Multifunctional high-absorption chrome tanning auxiliary containing barbituric acid structure and preparation method thereof

Abstract

The application discloses a multifunctional high-absorption chrome tanning auxiliary agent containing a barbituric acid structure, and the auxiliary agent is a polycarboxylic acid compound containing a barbituric acid structure. The application discloses a preparation method of the high-absorption chrome tanning auxiliary agent, which comprises four reaction steps, namely, C-alkylation reaction, cyclization reaction, N-alkylation reaction and hydrolysis reaction. The high-absorption chrome tanning auxiliary agent contains 2-3 ketone carbonyl groups and 2-4 carboxyl groups, wherein the ortho ketone carbonyl group and the carboxyl group can be cyclized with arginine in collagen protein, collagen modification is realized, carboxyl groups are introduced, the number of side chain carboxyl groups of collagen is increased, the coordination sites of chromium are increased, the absorption of trivalent chromium can be significantly improved, the concentration of trivalent chromium in chrome tanning wastewater is reduced, the high-absorption chrome tanning target is realized, and clean production of the leather-making industry is promoted. The application provides a new idea for the design and preparation of the high-absorption chrome tanning auxiliary agent.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chrome tanning aids, and particularly relates to a multifunctional high-absorption chrome tanning aid containing a barbituric acid structure and a preparation method thereof. BACKGROUND

[0002] Chrome tanning is the most important and widely used tanning method in leather manufacturing so far, which endows leather with high thermal stability, comfortable hand feeling and excellent leather performance. At present, it occupies an absolute dominant position in the leather industry (China C.R. et al. Chemosphere, 2020, 254: 126804). However, in the traditional tanning process, the absorption rate of chrome tanning agent is usually only about 70%, resulting in high-concentration chromium-containing wastewater. This not only increases the environmental pollution load and wastewater treatment cost, but also causes great resource waste. Due to the adverse effects of chromium pollutants on the environment, the leather industry has been listed as one of the high-pollution industries. Therefore, how to maximize the absorption of chromium and the utilization rate of chrome tanning agent in the tanning process to achieve high-absorption chrome tanning is a widely concerned problem in the academic and industrial circles of leather manufacturing in recent years, and is also a key scientific and technological problem that needs to be solved urgently to ensure the sustainable development of the leather industry (Ouyang Mai et al. Review on High-Absorption Chrome Tanning and High-Absorption Chrome Tanning Aids [J]. West China Leather, 2022, 44(07): 13-20; Chen Bo, Zhang Hui, Qiang Xihuai, et al. Research Progress of High-Absorption Chrome Tanning Aids [J]. China Leather, 2019, 48(04): 41-46).

[0003] High-absorption chrome tanning technology is based on the existing chrome tanning method, which improves the absorption rate of chrome tanning agent in collagen to 80% to 98% through optimization of leather-making process or addition of chemical aids, reduces the chromium discharge in waste liquid, and effectively improves the environmental problems caused by the leather industry. The added chemical aid is called high-absorption chrome tanning aid.

[0004] High-absorption chrome tanning auxiliaries have attracted extensive attention from leather manufacturers and researchers. Leather workers have developed a variety of high-absorption chrome tanning auxiliaries, such as hyperbranched polymers, nanocomposites, waterborne epoxy resins, dicarboxylic acid compounds, hydroxy acid compounds, aromatic sulfonic acids, aldehyde acid compounds, and ketone acid compounds. However, current high-absorption chrome tanning auxiliaries have their own shortcomings. The synthesis of high-molecular-weight auxiliaries is complicated and costly. The large molecular weight results in poor penetration in collagen, leading to a low binding capacity with collagen. The excessive active groups make it difficult to control the production, as they can bind to collagen fibers and Cr(III) in various ways. Small-molecular-weight auxiliaries have a small molecular weight and a single type of functional group, and their interaction with collagen fibers is mainly electrostatic interaction, ionic bonding, and hydrogen bonding. Aldehyde acid compounds such as glyoxylic acid can form covalent bonds with collagen side chains, but the stability of the bonds is low, and the amount of introduced carboxyl groups is insufficient, limiting the increase in coordination sites.

