The competitive formation mechanism of N-nitrosodimethylamine and formaldehyde dimethylhydrazone from 1,1-dimethylhydrazine during ozonation in air: A combined theoretical and experimental study

摘要

In order to controlling the yields of N-nitrosodimethylamine (NDMA), a highly human carcinogen, the competitive formation mechanism of NDMA and formaldehyde dimethylhydrazone (FDMH) from 1,1-dimethylhydrazine (UDMH) ozonation have been explored experimentally using gas chromatography-mass spectroscopy (GC-MS). Further, the results have been explained computationally using density functional theory (DFT) methods, as well as coupled cluster single-double (CCSD) methods, FDMH is not only an intermediate, but also a competitor for NDMA formation from UDMH. NDMA formation proceeds via H-abstraction from -NH2 moiety, while FDMH formation proceeds via H-abstraction from -CH3 moiety. The newly discovered NDMA formation mechanisms are: H-abstraction, diazene formation, O-addition. As ozone concentrations increases, the yields of NDMA rise accordingly. In addition, the theory results show that it is easier for NDMA to form from FDMH than that from UDMH. This study aims in providing a more detailed NDMA formation mechanism from UDMH than previous studies.