V. Petrow, O. Stephenson and B. Sturgeon, J.Pharm. Pharmacol., 1952, 4, 693. 4 C. H. Heathcock, S. Kiyooka and T. A. Blumenkopf, J. Org. Chem., 1984, 49, 4214. † Part of this work was reported at the 19th International Carbohydrate Symposium, San Diego, USA, 1998. ‡ 5-Phthalimido-1-penten-4-ol 1 (X = phtN) was prepared by the treatment of phthalimidoacetaldehyde3 with allyltrimethylsilane and SnCl4 in CH2Cl2 (–55 °C) using a procedure described earlier.4 Bis(4-chloro-6-methyl-2-tetrahydropyranyl)methane 3.A solution of TiCl4 (25.0 g, 0.132 mol) in CH2Cl2 (200 ml) was added dropwise in 2 h to a stirred cold (–55 °C) solution of 4-penten-2-ol1,2 (9.5 g, 0.11 mol) and malonaldehyde bis(dimethylacetal) (Aldrich; 8.2 g, 0.05 mol) in CH2Cl2 (300 ml) under N2. The mixture was stirred for 24 h at room temperature, cooled (0 °C) and quenched by dropwise addition of cold 1 M HCl (250 ml).The aqueous layer was extracted with CH2Cl2 (2×50 ml). The standard procedure gave 13.9 g of slightly brown crystals containing approximately equal amounts of DL-3 and meso-3 (1H, 13C NMR). Separation by flash chromatography (silica gel, CHCl3) of a 5 g aliquot portion afforded 1.5 g of DL-3 (mp 122 °C, yield 30%), 1.56 g of a mixture of DL-3 and meso-3 (yield 31%), and 1.65 g of meso-3 (mp 112 °C, yield 33%).Found for DL-3 (%): C, 55.43; H, 7.89. Found for meso-3 (%): C, 55.71; H, 7.97. Calc. for C13H22Cl2O2 (%): C, 55.52; H, 7.89. Bis(4-chloro-6-phthalimidomethyl-2-tetrahydropyranyl)methane 4: SnCl4 was used as a reagent. A mixture containing DL-4, meso-4 and two minor stereoisomers with the axial position of chlorine atoms (1H, 13C NMR) was obtained in 73% yield.Found (%): C, 61.12; H, 5.01; N, 4.86. Calc. for C29H28Cl2N2O6 (%): C, 60.95; H, 4.94; N, 4.90. A sample of DL-4 was isolated from the mixture by flash chromatography (silica gel, CH2Cl2 + 5% MeOH; mp 213–215 °C). OH X OMe MeO OMe OMe HO X TiCl4 or SnCl4 CH2Cl2, –55 °C O O Cl Cl Hb Ha X X O Cl X O Cl X Ha Ha meso-3,4 D,L-3,4 1 1 2 3 X = H (93%) 4 X = phthalimido (phtN) (73%) 2 3 4 5 6 Received: Cambridge, 18th December 1998 Moscow, 10th January 1999; Com. 8/09855G § DL-3: 1H NMR, d: 1.19 (d, 6H, Me, J 6.2 Hz), 1.47 [dt, 4H, H(3)ax + + H(5)ax, J 12.6 and 11.6 Hz], 1.58 (dd, 2H, CH2-bridge, J 5.5 and 6.8 Hz), 2.09 [m, 4H, H(3)eq + H(5)eq], 3.45 [ddq, 2H, H(6), J 1.8, 11.3 and 6.2 Hz], 3.53 [dddd, 2H, H(2), J 1.8, 5.4, 6.8 and 11.5 Hz], 4.00 [tt, 2H, H(4), J 4.5 and 11.7 Hz]. 13C NMR, d: 21.79 (Me), 42.60 (CH2- bridge), 42.89, 44.32 (CH2), 55.79 [C(4)], 72.76, 73.02 [C(2)/C(6)]. meso-3: 1HNMR, d: 1.20 (d, 6H, Me, J 6.3 Hz), 1.50 [dt, 4H, H(3)ax + + H(5)ax, J 12.7 and 11.5 Hz], 1.55 (dt, 1H, CH2-bridge, J 13.9 and 6.0 Hz), 1.92 (dt, 1H, CH2-bridge, J 14.1 and 7.1 Hz), 2.13 [m, 4H, H(3)eq + H(5)eq, J 12.9 Hz], 3.44 [ddq, 2H, H(6), J 1.9, 11.0 and 6.2 Hz], 3.48 [dddd, 2H, H(2), J 1.9, 6.0, 7.0 and 11.5 Hz], 4.01 [tt, 2H, H(4), J 4.5 and 11.8 Hz]. 13C NMR, d: 21.74 (Me), 41.82 (CH2-bridge), 42.07 (CH2), 44.21 (CH2), 55.77 [C(4)], 72.82, 73.06 [C(2)/C(6)]. DL-4: 1H NMR, d: 1.42 [q, 2H, H(3)ax/H(5)ax, J 12.1 Hz], 1.47 [q, 2H, H(5)ax/H(3)ax, J 12.0 Hz], 1.49 (dd, 2H, CH2-bridge, J 5.8 and 6.6 Hz), 1.96 [m, 2H, H(3)eq], 2.02 [m, 2H, H(5)eq], 3.16 [m, 4H, H(2) + H(6)], 3.53 (dd, 2H, CH2N, J 4.1 and 13.7 Hz), 3.67 [tt, 2H, H(4), J 4.4 and 11.8 Hz], 3.72 (dd, 2H, CH2N, J 8.3 and 13.7 Hz) 7.76 (m, 4H, Ar), 7.89 (m, 4H, Ar). 13C NMR, d: 39.91 (CH2), 41.63 (CH2-bridge), 42.13 (CH2), 42.40 (CH2), 54.94 [C(4)], 72.94, 73.7 [C(2)/C(6)], 123.43, 131.99, 134.06 (CAr), 167.94 (CO).

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) EPR study of the reaction of C60 with chlorine dioxide: experimental evidence for the formation of the C60 radical cation Vyacheslav I. Sokolov,a Vasily V. Bashilov,a Qadir K. Timerghazin,b Elena V. Avzyanova,b Alexey F. Khalizov,b Nikolay M. Shishlovb and Valery V. Shereshovets*b a A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation. Fax: +7 095 135 5085; e-mail: sokol@ineos.ac.ru b Institute of Organic Chemistry, Ufa Research Centre of the Russian Academy of Sciences, 450054 Ufa, Russian Federation.Fax: +7 347 235 6066; e-mail: chemox@bash.ac.ru The interaction of chlorine dioxide with fullerene C60 affords a brown precipitate, and its EPR spectrum exhibits an asymmetric singlet signal (g = 2.0029, DHpp = 0.2 mT) tentatively assigned to the fullerene radical cation.With the development of a large-scale method for preparing fullerenes,1 the investigation of chemical properties of C60 became possible. It was found that C60 was reversibly reduced accepting up to six electrons with formation of the radical anions C60 ·n– or the anions C60 n–.2 On the other hand, oxidation of the fullerene is limited by the transfer of only one electron, yielding the radical cation C60 ·+. The formation of C60 ·+ in solution was observed upon oxidation of ground-state3,4 or triplet5–7 fullerene, as well as upon disproportionation of two 3C60 molecules.8 Chlorine dioxide9,10 is a mild one-electron oxidant [E(ClO2/ClO2 –) = 0.94 V, NHE, water11], which readily oxidises polyaromatic and heteroaromatic compounds into corresponding radical cations.12 At the same time, the redox potential of ClO2 is insufficient for the direct oxidation of ground-state fullerene [E(C60 ·+ /C60) = 2.00 V, NHE, benzonitrile13].Here we report the first investigation of a reaction between chlorine dioxide and fullerene C60. A solution of ClO2 in benzene (0.03–0.14 M) was added to a C60 solution in the same solvent (0.014 M); the ratios [ClO2]0:[C60]0 varied from 5:1 to 125:1 (25 °C).The solution turned opalescent, and a brown precipitate was formed 10–30 s after the reactants were mixed. At the instant the precipitate was formed, a flash of visible (350–600 nm) and IR (1000–1300 nm) chemiluminescence was observed (Figure 1).The EPR spectrum of the precipitate exhibits an asymmetric singlet with g = 2.0029±0.0002, DHpp = = 0.2 mT and the a/b ratio 0.75 (Figure 2). Similar singlets of the anti-Dysonian type were observed in the EPR spectra of hole-conduction polymers.14,15 The EPR spectra of a sample that was prepared in situ and of a sample isolated by centrifugation and dried in a vacuum were identical.No considerable EPR signals were detected in the solution over the precipitate. The estimated yield of spins is 0.3% with respect to the initial fullerene. Chlorine dioxide was completely consumed in the reaction with C60 up to the molar ratio [ClO2]0:[C60]0 = 60:1. As the [ClO2]0:[C60]0 ratio was further increased, unreacted chlorine dioxide could be detected in solution by EPR and UV-VIS spectroscopy.Thus, up to 60 molecules of ClO2 were consumed by one fullerene molecule. In the presence of even very small amounts of ethanol (ca. 1%), neither the precipitate formation nor the EPR signal were observed. Furthermore, the addition of ethanol to the precipitate led to a decrease in the EPR signal intensity.Two new bands at 900–1400 (br.) and 1732 cm–1 appeared in the IR spectra (KBr) of the precipitate obtained at the ratio [ClO2]0:[C60]0 = 20:1, whereas the characteristic bands of the fullerene at 528, 578, 1180 and 1428 cm–1 disappeared. We attributed this EPR signal to a radical cation of the fullerene or its derivative. Parameters of the signal are similar to those reported for C60 ·+ (g = 2.0024, DHpp = 0.08–0.13 mT), the DHpp value and the intensity weakly depend on temperature.8 Disappearance of the signal with the addition of ethanol testifies in favour of the radical cation nature of the signal, because it has been shown previously that alcohols readily react with C60 ·+.8 An induction period and high stoichiometry indicate that a multi-step process occurs in this system; apparently, chain decomposition of ClO2 takes place.The chemiluminescence during the reaction is also indicative of the complex character of this process. The origin of this chemiluminescence and its possible emitters are unclear at this time. The oxidation potential of the fullerene (C60 ·+ /C60) is substantially higher than the reduction potential of chlorine dioxide (ClO2/ClO2 – ).Thus, direct oxidation of the fullerene is highly improbable. The first step of the reaction can be the formation of a product of covalent addition of ClO2 to the fullerene, and its further oxidation by chlorine dioxide can lead to the radical cation. During the chain reaction, the formation of much stronger oxidants (e.g., ClO) is also possible.These oxidants can further react with C60 to form the radical cation. The latter can undergo the Friedel–Crafts type addition to an aromatic solvent (benzene or toluene) to give phenyl-substituted fullerenes.8 Intensity IR UV-VIS 0 20 40 60 80 t/s Figure 1 IR and visible chemiluminescence during the ClO2–C60 reaction ([C60] = 1.4×10–3 M, [ClO2] = 2.5×10–2 M, benzene solution, 25 °C).a b 334 335 336 337 H/mT Figure 2 EPR spectrum of the precipitate obtained at the ratio [ClO2]0/ [C60]0 = 20:1.Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) References 1 W. Kratschmer, L. D. Lamb, K. Fostiropoulos and R. D. Huffman, Nature, 1990, 347, 354. 2 D. Dubois, K. M. Kadish, S. Flanagan, R. E. Haufler, L. P. F. Chibante and L. J. Wilson, J.Am. Chem. Soc., 1991, 113, 4364. 3 J. W. Bausch, G. K. S. Prakash, G. A. Olah, D. S. Tse, D. C. Lorents, Y. K. Bae and R. Malhotra, J. Am. Chem. Soc., 1991, 113, 3205. 4 S. Nonell, J. W. Arbogast and C. S. Foote, J. Phys. Chem., 1992, 96, 4169. 5 S. Michaeli, V. Meiklyar, M. Shulz, K. Mobius and H. Levanon, J. Phys. Chem., 1994, 98, 7444. 6 G. Lem, D. I. Schuster, S. H. Courtney, Q.Lu and S. R. Wilson, J. Am. Chem. Soc., 1995, 117, 554. 7 M. Fujitsuka, A. Watanabe, O. Ito, K. Yamamoto and H. Funasaka, J. Phys. Chem., 1997, 101, 7960. 8 C. C. Yang and K. C. Hwang, J. Am. Chem. Soc., 1996, 118, 4693. 9 W. J. Masschelin and R. G. Rice, Chlorine Dioxide, Chemistry and Environmental Impact of Oxychlorine Compounds, Ann Arbor Science, Ann Arbor, 1979. 10 R. G. Gordon, R. G. Kieffer and D. H. Rosenblatt, Prog. Inorg. Chem., 1972, 15, 201. 11 N. V. Troitskaya, K. P. Mishchenko and I. E. Flis, Zh. Fiz. Khim., 1959, 33, 1614 (J. Phys. Chem. USSR, 1959, 33, 1577). 12 K. L. Handoo, S. K. Handoo, K. Gadru and A. Kaul, Tetrahedron Lett., 1985, 26, 1765. 13 D. Dubois, K. M. Kadish, S. Flanagan and L. Wilson, J. Am. Chem. Soc., 1991, 113, 7773. 14 M. Peo, S. Roth, K. Dransfeld, B. Tieke, J. Hocker, H. Cross, A. Grupp and H. Sixl, Solid State Commun., 1980, 35, 119. 15 N. M. Shishlov, I. V. Novoselov and M. G. Zolotukhin, Synth. Met., 1997, 84, 849. Received: 15th September 1998; Com. 8/07877G

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) Analysis of the phase equilibria in multicomponent systems using graphs Evgenii M. Slyusarenko,* Mikhail V. Sofin and Elshat Yu. Kerimov Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax +7 095 939 0171; e-mail: slusarenko@laincom.chem.msu.ru The possibility of polyhedration of multicomponent systems by the graph method was demonstrated using the Ni–V–Cr–Mo–Re system as an example.Phase diagrams form the basis for the majority of studies in the solid-state chemistry and materials science. However, promising multicomponent (n > 4) phase diagrams are presently difficult to study and very labour intensive. It is reasonable to subdivide this problem into two parts.Firstly, all phases formed in the test system and the phase equilibria are determined. This procedure is called the polyhedration of the system. Next, a portion of the system is examined in detail. This portion that shows promise for the development of new materials is chosen on the basis of data obtained at the first stage. Thus, the number of required experiments is considerably decreased.The graph method1–3 is holds the greatest promise for formalisation, systematisation, analysis and prediction of the structure of multicomponent systems. Essentially, this method consists in that any N-phase equilibrium can be represented as a complete graph with N vertices (Figure 1). In this case, each phase is depicted as a node of the graph (a point regardless of the number of components), and the edges represent the existing equilibria between the two corresponding phases.The graph that includes all equilibria in the system at specified temperature and pressure is a formalised isothermal cross-section of the phase diagram. The polyhedration of an n-component phase diagram by the graph method can be performed using data on the phase equilibria in (n – 1)-component systems in the following three consecutive stages: (1) Presentation of the isothermal cross-sections of (n – 1)- component systems as graphs.As an example, Figure 2 shows the graphs of the simplest isothermal cross-sections of ternary systems. Combinations of these graphs can give any formalised isothermal cross-section. (2) Construction of the graph of an n-component system (a total graph) is performed by taking the sum of the graphs of the (n – 1)-component systems.The number of nodes (points on the plane) of the resulting graph is equal to the number of phases in the n-component system. The edges of the graph are obtained by copying all edges from the source graphs of the (n – 1)-component systems to the graph of the n-component system. 1 2 3 4 5 6 Figure 1 Multiphase equilibria represented as graphs. A B C a b g A B C A B C A B C a a a b b a g a a a b (a) (b) (c) (d) Figure 2 The simplest isothermal cross-sections of ternary systems represented as graphs. Re Ni V s s' b g Re Mo Ni P g c d s' b Ni V Mo s d s' c Re Mo V P s b d g Cr Mo Ni Cr V Ni V Cr Mo Re Ni Cr Re Cr Mo Re Ni V s b g b s' b g b c s' s' s b g g b s Re s' Re P g d b s' c d s g b c s' b Re s P d g b g s' Re b b b g s s' Re c Re g s' b s Figure 3 Ternary isotherms and their graphs in the Ni–V–Cr–Mo–Re system at 1425 K.Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) (3) Decomposition of the total graph of the n-component system into graphs of the N- and (N – 1)-phase equilibria.Moreover, this division can be performed in a variety of fashions. In the division of a graph, it should be taken into account that phase equilibria in the (n – 1)-component systems provide incomplete information on all phase equilibria in the n-component system. Thus, the (N – 1)-phase equilibrium in the n-component Re s b d c g P s' Re g b Re s' b g s' P b P s' g P P b d g s g b s b g c s' Re d g P b P d s' s' Re P g b P s' b g g b s' Re b s' g s b Re s' g Re s' b Re s' c c Re s' b V–Cr–Mo–Re s' Re b g s Ni–V–Cr–Re c Re P g d b s' Ni–Cr–Mo–Re b s g d P Ni–V–Cr–Mo s b g Re c s' P d Ni–V–Mo–Re Figure 4 Total graphs of the quaternary systems and their decomposition into the graphs of three- and four-phase equilibria.Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) system can (i) degenerate into the n-component (N – 2)-phase equilibrium [Figure 2(b)]; (ii) recombine with the same (N – 1)- phase equilibrium to form the (N – 1)-phase region [Figure 2(c)]; (iii) participate in the formation of the N-phase equilibrium [Figure 2(d)]. Taking into account the aforesaid, the degenerated and recombined (N – 1)-phase equilibria should be separated from the total graph. The resulting graph will represent a collection of N-phase equilibria in the n-component system.The resulting graph completely characterises the number and composition of the N-phase equilibria, only if they do not form a general block. This is observed when several N-phase equilibria have alike (N – 1)-phase equilibria in a polyhedron.For instance, five phases in a four-component system can give two four-phase equilibria when two tetrahedrons come into contact by faces or three four-phase equilibria when three tetrahedrons come into contact by two faces. In a similar way, four tetrahedrons may come into contact by three faces. However, in this case, the fifth quaternary phase has no regions in the ternary isothermal crosssections, and the equilibrium is interpreted as four-phase.These quaternary phases are observed when a new compound that did not exist in the (n – 1)-component systems is formed. The method gives good results in metallic systems where the phases, as a rule, exhibit tightly packed structures. Consequently, the formation of multicomponent phases that do not occur in binary and ternary isothermal cross-sections is unlikely.We consider the five-component Ni–Cr–Mo–V–Re system starting from the three-component systems.1,2,4–10 Figure 3 demonstrates ten ternary isothermal cross-sections that form this quinary system and the corresponding graphs. Information on the phase equilibria in four-component systems can be obtained from the data on ternary systems using the above algorithm.Figure 4 shows the graphs of five fourcomponent systems (the total graphs), which were obtained by summation of the four corresponding graphs of ternary systems, and the decomposition of the total graphs into the elementary graphs of three- and four-phase equilibria. Note that several alternative four-phase equilibria can occur in only two systems (Ni–V–Mo–Re and Ni–V–Cr–Mo).In this case, as an initial approximation, we decided on a configuration in which the tetrahedrons of four-phase equilibria form a circuit. The obtained three-phase equilibria that have no regions in the ternary isotherms are shown as dashed lines. It was found1 that two four-phase equilibria, which come into contact via the three-phase equilibrium b–g–P, and the recombining three-phase equilibrium b–s–P occurred in the Ni–V–Cr–Mo system at 1425 K.These data are in complete agreement with the results of this work. To confirm the occurrence of the obtained phase equilibria in the Ni–V–Mo–Re, Ni–Cr–Mo–Re and Ni–V–Cr–Re systems, we experimentally examined the isothermal crosssections of these systems. The systems