[0005] Ouyang M. et al. prepared a ketonic acid high-absorption chrome tanning auxiliary 4-acetyl heptanedioic acid (AHA) by Michael addition reaction using acetylacetone and acrylic ester as raw materials, and applied it in the chrome retanning process. When the dosage of chrome retanning agent was 4%, the chromium content in the leather increased significantly (82.43%), the chromium content in the retanning effluent decreased significantly, the chemical oxygen demand (COD) of the effluent decreased by 43.82%, and the total dissolved solids (TDS) decreased by 31.46%. In addition, the wet heat stability and mechanical properties of the leather were also improved (Ouyang M. et al. Journal of Cleaner Production, 2022, 367: 133125).

[0006] Wang G. et al. reported a kind of polybasic acid high-absorption chrome tanning auxiliary containing ketone carbonyl in Chinese invention patent ZL202011536195.3 (Wang G., Ouyang M., Hu K., Zhuang L. A multi-functional high-absorption chrome tanning auxiliary and its preparation method and application [P]. ZL202011536195.3, 20220617). Using compounds containing active methylene groups (such as 3-keto-glutaric acid diester, 2-keto-glutaric acid diester, and methyl benzene formate) and α, β-unsaturated compounds (such as methyl acrylate, ethyl acrylate, or acrylonitrile) as raw materials, a Michael addition reaction was carried out to obtain a polybasic acid ester, which was then hydrolyzed to obtain a polybasic acid compound containing a ketone carbonyl group. Through collagen modification, six carboxyl groups were introduced into the collagen, significantly increasing the coordination sites of chromium, significantly improving the absorption of trivalent chromium, reducing the concentration of trivalent chromium in chrome tanning wastewater, reducing environmental pollution in the leather industry, and promoting clean production in the leather industry.

[0007] Guowei Wang et al. reported a high absorption chrome tanning auxiliary containing ketone carboxylic acid structure in Chinese invention patent ZL202011431991.0 (Guowei Wang, Hu Kehui, Ouyangmai, Zhuanglinghua. Preparation and application of a high absorption chrome tanning auxiliary containing ketone carboxylic acid structure [P]. ZL202011431991.0, 20230519). With active methylene compounds (acetylacetone, dibenzoylmethane, benzoylacetone or 3,5-dioctanone) and compounds containing α, β-unsaturated nitrile or compounds containing α, β-unsaturated carboxylic acid ester or compounds containing α, β-unsaturated amide (methyl acrylate, ethyl acrylate, acrylonitrile, acrylamide, etc.) as raw materials, polybasic carboxylic acid ester is prepared by double Michael addition reaction, and then hydrolysis to prepare high absorption chrome tanning auxiliary containing ketone carboxylic acid structure. The auxiliary modifies collagen, introduces multiple carboxyl groups in skin collagen, significantly increases the coordination site of trivalent chromium, reduces the concentration of trivalent chromium in chrome tanning wastewater, realizes high absorption chrome tanning, and promotes clean production of leather industry.

[0008] With the continuous deepening of the research on high absorption chrome tanning technology, the high absorption chrome tanning auxiliary containing ketone carboxylic acid structure has been unable to meet the needs of high absorption chrome tanning process. The absorption rate of chrome tanning agent in skin collagen is maintained at 85-92%, which cannot be further improved, and the wet heat stability and mechanical properties of leather cannot meet the requirements of high-grade leather at present. It is necessary to further optimize the structure and application performance of the high absorption chrome tanning auxiliary containing ketone carboxylic acid structure. SUMMARY

[0009] The first purpose of the present application is to provide a multi-functional high absorption chrome tanning auxiliary containing barbituric acid structure, and the second purpose of the present application is to provide a preparation method of the multi-functional high absorption chrome tanning auxiliary containing barbituric acid structure.

