Preparation method and application of a natural hair dyeing ingredient, gallic acid

Abstract

The present invention discloses a preparation method and application of natural hair dyeing ingredient gallic acid. The preparation method of gallic acid is as follows: Using vanillin shown in formula (I) as the starting material, reacting with sodium bromide, sulfuric acid and hydrogen peroxide by a one-pot method to simultaneously carry out bromination and oxidation reactions to obtain a compound of formula (II), and then under the co-catalysis of cuprous bromide and methyl formate, the compound of formula (II) reacts with sodium methoxide in a methanol solvent to prepare a compound of formula (III), and finally a demethylation reaction occurs in a LiBr / HCl solution system to obtain gallic acid of formula (IV). The reaction formula is as follows:. The process route for synthesizing gallic acid in 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 good industrialization prospects.

Description

Technical Field

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

[0002] Most of the existing hair dyes are prepared from chemically synthesized dye pigments, and their main raw materials are phenylenediamine and hydroquinone compounds. Through the action of oxidants such as hydrogen peroxide, the dyeing effect is achieved. Since such hair dyes contain toxic chemical substances, they are likely to cause allergies, resulting in discomfort such as skin redness and stinging. Long-term use may even cause canceration. To solve this problem, on the one hand, new safe hair dye intermediates such as 2,5-diaminophenylethanol are used, and on the other hand, safe and non-toxic natural plant pigments are extracted from natural plants such as branches, leaves, flowers, herbs, and traditional Chinese medicines such as Polygonum multiflorum as hair dyeing ingredients.

[0003] Gallic acid, with the chemical name 3,4,5-trihydroxybenzoic acid, is an ideal natural plant hair dyeing ingredient, which is widely present in plants such as Rheum palmatum, Eucalyptus robusta, Cornus officinalis, tea, and grapes. It has a wide source, is safe and non-toxic, and will 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 forms a network structure by complexing with ferrous or ferric ions and then coats the surface of the hair, thereby achieving the purpose of hair dyeing. In addition, gallic acid also has various 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 the fields of medicine, food, biology, chemical engineering, etc., and the demand is increasing year by year. In view of this, the preparation method of gallic acid has received wide attention.

[0004] At present, gallic acid is usually prepared by acid-base method, fermentation method or enzymatic hydrolysis using tannin-containing biomass such as Chinese gallnut or tara:

[0005] 1) Acid-base hydrolysis method, that is, crushing the tannin-containing biomass Chinese gallnut or tara, extracting with hot water, filtering out the residue to obtain the tannic acid stock solution. Concentrating the stock solution, and then adding inorganic acid or alkali for hydrolysis to obtain gallic acid and glucose; then through separation, decolorization, refining, and drying to obtain gallic acid. In this process, the hydrolysis of tannin is incomplete, the yield of gallic acid is not high, the product quality is unstable, especially the amount of acid or alkali used is large, the equipment corrosion is serious, the production cost is high, the environmental pollution is serious, and the cost of treating the three wastes is high.

[0006] 2) The fermentation method is to use microorganisms to ferment in a tannin-containing aqueous solution. The bioenzymes induced by the microorganisms catalyze the hydrolysis of tannin to obtain gallic acid. In the fermentation method, the formation of bioenzymes and the hydrolysis of tannin are carried out in the same reaction vessel, and the process conditions are difficult to reach the optimal state, resulting in a reaction cycle of several days, and the hydrolysis of tannin is incomplete and the yield of gallic acid is not high.

[0007] 3) In the enzymatic method, the processes of enzyme production and acid production are carried out in two separate reaction vessels respectively, which can enable both to reach an optimal reaction state, shorten the reaction time to a certain extent, and improve the hydrolysis rate of tannin and the yield of gallic acid. However, currently, the tannase used for catalytic synthesis of gallic acid mostly comes from fungi such as Aspergillus oryzae, Aspergillus niger, Trichoderma reesei, etc. The tannase derived from these strains still has low activity, poor thermal stability and poor tolerance to gallic acid, thus limiting its industrial application.

