METHOD FOR SYNTHESIS OF 4-(3,4-DIAMINOPHENOXY)BENZOIC ACID ESTERS Russian patent published in 2011 - IPC C07C217/90 C07C213/06 C07C213/02 

FIELD: chemistry.

SUBSTANCE: invention relates to an improved method for synthesis of 4-(3,4-diaminophenoxy)benzoic acid esters of general formula where R = CH₃, CH(CH)₃, which are used as an intermediate product in synthesis of thermally stable polymer materials. The desired compounds are obtained through acylation of 2-nitro-5-chloroaniline with acetic anhydride, nucleophilic substitution of the chlorine atom during reaction with 4-hydroxybenzoic acid in DMSO in the presence of K₂CO₃, removal the acyl protection of the amine group as a result alkaline hydrolysis, simultaneous reduction and formation of an ester bond of 4-(3-amino-4-nitrophenoxy)benzoic acid. Acylation of 2-nitro-5-chloroaniline is carried out at temperature 90°C for 1 hour and molar ratio of 2-nitro-5-chloroaniline: acetic anhydride = 1:2. Nucleophilic substitution of the chlorine atom is carried out in 8 hours at temperature 105°C and molar ratio of N-acetyl-5-chloro-2-nitrianiline: 4-hydroxybenzoic acid = 1:1.05. Removal of the acyl protection is carried out in 0.5 hours at temperature 60°C in 20% aqueous solution of KOH. Reduction with simultaneous formation of an ester bond is carried out in aliphatic alcohol using a solution of SnCl₂·2H₂O in concentrated hydrochloric acid at boiling point of the alcohol for 1 hour and molar ratio 4-(3-amino-4-nitrophenoxy)benzoic acid: SnCl₂·2H₂O = 1:3.35.

EFFECT: fewer steps, lower process temperature, high purity and output of the end products.

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