[0010] Technical scheme: The multi-functional high absorption chrome tanning auxiliary containing barbituric acid structure of the present application has the following molecular structure:

[0011]

[0012] In which X is O or S, R1=H, CH3, C2H5, R2=H, CH3, C2H5, C3H5, C3H7, C4H9, C5H9, C6H5, C6H 11 , C7H7, Cl, Br.

[0013] The preparation method of the multi-functional high absorption chrome tanning auxiliary containing barbituric acid structure of the present application comprises the following steps:

[0014] (1) C-alkylation reaction

[0015] The malonic acid diester compound and the halogenated carboxylic acid ester compound are used as raw materials, an inorganic base is used as base agent, and the reaction is carried out in an organic solvent under the catalysis of a phase transfer catalyst at 60-100℃ for 6-12h to obtain the carboxylic acid ester compound A; the molar ratio of the malonic acid diester compound to the halogenated carboxylic acid ester compound is 1:(1.0-2.05), and the molar ratio of the malonic acid diester compound to the base agent and the phase transfer catalyst is 1:(0.2-0.4):(0.02-0.06);

[0016] (2) Cyclization reaction

[0017] The carboxylic acid ester compound A and urea or thiourea are used as raw materials, and an inorganic base or an organic base is used as catalyst, and the reaction is carried out in an organic solvent at 80-100℃ for 4-6h to obtain the barbituric acid derivative or 2-thiobarbituric acid derivative B; the molar ratio of the carboxylic acid ester compound A to urea or thiourea is 1:(0.95-1.05), and the molar ratio of the carboxylic acid ester compound A to the organic base or the inorganic base is 1:(0.1-0.3);

[0018] (3) N-alkylation reaction

[0019] The barbituric acid derivative or 2-thiobarbituric acid derivative B and the halogenated carboxylic acid ester are used as raw materials, an inorganic base is used as base agent, and the reaction is carried out in an organic solvent under the catalysis of a phase transfer catalyst at 60-100℃ for 4-8h to prepare the barbituric acid derivative containing polycarboxylic acid ester or the 2-thiobarbituric acid derivative containing polycarboxylic acid ester C; the molar ratio of the barbituric acid derivative or 2-thiobarbituric acid derivative B to the halogenated carboxylic acid ester is 1:(1.0-2.05), and the molar ratio of the barbituric acid derivative or 2-thiobarbituric acid derivative B to the base agent and the phase transfer catalyst is 1:(0.2-0.4):(0.02-0.06);

[0020] (4) Hydrolysis reaction

[0021] The barbituric acid derivative containing polycarboxylic acid ester or the 2-thiobarbituric acid derivative containing polycarboxylic acid ester C is hydrolyzed under alkaline conditions at 70-100℃ for 4-12h, cooled to room temperature, and then adjusted to pH 4-5 with an acid to precipitate a solid, which is filtered to obtain the high-absorption chrome tanning auxiliary; the alkaline solution used in the alkaline conditions is a 10%-20% sodium hydroxide or potassium hydroxide solution by mass fraction; and the acid is one of a 5%-15% hydrochloric acid solution, a sulfuric acid solution, and a phosphoric acid solution by mass fraction.

[0022] Further, in step (1), the malonic acid diester compound is one of dimethyl malonate, dimethyl 2-methylmalonate, dimethyl 2-ethylmalonate, dimethyl 2-propylmalonate, dimethyl 2-butylmalonate, dimethyl 2-isobutylmalonate, dimethyl 2-allylmalonate, dimethyl 2-cyclopentylmalonate, dimethyl 2-phenylmalonate, dimethyl 2-cyclohexylmalonate, dimethyl 2-benzylmalonate, dimethyl 2-chloromalonate, dimethyl 2-bromomalonate, diethyl malonate, diethyl 2-methylmalonate, diethyl 2-propylmalonate, diethyl 2-butylmalonate, diethyl 2-isobutylmalonate, diethyl 2-allylmalonate, diethyl 2-cyclopentylmalonate, diethyl 2-phenylmalonate, diethyl 2-cyclohexylmalonate, diethyl 2-benzylmalonate, diethyl 2-chloromalonate, diethyl 2-bromomalonate, dipropyl malonate, diisopropyl malonate, dibutyl malonate, di-t-butyl malonate, dihexyl malonate.

