4-(5-amino-6-hydroxybenzoxazol-2-yl) ammonium benzoate and preparation method and use thereof

Abstract

Disclosed in the present invention are 4-(5-amino-6-hydroxybenzoxazol-2-yl)ammonium benzoate shown in formula (I) and the preparation method and use thereof. The preparation method comprises: fully reacting 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid shown in formula (II) or 4-(5-amino-6-hydroxybenzoxazol-2-yl)carboxamide benzoate, as a raw material, with ammonia in an aqueous solvent, and directly heating the obtained reaction liquid to remove excess ammonia, so as to obtain 4-(5-amino-6-hydroxybenzoxazol-2-yl)ammonium benzoate. The mass of the 4-(5-amino-6-hydroxybenzoxazol-2-yl)ammonium benzoate (ABAA) prepared in the present invention can reach a polymer grade (where the purity is above 99.5%, the content of metal ions is below 200 ppm, and containing no DMF polymerization inhibition impurities), and the 4-(5-amino-6-hydroxybenzoxazol-2-yl)ammonium benzoate can be used as an AB type monomer for preparing PBO and modified PBO fibers, the resulting PBO having an intrinsic viscosity ηof up to 38/dl/g, and the method has such features as ABAA being highly soluble in PPA, a fast polymerization speed, a short time of 2-4 h, a low temperature of 150° C., a high molecular weight of the polymer, fibers of excellent tensile property, being easy to industrialize, etc.

Claims

1. Ammonium 4-(5-amino-6-hydroxybenzoxazole-2-yl)benzoate, which is represented by the formula (I): ##STR00007##

2. A method of preparing ammonium 4-(5-amino-6-hydroxybenzoxazol-2-yl) benzoate as claimed in claim 1, includes the following step: 1) using 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid of formula (II) or 4-(5-amino-6-hydroxybenzoxazol-2-yl) benzoic acid carboxy-amino inner salt of formula (III) as a raw material, reacting the raw material with ammonia in water, after the reaction is completed, removing excess ammonia from the reaction solution by heating and keeping water content in the reaction solution constant during the process of removing ammonia, then cooling the reaction solution, subjecting it to filtration, washing and drying the solids to obtain ammonium 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoate (ABAA); ##STR00008##

3. The method as claimed in claim 2, wherein the method also include a refining step 2) as follows: 2) dissolving ammonium 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoate with ammonia water to obtain an ABAA solution, heating the solution to remove excess ammonia, keeping the content of water in the system constant during the process of ammonia removal, then cooling the reaction solution, subjecting it to filtration, washing and drying the solids to obtain refined ammonium 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoate.

4. The method as claimed in claim 2, wherein, in step 1), the molar ratio of ammonia to 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid or 4-(5-amino-6-hydroxybenzoxazol-2-yl) benzoic acid carboxy-amino inner salt is between 8:1 and 30:1, the water is 16˜70 times the weight of 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid or 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid carboxy-amino inner salt.

5. The method as claimed in claim 3, wherein, in step 2), the molar ratio of ammonia to ammonium 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoate is between 8:1 and 30:1, the water is 16˜70 times the weight of ammonium 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoate.

6. The method as claimed in any one of claims 2 to 5, wherein said step 1) also includes a step of impurity removal as follows: adding activated carbon into the reaction solution to absorb the impurities, then subjecting the reaction system to filtration to remove waste carbon, and then directly heating the filtrate to remove excess ammonia.

7. The method as claimed in claim 3 or 5, wherein said step 2) also includes a step of impurity removal as follows: adding activated carbon into the ABAA solution to absorb impurities, then subjecting the mixture to filtration to remove waste carbon, and directly heating the filtrate to remove excess ammonia.

8. The method as claimed in any one of claims 2 to 5, wherein said step 1) also includes an antioxidation step as follows: adding ammonium sulfite to the reaction solution as an antioxidant, and then directly heating the mixture to remove excess ammonia.

9. The method as claimed in claim 6, wherein said step 1) also includes an antioxidation step as follows: adding ammonium sulfite to the filtrate obtained in the step of impurity removal as an antioxidant, and then directly heating the mixture to remove excess ammonia.

10. The method as claimed in claim 3 or 5, wherein said refining step 2) also includes an antioxidation step as follows: adding ammonium sulfite to the ABAA solution as an antioxidant, and then directly heating the mixture to remove excess ammonia.

11. The method as claimed in claim 7, wherein said refining step 2) also includes an antioxidation step as follows: adding ammonium sulfite to the filtrate obtained in the step of impurity removal as an antioxidant, and then directly heating the mixture to remove excess ammonia.

12. The method as claimed in claim 2, wherein in step 1), the reaction of the raw material with ammonia is carried out at a temperature between 40° C. and 80° C. with stirring until dissolved; and removing excess ammonia by heating is carried out at a temperature not higher than 80° C. until the pH of the reaction system reaches 7.0 to 7.5.

13. The method as claimed in claim 3, wherein in step 2), dissolving ammonium 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoate with ammonia water is carried out at a temperature ranging from 40° C. to 80° C. with stirring; and removing excess ammonia by heating is carried out at a temperature not higher than 80° C. until the pH of the reaction system reaches 7.0 to 7.5.

