Mass spectrometry of 1 phenyl-1, 2-dibromopropylphosphonic acid and its methyl ester

$\text{erythro}$-1-Phenyl-1,2-dibromopropylphosphonic acid is known to decompose rapidly into the monomeric metaphospbate-anion (PO₃), 1-phenyl-1-bromopropene, and bromide ion in protic or aprotic solvents in the presence of a hindered tertiary amine. The present study compares the behavior of this phosphonic acid in solution and in the gas phase. The gas-phase thermolysis of the acid involves mainly the loss of bromine and of the phosphoryl group, -P(O)(OR) (OR') (R = R' = H). The same type of pathway is followed in the ionization/excitation processes (“cationic reactions”) that follow from electron impact in mass spectrometry. The thermal and cationic reactions of the monomethyl and dimethyl esters of the phosphoric acids (R=H,R'= CH₃ and R = R' = CH₃, respectively, in -P(O)(OR)(OR')) are entirely analogous to those of the free dibasic acid.