Preparation method and application of natural hair dyeing component gallic acid

Abstract

The invention discloses a preparation method and application of natural hair dyeing component gallic acid, and the preparation method of gallic acid comprises the following steps: by taking vanillin shown in a formula (I) as an initial raw material, carrying out one-pot reaction with sodium bromide, sulfuric acid and hydrogen peroxide, and simultaneously carrying out bromination and oxidation reaction to obtain a compound shown in a formula (II); the preparation method comprises the following steps: reacting a compound shown as a formula (II) with sodium methoxide in a methanol solvent under the co-catalysis of cuprous bromide and methyl formate to prepare a compound shown as a formula (III), and finally carrying out demethylation reaction in a LiBr / HCl solution system to obtain gallic acid shown as a formula (IV), and the reaction formula is as follows: # imgabs0 #. The process route for synthesizing gallic acid is simple in raw material source and conventional in synthesis method, and has the advantages of mild reaction conditions, simplicity in operation, high yield and the like; compared with a traditional acid-base hydrolysis method, the amount of three wastes is greatly reduced, and the method has a good industrialization prospect.

Description

Technical Field

[0001] The invention relates to a preparation method and application of gallic acid, a natural hair dyeing ingredient. Background Art

[0002] Most of the existing hair dyes are made from chemically synthesized dye pigments, and their main raw materials are diphenylamine and diphenylphenol compounds, which are dyed with oxidants such as hydrogen peroxide. Because these hair dyes contain toxic chemicals, they are prone to allergies, causing discomfort such as skin redness, swelling, and stinging. Long-term use can even cause cancer. To solve this problem, researchers have used new and safe hair dye intermediates such as 2,5-diaminophenylethanol, and on the other hand, extracted safe and non-toxic natural plant pigments from natural plants, such as branches, leaves, flowers, grasses, and Chinese medicinal materials such as Polygonum multiflorum as hair dye ingredients.

[0003] Gallic acid, chemical name 3,4,5-trihydroxybenzoic acid, is an ideal natural plant hair dye ingredient. It is widely found in plants such as Rheum palmatum, Eucalyptus globulus, Cornus officinalis, tea, grapes, etc. It has a wide range of sources, is safe and non-toxic, and does not cause contact allergies. At present, there have been many reports on the application of gallic acid in the field of hair dyes. Its dyeing principle is mainly that gallic acid and ferrous or ferric ions are complexed to form a network structure and then coated on the surface of hair, thereby achieving the purpose of dyeing hair. In addition, gallic acid also has multiple biological activities such as anti-tumor, anti-inflammatory, anti-mutation, antioxidant, and anti-free radical. As an important organic raw material, it is widely used in medicine, food, biology, chemical industry and other fields, and the demand is increasing year by year. In view of this, the preparation method of gallic acid has received widespread attention.

[0004] At present, gallic acid is usually produced by hydrolysis of tannin-containing biomass such as gallnut or tara by acid-base method, fermentation method or enzyme method: 1) Acid-base hydrolysis method, that is, crush the tannin-containing biomass gallnut or tara, extract it with hot water, filter out the residue, and wait for the tannic acid liquid. Concentrate the liquid, then add inorganic acid or alkali to hydrolyze to obtain gallic acid and glucose; then separate, decolorize, refine, and dry to obtain gallic acid. This process does not completely hydrolyze tannins, the gallic acid yield is not high, and the product quality is unstable, especially the amount of acid or alkali used is large, the equipment is severely corroded, the production cost is high, the environmental pollution is serious, and the cost of three wastes treatment is high.

[0005] 2) The fermentation method is to use microorganisms to ferment in a tannin-containing aqueous solution. The biological enzymes produced by the microorganisms after induction catalyze the hydrolysis of tannins to produce gallic acid. In the fermentation method, the formation of biological enzymes and the hydrolysis of tannins are carried out in the same reaction vessel. The process conditions are difficult to reach the optimal state, resulting in a reaction cycle of several days, incomplete tannin hydrolysis, and a low gallic acid yield.

