INHIBITION OF NITROSATION BY STERIC HINDRANCE

The nitrosation of piperidine, 2-methylpiperidine, 4-methylpiperidine, 2,6-dimethylpiperidine, and 2-ethylpiperidine in acid medium was stud ied. Kinetic monitoring of the reactions was accomplished by spectroph otometric analysis of the nitrosamine formed at lambda = 249 nm. In ea ch case, the value of the rate constant of the determining step R(2)NH + N2O3 --> R(2)NNO + HNO2 was calculated observing the following sequ ence of reactivities: piperidine approximate to 4-methylpiperidine > 2 -methylpiperidine approximate to 2-ethylpiperidine > 2,6-dimethylpiper idine. In the case of 2,6-dimethylpiperidine, no nitrosation was obser ved. The results are interpreted in terms of the steric hindrance of t he alkyl groups to attack of the secondary amine group by dinitrogen t rioxide. The results open the possibility of blocking the undesirable mechanisms of formation of N-nitroso compounds.