Method for producing 2-halo-6-nitrobenzoic acids
View Patent ↗The present invention relates to a process for the preparation of 2-halo-6-nitrobenzoic acids by oxidation of 2-halo-6-nitro-benzyl alcohols, esters, ethers, or mixtures thereof with nitric acid and to the use of this process as a step in the preparation of 2-halo-6-nitrobenzoic acids from 2-halo-6-nitrotoluenes.
1. A process for the preparation of 2-halo-6-nitrobenzoic acids of formula (I)
wherein
R 1 , R 2 , and R 3 , independently of one another, are hydrogen, fluorine, chlorine, bromine, nitro, or carboxyl, and
Hal is fluorine, chlorine, or bromine,
comprising heating a 2-halo-6-nitrobenzyl alcohol, ester, or ether of formula (II) or a mixture thereof,
wherein
R 1 , R 2 , R 3 , and Hal have the meanings given above for formula (I), and
R 4 is hydrogen, C 1 -C 10 -alkyl, C 1 -C 10 -carbonylalkyl, or 2-halo-6-nitrobenzyl, in the presence of between 1 and 10 mol, per mole of alcohol, ester, or ether of formula (II), of nitric acid comprising between 35 and 90% by weight of water at a temperature between 50 and 200° C.
2. A process according to claim 1 wherein R 1 , R 2 , R 3 , and R 4 are hydrogen and Hal is fluorine or chlorine.
3. A process according to claim 1 wherein the 2-halo-6-nitrobenzyl compound of formula (II) is 2-chloro-6-nitrobenzyl alcohol.
4. A process according to claim 1 wherein 2 to 8 mol of nitric acid are used per mole of the 2-halo-6-nitrobenzyl alcohol, ester, or ether of formula (II).
5. A process according to claim 1 wherein some or all of the nitric acid is introduced before the 2-halo-6-nitrobenzyl alcohol, ester, or ether of formula (II) is metered in.
6. A process according to claim 1 wherein not more than 20% by weight of a solvent, based on the 2-halo-6-nitrobenzyl alcohol, ester, or ether of formula (II), is admixed with the 2-halo-6-nitrobenzyl alcohol, ester, or ether of formula (II).
7. A process for the preparation of 2-halo-6-nitrobenzoic acids of formula (I) comprising
(1) converting a 2-halo-6-nitrotoluene of formula (III)
wherein
R 1 , R 2 , and R 3 , independently of one another, are hydrogen, fluorine, chlorine, bromine, nitro, or carboxyl, and
Hal is fluorine, chlorine or bromine,
by a bromination into the corresponding 2-halo-6-nitrobenzyl bromide,
(2) carrying out a nucleophilic substitution of the 2-halo-6-nitrobenzyl bromide to form a 2-halo-6-nitrobenzyl alcohol, ester, or ether of formula (II) or a mixture thereof,
wherein
R 1 , R 2 , R 3 , and Hal have the meanings given above for formula (I), and
R 4 is hydrogen, C 1 -C 10 -alkyl, C 1 -C 10 -carbonylalkyl, or 2-halo-6-nitrobenzyl, and
(3) heating the 2-halo-6-nitrobenzyl alcohol, ester, or ether of formula (II) or a mixture thereof in the presence of between 1 and 10 mol, per mole of alcohol, ester, or ether of formula (II), of nitric acid comprising between 35 and 90% by weight of water at a temperature between 50 and 200° C.
8. A process according to claim 7 wherein for the 2-halo-6-nitrotoluene of formula (III) wherein R 1 , R 2 , and R 3 are hydrogen and Hal is fluorine or chlorine.
9. A process according to claim 7 wherein the 2-halo-6-nitrobenzyl compound of formula (II) is 2-chloro-6-nitrobenzyl alcohol.
10. A process according to claim 7 wherein the nucleophilic substitution is carried out by reaction of the 2-halo-6-nitrobenzyl bromide with an alkali metal or alkaline earth metal carbonate and/or hydrogen carbonate, an organic alkali metal or alkaline earth metal carboxylate, or an alkali metal or alkaline earth metal alkoxide or hydroxide.
11. A process according to claim 7 wherein 2 to 8 mol of nitric acid are used per mole of the 2-halo-6-nitrobenzyl alcohol, ester, or ether of formula (II).
12. A process according to claim 7 wherein some or all of the nitric acid is introduced before the 2-halo-6-nitrobenzyl alcohol, ester, or ether of formula (II) is metered in.
13. A process according to claim 7 wherein the bromination and the nucleophilic substitution steps are carried out without isolation of the respective resulting products.
14. A process according to claim 7 wherein
(i) the bromination and nucleophilic substitution steps are each carried out in the presence of a solvent, wherein the solvents for each step are optionally the same or different,
(ii) the solvent is removed such that not more than 20% by weight of solvent, based on the 2-halo-6-nitrobenzyl alcohol, ester, or ether of formula (II), are present, and
(iii) the 2-halo-6-nitrobenzyl alcohol, ester, or ether of formula (II) is oxidized.