PREPARATION METHOD FOR GRANULAR OCTENYL SUCCINIC ANHYDRIDE STARCH ESTER

Abstract

An efficient preparation method for a novel octenyl succinic anhydride granular starch ester is provided. The preparation method includes: taking an ionic liquid composite solution as a medium and generating an octenyl succinic anhydride granular starch ester through an esterification reaction between starch and octenyl succinic anhydride, wherein the ionic liquid is a 1-ethyl-3-methylimidazolium acetate ionic liquid. The preparation method for an octenyl succinic anhydride starch ester firstly applies an ionic liquid aqueous solution system to preparation of an octenyl succinic anhydride granular starch ester of different types of starch, the synthesis efficiency of the octenyl succinic anhydride starch ester is effectively improved, a granular structure of a final product is remained, and functional properties of the final product are improved.

Claims

1. A preparation method for an octenyl succinic anhydride starch ester, comprising the following steps: 1) preparing an ionic liquid composite solution under conditions of room temperature and stirring, wherein the ionic liquid composite solution is a mixed liquid of a 1-ethyl-3-methylimidazoliumacetate ionic liquid and deionized water; and 2) preparing starch emulsion from starch and the ionic liquid composite solution; then, adding a sodium hydroxide solution to adjust a pH value of the starch emulsion to 8.5; at a room temperature, adding octenyl succinic anhydride into the starch emulsion to take an esterification reaction, maintaining a pH value of a reaction system at 8.4 to 8.5, and continuously performing stirring; after the reaction is completed, adjusting a pH value of a reacted emulsion to 6.5 by a hydrochloric acid solution; then, performing centrifugation and washing, and next performing drying to obtain the octenyl succinic anhydride starch ester, wherein the obtained starch ester is granular starch ester.

2. The preparation method for an octenyl succinic anhydride starch ester according to claim 1, wherein the centrifugation and washing are alternately performed with deionized water and 70% ethanol.

3. The preparation method for an octenyl succinic anhydride starch ester according to claim 1, wherein a mass ratio of the 1-ethyl-3-methylimidazoliumacetate ionic liquid to deionized water in the ionic liquid composite solution is 2:8 to 8:2.

4. The preparation method for an octenyl succinic anhydride starch ester according to claim 1, wherein a mass ratio of the 1-ethyl-3-methylimidazoliumacetate ionic liquid to deionized water in the ionic liquid composite solution is 2:8, 5:5 or 8:2.

5. The preparation method for an octenyl succinic anhydride starch ester according to claim 1, wherein a mass ratio of the 1-ethyl-3-methylimidazoliumacetate ionic liquid to deionized water in the ionic liquid composite solution is 2:8.

6. The preparation method for an octenyl succinic anhydride starch ester according to claim 1, wherein in the step 1), a temperature for preparing the ionic liquid composite solution is 23° C., and a stirring speed is 300 rpm.

7. The preparation method for an octenyl succinic anhydride starch ester according to claim 1, wherein in the step 2), preparing starch emulsion from starch with the prepared ionic liquid composite solution; then, adding a sodium hydroxide solution to adjust a pH value of the starch emulsion to 8.5; at a room temperature, adding octenyl succinic anhydride into the starch emulsion to take an esterification reaction, maintaining a pH value of a reaction system at 8.4 to 8.5, and continuously performing stirring; after the reaction is completed, adjusting a pH value of a reacted emulsion to 6.5 by a hydrochloric acid solution; and then, performing centrifugation and washing alternately with deionized water and 70% ethanol, and next performing drying to obtain octenyl succinic anhydride granular starch ester.

8. The preparation method for an octenyl succinic anhydride starch ester according to claim 6, wherein in the step 2), preparing starch emulsion with a concentration of 15 wt % from starch with the prepared ionic liquid composite solution; then, adding a sodium hydroxide solution with a concentration of 3% to adjust a pH value of the starch emulsion to 8.5; firstly weighing octenyl succinic anhydride of 3% on a dry starch weight basis, diluting the octenyl succinic anhydride for 3 to 6 times with isopropanol, and at a temperature of 20 to 40° C., dropwise adding the diluted octenyl succinic anhydride into the starch emulsion within 2 hours to take an esterification reaction; performing magnetic stirring during the esterification reaction at a rotating speed of 200 rpm; controlling the whole reaction time to be 3 to 5 hours; after the reaction is completed, adjusting a pH value of a reacted emulsion to 6.5 by a hydrochloric acid solution with a concentration of 3%; performing centrifugation and washing alternately with deionized water and 70% ethanol for three times at centrifugation force of 4500 g for centrifugation time of 10 minutes; and performing drying in mode of being placed in a baking oven of 30° C. for 12 hours to obtain an octenyl succinic anhydride granular starch ester.

