Rates of Oxidation of o-Nitrobenzeneselenenyl Compounds by m-Chloroperoxybenzoic Acid and the Rate of Reaction of o-Nitrobenzeneselenol with o-Nitrobenzeneselenenic Acid

Article abstract of DOI:10.1021/jo00353a003

Rate constants for the oxidation of a series of o-nitrobenzeneselenenyl derivatives (Ar = o-O2NC6H4) by m-chloroperoxybenzoic acid (MCPBA) have been measured at 25 deg C in ethanol (compound, k_PA (M^-1s^-1)): ArSeH, 1.1 * 10⁴; ArSeOH, 80; ArSeOSeAr, 12; ArSeOEt, 4; ArSeSeAr, 0.15.The rate constant (k_ArSeH = 1.0 * 10² M^-1s^-1) for the reaction of ArSeH with ArSeOH to give ArSeSeAr (eq 3), which is pH independent in acid solution, has also been determined.Significant practical consequences of these and related results include the following: (a) the rate of oxidation of selenol (ArSeH) to selenenic acid (ArSeOH) is enough faster than either the oxidation of ArSeOH to seleninic acid (ArSeO2H) or eq 3 so that oxidation of the selenol with 1 molar equiv of MCPBA gives ArSeOH in high yield; (b) with a weaker oxidant, hydrogen peroxide, the rate of oxidation of the selenol is enough slower than the rate of eq 3 that the diselenide (ArSeSeAr) becomes the almost exclusive product; (c) the rate of oxidation of the diselenide is so much smaller than that of any of the other compounds that its initial oxidation to ArSeOSeAr is far and away the slowest step in its overall oxidation to seleninic acid by excess peracid.