Preparation method of 5, 5 '-dihydroxy-observation blue

Abstract

The invention discloses a preparation method of 5, 5 '-dihydroxy-observation blue, and relates to the technical field of compound preparation. According to the preparation method of the 5, 5 '-dihydroxy-observation blue, provided by the invention, a diazotization-hydrolysis reaction route is followed, and the dropwise adding time of nitrite, the temperature of a reaction system and the stirring rotating speed are cooperatively regulated and controlled in the diazotization step, so that diazonium salt of the observation blue can be generated at a proper speed; meanwhile, the self-coupling side reaction of the observation blue mother nucleus and the diazonium salt in the reaction process can be avoided, so that the target product with the purity of 98.64% or above and the yield of 64.28% or above can be prepared within 3 hours, the preparation process is simple and convenient, the preparation efficiency is excellent, and the subsequent industrial production of the 5, 5 '-dihydroxy-observation blue is facilitated.

Description

Technical Field

[0001] This invention relates to the field of compound preparation technology, and more specifically, to a method for preparing 5,5′-dihydroxy-blue. Background Technology

[0002] As one of the three primary colors, blue can be combined with red and yellow pigments to create a rich variety of hues, thus possessing excellent application value. As the dye industry and other sectors gradually move towards environmental protection, natural blue pigments are beginning to replace synthetic blue pigments in specific applications such as food and textiles. Among these, indigo, a natural blue pigment obtained through microbial fermentation, is mainly produced by fermentation of strains such as *E. coli*. It boasts advantages such as high yield and environmental friendliness, overcoming the shortcomings of low content and poor reproducibility of plant-derived blue dyes. However, indigo is a non-water-soluble blue pigment, and the current dyeing method in textiles is still the reduction-oxidation method, requiring the use of sodium hydrosulfite and caustic soda to prepare the dyeing solution, causing significant environmental pollution. In response, patent CN120004794A discloses a method to convert indigo into 5,5′-dihydroxy-indigo, transforming it from a vat dye into a direct dye, thereby reducing its pollution during textile applications. However, this production process requires dispersing indigo in an acidic aqueous solution for the reaction, but indigo has very poor solubility in the aqueous phase, resulting in a solid-liquid two-phase reaction with a slow reaction rate and low product purity. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides an efficient method for preparing 5,5′-dihydroxy-blue pigment, while achieving excellent product yield and purity.

[0004] The above-mentioned objective of this invention is achieved through the following technical solution: A method for preparing 5,5′-dihydroxy-blue pigment includes the following steps: S1. Disperse the indigo powder in an acidic solution to obtain a suspension. Under stirring conditions of 8-15℃ and 30-50 rpm, add nitrite solution dropwise to the suspension for 5-10 minutes. After the addition is complete, continue the reaction. After the reaction, separate the solid and liquid, and take the liquid to obtain the indigo diazonium salt. The molar ratio of nitrite to indigo powder in the nitrite solution is (2.1-2.2):1. S2. Under the condition of a catalyst, the diazonium salt of 5,5′-dihydroxy-5,5′ ...

[0005] The method for preparing 5,5′-dihydroxy-Glauber's bromide provided by this invention converts the amino group on the core of Gallbladder's bromide into a hydroxyl group via a diazotization-hydrolysis reaction route. Furthermore, Gallbladder's bromide diazonium salt exhibits excellent water solubility, thereby transforming the solid-liquid two-phase reaction into a single-phase reaction, significantly improving reaction efficiency, product purity, and yield. However, the inventors of this application surprisingly discovered in experiments that during the diazotization reaction, it is essential to coordinate and control the dropping time (which allows for adjustment of the dropping rate), stirring speed, and temperature to achieve a simultaneous increase in reaction efficiency, product yield, and purity in this step. Moreover, as a key step in this invention, improving the diazotization step enhances the overall reaction efficiency.

