摘要:

Ten nm nonstoichiometric compound Cu2 –xSe was firstly synthesized at room temperature by &ggr;-irradiation, using sodium selenosulfate as the selenium source. The influence of the coordination of copper ions and the pH value of the solutions on the formation of Cu2 –xSe has been studied. The Cu2 –xSe was prepared here forx= 0.13.Key words: copper selenide, nanocrystalline, &ggr;-irradiati

ISSN:0008-4042    

DOI:10.1139/v00-115

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The syntheses of the first examples of selenoparabanic acid derivatives (dialkylimidazolidine-2-selone-4,5-dione,3eRR = Me, Et, Bu) are presented along with the X-ray crystal structure determination of3eEt. To gain an insight in the properties of parabanic acid derivatives on the basis of their electronic structures, we report the results of comparative hybrid-DFT calculations performed on parabanic, thioparabanic, and selenoparabanic acids (3aH,3bH, and3eH) and on theirN,N' -dimethyl derivatives (3aMe,3bMe, and3eMe). Calculations show that the different nature of the frontier orbitals of3aRcompared to those of3bRand3eR, might account for the different reactivities of these compounds. Moreover, the weak donor character of3bRand3eRtowards molecular di-iodine, estimated by FT-Raman measurements is in agreement with the calculated NBO-charge distribution.Key words: selenation, selenoparabanic derivatives, crystal structure, DFT calculations.

ISSN:0008-4042    

DOI:10.1139/v00-117

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A simple and convenient synthesis of pyrido(2,3,4-kl)acridine (1), the main skeleton of some marine alkaloids, via cyclization and intramolecular nitrene insertion, is described. The importance of the planarity of the molecule during the nitrene insertion is explained.Key words: pyridoacridine, marine alkaloids, nitrene insertion, quinoline, quinolinone.

ISSN:0008-4042    

DOI:10.1139/v00-119

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The synthesis of the phenolic tetrahydroprotoberberine alkaloid (±)-schefferine is reported, featuring as key steps a tosyliminium ion-mediated Friedel-Crafts alkylation of eugenol dimethyl ether and an intramolecular Mitsunobu-type amination.Key words: total synthesis, (±)-schefferine, natural product, tosyliminium ion, Mitsunobu amination.

ISSN:0008-4042    

DOI:10.1139/v00-120

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The electrochemical behaviour of Schiff base compounds derived from an antipyrine nucleus was investigated in 30% (v/v) ethanolic buffer solutions (pH 3-11) using various electrochemical techniques at mercury electrode. The results showed that, the total limiting current of each of the studied compounds corresponds to 2-electron transfer process. The mechanistic pathway of the electrode reaction of the investigated compounds at mercury electrode, the effect of the medium, and the evaluation of the electrode reaction parameters were illustrated and discussed.Key words: Schiff base, antipyrine nucleus, electrode reaction, electrochemical parameters, cyclic voltammetry.

ISSN:0008-4042    

DOI:10.1139/v00-108

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

This paper describes the behavior in aqueous solutions of the two electron oxidation products of the carcinogens benzidine andN,N-dimethylbenzidine. In biological systems there is evidence that these diamines are oxidized by peroxidases, and that a product of this oxidation may be partly responsible for carcinogenicity. Entry into the oxidation products in the present study was provided through the bis-perchlorate salts of dications obtained upon chemical oxidation and through the irradiation of 4'-amino and 4'-N,N-dimethylamino-4-azidobiphenyls. The benzidine oxidation product exists in three conjugate acid-base forms, a dication, a monocation and neutral bisimine, with pKa(1) = 5.0 and pKa(2) = 9.0. These values stand in marked contrast to ones previously obtained for the two electron oxidation product ofp-phenylenediamine, pKa(1) < 1.5 and pKa(2) = 5.75. The dimethylamino derivative, blocked from forming the neutral form, exists as a dication and monocation, with pKa= 5.0. Both systems are quite long-lived in aqueous solution, but they do decay on the minutes-to-hours time scale. The kinetics can be explained by reactions of both the dication and the monocation with water, with a reaction of hydroxide and the monocation becoming important around pH 10. One surprising result is that the monocations are two orders of magnitude more reactive than the dications. Thus, at neutral pH the form that exists in both systems is the monocation, and this is the species that is the most reactive towards the solvent. One of the resonance contributors in the monocation is a 4-biphenylylnitrenium ion. Comparison with other 4'-substituted-4-biphenylylnitrenium ions studied by laser flash photolysis shows that the 4'-amino- and 4'-dimethylamino substituents are highly kinetically stabilizing. These cations, for example, are a billion-fold longer-lived in aqueous solution than the parent 4-biphenylylnitrenium ion.Key words: quinone bisimine, nitrenium, aryl azide.

