Composition of technical ethephon [(2-chloroethyl)phosphonic acid] and some analogs relative to their reactivity and biological activity

Abstract

The phosphorus-containing components in technical ethephon, 10 2 2 (0)( )2, were assigned by comparisons with standards from synthesis involving 31P NMR and GC/CI-MS (after derivatization with diazomethane). They were C1CH2CH2P(0)(0H)2 (90%), (H0)2P(0)CH2CH2P(0)(0H)2 (3%), ClCH2CH2P(0)(0H)0CH2CH2Cl,ClCH2CH20CH2CH2P(0)(0H)2,andH2C=CHP(0)(0H)2 (each 1.5-1.8%), and H0CH2CH2P(0)(0H)2, HP(0)(0H)2, and H0P(0)(0H)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, H0P(0)(0H)2, and unmetabolized (H0)2P(0)CH2CH2P(0)(0H)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.

Phosphobutyrylcholinesterase: Phosphorylation of the Esteratic Site of Butyrylcholinesterase by Ethephon [(2-Chloroethyl)phosphonic Acid] Dianion

“…BuChE inhibition by this series depends on both the binding affinity and the phosphorylation rate. The fluoroethyl compound is not an inhibitor (9). The apparent affinity for BuChE decreases in the following order: chloroethyl > bromoethyl > iodoethyl > 2-chlorohexyl; the phosphorylation rate decreases in the following order: bromoethyl ) iodoethyl > chloroethyl ) 2-chlorohexyl.…”

Thermal fragmentation of 2-chloropentylphosphonic salts in the solid state. Counter-ion effects on reactivity and selectivity

“…Competitive formation of the vinylphosphonic product 2 was reported by several researchers [2,4,8], and SCHEME 2 it seems that the relative contributions of pathways (a) and (b) (Scheme 2) to the fragmentation of the 2-haloalkylphosphonic system is a complex function of the medium, the base, the temperature, and the substituents in the phosphonate group (e.g., phosphonic acids vs. phosphonic monoesters). It has been demonstrated that samples of technical ethephone (Union Carbide Agricultural Products) contain up to 1.8% of vinylphosphonic acid, the product of a spontaneous dehydrochlorination of the plant growth regulator [9]. Since it is well established that the ionized (mono-or dianionic) form of a 2-haloalkylphosphonic acid represents the reactive species, it is likely that the nature of the counter ion has an effect on the fragmentation.…”

Significance of impurities in the safety evaluation of crop protection products (IUPAC Technical Report)

“…GC/MS alone cannot usually be used for identification of unknown substances [51]. In many cases, 1 H, 13 C, 31 P NMR [28,34,45], and other spectroscopic methods have been successfully applied for the identification of unknown impurities.…”