The IR laser photochemistry of methyl-substituted tetrahydrofurans

Abstract

The products from the decomposition of 2-methyltetrahydrofuran (2-MTHF), a mixture of cis- and trans-2,5-dimethyltetrahydrofuran (2,5-DMTHF) and 3-methyltetrahydrofuran (3-MTHF) induced by a pulsed CO 2 laser were determined by gas chromatography as a function of the reactant pressure, the focal length of the lens and the SiF 4 sensitization. The major hydrocarbon products at a pressure of 0.3 Torr were C 2H 4 (2-MTHF), C 3H 6 (2,5-DMTHF) and 1-C 4H 8 (3-MTHF). With a tenfold increase in pressure C 2H 4 became a major hydrocarbon product for all three methyl-substituted tetrahydrofurans. At 10 Torr, CO was the major oxygenated species for 2-MTHF and 2,5-DMTHF, whereas for 3-MTHF it was H 2CO. For 2-MTHF the product distribution was interpreted as arising principally from breakage of the CO bond and a ring CC bond to form C 2H 4 and a 1,3 diradical. The product distribution from 2,5-DMTHF at low pressure was explained by cleavage of CH 3 followed by decomposition of the resulting tetrahydrofuranyl radical. Both the diradical and CH 3 cleavage mechanisms were used to account for the product distribution from 3-MTHF.