摘要:

The new complex [Ag2(hfac)2(μ-dmpm)2] (hfac = hexafluoroacetylacetonato, dmpm = Me2PCH2PMe2) has been prepared and characterized both spectroscopically and by an X-ray structure determination (orthorhombic,Pbca(No. 61),a = 9.960(2),b = 14.694(3),c = 22.548(3) Å,Z = 4,R = 0.0495,Rw = 0.0532). The data indicate that the hfac−ligands have mostly ionic character and it is suggested that this may be responsible for the low volatility of complexes [Ag(hfac)Ln] compared to [Cu(hfac)Ln]; these complexes are of interest as precursors for chemical vapour deposition of silver.

ISSN:0008-4042    

DOI:10.1139/v94-200

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The 3-(3-nitroaryl)sydnones were prepared in good yields by the nitration of 3-aryl-4-acetylsydnones followed by deacetylation with aqueous barium hydroxide.

ISSN:0008-4042    

DOI:10.1139/v94-201

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A new "drift-type" crown ether phase transfer catalyst, 4′-carboxybenzo-15-crown-5 adsorbed on poly(styrene/divinylbenzene)-NR2resin, was synthesized and applied to catalyze the oxidation of benzhydrol with NaMNO4as an oxidant. Before the reaction, the drift-type crown ether catalyst was adsorbed on the resin with ion-pair (resin-NR2H+−O2C-monobenzo-15-crown-5) formation. During the reaction period the crown ether catalyst was released from the resin into the reaction solution as a homogeneous catalyst by adjusting the acidity of the solution to 10−1 M HCl to destroy the ion pair between the catalyst and the resin. After the reaction, the crown ether catalyst could be readsorbed on the resin by adjusting the concentration of HCl to 10−5 M and could be readily recovered by filtration. The catalyst, 4′-carboxybenzo- 15-crown-5, was found to be a more effective catalyst than other crown ethers, such as 15-crown-5, 18-crown-6, monobenzo-15-crown-5, and dibenzo-18-crown-5.

ISSN:0008-4042    

DOI:10.1139/v94-202

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The reaction ofD-penicillamine and benzaldehyde yielded 2-phenyl-5,5-dimethylthiazolidine-4-carboxylic acid. The structure was determined by single crystal X-ray diffraction. Crystals were monoclinic,P21,a = 9.785(2),b = 6.941(1),c = 10.399(2) Å, β = 114.06(3)°,Z = 2. Intensities were measured on a Rigaku AFC6R diffractometer with Cu Kα radiation and 1881 reflections were used to determine the structure.R = 0.076,wR = 0.048. The compound exists as an amino acid in the 2S,4Sconfiguration. The conformation of the thiazolidine ring is determined by intermolecular hydrogen bonding. Bond lengths and angles are normal.1H and13C NMR spectra showed that epimerization takes place ind4-CH3OH solution, and the ratio of 2S,4Sdiastereomer to 2R,4Sdiastereomer at room temperature is 65:35.

ISSN:0008-4042    

DOI:10.1139/v94-203

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Radiolysis free ion yields, electron mobilities, and ion mobilities were measured as functions of applied electric field strength in the liquidscis- andtrans-butene-2 at temperatures from near their freezing points to near their critical points. The dielectric permittivities were also measured, to permit extraction of electron thermalization distances from free ion yield data. The thermalization distance distribution in each liquid was found to be the Gaussian YGP, rather than the exponential YE or YEP. This indicates that electrons are not captured before thermalization in either liquid. The density-normalized thermalization distancesbGPdwere ∼40% larger incis- than intrans-butene-2; this correlates with the more globular structure of thecis- molecules, which decreases the efficiency of electron energy loss collisions in the liquid phase. Electron mobilities were not appreciably different from those reported earlier. Cation mobilities in the liquids from the freezing points (T/Tc ≈ 0.35,d/dc ≈ 3.2 ) up to ∼400 K (T/Tc ≈ 0.92,d/dc ≈ 2.0) are adequately described by the free-volume model. At densitiesd/dc < 2.0 the mobilities are smaller than predicted by the free-volum

ISSN:0008-4042    

DOI:10.1139/v94-204

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The hydrolysis ofcis- andtrans-1-methoxy-1,3-butadiene in aqueous solution occurs by hydron transfer to the δ-carbon atom with little or no β-hydronation to give crotonaldehyde as essentially the sole aldehyde product. The reaction gives appreciable hydronium-ion isotope effects in the normal directionand shows general acid catalysis; five carboxylic acid catalytic coefficients for hydrolysis of thetransisomer give a good Brønsted relation with the exponent α = 0.59. This is taken as evidence that these reactions occur by the conventional mechanism for vinyl ether hydrolysis involving rate-determining hydron transfer to substrate carbon followed by rapid formation and decomposition of a hemiacetal intermediate. Comparison of the reactivity of the present dienyl ethers with that of their monoenyl analog, methyl vinyl ether, shows that introduction of the second double bond decreases reactivity considerably: the hydronium-ion catalytic coefficient is reduced by a factor of 8.3 for thetransisomer and by a factor of 160 for thecisisomer. This reduction supports a hypothesis advanced to explain the occurrence of reaction by a different mechanism recently discovered in the hydrolysis of the strongly mutagenic polyenyl ether, fecapentaene-12.