[0006] Specifically, controlling the reaction system temperature to 8-15℃ can regulate the Brownian motion rate of the *Gynostemma pentaphyllum* powder in the suspension. Higher temperatures result in faster powder movement, making it easier for the powder to contact nitrite and react to form diazonium salts. Furthermore, the presence of an electron-withdrawing ketone carbonyl group in the *Gynostemma pentaphyllum* core enhances the conjugation between the core and the diazonium structure, improving the stability of the diazonium salt and thus increasing reaction efficiency and product yield. However, excessively high temperatures can lead to the decomposition of the formed diazonium salt and self-coupling reactions, conversely reducing the yield of the target product and resulting in a higher proportion of byproducts. Therefore, under the condition of temperature control, this application also needs to control the reaction in step S1 to be carried out under stirring conditions and control the stirring speed to 30-50 rpm. It is also necessary to further control the addition time of the raw material nitrite. The inventors found that when the stirring speed is 30-50 rpm, the molar ratio of nitrite to lanthanum powder in the nitrite solution is (2.1-2.2):1, and the dropping time is 5-10 min, the appropriate dropping speed can match the movement speed of the lanthanum powder, so that the two raw materials, lanthanum and nitrite, can generate diazonium salt at an appropriate speed, improve the reaction rate and product yield, and ensure that most of the products generated by the reaction are diazonium salts, avoiding the coupling of diazonium salt and lanthanum, thus also improving the purity of the product. Too low a stirring speed or dropping rate of nitrite can easily lead to side reactions (self-coupling of the blue and diazonium salts), reducing product yield and reaction efficiency. Conversely, too high a stirring speed or dropping rate of nitrite (too short a dropping time) can cause the reaction and dispersion rates to become mismatched, resulting in localized inhomogeneity. Furthermore, excessively high stirring speeds can introduce air into the system, leading to oxidation reactions. Excessive dropping rate of nitrite can also cause nitrite to decompose directly into nitric oxide and nitrogen dioxide. Therefore, excessively high stirring speeds and dropping rates also negatively impact product yield.

[0007] It should be noted that the hydrolysis in step S2 needs to be carried out at a temperature below 90°C in the presence of a copper-based catalyst. Excessive temperature will cause the diazonium salt to decompose, and other metal-based catalysts besides the copper-based catalyst will have insufficient catalytic activity for the hydrolysis of the diazonium salt.

[0008] Preferably, the mass ratio of the blue powder to the acid solution in step S1 is (20-40):100.

[0009] By limiting the concentration of acid and the ratio of lanthanum to acid, it is possible to ensure that the system contains an excess of acid. On the one hand, this can maintain the pH of the system and ensure the stable existence of lanthanum diazonium salt. On the other hand, it can prevent the self-coupling side reaction between lanthanum and diazonium salt.

[0010] Preferably, the pH of the acid solution in step S1 is ≤2.

[0011] The pH conditions described above are conducive to maintaining the stable existence of the blue diazonium salt.

[0012] More preferably, the acid solution in step S1 includes at least one of hydrochloric acid solution, sulfuric acid solution, phosphoric acid solution, and hydrobromic acid solution, and the mass concentration of the acid solution is ≥10%.

[0013] More preferably, the mass concentration of the hydrochloric acid solution is 10-20%.

[0014] More preferably, the sulfuric acid solution has a mass concentration of 10-20%.

[0015] More preferably, the mass concentration of the phosphoric acid solution is 20-30%.

[0016] More preferably, the mass concentration of the hydrobromic acid solution is 10-20%.

[0017] Preferably, the nitrite solution in step S1 is an aqueous solution of nitrite, and the concentration of nitrite in the nitrite solution is 50-100 g / L.

[0018] Preferably, the nitrite in step S1 includes at least one of sodium nitrite and potassium nitrite.

[0019] Preferably, the particle size D50 of the blue powder in step S1 is 180-220 μm.

[0020] In a specific embodiment of the present invention, step S1 involves adjusting the average particle size of the indigo powder by ball milling. The higher the ball milling speed and the longer the time, the lower the average particle size of the indigo powder.

[0021] More preferably, the reaction time in step S1 is 0.1-1 h.

[0022] More preferably, the reaction time in step S1 is 0.5 h.

[0023] Preferably, the hydrolysis in step S2 is carried out at a temperature of 45-65°C for 0.5-1.5 hours.

[0024] In a specific embodiment of the present invention, the endpoint of the hydrolysis reaction is the change of the aqueous phase from red to blue. When the hydrolysis reaction is carried out at 45-65°C, the time to reach the endpoint is 0.5-1.5 hours.

[0025] Preferably, the copper-based catalyst in step S2 includes at least one of copper chloride, copper sulfate, copper oxide, copper sulfide, copper carbonate, and copper nitrate.

[0026] Preferably, the molar ratio of copper atoms in the copper-based catalyst in step S2 to the blue powder in step S1 is (1-1.5):100.

