Air-stability of aqueous solutions of (HOCH2)3P and (HOCH2CH2CH2)3P

The air-stabilities of buffered solutions of (HOCH2)(3)P [tris(hydroxymethyl) phosphine, THP] and the hydroxypropyl analogue [HO(CH2)(3)](3)P (THPP) under ambient conditions are reported. Both phosphines have a stability zone where no decomposition or oxidation is observed: THP (of industrial importance) is stable between pH 7 and 8 for 7 days, while THPP is stable at pH 10-12 for 3 days. At pH <7, THP dis-proportionates to bis(hydroxymethyl)phosphine (HOCH2)(2)PH = BHP) and the tetrakis(hydroxymethyl) phosphonium cation (HOCH2)(4)P+), while the rate of aerial-oxidation of THP and of BHP then increases with decreasing pH. At pH >10, a known, base-promoted oxidation of THP takes place, and the rate of this increases with increasing pH; in a 0.1 N NaOH solution, THP is oxidized to the phosphine oxide within similar to 10 min with concomitant generation of H-2. Aerial oxidation of THPP is maximized at pH similar to 8, while at lower pH the oxidation is slower due to conversion of THPP into the phosphonium cation [HO(CH2)(3)](3)PH+; at pH <= 4, no oxidation products are detected, while at pH >12, the base-promoted oxidation of THPP takes place. (C) 2011 Elsevier B.V. All rights reserved.