Nitrosation of amines in nonaqueous solvents. 3. Direct observation of theintermediate in cyclohexane

The reactions of N-methylaniline (MeAn) with 2,2-dichloroethylnitrite (DCEN ) and 2,2,2-trichloroethylnitrite (TCEN) in cyclohexane, and N-methylmethox yamine (MMA) with TCEN in the same solvent, all gave the expected N-nitrosa mines. Spectrophotometric monitoring of the MeAn/DCEN and MMA/TCEN reaction s showed accumulation of the reaction intermediate. These are the first nit rosations of amines by alkyl nitrites in which observation of the intermedi ate has been possible; this is attributed to the low basicity of these amin es (a) having effectively eliminated the possibility of the intermediate de composing by base catalysis and (b) having decreased the rate of spontaneou s decomposition of the intermediate more than the rate of its formation. Be cause of the scant capacity of cyclohexane to stabilize charge, it is assum ed 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 transf er of the amine proton to this group, decomposition through simultaneous cl eavage of the N-O bond, and protonation of the alkoxide leaving group.