[0008] In summary, currently, the preparation of gallic acid usually uses natural tannin-containing biomass such as Chinese gallnut or tara as raw materials. The raw material sources are limited and it is not suitable for large-scale production. Summary of the Invention

[0009] Aiming at the above technical problems existing in the prior art, the purpose of the present invention is to provide a preparation method and application of a natural hair dyeing ingredient, gallic acid.

[0010] The technical solution adopted by the present invention is as follows:

[0011] A preparation method of a natural hair dyeing ingredient, gallic acid, is characterized by comprising the following steps:

[0012] 1) Using vanillin shown in formula (I) as the starting material, reacting with sodium bromide, sulfuric acid and hydrogen peroxide by a one-pot method to simultaneously carry out bromination and oxidation reactions to obtain 3-bromo-4-hydroxy-5-methoxybenzoic acid shown in formula (II);

[0013] 2) Then, under the co-catalysis of cuprous bromide and methyl formate, 3-bromo-4-hydroxy-5-methoxybenzoic acid shown in formula (II) reacts with sodium methoxide in a methanol solvent to prepare 4-hydroxy-3,5-dimethoxybenzoic acid shown in formula (III);

[0014] 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 shown in formula (IV), that is, gallic acid; the reaction equation is as follows:

[0015] .

[0016] The present invention describes each step in detail as follows:

[0017] 1) Preparation of 3-bromo-4-hydroxy-5-methoxybenzoic acid shown in formula (II)

[0018] Vanillin shown in formula (I) is put into an acetonitrile solvent. Sodium bromide and 98% concentrated sulfuric acid are added at room temperature. 30% hydrogen peroxide is slowly added dropwise with stirring, and the reaction temperature is controlled at 40 - 60 °C. After the addition is complete, the reaction is carried out under insulation for 10 - 16 hours. 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 shown in formula (II).

[0019] 2) Preparation of 4-hydroxy-3,5-dimethoxybenzoic acid shown in formula (III)

[0020] In an autoclave, 3-bromo-4-hydroxy-5-methoxybenzoic acid (II) obtained in step 1) and the solvent methanol are put in, and then sodium methoxide, cuprous bromide, and methyl formate are added. It is heated to 100 - 130 °C with stirring and reacted for 2 - 4 h. After the reaction is completed, it is cooled to room temperature. After the reaction solution is concentrated to remove methanol, ether and 1 - 2 mol / L dilute hydrochloric acid are added with stirring. Liquid separation is carried out, and the aqueous phase is extracted with ether several times. The organic phases are combined, dried over anhydrous sodium sulfate, and the solvent is removed to obtain 4-hydroxy-3,5-dimethoxybenzoic acid shown in formula (III).

[0021] 3) Preparation of the target product gallic acid shown in formula (IV)

[0022] In an autoclave, 4-hydroxy-3,5-dimethoxybenzoic acid (III) obtained in step 2) is put in, and then lithium bromide and hydrochloric acid solution are added. It is heated to 100 - 120 °C with stirring and reacted for 1 - 2 h. After the reaction is completed, it is cooled to room temperature. The reaction solution is poured into saturated brine, and extracted with ethyl acetate several times. The organic phases are combined, dried, the solvent is removed, and washed with petroleum ether to obtain the target product 3,4,5-trihydroxybenzoic acid, namely gallic acid, shown in formula (IV).

[0023] Furthermore, in step 1), the volume of the acetonitrile solvent is 1.0 - 2.0 mL / mmol based on the amount of substance of vanillin, preferably 1.4 - 1.8 mL / mmol; 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 in the feeding is 1 : 0.5 - 1.0, preferably 1 : 0.6 - 0.8.

[0024] Further, in step 2), the molar ratio of 3-bromo-4-hydroxy-5-methoxybenzoic acid shown in 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 respectively 3.0 - 5.0 mol% and 35.0 - 45.0 mol% of the molar amount of 3-bromo-4-hydroxy-5-methoxybenzoic acid shown in formula (II), preferably 3.6 - 4.4 mol% and 38.0 - 42.0 mol% respectively; the volume amount of the solvent methanol is 1.0 - 2.0 mL / mmol based on the amount of substance of 3-bromo-4-hydroxy-5-methoxybenzoic acid shown in formula (II).