ISSN:0008-4042    

DOI:10.1139/v00-123

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The tamoxifen carbocation (Ph(Ar)C=CPh-CH+-CH3, Ar = 4-Me2NCH2CH2OC6H4) is generated from acetate and sulfate precursors by SN1 ionization in water. The cation exists in (E) and (Z) forms which equilibrate before reaction. The major products are the &agr;-hydroxytamoxifens Ph(Ar)C=CPh-CHOH-CH3, both (E) 64% and (Z) 29%, with the ratio independent of the configuration of the starting ester. Two minor products with a total yield of 7% account for the rest of the products. These have been characterized as indenes derived from intramolecular cyclization, a 4.5% yield of the indene derived from cyclization into the Ar ring with 2.5% due to cyclization into the phenyl ring. Experiments in acid solutions (0.01-0.1 M HCl) starting with pure (E)- or (Z)-&agr;-hydroxytamoxifen reveal that the two alcohols equilibrate. This occurs by H+-catalyzed formation of the carbocation followed by water capture. Occurring about 10-fold slower than this isomerization is an irreversible process resulting in the two indenes. This cyclization will result in the destruction of the &agr;-hydroxytamoxifens upon exposure to acidic conditions and also makes the direct observation of the tamoxifen carbocation under super-acid conditions difficult, if not impossible. The indenes do form in low yield whenever the tamoxifen carbocation is generated from an SN1 precursor. Thus these products could serve as markers for the formation of the tamoxifen carbocation in cellular systems or in in vivo experiments.Key words: carbocation, indene, allylic cation, isomerization.

ISSN:0008-4042    

DOI:10.1139/v00-122

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

A cyclopropanone, a cyclopropenone, cyclobutanones, a cyclobutane-1,3-dione, and a cyclobutene-1,2-dione reacted with dimethoxycarbene to afford acetals of the next larger ring by formal insertion of the carbene into a C—C bond &agr; to the carbonyl group. When either of two saturated &agr;-ring carbons could be involved in the process, the ring expansion was selective, affording primarily the product of apparent insertion into the more substituted ring bond. With 2,3-dimethoxycyclobutene-1,2-dione, insertion occurred between the carbonyl groups and with &bgr;-propiolactone it occurred at the lactone bond. &bgr;-Propiolactam, however, reacted by insertion of the carbene into the N—H bond.Key words: &bgr;-propiolactone, cyclobutanone, cyclobutananedione, cyclopropanone, dialkoxycarben