[0006] 3) The two processes of enzyme production and acid production are carried out in two reaction vessels respectively, which can make both of them reach the best reaction state, shorten the reaction time to a certain extent, and improve the hydrolysis rate of tannin and the yield of gallic acid. However, the tannases currently used to catalyze the synthesis of gallic acid are mostly derived from fungi, such as Aspergillus oryzae, Aspergillus niger, and Trichoderma reesei. The tannases derived from these strains still have low activity, poor thermal stability and gallic acid tolerance, which limits their application in industry.

[0007] In summary, the current preparation of gallic acid usually uses natural tannin-containing biomass such as gallnut or tala as raw materials, and the raw material sources are limited and are not suitable for large-scale production. Summary of the invention

[0008] In view of the above technical problems existing in the prior art, the object of the present invention is to provide a preparation method and application of gallic acid, a natural hair dyeing ingredient.

[0009] The technical solution adopted by the present invention is as follows: A method for preparing gallic acid, a natural hair dyeing ingredient, is characterized by comprising the following steps: 1) Using vanillin represented by formula (I) as a starting material, and reacting it with sodium bromide, sulfuric acid and hydrogen peroxide in a one-pot process to simultaneously undergo bromination and oxidation reactions to obtain 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II); 2) then, under the catalysis of cuprous bromide and methyl formate, 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II) reacts with sodium methoxide in a methanol solvent to prepare 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III); 3) Finally, 4-hydroxy-3,5-dimethoxybenzoic acid shown in formula (III) undergoes a demethylation reaction in a LiBr / HCl solution system to obtain the target product 3,4,5-trihydroxybenzoic acid, i.e., gallic acid, shown in formula (IV); the reaction equation is as follows: .

[0010] The present invention describes each step in detail, which is as follows: 1) Preparation of 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II) The vanillin represented by formula (I) is added to an acetonitrile solvent, sodium bromide and 98% concentrated sulfuric acid are added at room temperature, 30% hydrogen peroxide is slowly added dropwise under stirring, the reaction temperature is controlled at 40-60°C, and the reaction is kept warm for 10-16 hours after the addition is completed. After the reaction is completed, the reaction solution is poured into water, stirred, filtered, and dried to obtain 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II).

[0011] 2) Preparation of 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III) In an autoclave, 3-bromo-4-hydroxy-5-methoxybenzoic acid (II) obtained in step 1) and methanol solvent are added, and then sodium methoxide, cuprous bromide, and methyl formate are added, and the mixture is heated to 100-130°C with stirring, and the reaction is carried out for 2-4 hours. After the reaction is completed, the mixture is cooled to room temperature, the reaction solution is concentrated to remove methanol, and ether and 1-2 mol / L dilute hydrochloric acid are added with stirring, and the liquid is separated, the aqueous phase is extracted with ether several times, the organic phases are combined, dried over anhydrous sodium sulfate, and the 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III) is obtained by desolvation.

[0012] 3) Preparation of the target product gallic acid represented by formula (IV) In an autoclave, add 4-hydroxy-3,5-dimethoxybenzoic acid (III) obtained in step 2), then add lithium bromide and hydrochloric acid solution, heat to 100-120°C with stirring, and react for 1-2 hours. After the reaction is completed, cool to room temperature, pour the reaction solution into saturated brine, extract with ethyl acetate several times, combine the organic phases, dry, desolventize, and wash with petroleum ether to obtain the target product 3,4,5-trihydroxybenzoic acid shown in formula (IV), i.e., gallic acid.

[0013] Furthermore, in step 1), the volume of the acetonitrile solvent is 1.0-2.0 mL / mmol, preferably 1.4-1.8 mL / mmol, based on the amount of vanillin; the molar ratio of vanillin to sodium bromide and hydrogen peroxide is 1: 1.0-2.2: 2.0-4.0, preferably 1: 1.4-1.8: 2.5-3.5; the molar ratio of sodium bromide to concentrated sulfuric acid is 1: 0.5-1.0, preferably 1: 0.6-0.8.

[0014] Further, in step 2), the molar ratio of 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II) to sodium methoxide is 1:1.5-2.5, preferably 1:1.8-2.2; the molar amounts of the catalyst cuprous bromide and methyl formate are 3.0-5.0 mol% and 35.0-45.0 mol% of the molar amount of 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II), respectively, and preferably 3.6-4.4 mol% and 38.0-42.0 mol%, respectively; and the volumetric amount of the solvent methanol is 1.0-2.0 mL / mmol based on the amount of 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II).

