STUDY OF INTERMOLECULAR INTERACTIONS IN THE EQUILIBRIUM CATALYTIC TRANSESTERIFICATION OF ESTERS .4. FOURIER IR ANALYSIS OF THE INTERACTION OF ALCOHOLS WITH ESTERS

The interaction of alcohols ROH with esters PhCOOR (R = Me, n-Bu, n-C7 H15) in binary mixtures and in solutions in non-polar solvents (CCl4, cyclohexane) was studied over a wide temperature range by Fourier IR s pectroscopy. Even with a great excess of alcohol (up to 3000-fold mola r excess), two bands are observed in the region of v(CO) vibrations. T he low-frequency band, which is down-shifted by 15-20 cm-1 with respec t to the v(CO) band in the absence of alcohol, corresponds to ester mo lecules bonded by hydrogen bonds of the C=O ... HO type. The high-freq uency band is up-shifted by 3-5 cm-1 with respect to the ester v(CO) b and. The discreteness of the shift, which is confirmed by the appearan ce of an isobestic point, indicates that an H-complex of yet another t ype is formed between the alcohol and the ester. The analysis of the d ata available allows one to conclude that complex formation involves t he alkoxyl oxygen atom of the ester. The enthalpies of formation were determined for n-BuOH H-bonds with the esters and with the transesteri fication catalysts. i.e., As(OBU)3, B(OBu)3, and Ti(OBu)4.