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8160230 
Journal Article 
The mechanism of hydrolysis of ortho esters 
Kresge, AJ; Preto, RJ 
1965 
Yes 
Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 
87 
20 
4593-4596 
English 
The hydrolysis of ethyl orthocarbonate in cacodylic acid buffers at 30° occurs at the same rate in the presence of sodium iodide as in the presence of sodium perchlorate. Since, under the conditions of these experiments, nucleophilic attack of the iodide ion on the conjugate acid of the ortho ester would be expected to increase the rate of reaction by more than 100%, nucleophile catalysis is absent and an A2 mechanism for this reaction can be ruled out. Because the reaction is catalyzed by general acids, its mechanism must therefore involve rate-determining proton transfer from the catalyst to the substrate. Though proton transfer is probably concerted with carbon-oxygen bond breaking and proton attack occurs on the electrons of this bond, even proton addition to an unshared electron pair of oxygen (proton transfer between two oxygen atoms) could be slow in this case since ethyl orthocarbonate is only very weakly basic. This mechanism is also consistent with the solvent isotope effect on this reaction.