Method for producing substituted nitro benzoic acids by oxidation of corresponding nitro toluenes, nitro benzyl alcohols, esters and/or ethers

A process for preparing nitrobenzoic acids of the general formula (I)

• where
• each X is independently nitro, cyano, sulfonyl, carboxyl, carbonylphenyl, trifluoromethyl or trichloromethyl,
• each Y is independently phenyl, fluorine, chlorine, bromine or iodine and the phenyl radical, optionally substituted by up to 3 X and/or Y radicals other than hydrogen,
• m has the value 0, 1, 2 or 3 and
• n has the value 0, 1, 2 or 3,
• and the sum of m and n has the value 1, 2, 3 or 4,
• from compounds of the general formula (II)
• where
• X, Y m, n and also the sum of n and m are each as defined above for the general formula (I) and
• R is H or an OR′ radical and
• R′ is H, straight-chain or branched C1–C10–alkyl or straight-chain or branched C1–C10-carbonylalkyl or R′ is a radical of the general formula (III)
• or a radical of the general formula (IV),
• where X, Y, n, m, and the sum of n and m are each as defined for the general formula (I),
• comprising heating a mixture of nitric acid and water at a pressure in the range of 2–20 bar at temperatures in the range of 100–220° C. and metering the compound of the general formula (II) into the heated mixture of nitric acid and water,
• with the proviso that compounds of the general formula (II) exclude 2-halo-6-nitrobenzyl alcohols, esters or ethers of the general formula (V) and
• where
• R′ is as defined for the general formula (II),
• R1, R2 and R3 are each independently H, fluorine, chlorine, bromine, nitro or carboxyl and
• Hal is fluorine, chlorine or bromine.