The thermal decomposition of nitromethane under highly diluted conditions in shock tubes has been analyzed in terms of a detailed chemical kinetic model. The experimental data were adopted from Glä nzer and Troe, Hsu and Lin, and Zhang and Bauer, respectively; they cover the temperature range and pressures from 0.5 to 6.0 bar. Based on 1000-1400 K these results, rate constants for the reactions (R1) andThe high and low pressure limits for reaction (R1) determined by Glä nzer and Troe have been shown to be consistent with more recent shock tube data, provided a center broadening parameter is introduced to describe the fall-off behavior. Our reinterpretation of the shock tube results of Glä nzer and Troe together with room temperature measurements indicate that the rate constant for (R14) decreases slightly with temperature, as cm mol s . order of magnitude faster than recombination of CH 3 and NO 2 to form nitromethane. Based on the available data for the forward and reverse rate of reaction (R1) a value of 66.7 Ϯ 2.0 cal/(mol K) for the entropy S 0,298 of CH 3 NO 2 is estimated.

An experimental investigation of methane oxidation in the presence of NO and N0 2 has been made in an isothermal plug-flow reactor at 750-1250K. The temperature for on-set of oxidation was lowered by 250 K in the presence of NO or NO z at residence times of 200 ms. At shorter residence times (140 ms) this enhancement effect is reduced for NO but maintained for N0 2 . Furthermore two temperature regimes of oxidation separated by an intermediate regime where only little oxidation takes place exist at residence times of 140 ms, if NO is the only nitrogen oxide initially present. The results were explained by the competition between three reaction paths from CH 3 to CHzO. A direct high temperature path (A), a two-step N0 2 enhanced low temperature path (B) and a slow three step NO enhanced path (C), which may produce N0 2 to activate path B. The negative temperature coefficient behaviour was explained by a competition between paths (A) and (C). A previously published reaction set was modified to take these reaction patterns into account.The processes discussed here presumably occur to some extent in the exhaust of natural gas engines, but conditions may be modified, either to ensure an enhanced activity to oxidize methane in the exhaust, or alternatively to decrease the activity to reduce the production of unwanted intennediates such as fonnaldehyde.

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A simple and very sensitive spectrophotometric flow injection (FI) procedure for the determination of trace amounts of thiocyanate is described. The proposed method is based on the reaction between thiocyanate and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol, which, in 2 mol dm-3 acidic media in the presence of a strong oxidizing agent, produces an intensely coloured product. Several oxidants are potentially applicable, but it is shown that dichromate is preferable. As the reaction product formed is unstable and the signal inherently is recorded on a high background level, it is demonstrated that FI constitutes an ideal method in order to monitor reproducibly and repeatedly the kinetically transient signal that is obtained. Based on optimization by a factorial experimental design, the detection limit of the procedure was found to be 3.5 mumol dm-3, and the standard deviation between samples was 0.16 mumol dm-3. No significant interferences were observed; a 1000-fold excess of cyanide could readily be tolerated within the experimental error. With a sample volume of 50 microliters being injected, the sampling frequency was 60 samples h-1. The system was tested with saliva samples from non-smokers and smokers, and the results show that it is possible to distinguish between these two categories of individuals. As an added benefit, the detection limit of the analytical procedure allows the samples to be diluted 100-fold, so that centrifugation for 5 min is the only preliminary sample preparation that is necessary.

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