Effect of solvent on the dehydrogenation of poly(1,3-cyclohexadiene): Formation and characteristics of benzoquinone-aromatic hydrocarbon charge-transfer complexes

Abstract

The effect of solvent on the dehydrogenation of poly(1,3-cyclohexadiene) (PCHD) with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) [or 2,3,5,6-tetrachloro-1,4-(p-)-benzoquinone (TCQ)] was examined to improve the reactivity of benzoquinones for this dehydrogenation reaction. The dehydrogenation of PCHD with DDQ (or TCQ) was strongly affected by the type of solvent, and aromatic hydrocarbon based solvents were appropriate for this dehydrogenation reaction. A charge-transfer complex between DDQ (or TCQ) and aromatic hydrocarbons was formed in the reaction mixture, and the reactivity of the complex was much higher than that of free DDQ (or TCQ). The formation of a DDQ–aromatic hydrocarbon complex, which has a large diamagnetic shift of the 13C NMR signals with respect to DDQ, was the primary factor for improvement of the reactivity of DDQ. For the TCQ–aromatic hydrocarbon complex, the existence of an electron-withdrawing group on the aromatic hydrocarbon was the major factor for improvement of the reactivity of TCQ. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 342–350, 2010