Uncatalysed alcoholysis of alkyl acetoacetates and malonates occurs via a unimolecular dissociative mechanism involving concerted elimination of alcohol with resultant formation of substituted ketens as reactive intermediates.
Two types of reaction are observed when p-arylsulphonylethanesulphonamides are treated with sodium ethoxide: elimination of a proton and aryl sulphinate gives an ethylenesulphonamide, and elimination of a proton and sulphimate gives aryl vinyl sulphone; nucleophilic addition to both vinyl sulphonamide and aryl vinyl sulphone follows. Attempts to characterise sulphimate ions have failed; immediate decomposition to sulphite and amine occurs.With sulphonamides of secondary amines, relatively slight changes in the distribution of products are caused by variation of the amine. With sulphonamides of primary amines, however, elimination of the sulphonamido-group occurs almost exclusively and the reaction constitutes a potential method for the protection of primary amino-groups.THE ready replacement of certain P-substituents in sulphones under basic conditions has been known for some time,2 and more recently the mechanisms of such reactions have received at tent ion .3-6 In the present investigation, reactions of b-arylsulphonylethanesulphonamides have been studied in order to determine whether the sulphonamido-group, like the sulphonyl group,3,4 can behave as a leaving group, and also whether it can behave as an activating group for the elimination of P-substituents. Elimination of sulphonamido-groups, in which C-N fission is involved, have been observed previously.7~ 8 This Paper is concerned with eliminations in which C-S fission occurs and there appear to be no previous instances of this type of reaction. Elimination of P-substituents in sulphonamides has not been studied and, although treatment of 2-chloroethanesulphonyl chloride with aromatic amines is known to give ethylenesulphonamides,g, 10 this reaction probably involves an initial dehydrohalogenation and subsequent reaction of ethylenesulphonyl chloride with the amine. There is evidence from the reactions of 2-chloroethanesulphonyl chloride 10 and of ethane-1,2disulphonyl chloride 11912 that the chlorosulphonyl group strongly promotes @-elimination and
The kinetics of the reaction between 2.4-dinitrobenzenesulphenyl bromide and cyclohexene have been studied in benzene and in chloroform. In the latter the reaction is of the second order, first-order in each reactant, but in the former the order is greater than unity in sulphenyl bromide and the reaction is accelerated by the product. The rate equation proposed for benzene solution is :where B = cyclohexene and P = product. These results are compared with previous ones for the addition of 2,4-dinitrobenzenesulphenyl halides to cyclohexene in various solvents, and the velocity constants correlated with €,-values for solvent polarity. The mechanism and kinetics of these reactions are discussed.
The reaction between 2.4-dinitrobenzenesulphenyl bromide and cyclohexene in carbon tetrachloride solution appears to be essentially homogeneous, and polar. Kinetically it is complex, like many electrophilic additions in relatively non-polar solvents, the reaction being first-order in cyclohexene, and above first-oraer in sulphenyl bromide. The rate equation, Initial rate = k," [B] [ArSBr] + k,[B] [ArSBrIZ + k,[B] [ArSBrI3 where B = cyclohexene, is proposed, and the complexity of this equation attributed to solvation assistance in the transition state by molecules of sulphenyl bromide.
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