Butyl halides pyrolysis

This study on the kinetic chlorine isotope effect in ethyl chloride50 was extended to secondary and tertiary alkyl halides pyrolyses51. The isotope effects on isopropyl chloride and terf-butyl chloride pyrolysis were found to be primary and exhibited a definite dependence on temperature. They increased with increasing methyl substitution on the central carbon atom. The pyrolysis results and model calculations implied that all alkyl chlorides involve the same type of activated complex. The C—Cl bond is not completely broken in the activated complex, yet the chlorine participation involves a combination of bending and stretching modes. 

No examples of catalysis of unimolecular elimination from halides or esters have been reported. Fades and Stimson (1962) have shown that t-butyl chloride undergoes elimination in the gas-phase at a rate independent of the partial pressure of added sulphur hexafluoride, a substance known to accelerate certain decompositions (Bose and Hinshelwood, 1959). However, the pyrolysis of alcohols, first studied by Kistiakowsky and Schultz (1934) is accelerated by the presence of hydrogen halides (Maccoll and Stimson, 1960). The former authors showed that t-butyl alcohol decomposed homogeneously to yield isobutene and water, at a rate given by... 

Slightly greater variations in the activation entropy are noted in ester than the halide thermolyses, but the A values again approximate to 10 and indicate the cyclic unimolecular nature of the transition states. With changing ester, the rate of pyrolysis and strength of the liberated acid qualitatively increase in the same direction" . The dichloroacetate, chloroacetate and acetate of t-butyl alcohol exemplify this relationship and at 250°C their rates of pyrolysis follow the order 18.6 4.4 1 (ref. 406). Nucleophilicity of the carbonyl function cannot be the dominating influence as a reverse order of reactivity would be predicted . 

The dianion of a-phenylsulphinylcyclopentanone (formed by treatment of the P-ketosulphoxide with sodium hydride and n-butyl-lithium in THF-HMPA) is alkylated at C-5 exclusively by alkyl halides in 34—65% yield. Pyrolysis of the products in CCI4 under nitrogen at 75°C gave 43—82% yields of the 2-alkyl-A -cyclopentenones. 

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