Methylphosphonic acid adduct

Figure 61.1 shows the mass spectrum of the nonapeptide with methylphosphonic acid adduct that resulted after exposure to a rapid aging nerve agent such as soman. This mass spectrum has been acquired on the QTOF instrument with accurate mass determination. The spectrum shows that the mass difference between the protonated parent ion and the highest fragment corresponds with the theoretical mass of methylphosphonic... 

Methylenation. This phosphonate ester is generally regarded as unsuitable for methylenation of ketones, even though the anion forms the intermediate adduct in satisfactory yield. However, under suitable experimental conditions, this reagent was used for methylenation of 1 to give 2 in 90% yield, higher than that obtained with methylphosphonic acid bis(dimethylamide) (78%).1 The optimum yield is obtained if exactly 2 equiv. of base and 1 equiv. of water are used to quench the adduct before cycloelimination. 

Figure 10 compares the El, methane Cl and ammonia Cl mass spectra obtained for a representative member of this series, the TMS derivative of pinacolyl methylphosphonic acid. No El molecular ion is observed. The methane Cl [M+H] ion is small, less than 10% of the base peak. As shown previously in Figures 8 and 9, this class of compounds gives very similar El mass spectra, which is excellent for class screening but not for compound identification. Of the three methods of ionization, ammonia Cl is the method of choice for identification and molecular weight confirmation. The [M+H] ion is the base peak. The [M+NH4] adduct ion is also observed (20% of base peak in the above example). 

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