ISSN:0165-0513    

DOI:10.1002/recl.19670860802

出版商:WILEY‐VCH Verlag    

年代:1967

数据来源: WILEY

摘要:

AbstractProtonation of aliphatic carboxylic acids RCOOH in HF‐BF3solution at low temperature leads to dihydroxycarbonium ions. The configurations as regards the groups R and H at the partly doublebonds depend on the steric requirements of group R: In the case of RCH3, CH2Cl, CH3CH2and (CH3)2CH both acis‐ and atrans‐configuration, and in the case of R(CH3)3C twotrans‐configurations probably exist.The rate constants of the dehydration of the protonated acids to acyl cations that takes place at higher temperatures proved to vary only slightly for RCH3, CH3CH2, (CH3)2CH and (CH3)3C. In agreement with previous work on protonated formic acid the rates were found to be much lower in HF‐BF3than in sulfuric acid solution (as estimated fromDeno's results), possibly due to a difference in molecularity

ISSN:0165-0513    

DOI:10.1002/recl.19670860803

出版商:WILEY‐VCH Verlag    

年代:1967

数据来源: WILEY

摘要:

AbstractThe quantitative conversion of some esters into the corresponding hydroxyalkoxy‐carbonium ions by protonation in HF‐BF3solution at about −80 °C is reported. The probable configuration of the ions is deduced from NMR spectroscopic information. The decomposition route of these carbonium ions at higher temperatures depends on the species in

ISSN:0165-0513    

DOI:10.1002/recl.19670860804

出版商:WILEY‐VCH Verlag    

年代:1967

数据来源: WILEY

摘要:

AbstractThe mixture of products formed by irradiation of dibenzyl sulfide has been analyzed by G.L.C. Dibenzyl and phenanthrene appeared to be the major products. In addition, several other products were characterized.Benzyl 1,2‐diphenylethyl sulfide was found to be a precursor in the formation of phenanthrene. The suggestion has been made that thermolysis of dibenzyl sulfide follows the same free radical mechanism as the photolysi

ISSN:0165-0513    

DOI:10.1002/recl.19670860805

出版商:WILEY‐VCH Verlag    

年代:1967

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19670860806

出版商:WILEY‐VCH Verlag    

年代:1967

数据来源: WILEY

摘要:

AbstractOrganic hydroperoxide formation has to be regarded as the primary process in the autoxidation of partially reduced pteridines and flavins, to be distinguished from secondary oxidations and H2O2‐production. Material balances between oxidized products, O2‐uptake and H2O2‐formation have been determined under varying experimental conditions and found to be in agreement with a general formula based on the new theory. Spontaneous oxidation of a blocked dihydroalloxazine afforded a tetrahydroquinoxaline‐2‐spiro‐5′‐hydantoin as the ring‐contraction product of the transient hydroperoxide, confirming the structure previous

ISSN:0165-0513    

DOI:10.1002/recl.19670860807

出版商:WILEY‐VCH Verlag    

年代:1967

数据来源: WILEY

摘要:

AbstractTo investigate the variation with alcohol‐percentage of the standard potential of glass electrodes of a wide range of types and manufactures, e.m.f.‐measurements have been made on cells of the type: glass electrode/standard buffer solution/saturated KCl‐solution (aq.)/Hg2Cl2‐Hg, using standard succinate buffer solutions in methanol‐water and ethanol‐water mixtures.An analysis is given of the accuracy of pH‐determinations in alcohol‐water mixtures, using both standard buffer solutions in the same solvent and aqueous standard buffer solutions

ISSN:0165-0513    

DOI:10.1002/recl.19670860808

出版商:WILEY‐VCH Verlag    

年代:1967

数据来源: WILEY

摘要:

AbstractChlorobenzene has been sulfonated homogeneously in aqueous sulfuric acid varying from 83.4 to 99.6 wt‐%, at 25°. The isomer distribution‐98.8%para, 0.8%ortho, 0.4%meta‐ is constant over the acid range studied. The substrate isotope effect has been determined under conditions of rapid hydrogen exchange;kD/kHvaries from 0.8 in 95% sulfuric acid to 0.4 in 97%. The dependence of the reaction rate and the isotope effect on the acid concentration is explained by an SE2‐mechanism involving attack by H2S2O7followed by proton removal from the σ‐complex by HSO4−; the latter process is partly rate‐limiting at high acid

ISSN:0165-0513    

DOI:10.1002/recl.19670860809

出版商:WILEY‐VCH Verlag    

年代:1967

数据来源: WILEY

摘要:

AbstractThe degree ofortho‐substitution in the sulfonation of toluene, ethylbenzene and isopropylbenzene with sulfuric acid varying in concentration from 80.6 to 98.5% H2SO4at 25° was determined. For a given sulfuric acid concentration the ratio ofortho‐ to (para‐ +meta‐) substitution decreases with increasing size of the alkyl group, whereas for a given alkyl group this ratio decreases with decreasing sulfuric acid concentration.Partial rate factors for the homogeneous sulfonation of toluene, ethylbenzene, isopropylbenzene andt‐butylbenzene in 86.3% sulfuric acid at 25° were calculated. The partial rate factors forortho‐substitution decrease with increasing size of the alkyl group, while those forpara‐substitution follow theBaker‐Nathanorder.Introduction of a sulfonic acid grouporthoto the alkyl group of an alkylbenzene can be effected with weak oleum (∼ 16%) as reagent under conditions of disulfonation with toluene, ethylbenzene and isopropylbenzene, but not

ISSN:0165-0513    

DOI:10.1002/recl.19670860810

出版商:WILEY‐VCH Verlag    

年代:1967

数据来源: WILEY

摘要:

AbstractProton magnetic resonance spectra of eight protonated dialkylketones (dialkylhydroxycarbonium ions) have been measured in HF ‐ SbF5. Due to restricted rotation about the partially double C ‐ O bond, which leads tosynantiisomerism, symmetric ketones (R1= R2) give cations with non‐equivalent alkyl groups. Unsymmetric ketones (R1≠ R2) give two isomeric cations which are spectroscopically distinguishable below 0°C. The free energy barrier to rotation is at least 17 kcal/mole. Assignments of the observed PMR signals to the one or the other isomer of dialkylhydroxycarbonium ions are given. The preference of the hydroxyl proton for beingsynto an alkyl group increases in the ordertert‐butyl

ISSN:0165-0513    

DOI:10.1002/recl.19670860811

出版商:WILEY‐VCH Verlag    

年代:1967

数据来源: WILEY