The Study On Solvent Effects Of Aromatic Carboxylic Acid By Ftir Spectroscopy

The frequencies of carbonyl stretching vibrations ofphenylacetic acid, benzoic aicd, 4-propylphenylacetic acid, 3-methoxylbenzoic acid, 2-chloro-5-iodobenzoic acid in single and binary solvent systems were measured with IR spectroscopy respectively, and the solvent effects were discussed in detail.The frequencies of the carbonyl stretching vibrations in single solvent systems were correlated with empirical parameters of solvent polarity that include single empirical parameters and multiparameter approaches. The single empirical parameters include solvent acceptor number (AN), Brownstein's parameter S, Dimroth and Reichardt's parameter E_T(30), and Schleyer's linear free energy equation (LFE). The multiparameter approaches are Kirkwood-Bauer-Magat (KBM) relationship, Swain's two-parameter, linear solvation energy relationships (LSER) treatment of solvent effects. It showed that the relation results with single parameters are not good due to the complicated solute-solvent interactions. The multiparameters, especially the linear solvation energy relationships approaches, were more suitable than the single empirical parameters for solvent effects research in this paper.In binary solvent systems, the solute-solvent interactions were discussed in detail with the solvent-composition change. The binary solvents were composed of the solvent systems of Hexane/Benzene, Hexane/Tetrahydrofuran, Hexane/Chloroform and Hexane/Ethanol. Hexane and Benzene belong to the non-polar solvents; Tetrahydrofuran is the non-polar solvent with lone pair electrons. Chloroform and ethanol fall into polar solvents with active hydrogen. It showed that the monomers of phenylacetic acid, benzoic aicd, 4-propylphenylacetic acid and 3-methoxylbenzoic acid interacted with Benzene by non-specific solute-solvent interactions and with Tetrahydrofuran, Chloroform and Ethanol by specific interactions(hydrogen bonding). The dimers of solutes are slightly influenced with the solvent-composition change. 2-chloro-5-iodobenzoic acid existed in solutions only with monomer form due to its molecular inner hydrogen bond. It interacted with Benzene, Tetrahydrofuran by non-specific solute-solvent interactions and with Chloroform and Ethanol by specific interactions.