14. The method as claimed in claim 2, wherein the raw material 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid of formula (II) is prepared by subjecting methyl 4-(5-nitro-6-hydroxybenzoxazol-2-yl)benzoate of formula (IV) to hydrolysis of ester group and then reduction of nitro group (Scheme A), or by subjecting methyl 4-(5-nitro-6-hydroxybenzoxazol-2-yl)benzoate of formula (IV) to reduction of nitro group and then hydrolysis of ester group (Scheme B); in which, the reduction of nitro group uses hydrazine hydrate as a reductant and Fe.sup.2+/C or Fe.sup.3+/C as a catalyst, the catalyst Fe.sup.2+/C is composed of activated carbon and a water-soluble ferrous salt, and the catalyst Fe.sup.3+/C is composed of activated carbon and a water-soluble ferric salt; ##STR00009## said Scheme A is carried out as follows: add methyl 4-(5-nitro-6-hydroxybenzoxazole-2-yl)benzoate of formula (IV), an alcohol-water solvent and KOH, carry out hydrolysis of ester group under alkaline condition to obtain 4-(5-nitro-6-hydroxybenzoxazol-2-yl)benzoic acid of formula (V); then without any separation add Fe.sup.2+/C or Fe.sup.3+/C and hydrazine hydrate to the reaction system to carry out reduction of nitro group, subject the reaction solution to aftertreatment to obtain 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid of formula (II); and said Scheme B is carried out as follows: add methyl 4-(5-nitro-6-hydroxybenzoxazole-2-yl)benzoate of formula (IV), an alcohol solvent, Fe.sup.2+/C or Fe.sup.3+/C and hydrazine hydrate, carry out reduction of nitro group to obtain methyl 4-(5-amino-6- hydroxybenzoxazole-2-yl)benzoate of formula (VI), then without any separation add NaOH and water to carry out hydrolysis of ester group, subject the reaction solution to aftertreatment to obtain 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid of formula (II).

15. The method as claimed in claim 14, wherein Scheme A is specifically carried out as follows: add methyl 4-(5-nitro-6-hydroxybenzoxazole-2-yl)benzoate of formula (IV) (MNB), alcohol, water and KOH to a reactor, heat the mixture to reflux temperature with stirring and react for 0.5 h to 2.5 h; add the catalyst Fe.sup.2+/C or Fe.sup.3+/C and hydrazine hydrate to the reaction mixture, then add some alcohol, heat the obtained mixture to reflux temperature and react for 1.25 h to 4.5 h, after the reaction is complete, subject the resulting reaction mixture to filtration while hot to remove waste carbon, the filtrate is added with hydrochloric acid to precipitate solids and filtered, the solids are washed with water and vacuum dried to obtain 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid; in which, the weight ratio of water to MNB is between 1.9:1 and 3.8:1, the weight ratio of alcohol to MNB is between 13:1 and 26:1, the molar ratio of KOH to MNB is between 2.50:1 and 2.82:1, the molar ratio of hydrazine hydrate to MNB is between 4:1 and 4.5:1, the weight ratio of the water-soluble ferrous or ferric salt to MNB is between 0.08:1 and 0.12:1, and the weight ratio of activated carbon to MNB is between 0.17:1 and 0.21:1.

16. The method as claimed in claim 14, wherein Scheme B is specifically carried out as follows: add methyl 4-(5-nitro-6-hydroxybenzoxazole-2-yl)benzoate of formula (IV) (MNB), the catalyst Fe.sup.2+/C or Fe.sup.3+/C, hydrazine hydrate and an alcohol to a reactor, heat the mixture to reflux temperature with stirring and react for 2 h to 4 h; add NaOH and water to the reaction mixture, continue to react at reflux temperature for 1 h to 3 h, after the reaction is complete, the resulting reaction mixture is filtered while hot to remove waste carbon, the filtrate is added with hydrochloric acid to precipitate yellow solids and filtered, the solids are washed with water and vacuum dried to obtain 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid; in which, the alcohol is 11.2˜20.5 times the weight of MNB, the molar ratio of hydrazine hydrate to MNB is between 2.47:1 and 3.35:1, the weight ratio of the water-soluble ferric or ferrous salt to MNB is between 0.12:1 and 0.15:1, the weight ratio of activated carbon to MNB is between 0.18:1 and 0.21:1, the molar ratio of NaOH to MNB is between 3.09:1 to 4.19:1, and the water is 0.2˜0.8 times the weight of MNB.

17. A method of preparing PBO of formula (VII) or modified PBO of formula (VIII), the method comprising: obtaining ammonium 4-(5-amino-6-hydroxybenzoxazole-2-yl)benzoate (ABAA) as claimed in claim 1; and using ABAA as a monomer in preparing PBO of formula (IV) by homo-polycondensation or modified PBO of formula (VIII) by co-polycondensation. ##STR00010##

18. The method of claim 17, wherein the method comprises: using polyphosphoric acid as a solvent and phosphorus pentoxide as a dehydrating agent, subjecting ammonium 4-(5-amino-6-hydroxybenzoxazole-2-yl)benzoate to homo-polycondensation to obtain a liquid crystalline solution of PBO or subjecting ammonium 4-(5-amino-6-hydroxybenzoxazole-2-yl)benzoate and 4-amino-3-hydroxybenzoic acid to co-polycondensation to obtain a liquid crystalline solution of modified PBO, and then preparing PBO of formula (IV) or modified PBO of formula (V) fibers by dry-jet wet spinning of the liquid crystalline solution.