[0025] Further, in step 3), the molar ratio of 4-hydroxy-3,5-dimethoxybenzoic acid shown in 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 volume amount of the HCl solution is 1.0 - 2.0 mL / mmol based on the amount of substance of 4-hydroxy-3,5-dimethoxybenzoic acid shown in formula (III).

[0026] The present invention also defines the application of the prepared gallic acid in the preparation of a hair blackening agent, and the hair blackening agent includes agent 1, agent 2, and agent 3. The names of the components and the mass percentage contents of the components in agent 1, agent 2, and agent 3 of the hair blackening agent are respectively listed in Table 1:

[0027] Table 1 List of components in agent 1, agent 2, and agent 3 of the hair blackening agent

[0028] 。

[0029] Agent 1, agent 2, and agent 3 of the hair blackening agent are separately and independently prepared, and the preparation method includes the following steps: heating phase A and phase B to about 85°C respectively; then adding phase A to phase B and stirring and homogenizing for 20 - 30 minutes; after cooling to about 45°C, adding phase C, stirring evenly, cooling to room temperature, and discharging and filling.

[0030] The using method of the hair blackening agent of the present invention is carried out according to the following steps: according to the length of the hair, each of agent 1, agent 2, and agent 3 only needs to wet the hair. First, evenly apply agent 1 on the hair with a small brush and wet the hair, let it stand at room temperature for 10 - 20 minutes, and wash off the remaining agent 1 with clean water; then evenly apply agent 2 on the hair and wet the hair, let it stand at room temperature for 25 - 40 minutes, and wash off the remaining agent 2 with clean water; then evenly apply agent 3 on the hair with a small brush or the like and wet the hair, let it stand at room temperature for 10 - 20 minutes, wash it with shampoo and then rinse it clean with clean water and dry it, and the hair will be dyed black.

[0031] The method for using the black hair dye is carried out according to the following steps: Take 25 - 70 ml of each of Agent 1, Agent 2, and Agent 3. Determine the dosages of Agent 1, Agent 2, and Agent 3 specifically according to the amount of hair. Generally, for short hair within 10 cm, use 25 ml of each of Agent 1, Agent 2, and Agent 3, and for long hair about 30 cm, use 70 ml of each. It is not required that the amounts of Agent 1, Agent 2, and Agent 3 be equal. First, evenly apply Agent 1 to the hair with a small brush, let it stand at room temperature for 10 - 20 minutes, preferably about 15 minutes, and then wash off the residual Agent 1 with clear water; then evenly apply Agent 2 to the hair, let it stand at room temperature for 25 - 40 minutes, preferably about 30 minutes, and wash off the residual Agent 2 with clear water; then evenly apply Agent 3 to the hair in the same way with a small brush, etc., let it stand at room temperature for 10 - 20 minutes, preferably about 15 minutes, wash it with shampoo and then rinse it with clear water and dry it. The hair will be dyed black, and the color is natural and the hair quality is smooth.

[0032] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0033] 1) The present invention provides a new method for preparing natural hair dye component gallic acid from natural vanillin. Although vanillin is a natural component, it is also one of the synthetic fragrance varieties with the largest global production, and the source is abundant, which solves the problem of limited raw material sources and unsuitability for large-scale production caused by the traditional preparation method of gallic acid using natural tannin-containing biomasses such as Chinese gallnuts or tara as raw materials; at the same time, it also broadens the application range of vanillin;

[0034] 2) The process route for synthesizing gallic acid in the present invention has simple raw material sources and conventional synthesis methods, and has the advantages of mild reaction conditions, simple operation, high yield, etc.; compared with the traditional acid-base hydrolysis method, the amount of three wastes is greatly reduced, and it has good industrialization prospects;

[0035] 3) The present invention also provides the application of natural component gallic acid obtained by a defined method as a dye component in a hair dye. This hair dye uses natural plant component gallic acid as the main hair dye 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 wash resistance. Specific Embodiments

[0036] 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.

[0037] The present invention first gives a synthesis example of natural hair dye component gallic acid.