were investigated using diffusion couples, the superposition of diffusion zones and equilibrium alloys.11,12 Scanning electron microscopy, microprobe analysis on a CAMEBAX-microBEAM instrument and X-ray diffraction analysis were used.It was found both theoretically and experimentally that the following phase equilibria occur in the quaternary systems: (1) b–d–g–P, b–g–s'–P, s'–P–g–(Re), (Re)–s'–c, (Re)–s'–b and s–b–g in the Ni–V–Mo–Re system; (2) b–d–g–P, b–g–s'–P and s–b–g in the Ni–V–Cr–Mo system; (3) s'–P–g–(Re), s'–b–g, s'–b–P, b–P–d; P–d–g and (Re)– s'–c in the Ni–Cr–Mo–Re system; (4) (Re)–g–s', s'–b–g, s'–(Re)–b and s–b–g in the Ni–V– Cr–Re system; (5) s'–c–(Re) and s'–b–(Re) in the V–Cr–Mo–Re system.Based on the data concerning phase equilibria in the quaternary systems, phase equilibria in the quinary system can be determined.The following six four-phase equilibria occur in the Ni–V–Mo–Re, Ni–V–Cr–Re, Ni–Cr–Mo–Re, Ni–V–Cr–Mo and V–Cr–Mo–Re quaternary systems at 1425 K: b–d–g–P and b–g–s'–P in the Ni–V–Mo–Re system; s'–P–g–(Re) in the Ni– V–Mo–Re system; b–d–g–P and b–g–s'–P in the Ni–V–Cr–Mo system; s'–P–g–(Re) in the Ni–Cr–Mo–Re system.The identical four-phase equilibria recombine. Thus, the following three fourphase equilibria occur in the five-component Ni–V–Cr–Mo–Re system: (i) b–d–g–P formed by equilibria of the Ni–V–Mo–Re and Ni–V–Cr–Mo systems; (ii) b–g–s'–P formed by equilibria of the Ni–V–Mo–Re and Ni–V–Cr–Mo systems; (iii) s'–P–g– (Re) formed by equilibria of the Ni–V–Mo–Re and Ni–Cr–Mo– Re systems.In addition, there is also a three-phase region (s'–c–Re), which is the constituent of unknown four-phase equilibria including all these three phases. These four-phase equilibria can occur on the addition of a sixth component to the system. Next, we consider the equilibrium b + g (a region of chemical compatibility of fcc and bcc metals) in more detail. This equilibrium is involved in the two four-phase equilibria s'–P–b–g and d–P–b–g. Consequently, the two-phase region b + g is limited by three-phase equilibria (d–b–g, s'–b–g and P–b–g) in the sequence (s'–b–g) (P–b–g) (d–b–g).Thus, if all of the three phases (P, d, s') occur in a ternary or quaternary system along with the b- and g-solid solutions, two four-phase equilibria will occur in the quaternary system (Ni–V–Cr–Mo), and four-phase equilibria will degenerate in the ternary systems to result in the disappearance of the equilibrium b + g (Ni–Cr–Mo, Ni–Mo–Re).If one of these phases is absent from the ternary or quaternary system, for example, the P-phase, the four-phase equilibria will not occur, and a wide b + g region is limited by the three-phase equilibria d–b–g and s'–b–g (Ni–V–Mo).In the absence of d- and P-phases, the fourphase equilibria do not occur, and the two-phase b + g region is limited by only the three-phase equilibrium s–b–g (Ni–V–Cr, Ni–V–Cr–Re). The results of the polyhedration of the five-component system are important. First, the polyhedration was accomplished without problems in spite of the fact that only information on ternary systems was used.Second, multiphase equilibria in a multicomponent (n > 4) system are unlike, because a five-phase equilibrium was absent from the five-component system. Third, it is likely that the overlapping of several blocks of N-phase equilibria through the regions of (N – 1)-phase equilibria is represented as circuits without the formation of ring configurations; this fact makes it possible to restore missing data without difficulty.This work was supported by the Russian Foundation for Basic Research (grant no. 99-01-01197). References 1 E. M. Slyusarenko, Tezisy dokladov 5-oi Vsesoyuznoi konferentsii po kristallokhimii intermetallicheskikh soedinenii (Abstracts of Papers of the 5th All-Union Conference on the Crystal Chemistry of Intermetallic Compounds), L’vov, 1989, p. 94 (in Russian). 2 V. A. Borisov, PhD Thesis, Moscow, 1993 (in Russian). 3 V. A. Borisov, E. M. Slyusarenko, S. F. Dunaev and A. P. Babkin, Vestn. Mosk. Univ., Ser. 2: Khim., 1995, 36, 564 (in Russian). 4 E. M. Slyusarenko, A. V. Peristyi, E. Yu. Kerimov, M. V. Sofin and D. Yu. Skorbov, J. Alloys Compd., 1998, 264, 180. 5 M. Raghavan, R. R. Mueller and G.A. Vanghn, Metall. Mater. Trans. A, 1984, 15, 783. 6 A. A. Kodenzov, S. F. Dunaev and E. M. Slyusarenko, J. Less-Common Met., 1987, 141, 225. 7 A. A. Kodenzov, S. F. Dunaev and E. M. Slyusarenko, J. Less-Common Met., 1987, 135, 15. 8 S. B. Prima, V. N. Eremenko and T. N. Zhigunova, in Stabil’nye i metastabil’nye fazy v materialovedenii (Stable and Metastable Phases in the Materials Science), ed.V. N. Eremenko, Inst. problem materialovedeniya Akad. Nauk UkSSR, Kiev, 1987, p. 115 (in Russian). 9 S. B. Prima, L. A. Tretyachenko and G. I. Kostrigina, Dokl. Akad. Nauk UkSSR, Ser. A, 1979, 3, 230 (in Russian). 10 A. A. Kodenzov and E. M. Slyusarenko, J. Less-Common Met., 1989, 153, 15. 11 E. M. Slyusarenko, S. F. Dunaev, E. M. Sokolovskaya and A. A. Kodentzov, in Diagrammy sostoyaniya v materialovedenii (Phase Diagrams in the Materials Science), ed. V. N. Eremenko, Inst. problem materialovedeniya Akad. Nauk UkSSR, Kiev, 1984, p. 73 (in Russian).Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) 12 E. M. Slyusarenko, S. F. Dunaev and E. M. Sokolovskaya, Tezisy dokladov 6-go Vsesoyuznogo soveshchaniya ‘Diagrammy sostoyaniya metallicheskikh sistem’ (Abstracts of Papers of the 6th All-Union Conference ‘Phase Diagrams of Metal Systems’), Nauka, Moscow, 1982, p. 53 (in Russian). Received: Moscow, 20th July 1998 Cambridge, 1st October 1998; Com. 8/06224B

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) Nanoparticles of Ti and Zr in organosilicon polymer ceramic precursors Sergei P. Gubin,*a Ella M. Moroz,b Andrei I. Boronin,b Vladimir V. Kriventsov,b Dmitrii A. Zyuzin,b Nina A. Popova,c Elena K. Florinac and Alexander M. Tsirlinc a N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 117907 Moscow, Russian Federation.Fax: +7 095 954 1259 b G. K. Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation. Fax: +7 383 234 3056 c State Scientific Centre, Institute of Chemistry and Technology of Organoelement Compounds, 111123 Moscow, Russian Federation. Fax: +7 095 273 1323 A procedure was developed for introducing Ti and Zr nanoparticles into organosilicon polymer ceramic precursors; all of the particles were found to be multiphase and to contain the metals, metal carbides, and metal oxides assosiated with the polymer matrix.Organic polymers that contain metal nanoparticles occupy a significant place among nanostructured materials, the interest in which is currently growing like an avalanche.1 Metal nanoparticles (d < 10 nm) are unstable and highly reactive; they attracted considerable interest because of their unique physical properties. The up-to-date level of ceramic polymer technology is sufficiently high, and therefore, polymer matrices are preferable for the stabilisation of metal nanoparticles from the practical standpoint of the material science.It is well known that refractory metal heteroatoms of (Ti, Zr etc.) are effective stabilisers for ultrafine ceramic structures. Moreover, they also give an improvement in the refractory properties, thermal resistance and sintering ability.2 The direct introduction of metals into a ceramics is a rather difficult task because homogeneous distribution of metal nanoparticles in the solid structure is required, and no additional oxygen should be introduced.It is believed that the formation of ceramic materials via polymeric precursors3 opens up a new and effective way in this direction on condition that new methods for introducing metal nanoparticles will be developed. In recent years the problem of polymer stabilisation by metal nanoparticles has provoked considerable interest. Some ways have been proposed to introduce metal nanoparticles into organic polymer matrices.In chemically inert linear polymers such as polyethylene, metal nanoparticles are usually formed in situ as a result of fast thermal decomposition of a solution of metalcontaining compounds, which is introduced into a polymer solution or melt.4 The metal nanoparticles (stabilisers) primarily react with oxygen to yield inert products and hence prolong the lifetime of the polymer (prevent the degradation).5 In this study, polycarbosilane was chosen as the basic polymer; this ceramic precursor is usually formed by thermal rearrangement of polydimethylsilane.6 Polycarbosilane is a lowmolecular- weight polymer (MM = 1200–2000) with active Si–H and Si–C bonds; it is considerably different from polyethylene as a matrix.We performed a detailed investigation of the polydimethylsilane conversion into polycarbosilane to find optimum time and temperature for the introduction of metal-containing compounds. The intermediate and final products of polymer transformations were analysed by NMR, UV