Formate and Methoxymethyl Acetate

The acid-catalyzed hydrolysis of simple partial acylals has been studied in condensed phase, and a study of the behavior of methoxymethyl formate and methoxymethyl acetate in chemical ionization mass spectrometry was undertaken to provide a comparison of the gaseous and solution phase chemistry of these simple partial acylals. Methoxymethyl formate and methoxymethyl acetate undergo hydrolysis in aqueous acid by an A lI mechanism, 

In aqueous hydrochloric acid the formate hydrolyzes about three times faster than acetate, and it was hoped that in chemical ionization mass spectrometry the same pattern would be observed, namely that under the same conditions the formate would be more extensively ionized to the methoxymethyl cation. The chemical ionization mass spectra of 

The spectra of methoxymethyl formate are very similar to those of methoxymethyl acetate, but again with one significant difference. A fairly intense (M — 3) ion is observed in the acetate ester at mje = 101, but in the formate ester none of this ion is observed. However, the most intense ion in the spectrum (relative intensity = 51%) is mje = 101, which is the same mje value as is found for the (M — 3) ion in the acetate ester. From a study 

TABLE XVI. Chemical Ionization Mass Spectra of Methoxymethyl Acetate and Isobutane Reactant  

This example involves the use of a methoxymethyl group as the second nucleophilic center in the molecule in the case of the benzyl esters the phenyl ring provides this function, and reaction (46) results. 

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