[0038] Example 1 Synthesis of Natural Hair Dye Component Gallic Acid

[0039] (1) Synthesis of 3-bromo-4-hydroxy-5-methoxybenzoic acid (II)

[0040] Vanillin (I) (100 mmol) was added to 140 mL of acetonitrile. Sodium bromide (140 mmol) and 98% sulfuric acid (84 mmol, 8.40 g) were added at room temperature. 30% hydrogen peroxide (250 mmol, 28.35 g) was slowly added dropwise with stirring, and the reaction temperature was controlled at 50 °C. After the addition was complete, the reaction mixture was kept at this temperature for 10 h. 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 a white powder, namely 3-bromo-4-hydroxy-5-methoxybenzoic acid shown in formula (II), with a yield of 95.04%.

[0041] (2) Synthesis of 4-hydroxy-3,5-dimethoxybenzoic acid (III)

[0042] 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. The mixture was heated to 120 °C with stirring and reacted for 3 h. After the reaction was completed, it was cooled to room temperature. After the reaction solution was concentrated to remove methanol, diethyl ether (135 mL) and dilute hydrochloric acid (1.6 mol / L, 135 mL) were added with stirring. The layers were separated, and the aqueous phase was extracted with diethyl ether three times (3×135 mL). The organic phases were combined, dried over anhydrous sodium sulfate, and the solvent was removed to obtain 16.82 g of a white solid, namely 4-hydroxy-3,5-dimethoxybenzoic acid shown in formula (III), with a yield of 94.31%.

[0043] (3) Synthesis of the target product gallic acid (IV)

[0044] 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. The mixture was heated to 110 °C with stirring and reacted for 1 h. After the reaction was completed, it was cooled to room temperature. 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, the solvent was removed, and it was 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) shown in formula (IV), with a yield of 98.39%; purity 99.15%; m.p.: 251~252 °C. 1 HNMR (400 MHz,CD3OD) δ: 7.04 (s, 2H); 1313C NMR (100 MHz, CD3OD) δ: 110.3, 122.5, 139.5, 146.3, 171.0; HRMS (ESI) calcd for C7H7O5 [M+H] + 171.0215, found 171.0208。

[0045] Example 2 Synthesis of Natural Hair Dyeing Ingredient Gallic Acid

[0046] (1) Synthesis of 3-Bromo-4-hydroxy-5-methoxybenzoic Acid (II)

[0047] Vanillin (I) (100 mmol) was added to 180 mL of acetonitrile. Sodium bromide (180 mmol) and 98% sulfuric acid (144 mmol, 14.40 g) were added at room temperature. 30% hydrogen peroxide (350 mmol, 39.69 g) was slowly added dropwise with stirring, and the reaction temperature was controlled at 40 °C. After the addition, the reaction mixture 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 a white powder, namely 3-bromo-4-hydroxy-5-methoxybenzoic acid of formula (II), with a yield of 98.12%.

[0048] (2) Synthesis of 4-Hydroxy-3,5-dimethoxybenzoic Acid (III)

[0049] 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. The mixture was heated to 130 °C with stirring and reacted for 4 h. After the reaction was completed, it was cooled to room temperature. After 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. The layers were separated, and the aqueous phase was extracted with ether three times (3 × 180 mL). The organic phases were combined, dried over anhydrous sodium sulfate, and the solvent was removed to obtain 17.34 g of a white solid, namely 4-hydroxy-3,5-dimethoxybenzoic acid of formula (III), with a yield of 97.22%.

[0050] (3) Synthesis of the Target Product Gallic Acid (IV)

[0051] In an autoclave, 4-hydroxy-3,5-dimethoxybenzoic acid (III) (80 mmol) obtained in step (2) was charged, and then lithium bromide (32 mmol) and hydrochloric acid solution (1.8 mol / L, 80 mL) were added. The mixture was heated to 100 °C with stirring and reacted for 2 h. After the reaction was completed, it was cooled to room temperature. 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, concentrated, 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) shown in formula (IV), with a yield of 97.95% and a purity of 99.22%.