9. The preparation method for an octenyl succinic anhydride starch ester according to claim 8, wherein the starch is corn starch, potato starch, mung bean starch, sweet potato starch and rice starch.

10. The preparation method for an octenyl succinic anhydride starch ester according to claim 1, wherein in the step 2), preparing starch emulsion with a concentration of 15 wt % from starch with the prepared ionic liquid composite solution; then, adding a sodium hydroxide solution with a concentration of 3% to adjust a pH value of the starch emulsion to 8.5; firstly weighing octenyl succinic anhydride of 3% on a dry starch weight basis, diluting the octenyl succinic anhydride for 3 to 6 times with isopropanol, and at a temperature of 20 to 40° C., dropwise adding the diluted octenyl succinic anhydride into the starch emulsion within 2 hours to take an esterification reaction; performing magnetic stirring during the esterification reaction at a rotating speed of 200 rpm; controlling the whole reaction time to be 3 to 5 hours; after the reaction is completed, adjusting a pH value of a reacted emulsion to 6.5 by a hydrochloric acid solution with a concentration of 3%; performing centrifugation and washing alternately with deionized water and 70% ethanol for three times at centrifugation force of 4500 g for centrifugation time of 10 minutes; and performing drying in mode of being placed in a baking oven of 30° C. for 12 hours to obtain the octenyl succinic anhydride granular starch ester.

11. The preparation method for an octenyl succinic anhydride starch ester according to claim 5, wherein in the step 2), preparing starch emulsion with a concentration of 15 wt % from starch with the prepared ionic liquid composite solution; then, adding a sodium hydroxide solution with a concentration of 3% to adjust a pH value of the starch emulsion to 8.5; firstly weighing octenyl succinic anhydride of 3% on a dry starch weight basis, diluting the octenyl succinic anhydride for 3 to 6 times with isopropanol, and at a temperature of 20 to 40° C., dropwise adding the diluted octenyl succinic anhydride into the starch emulsion within 2 hours to take an esterification reaction; performing magnetic stirring during the esterification reaction at a rotating speed of 200 rpm; controlling the whole reaction time to be 3 to 5 hours; after the reaction is completed, adjusting a pH value of a reacted emulsion to 6.5 by a hydrochloric acid solution with a concentration of 3%; performing centrifugation and washing alternately with deionized water and 70% ethanol for three times at centrifugation force of 4500 g for centrifugation time of 10 minutes; and performing drying in mode of being placed in a baking oven of 30° C. for 12 hours to obtain the octenyl succinic anhydride granular starch ester.

12. An octenyl succinic anhydride granular starch ester prepared from the preparation method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 shows an electron scanning microscope granular microstructure of an octenyl succinic anhydride starch ester according to Embodiment 8.

[0018] FIG. 2 shows an electron scanning microscope microstructure of a starch ester according to Comparative example 1.

[0019] FIG. 3 shows an electron scanning microscope microstructure of a starch ester according to Comparative example 2.

[0020] FIG. 4 shows an electron scanning microscope microstructure of a starch ester according to Comparative example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] Illustrative implementations of the disclosure will be further described in detail hereafter for further illustrating the present invention. Although exemplary implementations of the disclosure are shown in the specification, it should be understood that the disclosure may be realized in various forms and should not be limited to the implementations set forth herein. Oppositely, these implementations are provided so that this disclosure will be more thoroughly understood, and the scope of the disclosure will be completely told to those skilled in the art, so as to provide those skilled in the art with a more complete, accurate and thorough understanding of the inventive concepts and technical solutions of the present invention.

Embodiment 1

[0022] 1) Ionic liquid aqueous solution systems with different mass ratios were prepared at a room temperature (20 to 25° C.) for modifying octenyl succinic anhydride of a granular starch ester. [0023] 2) An octenyl succinic anhydride granular starch ester was prepared by adopting a wet process and taking an esterification reaction between starch from different plants and the octenyl succinic anhydride in the ionic liquid aqueous solution system.

