SYNTHESIS AND INFLUENCE OF FATTY-ACID ESTERS ON THE FOLIAR PENETRATION OF HERBICIDES

Synthesis of mono-esters of tetraethylene glycol and di-esters of tetr aethylene glycol was accomplished from fatty acids and tetraethylene g lycol in the absence of solvent and catalyst. Esterification was studi ed in a batch reactor by using a response surface methodology to evalu ate the influence of synthesis variables such as molar substrate ratio of fatty acid relative to tetraethylene glycol (1.39-7.52), temperatu re (145-167 degrees C), reaction time (0.5-8 h) on the yield of mono-a nd di-esters of tetraethylene glycol. A multipurpose reactor was devel oped for the transformation of fatty acids into pure alpha-monoglyceri des. The 1-monoglycerides of heptanoic, undecelenic, oleic, linoleic a nd erucic acids and tetraethylene glycol esters, mono- and di-esters o f undecelenic, mono-and di-oleic acids, were evaluated as co-formulant s for the herbicides phenmedipham and 2,4-D. The test plants were chos en according to the structure of their epicuticular wax: amorphous in Galium aparine L. (cleavers), crystalline in barley (Hordeum vulgare L .) and pea (Pisum sativum L.). Foliar penetration studies were used as a rapid test for co-formulants. Some of the monoglycerides and the te traethylene glycol esters studied showed a strong enhancing effect on the foliar penetration of 2,PD and phenmedipham. In some cases, the ex tent of the effect seemed to depend on the relative lipophilicities of the ester and of the herbicide. The mono acyl glycerols impaired the crystallisation of phenmedipham but, with the exception of the undecel enic derivative, did not affect the diffusion of phenmedipham in model wax. (C) 1998 Elsevier Science B.V. All rights reserved.