[0052] Example 3 Synthesis of Gallic Acid as a Natural Hair Dyeing Ingredient

[0053] (1) Synthesis of 3-bromo-4-hydroxy-5-methoxybenzoic acid (II)

[0054] Vanillin (I) (100 mmol) was charged into 160 mL of acetonitrile. Sodium bromide (160 mmol) and 98% sulfuric acid (112 mmol, 11.20 g) were added at room temperature. 30% hydrogen peroxide (300 mmol, 34.02 g) was slowly added dropwise with stirring, and the reaction temperature was controlled at 60 °C. After the addition was completed, the reaction mixture was kept warm for 16 hours. 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 a white powder, which was 3-bromo-4-hydroxy-5-methoxybenzoic acid shown in formula (II), with a yield of 97.55%.

[0055] (2) Synthesis of 4-hydroxy-3,5-dimethoxybenzoic acid (III)

[0056] In an autoclave, 3-bromo-4-hydroxy-5-methoxybenzoic acid (II) (90 mmol) obtained in step (1) was charged into 150 mL of methanol, and then sodium methoxide (180 mmol), cuprous bromide (3.60 mmol), and methyl formate (36.00 mmol) were added. The mixture was heated to 100 °C with stirring and reacted for 2 h. After the reaction was completed, it was cooled to room temperature. After 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. The layers were separated, and the aqueous phase was extracted with ether three times (3×145 mL). The organic phases were combined, dried over anhydrous sodium sulfate, and concentrated to obtain 17.21 g of a white solid, which was 4-hydroxy-3,5-dimethoxybenzoic acid shown in formula (III), with a yield of 96.49%.

[0057] (3) Synthesis of the Target Product Gallic Acid (IV)

[0058] In an autoclave, 4-hydroxy-3,5-dimethoxybenzoic acid (III) (80 mmol) obtained in step (2) was charged, and then lithium bromide (30 mmol) and hydrochloric acid solution (1.6 mol / L, 160 mL) were added. The mixture was heated to 120 °C with stirring and reacted for 1.5 h. After the reaction was completed, it was cooled to room temperature. The reaction solution was poured into 100 mL of saturated brine and extracted three times with ethyl acetate (3 × 120 mL). The organic phases were combined, dried, concentrated, 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) shown in formula (IV), with a yield of 97.21% and a purity of 99.05%.

[0059] Example 4 Synthesis of Gallic Acid as a Natural Hair Dyeing Ingredient

[0060] (1) Synthesis of 3-bromo-4-hydroxy-5-methoxybenzoic acid (II)

[0061] Vanillin (I) (100 mmol) was charged into 150 mL of acetonitrile. Sodium bromide (170 mmol) and 98% sulfuric acid (136 mmol, 13.60 g) were added at room temperature. 30% hydrogen peroxide (320 mmol, 36.29 g) was slowly added dropwise with stirring, and the reaction temperature was controlled at 55 °C. After the addition was completed, the mixture was kept warm and reacted for 15 hours. 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 a white powder, which was 3-bromo-4-hydroxy-5-methoxybenzoic acid shown in formula (II), with a yield of 96.38%.

[0062] (2) Synthesis of 4-hydroxy-3,5-dimethoxybenzoic acid (III)

[0063] In an autoclave, 3-bromo-4-hydroxy-5-methoxybenzoic acid (II) (90 mmol) obtained in step (1) was charged into 120 mL of methanol, and then sodium methoxide (190 mmol), cuprous bromide (3.50 mmol), and methyl formate (36.00 mmol) were added. The mixture was heated to 110 °C with stirring and reacted for 3.5 h. After the reaction was completed, it was cooled to room temperature. After 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. The layers were separated, and the aqueous phase was extracted three times with ether (3 × 160 mL). The organic phases were combined, dried over anhydrous sodium sulfate, and concentrated to obtain 17.10 g of a white solid, which was 4-hydroxy-3,5-dimethoxybenzoic acid shown in formula (III), with a yield of 95.87%.

