摘要:

326 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 326–327† Kinetic and Spectroscopic Evidence for the Formation of Ion-pairs between Crystal Violet and Perchlorate Ion† Luis Garc�ýa-R�ýo,b Pablo Herv�es,a J. Ramon Leis*b and Juan C. Mejutoa aDepartamento de Qu�ýmica Pura y Aplicada, Facultad de Ciencias, Universidad de Vigo, Spain bDepartamento de Qu�ýmica F�ýsica, Facultad de Qu�ýmica, Univesidad de Santiago de Compostela, Spain Kinetic data for the inhibition of the reaction between Crystal Violet (CV) and hydroxide ions by perchlorate ions are used to determine the equilibrium constant for the formation of ClO4–CV ion-pairs; K is obtained as 110�14 dm3 molµ1 at 25 °C and ionic strength (I)=0 mol dmµ3.Crystal Violet (CV) is a carbonium ion that is stabilized by the presence of aromatic rings which give it strong resonance that results in a deep blue-violet colour with an absorption maximum in the visible region (lmax=590 nm). The CV cation occurs as two helicoidal isomers1 owing to the strong steric hindrance between the benzene ortho protons which lead to a non-planar configuration.The two isomers have the same typical helicoidal structures as carbonium ions possessing three benzene rings.2 The presence of these two isomers gives rise to two different absorption bands in the visible spectrum at 590 and 540 nm.1 The reactivity of this cation is of high physicochemical interest since it was used, together with those of similar cations, for establishing Ritchie’s N+ nucleophilic index.Its reactivity towards the hydroxide ion, which was used in this work as a kinetic probe to determine the formation constant for the ion-pair, has been widely studied in aqueous solutions4 and alternative media.4,5 This paper contributes experimental evidence for the formation of ion-pairs between the perchlorate ion and Crystal Violet based on spectrophotometric and kinetic data. We chose the perchlorate ion because its salts are widely used to fix the ionic strength in kinetics studies and because we had earlier found ion-pair complexes between perchlorate ions and nitrogen cations.7 We did not detect the formation of ion-pairs between CV and other anions such as azide, sulfate or thiocyanate.Experimental All chemicals used were of the highest commercially available purity and none required further purification. The experimental procedure employed has been described in detail elsewhere.6 Results and Discussion The spectral behaviour of CV in the presence of perchlorate ions was found to be anomalous as regards the relative heights of the two bands exhibited by the dye.These bands correspond to the absorption of the two helicoidal isomers of CV.1 The ratio of band A to B for CV, which is proportional to the relative populations of the two isomers, is highly sensitive to the presence of inert electrolyte and polarity changes in the CV environment.Perchlorate ions cause a strong change in the CV spectrum as regards both the positions of the bands and their relative intensity. The effect is so marked that it is visually apparent in both the hue and colour depth of the CV solution. Table 1 illustrates the spectral changes caused by variable amounts of sodium perchlorate in terms of the ratio of band A to band B absorption. Such a ratio, which was determined to be 1.48 in aqueous solutions, is markedly changed by high perchlorate ion concentrations.The effect can be so strong as to invert the populations of the two CV isomers leading to a ratio of only 0.84 in the presence of 0.3 M NaClO4. However, the effect cannot be exclusively ascribed to general salt effect factors because, as can be seen from Table 1, A:B remains constant in the presence of similar amounts of NaCl. In other words, the effect is due to the perchlorate ions. This behaviour confirms a strong association between the perchlorate ion, as a counterion, and the organic cation, with which it is likely to form an ion-pair.The mechanism by which the ratio of CV isomers is changed can be explained if it is assumed that the perchlorate ion preferably forms an ion-pair with the CV isomer in which the positive charge is located over the nitrogen atom (lmax=540 nm), and therefore the relative population of the CV isomer with the charge over the carbon atom (lmax=590 nm) decreases with the increase in the perchlorate ion concentration. Another anomalous and probably related behaviour was observed in the well-known reaction between CV and OHµ ions, which was strongly inhibited by the addition of perchlorate ions to the medium (Fig. 1). Again, this behaviour cannot be ascri- *To receive any correspondence. †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem.Research (M). Table 1 Influence of the NaClO4 concentration on the height ratio of the spectral bands for Crystal Violet (lA=590, lB=540 nm) [NaClO4] /M Isomer A: Isomer B [NaCl] /M Isomer A: Isomer B 0 0.0580 0.1120 0.1749 0.2330 0.2920 1.48 1.03 0.96 0.87 0.86 0.84 0 0.0580 0.1120 0.1749 0.2330 0.2920 1.49 1.47 1.48 1.46 1.47 1.47 Fig. 1 Inhibitory effect of the presence of sodium perchlorate (d) and sodium chloride (s) in terms of ionic strength on the basic hydrolysis of Crystal Violet.[CV] =8.33Å10µ6 M; [NaOH] =0.15 MCV + CIO4 – CV CIO4 K + HO– CV OH K = [CV CIO4] [CV] [HO– ] k J. CHEM. RESEARCH (S), 1997 327 bed to a general salt effect since similar concentrations of NaCl resulted in a much weaker inhibition (Fig. 1). This situation can be interpreted in quantitative terms by assuming that the CV engaged in the formation of the ionpairs cannot undergo attack by the OHµ ions. Based on Scheme 1, the hydrolysis rate of CV can be described in terms of the amount of free CV in solution, which will be determined by the equilibrium constant for ion-pair formation.v=k[HOµ][CV]free (1) A mass balance for the CV concentration and substitution of its result into eqn. (1) yields an expression for the reaction rate in the presence of sodium perchlorate, eqn. (2). v=k[HOµ] [CV]total 1+K[ClO4 µ] (2) Therefore, the observed rate constant can be expressed in terms of the NaClO4 concentration in the reaction medium, k0=k[HOµ] 1 1+K[ClO4 µ] (3) which can be readily linearized. However, because the formation of the ion-pair is accompanied by the effect of the ionic strength due to the presence of substantial amounts of sodium perchlorate in the medium, the experimental data given in Table 2 cannot be directly processed by using eqn.(3) in a linearized form. Instead, the data were corrected by using NaCl inhibition data on the assumption that the inhibitory effect of the ionic strength introduced by both salts, in the absence of specific interactions, was similar.In this way, after establishing the range where the Br�onsted –Bjerrum equation is fulfilled (where the Br�onsted– Bjerrum equation is kept linear using the inert electrolyte NaCl), one can isolate the effects of the ion-pair formation and those arising from changes in the ionic strength of the medium. After the pertinent corrected rate constant values are obtained, eqn. (3) in a linearized form can be used and the data found to conform to the proposed model.By fitting experimental data to this equation, the formation constant for the ion-pair was found to be 110�14 dm3 molµ1. Such a large constant is consistent with a strong association beween CV and sodium perchlorate. Ascribing this experimental data to the formation of an ion-pair is consistent with the kinetic and spectroscopic evidence previously obtained for other carbonium ions such as tri-p-anisylmethylium,8 tri-p-methoxyphenylmethylium9 and triphenylmethylium.10 Financial support from the Direcci�on General de Investigaci �on Cient�ýfica y T�ecnica of Spain (Project PB93-0524) is gratefully acknowledged.J. C. M. thanks Xunta de Galicia for a Research Training Grant. Received, 4th February 1997r E/7/00795G References 1 G. N. Lewis, T. T. Magel and D. Lipkin, J. Am. Chem. Soc., 1942, 64, 1774. 2 H. H. Freedman, Carbonium Ions, ed. G. Olah and P. V. Schleyer, Interscience, New York, 1973, vol.IV. 3 C. D. Ridchie, Can. J. Chem., 1986, 64, 2239. 4 C. D. Ridchie, D. J. Wright, H. Der-Sing and A. A. Kamego, J. Am. Chem. Soc., 1975, 97, 1163. 5 E. F. G. Duynstee and E. Grunwald, J. Am. Chem. Soc., 1959, 81, 4540; E. F. G. Duynstee and E. Grunwald, J. Am. Chem. Soc., 1959, 81, 4542; M. J. Blandamer, B. Clark and J. Burgess, J. Chem. Soc., Faraday Trans. 1, 1984, 80, 1651; M. Valiente and E. R�odenas, J. Phys. Chem., 1991, 95, 3368; K. Tamura and N. Nii, J. Phys. Chem., 1989, 93, 4825; C. Izquierdo, J. Casado, A. Rodr�ýguez and M. L. Moy�a, Int. J. Chem. Kinet., 1992, 24, 19; C. A. Bunton and E. L. Dorwin, J. Org. Chem., 1986, 51, 4093. 6 J. R. Leis, J. C. Mejuto and M. E. Pe�na, Langmuir, 1993, 9, 889. 7 P. Herv�es and J. R. Leis, J. Chem. Soc., Perkin Trans. 2, 1995, 2035. 8 C. A. Bunton and S. K. Huang, J. Am. Chem. Soc., 1972, 94, 3536. 9 M. J. Posble and P. A. H. Wyatt, J. Chem. Soc., Perkin Trans. 2, 1972, 474. 10 J. N. Ride and P. A. H. Wyatt, J. Chem. Soc., Perkin Trans. 2, 1973, 746; Y. K. Mo, R. E. Linder, G. Barth, E. Bunnenberg and C. Djerassi, J. Am. Chem. Soc., 1974, 96, 3309. Scheme 1 Table 2 Corrected rate constant at I=0 for the inhibition of the basic hydrolysis of CV obtained from eqn. (3). [CV] =8.33Å10µ6 M; [NaOH] =0.15 M [ClO4Na]/M 103 k0/sµ1 103 kcorr/sµ1 0 0.02 0.06 0.09 0.14 20.0 7.73 2.56 1.27 0.97 49.7 20.4 7.51

