Ethyl alcohol protonated, reactivity

The influence of the alcohol on the reaction was evaluated (Scheme 26). The results of a competition experiment between the alcohols are shown in Table 7. Both alcohols were treated with mono-alkoxysilane le using 10 % Pd/C as the catalyst. The silyl ketals of both alcohols were isolated as a mixture and the area under the methine protons, from the (+)-ethyl lactate moiety of both silyl ketals, was compared by NMR analysis. The difference in reactivity of primary, versus secondary, versus tertiary alcohol was small. The differences in reactivity range from 1.5 1 for 1° vs 2°, to 3 1 for 1° vs 3°. The reactivity of a benzyl alcohol is slower than the aliphatic alcohol as shown in entries 4 to 6. Entries 4 and 5 show an increase in the ratio of 1° 2° alcohol and a decrease in ratio for the 2° 3° for the secondary benzyl alcohol. Entries 6 and 7 confirm that benzyl alcohols are less reactive than aliphatic alcohols. The inductive electron withdrawing effect of the aryl group in the benzyl alcohol renders it less nucleophillic and this may affect the rate of reaction with the silane. Although the difference in reactivity is small, this trend may be informative. The influence of the alcohol s nucleophilicity on the reaction mechanism will be addressed in a later section. 

By inclusion of a proton source, such as H3PO4, water, or an alcohol, these oligomers can be made with hydroxyl functionality. Thus, a hydroxyl-terminated ethyl ethylene phosphate, Exolit OP 550, is made from triethyl phosphate, P2O5, phosphoric acid, water, and ethylene oxide. It has been introduced by Clariant as a reactive flame retardant for polyurethane foams (135). 

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