METHOD OF PRODUCING INTRAMOLECULAR ANHYDRIDES OF BENZENE POLYCARBOXYLIC ACIDS Russian patent published in 2011 - IPC C07D307/89 C07C51/265 

FIELD: chemistry.

SUBSTANCE: invention relates to production of ortho-substituted benzene polycarboxylic acids and their intramolecular anhydrides, particularly trimellitic acid and its anhydride, pyromellitic acid and its dianhydride. The object of invention is achieved due that the initial hydrocarbons used are tri- and tetra-alkylbenzenes which contain methyl and isopropyl, methyl and ethyl or only methyl substitutes of general formula:

a) b)

where: a) R₁, R₃-CH₃, R₂-C₃H₇ or -C₂H₅; R₁, R₂, R₃-CH₃ b) R₁, R₂, R₃-CH₃, R₄-C₃H₇ or C₂H₅; R₁, R₃-CH₃, R₂, R₄-C₃H₇ or C₂H₅; R₁, R₂, R₃, R₄-CH₃, for example isopropyl-p-xylene, ethyl-p-xylene, pseudocumene, 5-isopropylpseudocumene, 2,5-diisopropyl-p-xylene, 5-ethylpseudocumene, durene and others. Said compounds are oxidised in three steps with concentration of the dissolved oxygen in the liquid phase of oxidation products at each step in the range of 0.11-0.15 mol/l while maintaining pressure which is 16-18, 3.6-4.16 and 1.25-1.4 times higher, respectively, in reaction zones P_izb relative vapour pressure of the liquid reaction mass P_up, while raising temperature step-by-step in the range, °C: 120-135, 140-185, 190-215, discrete increase in concentration of metal ions of a Co²⁺ and Mn²⁺ catalyst and a Br- promoter. Obtained acids undergo thermal dehydration at temperature 230-240°C. The obtained anhydride solution undergoes purification through crystallisation in two steps in naturally different individual and binary solvents. The precipitated complex salt of the intramolecular anhydride is dried at temperature ≥125°C, which ensures decomposition of the complex to form a highly pure end product.

EFFECT: high efficiency of the process and high output of the end product.

3 cl, 2 dwg, 2 tbl, 11 ex