[0015] Furthermore, in step 3), the molar ratio of 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III) to LiBr is 1:0.3-0.4, the concentration of the HCl solution is 1.5-1.8 mol / L, and the volumetric dosage of the HCl solution is 1.0-2.0 mL / mmol based on the amount of 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III).

[0016] The present invention also defines the use of the prepared gallic acid in the preparation of a black hair dye, wherein the black hair dye comprises a first dose, a second dose and a third dose. The names of the components in the first dose, the second dose and the third dose, and the mass percentage of the components are respectively listed in Table 1: Table 1 List of ingredients in black hair dye 1, 2 and 3 .

[0017] The black hair dye 1, 2 and 3 are independently prepared, and the preparation method comprises the following steps: heating phase A and phase B to about 85°C respectively; then adding phase A to phase B and stirring for 20-30 minutes; after cooling to about 45°C, adding phase C, stirring evenly, cooling to room temperature, and discharging and filling.

[0018] The method for using the black hair dye of the present invention is carried out according to the following steps: according to the length of the hair, one dose, two doses or three doses are used to soak the hair, firstly, the first dose is evenly applied to the hair with a small brush to soak the hair, the hair is left standing at room temperature for 10-20 minutes, and the remaining first dose is washed away with clean water; then, the second dose is evenly applied to the hair to soak the hair, the hair is left standing at room temperature for 25-40 minutes, and the remaining second dose is washed away with clean water; then, the third dose is evenly applied to the hair with a small brush to soak the hair, the hair is left standing at room temperature for 10-20 minutes, the hair is washed with shampoo, and then washed with clean water and blow-dried, and the hair is dyed black.

[0019] The method for using the black hair dye is as follows: take 1 dose, 2 doses, and 3 doses, each of which is 25 to 70 ml. The dosage of 1 dose, 2 doses, and 3 doses is determined according to the amount of hair. Generally, 1 dose, 2 doses, and 3 doses are used for short hair within 10 cm, each of which is 25 ml, and 70 ml is used for long hair of about 30 cm. 1 dose, 2 doses, and 3 doses are not required to be equal. First, apply 1 dose evenly on the hair with a small brush, let it stand at room temperature for 10-20 minutes, preferably for about 15 minutes, and wash away the remaining 1 dose with clean water; then apply 2 doses evenly on the hair, let it stand at room temperature for 25-40 minutes, preferably for about 30 minutes, and wash away the remaining 2 doses with clean water; then apply 3 doses evenly on the hair with a small brush, let it stand at room temperature for 10-20 minutes, preferably for about 15 minutes, and then wash it with shampoo and then rinse it with clean water and blow dry it. The hair is dyed black, and the color is natural and the hair is smooth.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The present invention provides a new method for preparing gallic acid, a natural hair dyeing ingredient, from natural vanillin. Although vanillin is a natural ingredient, it is also one of the most produced synthetic fragrances in the world and has abundant sources. This solves the problem that the traditional preparation method of gallic acid mostly uses natural tannin-containing biomass such as gallnut or tara as raw materials, which leads to limited raw material sources and is not suitable for large-scale production; at the same time, it also broadens the application range of vanillin; 2) The process route for synthesizing gallic acid of the present invention has simple raw material sources and conventional synthesis methods, and has the advantages of mild reaction conditions, simple operation, and high yield. Compared with the traditional acid-base hydrolysis method, the amount of three wastes is greatly reduced, and it has a good industrialization prospect; 3) The present invention also provides the use of gallic acid, a natural ingredient obtained by a defined method, as a dye component in a hair dye. The hair dye uses gallic acid, a natural plant ingredient, as the main hair dyeing component, does not contain chemical substances such as aniline and strong oxidants, is safe and non-toxic, has good blackening effect, good color fastness, and good washing resistance. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0022] The present invention first provides a synthesis example of gallic acid, a natural hair dyeing ingredient.

[0023] Example 1 Synthesis of natural hair dye ingredient gallic acid (1) Synthesis of 3-bromo-4-hydroxy-5-methoxybenzoic acid (II) Vanillin (I) (100 mmol) was added to 140 mL of acetonitrile, sodium bromide (140 mmol) and 98% concentrated sulfuric acid (84 mmol, 8.40 g) were added at room temperature, and 30% hydrogen peroxide (250 mmol, 28.35 g) was slowly added dropwise under stirring, and the reaction temperature was controlled at 50°C. After the addition, the reaction was kept warm for 10 hours. After the reaction was completed, the reaction solution was poured into 50 mL of water, stirred, filtered, and dried to obtain 23.48 g of white powder, namely 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II), with a yield of 95.04%.

