Ethylene Evolution From 2-Chloroethylphosphonic Acid

Abstract

2-Chloroethylphosphonic acid (CEPA. "Am-chem 66-329", "Ethrel"; ref. 1), a new plant growth regulator, degrades to yield ethylene in an alkaline solution. When applied to plants, it has been very effective in causing responses characteristic of ethyl-ene treatment (3, 4, 6, 7). The formation of ethvlene or its alkene homologs from CEPA or its homologs was studied and deFcribed in detail in 1963 by May-nard and Swan (5) including the probable reaction mechanism. Nevertheless, several reports have since appeared describing the same reaction wi.thout citing (4, 8) or properly acknowledging (3) their work. Some investigators (7) have since suggested that the growth regulatory action of CEPA is due to the stimulation of ethylene production within the plant tissues without discussing the fact that CEPA itself is the ethylene producer. The chemical mechanism of ethylene production from CEPA suggested by Maynard and Swan (5) involves the nucleophilic attack on -the phosphonate dianion by a water molecule and the concerted elimi-nation of chlorine, leading to direct formation of phosphate and chloride as shown in equation (I). Probably the OH-ion may also serve as an nucleo-phile in the reaction. I -C;H -CH2-P.-, ~H 0(or OH-) 01 O-HOHP -2 H H C1 + CH2=CH2 + H2 PO (or HPO4) (I) When tested, the yield of ethylene equals that of phosphate as shown in table I. Recently Warner and Leopold (8) studied ethyl-ene evolution from CEPA and suggested a reaction mechanism which involves the removal of the phos-phonate as phos.phonate salt, followed by dehydro-halogena.tion as shown in equation (II). -o