Nitrosation of amines in nonaqueous solvents.: 3.: Direct observation of the intermediate in cyclohexane

The reactions of N-methylaniline (MeAn) with 2,2-dichloroethylnitrite (DCEN) and 2,2,2-trichloroethylnitrite (TCEN) in cyclohexane, and N-methylmethoxyamine (MMA) with TCEN in the same solvent, all gave the expected N-nitrosamines. Spectrophotometric monitoring of the MeAn/DCEN and MMA/TCEN reactions showed accumulation of the reaction intermediate. These are the first nitrosations of amines by alkyl nitrites in which observation of the intermediate has been possible; this is attributed to the low basicity of these amines (a) having effectively eliminated the possibility of the intermediate decomposing by base catalysis and (b) having decreased the rate of spontaneous decomposition of the intermediate more than the rate of its formation. Because of the scant capacity of cyclohexane to stabilize charge, it is assumed that both the formation and decomposition of the intermediate occur via concerted mechanisms with four-center transition states: formation through nucleophilic attack by the amine on the nitroso group accompanied by transfer of the amine proton to this group, decomposition through simultaneous cleavage of the N-O bond, and protonation of the alkoxide leaving group.