[0024] (2) Synthesis of 4-hydroxy-3,5-dimethoxybenzoic acid (III) In an autoclave, 3-bromo-4-hydroxy-5-methoxybenzoic acid (II) (90 mmol) obtained in step (1) was added to 90 mL of methanol, and then sodium methoxide (162 mmol), cuprous bromide (3.24 mmol), and methyl formate (34.2 mmol) were added, and the mixture was heated to 120 °C with stirring for 3 h. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was concentrated to remove methanol. Ether (135 mL) and dilute hydrochloric acid (1.6 mol / L, 135 mL) were added with stirring, and the liquid was separated. The aqueous phase was extracted with ether three times (3×135 mL), and the organic phases were combined, dried over anhydrous sodium sulfate, and desolventized to obtain 16.82 g of a white solid, namely 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III), with a yield of 94.31%.

[0025] (3) Synthesis of target product gallic acid (IV) In an autoclave, 4-hydroxy-3,5-dimethoxybenzoic acid (III) (80 mmol) obtained in step (2) was added, and then lithium bromide (24 mmol) and hydrochloric acid solution (1.5 mol / L, 120 mL) were added, and the mixture was heated to 110 °C with stirring and reacted for 1 h. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into 80 mL of saturated brine and extracted with ethyl acetate three times (3×80 mL). The organic phases were combined, dried, desolventized, and washed with petroleum ether to obtain 13.39 g of a white solid, which was the target product 3,4,5-trihydroxybenzoic acid (gallic acid) represented by formula (IV), with a yield of 98.39% and a purity of 99.15%; mp: 251~252 °C. 1 HNMR (400 MHz, CD 3 OD) δ: 7.04 (s, 2H); 13 C NMR (100 MHz, CD 3 OD) δ: 110.3, 122.5,139.5, 146.3, 171.0; HRMS (ESI) calcd C 7 H 7 O 5 [M+H] + 171.0215, found 171.0208.

[0026] Example 2 Synthesis of natural hair dye ingredient gallic acid (1) Synthesis of 3-bromo-4-hydroxy-5-methoxybenzoic acid (II) Vanillin (I) (100 mmol) was added to 180 mL of acetonitrile, sodium bromide (180 mmol) and 98% concentrated sulfuric acid (144 mmol, 14.40 g) were added at room temperature, and 30% hydrogen peroxide (350 mmol, 39.69 g) was slowly added dropwise under stirring, and the reaction temperature was controlled at 40°C. After the addition, the reaction was kept warm for 14 hours. After the reaction was completed, the reaction solution was poured into 60 mL of water, stirred, filtered, and dried to obtain 24.24 g of white powder, namely 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II), with a yield of 98.12%.

[0027] (2) Synthesis of 4-hydroxy-3,5-dimethoxybenzoic acid (III) In an autoclave, 3-bromo-4-hydroxy-5-methoxybenzoic acid (II) (90 mmol) obtained in step (1) was added to 180 mL of methanol, and then sodium methoxide (198 mmol), cuprous bromide (3.96 mmol), and methyl formate (37.8 mmol) were added, and the mixture was heated to 130°C with stirring for 4 h. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was concentrated to remove methanol. Ether (180 mL) and dilute hydrochloric acid (1.6 mol / L, 180 mL) were added with stirring, and the liquid was separated. The aqueous phase was extracted with ether three times (3×180 mL), and the organic phases were combined, dried over anhydrous sodium sulfate, and desolventized to obtain 17.34 g of a white solid, namely 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III), with a yield of 97.22%.

[0028] (3) Synthesis of target product gallic acid (IV) In an autoclave, 4-hydroxy-3,5-dimethoxybenzoic acid (III) (80 mmol) obtained in step (2) was added, and then lithium bromide (32 mmol) and hydrochloric acid solution (1.8 mol / L, 80 mL) were added, and the mixture was heated to 100 °C with stirring for 2 h. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into 160 mL of saturated brine, and extracted with ethyl acetate three times (3×160 mL). The organic phases were combined, dried, desolventized, and washed with petroleum ether to obtain 13.33 g of a white solid, which was the target product 3,4,5-trihydroxybenzoic acid (gallic acid) represented by formula (IV), with a yield of 97.95% and a purity of 99.22%.