Embodiment 2

[0024] Corn starch or potato starch was respectively used as raw material examples to prepare an octenyl succinic anhydride granular starch ester specifically according to the following steps:

1) Preparation of an ionic liquid composite solution: a certain mass of deionized water was added into a certain amount of 1-ethyl-3-methylimidazolium acetate ionic liquid to be prepared into a mixed solution of 2:8 (w/w), and magnetic stirring (300 rpm) was performed at a room temperature for 3 min to obtain the ionic liquid composite solution.
2) Starch emulsion was prepared from corn starch or potato starch with the prepared ionic liquid composite solution. Then, a sodium hydroxide solution was added to adjust a pH value of the starch emulsion to 8.5, at a certain temperature, octenyl succinic anhydride was added into the starch emulsion to take an esterification reaction, a pH value of a reaction system was maintained at 8.4 to 8.5, and stirring was continuously performed. After the reaction was completed, a pH value of a reacted emulsion was adjusted to 6.5 by a hydrochloric acid solution. Then, centrifugation and washing were alternately performed with deionized water and 70% ethanol, and next drying was performed to obtain an octenyl succinic anhydride granular starch ester.

Embodiment 3

[0025] Corn starch or potato starch was respectively used as raw material examples to prepare an octenyl succinic anhydride granular starch ester specifically according to the following steps:

1) Preparation of an ionic liquid composite solution: a certain mass of deionized water was added into a certain amount of 1-ethyl-3-methylimidazolium acetate ionic liquid to be prepared into a mixed solution of 5:5 (w/w), and magnetic stirring (300 rpm) was performed at a room temperature for 3 min to obtain an ionic liquid aqueous solution, i.e. the ionic liquid composite solution.
2) Starch emulsion was prepared from corn starch or potato starch with the prepared ionic liquid composite solution. Then, a sodium hydroxide solution was added to adjust a pH value of the starch emulsion to 8.5, at a certain temperature, octenyl succinic anhydride was added into the starch emulsion to take an esterification reaction, a pH value of a reaction system was maintained at 8.4 to 8.5, and stirring was continuously performed. After the reaction was completed, a pH value of a reacted emulsion was adjusted to 6.5 by a hydrochloric acid solution. Then, centrifugation and washing were alternately performed with deionized water and 70% ethanol, and next drying was performed to obtain an octenyl succinic anhydride granular starch ester.

Embodiment 4

[0026] Corn starch or potato starch was respectively used as raw material examples to prepare an octenyl succinic anhydride granular starch ester specifically according to the following steps:

1) Preparation of an ionic liquid composite solution: a certain mass of deionized water was added into a certain amount of 1-ethyl-3-methylimidazolium acetate ionic liquid to be prepared into a mixed solution of 8:2 (w/w), and magnetic stirring (300 rpm) was performed at a room temperature for 3 min to obtain the ionic liquid composite solution.
2) Starch emulsion was prepared from corn starch and potato starch with the prepared ionic liquid composite solution. Then, a sodium hydroxide solution was added to adjust a pH value of the starch emulsion to 8.5, at a certain temperature, octenyl succinic anhydride was added into the starch emulsion to take an esterification reaction, a pH value of a reaction system was maintained at 8.4 to 8.5, and stirring was continuously performed. After the reaction was completed, a pH value of a reacted emulsion was adjusted to 6.5 by a hydrochloric acid solution. Then, centrifugation and washing were alternately performed with deionized water and 70% ethanol, and next drying was performed to obtain an octenyl succinic anhydride granular starch ester.

Embodiment 5

[0027] Corn starch or potato starch was respectively used as raw material examples to prepare an octenyl succinic anhydride granular starch ester specifically according to the following steps:

