SOLVATION OF LAURIC ACID STUDIED BY VIBRATIONAL SPECTROSCOPIES

Solvation of lauric acid [CH3(CH2)(1)0COOH] has been investigated in d ifferent solvents (apolar, polar-aprotic, and protic solvents) by infr ared absorption and Raman scattering in a large molar ratio range in o rder to investigate the intermolecular interactions between fatty acid s and molecules of different types of solvents. Temperature effects on these mixtures have also been investigated between 24 and 95 degrees C. We have especially concentrated on the carbonyl stretching region ( between 1600 and 1800 cm(-1)), the hydroxyl stretching region (between 2500 and 3600 cm(-1)), and the C-H stretching region (2800-3000 cm(-1 )). Chloroform behaves, with respect to lauric acid, almost as an apol ar solvent. In acetone and in DMSO, a dynamical equilibrium between bo th cyclic dimers and II-bonded lauric acid molecules with solvent mole cules seems to occur, the proportion of the two species depending on t he lauric acid concentration. Cyclic dimers appear for a lauric acid : DMSO molar ratio x > 0.5 (x > 0.2 in acetone). In alcohols, cyclic di mers are present from x approximate to 0.2. For x < 0.2, two different complexes exist, in contrast with results from recent literature. The se may be monosolvate and disolvate complexes. When the alcohol is deu terated, exchange between hydroxyl groups of both components is observ ed. Finally, Raman scattering appears as a powerful tool to clarify IR spectra in the case of solvated carboxylic acids.