[0027] Excessive addition of copper-based catalyst does not significantly promote the reaction but increases costs. Therefore, in this application, the preferred molar ratio of copper atoms to blue powder in the copper-based catalyst is (1-1.5):100.

[0028] Preferably, step S2 further includes solid-liquid separation to obtain solids, washing, and drying after hydrolysis.

[0029] More preferably, the solid-liquid separation is performed by vacuum filtration. More preferably, the washing is water washing. More preferably, the drying temperature is 50-80°C.

[0030] Compared with the prior art, the present invention has the following beneficial effects: The method for preparing 5,5′-dihydroxy-viscose provided by this invention can obtain the target product with a purity of over 98.64% and a yield of over 64.28% within 3 hours. The preparation process is simple and has excellent efficiency, which is beneficial for the subsequent industrial production of 5,5′-dihydroxy-viscose. Attached Figure Description

[0031] Figure 1 The HPLC chromatogram is for 5,5′-dihydroxy-viscose blue. Figure 1 -A is the HPLC chromatogram of Example 1 of the present invention. Figure 1 -B is the HPLC chromatogram of Comparative Example 1.

[0032] Figure 2 The light absorption spectrum of 5,5′-dihydroxy-viscose blue is shown. Figure 2 -A is the light absorption spectrum of Example 1. Figure 2 -B is the light absorption spectrum of Comparative Example 1.

[0033] Figure 3 Images showing the effects of different staining lane numbers for 5,5′-dihydroxy-viscose blue. Figure 3 -A shows the staining results of steps 1-7 in Example 1. Figure 3 -B shows the staining results for lines 1-7 of Comparative Example 1. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents. The raw material information used in each embodiment and comparative example is as follows: Blue powder: provided by Nanjing Hegu Life Biotechnology Co., Ltd., was ball-milled with zirconium oxide as the ball milling medium at 50 rpm for 30 min, with a particle size D50 of 200 μm.

[0035] Example 1 A method for preparing 5,5′-dihydroxy-blue pigment includes the following steps: S1. Disperse 2.5g of *Gynostemma pentaphyllum* powder in 12.5g of hydrochloric acid aqueous solution (concentration 20wt%, pH < 2) to obtain a suspension. Under stirring conditions of 8℃ and 30rpm, add 29mL of sodium nitrite aqueous solution (concentration 50g / L) dropwise to the suspension over a period of 8min. After the addition is complete, continue the reaction at 8℃ for 20min. After the reaction, separate the solid and liquid, and take the liquid to obtain the *Gynostemma pentaphyllum* diazonium salt solution. The molar ratio of nitrite to *Gynostemma pentaphyllum* powder in the nitrite solution is 2.1:1. S2. Add 0.02 g of copper sulfate (the molar ratio of copper atoms to lanthanum powder is 1.25:100) to the lanthanum diazonium salt solution obtained in step S1, heat to 45℃ to carry out hydrolysis reaction, and after 1.5 h of reaction, the aqueous phase changes from red to blue. Stop the reaction, filter the solid, wash it with water 3 times, and dry it at 80℃ for 6 h to obtain 5,5′-dihydroxy-lanthanum.

[0036] Example 2 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, sodium nitrite aqueous solution is added to the suspension under stirring conditions of 15℃ and 50 rpm for 5 minutes; after addition, the reaction is continued at 15℃. In step S2, the molar ratio of copper atoms in the copper-based catalyst to the blue powder in step S1 is 1.5:100 (0.024g of copper sulfate is added).

[0037] Example 3 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, the amount of blue azurite added was increased from 2.5g to 5.0g, and the amount of sodium nitrite aqueous solution added was 30.4mL, with a sodium nitrite concentration of 100g / L; the nitrite aqueous solution was added dropwise over a period of 10min; and the reaction was continued for 30min at 8℃ with stirring. In step S2, the molar ratio of copper atoms in the copper-based catalyst to the blue powder in step S1 is 1:100 (0.016 g of copper sulfate is added), and the reaction time is 0.8 h (48 min).

[0038] Example 4 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, the 20wt% hydrochloric acid aqueous solution was replaced with an equal volume of 10wt% hydrochloric acid aqueous solution (pH < 2), and the reaction was continued for 30 min with stirring at 8°C.

