A mechanistic study of the solvolyis reactions of selected phosphoryl chlorides and p-anisoyl chloride

• Main Author: Ebdon, D. N.
• Published: Swansea University 1999
• Subjects: 547.13
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636761

Throughout the 1990's several investigators have used a mechanistic theory based upon third order kinetics to explain the rates of the reactions of several substrates in aqueous mixtures of protic (e.g. methanol) an aprotic (e.g. acetone) solvents. Such substrates investigated have included <I>p</I>-nitrobenzoyl chloride and <I>p</I>-nitrobenzenesulfonyl chloride. Reactions of these substrates in aqueous alcohols yield two products; an acid (RCO<SUB>2</SUB>H and RSO<SUB>3</SUB>H) and an ester (RCO<SUB>2</SUB>R and RSO<SUB>3</SUB>R). Measurements of the relative amounts of the products obtained from these reactions has enabled investigators to calculate selectivity values, S (S = [Ester]/[Acid] x [Water]/[Alcohol]). Both the rates and products (selectivities) of these reactions have been successfully explained by this third order theory. This thesis (Chapters 1-5) is primarily concerned with testing the third order theory further by investigating the reactions of selected phosphoryl chlorides (e.g. diphenyl-chlorophosphate, (PhO)<SUB>2</SUB>POCl) in aqueous mixtures of protic and aprotic solvents. Some of the results obtained in this thesis strongly support the theory whilst some unexpected results have been explained by initial state solvation effects. Unexpected changes in selectivity in highly aqueous mixtures of methanol and ethanol (e.g. 10-30%) may be caused by complex solvent-solvent interactions in these solvents. Chapter six of this thesis is not concerned with the third order theory investigated in Chapters 1-5. Previous investigations of the solvolyses of <I>p</I>-methoxybenzoyl (anisoyl) chloride in aqueous methanol and ethanol have resulted in an S<SUB>N</SUB>1 type mechanism involving solvent separated ion pairs being postulated. Selectivities for these solvolyses are constant over the whole range of methanol-water and ethanol-water mixtures investigated (10-90%, % v/v) with the selectivity in ethanol being less than in methanol. These constant selectivities have provided an opportunity to investigate aqueous mixtures of other alcohols (e.g. propanols and butanols) and to discover whether effects such selective solvation of anisoyl chloride by alcohol occurs. Any changes in the pattern of selectivity might be due to such effects and not a change in mechanism because anisoyl chloride is reluctant to react via associative mechanisms even in solvents of low ionising power (e.g. ethanol).