Edwin N. Givens

Mass spectra of benzofurans

Abstract The mass spectra of a number of substituted benzofurans are reported. Ring fragmentation as opposed to substituent fragmentation was observed in halogenated benzofurans. Initial loss of carbon monoxide was found without any evidence for loss of formyl radical (HCO). Benzocyclopropenecarboxaldehyde is proposed as a possible intermediate ion. Hydrogen scrambling observed with deuterated substrates occurred in either the molecular ion, the carboxaldehyde radical ion or the CO elimination product, the benzocyclopropene radical ion. The chlorobenzofurans and, in part, bromobenzofuran fragmented by successive loss of CO and halogen atom. The bromobenzfuran molecular ion also showed the inverted sequence of initial loss of bromine followed by loss of CO. This process was examined by use of the spectra of nitro- and methoxy-benzofurans. Fluorobenzofurans showed little fluorine loss in the early stages of the fragmentation process.

Benzofurans from 2-ethylphenols

Abstract Substituted 2-ethylphenols when heated at or above 550 °C produce substituted benzofurans along with other products. 4-Methyl-, 4-ethyl-, 4,5-dimethyl, 4-fluoro-, 6-fluoro-, 4-chloro-, 6-chloro-, 4,6-dichloro-, and 4-bromo-2-ethylphenols gave the appropriately substituted benzofurans. Substitutent loss was observed in several cases but was most pronounced with the bromo-substituent. Substituent rearrangement with these reactants was absent. Side-chain substitution as in 2-propylphenol gave 2-methylbenzofuran along with some 3-methylbenzofuran. Rearrangements of furan ring substituents were common. 2-Ethylanisole also undergoes the same reaction. 2-Ethylanisole-4- d cyclized to benzofuran-5- d without scrambling. Various catalysts and carrier gases were examined, of which carbonyl sulfide was most selective for benzofuran formation.