ISSN:0308-2342    

DOI:10.1039/a700795g

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

328 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 328–329† CeF3 as a Novel Support for Preparing Highly Active and Selective Vanadia Catalysts for the Ammoxidation of 3-Picoline† Kalevaru Venkata Narayana, Sheik Khaja Masthan, Vattikonda Venkat Rao and Panja Kanta Rao Catalysis & Physical Chemistry, Indian Institute of Chemical Technology, Hyderabad 500 007, India V2O5–CeF3 catalysts are found to be highly active and selective in the ammoxidation of 3-picoline; the catalytic performance is attributed to the formation of CeVO4 as evidenced by XRD.Vanadia supported on oxides like TiO2, SiO2 and ZrO2 have been used as catalysts for oxidation, oxidative dehydrogenation and ammoxidation reactions.1–6 The search for new supports for vanadia is continuing in order to design oxidation and ammoxidation catalysts with improved selectivity. We found that CeF3 can be used as an effective support to disperse vanadia and the resulting V2O5–CeF3 catalyst showed high activity and selectivity in the industrially important ammoxidation of 3-picoline to nicotinonitrile.Experimental V2O5–CeF3 catalysts were prepared by impregnating CeF3 support (Fluka, Switzerland, BET surface area of 33.9 m2 gµ1) in aqueous oxalic acid containing a requisite amount of NH4VO3 (Aldrich, USA). The solution was evaporated to dryness on a water bath and the resulting mass was calcined at 450 °C for 4 h. The experimental procedure for determining the ammoxidation activity of the catalysts for 3-picoline was similar to the one used for V2O5–TiO2 catalysts.7 The ammoxidation runs were carried out in a fixed bed microcatalytic reactor made of pyrex glass of length 350 mm and an id of 25 mm which was heated in an electrical furnace.About 2 g of catalyst particles (µ18 to +25 BS mesh) mixed with glass beads were packed in between two quartz wool plugs and reduced in a stream of hydrogen at 450 °C for 2 h. The temperature of the catalyst bed was measured with a Pt–Rh thermocouple inserted into the thermowell in the middle of the catalyst bed and connected to a temperature indicator controller.The catalyst bed was cooled to an ambient temperature in a H2 stream. The H2 gas was replaced by a mixture of NH3 and air from pressurised gas cylinders and the catalyst bed was raised to reaction temperature. 3-Picoline dissolved in H2O (1:13) was passed into the catalyst bed by means of an infusion pump (M/S.B.Braun, Perfusor Secura FT).The reaction mixture (3-picoline:H2O: NH3:air=1:13:6:44) was preheated in a preheater zone filled with beads. The non-gaseous products and unreacted 3-picoline were trapped in condensers at below µ10 °C. The liquid products collected were analysed by a gas chromatograph equipped with FID with a column of 10% OV-17 on Chromosorb W (3 mmÅ3 m). Results and Discussion The BET surface areas of the catalysts determined by N2 adsorption at 77 K decreased from 26 m2 gµ1 at 2 mass% V2O5 to 19 m2 gµ1 at 15 mass% V2O5 loading on CeF3.The vanadia loading on CeF3 and the reaction temperature have significant effect on the ammoxidation activity of the catalysts. Both the conversion of 3-picoline and the selectivity for nitocinonitrile (Table 1), at 390 °C and at a 3-picoline: H2O:NH3:air mole ratio of 1:13:6:44, increase with increase in vanadia loading up to 89.2 and 94.1% respectively. The other reaction product was pyridine, produced as a result of dealkylation.On a 15 mass% V2O5–CeF3 catalyst, while the 3-picoline conversion increases with increase in reaction temperature from 25% at 300 °C to 91.3% at 410 °C, the selectivity to nicotinonitrile remains almost the same (ca. 94%) at all the temperatures studied (Fig. 1). These observations indicate the facile nature of the active sites on the 15 mass% V2O5–CeF3 catalyst. X-Ray diffractograms of the catalysts (Fig. 2), taken on a Phillips PW 1140 X-ray diffractometer, provide information on the species present in the V2O5–CeF3 catalysts.At 7.5 mass% V2O5 content very weak peaks of CeVO4 appear and the intensity of these peaks increases with an increase in the V2O5 content of the catalysts. The presence of traces of free V2O5 is indicated by very weak XRD peaks with d-values of 4.38 and 3.4 Å in the X-ray diffractogram of the catalyst with the highest vanadia loading (15 mass%). These findings suggest that the active sites on V2O5–CeF3 that catalyse the ammoxidation of 3-picoline may not only be the V4+ ions in the V-oxide structures that can be visualised in the V2O5–TiO2 catalysts,7 but are perhaps V4+ ions associated with CeVO4 formed from CeF3 and V2O5 when calcined at 450 °C. CeF3 is a strong Lewis acid catalyst.The ammoxidation activity and selectivity appears to be related to the acid–base and redox properties of the catalysts. Formation of *To receive any correspondence. †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J.Chem. Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem. Research (M). Fig. 1 Effect of temperature on 3-picoline conversion (h) and nicotinonitrile selectivity (D) over 15 mass% V2O5–CeF3 catalyst at 2 ml hµ1 feed rate. Mass of the catalyst=2 g Table 1 Influence of vanadia loading on BET surface area, activity and selelctivity of various V2O5/CeF3 catalysts in the ammoxidation of 3-picoline.Reaction temperature: 390 °C; Feed Rate: 2 ml/h; Wt. of the catalyst 2 g; Molar Ratio of 3-picoline:H2O:NH3:Air=1:13:6:44; N-S=Nicotinonitrile selectivity; P-S=Pyridine selectivity % Selectivity Catalyst BET SA (% V2O5) (m2gµ1) % Conv. N-S P-S Others 2.0 5.0 7.5 10.0 15.0 26.0 25.0 23.4 19.3 19.1 57.9 61.7 67.0 74.1 89.2 65.4 72.2 84.0 86.8 94.1 17.5 11.3 7.2 6.1 4.1 17.1 16.5 8.8 7.1 1.8J. CHEM. RESEARCH (S), 1997 329 this compound appears to be essential for obtaining catalysts with high activity and nicotinonitrile selectivity.At lower V2O5 loadings where CeVO4 formation was low (Fig. 2), more pyridine was formed due to dealkylation (Table 1) over the acidic surface of the support, CeF3. This study has shown that CeF3 is an effective and novel support for V2O5. 15 mass% V2O5 catalyst is a highly active and selective catalyst for the ammoxidation of 3-picoline to nicotinonitrile with a conversion of 91.3% and a selectivity of 94% at 410 °C.This compares well with the performance of V2O5–TiO2 catalysts.7 The results of this investigation on the V2O5–CeF3 system are expected to help in the development of a new class of efficient catalysts for ammoxidation reactions. K. V. N. thanks the CSIR, New Delhi, for the award of a Senior Research Fellowship. Received, 13th May 1997; Accepted, 15th May 1997 Paper E/7/03328A References 1 G. Deo, I. E. Wachs and J. Haber, Crit. Rev. Surf. Chem., 1994, 4, 141. 2 G. Busca and L. Marchetti, J. Chem. Soc., Faraday Trans. 1, 1985, 81, 1003. 3 C. R. Dias, M. F. Portela and G. C. Bond, J. Catal., 1995, 157, 344. 4 E. A. Mamedov and V. C. Corberon, Appl. Catal., 1995, 127, 1. 5 A. Andersson and S. L. T. Lundin, J. Catal., 1980, 65, 9. 6 B. Jonson, B. Rebenstorf, R. Larsson and S. L. T. Andersson, J. Chem. Soc., Faraday Trans., 1988, 84, 1897. 7 K. V. Narayana, A. Venugopal, K. S. Rama Rao, V. Venkat Rao, S. Khaja Masthan and P. Kanta Rao, Appl. Catal., 1997, 150, 269. Fig. 2 X-Ray diffractograms of V2O5–CeF3 catalysts with different V2O5 loadings. (a) 2.0 mass%; (b) 5.0 mass%; (c) 7.5 mass%; (d) 10.0 mass%; (e) 15.0 mass%. XRD peaks with d-values 3.20, 2.01, 2.06, 3.64 Å (ASTM Card No. 8-45) belong to the CeF3 phase; XRD peaks with d-values 3.70, 2.76, 1.90 and 4.89 Å (ASTM Card No. 12-757) belong to the CeVO4 phase. XRD peaks with d-values 4.38 and 3.4 Å (ASTM Card No. 9-387) belong to the V2O5 phase

ISSN:0308-2342    

DOI:10.1039/a703328a

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

330 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 330–331† Regioselective Reductive Cleavage of Terminal Epoxides with Polymer-supported Chloroaluminium Tetrahydroborate† Bahman Tamami,* M. Mansour Lakouraj and Hamid Yeganeh Department of Chemistry, Shiraz University, Shiraz, Iran Epoxides are reduced exclusively to the less substituted alcohols with regenerable polyvinylpyridine-supported chloroaluminium tetrahydroborate in high yields. The reductive cleavage of epoxides to alcohols is one of the most useful reactions in organic synthesis.1 Cleavage of unsymmetrical substituted epoxides with most conventional reducing agents generally results in the more substituted alcohols.2 Considerable effort has focused on the development of methods for regioselective epoxide cleavage to the less substituted alcohols, and for this purpose several types of reagents have been used.2,3 However, in most cases mixtures of alcohols have been obtained.The most satisfactory results have been achieved only with a limited number of reagents such as sodium cyanotrihydroborate–BF3 etherate,3b potassium triphenylhydroborate–Ph3B3c system and recently silica gel-supported zinc tetrahydroborate reported by Ranu3e, f and the sodium tetrahydroborate–amine system via a photochemical approach.3h Polymer-supported reducing agents have received considerable attention in recent years and a variety of them, while exhibiting the advantages of polymeric reagents, have been used in the mild and selective reduction of organic compounds.4 The only reported polymer-supported tetrahydroborate reagents are Amberlyst anion exchange resinsupported tetrahydroborate and cyanotrihydroborate5 as well as polymer-supported zinc6 and zirconium7 tetrahydroborates which we recently reported as stable, efficient and selective reducing agents for a variety of organic functional groups.8 With these polymer-supported metal tetrahydroborates, however, the regioselective reduction of epoxides was not possible and a mixture of alcohols was obtained with the more substituted alcohols being the major products.8 We now report that in the course of our studies on a new polymer-supported metal tetrahydroborate, namely, polyvinylpyridine- supported chloroaluminium tetrahydroborate, we found that it can reduce epoxides exclusively to their lesser substituted alcohols in almost quantitative yields.Aluminium chloride was supported on crosslinked poly- (4-vinylpyridine) by adding a solution of the metal salt to an alcoholic suspension of the polymer.The polymeric reagent was then obtained by an exchange reaction between the polymer- supported aluminium chloride and lithium tetrahydroborate. It was a white-cream, stable and non-hygroscopic powder. The capacity of the reagent was 1.8 mmol BH4 per gram. Data obtained on the Al and Cl content by atomic absorption and potentiometric titration techniques showed, within experimental error, that the reducing species are in the form of AlCl2(BH4) supported on the polymeric ligand (such species are known to be formed as unstable intermediates in the formation of aluminium tetrahydroborate from the reaction of AlCl3 and LiBH4).9 Attempts to prepare polymer-supported aluminium tetrahydroborate, Al(BH4)3, were not successful.Regioselective reduction of various epoxides to their corresponding less substituted alcohols were performed using this reagent and the results are shown in Table 1.The reductions were performed in solvents such as diethyl ether, tetrahydrofuran, dichloromethane, acetonitrile, methanol and ethanol under reflux. The reagent was most efficient in absolute ethanol. No solvolytic ring opening of the epoxides was detected in this solvent. Identification and analysis of the products were made on the basis of IR, 1H NMR and GLC evidence compared with the authentic samples. Regeneration of the reagent was achieved by washing with acid and then base to obtain the original polymer followed by complexation and exchange reactions.The regenerated polymeric reagent, except for a small weight loss in each cycle, had almost the same capacity and performance as the original reagent. In conclusion, this regenerable polymer-supported reducing agent provides an efficient methodology for excellent regioselective cleavage of terminal epoxides to the less substituted alcohols.Moreover, the mildness, convenience and high yield make this reagent an attractive reagent for such an epoxide cleavage. Further utilization of this new stable polymer- supported metal tetrahydroborate reducing agent for different reductive transformations will be reported in due course. Experimental Preparation of Poly(4-vinylpyridine)-supported Chloroaluminium Tetrahydroborate.·Crosslinked poly(4-vinylpyridine) (2% divinyl benzene, Fluka AG) (5.0 g) was suspended in methanol (50 ml) and stirred for 1 h.A solution of AlCl3 (20 g, 0.15 mol) in THF– MeOH (4:1, 150 ml) was added to the polymer suspension. The mixture was then stirred for 12 h at room temperature and the precipitate filtered off, washed with excess methanol and diethyl ether and then dried in vacuum at 40 °C to yield 7.39 g polymersupported aluminium chloride as a light yellow powder. To a solution of LiBH4 (3.0 g, 0.14 mol) in dry THF (100 ml), the above supported polymer was added portionwise at 0–5 °C and stirred for 3 h.The resulting material was separated and washed several times with THF and diethyl ether and then dried under vacuum to produce a white-cream stable and non-hygroscopic powder. The capacity of the reagent was determined by iodometric titration method to be 1.8 mmol BH4 µ per gram. The amount of aluminium determined by atomic absorption spectroscopy and the Clµ content determined by potentiometric titration were 1.90 and 3.85 mmol per gram of polymer respectively.General Procedure for the Reductive Cleavage of Epoxides.·In a flask (100 ml) equipped with a condenser and a magnetic stirrer, a solution of epoxide (1 mmol) in absolute ethanol (10 ml) was prepared. The supported reagent (1.5 g) was added and the reaction mixture stirred while being refluxed. Progress of the reaction was monitored by TLC (CCl4–diethyl ether as 5:1) or GC. On completion of the reaction, water (100 ml) was added and the solution stirred for 5 min.The mixture was then filtered and the filter cake washed several times with diethyl ether. The organic layer was separated and dried over MgSO4. On evaporation of solvent the pure product was obtained in high yield. Regeneration of the Reagent.·The spent reagent (5 g) was treated with hydrochloric acid (20 ml, 0.1 M), stirred for 0.5 h and then filtered. The resulting filter cake was washed first with sodium hydroxide (3Å10 ml, 0.1 M) and then with distilled water, acetone and diethyl ether.The solid was dried in vacuum at 60 °C to give the original polymer (4.8 g) which could then be supported and used again. *To receive any correspondence. †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem. Research (M).O Ph O P-ClPh O Ph O O O O Ph O O O O O O O Ph OH P-ClPh OH Ph OH OH OH O Ph OH O O OH O O OH O OH J.CHEM. RESEARCH (S), 1997 331 We are grateful to Shiraz University research council for partial support of this work. Received, 13th May 1997; Accepted, 15th May 1997 Paper E/7/03327C References 1 H. O. House, Modern Synthetic Reactions, W. A. Benzamin, California, 1972; F. A. Carey and R. J. Sandberg, Advanced Organic Chemistry, Part B, Plenum Press, New York, 1977. 2 (a) H. C. Brown and N. M. Yoon, J. Chem. Soc., Chem. Commun., 1968, 1519; (b) R. O. Hutchins, I.M. Taffer and W. Burgoynes, J. Org. Chem., 1981, 46, 5214 and references cited therein; (c) N. M. Yoon and K. E. Kim, J. Org. Chem., 1987, 52, 5364; (d) J. J. Eisch, Z. R. Liu and M. Singh, J. Org. Chem., 1992, 57, 1618; (e) B. C. Ranu and A. R. Das, J. Chem. Soc., Chem. Commun., 1990, 1334; ( f ) B. C. Ranu and A. R. Das, J. Chem. Soc., Perkin Trans., 1992, 1881; (g) A. C. Bonini, G. Righi and G. Sotgiu, J. Org. Chem., 1991, 56, 6206; (h) G. A. Epling and Q. Wang, J. Chem. Soc., Chem. Commun., 1992, 1133. 4 D. C. Sherrington and P. Hodge, Synthesis and Separations Using Functional Polymers, Wiley, New York, 1988. 5 H. W. Gibson and F. C. Bailey, J. Chem. Soc., Chem. Commun., 1977, 815; R. O. Hutchins, N. R. Natal and I. M. Taffer, J. Chem. Soc., Chem. Commun., 1978, 1088. 6 H. Firouzabadi, B. Tamami and N. Goudarzian, Synth. Commun., 1991, 21, 2275. 7 B. Tamami and N. Goudarzian, J. Chem. Soc., Chem. Commun., 1994, 1079. 8 B. Tamami and N. Goudarzian, Iranian J. Chem. Eng., in the press. 9 W. M. Olson and R. T. Sanderson, J. Inorg. Nucl. Chem., 1958, 7, 228. Table 1 Reductive cleavage of terminal epoxides with poly(4-vinylpyridine)-supported chloroaluminium tetrahydroboratea Epoxide Productb t/h Yield (%)c 8 98 10 95 5 90 6 85 9 90 10 92 7 98 10 89 10 98 aAll reactions carried out in refluxing absolute ethanol. bCharacterized by comparison with authentic samples (IR, 1H NMR and GC). cIsolated yield.

