Solute–solute–solvent interactions in aqueous solutions of triethanolamine and dimethylsulfoxide. Microcalorimetric study

Abstract

GIANNA BORCHESANI and FERNANDO PULIDORI. Can. J. Chem. 62, 2898 (1984).The heats of dilution of aqueous solutions of triethanolamine (TELA) and dimethylsulfoxide (DMSO) were determined up to -3 mol kg-', at 25'C.The various enthalpic pair and triplet interaction coefficients, h,,, h,,,, have been evaluated from the data. The h,, for both TELA and DMSO are positive and indicate a prevailing hydrophobic character of TELA and DMSO interactions in highly dilute aqueous solutions.The triplet coefficients are small and negative for both compounds. Dipolar interactions and normal solvation through H-bonding seem to be more important than the size or the solvophobic effect in determining the triplet enthalpic coefficients.GIANNA BORCHESANI et FERNANDO PULIDORI. Can. J. Chem. 62, 2898Chem. 62, (1984.Operant a 25°C et h des concentrations allant jusqu'h environ 3 mollkg, on a dCterminC les chaleurs de dilution de solutions aqueuses de trikthanolamine (TELA) et de dimCthylsulfoxyde (DMSO).Utilisant ces donnCes, on a tvalut les divers coefficients, h,, et h,,,, d'interaction enthalpique. Les valeurs de h,, tant pour la TELA que pour le DMSO sont positives; ces rtsultats indiquent que, en solutions aqueuses trks diludes, les interactions de la TELA et du DMSO ont un caractkre predominant qui est hydrophobe.Pour chacun des composts, les coefficients triplets sont petits et nkgatifs. Les interactions dipolaires et la solvatation normale par le biais de liaisons hydrogttnes semblent donc des facteurs plus importants que la taille ou l'effet solvophobe dans la dttermination des coefficients enthalpiques triplets.[Traduit par le journal]Triethanolamine (TELA) and dimethylsulfoxide (DMSO) belong to different classes of polar organic compounds which are miscible with water in any proportion. Whereas TELA, often defined as a highly hydrophilic substance, is polyfunctional in its interactions with water, DMSO is controversially defined (1, 2) and is only capable of acting as an H-acceptor in H-bonding with water.The physicochemical properties, thermochemical ones in particular, of TELA and related compounds in aqueous solutions have not been extensively studied (3-7).On the contrary, extensive studies have been performed on the therrnochemical properties (1, 8-13) as well as other thermodynamic properties (14, 15) of DMSO-H20 mixtures. Some of the works quoted, together with spectroscopic evidence of various nature (6,8,12,(16)(17)(18)(19), underline the formation of H-bonded DMSO-H,O complexes. Cautious and more in depth analysis (1 1, 19) points out the possibility of different kinds of interactions between DMSO and water in different concentration regions. However, although some peculiarities of the above mentioned systems can be deduced from the analysis of the physicochemical properties over the whole composition range, the relationships between these properties, excess ones in particular, and composition are rather complicated, especially for sufficiently high organic concentrations. Thus from these rela-. tionships it i s di...