As part of a study of nitrogen vs sulfur nucleophiles, the behavior of methylation products from dimethyl‐(2‐methylthioethyl)amine CH3SCH2CH2N(CH3)2 1 is described. Of the 2 potential products (a sulfonium salt or an ammonium salt), the ammonium salt from N‐methylation 2 dominated. The isomeric sulfonium salt 3 prepared by an independent route was found to be unstable and rearranged to the isomeric ammonium salt. The rearrangement pathway was investigated using deuterium‐labeled reactants. The sulfonium salt 3 also produced a piperazinium double salt 9 on heating. The reaction pathway was also followed by deuterium labeling. The results support the conclusion that production of the double salt 9 involves intermediate formation of N,N‐dimethylaziridium ion 4.

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