THE CHEMISORPTION OF ACID-CHLORIDES ON THE SILICA SURFACE

The interaction of silica silanol groups with acid chlorides (SOCl2 an d CH3COCl) has been studied by the semiempirical quantum chemical MNDO and AM1 procedures. First, the acid chlorides react with silanol grou ps forming mono-orthoesters of acid chlorides, For thionyl and acetyl chloride reactions this step is appreciably exothermic (238.1 and 50.6 kJ mol(-1), respectively). The next endothermic step involves the eli mination of HCl (-56.5 and -17.6kJ mol(-1) respectively), and the last step in the silica chlorination process is the most endothermic (-150 .6 kJ mol(-1)). The activation energies of the first exothermic step a re rather low and those for the subsequent steps are considerably larg er and approximately equal.