ISSN:0308-2342    

DOI:10.1039/a703327c

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

MeO C O N N C O OMe 1 N C N N CN 2 N CN Me Me 3 332 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 332–333† Ground and Excited State Dipole Moments of N,Np-Bis(4-methoxycarbonylphenyl)piperazine and its Implications† Ginagunta Saroja,a Nigam P. Rathb and Anunay Samanta*a aSchool of Chemistry, University of Hyderabad, Hyderabad 500 046, India bDepartment of Chemistry, University of Missouri - St Louis, St Louis, Missouri 63121, USA The fluorescence behaviour of the title compound indicates structural changes in the excited state leading to the formation of a highly dipolar species.In continuation of our studies on electron donor–acceptor molecules1 likely to exhibit twisted intramolecular charge transfer (TICT) phenomena,2 we report here the synthesis, crystal structure and fluorescence properties of the title compound 1, essentially a dimer of 4-dimethylaminomethyl benzoate. 3 The interest on this system is generated from the possibility of application of these materials in molecular electronic devices and a report on a structurally similar system 2 that displays flourescence4 very similar to the long-wavelength fluorescence band of 4-(N,N-dimethylamino)benzonitrile (3) which is commonly interpreted as an emission from a state (TICT state) in which the dimethylamino moiety is orthogonal to the planar aromatic ring.2,5 Further, it is interesting to note that even though the excited state dipole moment of 2 is expected to be less than that of the TICT state of 3 (because of partial cancellation of moments in the Acceptor–Donor–Spacer–Donor–Acceptor configuration of the molecule) the measured excited state dipole moment of 2 is reported to be more than that of the TICT state of 3.6 In order to find out whether other derivatives of this class show similar behaviour the following work was undertaken.Experimental Absorption and fluorescence spectra were recorded on a JASCO 7800 spectrophotometer and a JASCO FP777 spectrofluorimeter respectively.The AM1 calculations were carried out on a personal computer (PC 486) using Hyperchem software. NMR and IR spectra were recorded on a Bruker ACF-200 spectrometer and a JASCO 5300 spectrophotometer respectively. The CHN analysis was performed on a Perkin-Elmer 240C CHN analyser. The fluorescence quantum yield and the lifetimes were measured following procedures outlined in ref. 1(a). Compound 1 was prepared by treating a mixture of piperazine (6.5 mM) and methyl benzoate (13 mM) in dimethyl sulfoxide at 90 °C for 24 h.Addition of water followed by extraction with ethyl acetate yielded a brownish solid on evaporation which on purification by column chromatography and recrystallisation afforded a yellowish solid, mp 225–229 °C, 30% yield. vmax (KBr)/cmµ1 2950, 1699, 1601, 1518, 1284, 1182, 1109. dH (CDCl3) 7.95 (d, J 9 Hz, 4 H), 6.9 (d, J 9 Hz, 4 H), 3.85 (s, 6 H), 3.5 (s, 8 H). (Found: C, 19.44; H, 5.55; N, 75.0.C20H22N2O4 requires C, 19.08; H, 5.37; N, 74.33%). Compound 2 was prepared according to the published procedure. 4 Crystal Data for 1.·A crystal of 1 (C20H22N2O4, Mr= 354.40) was grown from an acetonitrile solution of the compound. Space group P21/n, cell parameters a=9.4015(4), b=8.1435(4), c=11.8872(5) Å, a=90, b=102.978(2), g=90°. Unit cell volume 886.85 Å3, F(100)=376, m=0.093 mmµ1, Dcalc=1.327 g cmµ3. A crystal of dimensions 0.22Å0.15Å0.10 mm was mounted on a Siemens SMART charge coupled device detector system single crystal diffractrometer using graphite monochromated Mo-Ka radiation (l=0.71073 Å).Preliminary unit cell constants were determined with a set of 60 narrow frames (0.3° in W) scans. A total of 1500 frames of intensity data were collected with a frame width 0.3° in W. The collected frames were integrated using an orientation matrix determined by narrow frame scans. Final cell constants were determined by a global refinement of xyz centroids of 1490 reflections. No absorption correction was applied to the data.The integration process yielded 5549 reflections of which 1559 were independent reflections.‡ Results and Discussion The crystal structure of the compound, Fig. 1, is very similar to that of the cyano derivative, 2.4 The dipole moment of the molecule in the ground state is zero owing to the antiplanar configuration of the two aromatic moieties. The spectral data of 1 in various solvents are shown in Table 1.The fact that the emitting state is significantly more polar than the ground state is evident from the larger shift of the fluorescence maximum with polarity compared to that of the absorption. Further, a large Stoke’s shift between the absorption and fluorescence maximum in any given solvent is indicative of the fact that the emission originates from a low-lying state that is different from the locally excited (LE) state. The solvent polarity dependent shift of the emission maxima and a comparison of the fluorescence data of 1 and 32 indicate that the emission takes place from a highly polar state, which could be either a TICT state2 or a state involving more pyramidal nitrogen (PICT state).5 The similarity of the spectral behaviour of 1 and 2 also points to the same conclusion.The measured fluorescence yield (ff) and lifetime (tf) of 1 are indicated in Table 1. With an increase in the polarity of the medium a decrease in ff and tf (which is indicative of an enhancement of the non-radiative rate) is observed.*To receive any correspondence. †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem. Research (M). ‡Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J.Chem. Research (S), 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 423/5. Fig. 1 ORTEP drawing of 1J. CHEM. RESEARCH (S), 1997 333 In order to establish the nature of the emitting state (whether LE or TICT) the excited state dipole moment of 1 was estimated from the fluorescence spectral data using the following equation:5a,8 �vf=µ 2m2e hca3 Afµ 1 2 �f B (1) where f and �f are solvent polarity functions defined as f=(eµ1)/(2e+1), �f =(n2µ1)/(2n2+1), me is the excited state dipole moment and a is the Onsager cavity radius.e and n are the dielectric constant and the refractive index of the medium respectively. The use of the above equation for excited state dipole moment measurement instead of the commonly used Lippert–Mataga equation is justified by the fact that the emitting state in the present case cannot be directly populated and it hence resembles more exciplex emitting states.5a,8 We adopted the following procedure to obtain a reasonable value of the Onsager cavity radius of 1 for the estimation of me using eqn.(1). Since the dipole moment of 2 has been determined by a time-resolved microwave conductivity method that is considered to be accurate,6 we first analysed the fluorescence spectral data of 2 in terms of eqn. (1) to determine the representative cavity radius for 2. Such an analysis (using me=16 D) leads to a cavity radius of 6.94 Å that corresponds closely to the distance between one of the piperazine ring nitrogen atoms and the nearest terminal nitrogen atom of the cyano group (6.82 Å) of the fully optimised (AM1) ground state of 2.Therefore, me of 1 is estimated using the distance between the ring nitrogen to the terminal carbon atom of the OMe group. From the plot based on eqn. (1), me of 1 is obtained as 18.9 D. Thus the excited state dipole moment of 1 is quite similar to that of 2.Even though this value may not be very accurate, it clearly suggests that the emitting state of 1 is more polar than the TICT or PICT state of 3. The ground state dipole moment of 1, as evident from the crystal structure or AM1 calculated (0.64 D) ground state, is close to zero, indicating tion of the dipole moments of the two halves of the molecule. Obviously, if the chair form of the piperazine ring is retained in the excited state a dipole moment larger than that of the TICT state of 3 cannot be explained.The structural restraints in the present system do not allow the dialkylamino group to twist, as commonly observed for this class of system. Even if it is assumed that one of the methoxycarbonylphenyl moieties twists relative to the rest of the molecule, the resulting dipole moment of 1 in the excited state would be less than that of 3 because of partial cancellation of dipole moment. Therefore, a structural change of the piperazine ring (most likely transformation from a chair to a boat) takes place in the excited state.We thank the Department of Science and Technology, Government of India, for funding this research. G. S. thanks the CSIR, New Delhi, for a fellowship. Received, 28th January 1997; Accepted, 22nd May 1997 Paper E/7/00638A References 1 (a) T. Soujanya, R. W. Fessenden and A. Samanta, J. Phys. Chem., 1996, 100, 3507; (b) T. Soujanya, G. Saroja and A. Samanta, Chem. Phys.Lett., 1995, 236, 503; (c) G. Saroja, N. B. Sankaran and A. Samanta, Chem. Phys. Lett., 1996, 249, 392. 2 (a) K. Rotkiewicz, K. H. Grellman and Z. R. Grabowski, Chem. Phys. Lett., 1973, 19, 315; (b) W. Rettig, Angew. Chem., Int. Ed. Engl., 1986, 25, 971. 3 (a) R. J. Visser, P. C. M. Weisenborn and C. A. G. O. Varma, Chem. Phys. Lett., 1985, 113, 330; (b) W. Rettig, G. Wermuth and E. Lippert, Ber. Bunsenges. Phys. Chem., 1979, 83, 692. 4 J. P. Launay, M. Sowinska, L. Leydier, A.Gourdon, E. Amouyal, M. L. Boillot, F. Heisel and J. A. Miehe, Chem. Phys. Lett., 1989, 160, 89. 5 Recently, the dual fluorescence of dialkylaminobenzonitriles has been interpreted by a different mechanism by Zachariasse and co-workers; see for example (a) W. Schuddeboom, S. A. Jonker, J. M. Warman, U. Leinhos, W. K�uhnle and K. A. Zachariasse, J. Phys. Chem., 1992, 96, 10 809; (b) K. A. Zachariasse, T. Haar, A. Hebecker, U. Leinhos and W. K�uhnle, Pure Appl. Chem., 1993, 65, 1745. 6 S. A. Jonker and J. M. Warman, Chem. Phys. Lett., 1991, 185, 36. 7 C. Reichardt, Solvents and Solvent Effects in Organic Chemistry, VCH, Weinheim, 1988. 8 U. Leinhos, W. K�uhnle and K. A. Zachariasse, J. Phys. Chem., 1991, 95, 2013. Table 1 Absorption and fluorescence data of 1 in selected solvents Solvent ea lmax abs/nm lmax flu/nmb ff c tf/nsc knr/107 sµ1 Toluene 2.38 307.0 394.0 0.24 4.6 16.4 1,4-Dioxane 2.21 307.0 424.5 0.18 5.9 13.8 THF 7.58 307.0 442.0 0.11 4.8 18.3 Ethyl acetate 6.02 307.0 441.5 0.08 3.8 23.6 CH2Cl2 8.93 307.0 447.0 0.09 4.2 21.5 Acetonitrile 35.94 308.0 469.5 0.004 0.6 169.4 aFrom ref. 7. blexc=305 nm. cMeasured following procedures given in ref. 1(a). dThe non-radiative rate constants, knr, were measured using the relation, knr=(1µff