and IR spectroscopy, gas chromatography–mass spectrometry, gas chromatography and high-performance liquid chromatography.For the formation of Ti- and Zr-containing metal nanoparticles, we decided on oxygen-free compounds of these metals. We found that thermal decomposition of MCl4 (M = Ti or Zr) requires a large amount of active Si–H hydrogen to reduce the metal during the formation of metal nanoparticles.A different situation arises with thermal decomposition of (C6H5CH2)4Ti in polycarbosilane: toluene and dibenzyl (1:3) were quantitatively detected in the distillation products. That is, all benzyl radicals from the initial metal-containing compound7 predominantly undergo a homotransformation to release naked hot metal atoms, which become aggregated into metal nanoparticles. Cp2MCl2 (M = Ti or Zr) exhibits an intermediate behaviour under conditions of thermal degradation.It was experimentally found that the principal features of the process are the same as in the case of polyethylene: drop-by-drop addition and very fast thermal decomposition of metalcontaining compounds, complete removal of organic ligands and homogeneous distribution of metal nanoparticles as a result of intense agitation of the oligomer/polymer reaction mixture. It is believed that the polymer melt contains a large number of cavities (domains) distributed throughout a continuous medium.The decomposition of metal-containing compounds and subsequent particle nucleation proceed in these cavities.8 The transformation of polydimethylsilane into polycarbosilane at 300–380 °C usually takes about 28 h.It was found that the introduction of metals at an intermediate stage of synthesis is most effective. If the reaction is carried out in the presence of the products of thermal decomposition of the above Ti- or Zr-containing compounds, the reaction time can be shortened to 3–5 h. The process speeds up after the introduction of metals; however, any negative side effects were not detected.The study showed that, in this case, metal nanoparticles took part in rearrangement and polycondensation. An optimum time of contact between metal nanoparticles and the reaction mixture depends on the number of Si–Si bonds to be ruptured. The presence of additional Si–H groups in the polymer provides an opportunity to graft new active functional groups. The aforesaid suggests more active interaction between metal nanoparticles and polycarbosilane as compared with carbon-chain polymers.Polycarbosilane samples containing metal nanoparticles (nano- MPCS) with the Ti or Zr content no higher than 5 wt% were prepared from different metal-containing compounds.† Two † Satisfactory analyses for C, H, Si and metals were obtained for all samples by standard procedures.Zr/PCS PCS (initial) Differential curve 200 150 100 50 0 0 2 4 6 r/Å 4pr2r(r)/eI2 Å–2 Figure 1 X-ray RED curves for nano-ZrPCS.Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) series of analytical experiments were carried out with these materials. First of all, the polymeric portion of nano-MPCS was examined in comparison with the initial metal-free polycarbosilane.It was found that the method used for preparing nano- MPCS did not introduce additional oxygen, provided more regular polymeric structure and increased the amount of Si–H groups. The molecular-weight distribution (MWD) is consistent with that of the best samples of starting polycarbosilane. A narrow unimodal MWD a polydispersity index of about 2 was observed. The average molecular weight lied in the range 1000 to 1200.High-molecular-weight components (tails) were absent.‡ According to their rheological characteristics, nano-MPCS can be used as spinning melts at lower temperatures in comparison with unmodified polycarbosilane. A viscosity§ of about 1000 P, which is needed for the spinnability, was achieved at about 120–150 °C instead of initial 250–280 °C.Preliminary experiments showed that metal contents of up to 3% did not prevent stable spinning of fibres. TGA¶ of nano-ZrPCS exhibited a considerably larger yield of the solid phase (up to 10% at 1.0–1.3% of the metal) in comparison with the initial polycarbosilane. DSC analysis showed active exothermic processes over a broad temperature range and demonstrates some differences between nano-TiPCS and nano-ZrPCS.The behaviour of the latter is similar to that of the starting polycarbosilane. This is likely due to the wellknown fact that titanium, especially finely divided, exhibit higher catalytic activity. The nature of metal nanoparticles in polycarbosilane matrices was also analysed. Earlier, we have examined similarly obtained samples of model nano-MPCS containing up to 5 wt% Fe using X-ray emission and Mössbauer spectroscopy.9 We have found that polycarbosilane as a matrix does not differ from other examined polymers in both the structure of nanoparticles and the particle-size distribution: more than 80% of particles had a size of no more than 5 nm.All particles were multiphase: they contained iron, iron carbide and iron oxides.The formation of a FeSi phase was reliably detected; bonds between nanoparticles and the matrix were also detected as in other nanometallic polymers.10 It is known that Ti and Zr nanoparticles exhibit the highest chemical activity; thus, it is clear that their effect on transformations of the matrix will be no less than that of Fe nanoparticles.The phase analysis of nano-MPCS samples (M = Ti or Zr) was performed by two techniques. One of them consisted in the construction of radial electron-density distribution functions obtained from the intensity curve of X-ray scattering (X-ray RED), and the other was EXAFS spectroscopy. The advantage of EXAFS spectroscopy consists in its selectivity, which makes it possible to obtain the atomic radial distribution curve for the local arrangement of a selected chemical element in the sample.Both of these techniques give interatomic distances (r) and coordination numbers (Z), which can be compared with those calculated from structural data for a particular phase. Thus, X-ray RED and EXAFS techniques inspect and supplement each other.Experimental EXAFS data†† on r and Z for nano-ZrPCS showed that the sample contained zirconium metal (the interatomic distances 3.11, 3.27 and 5.58 Å agree well with the calculated data). The peak with r = 1.97 Å can be assigned to the Zr–C distance and is indicative of the metal–matrix interaction. The ZrO2 phase was absent from the sample since there are no Zr–Zr and Zr–O peaks characteristic of this phase.The alternative results were obtained by EXAFS for nano- TiPCS: the sample contained both the metal phase and the ‡ MWD curves were obtained by exclusive gel-permeation chromatography on Shodex styrogel columns (Knauer) with a UV detector. Dry THF was used as a solvent, and polystyrene was used as the reference substance for calibration. § Rheological characteristics were measured in an argon atmosphere using a Reotest-Lovo instrument; the heating rate was 5–10 K min–1.¶ TGA was performed within the range 20–800 °C (He, 5 K min–1); DSC analysis was performed at 20–600 °C in Ar; 2, 5 or 10 K min–1 (DuPont). TiO2 phase (probably anatase). The distance r = 1.82 Å may correspond to the Ti–C bond resulting from partial replacement of silicon in the Si–C chains of a polymeric matrix.X-ray diffraction analysis showed that all samples were amorphous; this means that the size of the crystallites (nanoparticles) is less than 20 Å. Figure 1 compares the RED curve of nano-ZrPCS with the RED curve of the initial matrix;‡‡ a differential curve is also presented. As in the case of EXAFS, the differential curve exhibits peaks due to the Zr0 phase (r = = 3.20 and 5.60 Å).The phase composition of metal nanoparticles in the nano-TiPCS sample is different: both metal and oxide phases were observed. The modelling of X-ray RED curves showed that the inserted Ti is distributed between the Ti0 and TiO2 phases in the ratio 1:5 (Figure 2). The formation of TiO2 in the nano-TiPCS sample was supported by XPS analysis.