[0039] Example 5 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, the 20% hydrochloric acid aqueous solution was replaced with an equal volume of 20% sulfuric acid aqueous solution. Sodium nitrite aqueous solution was added to the suspension under stirring conditions of 12°C and 40 rpm. After the addition, the reaction was continued at 12°C. The reaction time in step S2 is 1 hour.

[0040] Example 6 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, the 20% hydrochloric acid aqueous solution was replaced with an equal volume of 10% hydrobromic acid aqueous solution. Sodium nitrite aqueous solution was added to the suspension under stirring conditions of 10°C and 35 rpm. After the addition, the mixture was stirred at 10°C and the reaction continued for 60 min. In step S2, the temperature is raised to 50°C to carry out the hydrolysis reaction, and the reaction time is 1 hour.

[0041] Example 7 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S2, copper sulfate is replaced with an equal mass of copper chloride, and the temperature is raised to 65°C to carry out a hydrolysis reaction for 0.5 hours.

[0042] Example 8 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S2, the temperature is raised to 75°C to carry out the hydrolysis reaction.

[0043] Example 9 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S2, the molar ratio of copper atoms in the copper-based catalyst to the blue powder in step S1 is 0.5:100 (0.008g of copper sulfate is added).

[0044] Example 10 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, the amount of blue azurite added was increased from 2.5g to 7.5g, and the amount of sodium nitrite aqueous solution added was 58mL, in which the concentration of sodium nitrite was 75g / L; the reaction was continued for 6min at 8℃.

[0045] Comparative Example 1 A conventional method for preparing 5,5′-dihydroxy-viscose blue includes the following steps: 5.0 g of safflower raw material was dispersed in 50 mL of 10% hydrochloric acid aqueous solution. 0.005 g of sodium metavanadate (the molar ratio of vanadium atoms to safflower was 0.2:100) was added. The mixture was heated under reflux at 120 °C to induce hydroxylation of safflower. After 5 h of reaction, a sample was taken. High performance liquid chromatography was used to detect the absence of safflower substrate in the reaction system, and the reaction was terminated. The solid (i.e., the reaction product) was collected by vacuum filtration. Three times the mass of the reaction product was added to deionized water and the mixture was stirred and washed three times. The water was then removed by vacuum filtration and dried in an oven at 60 °C for 8 h to obtain 5,5′-dihydroxy-safflower. The dry weight of the reaction product was 4.8 g.

[0046] Comparative Example 2 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, an aqueous solution of sodium nitrite is added at 5°C and the reaction continues at 5°C.

[0047] Comparative Example 3 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, an aqueous solution of sodium nitrite is added at 20°C and the reaction continues at 20°C.

[0048] Comparative Example 4 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, the sodium nitrite aqueous solution is added dropwise over a period of 15 minutes.

[0049] Comparative Example 5 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, the sodium nitrite aqueous solution is added dropwise over a period of 2 minutes.

[0050] Comparative Example 6 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, the stirring speed is 60 rpm.

[0051] Comparative Example 7 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, the stirring speed is 20 rpm.

[0052] Comparative Example 8 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S2, the hydrolysis reaction is carried out at 90°C.

[0053] Comparative Example 9 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S2, copper sulfate is replaced with an equal amount of ferric sulfate (the molar ratio of iron atoms to blue remains unchanged).

[0054] Comparative Example 10 A method for preparing 5,5′-dihydroxy-blue, wherein the only difference from Example 1 is: In step S1, the volume of sodium nitrite in the nitrite aqueous solution is 26.23 mL.

[0055] Performance testing Yield and purity testing: The products of the examples and comparative examples were analyzed by high-performance liquid chromatography (HPLC) according to the following methods: Chromatographic conditions: Mobile phase: gradient elution of methanol and pure water, as shown in the gradient table below: time min A (pure water)% B(methanol)% 0 70 30 9 40 60 13 70 30 18 70 30 Wavelength 600 nm, flow rate 0.6 mL / min, sample solution: DMSO, injection volume: 10 μL, column temperature 35℃, run time 20 min. Column: Galasil EF-C18M 4.6 mm id × 250 mm L (SN B06211801).

[0056] The product sample obtained in Example 1 was analyzed by high-performance liquid chromatography (HPLC), and a peak was observed at 5.014 min, with a corresponding maximum absorption wavelength of 623 nm. This confirms that the peak is a characteristic absorption peak of 5,5′-dihydroxy-glucan.