[0029] Example 3 Synthesis of natural hair dye ingredient gallic acid (1) Synthesis of 3-bromo-4-hydroxy-5-methoxybenzoic acid (II) Vanillin (I) (100 mmol) was added to 160 mL of acetonitrile, sodium bromide (160 mmol) and 98% concentrated sulfuric acid (112 mmol, 11.20 g) were added at room temperature, 30% hydrogen peroxide (300 mmol, 34.02 g) was slowly added dropwise under stirring, the reaction temperature was controlled at 60°C, and the reaction was kept warm for 16 hours after the addition was completed. After the reaction was completed, the reaction solution was poured into 55 mL of water, stirred, filtered, and dried to obtain 24.10 g of white powder, namely 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II), with a yield of 97.55%.

[0030] (2) Synthesis of 4-hydroxy-3,5-dimethoxybenzoic acid (III) In an autoclave, 3-bromo-4-hydroxy-5-methoxybenzoic acid (II) (90 mmol) obtained in step (1) was added to 150 mL of methanol, and then sodium methoxide (180 mmol), cuprous bromide (3.60 mmol), and methyl formate (36.00 mmol) were added, and the mixture was heated to 100°C with stirring for 2 h. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was concentrated to remove methanol. Ether (160 mL) and dilute hydrochloric acid (1.6 mol / L, 160 mL) were added with stirring, and the liquids were separated. The aqueous phase was extracted with ether three times (3×145 mL), and the organic phases were combined, dried over anhydrous sodium sulfate, and desolventized to obtain 17.21 g of a white solid, namely 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III), with a yield of 96.49%.

[0031] (3) Synthesis of target product gallic acid (IV) In an autoclave, 4-hydroxy-3,5-dimethoxybenzoic acid (III) (80 mmol) obtained in step (2) was added, and then lithium bromide (30 mmol) and hydrochloric acid solution (1.6 mol / L, 160 mL) were added, and the mixture was heated to 120 °C with stirring and reacted for 1.5 h. After the reaction was completed, the mixture was cooled to room temperature, poured into 100 mL of saturated brine, and extracted with ethyl acetate three times (3×120 mL). The organic phases were combined, dried, desolventized, and washed with petroleum ether to obtain 13.23 g of a white solid, which was the target product 3,4,5-trihydroxybenzoic acid (gallic acid) represented by formula (IV), with a yield of 97.21% and a purity of 99.05%.

[0032] Example 4 Synthesis of natural hair dye ingredient gallic acid (1) Synthesis of 3-bromo-4-hydroxy-5-methoxybenzoic acid (II) Vanillin (I) (100 mmol) was added to 150 mL of acetonitrile, sodium bromide (170 mmol) and 98% concentrated sulfuric acid (136 mmol, 13.60 g) were added at room temperature, 30% hydrogen peroxide (320 mmol, 36.29 g) was slowly added dropwise under stirring, the reaction temperature was controlled at 55 °C, and the reaction was kept warm for 15 hours after the addition was completed. After the reaction was completed, the reaction solution was poured into 60 mL of water, stirred, filtered, and dried to obtain 23.81 g of white powder, namely 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II), with a yield of 96.38%.

[0033] (2) Synthesis of 4-hydroxy-3,5-dimethoxybenzoic acid (III) In an autoclave, 3-bromo-4-hydroxy-5-methoxybenzoic acid (II) (90 mmol) obtained in step (1) was added to 120 mL of methanol, and then sodium methoxide (190 mmol), cuprous bromide (3.50 mmol), and methyl formate (36.00 mmol) were added, and the mixture was heated to 110°C with stirring and reacted for 3.5 h. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was concentrated to remove methanol. Ether (150 mL) and dilute hydrochloric acid (1.6 mol / L, 150 mL) were added with stirring, and the liquids were separated. The aqueous phase was extracted with ether three times (3×160 mL), and the organic phases were combined, dried over anhydrous sodium sulfate, and desolventized to obtain 17.10 g of a white solid, namely 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III), with a yield of 95.87%.

