ISSN:0008-4042    

DOI:10.1139/v78-496

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The kinetics of oxidation of a number of alkyl aryl sulfides with potassium peroxydisulfate in aqueous ethanol have been investigated. The effect of substituents on the oxidation has been studied by employing a number ofp-andm-substituted phenyl methyl sulfides: the reaction is accelerated by electron-releasing and retarded by electron-withdrawing substituents, indicating a rate-determining electrophilic attack by the peroxydisulfate ion at the reaction site, sulfur. A good correlation is found to exist between the rate constants and the Hammett σ+/σ−constants, the ρ+value for the reaction being −0.56 with a correlation coefficient of 0.979. The activation parameters have also been determined.Studies with different alkyl phenyl sulfides clearly indicate that the reaction is quite sensitive to steric congestion around the reaction site. The results obtained in this study are compared with those found for the oxidation of the same set of sulfides with different oxidants.

ISSN:0008-4042    

DOI:10.1139/v78-497

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

Rate constants for abstraction of secondary and tertiary hydrogens from structurally different alkanes by thetert-butylperoxy radical in solution at 30 °C have been determined by competitive experiments in the presence oftert-butyl hydroperoxide. Rate constants fall in the range 1 × 10−4to 9 × 10−4and 1 × 10−3–2 × 10−2 M−1s−1for secondary and tertiary aliphatic C—H bonds, respectively. The most reactive secondary hydrogen is, therefore, almost as reactive as the least reactive tertiary hydrogen. Differences in reactivity within a type of aliphatic C—H bond are governed by differences in steric hindrance to attack by the peroxy radical and by relief of steric strain upon removal of the labile hydrogen. Rate constants for reaction of perdeuterated methylcyclohexane and 3-methylpentane are much smaller than the values calculated from the maximum primary kinetic isotope effect for this reaction.

ISSN:0008-4042    

DOI:10.1139/v78-498

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The phenolic metabolite, 1-(4-hydroxyphenyl)-2-methyl-2-(n-propylamino)propane (1e) was prepared by a Ritter reaction from either 3-(4-methoxyphenyl)-2-methyl-1-propene or 3-(4-methoxyphenyl)-2-methyl-2-propanol and propionitrile. Three other products of the Ritter reaction were isolated and identified by interpretation of their mass spectra. Another phenolic metabolite, 1-(4-hydroxy-3-methoxyphenyl)-2-methyl-2-(n-propylamino)propane (1f) could not be prepared by a Ritter reaction but was obtained from the product of the reaction between 3-(4-benzyloxy-3-methoxyphenyl)-2-methyl-1-propene and iodine isocyanate.

ISSN:0008-4042    

DOI:10.1139/v78-499

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The dissociation constants of a series of 28 α-substituted 2-methylpyridinium ions in water at 25 °C have been measured by potentiometric and spectrophotometric methods. Correlation of the −pKvalues with σIvalues gives slope ρI = 5.45, intercept −pK0 = −5.81, correlation coefficientr = 0.991, and enables new σIvalues to be evaluated. Dissociation constants for the 2-pyridinylmethylammonium ion and itsN-methyl andN,N-dimethyl derivatives are also reported.

ISSN:0008-4042    

DOI:10.1139/v78-500

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The dissociation constants of 30 α-substituted 3-methylpyridinium ions in water at 25 °C have been measured by potentiometric and spectrophotometric methods. Correlation of the pKvalues with σIvalues gives, forn = 16, slope ρI = 3.044, intercept −pK0 = −5.59, correlation coefficientr = 0.993, and enables new σIvalues to be evaluated. Application of the dual substituent parameter equation gives λ(≡ρR/ρI) = 0.04, confirming that resonance effects are negligible in this series. Dissociation constants of the 3-pyridinylmethylammonium ion and itsN-methyl andN,N-dimethyl derivatives are also reported.

ISSN:0008-4042    

DOI:10.1139/v78-501

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The dissociation constants of 29 α-substituted 4-methylpyridinium ions in water at 25 °C have been measured by potentiometric or spectrophotometric methods. Correlation of the logKvalues with σIvalues gives, forn = 13, slope ρ = 2.922, intercept logK0 = 5.93, correlation coefficientr = 0.990. Effective σIvalues evaluated from the dissociation of substituted 4-picolinium ions are in good agreement with those calculated from dissociation of substituted 2- and 3-picolinium ions and with literature values. pKvalues of the 4-pyridinylmethylammonium ion and itsN-methyl andN,N-dimethyl derivatives are 8.22, 8.48, and 7.63, respectively.

ISSN:0008-4042    

DOI:10.1139/v78-502

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The oxygen exchange reaction between O2/C18O2and the surfaces of vanadium pentoxide and promoted vanadium pentoxide catalysts has been studied in a circulation system using a quartz differential reactor. Isotopic compositions were analysed with an in-line mass spectrometer. Alkali metal sulphates, Li to Cs, were added to the pentoxide as individual promoters at a concentration level of 9 mol % and the effect of variation of promoter concentration was examined with melts containing potassium sulphate at additional levels of 1, 2, and 5 mol%. The structures of the solids were studied by X-ray diffraction and by ATR and transmission infrared spectroscopy. The latter results have been used to explain the two activity series for the exchange rates: (i)V2O5 < Na < Li < K < Rb < Cs (melts) and (ii) V2O5 < 1 mol% < 2 mol% < 5 mol% < 9 mol% (K), in terms of additive effects on the relative abundance and strength of identified vanadium/oxygen linkages in the surfaces of the catalysts.

ISSN:0008-4042    

DOI:10.1139/v78-503

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

We have made calorimetric measurements of the enthalpies of reaction of I2O5(c) with water and with a small excess of OH−(aq) and have combined the results to obtain ΔH0 = 13.340 kcal mol−1for the standard enthalpy of ionization of water. It is suggested that this approach can be applied usefully to investigation of the enthalpy of ionization of D2O for which there are still unresolved differences between reported values.

ISSN:0008-4042    

DOI:10.1139/v78-504

出版商:NRC Research Press    

年代:1978

数据来源: NRC

摘要:

The methyl 4,6-O-benzylidene-2,3-dideoxy-3-nitrohex-2-enopyranosides having the β-D-erythro(1), α-D-erythro(2), β-D-threo(3), and α-D-threo(4) configurations reacted with diazomethane to give high yields of 2,3-(1′-pyrazolino-3′,4′) derivatives (5–8). The pyrazolines5and6(from1and2) were deduced on the basis of nuclear magnetic resonance and optical rotatory dispersion data to possess the β- and α-D-glucoconfigurations, and7and8(from3and4), to have the β- and α-D-idoconfigurations, respectively. Thermolysis of5,6, and8led to the methyl-branched, nitroolefinic glycosides9,10, and11(the 2-C-methyl derivatives of1,2, and4), whereas7afforded the corresponding 2,3-C-methylene derivative12, a cyclopropano sugar. The α-anomeric cyclopropano derivative13was obtained from8by decomposition on silica gel.

ISSN:0008-4042    

DOI:10.1139/v78-505

出版商:NRC Research Press    

年代:1978

数据来源: NRC