[0057] The high-performance liquid chromatography (HPLC) detection data for each embodiment and comparative example are shown in Table 1 below: Table 1. Note: " / " indicates that the desired product could not be produced.

[0058] As can be seen from Table 1 above, the preparation method of 5,5′-dihydroxy-viscose provided by the present invention can obtain the target product with a purity of over 98.64% and a yield of over 64.28% within 3 hours. The preparation process is simple and the preparation efficiency is excellent, which is beneficial to the subsequent industrial production of 5,5′-dihydroxy-viscose.

[0059] According to Examples 1 and 9, when the atomic molar ratio of catalyst to 5,5′-dihydroxy-5,5′ ...

[0060] According to Examples 1 and 10, the mass ratio of lanthanum powder to acid solution in step S1 is too high, making it difficult to ensure that the system contains an excess of acid. On the one hand, it is difficult to maintain the pH of the system and ensure the stable existence of lanthanum diazonium salt. On the other hand, it may lead to a self-coupling side reaction between lanthanum and diazonium salt.

[0061] According to Comparative Example 1, existing methods for preparing 5,5′-dihydroxy-blue pigment in the art cannot achieve the purity of over 98.64% and the yield of over 92.45% of the present invention.

[0062] According to Comparative Examples 2-3, an unsuitable temperature for the formation of diazonium salts in step S1 can lead to a decrease in yield.

[0063] According to Comparative Examples 4-7, the stirring speed and the rate of dropwise dispersion in step S1 are not suitable, which will prevent the two raw materials, styrax and nitrite, from forming diazonium salt at an appropriate rate, thereby reducing the reaction rate and the yield of the product.

[0064] According to Comparative Example 9, iron ions do not have a catalytic effect on the hydrolysis reaction of diazonium salts.

[0065] According to Comparative Example 10, the volume of nitrite was unsuitable, and a suitable diazonium salt could not be formed.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing 5,5'-dihydroxy-blue pigment, characterized in that, Includes the following steps: S1. Disperse the indigo powder in an acidic solution to obtain a suspension. Under stirring conditions of 8-15℃ and 30-50 rpm, add nitrite solution dropwise to the suspension for 5-10 minutes. After the addition is complete, continue the reaction. After the reaction, separate the solid and liquid, and take the liquid to obtain the indigo diazonium salt. The molar ratio of nitrite to indigo powder in the nitrite solution is (2.1-2.2):

1. S2. Under the condition of a catalyst, the diazonium salt of 5,5'-dihydroxy-5,5' ...

2. The method for preparing 5,5'-dihydroxy-blue as described in claim 1, characterized in that, The mass ratio of the blue powder to the acid solution in step S1 is (20-40):

100.

3. The method for preparing 5,5'-dihydroxy-blue as described in claim 1 or 2, characterized in that, The pH of the acid solution in step S1 is ≤2.

4. The method for preparing 5,5'-dihydroxy-blue as described in claim 3, characterized in that, The acid solution in step S1 includes at least one of hydrochloric acid solution, sulfuric acid solution, phosphoric acid solution, and hydrobromic acid solution, and the mass concentration of the acid solution is ≥10%.

5. The method for preparing 5,5'-dihydroxy-blue as described in claim 1, characterized in that, The nitrite solution mentioned in step S1 is an aqueous solution of nitrite, wherein the concentration of nitrite is 50-100 g / L.

6. The method for preparing 5,5'-dihydroxy-blue as described in claim 5, characterized in that, The nitrite in step S1 includes at least one of sodium nitrite and potassium nitrite.

7. The method for preparing 5,5'-dihydroxy-blue as described in claim 1, characterized in that, The particle size D50 of the blue powder mentioned in step S1 is 180-220 μm; And / or, the reaction time described in step S1 is 0.1-1 h.

8. The method for preparing 5,5'-dihydroxy-blue as described in claim 1, characterized in that, The hydrolysis in step S2 is carried out at a temperature of 45-65℃ for a time of 0.5-1.5h.

9. The method for preparing 5,5'-dihydroxy-blue as described in claim 1, characterized in that, The copper-based catalyst in step S2 includes at least one of copper chloride, copper sulfate, copper oxide, copper sulfide, copper carbonate, and copper nitrate.

10. The method for preparing 5,5'-dihydroxy-blue as described in claim 9, characterized in that, The molar ratio of copper atoms in the copper-based catalyst described in step S2 to the blue powder in step S1 is (1-1.5):100.

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