Synthesis and Monomer-Dimer Equilibrium of Cyclic Methylphenyl(o-phenylenedioxy)silane

Abstract

Cyclic methylphenyl(o-phenylenedioxy)silane [ 1 ] was synthesized by the reaction of methylphenyldichlorosilane with catechol in the presence of pyridine in 72% yield, and could also be prepared by the alcohol interchange reaction of methylphenyldimethoxysilane and catechol in 83% yield. The product [ 1 ], after distillation, crystallizes readily as a mixture of two isomeric dimers C_2CJ, mp 100-110° C. One of the isomer (mp 121° C) C_2C which was isolated by slow recrystallization, was assigned to the trans dimer on the NMR chemical shift (8(s1cH) O.53 ppm), and the other (mp 105° C) C_2C cp which was separated by rapid extraction from the mixture, the cis one (8(sicn3) 0.68 ppm).
The degree of polymerization in solution changed with time and finally reached a constant value between 1 and 2, which depends on the temperature and the concentration (Fig.1, Table 1). It was confirmed from NMR spectrum patterns (Figs.2, 3) that in solution, two isomeric dimers [2 t] and [2 c] were in equilibrium with monomer. Mole fractions of the monomer and two dimers at equilibrium state were obtained at various temperatures (Fig.4) and activa- tion energies (-4E) were found to be 7.5 kcal/mol for [2 t] and 8.3 kcal/mol for [2 c].