ISSN:0008-4042    

DOI:10.1139/v00-118

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Literature data for the saturation vapor pressureP(hl1g) of hydrogen sulfide hydrate with water, at 43 temperatures between quadruple pointsQ(hs1l1g) at –0.4°C andQ(hl1l2g) at 29.484°C, are properly represented by a six-parameter equation to give a standard error (SE) of 0.13% on a hydrate pressure measurement of unit weight. Equilibrium hydrogen sulfide and water fugacities and the gas and aqueous phase compositions are derived using the Redlich–Kwong equation of state. Literature data for the saturation vapor pressureP(hs1g) of hydrogen sulfide hydrate with ice, at 15 temperatures between –1.249 and –21.083°C, are properly represented by a two-parameter equation to give a SE of 0.26% on a single hydrate pressure measurement. Quadruple pointQ(hs1l1g) is evaluated at temperature –0.413° with SE 0.042°C and at pressure 94.7 with SE 0.26 kPa. Using the thermodynamic method, described for deuterium sulfide D-hydrate, the equilibrium fugacities of hydrogen sulfide are used to define 43 equilibrium constantsKp(hl1g) for hydrate dissociation into water and hydrogen sulfide gas. The temperature dependence of lnKp(hl1g) is represented by a three-parameter thermodynamic equation which gives both values and standard errors (i) forKp(hl1g), and for &dgr;Hot(hl1g) and &dgr;Cpot(hl1g), the standard enthalpy and heat capacity changes for hydrate dissociation and (ii) forn=rthe approximate formula number of the hydrate H2S·nH2O at each experimental temperature. The formula H2S·6.119H2O with standard error 0.029H2O is found for hydrogen sulfide hydrate with water at lower quadruple pointQ(hs1l1g) –0.413°C: an approximate formula H2S·5.869H2O with SE 0.026H2O is found at upper quadruple pointQ(hl1l2g) 29.484°C. These estimates for the formula of hydrogen sulfide hydrate at its quadruple points are not significantly different from those found for the deuterium sulfide D-hydrate.Key words: clathrate hydrate of hydrogen sulfide, hydrogen sulfide hydrate, formula of hydrogen sulfide hydrate, thermodynamics of clathrate hydrate dissociation, dissociation equilibrium constant of hydrogen sulfide hydrate, standard enthalpy and heat capacity changes for dissociation of hydrogen sul

ISSN:0008-4042    

DOI:10.1139/v00-121

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

O-alkyl monothiocarbonate (monoxanthate) derivatives of tin were obtained by the reaction of a sodium salt of the monothiocarbonic acid with an organotin chloride to give Ph3Sn[SCO2R], Ph2Sn[SCO2R]2, and Me3Sn[SCO2R], where R = Me and i-Pr. The compounds have been characterized by infrared, Raman,1H NMR, and13C NMR spectroscopy, as well as mass spectrometry, and in two cases by X-ray crystallography. Ph3Sn[SCO2Me] (1) and Ph3Sn[SCO2(i-Pr)] (2), crystallize in the triclinic space groupP(no. 2) with cell parametersa= 10.218(4),b= 10.568(6),c= 9.366(7) Å, &agr; = 106.73(5), &bgr; = 96.99(5), &ggr; = 85.55(4)°,V= 960(1) Å3, andZ= 2 for1; anda= 14.793(2),b= 17.856(3),c= 9.813(3) Å, &agr; = 103.86(5), &bgr; = 98.36(5), &ggr; = 106.85(4)°,V= 2343(1) Å3, andZ= 2 for2. The latter has two molecules in the asymmetric unit. The immediate environment about tin in both1and2is that of the expected distorted tetrahedron. However, the orientation of the monothiocarbonate group is such that there is an Sn-O intramolecular interaction of 3.040(8) for1and 3.05(2) Å on average for2. Thus, the considerable distortion is consistent with a tendency to form a five-coordinate, trigonal bipyramidal species with one of the O-Sn-C angles approaching 180o(153.4(4) for1and an average of 157.1(6) for2). Estimations of the Pauling partial bond orders suggest this weak Sn-O interaction is slightly stronger than the corresponding Ge-O interaction in the analogous germanium derivative, Ph3Ge[SCO2Me].Key words: structure, tin, methyl, phenyl, isopropyl, monothiocarb

ISSN:0008-4042    

DOI:10.1139/v00-116

出版商:NRC Research Press    

年代:2000

数据来源: NRC