5-sulfur substituted pyridine monocarboxylic herbicides

#This invention relates to a new class of 2,6-substituted pyridinecarboxylic acid derivatives having a wide range of activity as herbicides.

#Pyridine derivatives have, for many years, been investigated for use in the biological sciences. For example, 2,6-bis-(trifluoromethyl)-4-pyridinols have been found useful as herbicides and fungicides as disclosed in U.S. Pat. No. 3,748,334. Such compounds are characterized by substitution in the 4-position by a hydroxyl radical. In addition to the hydroxyl radical, the pyridine nucleus may also be substituted with bromo, chloro or iodo radicals. Trifluoromethyl pyridine derivatives have also been disclosed in U.S. Pat. Nos. 2,516,402 and 3,705,170 wherein the nucleus is further substituted by halogens as well as numerous other substituents. Some of these compounds are also noted to be useful as herbicides.

#Also known because of their fungicidal activity are 4-substituted 2,6-dichloro-3,5-dicyanopyridines wherein the 4-position is substituted with alkyl, phenyl, naphthyl or pyridyl groups. Such compounds are disclosed in U.S. Pat. No. 3,284,293, while similar compounds are disclosed in U.S. Pat. No. 3,629,270 wherein the 4-position is substituted with a heterocyclic group wherein the hetero atom is oxygen or sulfur.

#Preparation of 5-Bromo Pyridinemonocarboxylate precursors. Preparation of the 5-bromo substituted precursors of the compounds of the present invention from compounds known in the art is illustrated by the following Examples A-C.

#Step 1: 3-Pyridinecarboxylic acid, 5-amino-6-(difluoromethyl)-4-methyl-2-(trifluoromethyl)-, ethyl ester. To a slurry of 50 g of sodium azide, 90 mL of water and 315 mL of acetone was added 0.474 mol of product of Example 44 of European Patent Application No. 133,612 published (Feb. 27, 1985, in 35 mL of acetone with rapid stirring. An exothermic reaction resulted with vigorous gas evolution. After the reaction mixture cooled to room temperature, it was diluted with 200 mL of water and extracted with chloroform. Normal workup afforded 86.3 g (82%) of product as a white solid. Recrystallization from ethyl acetate/cyclohexane afforded analytically pure material, mp 71.degree.-72.degree. C.

#______________________________________ Elemental Analysis: C H N ______________________________________ Calculated 44.30 3.72 9.39 Found 44.30 3.73 9.40 ______________________________________