Alkyl-Substituent Effect in the Hydrolysis of Sarin

摘要

Isopropyl t-butylphosphonofluoridate (EA 5928) denotes anorganophosphonofluoridate ester (R(OR')P(0)F, R = t-butyl and R' = isopropyl) than resembles the structure of sarin (R = methyl). The hydrolysis of EA 5928 has been investigated with 31p NMR at 20 C and compared with sarin in buffer solutions at pH values of 4.0, 7.2, 9.2, and 10.0. The observed rate ratio of sarin to EA 2938 at pH 10 is 20,000. In addition, while sarin forms exclusively O-isopropyl methylphosphonic acid from displacement of the fluorine, EA 5928 hydrolyzes by parallel reaction paths: both O-isopropyl t-butylphosphonic acid and t-butyl phosphonofluoridic acid (displacement of the O-isopropyl group) are produced. Below a pH of 9, the latter product predominates.