Preparation method of 2-chloronicotinic acid

Abstract

The invention discloses a preparation process for 2-Chloronicotinic acid. In the prior art, the disadvantage is that the overdosed catalyzer is used and has a bad effect, the oxidation yields are very low; during the chlorination reaction, POCl3 can make chloro-substitutions on a plurality of positions of nicolinamide- N- oxido, which leads to that the chloro-substitution products on 2-position have low yields. In the invention, with the existence of acetyl pyruvic molybdenum, the 3-Pyridinecarbonitrile takes water as the solvent and is dripped in 20 to 30 percent of H2O2, and then is made a heat preservation to realize a full oxidation reaction; under the anhydrous reaction and with the positive pressure protection of nitrogen, the acquired nicolinamide- N- oxido is cooled between minus 10 and 10 DEG C to be diluted by the halohydrocarbon solvent, and then is dripped in the organic base, and is reacted with the chlorination reagent under the action of phenyl dichlorophosphate; the strong alkaline solution is used to make a dehydration reaction with the acquired 2-chloro-3-cyanopyridine. The invention takes the acetyl pyruvic molybdenum as the catalyzer and oxidizer, has high oxidation yields; adopts the organic base as the acid-binding agent, makes chloro-substitutions between the chlorination reagent and the nicolinamide- N- oxido, and has above 85 percent of chloro-substitution yields.

Description

Technical field [0001] The invention belongs to the field of organic chemistry, and specifically is a method for preparing 2-chloronicotinic acid. Background technique [0002] 2-Chloronicotinic acid can produce more pesticides or medicines. It is an intermediate for the synthesis of the herbicides diflufenican and nicosulfuron. It is also used for the synthesis of high-efficiency anti-inflammatory and analgesics such as niflumic acid and praprofen. Intermediate. An existing method for the synthesis of 2-chloronicotinic acid is as follows (3-cyanopyridine nitroxidation-chlorination-hydrolysis method): Japanese patent JP59-144759 uses 3-cyanopyridine (2) in an aqueous medium and tungstic acid In the presence of sodium, add 30% H dropwise within 1.5 hours at 80°C 2 O 2 , Maintain the reaction at 90°C for 3 hours to obtain nicotinic acid amide N-oxide (3) with a yield of 80%, and then mix it with POCl 3 Heated at reflux for 4 hours, hydrolyzed to obtain 2-chloro-3-cyanopyridine (4) ...

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Problems solved by technology

[0004] The disadvantages of this method are as follows: the consumption of sodium tungstate is too large, the catalytic effect is not good, the oxidation yield is 80%, and the yield is relatively low; during the chlorination reaction, POCl 3 Chlorination can be carried out at multiple positions of nicotinic acid amide N-oxide (3), resulting in a very low chlorination yield of chlorinated products at the 2-position, only 65%; due to the chlorination reaction in the presence of water under state, POCl 3 Partially reacts with water, POCl 3 Large amount of decomposition, POCl 3 The consumption is large, there is a serious problem of waste pollution, and it is difficult to meet the requirements of environmental protection; there is a flushing phenomenon (a large amount of gas release) in the chlorination reaction, and it is difficult to produce industrially

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