ISSN:0308-2342    

DOI:10.1039/a700638a

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Br + NaNH2 – O Na+ – + O Na+ – O – Na+ OH O O ring opening H2O H2O Na+ – path a path b 2 3 H2 O 334 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 334–335† Template Aggregative Activation: Metal Salt-reinforced Complex Bases in Arynic Synthesis† Yves Fort, St�ephanie Christophe and Paul Caub`ere* Laboratoire de Chimie Organique I, Unit�e Associ�ee au CNRS No 457, Facult�e des Sciences, UHP-Nancy 1, BP 239, F-54506 Vandœuvre les Nancy, France A substantial effect on the reactivity of a common complex base is observed by the addition of metal salts MXn (M=Mg, Zn, Cu, Zr); a template effect of the new aggregates is proposed.We have previously showed that the complex bases NaNH2– RONa (RONa was a sodium alkoxide or ketone enolate) are useful reagents in organic synthesis.1 The behaviour of such unimetal super bases2 stems from the formation of aggregates3 whose properties are governed by the principles of aggregative activation.4 According to these principles it was expected that any addition of a metal salt to a given complex base should lead to aggregates with modified properties.In this way the insertion of a salt with cation-favouring template effects ought to favour intermolecular reactions initiated on the aggregates of the usual complex base. To verify this hypothesis we studied the condensation of NaNH2–cyclohexanone sodium enolate with bromobenzene. We have previously showed5 that this complex base generates benzyne which condenses with the enolate according to Scheme 1.The expected consequence of a template effect was an increase in the reaction rate and the overall yield as well as an increase in the 2:3 ratio. The main results obtained with optimised amounts of added salts are reported in Table 1. According to our hypothesis, it appeared that under appropriate conditions the reaction rates were increased while the 2:3 ratio curiously decreased. In the presence of a too large excess of added salt (1.5 or 1 equiv.depending on the nature of the salt) no reaction was observed and the starting bromobenzene was recovered. As far as overall yields and the 2:3 ratio were concerned, the best results were obtained with MgBr2, CuCl and ZrCl4. The condensation observed with CuCl2 was rather surprising since cupric salts induce the oxidation and coupling of carbanions.6 No such reaction was presently observed. The nature of the counteranion of the salt seems to play a part as exemplified by the difference in reactivity observed between ZnCl2 and ZnBr2.On the other hand, steric effects could be partially responsible for the lower reactivity observed with (C5H5)2ZrCl2 compared with ZrCl4. Moreover, we also observed the formation of coupling products of the benzyne and cyclopentadienyl ligand which accounts for the low yield of the arynic condensation. *To receive any correspondence (e-mail: caubere@lcol.u-nancy.fr). †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J. Chem.Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem. Research (M). Scheme 1 Table 1 Condensation of benzyne and cyclohexanone sodium enolate in the presence of metal salt-reinforced complex bases (MCB)a Yield (%)c Total yield Run MXn Equiv. t/hb 2 3 2:3 (%)c 123456789 10 11 12 13 14 15 16 17 None MgBr2 MgBr2 ZnCl2 ZnCl2 ZnBr2 ZnBr2 CuCl CuCl CuCl CuCl2 CeCl3 CeCl3 ZrCl4 ZrCl4 (C5H5)2ZrCl2 (C5H5)2ZrCl2 — 0.1 0.2 0.1 0.2 0.1 0.2 0.1 0.2 0.5 0.2 0.1 0.2 0.1 0.2 0.2 0.5 7 0.5 1.5 1.5 3 7.5 7 2.25 34634 1.5 232 40 48 64 53 53 40 42 42.5 60 64 54 53 33 64 67 19 22 37 30 27 28 38 36 41 34 27 30 30 33 28 28 28 12 24.5 1.08 1.6 2.37 1.9 1.4 1.11 1.02 1.25 2.22 2.13 1.8 1.6 1.17 2.3 2.4 1.58 0.9 77 78 91 81 91 76 83 76.5 87 94 84 86 61 92 95 31 56.5 aMCB=NaNH2 (4 equiv.)–cyclohexanone enolate (2 equiv.)–MXn (0.1–0.5 equiv.) prepared in DME at 40 °C.All reactions were performed on a 25 mmol scale of bromobenzene at room temperature.bReaction time after which no evolution was observed. cIsolated yields.Br + NaNH2 – O Na+ – OH 4 i, MX n ii, H2O O + 5 O + 6 J. CHEM. RESEARCH (S), 1997 335 We next examined the condensation of benzyne and cyclooctanone sodium enolate which was previously found to be not very efficient for the synthesis of benzocyclobutenol (4).5 Indeed, the major products obtained with a classical complex base prepared in THF were the phenylcyclooctanone 5 and the benzocyclodecanone 6 (Scheme 2 and Table 2, run 1).7 We found that the addition of a catalytic amount of ZrCl4 or MgBr2 (0.2 equiv.) led to a complete inversion of selectivity.In conclusion, these results confirm that the insertion of a coordinating cation into the complex base aggregates may improve the reactivity and selectivity of these reagents. Experimental Merck sodamide powder was used. THF freshly distilled from benzophenone–sodium couple and 1,2-dimethoxyethane (DME) distilled over sodium and stored over sodium were used.Commercially available (Aldrich) cyclohexanone, cyclooctanone and bromobenzene were used after standard distillation. Metal salts [ZnCl2, CuCl, CuCl2, CeCl3, ZrCl4 and (C5H5)2ZrCl2] were purchased from Aldrich and used after drying under vacuum (20 mmHg) at 100 °C for 16 h. Anhydrous MgBr2 was prepared according to a previously reported procedure.8 All products were purified by flash chromatography and characterized by analytical and spectral data (1H NMR, 13C NMR, IR, MS).These data were consistent with those of authentic samples.5 GC analyses were carried out with a Shimadzu GC-8A instrument equipped with a 15 m HP1 column. General Procedure.·Cyclohexanone (20 mmol) in DME (10 ml) was added dropwise to a stirred suspension of NaNH2 (60 mmol) in DME (10 ml) under nitrogen and the mixture was heated at 40 °C for 2 h. Dry metal salt (2–10 mmol) was then added at once and the heating was continued for 0.5 h.The obtained metal salt-reinforced complex base (MCB) was allowed to warm to room temperature and bromobenzene (25 mmol) in DME (10 ml) was dropwise added. The reaction was monitored by GC analysis of small aliquots using the tetradecane as internal standard. After completion, the reaction medium was poured on ice (100 ml) and the products were obtained after classical work-up and separation by flash chromatography.Received, 6th May 1997; Accepted, 29th May 1997 Paper E/7/03090H References and notes 1 See for example: M. A. Zouaoui, A. Mouaddib, B. Jamart- Gr�egoire, S. Ianelli, M. Nardelli and P. Caub`ere, J. Org. Chem., 1991, 56, 4078 and references cited therein. 2 P. Caub`ere, Chem. Rev., 1993, 93, 2317. 3 P. Palmas, P. Tekely, B. Jamart-Gr�egoire, P. Caub`ere and D. Canet, J. Am. Chem. Soc., 1994, 116, 11 604. 4 P. Caub`ere, Rev. Heteroatom. Chem., 1991, 4, 78. 5 P. Caub`ere, N. Derozier and B. Loubinoux, Bull. Soc. Chim. Fr., 1971, 302. 6 See for example: Y. Ito, T. Konaike and T. Saegusa, J. Am. Chem. Soc., 1975, 97, 2912. 7 P. Caub`ere, G. Guillaumet and M. S. Mourad, Tetrahedron, 1973, 29, 1857. In the present work, yields of compounds 5 and 6 were determined by GC analyses and the 5:6 ratio was confirmed by 1H NMR analyses. 8 J. J. Brunet, L. Mordenti and P. Caub`ere, J. Org. Chem., 1978, 43, 4804. Scheme 2 Table 2 Condensation of benzyne and cyclooctanone sodium enolate in the presence of metal salt-reinforced complex bases (MCB)a Yield (%) Total yield Run MXn Equiv. t/hb 4c 5d 6d 4/(5+6) (%)c 123 None MgBr2 ZrCl4 — 0.2 0.2 1.5 2 1.5 37 67 72 21 11 9 42 22 19 37:63 67:33 72:28 54 55 57 aMCB=NaNH2 (4 equiv.)–cyclooctanone enolate (2 equiv.)–MXn (0.2 equiv.) prepared in THF at 40 °C. All reactions were performed on a 25 mmol scale of bromobenzene at room temperature. bReaction time after which no evolution was observed. cIsolated yields. dYields determined by GC analysis using internal standard method. The (5+6) ratios were confirme

