| 摘要 |
4-chloro-2-methylphenoxyalkanoic acids useful as herbicides, e.g. 4-chloro-2-methylphenoxyacetic acid (MCPA), 2-(4-chloro-2-methylphenoxy)propionic acid (MCPP) and 4-(4-chloro-2-methylphenoxy)butyric acid (MCPB), are prepared by reacting the corresponding 2-methylphenoxyalkanoic acid with a water-compatible chlorinating agent in an aqueous medium in the presence of a catalyst which is a chemical compound comprising two carbon atoms bonded together with a single bond or via a methylene or methine group, one of the carbon atoms being substituted with an electropositively functioning group, the other carbon atom being the carbon atom in an electronegatively functioning group. In particular, the catalyst is compound of the general formula (I) X - CR1R2 - (CHRx)n - CR3R4 - Z, wherein R1, R2, R3 and R4 each independently is hydrogen or C1-4 alkyl; or R1 and R2 together are oxo, and R3 and R4 each independently is hydrogen or C1-4 alkyl; n is an integer 0 or 1; and Rx is hydrogen; or, when n is 1, Rx and R4 may together designate a carbon-carbon bond; X, when R1 and R2 together are oxo, is C1-6 alkoxy, hydrogen, C1-6 alkyl or NR5R6, wherein R5 and R6 each independently is hydrogen or C1-6 alkyl; or X, when R1 and R2 are not together oxo, is NR'5R'6 wherein R'5 each is C1-4 alkyl; and Z is NR7R8, wherein R7 and R8 each independently is C1-4 alkyl. The catalyst ensures a high ratio between 4-chlorinated and 6-chlorinated reaction product of at least 15, preferably at least 25, and up to 50-150 and even higher. The method has a high environmental acceptability. |