[0023] Further, in step (1), the halogenated carboxylic acid ester is one of methyl chloroacetate, ethyl chloroacetate, butyl chloroacetate, t-butyl chloroacetate, ethyl bromoacetate, butyl bromoacetate, t-butyl bromoacetate, methyl 2-chloropropionate, ethyl 2-chloropropionate, methyl 2-bromopropionate, ethyl 2-bromopropionate, methyl 2-chlorobutyrate, ethyl 2-chlorobutyrate, methyl 2-bromobutyrate, ethyl 2-bromobutyrate; the inorganic base is one of anhydrous potassium carbonate, anhydrous sodium carbonate, potassium phosphate, sodium phosphate; the phase transfer catalyst is one of tetrabutylammonium bromide, tetrabutylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide; the organic solvent is one of petroleum ether, cyclohexane, n-hexane, ethyl acetate, 1,4-dioxane.

[0024] Further, in step (2), the inorganic base is one of sodium hydroxide, potassium hydroxide; the organic base is one of sodium ethoxide, sodium methoxide, sodium t-butoxide, potassium t-butoxide; the organic solvent is one of methanol, ethanol, isopropanol, n-butanol, t-butanol.

[0025] Further, in step (3), the halogenated carboxylic acid ester is one of methyl chloroacetate, ethyl chloroacetate, butyl chloroacetate, tert-butyl chloroacetate, ethyl bromoacetate, butyl bromoacetate, tert-butyl bromoacetate, methyl 2-chloropropionate, ethyl 2-chloropropionate, methyl 2-bromopropionate, ethyl 2-bromopropionate, methyl 2-chlorobutyrate, ethyl 2-chlorobutyrate, methyl 2-bromobutyrate, ethyl 2-bromobutyrate; the inorganic base is one of anhydrous potassium carbonate, anhydrous sodium carbonate, potassium phosphate, sodium phosphate; the phase transfer catalyst is one of tetrabutylammonium bromide, tetrabutylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide; and the organic solvent is one of 1,4-dioxane, methanol, ethanol, n-butanol.

[0026] The present application provides a multi-functional high-absorption chrome tanning auxiliary containing a barbituric acid structure, which comprises four steps of C-alkylation, cyclization, N-alkylation and hydrolysis. A carboxylic acid ester compound A is prepared by C-alkylation of a compound containing a reactive methylene group (such as dimethyl malonate, diethyl malonate, etc.) and a halogenated carboxylic acid ester (such as ethyl chloroacetate, ethyl 2-chloropropionate, etc.), the carboxylic acid ester compound A is cyclized with urea (or thiourea) to prepare a barbituric acid derivative or a 2-thiobarbituric acid derivative B, the barbituric acid derivative or the 2-thiobarbituric acid derivative B is subjected to N-alkylation with a halogenated carboxylic acid ester (such as ethyl chloroacetate, ethyl 2-chloropropionate, etc.) to prepare a barbituric acid derivative containing a polycarboxylic acid ester or a 2-thiobarbituric acid derivative containing a polycarboxylic acid ester C, and the high-absorption chrome tanning auxiliary containing a barbituric acid structure is prepared by further hydrolysis. The high-absorption chrome tanning auxiliary contains 2-3 ketone carbonyl groups and 2-4 carboxyl groups, wherein the adjacent ketone carbonyl group and carboxyl group can be cyclized with lysine or arginine in collagen protein to modify collagen, introduce carboxyl groups, increase the number of carboxyl groups in the side chain of collagen, increase the coordination sites of chromium, significantly improve the absorption of trivalent chromium, reduce the concentration of trivalent chromium in chrome tanning wastewater, achieve the goal of high-absorption chrome tanning, and promote clean production of the leather-making industry.