[0034] (3) Synthesis of target product gallic acid (IV) In an autoclave, 4-hydroxy-3,5-dimethoxybenzoic acid (III) (80 mmol) obtained in step (2) was added, and then lithium bromide (28 mmol) and hydrochloric acid solution (1.5 mol / L, 100 mL) were added, and the mixture was heated to 105 °C with stirring and reacted for 2 h. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into 120 mL of saturated brine and extracted with ethyl acetate three times (3×100 mL). The organic phases were combined, dried, desolventized, and washed with petroleum ether to obtain 13.18 g of a white solid, which was the target product 3,4,5-trihydroxybenzoic acid (gallic acid) represented by formula (IV), with a yield of 96.84% and a purity of 99.10%.

[0035] Application Example 1 Hair Dyeing Effect Test

[0036] The gallic acid obtained in Example 1 of the present invention was used as a hair dye component of a black hair dye, and corresponding black hair dyes 1, 2 and 3 were prepared according to the formula shown in Table 2 and the colorability and color fastness tests were carried out.

[0037] (1) Colorability test: Use the prepared black hair dye 1, 2 and 3 according to the above-mentioned method of use, that is, according to the length of the hair, each of the 1, 2 and 3 doses only needs to soak the hair. First, apply the 1 dose evenly to the hair with a small brush, let it stand at room temperature for about 15 minutes, and wash off the remaining 1 dose with clean water; then apply the 2 dose evenly to the hair, let it stand at room temperature for about 30 minutes, and wash off the remaining 2 dose with clean water; then apply the 3 dose evenly to the hair with a small brush, let it stand at room temperature for about 15 minutes, and then wash it with shampoo and then rinse it with clean water and blow dry it. Observe the color of the dyed hair, and score the colorability from 1 to 5 points. The higher the score, the more obvious the coloring. The dyeing situation is shown in Table 2.

[0038] (2) Color fastness test: The dyed hair was placed in an aqueous solution containing 5% shampoo (the shampoo was Zhencaotang Color Protecting and Nourishing Shampoo (Plant Conditioning Type), batch number 04 280803), and then placed on a vortex machine, with the speed controlled at 40 r / min for 5 min each time, rinsed, blow-dried, and repeated. The number of washes required for the first fading was observed, and the results are shown in Table 2.

[0039] Table 2 Some representative black hair dye examples and their hair dyeing effects .

[0040] As can be seen from Examples 5 to 8 in Table 2, the black hair dyes 1, 2 and 3 prepared according to the listed component formulas can dye white hair black when used according to the method. Generally speaking, the higher the gallic acid content, the better the blackening effect; when the mass concentration of gallic acid reaches 4.0%, the coloring index can reach 5, achieving a satisfactory blackening effect. The number of times the hair dyes of Examples 5 to 8 faded significantly after dyeing was more than 7 times, which shows that the black hair dyes of the present invention have good color fastness and good washing resistance.

[0041] In this embodiment, the gallic acid prepared in Examples 2-4 is used as a hair dye component to replace the gallic acid in Example 1, and the same technical effect can be achieved. Examples 1-4 are only changes in preparation parameters and do not affect the performance of the product.

[0042] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept. The protection scope of the present invention should not be regarded as limited to the specific forms described in the embodiments. The protection scope of the present invention is also limited to the equivalent technical means that can be thought of by those skilled in the art based on the inventive concept.

Claims

1. A method for preparing gallic acid, a natural hair dyeing ingredient, characterized in that The following steps are involved: 1) Using vanillin represented by formula (I) as a starting material, and reacting it with sodium bromide, sulfuric acid and hydrogen peroxide in a one-pot process to simultaneously undergo bromination and oxidation reactions to obtain 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II); 2) then, under the catalysis of cuprous bromide and methyl formate, 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II) reacts with sodium methoxide in a methanol solvent to prepare 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III); 3) Finally, 4-hydroxy-3,5-dimethoxybenzoic acid shown in formula (III) undergoes a demethylation reaction in a LiBr / HCl solution system to obtain the target product 3,4,5-trihydroxybenzoic acid, i.e., gallic acid, shown in formula (IV); the reaction equation is as follows: 。 2. The method for preparing gallic acid as a natural hair dyeing ingredient according to claim 1, characterized in that In step 1, the reaction solvent is acetonitrile, and the volume of the acetonitrile solvent is 1.0-2.0 mL / mmol based on the amount of vanillin; the molar ratio of vanillin to sodium bromide and hydrogen peroxide is 1: 1.0-2.2: 2.0-4.0; and the molar ratio of sodium bromide to concentrated sulfuric acid is 1: 0.5-1.

