Hydrolysis of tert-butyl formate: Kinetics, products, and implications forthe environmental impact of methyl tert-butyl ether

Assessing the environmental fate of methyl tert-butyl ether (MTBE) has beco me a subject of renewed interest because the large quantities of this compo und that are being used as an oxygenated additive in gasoline. Various stud ies on the fate of MTBE have shown that it can be degraded to tert-butyl fo rmate (TBF), particularly in the atmosphere. Although it is generally recog nized that TBF is subject to hydrolysis, the kinetics and products of this reaction under environmentally relevant conditions have not been described previously. In this study, we determined the kinetics of TBF hydrolysis as a function of pH and temperature. Over the pH range of 5 to 7, the neutral hydrolysis pathway predominates, with k(N) = (1.0 +/- 0.2) x 10(-6)/s. Outs ide this range, strong pH effects were observed because of acidic and basic hydrolyses, from which we determined that k(A) = (2.7 +/- 0.5) x 10(-3)/(M .s) and k(B) = 1.7 +/- 0.3/(M.s). Buffered and unbuffered systems gave the same hydrolysis rates for a given pH, indicating that buffer catalysis was not significant under the conditions tested. The activation energies corres ponding to k(N), k(A), and k(B) were determined to be 78 +/- 5, 59 +/- 4, a nd 88 +/- 11 kJ/mol, respectively. In all experiments, tert-butyl alcohol w as found at concentrations corresponding to stoichiometric formation from T BF. Based on our kinetics data, the expected half-life for hydrolysis of TB F at pH = 2 and 4 degrees C (as per some standard preservation protocols fo r water sampling) is 6 h. At neutral pH and 22 degrees C, the estimated hal f-life is 5 d, and at pH = 11 and 22 degrees C, the value is only 8 min.