GB912976A - Halogen substituted alkylbenzoic acids - Google Patents

Abstract

The invention comprises chloro- and/or bromo-substituted 2-alkyl benzoic acids of the general formula <FORM:0912976/IV (b)/1> wherein R is an alkyl group, X is a chlorine or bromine atom and Y is a chlorine, bromine or hydrogen atom. In an example, orthoxylene is chlorinated with gaseous chlorine, in the presence of iron filings, to produce a mixture of isomeric trichloroxylenes. Chlorination is then effected in a side-chain to give the corresponding trichloro - monomethyl - benzyl chlorides, which are converted into the acetates by reaction with sodium acetate. Finally, the mixture of isomeric esters is treated with concentrated nitric acid to obtain 2-methyl-3,5,6-trichlorobenzoic acid mixed with other isomers. The mixed acids may be esterified with an aliphatic alcohol; and the benzoate esters may then be separated, and subsequently hydrolysed with HCl to form the individual benzoic acids. 2 - Methyl-tetrachlorobenzoic acid may be prepared in a similar manner. In a second example, propylbenzene is monobrominated to form a mixture of o- and p-bromo-propylbenzenes, which are separated by distillation. Nuclear trichlorination of the ortho-bromo propylbenzene produces a mixture of isomers including 2-bromo-3,4,6-trichloro-propylbenzene. By the Grignard reaction utilizing magnesium, followed by treatment with CO2 gas in the presence of H2O, the bromine atom is replaced with a carboxyl group thereby producing a mixture of isomeric acids including 2-propyl-3,5,6-trichlorobenzoic acid. In a third example, dodecyl benzene is reacted with hydrochloric acid and formaldehyde, in the presence of zinc chloride, to form dodecyl-benzyl chloride, which is converted into the acetate. The acetate is oxidized with nitric acid to obtain dodecyl benzoic acid, which is then chlorinated to form dodecyl-trichlorobenzoic acid or dodecyl-tetrachlorobenzoic acid. Various salts of these substituted benzoic acids are referred to; viz. those of sodium, potassium, ammonium, calcium, barium, dimethylamine, and mono-, di- and triethanolamine. The esters and amides of the acids are also referred to. All these compounds have herbicidal activity (see Group VI).ALSO:Herbicidal comprise a chloro- and/or bromo substituted 2-alkyl benzoic acid of the general formula <FORM:0912976/VI/1> wherein R is an alkyl group, X is a chlorine or bromine atom and Y is a chlorine, bromine or hydrogen atom, mixed with a solvent or a particulate solid. The salts, amides and esters of the halo-substituted 2-alkyl benzoic acids may also be used in the herbicidal compositions. The examples indicate the effectiveness as herbicides of 2-methyl-trichlorobenzoic acid as its dimethylamine salt and of 2-methyl-tetrachlorobenzoic acid as its sodium salt in dilute aqueous solutions, containing 1, 10, 100 and 1000 parts per million of herbicide (calculated as the acid), by means of tests carried out on seeds of buckwheat, cucumber, rape, oats, tomato and lettuce.