19. The method of claim 18, wherein preparing PBO fibers includes the following steps: 1) adding ammonium 4-(5-amino-6-hydroxybenzoxazole-2-yl)benzoate (ABAA) into polyphosphoric acid with a concentration of P.sub.2O.sub.5 more than 84 wt. % until the mass concentration of ABAA is between 12% and 15%, heating the mixture gradually to a temperature between 100° C. and 160° C. and reacting for 2 h to 5 h to obtain a liquid crystal spinning solution of PBO; and 2) directly and continuously subjecting the liquid crystal spinning solution of PBO to wire drawing and then aftertreatment to obtain PBO fibers of formula (IV).

20. The method of claim 18, wherein preparing modified PBO fibers includes the following steps: a) adding monomers composed of 4-(5-amino-6-hydroxybenzoxazole-2-yl)benzoate (ABAA) and 4-amino-3-hydroxybenzoic acid with a mass ratio of ABAA to 4-amino-3-hydroxybenzoic acid between 60% to 40% and 80% to 20% into polyphosphoric acid with a concentration of P.sub.2O.sub.5 more than 84 wt. % until the total mass concentration of the monomers is between 12% and 15%, heating the mixture gradually to a temperature between 80° C. and 170° C. and reacting for 2 h to 5 h to obtain a liquid crystal spinning solution of modified PBO; and b) directly and continuously subjecting the liquid crystal spinning solution of modified PBO to wire drawing and then aftertreatment to obtain modified PBO fibers of formula (V).

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is the infrared spectrum of the product ABA.

(2) FIG. 2 is the infrared spectrum of the product ABAA.

(3) FIG. 3 is the infrared spectrum of the refined ABAA.

(4) FIG. 4 is the infrared spectrum of the refined ABAS recrystallized with DMF-methanol.

(5) FIG. 5 is the infrared spectrum of PBO fibers.

(6) FIGS. 6a) and 6b) are respectively the infrared spectrum of PBO fibers modified by R (poly-2,6-benzoxale, PBO.sup.o).

DETAILED DISCLOSURE

(7) The technical solutions of present invention are further introduced by the examples as follows:

EXAMPLE 1

Using ABA as the Raw Material to Prepare ABAA

(8) (1) 13.5 g (0.05 mol) of crude ABA (with purity of 98.82%, K.sup.+:5489 ppm, Na.sup.+:155 ppm, Fe:75 ppm, IR: FIG. 1) and 326 mL of deionized water were added into a reaction vessel. The mixture was stirred and heated to 60° C., and 50 g of 25% ammonia water (0.73 mol) was dropwise added within 5 min. After ABA dissolved, 1.5 g of activated carbon was added and the reaction mixture was heated to 80° C. After adsorbing impurities for 10 min, the reaction mixture was filtered at 65˜70° C., then, 4.5 g of ammonium sulfite was added into the filtrate, and ammonia was removed from the filtrate at 60˜80° C. for 1 h in vacuum until the pH of filtrate was 7.0. The reaction solution was cooled to room temperature and filtered again, the filter cake was mixed with 150 mL of deionized water, the mixture was filtered and the resulting filter cake was vacuum dried at 60° C. to get 10.8 g (0.0376 mol) of ABAA, which was a yellow crystal with purity of 99.41%, total content of metal ions of 176 ppm (K.sup.+: 161 ppm, Na.sup.+: 15 ppm, Fe: 0 ppm), and a yield of 75.26%. Its IR spectrum was showed in FIG. 2. IR (KBr, cm.sup.−1) 3328.8(m), 1627.1(m), 1592.3(s), 1561.0(s), 1538.8(s), 1379.9(s), 1334.0(s), 1311.4(s), 1210.2(s), 1132.2(s), 1072.4(s), 882.5 (s), 843.8(s), 790.2(s), 715.1(s), 436.8(s). Theoretical calculation of C.sub.14H.sub.13N.sub.3O.sub.4 (ABAA) element analysis: C, 58.53, H, 4.56, N, 14.63, O, 22.28. Measured: C, 58.55, H, 4.43, N, 13.44. So the product was determined qualitatively as ammonium 4-(5-amino-6-hydroxybenzoxazole-2-yl)benzoate (ABAA).

(9) (2) 13.5 g of ABA (prepared with NBA hydrogenation method of the literature, with purity of 94.21%, K.sup.+:264 ppm, Na.sup.+:347 ppm, Fe:132 ppm, IR similar to FIG. 1) was added, amounts of other materials used and operating conditions were the same as step (1). After vacuum dried at 60° C., 7.6 g (0.0265 mol) of ABAA, which was a khaki crystal with purity of 97.51%, total content of metal ions of 132 ppm (K.sup.+: 16 ppm, Na.sup.+: 67 ppm, Fe: 49 ppm), and a yield of 52.96%, was obtained. ABAS-IR is the same as FIG. 2.