§§ The spectrum of Ti 2p3/2 consists of three components; for chemical identification, we need to discuss only the peaks with Eb = 455.0 and 459.2 eV.According to reference data,14,15 the peak with Eb = 459.2 eV can be reliably assigned to Ti–O bonds in titania or titanate. The component with Eb = = 455.0 eV may be attributed to the Ti–C bond. Note that bulk metallic Ti has Eb = 454.0 eV, but the corresponding value for Ti nanoparticles is unknown for us.Note that modifications of matrices in the course of the formation of metal-containing polycarbosilane can be observed in the differential RED curve: there is strong disordering of bonds with lengths of about 2 and 4–5 Å in the case of nano- TiPCS. Analogous changes were observed for the nano-ZrPCS sample; it is not improbable that they are associated with the introduction of nanoparticles deep within the polymer structure. The XPS analysis also showed that no Ti or Zr (to within the limit of detection of 0.1–1 at%) were present at the surface of the investigated samples. Using long scanning it was possible to record the Ti 2p line and to determine the Ti concentration near the surface film to be equal to 2×10–2 at%; this value is lower †† The EXAFS spectra of K-edges of Ti or Zr were obtained on the EXAFS spectrometer at the Siberian Synchrotron Radiation Centre.The VEPP-3 storage ring with an electron-beam energy of 2 GeV and an average stored current of 80 mA were used as the radiation source. The X-ray energy was monitored with a channel cut Si(111) monochromator.All of the spectra were recorded in the transmission mode using two ionisation chambers as detectors. The harmonics rejection was performed for the Ti K-spectra. For the EXAFS measurements, the samples were prepared as pellets with thickness varied so that a 0.5–0.8 jump at the absorption K-edges of Ti or Zr was obtained. The EXAFS spectra were treated using standard procedures.11 The background was removed by extrapolating the pre-edge region to the EXAFS region in the form of Victoreen’s polynomials. Three cubic splines were used to construct the smooth part of the absorption coefficient.The inflection point of the edge of the X-ray absorption spectrum was used as the initial point (k = 0) of the EXAFS spectrum. The radial distribution of the atoms (RDA) function was calculated from the EXAFS spectra as k3c(k) using the Fourier analysis for the wavenumber range k = 4.0–12.0 Å–1. A curve fitting procedure with the EXCURV92 program12 was employed to determine precisely the distances, coordination numbers and the Debye– Waller factors. This was performed for k3c(k) over a similar wavenumber range after preliminary Fourier filtering with engaging known XRD data for bulk compounds.‡‡ X-ray RED: diffractometer; CuKa radiation monochromated with a graphite monochromator; all samples were X-ray amorphous; the diffraction pattern of the matrix had a wide halo with the intensity maximum at the interplanar distances d/n = 8.8 Å; this halo is shifted to d/n = 8.4 Å upon introducing Ti or Zr.For calculating the RED curves for all of the samples, the intensities of X-ray scattering in the angle range 3 to 150° (2q) at MoKa radiation were measured. For determining the phase composition of the supported component and the modification of a polymeric matrix (polycarbosilane), the difference RED curves were constructed; the technique for calculating the RED curves was described in ref. 13. §§The samples were analysed on a VG ESCALAB HP electron spectrometer. The samples were applied to a rough surface of copper plates or to the surface of an adhesive tape by pressing and powdering. Survey scans with the high pass energy HV = 100 eV were recorded to obtain high-sensitivity spectra. Particular spectral lines were taken with high resolution using HV = 20 eV.Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) than the Ti concentration in the sample. This observation can be easily explained by an effect of capsulation of Ti nanoparticles inside the cavities (domains) of an organic polymer matrix. This work was supported by INTAS (grant no. 96-1410) and by the Russian Foundation for Basic Research (grant no. 98-03-32677).References 1 (a) K. E. Drexler, Nanosystems: Molecular Machinery, Manufacturing, and Computation, New York, Wiley, 1992; see also (b) S. L. Gillett, Nanothechnology, 1996, 7, 168. 2 C. Y. Ho and S. K. El-Rahaiby, Ceram. Eng. Sci. Proc., 1992, 13, 3. 3 A. M. Tsirlin, V. G. Gerlivanov, N. A. Popova, S. P. Gubin, E. K. Florina, B. I. Shemaev and E. B. Reutskaya, ECCM-8, Symposium 6, Naples, 1998, 4, 137. 4 S.P. Gubin and I. D. Kosobudskii, Usp. Khim., 1983, 52, 1350 (Russ. Chem. Rev., 1983, 52, 766). 5 E. B. Brun, O. A. Shustova, S. I. Kuchanov and G. P. Gladyshev, J. Polymer Sci., 1980, 18, 2461. 6 T. Ishikawa, M. Shibuya and T. Yamamura, J. Mater. Sci., 1990, 25, 2809. 7 U. Zucchini, E. Albizzati and U. Giannini, J. Organomet. Chem., 1971, 26, 357. 8 T. W. Smith and D. Wychick, J. Phys. Chem., 1980, 84, 1621. 9 S. P. Gubin, A. V. Kozinkin, M. I. Afanasov, N. A. Popova, O. V. Sever, A. T. Shuvaev and A. M. Tsirlin, Neorg. Mater., 1999, 35, 237 (in Russian). 10 A. V. Kozinkin, V. G. Vlasenko, S. P. Gubin, A. T. Shuvaev and I. A. Dubovtsev, Neorg. Mater., 1996, 32, 422 [Inorg. Mater. (Engl. Transl.), 1996, 32, 376]. 11 D. J. Kochubey, EXAFS spektroskopiya katalizatorov (EXAFS spectroscopy of catalysts), Nauka, Novosibirsk, 1992 (in Russian). 12 N. Binsted, J. V. Campbell, S. J. Gurman and P. C. Stephenson, SERC Daresbury Laboratory EXCURVE-92 Program, 1991. 13 E. M. Moroz, Usp. Khim., 1992, 61, 188 (Russ. Chem. Rev., 1992, 61, 356). 14 Handbook of X-ray Photoelectron Spectroscopy, ed. G. E. Moulenberg, Eden Prairie, Minnesota, 1978, p. 190. 15 Handbook of X-ray Photoelectron Spectroscopy, ed. J. Chastain, Eden Prairie, Minnesota, 1992, p. 261. Differential curve Ti/PCS RED curve for the ratio Ti:TiO2 = 1:5 60 40 20 0 0 2 4 6 r/Å 4pr2r(r)/eI2 Å–2 Figure 2 Modelling of differential X-ray RED curves for nano-TiPCS. Received: Moscow, 1st September 1998 Cambridge, 17th November 1998; Com. 8/07872F

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) Microscopic model of charge density distribution for critical and supercritical states of carbon Sergei I. Kudryashov,* Nikita B. Zorov and Sergei G. Ionov Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 932 8846; e-mail: serge@laser.chem.msu.ru Mass and charge density fluctuations of carbon in critical and supercritical states result in multiply charged negative and positive nanocluster ions which are the main components of the weakly ionised electronless carbon plasma.The critical state of a single-component phase is usually described by certain parameters of ‘order’ (densities of mass and entropy), whose spatial fluctuations abnormally grow due to the cooperative (multi-body) nature of critical processes.1 At high critical temperatures substances exist as a plasma, which is also characterised by charge density as an additional parameter of ‘order’.Charge density fluctuations determine the electrical and optical characteristics of the medium thus stimulating considerable interest to study spatial or temporal charge density distributions, which are statistically equivalent according to the ergodic hypothesis.It is known that a substance in a critical or supercritical state has a ‘droplet-like’ microstructure due to long-lived mass density fluctuations.2 Under laser ablation of graphite, these carbon droplets were experimentally detected as charged carbon nanoclusters3 in a gas phase by a real-time electrostatic probe technique (Figure 1), and they were also observed by scanning electron microscopy as neutral carbon nanoclusters deposited on a graphite foil surface by the laser quenching under supercritical conditions.4 These experimental data3,4 allow us to estimate the correlation radius R of critical density fluctuations (a characteristic size of spherical nanoclusters), which is about 10–30 nm (104–106 atoms per cluster) for a mass density of the liquid carbon phase of near 2 g cm–3.5 The majority of physical and chemical properties of carbon nanoclusters are similar to those of a macroscopic condensed phase (e.g., thermionic emission,6 delocalisation of an excessive charge, high stability and slow growth of the consequent ionisation potentials of multiply charged ions7).A change in the electronic properties of carbon nanoparticles with their growth from several atoms to several hundreds of atoms results in a gradual decrease in their ionisation potential Ip and in an increase in their electron affinity Ea thus approaching the work function Ae of bulk graphite8 for large graphite-like carbon clusters C60–C900.9 Because liquid carbon is a conducting phase10 these tendencies are described11 by the following expressions for a conducting sphere of radius R: The differences between Ip, Ea and Ae calculated for various graphite-like carbon nanoclusters with 104–106 atoms per cluster are very small (0.05–0.2 and 0.08–0.3 eV, respectively) as compared with the Ae value of bulk graphite (4.6 eV12).Due to delocalisation of an excessive charge and similar Ip and Ea values the large carbon nanoclusters can readily form multiply charged negative and positive ions. Indeed, one- or multielectron charge-transfer processes between carbon nanoclusters occur at near-critical temperatures (kT £ £ 1 eV).13 The most probable process of single-electron transfer from the charged carbon nanocluster CN Z1 to a charged particle M is as follows: which describes not only electron transfer between carbon nanoclusters, but also direct gas-phase ionisation of nanoclusters by collisional ionisation and thermionic emission (where MZ2 – 1 is a collisional partner or a virtual particle, respectively).The equilibrium constant of reversible process (3) is where concentrations of the reacting species are placed in square brackets.It can be seen that a minimum value of a factor [D = Ip(CN Z 1) – Ea(MZ2)] from expression (4) is favourable for direct process (3). Some characteristic values are D ª 0 eV for the case of single-electron transfer between carbon nanoclusters (i.e. Ip ª Ea ª Ae), D > 1 eV for the electron transfer from a nanocluster to a small positive carbon cluster ion of several atoms (Ip > 8 eV, Ea < 3 eV8) and D ª Ae = 4.6 eV for the collisional ionisation or thermionic emission.These values indicate that a dominant channel of generalised process (3) is charging of the nanoclusters because the latter are not only effective Ip(R) = Ae + 0.375e2/R Ea(R) = Ae – 0.625e2/R (1) (2) CN Z 1 + MZ2 = CN Z1 + 1 + MZ2 –1 (3) Abundance of clasters (a.u.) Claster size (carbon atoms) 10–4 10–5 10–6 10–7 10–8 104 105 106 Figure 1 Dependence of the charge (Z[CN –Z]DZ) induced on an electrostatic probe by negative nanocluster ions on the size-to-charge ratio N/Z (curve 1); distribution (concentration [CN Z]) of nanocluster ions CN Z by N/Z (curve 2); size distribution of neutral nanoclusters CN 0 (curve 3).