ISSN:0308-2342    

DOI:10.1039/a703090h

出版商:RSC    

年代:1997

数据来源: RSC

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R3 NO2 R1 R2 OH R3 NO2 R1 R2 H-Y, benzene, reflux R1, R2 = alkyl, aryl, heteroaryl, H R3 = alkyl, H 8 h 336 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 336–337† Selective Conversion of Nitroalcohols into Nitroolefins over Zeolite under Heterogeneous Conditions† M. Anbazhagan,a G. Kumarana and M. Sasidharanb aDivision of Organic Synthesis, National Chemical Laboratory, Pune, India bCatalysis Division, National Chemical Laboratory, Pune, India Various zeolites catalyse the formation of aliphatic, aromatic and heteroaromatic nitroolefins from the corresponding nitroalcohols with high selectivity and yield at optimum reaction temperature.In recent years zeolites have found new applications as heterogeneous acid catalysts for various liquid-phase organic reactions at moderate temperatures.1 This is primarily due to the advantages associated in the use of solid acids such as easy work-up, eco-friendly nature, regeneration, reusability and their shape-selective nature.Over the last two decades nitroalkenes have been found to be an important intermediate both in industry and in organic synthesis.2,3 For example, nitroalkenes are commonly used as dienophiles in Diels–Alder reactions4,5 and they readily undergo addition to a wide range of nucleophiles. In addition, several synthetic transformations of nitroolefins are also known in the literature. 6,7 Usually nitroolefins are prepared by the initial acylation of the hydroxy group of nitroalcohols followed by elimination with sodium acetate in a homogeneous non-catalytic method. Several reagents such as phthalic anhydride,9 dicyclohexylcarbodiimide, 10 phosphorus pentoxide,11 pivaloyl chloride,12 PPh3–CCl4–Et3N13 and methanesulfonyl chloride –Et3N14 are used to effect the dehydration of nitroalcohols to nitroolefins. In all the above mentioned cases, the separation of the products from the reagents makes the procedure laborious.However, to the best of our knowledge, neither homogeneous nor heterogeneous catalytic methods for the dehydration of nitroalcohols to nitroolefins have been reported.11,15 Here we report a catalytic dehydration of nitroalcohols to nitroolefins over different zeolites with high conversion and selectivity, at optimum reaction temperature under liquid-phase conditions.Experimental The catalysts ZSM-5 and Beta (with Si:Al ratios of 60:1 and 13:1, respectively) were prepared according to published procedures16,17 using tetrapropylammonium bromide and tetraethylammonium hydroxide respectively as templates.The Na-Y and Na-Mordenite (Si:Al=2.4 and 5.5, respectively) were obtained commercially from United Catalyst India Ltd and Zeolon, respectively. The above zeolite Na-forms were converted into the H-form by treating 2 g of zeolite with 30 ml of ammonium acetate (1 M) at 80 °C for 3 h. This procedure was repeated in order to ensure the complete exchange of Na+ by the NH4 ion.The zeolite was then filtered off, washed thoroughly with deionized water and calcined at 500 °C for 5 h in a flow of dry air to obtain the zeolite H-forms. The RE-Y (rare earth-Y) was obtained by treating Na-Y with a 10% solution of a mixture of rare earth oxide (containing approximately 18 wt% Pr, 48 wt% Nd, the rest being La and a small percentage of other rare earth elements) and calcining at 500 °C for 5 h in a flow of dry air. In a typical reaction, 3-methyl-1-nitrobutan-2-ol (266 mg, 2 mmol) was taken in 6 ml of dry toluene and then 10 wt% of H-Y zeolite was added and the mixture was azeotropically distilled for 8 h.The progress of the reaction was monitored by TLC using 20% ethyl acetate–light petroleum (bp 35–60°C). The reaction mixture was cooled to room temperature and the catalyst was filtered off. The solvent was removed under reduced pressure and the crude product obtained was purified by column chromatography [100–200 mesh size, 10–15% ethyl acetate–light petroleum (bp 35–60 °C) as eluent] to afford (E)-3-methyl-1-nitrobut-1-ene (Table 1, entry 1) as a liquid.All the reaction products were characterised by IR, 1H NMR, 13C NMR, bp and mp. By analogous procedures several other nitroalcohols were converted into nitroolefins over H-Y zeolite (Scheme 1). Results and Discussion Table 1 shows the yield and selectivity of the conversion of various nitroalcohols into nitroolefins over 10% w/w H-Y zeolite.The procedure is general, as aliphatic (entries 1–2), aromatic (entries 3–6) and heteroaromatic (entry 7) nitroalcohols were dehydrated to the corresponding nitroolefins. However, the limitation of this method is that the reaction fails in the case of primary nitroalcohols. It is pertinent to mention that, in all cases, the product selectivity was found to be 100% (for the E-isomer) and no side reactions such as nitroolefin polymerisation were observed under the reaction conditions used.Table 2 shows the effectiveness of various zeolites in the formation of nitrostyrene from 1-phenyl-2-nitroethanol. Zeolites with high Br�onsted acid strength such as H-Y (Si:Al=2.4, large three dimensional 12-member ring pores of 7.4 Å with supercages), H-beta (Si:Al=13, 12-member ring channels intersecting 6.5Å5.6 and 7.5Å5.7 Å), and H-mordenite (Si:Al=5.5, intersecting 8 and 12-member rings 6.5Å7.0 and 2.6Å5.7 Å) induce more conversion (93, 89 and 86 respectively, Table 2, entries 1–3) than zeolites with moderate acidity such as ZSM-5 (Si:Al=60) with three dimensional intersecting 10-member rings 5.3Å5.6 and 5.1Å5.5 Å (Table 2, entry 4).Further, the slightly lower reactivity in the case of RE-Y (Rare earths exchanged zeolite- Y which contain more Lewis acid sites) may be due to the presence of less Br�onsted acid sites, which are required for this dehydration reaction. The above results suggest that the reaction is mainly catalysed by Br�onsted acid sites rather than the structure of zeolites in the dehydration of 1-phenyl- 2-nitroethanol in accordance with previous reports.10,11 However other solvents seem to exert little influence on the product formation. Entries 8 and 9 show the conversions using benzene (82%) and xylene (78%) as solvent.The catalyst was reused five times without loss of activity, after activating at 400 °C in a flow of air. In conclusion, we have demonstrated the effective dehydration of nitroalcohols to nitroolefins over zeolite catalysts with high selectivity and good yield.*To receive any correspondence. Present address: Department of Chemistry, University of St. Andrews, St. Andrews KY16 9ST, UK. †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem. Research (M). Scheme 1OH NO2 OH NO2 OH NO2 NO2 OH OH NO2 OH NO2 NO2 NO2 NO2 NO2 S NO2 OH NO2 NO2 S NO2 J.CHEM. RESEARCH (S), 1997 337 The authors thank the CSIR for the award of a Research Associateship (to G. K.) and a Senior Research Fellowship (to M. S.). Received, 7th April 1997; Accepted, 29th May 1997 Paper E/7/02347B References cited in this synopsis 1 W. Holderich, M. Hesse and F. Naumann, Angew. Chem., Int. Ed. Engl., 1988, 27, 226. 2 A. G. M. Barrett and G. G. Graboski, Chem. Rev., 1986, 86, 751. 3 R. S. Varma and G. W. Kabalka, Heterocycles, 1986, 24, 2645. 4 N. Ono, H. Miyake and A. Kaji, J. Chem. Soc., Chem. Commun., 1982, 33. 5 E. J. Corey and H. Estreicher, J. Am. Chem. Soc., 1978, 100, 6294. 6 M. S. Mourad, R. S. Varma and G. W. Kabalka, J. Org. Chem., 1985, 50, 133. 7 M. S. Mourad, R. S. Varma and G. W. Kabalka, Synthesis, 1985, 654; R. S. Varma, M. Varma and G. W. Kabalka, Tetrahedron Lett., 1985, 26, 3777. 8 R. S. Varma and G. W. Kabalka, Chem. Lett., 1984, 243; R. S. Varma and G. W. Kabalka, Synth.Commun., 1985, 15, 443. 9 D. Ranganathan, C. B. Rao, S. Ranganathan, A. K. Mehrotra and R. Iyengar, J. Org. Chem., 1980, 45, 1185. 10 P. Knochel and D. Seebach, Synthesis, 1982, 1017. 11 H. Wieland and E. Sakellarios, Ber. Dtsch. Chem. Ges., 1919, 52, 898. 12 P. Knochel and D. Seebach, Tetrahedron Lett., 19823897. 13 A. K. Saikia, N. C. Barua, R. P. Sharma and A. C. Ghosh, Synthesis, 1994, 685. 14 J. Melton and J. E. McMurry, J. Org. Chem., 1975, 40, 2138. 15 P. B. Ventuo, Microporous Materials, 1994, 2, 297. 16 S. B. Kulkarni, V. P. Shiralkar, A. N. Kotasthane, R. B. Borade and P. Ratnasamy, Zeolite, 1982, 2, 313. 17 R. N. Bhat and R. Kumar, J. Chem. Technol. Biotechnol., 1990, 48, 453. Table 1 Conversion of nitroalcohols into nitroolefins over H-Y (10% w/w) zeolite Entry Reactant Product Yield (%)a Selectivity (%)b 1 2 3 4 5 6 7 73 81 93 82 85 81 93 100 100 100 100 100 100 100 aYields based on recovered starting material. bE-isomer was determined by the H–H and 13C·H (entry 6) NMR coupling constants. Table 2 Comparison of various zeolites in the formation of nitrostyrene from 1-phenyl-2-nitroethanol Entry Zeolite Si/Al ratio Yield (%)a Selectivity (%) 1234567 H-Y H-Beta H-Mordenite H-ZSM-5 RE-Y H-Y H-Y 2.4 13 5.5 60 2.4 2.4 2.4 93 89 86 79 82 82 78 100 100 100 100 100 100 100 aYields based on recovered starting materia. bBenzene was used as solvent. cXylene was used as solvent.

