GB780713A - Improvements in or relating to herbicidal compositions containing esters and preparation thereof - Google Patents

Abstract

A pure N-chlorophenyl carbamic acid ester is prepared by (a) reacting a chloro-aniline and a haloformate in a reaction mixture containing less than 1 per cent carbonyl halide by weight of the haloformate; (b) by reacting chloroaniline with at least 10 per cent molar excess of a haloformate; or (c) by reacting a chloroaniline and a haloformate and washing the reacting product at a pH below 6.5. Method (a) reduces the amount of by-product di-(chlorophenyl) urea, and (b) and (c), which may be employed together, reduce the amount of chloraniline in the product. The haloformate is stripped of carbonyl halide by passage through a packed tower and condensing the up-flowing gases to liquefy the haloformate while the carbonyl halide passes out of the system. The chloro-, bromo-, iodo- or fluoroformates of monohydric alcohols, glycols and polyglycols (including those with up to 6 glycol units and/or 12 carbon atoms) may be used. Chloranilines specified are o-, m-, and p-chloraniline, 2,3- and 2,5-dichloraniline, 2,4,6-trichloraniline and tetra-and pentachloranilines. Organic and inorganic bases and solvents (preferably having a specific gravity substantially above or below 1) may be used. In examples: (1) isopropyl N-3-chlorophenyl carbamate is prepared by adding phosgene-free isopropyl chloroformate (5 per cent excess) and aqueous sodium hydroxide (10 per cent excess) to m-chloroaniline and water and reacting at 5 DEG to 10 DEG C.; (2) isopropyl chloroformate, previously treated to remove phosgene, is added to a mixture of m-chloraniline and aqueous sodium hydroxide either in the presence of or with the subsequent addition of perchloroethylene to form isopropyl N-3-chlorophenyl carbamate; (3) the isopropyl N-2-chlorophenyl carbamate obtained by reacting isopropyl chloroformate with 10 per cent excess of o-chloroaniline is washed with dilute hydrochloric acid; (4) isopropyl chloroformate and 10 per cent excess 2,5-dichloroaniline are reacted in the presence of benzene and aqueous sodium bicarbonate and the isopropyl N-2,5-dichlorophenyl carbamate obtained is washed with dilute hydrochloric acid; (5) isopropyl chloroformate and p-chloraniline (10 per cent excess) are reacted in the presence of aqueous sodium bicarbonate and benzene at 5 DEG to 10 DEG C. and the product, isopropyl N-4-chlorophenyl carbamate, is washed with dilute hydrochloric acid; (6) m-chloraniline and ethylene glycol bis-chloroformate are reacted in the presence of water and ethylene dichloride to give ethylene glycol bis-(N-3-chlorophenyl) carbamate; (7) isopropyl chloroformate freed from phosgene by passage down a filled column through which heated vapours of isopropyl chloroformate are passed upwardly, is added to a heated mixture of m-chloraniline in the presence of water and perchloroethylene simultaneously with aqueous sodium hydroxide and the isopropyl N-3-chlorophenyl carbamate obtained is washed with hydrochloric acid. In a similar manner there can be prepared b -chloroethyl N-3-chlorophenyl carbamate and a - chloropropyl N - 3 - chlorophenyl carbamate. The preparation of herbicidal compositions from these compounds is described (see Group VI). Specification 780,714 is referred to.ALSO:A herbicidal composition comprises a purified N-chlorophenyl carbamic acid ester and a carrier, in which said ester is prepared so as to contain less than one per cent chloroaniline by weight of the carbamate (whereby said composition is non-poisonous to human beings), and/or less than one per cent di-(chlorophenyl) urea, by weight of the carbamate (whereby said composition is suitable for use in a non-clogging liquid spray). The ester can be prepared by (a) reacting a chloroaniline and a haloformate in a reaction mixture containing less than 1 per cent carbonyl halide by weight of the haloformate, (b) by reacting chloroaniline with at least 10 per cent molar excess of a haloformate, or (c) by reacting a chloroaniline and a haloformate and washing the reaction product at a pH below 6.5. Suitable liquid carriers are xylene, toluene, gasoline, kerosene, methyl naphthalene, aliphatic alcohols, ethers, ketones and esters. Surface-active agents such as sodium alkylaryl sulphonates, sulphonated dicarboxylic acid esters, alkyl naphthalene sulphonic acids, e.g. in amount 10 to 30 per cent by weight of solvent and carbamate may be added. The use of a solvent having a density not different by more than 5 per cent from that of water is desirable. Solid compositions may be obtained by spraying the carbamate on to a highly absorbent solid such as silica. They may be further diluted with clay, talc, silica, bentonite, diatomaceous earth, chalk and wood flour and rendered wettable by adding wetting agents. An exemplified formulation comprises isopropyl N-3-chlorophenyl carbamate, xylene, isopropyl alcohol and polyoxyethylene sorbitol esters of mixed fatty and resin acids. Examples of the preparation of the carbamates are given (see Group IV (b)). Specification 780,714, [Group IV (b)], is referred to.