[CN Z1 + 1][MZ2 – 1] [CN Z1 ][MZ2] Kp = = exp{–[Ip(CN Z 1) – Ea(MZ2)]/kT} (4), f(z) = 0.14exp(–Z2/100) Charge of cluster ions (e.s.u.) 1 10–1 10–2 10–3 10–4 10–5 –30 –20 –10 0 10 20 30 Figure 2 Charge distribution of carbon nanoclusters of N = 5×105 atoms at T = Tcrit ª 7×103 K. Abundance of cluster ions (a.u.)Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) electron donors for small positive carbon cluster ions, but also effective acceptors of free electrons in a gas phase and acceptors of an excessive negative charge of small carbon cluster ions. Therefore, a critical or supercritical carbon plasma is electronless and mainly consists of positively and negatively charged nanoclusters. The probability of consequent ionisation of a nanocluster gradually diminishes with increasing charge due to an increase in the work function of the nanocluster.The electrostatic potential of electron transfer between nanoclusters can be approximately simulated by the potential of a spherical capacitor due to a spherical symmetry of a nanocluster ionised14 where Z and R are the charge and the radius of the nanocluster, respectively, e is the dielectric constant of the neutral vapour that separates the nanoclusters and e0 is the dielectric constant of vacuum.According to expression (5), D(Z) = eU(R) in (4) increases proportionally to the charge of the nanocluster CN Z as BZ, where the parameter B is also determined by expression (5). The abundance of multiply charged nanoclusters is not high, because equilibrium constant (4) is expressed by an exponential.For this reason, each multiply charged nanocluster mainly interacts with numerous weakly charged nanoclusters of opposite charge Zi from the surrounding ‘ion atmosphere’. Thus, the yield of multiply charged nanoclusters can be expressed by the equilibrium constant of multi-step process (3) where the sum by the integer index Z of the nanocluster charge is placed in braces.Accounting for expression (6), the material balance equation for nanoclusters CN with different charges is written as Thus, the resulting charge distribution f(Z) of nanoclusters CN can be presented as a normal statistical law with the continuous variable Z and parameters m = 0 and s = (kT/B)1/2 Equation (8), which describes normal charge density distribution for a critical (supercritical) state of carbon, is indicative of the independent character of fluctuations for this parameter of ‘order’.However, there is a relationship between the parameter s of charge density distribution and the radius R of nanoclusters (the average radius of fluctuations or correlations). For example, the maximum s value corresponds to the critical point of a substance, where R is maximum, and B is minimum.In a supercritical region, the R value is monotonously decreased1 with increasing T and the following increase of B results in decreasing s in accordance with expression (8) thus suppressing the fluctuations of charge density. Because expression (8) qualitatively describes the charge density distribution of the high-temperature critical and supercritical states of carbon, it was used for quantitative processing of time-of-flight electrostatic probe measurement data,3 namely, the dependence of the charge induced at an electrostatic probe (collector) by gas-phase negative carbon nanoclusters on their size-to-charge ratio N/Z.In order to determine the concentrations [CN Z] and [CN 0 ], the general function I(N/Z) (Figure 1, curve 1) was expanded over the range N/Z = 104–5×105 in a series of simple terms Zf(Z)DZ[CN –1] (with DZ= 1) starting from N/Z = = 5×105, where Z was assumed to be equal to –1.The variance s of the charge density distribution f(Z) was calculated from expressions (5) and (8) using kT = 0.6 eV (TªTcrit ª 7×103 K), e ª 1, R = [(3NMat)/(4prliq)]1/3 and r = 2R[(rliq/2rcrit)1/3 – 0.5], where Mat is the mass of a carbon atom (kg), rliq ª 1.5×103 kg m–3 is the density of carbon liquid at T < Tcrit and rcrit ª 640 kg m–3 is the density of carbon in the critical state.5 The calculated s values were equal to 3.5 and 7 for N = 3×104 and 5×105 atoms, respectively.One of the resulting distributions f(Z) for carbon nanoclusters of N = 5×105 atoms is given in Figure 2.Two main terms of the expanded function I(N/Z) are related to two modes of nanoclusters centred at N/Z = 3×104 and N/Z = = 5×105 atoms. These bimodal distributions of [CN Z ] by N/Z and [CN 0 ] by N are shown in Figure 1 (curves 2 and 3). Accounting for the exponential increase in the amplitude of the specific mode of fluctuations during spinodal decomposition of a labile liquid phase,2 we considered this bimodal distribution of carbon nanoclusters as two superimposed distributions.One distribution with N = 5×105 atoms and T ª Tcrit ª 7×103 K was well fitted by the function I(N/Z) over the range of N/Z = = 8×104–5×105 atoms, but over the range of N/Z = (2–4)×104 atoms, the experimental function I(N/Z) is inconsistent with the sharp distribution at N = 3×104 atoms and T ª Tcrit.The temperature of the smaller carbon nanoclusters is much higher in accordance with the predictions of a current theory of the supercritical state1 (R ~ T–2/3) and can be estimated as T ª ª 2.8×104 K. This temperature of a local region in a lasergenerated plasma, where spinodal decomposition of the largest carbon nanoclusters takes place, is consistent with the temperatures (T < 3×104 K) in a near-surface ‘opaqueness’ region of the carbon plasma.15 Thus, a microscopic theory of the charge density distribution for critical and supercritical phases of carbon was developed for the first time, and an electronless character of the high-temperature plasma of negatively and positively charged carbon nanoclusters was predicted.This theory adequately describes an experimental distribution of multiply charged nanoclusters. This work was supported in part by the Russian Foundation for Basic Research (grant nos. 96-03-33324 and 98-03-32679). References 1 Fizicheskaya entsiklopediya (Physical Encyclopaedia), ed. A. M. Prokhorov, Sovetskaya Entsiklopediya, Moscow, 1990, p. 353 (in Russian). 2 V. P. Skripov, E. N. Sinitsyn and P. A. Pavlov, Termodinamicheskie svoistva zhidkostei v metastabil’nom sostoyanii (Thermodynamic Properties of Liquids in Metastable State), Atomizdat, Moscow, 1980, ch. 1 (in Russian). 3 S. I. Kudryashov and N. B. Zorov, Mendeleev Commun., 1998, 178. 4 S. I. Kudryashov, S. G. Ionov and N. B. Zorov, Mendeleev Commun., 1999, 3. 5 H. R. Leider, O. H. Krikorian and D. A. Young, Carbon, 1973, 11, 555. 6 E. E. B. Campbell, G. Ulmer and I. V. Hertel, Phys. Rev. Lett., 1991, 67, 1986. 7 R. Volpel, G. Hofmann, M. Steidl and M. Stenke, Phys. Rev. Lett., 1993, 71, 3439. 8 J. A. Zimmerman and J. R. Eyler, J. Chem. Phys., 1991, 94, 3556. 9 P. Melinon, V. Paillard, V. Dupius, A. Perez, P. Jensen, A. Hoareau, J.P. Perez, J. Tuaillon, M. Broyer, J. L. Vialle, M. Pellarin, B. Baguenard and J. Lerme, Int. J. Modern Phys. B, 1995, 9, 339. 10 S. I. Kudryashov, A. A. Karabutov, V. I. Emelyanov and N. B. Zorov, Mendeleev Commun., 1997, 224. 11 H. Haberland, Proc. NATO Adv. Study Institute on Fundamental Processes of Atomic Dynamics, NATO ASI series, Plenum, London– New York, 1987. 12 Fiziko-khimicheskie svoistva poluprovodnikov (Physicochemical properties of semiconductors), ed. A. V. Novoselova, Nauka, Moscow, 1979 (in Russian). 13 G. Jahavery, H. Becker, S. Petrie and P.-C. Cheng, Org. Mass Spectrom., 1993, 28, 1005. 14 S. G. Kalashnikov, Elektrichestvo (Electricity), Nauka, Moscow, 1985, p. 48 (in Russian). 15 S. I. Kudryashov, A. A. Karabutov and N. B. Zorov, Techn. Digest of the 16th International Conference on Coherent and Nonlinear Optics ICONO’98, Moscow, 1998, p. 282. Ze 4pe0e U(r) = (R–1 – r–1) (5), [CN Z][MZi – 1]Z [CN 0 ][MZi]Z = exp{–[D(1) + ... + D(Z)]/kT} = exp(–BZ2/2kT) (6), [CN]S = [CN 0 ]Sexp(–BZ2/2kT) (7) +• –• f(Z) = (2pkT/B)–1/2exp(–BZ2/2kT) (8) Received: Moscow, 24th July 1998 Cambridge, 26th October 1998; Com. 8/06225K