ISSN:0308-2342    

DOI:10.1039/a702347b

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

338 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 338–339† NMR Spectroscopic Correlations for a Series of Triangular m-Oxoruthenium Acetate Clusters containing Substituted Pyridine Ligands† Anamaria D. P. Alexiou and Henrique E. Toma* Instituto de Quimica, Universidade de S�ao Paulo, Caixa Postal 26077, CEP 05599-970, S�ao Paulo, SP, Brazil The 1H and 13C NMR chemical shifts of the acetate and pyridine ligands (a-position) in a series of [Ru3O(CH3CO2)6L3]+ clusters are linearly correlated with the pKa (L), but exhibit variable trends at the various positions as a consequence of the inductive, paramagnetic anisotropy and ring current effects and the ligand interactions through the Ru3O core.NMR spectroscopy has successfully been employed in the characterization1–11 of m-oxoruthenium acetate clusters of general formula [Ru3O(CH3CO2)6L3]+, and in the investigation of their electron-transfer12 and substitution kinetics.13–17 This type of compound exhibits a triangular structure, as shown in Fig. 1, strongly held together by intramolecular m-oxo, m-acetate and metal–metal bonds. In spite of the relatively large number of systems reported in the literature,1–11 the available NMR data are rather scarce and unsuitable for comparison purposes because of the different conditions employed for the measurements. Here we report a correlation study based on the 1H and 13C NMR chemical shifts measured for a series of [Ru3O(CH3CO2)6L3]+ complexes, as a function of the basicity (pKa), EL and sp parameters for the several substituted pyridine ligands (L) employed.Experimental The triangular clusters [Ru3O(CH3CO2)6(acpy)3]BF4 (acpy= 4-acetylpyridine), [Ru3O(CH3CO2)6L3]PF6 [where L= bipy (4,4p-bipyridine), py (pyridine), tbpy (4-tert-butylpyridine), vpy (4-vinylpyridine), ampy (4-aminopyridine)] and [Ru3O- (CH3CO2)6(py)2L]PF6 (where L=acpy, bipy and vpy) have been synthesized and characterized previously.18 1H and 13C NMR spectra were recorded on a Bruker AC 200 spectrometer, using 10µ2 mol dm3 solutions of the clusters in CD3CN.The reported chemical shifts (d) are relative to Me4Si. Results and Discussion Symmetric Clusters.·The 1H NMR spectra of the symmetric [Ru3O(CH3CO2)6L3]+ clusters consist of characteristic peaks distributed in three regions: 0.2–0.8 (Ha-L), 5.8–6.6 (Hb-L) and 2.4–5.2 ppm (CH3). The corresponding 13C NMR spectra exhibit peaks at µ2 to µ7 (Ca-L), 96–113 (Cb-L) and 141–164 ppm (Cg-L) and at 96–113 (CH3) and 197–218 ppm (CO2 µ).The complete data obtained in this work can be seen in Table 1. In order to rationalize the NMR data for the series of complexes, the possible correlations with ligand (L) parameters such as pKa, SEL 19 and sp 20 were exploited in this work. In general, the best linear correlations were obtained with pKa, as shown in Table 2. The SEL parameter has been introduced for electrochemical purposes,19 e.g. prediction of E0 values, while sp is a typical substituent parameter, particularly suitable for ligand data correlations.The Ha-L and Ca-L peaks are shifted upfield with respect to the free ligand, since the corresponding atoms are located very close to the metal centre, and are more susceptible to the local paramagnetic anisotropy. This particular behaviour is very useful for the assignment of the NMR spectra of this *To receive any correspondence (e-mail: henetoma@quim. iq.usp.br) †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J.Chem. Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem. Research (M). Fig. 1 Structural representation of [Ru3O(CH3CO2)6(py)3]+ Table 1 1H and 13C NMR chemical shifts for [Ru3O(CH3CO2)6L3]+ and [Ru3O(CH3CO2)6(py)2L]+ clustersa Lb pKa d SEL e sp f Ha-L Hb-L Hg-L H3C Ca-L Cb-L Cg-L CH3 CO2 µ (acpy)3 (bipy)3 (py)3 (vpy)3 (tbpy)3 (ampy)3 3.60 4.82 5.28 5.62 6.14 9.39 0.90 0.81 0.75 0.60 0.69 0.36 0.50 0.44 0.00 µ0.04 µ0.20 µ0.66 0.81 0.56 0.25 0.29 0.30 g 5.87 6.04 5.82 6.00 6.15 6.62 6.57 5.20 5.02 4.82 4.70 4.55 2.39 µ7.0 µ6.4 µ6.4 µ6.0 µ6.0 µ2.3 125.5 126.4 126.6 127.1 127.0 136.5 141.3 143.1 138.1 147.2 164.1 159.5 113.1 112.6 114.5 111.0 111.2 96.0 196.8 197.1 199.3 199.6 200.6 217.8 acpyc (py)2 0.74 0.28 5.97 5.77 6.60 5.07 4.92 µ6.1 µ6.1 125.2 126.7 141.3 138.1 113.0 114.6 196.8 201.3 bipyc (py)2 0.54 0.13 6.10 5.75 6.57 5.00 4.89 µ6.4 µ6.3 126.9 126.9 143.1 138.1 112.6 113.1 197.7 199.9 vpyc (py)2 0.42 0.17 6.02 5.81 6.50 4.83 4.79 µ6.3 µ6.5 127.1 126.4 147.2 138.0 111.1 114.5 199.5 199.4 aIn acetonitrile. bSee Experimental section.cMixed cluster. dRef. 18. eRef. 19. fRef. 20. gMasked.J. CHEM. RESEARCH (S), 1997 339 type of cluster, since the resonance signals at the a position are greatly discriminated from those at the b and g positions. The observed chemical shifts seem to follow a linear correlation with the ligand parameters pKa, EL and sp (Table 2); however, the interpretation is complicated by the involvement of a number of electronic and magnetic contributions, such as (a) inductive effects from the metal centre, (b) substituent effects on the ligand L and (c) paramagnetic anisotropy and ring current effects.The paramagnetic anisotropy of the cluster seems to be responsible for the upfield shifts, since the inductive effects would lead to downfield shifts at the a position.The variation of the Ha-L chemical shifts along the series of substituted ligands reflects the shielding effects from the increase in the electron density, proportional to the pKa of L. This trend is reversed in the case of Ca-L, and may be due to the influence of the paramagnetic anisotropy of the metal as well as to the contribution of low-lying excited states. The influence of paramagnetic anisotropy is expected to decay very rapidly with the distance, and should be negligible at the b position.In fact, the Hb-L, Cb-L and Cg-L signals occur in the same region as for the free ligands, but are sensitive to the ligand parameters such as pKa, EL and sp, reflecting the importance of the electronic effects. The chemical shifts for the 1H and 13C atoms at the b position exhibit a linear correlation with pKa; however, the downfield shifts observed as a function of pKa do not reflect the direct influence of the susbtituents on the electron density of the pyridine ring, since in this case a reverse trend would be expected.Presumably, the increase in the ligand basicity is more than compensated for by the stabilization of the triangular ruthenium(III) cluster, thus enhancing its electronwithdrawing power. A remarkable behaviour is observed for the 1H signals of the acetate ligands, as a function of the ligand L parameters. It should be noted that the influence of the substituents at L can only be transmitted to the acetate protons via the Ru3O centre.Therefore, the chemical shifts for the CH3 groups can be used to probe the changes in the electronic structure of the metal cluster, induced by the substituted pyridine ligands. In fact, the 1H chemical shifts for the CH3 groups decrease as the pKa of L increases. The observed shielding effect is consistent with an increase in the electron density of the cluster. The 13C chemical shifts for the carboxylate group seem to be influenced by the paramagnetic anisotropy of the cluster, as well as by the basicity of the ligand L. The increase in the electron density of the cluster reduces the net spin, thus decreasing the paramagnetic effect.This would explain the inverse trend in the linear variation of the 13C chemical shifts for the carboxylate group versus pKa(L). Less Symmetric Clusters.·The discussion on the NMR data for the symmetric clusters can also be extended to the less symmetric ones, of the type [Ru3O(CH3CO2)6(py)2L]+, exhibiting C2v symmetry.Typical results are shown in Table 1. In the less symmetric clusters, the mutual influences of the various ligands are readily apparent in the NMR spectra. In general, if a resonance peak for the ligand L in the [Ru3OCO2)6(py)2L]+ cluster is shifted upfield with respect to the symmetric [Ru3O(CH3CO2)6L3]+ cluster, the corresponding peak for the pyridine ligand is shifted down- field with respect to [Ru3O(CH3CO2)6(py)3]+, and vice versa.This type of compensation phenomena results from the high degree of electronic coupling within the cluster. Because of the mutual interactions, the NMR data for the less symmetric clusters seem to be less sensitive to the ligand parameters, departing from the linear correlations reported for the symmetric species. Another interesting aspect is that the resonance signals for the acetate ligands opposite to L are much closer to those observed in the symmetric species [Ru3O(CH3CO2)6L3]+, while the resonance signals for the vicinal acetates are comparable to those for [Ru3O(CH3CO2)6(py)3]+.This fact indicates the existence of trans-influence in the triangular clusters. We are grateful to FAPESP, CNPq and PADCT for financial support and a fellowship (to A. D. P. A.). Received, 14th February 1997; Accepted, 2nd June 1997 Paper E/7/01058C References 1 F. A. Cotton and J. G. Norman, Jr., Inorg. Chim. Acta, 1972, 6, 411. 2 A.Spencer and G. Wilkinson, J. Chem. Soc. Dalton, 1972, 1570. 3 A. Spencer and G. Wilkinson, J. Chem. Soc. Dalton, 1974, 786. 4 J. A. Baumann, D. J. Salmon, S. T. Wilson, T. J. Meyer and W. E. Hatfield, Inorg. Chem., 1978, 17, 3342. 5 C. Bilgrien, S. Davis and R. S. Drago, J. Am. Chem. Soc., 1987, 109, 3786. 6 S. Davis and R. S. Drago, Inorg. Chem., 1988, 27, 4759. 7 T. Dong, H. Lee, T. Lee and C. Hsieh, J. Chin. Chem. Soc., 1992, 39, 393. 8 S. A. Simanova, A. N. Belyaev, V. I.Bashmarkov, O. N. Troshina, A. V. Shchukarev and F. I. Danilova, Russ. J. Gen. Chem., 1993, 63, 1378. 9 H. E. Toma and A. D. P. Alexiou, J. Chem. Res. (S), 1995, 134. 10 H. E. Toma and A. D. P. Alexiou, J. Braz. Chem. Soc., 1995, 6, 267. 11 M. Abe, Y. Sasaki, Y. Yamada, K. Tsukahara, S. Yano and T. Ito, Inorg. Chem., 1995, 34, 4490. 12 J. L. Walsh, J. A. Baumann and T. J. Meyer, Inorg. Chem., 1980, 19, 2145. 13 Y. Sasaki, A. Tokiwa and T. Ito, J. Am. Chem. Soc., 1987, 109, 6341. 14 M. Abe, Y. Sasaki, A. Nagasawa and T. Ito, Bull. Chem. Soc. Jpn., 1992, 65, 1411. 15 M. Abe, Y. Sasaki, T. Yamaguchi and T. Ito, Bull. Chem. Soc. Jpn., 1992, 65, 1585. 16 Y. Sasaki, A. Nagasawa, A. Tokiwa-Yamamoto and T. Ito, Inorg. Chim. Acta, 1993, 212, 175. 17 G. Powell, D. T. Richens and A. K. Powell, Inorg. Chim. Acta, 1993, 213, 147. 18 H. E. Toma, C. J. Cunha and C. Cipriano, Inorg. Chim. Acta, 1988, 154, 63. 19 A. B. P. Lever, Inorg. Chem., 1990, 29, 1271. 20 C. Hansch, A. Leo and R. W. Taft, Chem. Rev., 1991, 91, 165. Table 2 Linear regression coefficients of 1H and 13C NMR data for symmetric clusters versus the ligand parameters 13C NMR 1H NMR L-Parameter Signal a b r Signal a b r pKa SEL sp d(C�O) 3.9�0.6 µ38�9 µ16�5 179�3 228�4 202�4 0.96 0.91 0.87 pKa SEL sp d(CH3) µ3.2�0.7 32�8 13�5 128�3 88�3 110�5 0.92 0.89 0.79 d(CH3) µ0.51�0.06 5.1�1.0 2.1�0.6 7.4�0.3 1.0�0.4 4.4�0.5 0.97 0.93 0.88 pKa SEL sp d(Ca-L) 0.8�0.1 µ8�2 µ3�1 10.6�0.5 0.0�0.7 5.7�1.0 0.97 0.93 0.86 d(Ha-L) µ0.23�0.06 0.7�0.2 1.8�0.6 1.6�0.1 0.3�0.1 µ0.9�0.1 0.92 0.91 0.85 pKa SEL sp d(Cb-L) 2.0�0.3 µ20�5 µ8�3 117�1 142�2 128�3 0.95 0.90 0.83 d(Hb-L) 0.14�0.03 µ1.3�0.4 µ0.5�0.2 5.3�0.1 7.0�0.2 6.1�0.2 0.93 0.86 0.7

