The reactions of a series of phosphylating agents (RR′P(O)X) with ethanolamine have been examined, and relative yields of the products from the nucleophilic amino and hydroxyl moieties determined. In general the amount of O-phosphylation increased as R and R′ were changed from dimethylamino through alkoxy to methyl and as the leaving group (X) was changed from OP(O)RR′ to CN. The only exceptions occurred when R was dimethylamino and X was Cl. When X was F, only O-phosphylation was observed. Thus, a wide range of essentially continuously varying selectivities was found.The results are discussed in terms of the amount of charge transfer involved in the formation of the transition state which is assumed to be determined by the electrophile. When the charge transfer is small, the contributions to the activation energy of such factors as solvation and ionization potential of the nucleophile are most important, resulting in N-phosphylation. As the amount of charge transfer increases, the energy of bond formation becomes the dominant factor and O-phosphylation is preferred.
In common with other acylating agents, diisopropyl phosphorochloridate reacts with 2-methyl-Δ2-oxazoline in aqueous and ethereal media to yield N-phosphoryl derivatives. In both media, phosphorylation is followed by ring opening between positions 1 and 5, as shown by the isolation of diisopropyl N-acetyl-N-2-chloroethylphosphoramidate and diisopropyl N-acetyl-N-2-hydroxyethylphosphoramidate. The latter compound undergoes further rearrangement, being slowly converted to diisopropyl N-2-acetoxyethylphosphoramidate in aqueous bicarbonate solution.Nuclear magnetic resonance studies of 2-methyl-Δ2-oxazoline in aqueous bicarbonate solution (pH 8.5) reveal that it is all transformed to N-acetylethanolamine within 23 hours. This short lifetime allows speculation regarding the origin of 2-acetamidoethyl diisopropyl phosphate isolated from the reaction of the base with diisopropyl phosphorofluoridate.