COMPOSITION OF TECHNICAL ETHEPHON [(2-CHLOROETHYL)PHOSPHONIC ACID] AND SOME ANALOGS RELATIVE TO THEIR REACTIVITY AND BIOLOGICAL-ACTIVITY

The phosphorus-containing components in technical ethephon, ClCH2CH2P(O)(OH)2, were assigned by comparisons with standards from synthesis involving P-31 NMR and GC/CI-MS (after derivatization with diazomethane). They were ClCH2CH2P(O)(OH)2 (90%), (HO)2P(O)CH2CH2P(O)(OH)2 (3%), ClCH2CH2P(O)(OH)OCH2CH2Cl, ClCH2CH2OCH2CH2P(O)(OH)2, and H2C = CHP(O)(OH)2 (each 1.5-1.8%), and HOCH2CH2P(O)(OH)2, HP(O)(OH)2, and HOP(O)(OH)2 (each 0.3-0.6%), consistent with the synthetic route starting with tris(2-chloroethyl) phosphite and involving Arbuzov rearrangement and various hydrolysis and dehydrochlorination reactions. Urinary products of technical ethephon in rats are the parent compound, HOP(O)(OH)2, and unmetabolized (HO)2P(O)CH2CH2P(O)(OH)2. Ethephon and its 2-bromoethyl analogue are more potent than its 2-fluoroethyl and thioic acid analogues and the impurities present in the technical grade material as plant growth regulators (tomato epinasty assay), in vitro inhibitors of plasma cholinesterase, and phosphorylating agents. The biological activity of technical ethephon appears to be associated with the reactions of its principal component, particularly ethylene liberation, and possibly phosphorylating activity.