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) Interaction between cationic dyes and colloidal particles in a C60 hydrosol Nikolay O. Mchedlov-Petrossyan,*a Vladimir K. Klochkov,b Grigoriy V. Andrievsky,b Eleonora L. Karyakinac and Aleksandr A. Ishchenkod a Department of Chemistry, Khar’kov State University, 310077 Khar’kov, Ukraine. Fax: +38 057 243 7044; e-mail: kholin@fuzzy.univer.kharkov.ua b Institute for Therapy, Academy of Medical Sciences of Ukraine, 310039 Khar’kov, Ukraine.E-mail: yard@kharkov.ua c Ukrainian State Research Institute of Refractories, 310024 Khar’kov, Ukraine d Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 253094 Kiev, Ukraine. Fax: +38 044 543 6843 Strong interaction of cationic dyes with the dispersed phase of a C60 hydrosol results in the adsorption at the surface of colloidal particles and, finally, in coagulation of the sol.To extend the area of application of fullerenes (C60, C70 etc.), especially, to biophysics, biochemistry and medicine, it is important to have their aqueous solutions. Unfortunately, the equilibrium solubility of fullerenes in water was reported to be negligible.1 Recently, we prepared aqueous solutions of C60 without any stabilisers and chemical modification, which were reasonably concentrated (� 0.1 g dm–3) and stable over at least several months.The procedure is based on transferring fullerene from toluene into water using sonication.2 These solutions appeared to be colloidal systems.2–4 The C60 hydrosol is found to be a typical ultramicroheterogeneous hydrophobic dispersion with negatively charged particles.3,4 The C60 dispersions obtained by Scrivens et al.,5 were much coarser and very dilute (0.001 g dm–3).Presently, we can prepare colloidal solutions with C60 concentrations as high as 1.6 g dm–3. Hence, the research into the colloid chemistry of the C60 fullerene seems to be necessary and rather promising. Organic cations exert a strong coagulating effect on the sol; this effect increases with the surface activity of the cations.3,4 As organic dyes are also known to be efficient coagulants for ‘negative’ sols,6 we systematically studied the interaction of a C60 hydrosol with a number of cationic dyes.The general conclusion is following: the dyes are adsorbed at the surface of C60 colloidal particles, and this process finally results in coagulation of the sol.Here we report the data for the two dyes, which are prone to form dimers and other aggregates in aqueous media, Neutral Red and a methyl analogue of Pinacyanol. The changes in the absorption spectra of Neutral Red as the C60 was added (Figure 1 shows a typical example) give evidence of the dye–fullerene interaction. The measurements were performed on a Specord UV-Vis or SP 46 instrument against solvent blanks containing the sol without the dye at pH £ 5.The spectral changes are typical of dimerisation of the Neutral Red cation.7 Thus, the data in Figure 1 are indicative of the interaction between dye chromophores, which is induced by colloidal particles.Pinacyanol is used as a probe for studies of surfactant micellisation.8 At working concentrations (Figure 2), the dye 1,1'-dimethylquino-2-carbocyanine, used as the tosylate, is strongly dimerised in aqueous solution. The spectral changes observed upon addition of the C60 hydrosol are characteristic of the formation of H-aggregates of the dye.9 We also detected effects of this kind in the Pinacyanol–sodium dodecylsulfate system (in the presence of 0.01 mol dm–3 NaCl), at surfactant concentrations somewhat below the critical micelle concentration.Under these conditions, the formation of mixed dye– surfactant micelles is typical.8 If the number of homomicelles of the anionic surfactant became high enough, an intense band at 608 nm appeared. This band is typical of isolated solubilized dye monomers.Thus, in the colloidal C60 solution, coagulation takes place before the dye anions are adsorbed separately from each other. The critical coagulation concentrations (c.c.c.) were obtained as described earlier.3,4 Different aliquot portions of dye solutions were added to the sol; the final working concentration of C60 was always equal to 0.07 g dm–3.For Neutral Red and 1,1'-dimethylquino- 2-carbocyanine c.c.c. = 0.028 and 0.01 mmol dm–3, respectively. The attempts to determine the c.c.c. values by titration of the sol with microamounts of concentrated dye solutions lead, in contrast to the case of inorganic salts, to much higher values. All of the experiments with 1,1'-dimethylquino- 2-carbocyanine were performed in the presence of 1 vol% EtOH.The presence of the dyes in the coagulates was detected by mass spectrometry. The mass spectra were obtained on a time-of-flight MSBC mass spectrometer using 252Cf plasma 1.2 0.8 0.4 0.0 320 470 620 l/nm Absorbance (arbitrary units) 2 1 Figure 1 Absorption spectra of Neutral Red solutions (4.1×10–5 mol dm–3) (1) in the absence of the hydrosol and (2) at a C60 concentration of 0.021 g dm–3. 1.0 0.5 0.0 380 530 680 l/nm Absorbance (arbitrary units) 1 2 3 4 Figure 2 Absorption spectra of 1,1'-dimethylquino-2-carbocyanine (1.4×10–5 mol dm–3) at the C60 hydrosol concentrations: (1) 0, (2) 0.0115, (3) 0.023 and (4) 0.0346 g dm–3; 1 vol% EtOH.Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) desorption (PD) ionisation. Additional evidence of dye–fullerene interactions was obtained from the mass spectra of systems with dye concentrations somewhat lower than c.c.c.according to a previously developed approach.10 Essential differences in the peak intensities were found in the presence of colloidal C60 as compared with pure 1,1'–dimethylquino–2–carbocyanine (Figure 3, the same phenomenon was observed with Neutral Red).The mass spectrum of the latter compound is consistent with the reported data.11 Besides, the mass spectra show that the dye adsorption on the fullerene particles facilitates the formation of cluster ions in the region m/z 632–646 and of fragment ions in the region m/z 447–474. Transmission electron micrographs of the solid phase obtained from the sols after supporting on nitrocellulose and drying in air give an indication of the colloidal particles (Figure 4).The samples were examined using an EMV 100 AK electron microscope (voltage 75 kV, vacuum, 3 Pa). This study provides support for the ultramicroheterogeneous and polydisperse character of the system, which was found earlier.3,4 Isodiametrical particles from 7 to 40 nm in size, which consist of smaller spherical particles, are prone to further cluster formation.Note that the associates of amino acids and dipeptide derivatives of the C60 fullerene in solutions are larger by approximately two orders of magnitude.12 Thus, the specific surface area is about (1–5)×102 m2 g–1. It is likely that individual C60 molecules are detected in some regions of the micrographs.Electron diffraction patterns show the ordered (crystal-like) character of the primary aggregates. Thus, under conditions of changing absorption spectra of the dyes (Figures 1 and 2), and at the threshold of coagulation, the number of dye ions is one or two orders of magnitude higher than that of the colloidal particles of C60. Hence, it becomes apparent that the dye ions are concentrated at the surface of fullerene particles, resulting in interactions between the dye chromophores. Spectral effects of this type are referred to as ‘metachromasy’.13 On the other hand, this surface condensation of cations leads to neutralization of the negative surface charge and to further hydrophobization of the colloidal particles. Both of these effects cause coagulation of the C60 hydrosol.As a result, the coagulating power of the dyes is approximately 3×103 times higher than that of NaCl.3 References 1 D.Heymann, F ullerene Sci. and Technol., 1996, 4, 509. 2 G. V. Andrievsky, M. V. Kosevich, O. M. Vovk, V. S. Shelkovsky and LA. Vashchenko, J. Chem. Soc., Chem. Commun., 1995, 1281. 3 N. O. Mchedlov-Petrossyan, V. K. Klochkov and G.V. Andrievsky, J. Chem. Soc., Faraday Trans., 1997, 4343. 4 V. K. Klochkov, N. O. Mchedlov-Petrossyan and G. V. Andrievsky, Vestnik KhGU, Ser. Khim., 1997, 247 (in Russian). 5 W. A. Scrivens, J. M. Tour, K. F. Creek and L. Pirisi, J. Am. Chem. Soc., 1994, 116, 4517. 6 A. Sheludko, Kolloidnaya Khimiya (Colloid Chemistry), Mir, Moscow, 1984, p. 196 (in Russian). 7 P.Zanker, Z.Phys. Chem., N.F., 1956, 9, 95. 8 P. Mukerjee and K. J. Mysels, J. Am. Chem. Soc., 1955, 77, 2937. 9 A. A. Ishchenko, Stroenie i spectral’no-lyuminestsentnye svoistva polimetinovykh krasitelei (Structure and spectral-fluorescent properties of polymethine dyes), Naukova Dumka, Kiev, 1994, p. 232 (in Russian). 10 G. V. Andrievsky, Yu. V. Lisnyak, V. K. Klochkov, Yu. L. Volyansky and L.T. Malaya, Mass Spectrom. Ion Processes, 1997, 164, 1. 11 S. M. Scheifers, S. Verma and R. G. Cooks, Anal. Chem., 1983, 55, 2260. 12 M. E. Vol’pin, E. M. Belavtseva, V. S. Romanova, A. I. Lapshin, L. I. Aref’eva and Z. N. Parnes, Mendeleev Commun., 1995, 129. 13 A. N. Terenin, Fotonika molekul krasitelei i rodstvennykh soedinenii (Photonics of dye molecules and related substances), Nauka, Leningrad, 1967, p. 616 (in Russian). 300 200 100 0 90 190 290 390 490 590 690 790 Ion counts m/z (a) (b) 100 50 0 90 190 290 390 490 590 690 790 Ion counts m/z 128 143 168 295 309 325 720 128 143 168 295 309 325 Figure 3 252Cf PD mass spectra of 1,1'-dimethylquino-2-carbocyanine (a) in the absence and (b) in the presence of the C60 hydrosol. N N Me Me Figure 4 Transmission electron micrograph of C60 colloidal particles (×70000) obtained from a sol with a fullerene concentration of 0.13 g dm–3 (negative image). Received: Moscow, 10th September 1998 Cambridge, 10th November 1998; Com. 8/07874B

