Synthesis Of Hydroxy Terephthalic Acid And Its Derivatives And Their Application In New Polymers

Presently,high-performance fibers as poly(p-phenyleneterephthal amide)(PPTA)and poly(p-phenylenebenzobisoxazole)(PBO)have shortages like poor compressive strength and composite bonding properties.New polymers such as poly(hydroxy-p-phenyleneterephthalamide)(H-PPTA),poly(hydroxy-p-phenylenebenzobisoxazole)(H-PBO),poly(hydroxy-p-phenylenebenzobisimidazole)(H-PBI),poly(hydroxy-p-phenylenebenzobisoxazole amide)(H-PBOA)and poly(hydroxy-p-phenylenebenzimidazolebenzoxazole amide)(H-PBIOA)were designed for the monomer synthesis research and polymerization exploration of single hydroxy-modified high-performance fibers.Firstly,a new BB-type monomer,2-hydroxyterephthalic acid(HTA),was successfully synthesized by hydrolysis of dimethyl 2-bromo terephthalate(DMBT)and carboxylation of m-hydroxybenzoic acid(m-HBA).Comparing the two methods,it found that the carboxylation method is more prefered.Based on the purification of HTA,the synthesis of hydroxy-modified H-PPTA,H-PBO,H-PBI and other new polymers were also investigated.Secondly,2-hydroxy-4-(methoxycarbonyl)benzoic acid(?-MHT)and dimethyl 2-hydroxyterephthalate(DMHT),HTA derivatives,were high selectively synthesised by mono-esterification or di-esterification of HTA,catalyzed by concentrated sulfuric acid or thionyl chloride in methanol,and yields were 69.0%and 94.2%.3-hydroxy-4-(methoxycarbonyl)benzoic acid(?-MHT)were abtained through mono-hydrolysis of DMHT selectively in NaOH solution at low-temperature,and yield was 81.0%.Methyl 2-hydroxy-4-(6-hydroxy-5-nitrobenzoxazol-2-yl)benzoate(H-MNB),a new AB-type monomer precursor,was synthesised through five steps,which included hydroxy protection of a-MHT by acetylation,chlorination,condensation with 4-amino-6-nitrobenzene-1,3-diol hydrochloride(ANR·HCl)into amide,cyclization and de-protection reactions,the total yield of product was 45.8%.And then the synthesis of 4-(5-amino-6-hydroxybenzoxazol-2-yl)-2-hydroxybenzoic acid(H-ABA),the new AB-type monomer,were explored by hydrolysis of methyl ester and reduction of nitro group.Finally,the important intermediate 5-methoxy-2,4-dinitrophenol(MDNP)and 5-methoxy-2,4-dinitroaniline(MDNA)were developed by hydrolysis and alcoholysis or aminolysis and alcoholysis of 1,5-dichloro-2,4-dinitrobenzene(DCDNB)respectively.And then 2-amino-5-methoxy-4-nitrophenol(AMNP)and 4-methoxy-5-nitrobenzene-1,2-diamine(AMNA)were synthesised by selectively mono-reduction of nitro group by treating with sodium hydrosulfite and hydrazine hydrate respectively,and the total yield was 70.3%and 19.5%.Synthesis process of 6-methoxy-5-nitrobenzazol-2-amine(AMNBX),the new AA-monomer precursor for preparation of H-PBOA and H-PBIOA,was also investigated through condensation and cyclization of AMNP and AMNA with cyanamide.All structures of products were confirmed by IR,1H-NMR,MS qualitative analysis in this paper.