Thermal Reactions of cyclic Ethers at High Temperatures. 2. Pyrolysis of Tetrahydrofuran behind Reflected Shocks

Article abstract of DOI:10.1021/j100406a024

The thermal decomposition of tetrahydrofuran was studied behind reflected shocks in a single-pulse shock tube over the temperature range 1070-1530 K and overall densities ranging from 2 to 8 x 10^-5 mol/cm³.Over this temperature range the following products were obtained: H2, CH4, C2H4, C2H2, C3H4(allene), C3H4(methylacetylene), 1-C4H8, C4H6, C4H4, C4H2,and small quantities of c-C3H6, C6H5, C6H6, and C4H40.From a series of experiments using mixtures of tetrahydrofuran and tetrahydrofuran-d₈ and also partially deuterated (3,3,4,4,-d₄) reactant, the following initiation steps were suggested: tetrahydrofuran->C2H4 + (CH2)2-O, k_uni = 3.30 x 10¹⁶ exp(-83 x 10³/RT) s^-1; tetrahydrofuran ->C3H6 + CH2O, k_uni = 8.25 x 10¹⁵ exp(-83 x 10³/RT) s^-1.The (CH2)2-O residue neither isomerizes to acetaldehyde nor dissociates from a potential surface of the latter.It dissociates to methyl and formyl radycals, producing carbon monoxide as the only oxigenated product of this channel.It was shown that ethylene is formed by elimination from the tetrahydrofuran ring at the 2-3 (4-5) and 3-4 positions at a ratio of ca.2.2:1.A secondary isotope effect of ca. 1.65 in the production of both ethylene and propylene in favor of tetrahydrofuran over tetrahydrofuran-d₈ was noticed.It was also shown that allene and methylacetylene preserve the original skeleton of the tetrahydrofuran and are probably formed directly from propylene. 1-Butene on the other hand is produced by an attack of methyl radicals on propylene and does not preserve the skeleton of the tetrahydrofuran.