Info

FIGURE 6.21 FTIR spectra taken during reaction of CH3NHNH2 with 03: (a) 3.68 ppm CH3NHNH2 before reaction; (b) 2 min after injection of 2.8 ppm 03; (c) 2.8 ppm 03 injected 38 min after first injection (spectrum taken 2 min after second injection). NH3 absorptions have been subtracted from (a) and (b), and both NH3 and 03 absorptions from (c) (adapted from Tuazon et al, 1981).

observed products, but at least 95% of the initial nitrogen in CH3NHNH2 could not be found, indicating it likely formed N2.

The reaction mechanism proposed by Tuazon et al. (1981, 1982) to explain these results is analogous to that for N2H4. In this case, the intermediate CH3N=NH formed in the reaction analogous to (93) was identified by FTIR. Reactions (100a) and (100b) explain the formation of CH2N2:

In excess 03, CH2N2 can react via (100c):

The formation of CH3OOH, HCHO, CH3OH, and CH30N02 is expected from secondary reactions of the methyl radical as discussed earlier in this chapter.

The reaction of f,f-dimethylhydrazine with 03 gave the carcinogen N, N- d i m ethyl n itrosii m i n e as the major product in ~60% yields within 2- to 3-min reaction time (Tuazon et al., 1981). Minor products were HCHO, H202, HONO, and perhaps NOx. For a discussion of the complex mechanisms, the reader should consult the original reference.

N02 has also been shown to react with 1,1-dimethyl-hydrazine in air, forming HONO and tetramethyltetra-zine-2, (CH3)2NN=NN(CH3)2 (Tuazon et al., 1983b). The reaction is also proposed to involve abstraction of a hydrogen from the weak N-H bond by N02, forming HONO. The tetramethyltetrazine-2 is hypothesized to be formed by the addition of N02 to the (CH3)2NNH radical, followed by decomposition to (CH3)2N2 + HONO and the self-recombination of the (CH3)2N2 radicals (Tuazon et al., 1982). The apparent overall rate constant for the reaction was 2.3 X 10"17 cm3 molecule-1 s"1 so that the lifetime of 1,1-dimethylhy-drazine at an NOz concentration of O.f ppm would be ~ 5 h. Since the lifetimes with respect to O.f ppm 03 or f X 106 OH radicals cm-3 are ~7 min and 6 h, respectively, the reaction of N02 can contribute to the atmospheric reactions of the hydrazine only at low 03 levels.

Hydrazine, monomethylhydrazine, and asymmetrical dimethylhydrazine have also been shown to react rapidly (k > 10"15 cm3 molecule" 1 s" ') with HN03 in the gas phase to form the corresponding hydrazinium nitrate aerosols (Tuazon et al., 1982).

0 0

Post a comment