EXAMPLE 2

Using Crude ABA as the Raw Material to Prepare ABAA

(10) 20.0 g (0.074 mol) of crude ABA (with purity of 98.22%, content of inorganic salts of 10%, K.sup.+: 362 ppm, Na.sup.+: 50773 ppm, Fe: 239 ppm, IR similar to FIG. 1, prepared by NBA-sodium dithionite reduction in Patent CN 200610155719.8) and 400 mL of deionized water were added into a reaction vessel. The mixture was stirred and heated to 75° C., and 120 g of 25% ammonia water (1.76 mol) was added dropwise within 5 min. After the crude ABA dissolved, 2.0 g of activated carbon was added and the mixture was heated to 80° C. After adsorbing purities for 10 min, the mixture was filtered at 65˜70° C., then, 5.0 g of ammonium sulfite was added into the filtrate, ammonia was removed at 55˜70° C. for 1 h and 20 min in vacuum until the pH of filtrate was 7.0, then the filtrate was cooled to room temperature and filtered again. The filter cake was mixed with 200 mL of deionized water, the mixture was filtered and the resulting filter cake was vacuum dried at 60° C. to obtain 15.8 g (0.055 mol) of ABAA, which was a yellow crystal with purity of 99.27% (K.sup.+: 34 ppm, Na.sup.+: 3692 ppm, Fe: 22 ppm), and a yield of 74.32%. ABAS-IR spectrum was the same as FIG. 2, IR (KBr, cm.sup.−1) 3328.2(s), 1627.5(s), 1559.9(s), 1538.1(s), 1471.2(s), 1379.4(s), 1334.0(s), 1311.1(s), 1209.5(s), 1132.5(s), 1072.8(s), 883.9(s), 843.8 (s), 789.8(s),714.6(s).

EXAMPLE 3

Using ABAA as the Raw Material to Prepare ABAA

(11) 10.0 g of ABAA prepared by example 2 (with purity of 99.27%, K.sup.+: 34 ppm, Na.sup.+: 3692 ppm, Fe: 22 ppm) and 500 mL of deionized water were added into a reaction vessel. The mixture was stirred and heated to 60° C., and 70 g of 25% ammonia water (1.03 mol) was dropwise added within 5 min. After ABAA dissolved, 1.0 g of activated carbon was added and the mixture was heated to 80° C. After adsorbing impurities for 10 min, the mixture was filtered at 65˜70° C., then, 2.3 g of ammonium sulfite was added into the filtrate. Ammonia was removed at 60˜80° C. for 1 h in vacuum until the pH of filtrate was 7.5, then the filtrate was cooled to room temperature and filtered again. The filter cake was mixed with 150 mL of deionized water, the mixture was filtered and the resulting filter cake was vacuum dried at 60° C. to obtain 8.1 g of refined ABAA, which was a yellow crystal with purity of 99.53%, total content of metal ions of 176 ppm (K 0.0 ppm, Na 176 ppm, Fe 0.0 ppm), and a yield of 81.0%. The quality of refined ABAA reached the polymerization grade. ABAA-IR spectrum was showed in FIG. 3. IR (KBr, cm.sup.−1) 3329.2(s), 1627.3(s), 1592.3(s), 1561.0(s), 1538.7(s), 1379.9(s), 1334.1(s), 1311.5 (s), 1210.2(s), 1132.3(s), 1072.6(s), 883.3(s), 843.8(s), 790.1(s), 715.1(s), 437.1(s).

EXAMPLES 4˜11

(12) ABAA and polymerization grade ABAA were prepared under different conditions such as different weight ratio of H.sub.2O to the raw material, molecular ratio of NH.sub.3 to the raw material, weight ratio of ammonium sulfite to the raw material and weight ratio of activated carbon to the raw material, other operating conditions were the same as those in example 1, 2, 3. The results were showed in Table 1:

(13) TABLE-US-00001 TABLE 1 mass of Raw Purity content of total Yield material H.sub.2O/ NH.sub.3/ (NH.sub.4).sub.2SO.sub.3/ of Metal ion metal of (RM .sup.a) RM RM RM C/RM ABAA in ABAA/ppm ions/ ABAA/ Ref. Exp. (g) (wr) .sup.b (mr) .sup.b (wr) (wr) (%) K.sup.+ Na.sup.+ Fe ppm % Exp. 4 ABA 24.4 66.5 0.15 0.10 99.35 475 98 13 586 73.38 1(1) 40.5 5 ABA 21.4 28.8 0 0.10 99.15 511 159 18 688 65.50 1(1) 13.5 6 ABA 75.7 8.8 0.17 0.11 99.45 167 48 5 220 71.01 1(1) 13.5 7 ABA 69.4 14.7 0.17 0.07 99.52 239 101 0 340 71.78 1(1) 13.5 8 crude 13.3 17.3 0.14 0.10 98.73 125 366 2 493 71.49 2 ABA 20 9 ABAA 55.3 27.8 0.23 0.10 99.42 198 0 0 198 82.00 3 10 10 ABAS 31.5 7.9 0.20 0 98.68 247 1017 15 1279 74.70 1(1) 20 ABAA 16.1 11.9 0.15 0 99.00 32 386 0 418 83.50 3 15.8 11 ABA* 21.3 59.5 0.50 0.13 98.21 37 49 26 112 54.93 1(2) 4.0 .sup.a RM: Raw material .sup.b wr: weight ratio, mr: molecular ratio

(14) The raw material ABA was the same as that of example 1(1), and had purity of 98.82%, content of K.sup.+ of 5489 ppm, Na.sup.+ of 155 ppm, Fe of 75 ppm.

(15) The raw material crude ABA was prepared according to Patent CN 200610155719.8, and had purity of 98.02%, content of K.sup.+:662 ppm, Na.sup.+: 13773 ppm, Fe: 39 ppm.

(16) The raw material ABAS was prepared according to Patent 2 CN 200610155718.3, and had purity of 98.57%, content of K.sup.+: 573 ppm, Na.sup.+: 28390 ppm, Fe:109 ppm.

