摘要:

AbstractModifiedForsén‐Hoffmanexperiments (in the FT mode) show that, in 7‐substituted cyclohepta‐1,3,5‐trienes benzenesulphonyl groups migrate in a random way, while phenylthio substituents show a specific 1,2‐migration. Activation parameters for the migration process are given for a number of

ISSN:0165-0513    

DOI:10.1002/recl.19831020601

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe association constants (K) of the complexes of 18‐crown‐6 with dimethyl sulfate, dimethyl carbonate and dimethyl oxalate have been determined by a1H NMR method. TheKvalues of these complexes were found to be 0.6, 0.8 and 0.6 l/mol, respectively, which values are several orders of magnitude lower than those reported for crown ether/ammonium salt comple

ISSN:0165-0513    

DOI:10.1002/recl.19831020602

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe protonation of phenol (2), 4‐fluorophenol (3), phenyl methanesulfonate, potassium phenyl sulfate and the potassium 2‐ and ‐4‐sulfonates of both phenol and anisole in concentrated aqueous sulfuric acid at 30°C has been investigated using13C NMR spectroscopy. The results show that phenol and 4‐fluorophenol are protonated predominantly on the oxygen atom. This protonation is governed by theH0aacidity function. The pKaof the oxonium ions of2and3are ‐6.40 ± 0.05 and ‐6.41 ± 0.05, respectively. The protonation of phenyl methanesulfonate occurs at acid concentrations>100%. Potassium phenyl sulfate in ≥20% H2SO4hydrolyses very rapidly to give phenol. The 2‐ and 4‐sulfonates of both phenol and anisole are protonated on both the ‐OR (R = H, Me) and the ‐SO3−groups; the sulfuric acid concentrations of half‐protonation have been determined to be between 80.0 and 83.3% H2SO4, corresponding with pKa's of the conjugate acids between ‐6.3

ISSN:0165-0513    

DOI:10.1002/recl.19831020603

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe ionization of the oxonium ions of phenol, anisole, 4‐chloro‐ and 4‐methyl‐phenol and 4‐bromo‐, 4‐fluoro‐ and 4‐methyl‐anisole in concentrated aqueous sulfuric acid has been investigated using UV spectroscopy at 25°C. The sulfuric acid concentrations at half‐ionization are within the range 75.2 to 81.8% H2SO4, corresponding with pKa's between ‐5.87 and ‐6.52 based on theH0aacidity function. The substituent effects on the ionization of PhO+H2and PhO+HMe are small, theHammetρ values being 0.5 ± 0.1

ISSN:0165-0513    

DOI:10.1002/recl.19831020604

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe photochemical reactions of1band15b,i.e.the pivaloyl analogues of (E)‐α‐ (1a) and (E)‐β‐ionone (15a), have been examined. The replacement of the acetyl group in1aby a pivaloyl group does not change the initial photoreactions up to theretro‐ionone stage, although beyond this stage a change is observed. Theretro‐α‐ionone analogue4bundergoes α‐cleavage, followed by decarbonylation and recombination of the resulting radicals. Irradiation of theretro‐γ‐ionone analogue18byields the tricyclic oxetane19band the decarbonylated product22.The formation of11in the α‐series and of22in the β‐series is explained in terms of a photochemical [1,3]‐hydrog

ISSN:0165-0513    

DOI:10.1002/recl.19831020605

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe photochemistry of (E)‐α‐ and (E)‐β‐damascone has been studied. Upon triplet‐sensitized irradiation, both compounds exclusively undergo (E)‐(Z) isomerization. (E)‐β‐damascone, upon direct irradiation with λ 254, 300 or 350 nm innon‐alcoholicsolvents, exhibits only (E)‐(Z) isomerization. However, in analcoholicsolvent, direct irradiation induces cyclization and subsequent solvent incorporation, with formation ofexo‐8‐alkoxy‐1,5,5‐endo‐9‐tetramethyl‐cis‐bicyclo[4.3.0]nonan‐7‐one (12).(E)‐α‐damascone, upon direct irradiation, exhibits α‐cleavage with subsequent formation of the 1,3‐acyl shift product, and equal amounts of the dimerization products of the allylic radical,viz.9and10.The 1,3‐acyl shift product again undergoes photo‐α‐cleavage and the only product