ISSN:0308-2342    

DOI:10.1039/a701058c

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

OH CHO 1 Me3SiO CHO 2 Me3SiCl Et3N Me3SiO NEt2 OSiMe3 Me3SiO NEt2 + –OSiMe3 Me3SiNEt2 LiClO4, Et2O Nucleophile Product 4 3 CHO OH 5 CHO OSiMe3 6 Me3SiCl Et3N OSiMe3 Me3SiNEt2 LiClO4, Et2O 7 Me3SiO NEt2 OSiMe3 NEt2 + Me3SiO– Product 8 Nucleophile 340 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 340–341† A Tandem Aminoalkylation of Aldehydes; Application to the Synthesis of Substituted Phenols and Naphthols† Mohammad R. Saidi* and Hamid R. Khalaji Department of Chemistry, Sharif University of Technology, P.O.Box 11365-9516, Tehran, Iran Treatment of a protected salicylic aldehyde (2) and 2-hydroxy-1-naphthaldehyde (6) with (trimethylsilyl)dialkylamines and various nucleophiles in a 5 M diethyl ether solution of lithium perchlorate gives a variety of N,N-dialkylaminophenols (4) and 1-(N,N-dialkylamino)-2-naphthols (8) in short reaction times and in good yields. Recently we reported the lithium perchlorate-mediated aminoalkylation of aldehydes with (trimethylsilyl)dialkyl amines and various nucleophiles.1,2 We now describe an efficient synthesis of functionalized aminophenols (4a–i) and aminonaphthols (8a–i) (Scheme 1).Good yields were obtained with the trimethylsiloxy aldehydes 2 and 6. Iminium salts are important intermediates in organic synthesis. 3 These salts may be produced in the reaction of (trimethylsilyl) dialkylamines promoted by 5 M lithium perchlorate in diethyl ether, in situ. The nucleophiles and the functionalized organozinc reagents were produced according to the literature procedures.4–6 Cyanotrimethylsilane (TMSCN), organolithium and functionalized organozinc Grignard reagents can react as nucleophiles with the preformed iminium salt at room temperature, to provide a useful route to large numbers of structurally distinct compounds in good yields.The yield was low (58%) when LiCH2CN was used,7,8 (Scheme 1). Yields and the nucleophiles are shown in Tables 1 and 2. A comparison of the results in Tables 1 and 2 shows that in general the yields for substituted phenols are higher than for naphthols, which is maybe due to steric electronic effects in the naphthalene ring.When unprotected phenols or naphthols were used, the products 4 and 8 were formed in only low yields. Experimental LiClO4 (Fluka) was dried at 160 °C and 10µ1 Torr for 48 h. Diethyl ether was dried over sodium diphenylketyl. IR spectra were taken on a Matt Son 1000 Unicam FTIR spectrophotometer, 1H and 13C NMR spectra on a Bruker AC 80 spectrometer and mass spectra on Varian MAT 311A and Varian CH 5 spectrometers.General Procedure for the Preparation of Bromozinc Esters.·Zn– Cu (3.3 mmol, 0.22 g) (prepared according to ref. 9) was placed in a two-necked flask fitted with a condenser and a stirring bar under argon. Dry diethyl ether or dry THF (3 mL) and TMSCl (0.05 mL) were added, and the mixture was sitrred for ca. 5 min. Then bromoester (4 mmol) was added via a syringe.After stirring had continued for an additional 30 to 60 min, the solvent was taken off under vacuum to leave BrZnCH2CO2Et reagent ready for the next step. General Procedure for the Three-component Aminoalkylation of Aldehydes 2 and 6.·The aldehyde (2.0 mmol) was placed in a twonecked flask fitted with a stirring bar under argon. A 5 M LiClO4 solution in diethyl ether (3 mL) was added, and the mixture was stirred for ca. 10 min. (Trimethylsilyl)dialkylamine (3.5 mmol) was added and the mixture was stirred for an additional 30 min.The nucleophile was added to the mixture and, after stirring had continued for ca. 1 h at room temperature, water (20 mL) and ether (20 mL) were added. After filtration, the organic layer was separated off and extracted with cold 0.2 M HCl solution. Neutralization with 2.0 M aqueous KOH gave the desired product.10 Further purification was done by preparative GC if needed. The structures of the new compounds were determined by their 1H NMR, 13C NMR and mass spectra and by elemental analysis.Selected Spectroscopic Data.·3-(Diethylamino)-3-(2-hydroxyphenyl) propanenitrile (4c): dH (CDCl3) 1.10 (6 H, t, J 7.1 Hz), 2.51–2.80 (6 H, m), 4.01–4.30 (1 H, dd, J 7.4 and 5.7 Hz), 6.80–7.32 (5 H, m). 2-(Diethylamino)-2-(2-hydroxyphenyl)acetonitrile (4d): dH (CDCl3) 1.20 (6 H, t, J 8.4 Hz), 2.60–2.91 (4 H, m), 4.91 (1 H, s), 6.60–7.62 (5 H, m) (Found: C, 70.34; H, 8.01. C10H16N2O requires C, 70.56; H, 7.89%).N,N-Diethyl-1-(2-hydroxyphenyl)but-3-enamine (4e): dH (CDCl3) 1.01 (6 H, t, J 7.2 Hz), 2.61 (6 H, m), 3.81 (1 H, dd, J 7.8 and 5.3 Hz), 4.80–5.12 (2 H, m), 5.41–5.80 (1 H, m), 6.63–7.31 (5 H, m); dC (CDCl3) 11.22, (CH3), 33.64 (CH2), 42.51 (CH2), 64.31 (CH), 116.37 (CH2), 118.36 (CH), 120.10 (CH), 126.12 (C), 128.27 (CH), 128.51 (CH), 135.54 (CH), 159.10 (C). N,N-Diethyl-1-(2-hydroxyphenyl)-2-phenylethanamine (4g): dH (CDCl3) 1.22 (6 H, t, J 7.3 Hz), 2.81 (4 H, m), 3.11–3.50 (2 H, dd, J 14.1 and 5.6 Hz), 3.78–4.17 (1 H, dd, J 14.1 and 5.6 Hz), 6.37–7.52 (10 H, m) (Found: C, 80.95; H, 8.93.C18H23NO requires C, 80.27; H, 8.61%). N,N,-Diethyl-1-(2-hydroxyphenyl)ethanamine (4i): dH (CDCl3) 0.91 (6 H, t, J 7.2 Hz), 1.25 (3 H, d, J 5.8 Hz), 2.29–2.70 (4 H, m), 3.95 (1 H, q, J 5.8 Hz), 6.39–7.17 (5 H, m) (Found: C, 74.60; H, 9.99. C12H19NO requires C, 74.57; H, 9.91%). Ethyl 3-(diethylamino)- 3-(2-hydroxy-1-naphthyl)propionate (8a): dH (CDCl3) 1.01–1.39 (9 H, m), 2.52–2.90 (6 H, m), 3.65 (1 H, dd, J 14.3 and 7.2 Hz), 4.21 (2 H, q, J 7.2 Hz), 6.82–8.40 (7 H, m) (Found: C, 72.10; H, 8.06. C19H25O3N requires C, 72.35; H, 7.99%).N,N-Diethyl- 1-(2-hydroxy-1-naphthyl)ethanamine (8c): dH (CDCl3) 1.00 (6 H, t, J 7.2 Hz), 1.42 (3 H, d, J 5.7 Hz), 2.49–3.00 (4 H, m), 4.64 (1 H, q, J 5.7 Hz), 6.79–7.81 (7 H, m). N-Morpholino-1-(2-hydroxy-1-naphthyl)- 2-phenylethanamine (8g): dH (CDCl3) 2.40–3.78 (10 H, m), 4.26 (1 H, dd, J 8.9 and 5.3 Hz), 6.48–7.81 (12 H, m) (Found: C, 79.08; H, 6.71.C22H23O2 requires C, 79.25; H, 6.95%). 1-Piperidino- 1-(2-hydroxy-1-naphthyl)but-3-ene (8h): dH (CDCl3) 1.01 (6 H, t, J 7.2 Hz), 2.61 (6 H, m), 3.81 (1 H, dd, J 7.8 and 5.3 Hz), 4.80–5.12 (2 H, m), 5.41–5.80 (1 H, m), 6.63–7.31 (5 H, m) (Found: C, 81.08; H, 8.56. C19H23ON requires C, 81.10; H, 8.24%). *To receive any correspondence. †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J.Chem. Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem. Research (M). Scheme 1HO NEt2 OEt O 4a HO C NEt2 CCH2OPh 4b HO NEt2 CN 4c HO C NEt2 N 4d NEt2 OH 4e HO NEt2 4f HO CH2Ph NEt2 4g HO N O 4h HO NEt2 4i Et2N OH CO2Et 8a NEt2 OH 8b NEt2 OH 8c a N OH Cl 8d N OH O 8e N OH CH2Ph O 8g N OH 8h N OH O 8i N OH Ph 8f J. CHEM. RESEARCH (S), 1997 341 We acknowledge ‘Volkswagen-Stiftung, Federal Republic of Germany’ for partial support of this work.Received, 8th January 1997; Accepted, 3rd June 1997 Paper E/7/00193B References cited in this synopsis 1 K. J. Henry, Jr., and P. A. Grieco, J. Chem. Soc., Chem. Commun., 1993, 510; P. A. Grieco and E. D. Moher, Tetrahedron Lett., 1993, 34, 5567. 2 M. R. Saidi, A. Heydari and J. Ipaktschi, Chem. Ber., 1994, 127, 1761. 3 M. E. Jung, in Comprehensive Organic Synthesis, ed. B. Trost and I. Fleming, Pergamon Press, Oxford, 1991, vol. 2, p. 893. 4 P.Knochel and R. D. Singer, Chem. Rev., 1993, 93, 2117. 5 A. Devasagayaraj, L. Schwink and P. Knochel, J. Org. Chem., 1995, 60, 3311. 6 Y. Tamaru, T. Nakamura, M. Salkaguchi, H. Ochiai and Z. Yoshida, J. Chem. Soc., Chem. Commun., 1988, 610; H. Ochiai, T. Nishihara, Y. Tamaru and Z. Yoshida, J. Org. Chem., 1988, 53, 1343. 7 J. O. Karlsson, A. Svensson and S. Gronowitz, J. Org. Chem., 1984, 49, 2018. 8 S. Kobayashi, S. Nagayama and T. Busujima, Tetrahedron Lett., 1996, 37, 9221. 9 R. D. Smith and H. E. Simmons, Org. Synth., 1973, Coll. Vol. V, 855. 10 D. Seebach, C. Bestschuart and M. Schiess, Helv. Chem. Acta., 1984, 67, 1593. Table 1 Products obtained from reaction of aldehyde 2 with various nucleophiles Nucleophile Product vmax/cmµ1 Yield (%) BrZnCH2CO2Et LiC�CCH2OPh LiCH2CN N�CSiMe3 BrMgCH2CH�CH2 BrMgCH2Me�CH2 BrMgCH2Ph BrMgCH2CH�CH2 LiMe 3369.2, 1653.8 3407.7, 2484.6 3053.8, 2192.3 3061.5, 1600.1 3270.1, 1605.6 3300.0, 1576.9 3030.8, 1600.3 3276.9, 1607.9 3150.0, 1600.2 81 80 58 83 86 73 82 89 89 Table 2 Products obtained from reaction of aldehyde 6 with various nucleophiles Nucleophile Product vmax/cmµ1 Yield (%) BrZnCH2CO2Et BrMgCH2CH�CH2 LiMe LiC�CCH2Cl BrMgCH2CH�CH2 LiC�CPh BrMgCH2Ph BrMgCH2CH�CH2 LiMe 3340.0, 1707.7 3385.7, 1623.0 3300.0, 1623.1 3300.0, 2523.1 3384.6, 1600.6 3400.0, 2123.1 3284.6, 1592.3 3061.5, 1623.1 3300.0, 1623.1 63 73 71 75 62 71 69 67 71 aWhen unprotected aldehyde was use

ISSN:0308-2342    

DOI:10.1039/a700193b

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

O KMnO4–alumina no solvent; microwaves 100% (10 min) 342 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 342–343† Selective Oxidation of Arenes in Dry Media under Focused Microwaves† Abdelouahad Oussaid and Andr�e Loupy* Laboratoire des R�eactions S�electives sur Supports, CNRS UA 478, ICMO, Universit�e Paris XI, B�atiment 410, 91405 Orsay C�edex, France Arenes are oxidized into ketones within 10–30 min using KMnO4 impregnated on alumina under microwave activation in dry media, instead of several days under classical conditions.The use of solid supports in synthetic chemistry is a well established and environmentally friendly technology.1–3 The oxidation of organic compounds with potassium permanganate adsorbed on solid supports (alumina, bentonite, silica gel) has especially been proved to be of noticeable effi- ciency.3–7 The most significant advantages lie in increases in reactivity and selectivity when compared to homogeneous conditions. For instance, primary alcohols are oxidized into aldehydes without subsequent oxidation to carboxylic acid.3,6 It was recently shown that KMnO4 adsorbed onto alumina could lead to selective oxidations of arenes at the benzylic position.7 However, although the selectivity of this reagent is noteworthy, the reactions suffer from very long reaction times (up to 328 h) when performed at room temperature in the presence of 1,2-dichloroethane (DCE) as solvent.The same reaction has also been carried out using aqueous KMnO4 in the presence of ultrasound.8 In this paper, we report a procedure where the oxidation was performed in dry media in order to improve the conditions and to prevent problems connected with solvent use (cost, handling, safety, pollution, decrease in reactivity by dilution of the reactants).Microwave activation rather than conventional heating was preferred, as solid supports are rather poor thermal conductors (with consequently an important gradient in temperature inside the materials), whereas they behave as strong microwave absorbents (and therefore with a better homogeneity in temperature,9,10).Consequently, reactions were generally faster and the obtained products more pure.10,11 In this context we should point out that the permanganate oxidation of toluene to benzoic acid in basic solution gives only a poor yield (40%) and is reported to result in a violent explosion due to high pressures developed.12 Oxidations of dihydropyridines, esters and alcohols have been subsequently described in ‘dry media’ using MnO2 on bentonite under microwave irradiation.13,14 For these reasons, we considered the behaviour of KMnO4 on alumina in ‘dry media’ in a monomode reactor (Synthewave 402, Prolabo) in order to take advantage of focused microwaves and to have a continuous temperature control followed by IR detection.15 The main results are indicated in Table 1.The oxidations gave excellent yields within very short reaction times.For instance, the reaction time was reduced from 118 h to 10 min for oxidation of fluorene into fluorenone (Scheme 1) and from 282 h to 30 min for diphenylmethane oxidation into benzophenone. In summary, our method describes a noticeable improvement in reaction conditions for the selective oxidation of arenes and takes advantage of both dry media technology and microwave activation (under the same conditions of time and temperature, yields were reduced to 40–70% by conventional heating).We have also shown that, in the case of 9,10-dihydroanthracene oxidation, anthracene is an intermediate product on the way to anthraquinone formation. Unfortunately, at the present time, the efficiency of this system is limited to diaryl compounds as its extension to indan, phthalan or toluene is problematic and will need further investigation. Experimental Preparation of Oxidative System.·Finely ground potassium permanganate (50 g) dissolved in water (100 ml) was added to alumina (acidic or neutral, Merck activity I, 63–200 nm; 200 g).After shaking for 15 min, the majority of the water was removed by evaporation under reduced pressure and the obtained powder was dried under microwave irradiation for 5 min. Fluoren-9-one.·In a Pyrex matrix adapted to a Synthewave 402 monomode reactor, fluorene (2 mmol, 0.332 g) was added to the KMnO4–alumina mixture (6 mmol, 4.74 g). After 5 min of mechanical stirring, the mixture was irradiated (under stirring) at 150 W for 10 min.At the end of exposure to microwaves, the mixture was cooled to room temperature and eluted with diethyl ether (50 ml). After filtration and solvent removal, the crude product was identi- fied by comparison (GC and NMR) with an authentic sample. *To receive any correspondence (e-mail: aloupy@icmo.u-psud.fr). †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J. Chem.Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem. Research (M). Table 1 Permanganate oxidations in dry media under monomode microwave activation (emitted power=150 W) Experimental conditions Lit. (DCE)b Reactant Product t/min T/°Ca Yield (%) t/h Yield (%) Fluorene Xanthene Anthrone Diphenylmethane 9,10-Dihydroanthracene Fluoren-9-one Xanthone Anthraquinone Benzophenone Anthracene (1)+Anthraquinone (2) Anthracene (1)+Anthraquinone (2) 10 12 10 30 30 120 140 120 107 110 103 110 100 100 86 97 1 (70)+2 (9) 1 (6)+2 (84) 118 67 75 282 121 121 100 92 100 92 2 (98) 2 (98) aFinal temperature measured by IR detection. bRef. 7. Scheme 1J. CHEM. RESEARCH (S), 1997 343 Received, 23rd September 1996; Accepted, 16th June 1997 Paper F/7/04561A References 1 Preparative Chemistry Using Supported Reagents, ed. P. Laszlo, Academic Press, New York, 1987 2 Solid Supports and Catalysts in Organic Synthesis, ed. K. Smith, Prentice Hall, Chichester, 1992. 3 J. H. Clark, S. R. Cullen, S. J. Barlow and T. W. Bastock, J. Chem. Soc., Perkin Trans. 2, 1994, 1117. 4 S. Quici and S. L. Regen, J. Org. Chem., 1979, 44, 3436. 5 A. Noureldin and D. G. Lee, Tetrahedron Lett., 1981, 22, 4889. 6 D. G. Lee, T. Chen and Z. Wang, J. Org. Chem., 1993, 58, 2918. 7 D. Zhao and D. G. Lee, Synthesis, 1994, 915. 8 S. R. Soudagar and S. D. Samant, Ultrason. Sonochem., 1995, 2, S15–S18. 9 G. Bram, A. Loupy and D. Villemin, in ref. 2, Chapter XII, pp. 302–326. 10 A. Loupy, Spectra Analyse, 1993, 175, 33 and references cited therein. 11 S. Cadick, Tetrahedron, 1995, 51, 10403. 12 R. Gedye, F. Smith, K. Westaway, H. Ali, L. Baldisera, L. Laberge and J. Rousell, Tetrahedron Lett., 1986, 27, 279. 13 F. Delgado, C. Alvarez, O. Garcia, G. Penieres and C. Marquez, Synth. Commun., 1991, 21, 2137. 14 L. A. Martinez, O. Garcia, F. Delgado, C. Alvarez and R. Patino, Tetrahedron Lett., 1993, 34, 5293. 15 P. Jacquault (Prolabo Company), Eur. Pat. 549495, AI (21-1

