Date of Award
10-1987
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
First Advisor
Michael A. McKinney
Second Advisor
Daniel T. Haworth
Third Advisor
Sheldon E. Cremer
Fourth Advisor
William A. Donaldson
Fifth Advisor
Husam A.A. Rasoul
Abstract
The kinetics of cleavage of phenylcyclopropanone acetals, 2-phenyl-4,7-dioxaspiro (2.4) heptane (3) and 1,1-dimethoxy-2-phenyl cyclopropane (2) in aqueous sulfuric acid (57-77 wt %) have been investigated. The observed acidity dependence (X), enthalpy of activation ($\Delta$H$\sp{\ddagger}$ = 17.6 Kcal/mol), entropy of activation)$\Delta$S$\sp{\ddagger}$ = $-10.4$ eu) and deuterium solvent isotope effect (k$\sb{\rm H\sb3 O}\sp{+}$/k$\sb{\rm D\sb3 O}\sp{+}$ = 2.6) for the cleavage of 3 are consistent with a A-S$\sb{\rm E}$2 reaction mechanism which involves rate-determining protonation of the cyclopropane ring. Cyclopropanone acetal 2 was found to cleave by two competing mechanisms. An A-1 reaction predominates at high acidity as evidenced by the activation parameters ($\Delta$H$\sp{\ddagger}$ = 25.0 Kcal/mol, $\Delta$S$\sp{\ddagger}$ = 11.5 eu) and the deuterium solvent isotope effect (k$\sb{\rm H\sb3 O}\sp{+}$/k$\sb{\rm D\sb3 O}\sp{+}$ = 0.66). A mechanistic changeover to an A-S$\sb{\rm E}$2 reaction was observed at the low end of the acid range studied. A physical-organic study of the (3+2) cycloadditions of acetals 2 and 3 and their sulfur analogues, 1,1-dithiomethyl-2-phenylcyclopropane (4) and 2-phenyl-4,7-dithiospiro(2.4) heptane (5) with tetracyanoethylene (TCNE) was undertaken with a view to elucidate the reaction mechanism. The kinetic results indicate that the substrates exhibit a wide range in reactivity towards TCNE, spanning a factor of 10$\sp6$. The rates of cycloaddition of 2 and 3 with TCNE were found insensitive to solvent polarity. Intermolecular trapping experiments did not provide evidence for the intermediacy of zwitterions in the cycloadditions of 2, 3 and 4 with TCNE. However, the reaction of 3 with 1-chloro-2,2-di-cyanoethylene resulted in an open-chain adduct, which may be viewed as arising from the efficient intramolecular trapping of a 1,5-zwitterion by cholride ion. Acetal 3 was also found to participate readily in a (3+2) cycloaddition with 4-phenyl-1,2,4-triazoline-3,5-dione. The solvent effect on the rate of this cycloaddition is similar to that observed for the cycloaddition of 3 with TCNE implying a common mechanism. A comparison of the experimentally obtained free energy of activation, $\Delta$G$\sp{\ddagger}$, with the calculated free energy change, ($\Delta$G$\sb{\rm O}$), for the formation of radical-ion pair intermediates from reactants indicate that, for several of these cycloadditions, a single electron-transfer step may well be operative.