1) Preparation of an ionic liquid composite solution: a certain mass of deionized water was added into a certain amount of 1-ethyl-3-methylimidazolium acetate ionic liquid to be prepared into a mixed solution of 2:8 (w/w), and magnetic stirring (300 rpm) was performed at 23° C. for 3 min to obtain the ionic liquid composite solution.
2) Synthesis of octenyl succinic anhydride granular starch esters: 15 wt % starch emulsion was respectively prepared from corn starch and potato starch with the prepared ionic liquid composite solution. Then, a 3% NaOH solution was added to adjust a pH value of the starch emulsion to 8.5, and octenyl succinic anhydride of 3% on a dry starch weight basis was weighed, was diluted for 5 times with isopropanol, and was dropwise added into the starch emulsion within 2 hours. A pH value of the whole reaction system was maintained at 8.4 to 8.5 under the magnetic stirring at 35° C. A rotating speed of the magnetic stirring was 200 rpm, and the reaction was continuously performed for 4 h. Then, a pH value of the reacted starch emulsion was adjusted to 6.5 by a 3% HCl solution. The obtained starch emulsion was firstly subjected to centrifugation and washing once with 70% ethanol, and then subjected to centrifugation and washing once with deionized water, and the operation was repeated for 3 times at centrifugation force of 4500 g for centrifugation time of 10 min to obtain a starch ester sample. The starch ester sample was placed in a baking oven of 30° C. to be dried for 12 h, then, grinding was performed, sieving was performed by a 100-mesh sieve screen, and an octenyl succinic anhydride corn starch ester A1 and an octenyl succinic anhydride potato starch ester A2 were obtained.

Embodiment 6

[0028] Corn starch or potato starch was respectively used as raw material examples to prepare an octenyl succinic anhydride granular starch ester specifically according to the following steps:

1) Preparation of an ionic liquid composite solution: a certain mass of deionized water was added into a certain amount of 1-ethyl-3-methylimidazoliumacetate ionic liquid to be prepared into a mixed solution of 5:5 (w/w), and magnetic stirring (300 rpm) was performed at 23° C. for 3 min to obtain the ionic liquid composite solution.
2) Synthesis of octenyl succinic anhydride starch esters: 15 wt % starch emulsion was prepared from corn starch or potato starch with the prepared ionic liquid composite solution. Then, a 3% NaOH solution was added to adjust a pH value of the starch emulsion to 8.5, and octenyl succinic anhydride of 3% on a dry starch weight basis was weighed, was diluted for 6 times with isopropanol, and was dropwise added into the starch emulsion within 2 hours. A pH value of the whole reaction system was maintained at 8.4 to 8.5 under the magnetic stirring at 20° C. A rotating speed of the magnetic stirring was 200 rpm, and the reaction was continuously performed for 5 h. Then, a pH value of the reacted starch emulsion was adjusted to 6.5 by a 3% HCl solution. The obtained starch emulsion was firstly subjected to centrifugation and washing once with 70% ethanol, and then subjected to centrifugation and washing once with deionized water, and the operation was repeated for 3 times at centrifugation force of 4500 g for centrifugation time of 10 min to obtain a starch ester sample. The starch ester sample was placed in a baking oven of 30° C. to be dried for 12 h, then, grinding was performed, sieving was performed by a 100-mesh sieve screen, and an octenyl succinic anhydride corn starch ester B1 and an octenyl succinic anhydride potato starch ester B2 were obtained.

Embodiment 7

[0029] Corn starch or potato starch was respectively used as raw material examples to prepare an octenyl succinic anhydride granular starch ester specifically according to the following steps:

1) Preparation of an ionic liquid composite solution: a certain mass of deionized water was added into a certain amount of 1-ethyl-3-methylimidazoliumacetate ionic liquid to be prepared into a mixed solution of 8:2 (w/w), and magnetic stirring (300 rpm) was performed at 23° C. for 3 min to obtain the ionic liquid composite solution.
2) Synthesis of octenyl succinic anhydride starch esters: 15 wt % starch emulsion was prepared from corn starch or potato starch with the prepared ionic liquid composite solution. Then, a 3% NaOH solution was added to adjust a pH value of the starch emulsion to 8.5, and octenyl succinic anhydride of 3% on a dry starch weight basis was weighed, was diluted for 3 times with isopropanol, and was dropwise added into the starch emulsion within 2 hours. A pH value of the whole reaction system was maintained at 8.4 to 8.5 under the magnetic stirring at 40° C. A rotating speed of the magnetic stirring was 200 rpm, and the reaction was continuously performed for 3 h. Then, a pH value of the reacted starch emulsion was adjusted to 6.5 by a 3% HCl solution. The obtained starch emulsion was firstly subjected to centrifugation and washing once with 70% ethanol, and then subjected to centrifugation and washing once with deionized water, and the operation was repeated for 3 times at centrifugation force of 4500 g for centrifugation time of 10 min to obtain a starch ester sample. The starch ester sample was placed in a baking oven of 30° C. to be dried for 12 h, then, grinding was performed, sieving was performed by a 100-mesh sieve screen, and an octenyl succinic anhydride corn starch ester C1 and an octenyl succinic anhydride potato starch ester C2 were obtained.