[0064] (3) Synthesis of the Target Product Gallic Acid (IV)

[0065] In an autoclave, 4-hydroxy-3,5-dimethoxybenzoic acid (III) (80 mmol) obtained in step (2) was charged, and then lithium bromide (28 mmol) and hydrochloric acid solution (1.5 mol / L, 100 mL) were added. The mixture was heated to 105 °C with stirring and reacted for 2 h. After the reaction, it was cooled to room temperature, and the reaction solution was poured into 120 mL of saturated brine, extracted three times with ethyl acetate (3×100 mL). The organic phases were combined, dried, concentrated by evaporation, 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) shown in formula (IV), with a yield of 96.84% and a purity of 99.10%.

[0066] Application Example 1 Hair Dyeing Effect Test

[0067] Using the gallic acid obtained in Example 1 of the present invention as a hair dyeing component for black hair, corresponding hair dyes 1, 2, and 3 were prepared according to the formula shown in Table 2 by the aforementioned method, and the coloration property and color fastness tests were carried out.

[0068] (1) Coloration property test: The prepared hair dyes 1, 2, and 3 were used for hair dyeing according to the aforementioned usage method, that is: according to the hair length, for each of the hair dyes 1, 2, and 3, it was only necessary to moisten the hair. First, hair dye 1 was evenly applied to the hair with a small brush, left standing at room temperature for about 15 minutes, and then the residual hair dye 1 was washed off with water; then hair dye 2 was evenly applied to the hair, left standing at room temperature for about 30 minutes, and the residual hair dye 2 was washed off with water; then hair dye 3 was also evenly applied to the hair with a small brush or the like, left standing at room temperature for about 15 minutes, and then washed with shampoo and rinsed with water and dried. Observe the color of the dyed hair, and the coloration property was scored from 1 to 5 points. The higher the score, the more obvious the coloration. The dyeing situation is shown in Table 2.

[0069] (2) Color fastness test: The dyed hair was placed in an aqueous solution containing 5% shampoo (this shampoo is Zhencaotang Post-Dyeing Color-Caring Nourishing Shampoo (plant conditioning type), batch number 04 280803), and then placed on a vortex shaker, and rotated at a speed of 40 r / min for 5 minutes each time, rinsed and dried, and the test was repeated. Observe the number of water washes for the first fading, and the results are shown in Table 2.

[0070] Table 2 Examples of Several Representative Black Hair Dyes and Their Hair Dyeing Effects

[0071] .

[0072] As can be seen from Examples 5 to 8 in Table 2, when the hair dyes 1, 2, and 3 prepared according to the listed group distribution formula are used for hair dyeing according to the described usage method, white hair can be dyed black. 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 water washes with obvious fading after dyeing with the hair dyes described in Examples 5 to 8 is more than 7 times. It can be seen that the hair dyes described in the present invention all have good color fastness and good wash resistance.

[0073] In this example, using the gallic acid prepared in Examples 2-4 as a hair dyeing component to replace the gallic acid in Example 1 can achieve the same technical effects. Examples 1-4 are only changes in preparation parameters and do not affect the performance of their products.

[0074] The content described in this specification is only a list 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 stated in the examples. The protection scope of the present invention is also only equivalent technical means that can be conceived 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: Step 1: using vanillin represented by formula (I) as a starting material, 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); Step 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); Step 3: Finally, 4-hydroxy-3,5-dimethoxybenzoic acid represented by formula (III) undergoes a demethylation reaction in a LiBr / HCl solution system to obtain the target product 3,4,5-trihydroxybenzoic acid represented by formula (IV), i.e., gallic acid; the reaction equation is as follows: 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; the molar ratio of sodium bromide to concentrated sulfuric acid is 1:0.5-1.0; Step 1: The reaction temperature is 40 to 60° C., and the reaction time is 10 to 16 hours. 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); Step 2: The reaction temperature is 100-130°C, and the reaction time is 2-4h; 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.

2. The method for preparing gallic acid as a natural hair dyeing ingredient according to claim 1, characterized in that In step 2, the volume amount of the solvent methanol is 1.0 to 2.0 mL / mmol based on the amount of 3-bromo-4-hydroxy-5-methoxybenzoic acid represented by formula (II).

3. The method for preparing gallic acid as a natural hair dyeing ingredient according to claim 1, characterized in that After the reaction in step 2 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 shown in formula (III).

4. 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 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).

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 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.

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