Spectroscopic Study of 10-Benzoyl-9-anthrol and Its Anion in Basic Media. An Estimation of Microscopic Polarity of PMMA

Publisher Website
Google Scholar
Abstract
The acid-base equilibrium of the title compound (BAOH) was studied in various media containing 4% triethylamine (TEA) by volume as a base. As the polarity of solvents increases, the equilibrium shifts toward the base form (BAO−) and 100% yield of BAO− is achieved in solvents with dielectric constant (ε) greater than 20. The equilibrium is also affected by temperature, favoring the base form at lower temperatures. The associated enthalpy change is estimated to be −14.6 kJ mol−1. Of particular interest is the dominant existence of BAO− in poly(methyl methacrylate) (PMMA), since the acid form (BAOH) dominates in a monomeric solvent (MMA). The microscopic effective dielectric constant of PMMA is estimated to correspond to that of a solvent with ε=22–30 by comparing spectral data in PMMA with those in various solvents. No base form is formed in polystyrene, indicating that not only rigidity but also polar groups in PMMA may be responsible for the anomalously large dielectric constant of PMMA.