(17) The raw material ABA* was the same as that of example 1(2), and had purity of 94.21%, content of K.sup.+:264 ppm, Na.sup.+:347 ppm, Fe: 132 ppm.

COMPARATIVE EXAMPLE 1

DMF-CH3OH Recrystallization of ABAS

(18) 5.0 g of ABAS (with purity of 98.57%, K.sup.+:573 ppm, Na.sup.+:28390 ppm, Fe:109 ppm. prepared according to Patent 2 CN 200610155718.3) was added into a mixed solvent of 150 mL of DMF and 50 mL of CH.sub.3OH. The mixture was stirred and heated to 90° C. for 30 min until ABAS was dissolved. 0.5 g of activated carbon was added to adsorb impurities at 95° C. After 15 min, the reaction mixture was filtered, and 300 mL of methanol was added into the filtrate to precipitate crude product. The crude product was sequentially mixed with 50 mL and 100 mL of methanol and filtered, and then the resulting filter cake was vacuum dried at 60° C. to obtain 2.6 g of refined product, which was a light-gray crystal with purity of 98.04%, and a yield of 52%. The IR spectrum was showed in FIG. 4, IR (KBr, cm.sup.−1): 3270.2(m), 1673.5(s), 1617.8(s), 1581.0(s), 1466.9(s), 1411.0(s), 1381.6(s), 1295.7(s), 1178.7(s), 1129.1(s), 1054.0(s), 970.0(s), 860.3(s), 781.8(s), 710.2(s), 505.3(s). Theoretical calculation of C.sub.14H.sub.10N.sub.2O.sub.4 (ABA) element analysis: C, 62.22; H, 3.73; N, 10.37; O, 23.68. Measured: C, 61.86; H, 3.49; N, 10.85. So the product was determined qualitatively as 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid (ABA) and the metal content was showed in Table 2.

COMPARATIVE EXAMPLE 2˜3

DMF-CH3OH Recrystallization of ABA

COMPARATIVE EXAMPLE 2

(19) 5.0 g of ABA (the same as example 1(1), with purity of 98.82%, K.sup.+: 5489 ppm, Na.sup.+: 155 ppm, Fe: 75 ppm) was added into a mixed solvent of 150 mL of DMF and 50 mL of CH.sub.3OH. The mixture was stirred and heated to 90° C. for 30 min until ABA was dissolved. 0.5 g of activated carbon was added to adsorb impurities at 95° C. After 15 min, the reaction mixture was filtered, and 300 mL of methanol was added into the filtrate to precipitate crude product. The crude product was sequentially mixed with 50 mL and 100 mL of methanol and filtered, and then the resulting filter cake was vacuum dried at 60° C. to obtain 3.95 g of refined product ABA, which was a deep beige crystal, with purity of 98.01%, and a yield of 79%. ABA-IR spectrum of the product was the same as FIG. 4, IR (KBr, cm.sup.−1) 3271.1(m), 1682.7(s),1617.9(s), 1581.2(s), 1467.4(s), 1410.8(s), 1381.0(s), 1293.4(s), 1178.6(s), 1128.6(s), 1054.4(s), 971.9(s), 860.6(s), 781.9(s), 710.4(s), 505.2(s). So the product was determined qualitatively as ABA and the metal content was showed in Table 2.

COMPARATIVE EXAMPLE 3

(20) 5.0 g of Crude ABA (with purity of 94.21%, K: 264 ppm, Na: 347 ppm, Fe: 132 ppm. prepared by hydrolyzing MNB to obtain NBA according to scheme (3) in Patent 1(CN 200610155719.8), and then catalytic hydrogenating NBA in DMF according to scheme (1)) was added, and the feed ratios and operating conditions were the same as those of Comparative Example 1. After vacuum dried at 60° C., 3.0 g of refined product was obtained, which was a gray crystals, with purity of 97.42% and a refining yield of 60.0%. IR spectrum was the same as FIG. 4. The product was identified as ABA by IR. Its metal content was showed in Table 2.

(21) TABLE-US-00002 TABLE 2 Qualitative & Compare Crude DMF/ CH.sub.3OH/ Dissolved Activated CH.sub.3OH total HPLC Ref. Appearance Exp. product mL mL temp./° C. Carbon/g precip./mL metal/ppm purity/% yield/% of product 1 ABAS 150 50 95 0.5 300 1172 98.04 52.0 ABA light-gray 2 ABA 150 50 95 0.5 300 296 98.01 79.0 ABA deep-beige 3 ABA* 170 50 98 0.5 400 102 97.42 60.0 ABA Gray

EXAMPLE 12

Preparation of ABA (4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid)

(22) according to Scheme A: One-pot method by hydrolysis and then reduction

(23) 12.0 g (0.038 mol) of methyl 4-(5-nitro-6-hydroxybenzoxazol-2-yl)benzoate (MNB), 306 g of methanol, 45 g of water and 5.36 g (0.096 mol) of KOH were added into a reaction vessel. The mixture was stirred and heated to 75° C. to react under reflux condition, as the mixture turned into red floc from a yellow suspension, continued to react for 1 h. 1.2 g of ferrous chloride, 2.4 g of activated carbon and 10.2 g (0.163 mol) of 80% hydrazine hydrate were added into the reaction mixture, the resulting mixture was heated to 75° C. and reacted under reflux condition for 2 h, and the reaction mixture turned orange yellow. Waste carbon was removed by filtering while hot. 19 g of concentrated hydrochloric acid was added into the filtrate to precipitate yellow solids. After filtration, the solids were washed, and vacuum dried to obtain 9.52 g of ABA product, with purity of 96.2%, total content of metal ions (K.sup.+, Fe.sup.2+) of 3252 ppm and a yield of 92.25%. Its IR spectrum was showed in FIG. 1. The IR (KBr, cm.sup.−1) absorption peak was analyzed as follows:

