Orientation of benzoic acid and terephthalic acid on an alumina surface and their reactivities observed by infrared spectroscopy

The orientation of benzoic acid and terephthalic acid on alumina was ascertained by IR measurements. Benzoic acid was chemisorbed as a carboxylate anion with a vertical conformation of the benzene ring (0 < θ < 1.0) and as a mixture of the anion and the acid (1.0 < θ). Terephthalic acid was chemisorbed as a mixture of monocarboxylate anion (hydrogenterephthalate) and dicarboxylate anion (0 < θ < 0.3), as the monocarboxylate anion with a vertical conformation of benzene ring (0.3 < θ < 1.0) and a mixture of the monocarboxylate anion and terephthalic acid (1.0 < θ). The carboxyl group of expected hydrogenterephthalate adsorbed through the carboxylate anion on alumina (θ = 0.8 : 0.37 mmol g−1 alumina) readily reacted with dimethyl sulphate to form monomethyl terephthalate selectively.