0.

3. The method for preparing gallic acid as a natural hair dyeing ingredient according to claim 1, characterized in that Step 1: The reaction temperature is 40 to 60° C., the reaction time is 10 to 16 hours, and after the reaction is completed, the following post-treatment steps are included: pouring the reaction solution into water, stirring, filtering, and drying to obtain 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II).

4. The method for preparing gallic acid as a natural hair dyeing ingredient according to claim 1, characterized in that In step 2, the molar ratio of 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II) to sodium methoxide is 1:1.5-2.5; the molar amounts of the catalyst cuprous bromide and methyl formate are 3.0-5.0 mol% and 35.0-45.0 mol% of the molar amount of 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II), respectively; and the volumetric amount of the solvent methanol is 1.0-2.0 mL / mmol based on the amount of 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II).

5. The method for preparing gallic acid as a natural hair dyeing ingredient according to claim 1, characterized in that The reaction temperature of step 2 is 100-130° C., the reaction time is 2-4 h, and after the reaction is completed, the following post-treatment steps are included: cooling to room temperature, concentrating the reaction solution to remove methanol, adding ether and 1-2 mol / L dilute hydrochloric acid under stirring, separating the liquids, extracting the aqueous phase with ether several times, combining the organic phases, drying over anhydrous sodium sulfate, and desolventizing to obtain 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III).

6. The method for preparing gallic acid as a natural hair dyeing ingredient according to claim 1, characterized in that In step 3, the molar ratio of 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III) to LiBr is 1:0.3-0.4, the concentration of the HCl solution is 1.5-1.8 mol / L, and the volumetric amount of the HCl solution is 1.0-2.0 mL / mmol based on the amount of 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III).

7. The method for preparing gallic acid as a natural hair dyeing ingredient according to claim 1, characterized in that The reaction temperature of step 3 is 100-120°C, the reaction time is 1-2 h, and the following post-treatment steps are included after the reaction is completed: cooling to room temperature, pouring the reaction solution into saturated brine, extracting with ethyl acetate several times, combining the organic phases, drying, desolventizing, and washing with petroleum ether to obtain the target product 3,4,5-trihydroxybenzoic acid shown in formula (IV), i.e., gallic acid.

8. Use of gallic acid, a natural hair dyeing ingredient prepared by the method as described in any one of claims 1 to 7, in the preparation of a black hair dye.

9. The use according to claim 8, characterized in that The black hair dye comprises three types: 1 dose, 2 doses and 3 doses; The one dose is composed of the following components according to the percentage by mass: 3.0-8.0% of cetearyl alcohol, 1.0-3.0% of cetearyl alcohol polyether-20, 1.0-3.0% of thioglycolic acid, 0.2-0.5% of sodium sulfite, 2.0-6.0% of 25% ammonia water, 0-3.0% of ethanolamine, and the balance is water; The two doses are composed of the following components according to the percentage by mass: 3.0-8.0% cetearyl alcohol, 1.0-3.0% ceteareth-20, 0.2% methylparaben, 0.1% propylparaben, 2.0-8.0% ferrous sulfate, and the balance is water; The three doses are composed of the following components according to mass percentage: 3.0-8.0% cetearyl alcohol, 1.0-3.0% ceteareth-20, 1.0-10.0% gallic acid, and the balance is water.

10. The use according to claim 9, characterized in that The method for using the black hair dye is as follows: first, evenly apply the first dose to the hair with a small brush and soak the hair, let it stand at room temperature for 10-20 minutes, and wash away the remaining first dose with clean water; then evenly apply the second dose to the hair and soak the hair, let it stand at room temperature for 25-40 minutes, and wash away the remaining second dose with clean water; then evenly apply the third dose to the hair with a small brush and soak the hair, let it stand at room temperature for 10-20 minutes, wash with shampoo, then rinse with clean water and blow dry, and the hair is dyed black.

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