The mono (α-hydroxy) phosphines R2PCH (OH) R'(R= Ph, R'= H, Et, CH2Ph, Ph, pX-C6H4; R= cyclohexyl, R'= Ph) are prepared under solvent-free conditions by a 1: 1 reaction of Ph2PH with the appropriate aldehyde, and their stabilities (with respect to reversible dissociation into reactants), studied in DMSO, Et2O, and MeOH, increase with decreased basicity of the hydroxyphosphine; for example, for the Ph2PCH (OH) C6H4-pX ...