Abstract: The heats of immersion of orthoboric acid in twelve organic bases and the adsorption heats of nine organic bases on γ-alumina were determined. The heat values were correlated with the corresponding enthalpies of boron trifluoride and antimony penta chloride, the well-known homogeneous prototype of Lewis acid. The results show that the heats of immersion of H₃BO₃ appear to be well correlated with the thermochemical measurements of BF₃ and SbCl₅ (correlation coefficient are 0.98 and 0.97 respectively), but the correlation coefficient for the adsorption heats of γ-Al₂O₃ and the two homogeneous prototype of Lewis acid are only 0.95 and 0.92 respectively. It is concluded that the reaction of orthoboric acid with the organic bases is an essential Lewis acid-base interaction and the orthoboric acid could be used as a solid prototype of Lewis acid.

Key words: boron trifluoride, antimony pentachloride, solid model of Lewis acidity, heat of immersion, adsorption heat