(24) 3422.1 (s, hydroxy), 3336.3, 3270.7 (m, N—H of amino), 3099.6, 2601.5 (m, associating state of aromatic carboxylic acid with O—H), 1697.6 (s, C═O of aromatic carboxylic acid), 1616.6 (s, C═N of oxazole), 1580.2, 1557.9 (s, C═C of benzene ring), 1490.7, 1468.7 (s, oxazole hetero cycle), 1382.1 (s, phenolic hydroxy), 1327.3 (s, C—O of aromatic carboxylic acid), 1302.7 (s, C—N of primary aromatic amine), 1278.6 (s, C—O of oxazole), 1220.9, 1114.6 (s, C—O of hydroxy), 1411.0, 1053.8 (s, C—C skeleton of benzene ring), 860.5 (s, C—H of benzene ring para-disubstituent), 709.4 (s, benzoxazole). .sup.1H-NMR (DMSO): 6.94, 7.04, 8.10, 8.18. The product was determined qualitatively as 4-(5-amino-6-hydroxybenzoxazol-2-yl)benzoic acid (ABA).

EXAMPLES 13˜19

Preparation of ABA (Scheme A)

(25) ABA was prepared by the same operation of example 12, with 12 g of MNB, 10.2 g of 80% hydrazine hydrate, and different dosages of methanol, water, KOH and hydrochloric acid. The results were showed in Table 3.

(26) TABLE-US-00003 TABLE 3 MNB was hydrolyzed, and then reduced with hydrazine hydrate to prepare ABA in one-pot ABA Methanol KOH/MNB Hydrolysis Reduction Totalmetal Example dosage/g Water/g mol. ratio time/h time/h Purity/% ion/ppm Yield/% 13 170 30 2.82 1.5 3 96.4 3869 90.89 14 158 23 2.50 0.5 3 98.2 2963 93.14 15 159 45 2.56 1 1.25 98.0 3268 88.57 16 159 45 2.56 1 2 97.7 3106 90.99 17 170 30 2.82 2.5 3 96.4 3793 96.61 18 192 28 2.52 2 3.5 97.1 2840 84.50 19 192 23 2.52 0.75 4.5 97.0 3041 92.05

EXAMPLE 20

Preparation of ABA (Scheme B: Reduction and then Hydrolysis in One-Pot)

(27) 10 g (0.032 mol) of methyl 4-(5-nitro-6-hydroxybenzoxazole-2-yl)benzoate (MNB), 1.98 g of activated carbon, 1.4 g of ferric chloride, 5.9 g (0.094 mol) of 80% hydrazine hydrate and 202 g of methanol were added into a reaction vessel. The mixture was stirred and heated to refluxing temperature, after reacting for 3.5 h, the yellow reaction solution turned into brown. Then 8 g of water and 4.95 g (0.12 mol) of NaOH were added into the reduction solution, after reacting for 3 h, the materials were dissolved to obtain an orange yellow solution, then waste carbon was removed by filtering while hot, and the concentrated hydrochloric acid was added into the filtrate until the pH was 6˜7 to precipitate yellow solids. After filtration, the yellow solids were washed and vacuum dried to obtain 6.35 g of ABA, with purity of 95.34%, total content of metal ions (Na.sup.+, Fe.sup.2+) of 4415 ppm and a yield of 73.84%. Its IR spectrum was the same as FIG. 1. The product was identified as ABA by IR.

EXAMPLES 21˜25

Preparation of ABA (Scheme B)

(28) With 10 g of MNB, different dosage of hydrazine hydrate and NaOH, and different reduction and hydrolysis time, ABA was prepared by the same operation of example 20. The conditions and results were showed in Table 4.

(29) TABLE-US-00004 TABLE 4 MNB was reduced with hydrazine hydrate, then hydrolyzed to prepare ABA in one-pot N.sub.2H.sub.4H.sub.2O/ ABA Methanol MNB Reduction NaOH/MNB Hydrolysis Totalmetal Example dosage/g mol. ratio time/h mol. ratio Water/g time/h Purity/% ion/ppm Yield/% 21 112 2.47 3 3.23 2 1 95.14 3487 78.49 22 140 3.07 3 4.02 7 2 96.08 4672 93.05 23 149 2.95 2 3.09 7 1 95.69 3926 85.58 24 139 3.35 3 3.98 3 1 96.40 4893 84.53 25 130 3.20 3 4.19 8 1.5 95.50 5277 81.16