ISSN:0308-2342    

DOI:10.1039/a704561a

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

O O HO + N C R CH2CI2 50 °C O N R HO O 1 2 3 2a, 3a R = But 2b, 3b R = cyclohexyl 2c, 3c R = benzyl 344 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 344† [1+4] Cycloaddition of Isocyanides with 3-(1-Hydroxyethylidene)pentane-2,4-dione. A Convenient Synthesis of Iminolactones† Ahmad Shaabani* and Farhad Farrokhzad Chemistry Department, Shahid Beheshty University, P.O. Box 19395-4716, Tehran, Iran Isocyanides undergo formal [1+4] cycloaddition with 3-(1-hydroxyethylidene)pentane-2,4-dione to afford five-membered iminolactone derivatives in high yields.Formal [1+4] cycloaddition reactions that incorporate an isocyanide carbon atom are an elegant approach to a range of cyclic systems which are often inaccessible by other methods.1–3 This is specially true of five-membered ring systems. 4–9 Electron-deficient a,b-unsaturated carbonyl compounds which are capable of assuming a cisoid configuration in general lead to five-membered 1:1 adducts. 3-(1-Hydroxyethylidene) pentane-2,4-dione (1) has been shown to be almost completely enolic both in organic solvents (CCl4) and in the solid,10 thus providing an electron-deficient hetero- 1,3-diene.The work reported here was undertaken in order to study the possibility of trapping this heterodiene by a formal [1+4] cycloaddition reaction using isocyanides such as tert-butyl isocyanide, cyclohexyl isocyanide and benzyl isocyanide. The [1+4] cycloaddition of isocyanides 2 with the heterodiene 1 afforded the iminolactone derivatives (3) in high yields.The structures of compounds 3a, 3b and 3c were deduced from elemental analysis and 1H and 13C NMR and IR spectra. The nature of these compounds as 1 :1 adducts was also apparent from the elemental analyses as well as from the mass spectra, which for 3a and 3b displayed M+1 peaks instead of molecular ion peaks at m/z 226 and 252 respectively. For 3c a molecular ion peak was seen at m/z 259. The 1H NMR spectra of 3a exhibited five single lines, readily recognizable as arising from a tert-butyl group (d 1.62), three methyl groups (d 1.80, 2.20 and 2.50) and a hydroxy (d 3.85) group. The proton-decoupled 13C NMR spectrum of 3a displayed 10 single lines.The 1H and 13C NMR spectra of 3b and 3c are similar to that of 3a, except for the methylene group of 3c. The methylene group in 3c is attached to a ring system bearing an asymmetric carbon atom, and appears as an AB quartet (d 4.50, JAB 16.50 Hz).The structural assignments made on the basis of the NMR spectra of compounds 3a, 3b and 3c were supported by their IR spectra. Of special interest are the hydroxy absorptions at 3280, 3290 and 3325 cmµ1 of 3a, 3b and 3c, respectively. In summary, the major synthetic advantages of this reaction are the mild reaction conditions, the excellent yields and the experimental simplicity. Experimental All melting points are uncorrected. Elemental analyses were performed using a Heraeus CHN-O rapid analyser.Mass spectra were recorded on a Finnigan-Matt 8430 mass spectrometer operating at an ionization potential of 70 eV. IR spectra were measured on a Shimadzu IR-470 spectrometer. 1H and 13C NMR spectra were recorded on a Jeol EX-90A spectrometer at 90 and 22.6 MHz, respectively. Preparation of 4-Acetyl-2-tert-butylimino-3-hydroxy-3,5-dimethyl- 2,3-dihydrofuran (3a).·To a magnetically stirred solution of 1 (1.42 g, 10 mmol) in dichloromethane (10 ml) was added dropwise a mixture of tert-butyl isocyanide (0.83 g, 10 mmol) in dichloromethane (10 ml) at µ5 °C over 10 min.The reaction mixture was allowed to warm up to room temperature and then stirred for 24 h at 50 °C. After 12 h in a refrigerator at 5 °C white crystals (2.0 g, 90%) were collected by filtration. Mp 80 °C. vmax (KBr)/cmµ1 3280 (OH), 1690 (C�N), 1657 (C�O), 1634 (C�C). dH (CDCl3, Me4Si) 1.62 (9 H, s, But), 1.8 (3 H, s, Me), 2.2 (3 H, s, Me), 2.5 (3 H, s, Me), 3.85 (1 H, s, OH, exchange with D2O). dC (CDCl3, Me4Si) 11.20 (CH3), 26.31 (CH3), 28.79 (CH3), 31.56 (CH3), 56.60 (CMe3), 91.70 (C-OH), 140.40 (C�C-O), 147.94 (C�C-O), 169.03 (C�N), 197.37 (C�O). m/z 226 (MH+, 12%), 210 (M-CH3, 23), 152 (19), 83 (5), 58 (100).(Found: C, 63.9; H, 8.6; N, 6.1. C12H19NO3 requires C, 64; H, 8.4; N, 6.1%). Preparation of 4-Acetyl-2-cyclohexylimino-3-hydroxy-3,5-dimethyl- 2,3-dihydrofuran (3b).·Similar reaction conditions as above but using cyclohexyl isocyanide instead of tert-butyl isocyanides yielded a white powder (2.0 g, 82%).Mp 110 °C. vmax (KBr)/cmµ1 3290 (OH), 1690 (C�N), 1661 (C�O), 1620 (C�C). dH (CDCl3, Me4Si) 1–2.30 (11 H, m, C6H11), 1.65 (3 H, s, CH3), 2.30 (3 H, s, CH3), 2.52 (3 H, s, CH3), 3.4 (1 H, s, OH). dC (CDCl3, Me4Si) 11.08 (CH3), 23.86, 25.21 and 31.23 (3CH2), 26.26 (CH3), 29.93 (CH3), 52.08 (CH), 89.63 (C-OH), 141.71 (C�C-O), 147.37 (C�C-O), 167.65 (C�N), 196.64 (C�O). m/z 252 (MH+), 236, 170, 153, 125, 98, 83, 56.(Found: C, 67.0; H, 8.7; N, 5.5. C14H21NO3 requires C, 67.0; H, 8.4; N, 5.6%). Preparation of 4-Acetyl-2-benzylimino-3-hydroxy-3,5-dimethyl- 2,3-dihydrofuran (3c).·Similar reaction conditions as 3a but using benzyl isocyanide yielded a colourless powder (2.20 g, 85%). Mp 73 °C. vmax (KBr)/cmµ1 3325 (OH), 1699 (C�N), 1680 (C�O), 1638 (C�C). dH (CDCl3, Me4Si) 1.50 (3 H, s, CH3), 2.20 (3 H, s, CH3), 2.44 (3 H, s, CH3), 4.60 (AB-q, 2 H, Dv 24.0 Hz, J 16.5 Hz, Ph-CH2), 7.3 (5 H, m, C6H5).dC (CDCl3, Me4Si) 11.63 (CH3), 24.67 (CH3), 31.63 (CH3), 42.53 (CH2), 89.68 (C-OH), 127.59, 128.22, 128.79 and 138.32 (C6H5), 140.45 (C�C-O), 149.02 (C�C-O), 169.24 (C�N), 197.08 (C�O). m/z 259 (M+), 241, 137, 106, 91, 65. (Found: C, 69.5; H, 6.5; N, 5.5. C15H17NO3 requires C, 69.4; H, 6.5; N, 5.5%). We gratefully acknowledge financial support from the research council of Shahid Beheshty University. Received, 9th May 1997; Accepted, 12th May 1997 Paper E/7/03219F References 1 I.Ugi, Angew. Chem., Int. Ed. Engl., 1982, 21, 810. 2 H. M. Walborsky and M. P. Periasamy, in The Chemistry of Functional Groups, Supplement C, ed. S. Patai and Z. Rappoport, Wiley, New York, 1983, ch. 20, pp. 835–887. 3 S. Marcaccini and T. Torroba, Org. Prep. Proced. Int., 1993, 25, 141. 4 James H. Rigby and Maher Qabar, J. Am. Chem. Soc., 1991, 113, 8975. 5 Mark Westling and Tom Livinghouse, J. Am. Chem. Soc., 1987, 109, 590. 6 Dennis P. Curran and Hui Liu, J. Am. Chem. Soc., 1991, 113, 2127. 7 I. Yavari, A. Shaabani and M. T. Maghsoodlou, Monatsh. Chem., 1997, 128, 697. 8 G. Morel, E. Marchand and A. Foucaud, J. Org. Chem., 1990, 55, 1721. 9 D. Moderhack, Synthesis, 1985, 1083. 10 S. Forsen and M. Nilsson, Acta Chem. Scand., 1959, 44, 2997. *To receive any correspondence. †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is therefore no corres

ISSN:0308-2342    

DOI:10.1039/a703219f

出版商:RSC    

年代:1997

数据来源: RSC