ISSN:0165-0513    

DOI:10.1002/recl.19831020606

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe reaction of peroxyhexanoyl nitrate,1a, a homologue of the atmospheric pollutant “PAN”,1b, with some twenty thioethers, is described. At 0‐25°C, common thioethers such as Et2S or PhSMe are rapidly converted into sulfoxides in high yields in a variety of solvents, ranging from pentane and chloroform to acetic acid, methanol and aqueous acetonitrile. Rates are essentially solvent‐independent, although the reaction is subject to marked steric hindrance. Relative rates for fivep‐substituted thioanisoles in MeOH at 22°C, leading to aHammettρ‐value of ‐1.7, show that the sulfur atoms display nucleophilic character. Electron‐attracting groups on α‐carbon, such as in PhSCCl3and in MeSCH2OC(O)Ph, inhibit the formation of sulfoxide. Addition of EtSH lowers the yield of sulfoxide, producing instead EtSSEt and EtSNO. Oxidation of Me2S by1awith the NO2group labelled by18O does not give rise to18O‐enriched DMSO. Comparison of (CH3)2S with (CD3)2S revealed an inverse kinetic H/D isotope effect.The products obtained from1avary with solvent. In the presence of water or EtSH, hexanoic acid is formed, while methanol gives rise to methyl hexanoate, and in pentane/hexanoic acid, hexanoic anhydride is produced. In aprotic solvents, significant amounts of CO2are formed.These observations can best be rationalized on the basis of an intermediate sulfurane R1R2S(ONO2)(OCOR), (I), produced from thioether R1SR2and1a, in the first step. The fate ofIunder various conditions is discussed.Finally, the features of the oxidation of thioethers by peroxyacylnitrate are compared with those of acyl peroxides and peroxy esters. It is suggested that in each case formation of a sulfurane may

ISSN:0165-0513    

DOI:10.1002/recl.19831020607

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe composition of methylcopper(I) species, prepared from cuprous halides and MeM (M = Li, MgX or Mg1/2) in various ratios, has been studied by means of1H NMR spectroscopy. Tetrahydrofuran (THF) was used as solvent. Evidence is presented that in the presence of hexamethylphosphoric triamide (HMPT), methylhalocuprates, [MeCuX]M, can be obtained stoichiometrically pure. By means of1H NMR analysis it could be shown that the complex MeCu[P(OMe)3]3also exists in solution. The trimethyldicuprate [Me3Cu2]2Mg has only been obtained stoichiometrically pure on starting from MeMgCl and cuprous chloride; it was formed in equilibrium with [Me2Cu]2Mg and [MeCuBr]2Mg when the starting Grignard reagent or the cuprous halide contained bromide. Homocuprates [Me2Cu]M were always obtained in mixtures containing, in addition to the homocuprate, [Me3Cu2]M and MeM when the starting reagent MeM was a Grignard reagent. Attempts to prepare species with another stoichiometry failed when Grignard reagents MeM were used.

ISSN:0165-0513    

DOI:10.1002/recl.19831020608

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe synthesis of phenyl‐ andtert‐butyl‐phosphadibenzo‐18‐crown‐6 and phenylphosphadibenzo‐21‐crown‐7 is described. The complexation of alkali metal cations and rhodium(I) by these macrocycles and their phosphine oxides has been studied by NMR methods. The phosphorus crown ethers are all capable of solubilizing lithium cations into chloroform. The phosphine oxide macrocycles also solubilize sodium cations. It is remarkable thattert‐butyl‐phosphadibenzo‐18‐crown‐6 complexes the sodium cation, whereas phenylphosphadibenzo‐18‐crown‐6, whose cavity is about the same size, does not. The formation of a bimetallic (Rh(I),Li+) complex of phenylphosp

ISSN:0165-0513    

DOI:10.1002/recl.19831020609

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractOxidation of 1‐aryl‐3‐carbamoylpyridinium chlorides with immobilized rabbit liver aldehyde oxidase gave predominantly 1‐aryl‐1,6‐dihydro‐6‐oxo‐3‐pyridinecarboxamides, together with the corresponding 1‐aryl‐1,4‐dihydro‐4‐oxo‐3‐pyridinecarboxamides.In general, the site of oxidation by this enzyme is determined by steric factors. The rate of oxidation by free aldehyde oxidase is very sensitive to electronic effects. A more electron‐withdrawing aryl substituent increases the reaction rate for oxidation to 6‐oxo product. Consequently, a positive ρ value of about 3.6 was calculated for free aldehyde oxidase. Oxidation of these compounds by bovine milk xanthine oxidase yielded mainly 4‐oxo products. Preparative‐scale reactions with both free and immobilized xanthine oxidase gave low product yields. The oxidation rate of free xanthine oxidase is only slightly

ISSN:0165-0513    

DOI:10.1002/recl.19831020610

出版商:WILEY‐VCH Verlag    

年代:1983

数据来源: WILEY