APPLICATION EXAMPLE 1

Preparation of PBO Fibers by ABAA Homo-Polycondensation

(30) 3.2 g of P.sub.2O.sub.5 and 24.0 g of PPA with a P.sub.2O.sub.5 concentration of 83% were sequentially added into a self-made glass polymerization reactor. The mixture was heated to 90° C. and stirred for 1 h until it became transparent, and then a PPA solution with a P.sub.2O.sub.5 concentration of 85% was obtained. The PPA solution was slightly cooled by introducing nitrogen to the reactor, then 4.11 g (0.0143 mol) of ABAA prepared by example 3 was added into the reactor in nitrogen atmosphere and made the concentration of ABAA be 13.1% (wt). The mixture was heated to 110° C. and stirred for 1.5 h until the monomer was dissolved. Then, the mixture was heated gradually to 125° C. within 45 min and fluoresced. The prepolymerization reaction proceeded at 125° C. for 40 min, then the reaction mixture was gradually heated to 150° C. within 1 h, after silklike substances appeared, the mixture was heated to 160° C. and reacted for 20 min, then the polymerization reaction ended and a liquid crystal spinning solution of PBO was obtained. Fibers (about 8˜15 m) were formed via directly and continuously drawing from the liquid crystal spinning solution of PBO at 120° C., repeatedly washed with boiling water until neutral, dried at 110° C. to obtain golden as-spun PBO fibers. The fibers had tensile strength of 3.9 GPa, modulus of 152 GPa, an intrinsic viscosity of 31.2 dl/g and a total yield of 96.1%. IR spectrum of the PBO fibers was showed by FIG. 5.

APPLICATION EXAMPLE 2

(31) 21.3 g of a PPA solution with a P.sub.2O.sub.5 concentration of 83.8% and 3.76 g (0.0131 mol) of ABAA prepared by example 9 were successively added into a self-made glass polymerization reactor to obtain a mixture with a. monomer concentration of 15.0 wt. %. Under the protection of nitrogen, the mixture was heated to 120° C. within 15 min and stirred for 25 min, then the monomer was dissolved and the mixture fluoresced. After stirring at 120° C. for 1 h, the reaction system was quickly heated to 160° C., then polymerized for 45 min, when liquid crystal silklike substances appeared, the polymerization reaction ended and a liquid crystal spinning solution of PBO was obtained. Fibers (about 6˜8 m) was formed via directly and continuously drawing from the PBO liquid crystal spinning solution at 120° C., repeatedly washed with boiling water until neutral, dried at 110° C. to obtain golden as-spun PBO fibers. The fibers had tensile strength of 4.05 gpa, modulus of 249 gpa and intrinsic viscosity of 38.1 dl/g.

APPLICATION EXAMPLES 3˜5

(32) With different concentration of monomer (ABAA), different concentration of P.sub.2O.sub.5 in PPA, different polymerization temperature and time, PBO fibers were prepared by the same operation of application example 1. The conditions and results were showed in Table 5.

(33) TABLE-US-00005 TABLE 5 ABAA P.sub.2O.sub.5 intrinsic Application from ABAA In Polym. Polym Appearance viscosity/ strength/ modulus/ examp Example concn./% PPA/% temp./° C. time/h of fibers* Spinnability dl/g GPa GPa 1 3 13.1 85.0 100~160 2.75 golden Very good 31.2 3.91 151 2 9 15.0 83.8 100~160 2.25 Purple Very good 38.1 4.05 249 golden 3 1(1) 13.5 82.5 100~150 6.0 golden Very good 23.9 3.68 163 4 10  12.0 83.8  90~140 4.0 golden Very good 24.6 3.80 150 5 Compare 12.0 83.0  90~140 7.0 golden good 18.3 3.18 155 example 2 *aftertreatment: The drew fibers were diluted with water, washed with boiling water and vacuum dried to prepare PBO-AS fibers of 10~150 μm diameter range.

APPLICATION COMPARE EXAMPLE 1

Preparation of PBO by ABA Homo-Polycondensation

(34) (Literature: Polymer Preprints, 1990, 31(2), 681-682)

(35) 1.163 g (4.31 mol) of ABA, 0.766 g of P.sub.2O.sub.5 and 18.188 g of 115% PPA were sequentially added into a polymerization reactor. After well stirring, oxygen was removed by introducing nitrogen under a pressure-reducing condition of 0.09 MPa at 90° C. for 3 h, then nitrogen was introduced under normal pressure for 12 h until the reaction system became transparent. The polymerization was carried out at 120° C. for 3 h, then at 150° C. for 3 h, then at 180° C. for 1 h, and finally at 190˜200° C. for 2.5 h. After polymerization, the reaction mixture was put into water to precipitate solids and then filtered. The obtained filter cake was reflux washed with water for 12 h and then with acetone for 8 h, then it was vacuum dried at 175° C. for 3 h to obtain 0.94 g of PBO resin, with an intrinsic viscosity of 12.5 dl/g and a yield of 93.3%.

APPLICATION COMPARE EXAMPLE 2

(36) Replaced ABA in Application compare example 1 with refined ABA (with purity of 97.42%, K.sup.+: 39 ppm, Na.sup.+: 56 ppm, Fe: 7 ppm) prepared according to the method in the Literature (Polymer preprints, 1990, 31(2), 681-682), other polymerization operation was the same as that of application compare example 1, and then PBO resin with an intrinsic viscosity of 9.2 dl/g was obtained, whose spinnability was poor.

APPLICATION COMPARE EXAMPLE 3

According to Previous Patent 1: CN 2006 10155719.8

(37) 1.8 g of ABA (the same as ABA used in Example 1(1), with purity of 98.82%, K.sup.+:5489 ppm, Na.sup.+:155 ppm, Fe:75 ppm), 19.48 g of PPA and 9 g of P.sub.2O.sub.5 were added into a polymerization reactor and nitrogen was introduced. The mixture was stirred and heated to 120° C., after reacting for 3 h, the reaction solution became orange, then the reaction solution was further heated to 160° C., after reacting for 3 h, the reaction solution became tenne and exhibited opalescence phenomenon; then the reaction solution was further heated to 180° C., after reacting for 2 h, the reaction solution became brownish green; finally, the reaction solution was heated to 200° C., after reacting for 3 h, the reaction solution became greenblack, and the polymerization reaction ended. The reaction mixture was cooled, put into 100 mL of water, heated to 60° C., stirred and washed twice, and dried at 105° C. for 10 h, and then 1.76 g of PBO polymer with an intrinsic viscosity of 10.31 dl/g (30° C., MSA) was obtained.

APPLICATION COMPARE EXAMPLE 4

Preparation of PBO by ABAS Homo-Polycondensation

(38) (According to Patent 2: CN 2006 10155718.3)

(39) 1.8 g of ABAS (with purity of 98.57%, K.sup.+:573 ppm, Na.sup.+:28390 ppm, Fe:109 ppm, no DMF), 19.48 g of PPA and 9 g of P.sub.2O.sub.5 were added into a polymerization reactor and nitrogen was introduced. The mixture was stirred and heated to 120° C. after reacting for 3 h, the reaction solution became orange; then the reaction solution was further heated to 160° C., after reacting for 3 h, the reaction solution became tenne and exhibited opalescence phenomenon; then the reaction solution was further heated to 180° C., after reacting for 2 h, the reaction solution became brownish green; finally, the reaction solution was further heated to 200° C., after reacting for 3 h, the reaction solution became greenblack, and the polymerization reaction ended. The reaction mixture was cooled, put into 100 mL of water, heated to 60° C., stirred and washed twice, dried at 105° C. for 10 h, and then 1.76 g of PBO polymer with an intrinsic viscosity of 13.1 dl/g (30° C., MSA) was obtained.

(40) The conditions and results of application compare examples were showed in Table 6.

(41) TABLE-US-00006 TABLE 6 Application compare Monomer Monomer P.sub.2O.sub.5 Polym. Polym Appearance [η]/ example Abbreviations concn./% in PPA/% temp./° C. time/h of PBO Spinnability dl/g 1 ABA 5.8 85.0 120~200 9.5 copper — 12.5 2 ABA* 5.8 85.0 120~200 9.5 green- Poor 9.2 brown 3 ABA 6.0 86.3 120~200 11.0 Brown Good 10.3 4 ABAS 6.0 86.3 120~200 11.0 Brown Good 13.1

APPLICATION EXAMPLE 6

ABAA applied in the preparation of modified PBO fibers which is modified with poly-2,6-benzoxazole)(PBOo)

(42) (1) Synthesis of R-PBO Fibers (the Molecular Link Ratio of PBO.sup.o: PBO=1.7:1.0)

(43) 19.66 g of PPA was added into a polymerization reactor, and then heated to 80° C. 4.75 g of P.sub.2O.sub.5 was added, and the mixture was stirred until P.sub.2O.sub.5 was dissolved. 1.5 g of 4-amino-3-hydroxybenzoic acid (HABA) and 1.5 g of ABAA prepared by example 10 were added into the reactor. Raised the temperature to 100° C. and stirred for 3 h, then raised to 130° C. and stirred for 1 h, and then the reaction system became viscous and difficult to stir. When the temperature was raised to 150° C., the reaction system became dilute and had good fluidity, continued to react for 1 h, and the polymerization reaction ended. After the wire drawing, the resulting fibers were repeatedly washed with boiling water until neutral and vacuum dried at 100° C. to obtain as-spun R-PBO fibre mainly comprising poly-2,6-benzoxazole) (PBO.sup.o), which had an intrinsic viscosity of 14.6 dl/g, a decomposition temperature of 641.6° C. and tensile strength of 2.86 GPa. Its IR spectrum was showed in FIG. 6-a. (2) Synthesis of R-PBO (Molecular Link Ratio of PBO.sup.o to PBO was 0.44:1.0) Fibers

(44) 23.68 g of PPA was added into a polymerization reactor, then heated to 80° C., then 5.95 g of P.sub.2O.sub.5 was added, the mixture was stirred until P.sub.2O.sub.5 was dissolved, then 0.89 g of 4-amino-3-hydroxybenzoic acid (HABA) and 3.55 g ABAA prepared by example 10 were added into the reactor, the mixture was stirred for 0.5 h, then heated to 120° C., after reacting for 0.5 h, the reaction mixture was further heated to 126° C., bubble and fluorescence at the bottom appeared; then the mixture was further heated to 130° C., after stirring for 1 h, liquid crystallines appeared, after reacting for another 1 h, the mixture was then heated to 140° C., after reacting for 0.5 h, bubble disappeared, then the mixture was further heated to 155° C., after reacting for 0.5 h, further heated to 170° C., and then the polymerization reaction ended. After the wire drawing, the resulting fibers were repeatedly washed with boiling water until neutral and vacuum dried at 100° C. to obtain as-spun R-PBO fibre mainly comprising PBO, which had an intrinsic viscosity of 16.1 dl/g, a decomposition temperature of 669.8° C. and tensile strength of 3.23 GPa. Its IR spectrum was showed in FIG. 6-b.