An Oxygen Exchange of Arsenate and Alkylarsonate Ions with Water

The oxygen exchange rates, R′s, between the alkylarsonates (methyl- and butyl-) and water were measured over the pH range greater than 9 and at 30 °C. The rates were analyzed in terms of the rate law, R=k1[R′-AsO3H−]+k2[R′-AsO32−] (R′-; alkyl-) to obtain k1 to be 6.64×10−4 s−1 for methyl- and 4.38×10−4 s−1 for butylarsonate ions, respectively. The first-order oxygen exchange rate constants, k1’s, on the alkylarsonate univalent anions (methyl and butyl) are almost the same values, which indicates that the steric effect on the rate is absent. The rate constants, k1’s, correlate well with energy levels of the lowest unoccupied molecular orbitals (ELUMO’s) of univalent anions of arsenic, arsenious, and alkylarsonic acids.