The kinetic isotope effect of hydrogen in the sulphonation of [I ,3,5-2H3] benzene in trichlorofluoromethane has been determined askH/kD = 1.23 f 0.08 at -35"; with nitromethane as solvent kH/kD = 1.34 f 0.08 at 20'. The kinetic isotope effect for the accompanying sulphonylation in trichlorofluoromethane w a s found to be kH/kD = 1-1 f 0.1 at -35".These results are discussed in terms of the recently established mechanism for aromatic sulphonation with sulphur trioxide in aprotic solvents. It has been determined, by competitive experiments, that the sulphonation rate ratio of toluene to benzene and the degree of para-substitution in toluene are greater with nitromethane than with trichlorofluoromethane as solvent. The apparent greater selectivity in the case of the former solvent is explained in terms of complex formation between sulphur trioxide and nitromethane.
The sulfonation of chlorobenzene and p-dichlorobenzene with sulfur trioxide in nitromethane as solvent has been studied. The main reaction products are arenesulfonic anhydride and probably arenepyrosulfonic acid. With p-dichlorobenzene as substrate the amount of diary1 sulfone is undetectably small; with chlorobenzene it is < 1-mole % relative to the converted substrate. The sulfonation is of the first order with respect to the substrate and of the second order with respect to sulfur trioxide. For each mole of converted substrate two moles of sulfur trioxide are consumed. The sulfonation of p-dichlorobenzene proceeds without a primary kinetic isotope effect of hydrogen.It is suggested that the sulfonation proceeds via 1-arenonium-1-sulfonate and 1-arenonium-1-pyrosulfonate as the subsequent reactive intermediates, with the formation of the latter intermediate as the ratelimiting step. The kinetics of the formation of 4,4'-dichlorodiphenyl sulfone are compatible with a mechanism in which the species p-CIC~H&OgH is the effective sulfonylating entity. The literature on aromatic sulfonation with sulfur trioxide in aprotic solvents is critically reviewed.Extensive mechanistic studies on aromatic sulfonation have been performed with aqueous and fuming sulfuric acid as the reagent 2 . At the outset of this investigation, the number of kinetic studies pertaining to sulfur trioxide as reagent was, however, rather limited 3-8. It was therefore thought interesting to study the kinetics of aromatic sulfonation with this * Preceding paper: Rec. Trav. Chim. 87, 24 (1968).
Summaify Aromatic compounds are methylthiolated by for further substitution by the RS group introduced. This treatment with methyl methanethiosulphonate in the might explain why benzene and toluene, even when used in presence of aluminium chloride. excess (conditions denoted by A), gave complex mixtures of mono-and poly-substitution products. o-Xylene (in excess) yielded a mixture mainly consisting of the 4,5-and THE substitution of hydrogen in aromatic compounds by a methylthio-group using methanesulphenyl chloride and 3, G-disubstituted o-xylenes.Reactio?? of RSS0,R (0-1 nzol) with ArH (A, 100 ml; B, 0.1 in01 in 100 ml of MeNO,) upon gradual addifion of ,41C1, (0.1 mol) at room temperature and stirring for 8 ha
The kinetics of the reaction of bis‐phenylsulfonylmethane with thiosulfonic esters (RSSO2R′) have been measured in 100% ethanol, in the presence of triethylamine, at 20°. The kinetic data on the substitution of an ‘active’ hydrogen by a thioaryl or thioalkyl (RS) group are compatible with a two‐step mechanism. First the carbanion of bis‐phenylsulfonylmethane is formed by action of the base after which a bimolecular reaction occurs between the carbanion and the thiosulfonate. The reaction is retarded by introduction of electrondonating substituents in both R and R′. The possible structure of the transition state is discussed.
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