Solvent Properties of Dichloromethane. II. The Reactivity of Dichloromethane Toward Amines.

Abstract

The reactions of CHCl2 (I) with various amines have been studied under homogeneous conditions in I as solvent at 25.0°. With initial concns. of the amines in the 0.15-0.3 M range the tertiary amines yield 1 mol of ionic chloride per mol amine consumed while secondary and primary amines yield 1 mol of ionic chloride per 2 mol of amine. The mechanism of the reactions is discussed and it is concluded that the reactions exhibit the normal characteristics for SN2 reactions toward aliph. carbon and thus resemble the usual Menschutkin reactions between amines and alkyl halides. The reactions with secondary amines proceed more rapidly than the reactions with tertiary amines but no evidence for any inter- or intramol. N-H---Cl assistance could be obsd. The rates of the various reactions do not conform with the nucleophilicities of the amines as derived from rate studies of reactions between amines and the usual alkyl halides but seem to depend upon the steric requirements and particularly the basicities of the amines in a way which appears to be unique for I. N-Me-substituted amines are far more reactive toward I than the corresponding N-Et-substituted amines; the half-lives of the CH2Cl2-N-methylpiperidine and the CH2Cl2-N-ethylpiperidine reactions are ∼160 and ∼1070 h, resp. The CH2Cl2-NMe3 and the CH2Cl2-NEt3 reactions proceed with greatly different rates; half-lives of ∼18 and ∼580 h. The CH2Cl2-quinuclidine reaction is particularly rapid with a half-life of less than 2 h. The rate consts. of the CH2Cl2-piperidine and the CH2Cl2-morpholine reactions, half-lives of 15 and ∼330 h, and the CH2Cl2-N-methylpiperidine and the CH2Cl2-N-methylmorpholine reactions, half-lives of ∼160 and ∼3000 h, suggest the Broensted slope for CH2Cl2-amine reactions to be at least 0.55. [on SciFinder(R)]