Products and Mechanistic Investigations on the Reactions of Hydrazines with Ozone in Gas-Phase

Abstract

The toxic transformation products of hydrazines are of great concern. These products’ properties combined with their formation mechanisms are needed to assess their potential environmental and human impacts. In this study, the gas-phase reaction of hydrazine (N2H4), monomethyldrazine (MMH) and unsymmetrical dimethyhydrazine (UDMH) with O3 have been studied at varying reactant ratios, both in the presence and absence of a radical trap. Gas chromatography-mass spectroscopy (GC-MS) has been implied to follow reactant consumption and product formation. Apart from the reported products detected by Fourier transform infrared spectroscopy (FT-IR), the newly found compounds (hydrazones, formamides, dimethylamine, 1,1,4,4-tetramethyl-1,2-tetrazene,dimethylamino-acetonitrile, N2, H2O, et al.) are identified by GC-MS. The relative yields of the organic products vary considerably at different O3/MMH or UDMH ratios. UDMH and MMH are confirmed as high potential precursors of N-nitrosodimethylamine (NDMA). The presence of hydroxyl radicals (HO·) hinders NDMA formation in MMH-O3 system. Meanwhile, it increases NDMA formation in UDMH-O3 system. The suggested reaction mechanisms which account for the observed products are discussed.

Comprehensive computational study on reaction mechanism of N-Nitroso dimethyl amine formation from substituted hydrazine derivatives during ozonation

“…In order to reduce excessive NDMA formation, identifying potential NDMA precursors and their reactivity are crucial [ 39 , 40 ]. Organic hydrazine compounds such as unsymmetrical hydrazine (UDMH) and monomethylhydrazines (MMH), being the major NDMA precursors, upon ozonation form NDMA up to 90% in molar yields [ 41 ]. They act as eco-toxicants and can form several toxic transformation products, posing severe health risks [ 42 , 43 ].…”

“…Since these hydrazines do not undergo photolysis in the solar actinic region (>290nm), UDMH and MMH are more likely to react with ozone in the atmosphere to form NDMA along with other toxicants. Huang et al [ 41 ] found that the conversion rate of UDMH and MMH to NDMA on ozonation depends on the O 3 /MMH or UDMH ratios. With excess ozone, UDMH and MMH produce 88% and 58% of NDMA, respectively, in molar yields, making them the foremost ozone-NDMA precursors.…”