Theoretical investigation of N-nitrosodimethylamine formation from nitrosation of trimethylamine.
Tertiary amines have been demonstrated to be capable of undergoing nitrosative cleavage to produce carcinogenic N-nitrosamines. The reaction mechanism of the nitrosation of trimethylamine (TMA) to produce N-nitrosodimethylamine (NDMA) was investigated at the CBS-QB3 level of theory. The formation of NDMA from TMA was proposed to be initiated by the formation of an iminium ion, Me(2)N(+) horizontal lineCH(2). Two different mechanisms (NOH elimination mechanism and oxidation abstraction mechanism) leading to Me(2)N(+) horizontal lineCH(2) were investigated, and the oxidation abstraction mechanism was found to be mainly operative. This result indicates that the oxidation abstraction mechanism plays an important role in the nitrosation of both N,N-dialkyl aromatic and tertiary aliphatic amines. Starting from the iminium ion, two experimentally proposed mechanisms (pathways 1 and 2) and one new mechanism (pathway 3) were examined. Pathway 1 proposes that the iminium ion undergoes hydrolysis to give dimethylamine (DMA), which then can be further nitrosated to NDMA; pathway 2 proposes that the iminium ion reacts with NO(2)(-) and forms a neutral intermediate, which then collapses to NDMA. In pathway 3, the iminium ion reacts with N(2)O(3) to give NDMA. Calculation results indicate that in aqueous solution pathway 1 is more feasible than pathways 2 and 3; moreover, the transformation from the iminium ion to NDMA is the rate-determining step. This work will be helpful to elucidate the formation mechanisms of the carcinogenic N-nitrosamines from the nitrosation of tertiary amines.
Sun
Zhi
Z
College of Life Science & Bioengineering, Beijing University of Technology, Beijing 100124, PR China.
Liu
Yong Dong
YD
Zhong
Ru Gang
RG
D003198:Computer Simulation; D004128:Dimethylnitrosamine / Q000138:chemical synthesis* / Q000737:chemistry; D008744:Methylamines / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D015538:Nitrosation; D013237:Stereoisomerism
D008744:Methylamines; C023336:trimethylamine; D004128:Dimethylnitrosamine