Synthesis of new AB monomers of amino modified PBO

Using 4-methoxycarbonyl-2-nitro-benzoic acid (β-MNT) and 4-amino-6-nitroresorcinolhydrochloride (ANR·HCl) as the starting materials, we synthesized the intermediates 4-(5-nitro-6-hydroxybenzoxazole-2-yl)-3-nitro-methyl benzoate (3-NMNC), 4-(5-nitro-6-hydroxybenzoxazole-2-yl)-3-nitrobenzoate (3-NMNB), 4-(5-nitro -6-hydroxy benzoxazole-2-yl)-3-aminobenzoic acid (3-NNBA) and the final product 4-(5-amino-6-hydroxy benzoxazole-2-yl)-3-aminobenzoic acid (3-AABA) through a series of reaction, including acylchloride, N-acylation, cyclization, hydrolysis and catalytichydrogenation reduction reaction. The optimal cyclization, hydrolysis and catalytichydrogenation reduction conditions were obtained. The experimental results for the cyclization reaction showed that taking diethyleneglycol dimethyl ether as solvent, the polyphosphoric acid(PPA) as dehydrant and the content of P2O5 in PPA of 84%, w(3-NMNC):w(PPA)=1:9.5, the reaction temperature of 140℃ and the reaction time of 8h, we obtained the yield of 3-NMNB of 73.16% and its purity was 99. 10% as determined by HPLC. The experimental results for the hydrolysis reaction showed that using ethanol and water as solvent, n(K2CO3):n(3-NMNB)=1.8:1 and the reaction time of 2h, we got the yield of 3-NNBA of 74.19% and the purity was 98.59% as determined by HPLC. The experimental results for the hydrogenation reduction reaction showed that using methanol as solvent, w(10%Pd/C):w(3-NNBA)=1:20, pressure of hydrogen of 1. 0 MPa, reaction temperature of 80℃, reaction time of 5h, we had the yield of 3-AABA of 65. 08% based on 3-NNBA and the purity was 99. 43% as determined by HPLC. © 2016, Chemical Industry Press. All right reserved.