ISSN:0008-4042    

DOI:10.1139/v94-205

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The kinetics of formation of the thioester involved as an intermediate in the reaction between chromium(VI) andDL-penicillamine in aqueous media (pH = 1–8) containing different buffers (acetate, citrate, and phosphate) has been studied by monitoring the disappearance of chromium(VI) at 370 nm and application of the initial-rates method. The initial rate is directly proportional to the initial concentrations of both oxidant and reductant, and the rate vs. pH plots show bell-shaped profiles. The reaction is catalyzed by the buffer present in the medium, the catalytic power of each buffer increasing in the order acetate < citrate < phosphate. This is explained in terms of a mechanism involving the formation of a complex between the acidic form of the buffer and HCrO4−previous to the formation of the thioester. Potassium chloride and sodium sulfate do not seem to have important specific effects on the reaction rate, their effect being that of an acceleration of the reaction as the ionic strength increases. On the contrary, the sulfates of magnesium, manganese(II), and zinc (the latter only in the presence of acetate buffer) have specific effects, indicating the probable formation of several complexes. The spectrophotometric detection of the thioester at 430 nm has allowed to confirm some of the conclusions extracted from the measurement of initial rates, and suggests that this intermediate might approach a steady-state behavior in the three buffers at pH > 6.25, and also that a bimolecular reaction withDL-penicillamine might be involved in its destruction.

ISSN:0008-4042    

DOI:10.1139/v94-206

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The biosynthesis of 5-hydroxy-4-oxo-L-norvaline (HON) inStreptomycesakiyoshiensishas been investigated using13C-labelled substrates. Incorporations of13C label from sodium [1-13C]-, [2-13C]-, and [1,2-13C2]acetate indicated that HON was formed from a four-carbon compound derived from the citric acid cycle and the methyl carbon of acetate. Feeding experiments usingDL-[4-13C]- andDL-[2-13C,15N]aspartate demonstrated that aspartate served as the four-carbon precursor to HON. Both enantiomers of aspartate were metabolized byS.akiyoshiensis, but theDisomer was consumed at a slower rate. The distribution of13C label in the intracellularL-glutamic acid isolated in these feeding experiments is consistent with the operation of the citric acid cycle inS.akiyoshiensis. A biosynthetic hypothesis that involves a condensation reaction between acetyl or malonyl CoA and the β-carboxyl group of aspartate, and subsequent oxidative decarboxylation, is proposed to account for the incorporation results. An analogous condensation step has been proposed for the biosynthesis of other natural products, including the carbapenem antibiotics.DL-[2-13C,15N]Aspartate was synthesized from [2-13C]diethylmalonate and potassium [15N]phthalimide via diethyl [2-13C,15N]phthalimidomalonate.

ISSN:0008-4042    

DOI:10.1139/v94-207

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

An improved protocol for the construction of substituted indenones is presented. Also the effect of substitution on the intramolecular Friedel–Crafts acylation was noted. Specifically, if there is no substitution at the 2-position of the indenone poor yields of cyclized material were obtained, if at all, while the substitution of a methyl or ethyl group greatly improved the yield of cyclized material. Placement of a large group (e.g., benzyl) resulted in a diminuation of the improved yield. The new synthetic procedure could, in principle, allow for the construction of 2,3-disubstituted indenones. One example of this reaction mode was presented.

ISSN:0008-4042    

DOI:10.1139/v94-208

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Pyridines and benzopyridines substituted with trimethylsilylmethyl groups, α or γ to the nitrogen atom, have been found to react with formamides by way of a Peterson reaction to form enamines. Trimethylsilylmethylbenzene behaved similarly. The enamines prepared fromNb-formyl-Na,Nb-dimethyltryptamine cyclized readily to β-carbolines. The reaction of formamides with lithiated 4-methylpyridines as a route to enamines was examined but proved to be less general and proceeded in lower yield than the route by way of the Peterson reaction. The nuclear magnetic resonance and mass spectra of the enamines and β-carbolines derived from3are discussed.

ISSN:0008-4042    

DOI:10.1139/v94-209

出版商:NRC Research Press    

年代:1994

数据来源: NRC