BETA-CYCLODEXTRIN EFFECTS ON THE PHOTO-FRIES REARRANGEMENT OF AROMATIC ALKYL ESTERS

The photolysis of phenyl propionate (1a) and phenyl valerate (1b) in w ater and in solutions containing beta-cyclodextrin (CD) leads to the c orresponding p-hydroxyphenyl alkyl ketone 2, o-hydroxyphenyl alkyl ket one 3, and phenol 4. When the reactions are carried out in the presenc e of oxygen there is a decrease in the total amount of rearrangement p roducts, but the inhibition is less marked in the presence of CD. The [3]/[2] ratio for 1b increases when CD concentration changes from 0 to 10 mM. These changes are due to the increase in the quantum yield for the formation of 3 and a decrease in the quantum yield for 2 in solut ions containing CD. The [3]/[2] ratio for la decreases in the presence of CD although both quantum yields increase with CD concentration. Un der the conditions used in this study, the substrate reacted in the bu lk solution and in the cavity of CD. The quantum yields for the format ion of 3 and 4, PHI(CD)3 and PHI(CD)4, are higher for the included sub strate than the corresponding values for the free substrate while PHI( CD)2 is higher than PHI(w)2 for 1a but lower for 1b. This effect is at tributed to the different orientation of the substrates in the cavity of CD. Besides, PHI(CD)4 also increases due to the availability of hyd rogens bonded to secondary carbons in the cavity of the cyclodextrin.