Thermal Decomposition of 5-Methylisoxazole. Experimental and Modeling Study

DOI: 10.1021/j100197a043

Source and publish data:

Journal of Physical Chemistry p. 7367 - 7375 (1992)

Update date:2022-08-12

Topics:

Authors:

Lifshitz, Assa

Wohlfeiler, Dror

Read Full Text PDF DownLoad Join now for total 90,000,000 free articles

Article abstract of DOI:10.1021/j100197a043

The thermal decomposition of 5-methylisoxazole was studied behind reflected shocks in a pressurized driver single-pulse shock tube over the temperature range 850-1075 K and overall densities of ca. 2.5 * 10^-5 mol/cm³.Propionitrile and carbon monoxide are the major decomposition products, followed by ethane, methane, acetonitrile, and hydrogen cyanide.There is no effect of large quantities of toluene (/<5-methylisoxazole> ca. 10) on the concentrations of propionitrile and acetonitrile, indicating that no radical chains are involved in their production.It is suggested that the formation of C2H5CN and CO in 5-methylisoxazole involves an N-O bond cleavage in the 1,2-position, a methyl group shift from position 5 to 4, and a rupture of the C(4)-C(5) bond with the removal of carbon monoxide from the ring: 5,m-isox -> C2H5CN + CO (1).In contradiction to findings in isoxazole, this process requires a very large N-O bond stretch which results in a very loose transition state corresponding to a biradical mechanism.The rate constant for this reaction is k₁ = 10^17.76exp(-70 * 10³/RT) s^-1 where R is expressed in units of cal/(K mol).The presence of ethane and methane in the postshock mixtures indicates the presence of methyl radicals in the hot phase.It is suggested that the formation of methyl radicals involves the same N-O bond cleavage as in reaction 1 but without the methyl group shift: 5,m-isox -> CH2CN^. + CH3CO^. (2) followed by CH3CO^. -> CH3^. + CO (3).This is an endothermic reaction which proceeds at a lower rate than reaction 1 but at a much higher rate than a direct methyl group ejection from the ring.