Experimental Example 1

[0030] The octenyl succinic anhydride corn starch esters A1-C1 and octenyl succinic anhydride potato starch esters A2-C2 according to Embodiments 5-7 were compared to a traditional octenyl succinic anhydride corn/potato starch ester subjected to modification treatment in a water phase medium in two aspects of substitution degree and emulsification capability (emulsification activity and emulsification stability). At the same time, the octenyl succinic anhydride corn starch esters A1-C1 and octenyl succinic anhydride potato starch esters A2-C2 according to Embodiments 5-7 were compared to the traditional octenyl succinic anhydride corn/potato starch ester subjected to modification treatment in the water phase medium in an aspect of synthesis efficiency. Except for the reaction system, other steps of the traditional preparation methods were enabled to be identical to the steps of the preparation method of Embodiment 5. The comparison results were as shown in Table 1:

TABLE-US-00001 TABLE 1 Comparison of octenyl succinic anhydride starch esters prepared from different reaction media in aspects of substitution degree, reaction efficiency and emulsification capability Reaction Emulsification Substitution efficiency Emulsification stability Embodiment degree (%) activity (min) Octenyl succinic 0.0153 ± 0.0001b 65.7 ± 0.0b 1.23 ± 0.00c 338.17 ± 7.16c anhydride corn starch ester prepared in water phase Octenyl succinic 0.0207 ± 0.0001a 89.1 ± 0.6a 1.37 ± 0.01d 582.55 ± 3.64d anhydride corn starch ester A1 Octenyl succinic 0.0157 ± 0.0004b 67.4 ± 1.4b 1.23 ± 0.01c  325.23 ± 14.37c anhydride corn starch ester B1 Octenyl succinic 0.0095 ± 0.0003c 40.9 ± 1.1c 0.93 ± 0.00b 209.26 ± 2.29b anhydride corn starch ester C1 Octenyl succinic 0.0122 ± 0.0001b 52.2 ± 0.4b 0.93 ± 0.01d 297.34 ± 1.94d anhydride potato starch ester prepared in water phase Octenyl succinic 0.0137 ± 0.0003a 59.0 ± 1.3a 1.16 ± 0.01e 383.19 ± 9.79e anhydride potato starch ester A2 Octenyl succinic 0.0113 ± 0.0002c 48.6 ± 0.8c 0.88 ± 0.01c 250.72 ± 3.39c anhydride potato starch ester B2 Octenyl succinic 0.0088 ± 0.0000d 38.0 ± 0.2d 0.46 ± 0.02b 194.20 ± 3.62b anhydride potato starch ester C2 Note: each value is mean ± standard deviation. There was no statistical significance for differences of the values with same letters in the same column (p < 0.05).

[0031] From Table 1, it could be known that the substitution degrees of the octenyl succinic anhydride granular starch esters A1 and A2 prepared in the 1-ethyl-3-methylimidazoliumacetate ionic liquid aqueous solution were higher than that of the conventional octenyl succinic anhydride starch ester prepared in the water phase, the improvement effects of the reaction efficiency and substitution degree were obvious, and the emulsification activity and the emulsification stability were also greatly improved. It showed that by using a novel system of an “ionic liquid aqueous solution” as a reaction medium, an obvious promotion effect was achieved on the subsequent octenyl succinic anhydride modification. Each index of the octenyl succinic anhydride corn starch ester A1 was obviously superior to that of the octenyl succinic anhydride potato starch ester A2, and it showed that the corner starch achieved a better effect when being applied to the technical solution of the present invention.