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) Facile hydrolytic cleavage of a sulfonamide bond under microwave irradiation Irina V. Kubrakova,a Andrei A. Formanovskyb and Irina V. Mikhura*b a V. I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 117975 Moscow, Russian Federation. Fax: +7 095 938 2054 b M. M. Schemyakin and Yu.A. Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117871 Moscow, Russian Federation. Fax: +7 095 330 5592; e-mail: synorg@ibch.siobc.ras.ru The hydrolysis of a sulfonamide bond in 25% sulfuric acid under microwave irradiation was completed in 0.5 h. Acid hydrolysis reactions are widely used in organic synthesis. However, severe conditions of hydrolytic cleavage are responsible for undesired side reactions resulting in degradation of starting materials and reaction products.Therefore, it is of particular importance to select mild conditions for the hydrolytic removal of protective groups used in multistage syntheses. The tosyl (p-toluenesulfonyl) group is used as an activator or protector of terminal hydroxyl and amino groups in the Richman–Atkins synthesis of macroheterocyclic compounds.1 This group exhibits the following advantages: it is easy to introduce into reactant molecules and stable in the course of subsequent reactions.However, the necessity of removing this group under severe conditions is a consequence of its stability. The removal of protective tosyl groups under mild conditions can facilitate the synthesis, preclude many side reactions, and increase the yields of target compounds. In this case, compounds with a wide variety of functional groups that were unsuitable because of degradation in the course of subsequent severe acid hydrolysis of the sulfonamide bond can be used as the starting materials.Thus, a significantly greater number of macroheterocyclic compounds can be synthesised by the simple and convenient Richman–Atkins method.It has been found2–4 that the rate of hydrolysis of organic compounds was dramatically increased under microwave irradiation, and the use of concentrated acids was not necessary in these reactions. We believed that a similar effect will also occur in the hydrolysis of the sulfonamide bond and examined 1,10- ditosyl-1,10-diaza-4,7,13,16-dioxacyclooctadecane 1, 1,4,7,10- tetratosyl-1,4,7,10-tetraazacyclododecane 2 and 1-benzyl-4,7,10- tritosyl-1,4,7,10-tetraazacyclododecane 3 as examples. Table 1 summarises the reaction conditions and the yields of compounds 4–6.†,‡ Compounds 4 and 5 were identified by TLC using specially synthesised diaza-18-crown-64 and cyclen5 as the reference samples.Compound 6 was identified by the 1H NMR and mass spectrometry data. We have found that the rate of hydrolytic cleavage of the sulfonamide bond dramatically increased (by a factor of 100– 200) under microwave irradiation. Moreover, the substrate/acid ratios and the concentrations of acids can be considerably † Typical procedures of commonly used hydrolysis: a suspension of 1 (1.0 g, 1.75 mmol) in 5.5 ml of 33% HBr solution in glacial acetic acid was kept at 100 °C for 48 h.The solvent was evaporated to dryness; the residue was treated with 10 ml of anhydrous ether, filtered off, washed with 10 ml of anhydrous ether, and treated with 5 ml of a 20% NaOH solution. The aqueous solution was extracted with CHCl3 (5×2 ml), and the extract was dried with anhydrous Na2SO4.The solvent was evaporated, and the residue was recrystallised from benzene–heptane. Compound 4 (321 mg) was obtained, mp 115 °C. For 2: a suspension of 2 (1.0 g, 1.27 mmol) in 5.1 ml of 97% H2SO4 was kept at 100 °C for 100 h. After cooling, it was added to 20 ml of anhydrous ether; the precipitate was filtered off, washed with 10 ml of anhydrous ether and treated with 5 ml of 20% NaOH.The solution was extracted with CH2Cl2 (5×2 ml), and the extract was dried with Na2SO4. The solvent was evaporated, and the residue was recrystallised from heptane. Compound 5 (196 mg) was obtained, mp 111– 112 °C. For 3: a suspension of 3 (1.0 g, 1.38 mmol) in 5.0 ml of 97% H2SO4 was kept at 100 °C for 70 h. The subsequent procedure was analogous to that described for compound 2.The yield of 5 was 178 mg. decreased resulting in an increase in the yields and purity of the hydrolysis products. It has been found6 that detosylation of 3 with an HBr solution in acetic acid resulted in the removal of the benzyl group along with three tosyl groups. The same result has been obtained with the use of concentrated sulfuric acid (Table 1).Recently, it has been found5 that compound 6 is formed in 26% yield by treatment of a solution of compound 3 (3.5 g) in 1 l of liquid ammonia with 6 g of sodium metal. We found that the hydrolysis of 3 with a 25% sulfuric acid solution for 0.5 h under microwave irradiation gives rise to compound 6 in 80% yield (Table 1). Thus, the use of microwave heating significantly shortened the duration of hydrolysis of the N–Tos bond (by a factor of 100 or higher).The reaction was performed in a dilute acid; thus, the amount of strongly acidic waste solutions was significantly decreased. We believe that the effects observed resulted from a rapid increase in the temperature of the reaction mixture (up to a limiting value of 200 °C, which can be attained in the microwave oven used). Moreover, direct absorption of microwave radiation by the substrate cannot also be ignored.Whittaker and Mingos3 suggested that this absorption was the cause for significant acceleration of reactions in a microwave field. ‡ Typical procedures of hydrolysis under microwave irradiation: a mixture of 1 (1.0 g, 1.75 mmol) and 5 ml of a 25% H2SO4 solution was placed in a Teflon autoclave of an MDS-2000 microwave oven (CEM Corporation, USA) and exposed for 0.5 h at 350 W.Next, the pH of the solution was adjusted to 10 with 20% NaOH, and the solution was extracted with CHCl3 (5×2 ml). The extract was dried with Na2SO4, and the solvent was evaporated to dryness. Recrystallisation of the residue resulted in 436 mg of 4. For 2: 1.0 g (1.27 mmol) of 2 yielded 497 mg of 5 in a manner described above.For 3: 1.0 g (1.38 mmol) of 3 yielded 289 mg of 6 as colourless oil in a manner described above. 1H NMR spectrum for 6 (D2O, HCl) d: 3.2 (m, 16H, 8CH2), 4.1 (s, 2H, CH2Ph), 7.3 (s, 5H, C6H5). MS, m/z: 263 (M + 1)+. O O N O O N Ts Ts 1 H3O+ – TsOH O O HN O O NH 4 N N N N Ts Ts R Ts 2 R = Ts 3 R = CH2Ph H3O+ – TsOH HN NH N NH R 5 R = H 6 R = CH2Ph Scheme 1Mendeleev Communications Electronic Version, Issue 2, 1999 (pp. 45–86) References 1 E. J. Richman and T. J. Atkins, J. Am. Chem. Soc., 1974, 96, 2268. 2 R. A. Abramovich, Org. Prep. Proced. Int., 1991, 23, 685. 3 A. G. Whittaker and V. M. P. Mingos, J. Microwave Power and Electromagnetic Energy, 1994, 29, 195. 4 K. D. Raner, C. R. Strauss and R. W. Trainor, J. Org. Chem., 1995, 60, 2456. 5 D. D. Dishino, E. J. Delaney, J. E. Emswiler, E. T. Gaughan, J. S. Prasad, S. K. Srivastava and M. F. Tweedle, Inorg. Chem., 1991, 30, 1265. 6 D. I. Weisblat, B. J. Magerlein and D. R. Myers, J. Am. Chem. Soc., 1953, 75, 3630. Received: 2nd September 1998; Com. 8/07873D a See footnote †. b See footnote ‡. Table 1 Commonly used hydrolysis and hydrolysis under microwave irradiation of compounds 1–3. Starting materials Commonly used hydrolysisa Hydrolysis in a microwave fieldb Conditions Time/h Product Yield (%) Conditions Time/h Product Yield (%) 1 5.5 ml of 33% HBr in AcOH 48 4 70 5.0 ml of 25% H2SO4 0.5 4 95 2 5.1 ml of 97% H2SO4 100 5 90 5.0 ml of 25% H2SO4 0.5 5 90 3 5.0 ml of 97% H2SO4 70 5 75 5.0 ml of 25% H2SO4 0.5 6 80

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC