Perchlorate esters. 4. Kinetics and mechanism of the reactions of alkyl perchlorates with N,n-dimethylanilines in benzene12

The reactions in benzene of methyl, ethyl, and isopropyl perchlorates with N,N-dimethylanilines, to yield precipitates of the quaternary anilinium perchlorate, proceed with second-order kinetics and exhibit a large negative entropy of activation. At 25.00C, Hammett rho values of -3.05, -2.86, and -2.78, respectively, indicate appreciable bonding to the nitrogen within the transition state. In reaction with methyl perchlorate, the p-cyano and p-nitro derivatives require values intermediate between sigma/sup n/ and sigma- and a rho/sup r/ parameter (as defined by Young and Jencks) of -1.58 is indicated. The p-nitroso derivative reacts considerably faster than one would predict, and it is proposed that the nucleophilic center is the oxygen rather than the nitrogen. In reaction wth N,N-dimethylaniline at 25.00C, comparison of methyl perchlorate with methyl-d3 perchlorate leads to a k/sub H//k/sub D/ value of 0.942, and comparison with methyl iodide leads to a k/sub MeOClO3//k/sub MeI/ ratio of 1170. The present results are considered together with earlier studies using methyl iodide, and mechanistic implications are discussed. 8 tables