Embodiment 8

[0032] Mung bean starch, sweet potato starch or rice starch was respectively used as raw material examples to prepare an octenyl succinic anhydride granular starch ester specifically according to the following steps:

1) Preparation of an ionic liquid composite solution: a certain mass of deionized water was added into a certain amount of 1-ethyl-3-methylimidazoliumacetate ionic liquid to be prepared into a mixed solution of 2:8 (w/w), and magnetic stirring (300 rpm) was performed at 23° C. for 3 min to obtain the ionic liquid composite solution.
2) Synthesis of octenyl succinic anhydride granular starch esters: 15 wt % starch emulsion was respectively prepared from mung bean starch, sweet potato starch or rice starch with the prepared ionic liquid composite solution. Then, a 3% NaOH solution was added to adjust a pH value of the starch emulsion to 8.5, and octenyl succinic anhydride of 3% on a dry starch weight basis was weighed, was diluted for 5 times with isopropanol, and was dropwise added into the starch emulsion within 2 hours. A pH value of the whole reaction system was maintained at 8.4 to 8.5 under the magnetic stirring at 35° C. A rotating speed of the magnetic stirring was 200 rpm, and the reaction was continuously performed for 4 h. Then, a pH value of the reacted starch emulsion was adjusted to 6.5 by a 3% HCl solution. The obtained starch emulsion was firstly subjected to centrifugation and washing once with 70% ethanol, and then subjected to centrifugation and washing once with deionized water, and the operation was repeated for 3 times at centrifugation force of 4500 g for centrifugation time of 10 min to obtain a starch ester sample. The starch ester sample was placed in a baking oven of 30° C. to be dried for 12 h, then, grinding was performed, sieving was performed by a 100-mesh sieve screen, and an octenyl succinic anhydride mung bean starch ester A3, an octenyl succinic anhydride sweet potato starch ester A4 and an octenyl succinic anhydride and rice starch ester A5 were obtained.

[0033] Through detection, each index of the A3, A4 and A5 was similar to that of the A1 and A2, but was a little worse than that of the A1 and A2.

Comparative Example 1

[0034] Potato starch was used as a raw material example to prepare an octenyl succinic anhydride granular starch ester specifically according to the following steps:

1) Preparation of “pure ionic liquid system”: a 1-ethyl-3-methylimidazolium acetate ionic liquid was magnetically stirred for 1 h at 90° C. to obtain the pure ionic liquid system.
2) Synthesis of starch ester: 10 wt % starch emulsion was prepared from potato starch with the pure ionic liquid system in step 1), and other operations were the same as those in Embodiment 8.

[0035] An electron scanning microscope microstructure of the obtained starch ester was as shown in FIG. 2.

Comparative Example 2

[0036] Potato starch was used as a raw material example to prepare an octenyl succinic anhydride granular starch ester specifically according to the following steps:

1) Preparation of an ionic liquid composite solution: a 1-butyl-3-methylimidazolium chloride ionic liquid and water were mixed and magnetically stirred for 2 h at 100° C.
2) Synthesis of starch ester: 10 wt % starch emulsion was prepared from corn starch with the ionic liquid composite liquid prepared in step 1), and other operations were the same as those in Embodiment 8.

[0037] An electron scanning microscope microstructure of the obtained starch ester was as shown in FIG. 3.

Comparative Example 3

[0038] 1) Preparation of an ionic liquid composite solution: a 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid and water were mixed and magnetically stirred for 11 h at 80° C.
2) Synthesis of starch ester: 10 wt % starch emulsion was prepared from corn starch with the ionic liquid composite liquid prepared in step 1), and other operations were the same as those in Embodiment 8.

[0039] An electron scanning microscope microstructure of the starch ester was as shown in FIG. 4.

[0040] The method of the present application provides an octenyl succinic anhydride granular starch ester, the granule structure of the starch ester is remained, and the functional properties of the starch, such as swelling force, paste viscosity and gel performance are further remained. Usually, the substitution degree is difficult to improve, and the emulsification performance is low without damaging the granular structure. From Table 1 and Table 2, for the modified starch by the method of the present application, the substitution degree of the starch ester was further improved under the condition of remaining the granule structure, and the better emulsification performance was achieved when the granule state was maintained.

[0041] The preparation method of the embodiments of the present invention was performed at a room temperature of 20 to 25° C. without adding any catalyst, the reaction conditions were mild, the cost was low, the process was simple, and the industrial application was easy.

[0042] The contents mentioned above are only exemplary implementations of the present invention, but do not limit the protection scope of the present invention, and anyone skilled in the art may easily think of mortifications or alternations within the technical scope disclosed by the present invention, and all of these mortifications or alternations should be contained within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be defined by the protection scope of claims appended hereto.