The rate of decomposition of methyl nitrite (MN) has been studied in the presence of isobutane-t-BuH-(167-20O0C) and NO (170-200Β°C). In the presence of t-3uH (-0.9 atm), for low concentrations of MN (-10-4M) and small extents of reaction (4-10%), the firstorder homogeneous rates of methanol (MeOH) formation are a direct measure of reaction (1) since k&BuH) >> kz(NO): MN T Me0 + NO, Me0 + t-BuH f MeOH + (t-Bu). The results indicate that the termination process involves only t-Bu and NO: t-Bu + NO 5 products, such that k , -10'" M-1 . sec-'. Under these conditions small amounts of CHzO are formed ( 3 4 % of the MeOH). This is attributed to a molecular elimination of HNO from MN. The rate of MeOH formation shows a marked pressure dependence a t low pressures of t-BuH. Addition of large amounts of NO completely suppresses MeOH formation.
Since ( E l + R T ) and AH", are identical, within experimental error, both may be equated with D(Me0 -NO) = 41.8 + 1 kcal/mole and Ez = 0 3~ 1 kcal/mol. From ASo, and A,, kp is calculated to be 101a.1*o.8M-1 . s e c t , in good agreement with our values for other alkyl nitrites. These results reestablish NO as a good radical trap for the study of the reactions of alkoxyl radicals in particular. From an independent observation that k6/kZ = 0.17 independent of temperature, we conclude that E6 = 0 f 1 kcal/mol and ka = 109.3M-l . sec-l: Me0 + NO -i CHZO + HNO. From the independent observations that k2:kz': k6' was 1:0.37:0.04, we find that kz' = 10g.7M-1 . sec-l and k6' = 108.7M-1 . sec-,. In addition, the thermodynamics lead to the result kl' = 1015.7*0.6-40~6*1/0 8ec-l: MeONO, Me0 + NOz, Me0 + NOz -P
In the presence of NO (-0.9 atm) the products are CHzO and NzO (and presumably HzO) such that the ratio NZO/CH,O -0.5. The rate of CHzO formation was affected by the surface-to-volume ratio s / v for different reaction vessels, but it is concluded that, in a spherical reaction vessel, the CHZO arises as the result of an essentially homogeneous first-order, fourcenter elimination of HNO: MN $ CH20 + HNO. The rate of CHzO formation is given by 1
The rate constant for reaction (1) is given by k l = 1015.s*-o.6-41.z*1/e sec-1. 6 1' 6' 2 CHzO + HONO.