Synthesis of Fluroxypyr for the Use on Broad Leaf Plants

Fluroxypyr, 1-methylheptyl (4-amino-3,5-dichloro-6-fluoro-2-pyridinyloxy) acetate is used for the control of annual broad leaf weeds in cereals and perennial rye grass. The objective of this work was to develop an economically viable process for the bench synthesis of an organic herbicide fluroxypyr and to scale up the reaction to two litres. This was carried out according to a technical bulletin received from Agriguard Ltd. In addition an investigation into the synthesis and characterisation of impurities formed and reported to be formed, in the reaction process was carried out. The process developed began with pentachloropyridine which on reaction with potassium fluoride in an aprotic dipolar solvent yielded 3,5-dichloro-2,3,6-trifluoropyridine. This was then subjected to ammonation followed by hydrolysis to yield potassium 4-amino-3,5-dichlor-6-fluro-2-pyridinate. This was then alkylated to yield methyl (4-amino-3,5-dichloro-6-fluror-2-pyridinyloxy) acetate, which was then converted to 1-methylheptyl (4-amino-3,5-dicholor-6-fluoro-3 pyridinyloxy) acetate fluroxypyr. The yield of fluroxypyr produced was 47.89% with respect to pentachloropyridine. An alternative method for the synthesis of fluroxypyr was also investigated and the process developed had the first two stages the same as described above. The final stage of this alternative synthesis involved the preparation of fluroxypry by the alkylation of potassium 4-amino-3,5-dichloro-6-fluoro-2-pyridinate with methylheptyl chloroacetate. The overall yield for this alternative method with respect to pentachloropyridine was 40.96%. Methylhepyyl chloroacetate is not commercially available and was prepared in a 65.5% yield from 2-octanol and chloroacetic acid