[0027] Advantages: Compared with the prior art, the present application has the following obvious advantages:

[0028] (1) The preparation steps of the high-absorption chrome tanning auxiliary of the present application are simple, the auxiliary contains 2-3 ketone carbonyl groups and 2-4 carboxyl groups, and the functionality is high;

[0029] (2) The high-absorption chrome tanning auxiliary of the present application, wherein the adjacent ketone carbonyl group and carboxyl group can be cyclized with lysine or arginine in collagen protein to modify collagen;

[0030] (3) The high-absorption chrome tanning auxiliary of the present application contains polycarboxyl groups, which can form stable coordination with chromium, significantly improve the absorption rate of trivalent chromium, and achieve the goal of high-absorption chrome tanning;

[0031] (4) Without changing the steps of traditional tanning process, only need to add the assistant in the pickling process.

[0032] Drawings

[0033] Figure 1 Structure general formula of multifunctional high absorption chrome tanning assistant containing barbituric acid structure DETAILED DESCRIPTION

[0034] The application will be further described in conjunction with the following examples, but the embodiments of the application are not limited thereto.

[0035] Example 1

[0036] (I) Synthesis of tetra-carboxylic acid ester

[0037] In a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, 0.1 mol dimethyl malonate, anhydrous K2CO3 (0.1 mol), 1 g tetrabutylammonium bromide and 80 mL n-hexane were added, and 0.2 mol ethyl chloroacetate was added dropwise, and the reaction was carried out under reflux for 4 h, the stirring was stopped, and the product was obtained after post-processing. 3,3-dimethyl malonate-1,5-pentanedioic acid diethyl ester (C 13 H 20 O8, Mr = 304.12 g / mol), mass 28.3 g, yield 93.2%, and the product structure is as follows:

[0038]

[0039] Nuclear magnetic hydrogen spectrum (C 13 H 20 O 8， CDCl3)

[0040] 4.01 ppm (q, 4H, -CCH2COOCH2CH3), 3.66 ppm (s, 6H, -CCOOCH3), 2.93 ppm (s, 4H, -CCH2COOC2H5), 1.07 ppm (t, 6H, -CCH2COOCH2CH3).

[0041] Nuclear magnetic carbon spectrum (C 13 H 20 O 8， CDCl3)

[0042] 172.2 ppm, 170.4 ppm, 61.3 ppm, 52.2 ppm, 43.1 ppm, 37.2 ppm, 14.1 ppm.

[0043] Elemental analysis (C 13 H 20 O8)

[0044] Theoretical values ​​(%): C: 51.31, H: 6.63. Measured values ​​(%): C: 51.33, H: 6.65.

[0045] (II) Synthesis of barbituric acid

[0046] In a 250 mL four-necked flask equipped with a stirrer, thermometer, and reflux condenser, 80 mL of ethanol, 0.1 mol sodium ethoxide (6.8 g), 0.11 mol urea (6.6 g), and 0.1 mol dimethyl 3,3-dicarboxylate-1,5-pentanoic acid diethyl ester (30.4 g) were added. The mixture was reacted at 80 °C for 6 h, cooled to room temperature, quenched with saturated sodium bicarbonate aqueous solution, extracted with ethyl acetate, and the organic phases were combined, washed with saturated brine, dried over anhydrous sodium sulfate, filtered, and rotary evaporated to give the product 5,5-diacetic acid diethyl ester-2,4,6-trioxahexahydropyrimidine (C 12 H 16 The product (N2O7) weighed 28.4 g and had a yield of 94.6%. The structural formula of the product is as follows.

[0047] Nuclear magnetic resonance hydrogen spectrum (C10) 12 H 16 N2O7DMSO-d6)

[0048] 11.13ppm (s, 2H, -NHC(O)NH-), 4.01ppm (q, 4H, -CCH2COOCH2CH3), 2.71ppm (s, 4H, -CCH2COOC2H5), 1.07ppm (t, 6H, -CCH2COOCH2CH3).

[0049] Carbon NMR (C10) 12 H 16 N2O7DMSO-d6)

[0050] 174.0ppm, 170.4ppm, 150.4ppm, 61.3ppm, 46.8ppm, 37.8ppm, 14.1ppm.

[0051] Elemental analysis (C 12 H 16 N2O7)

[0052] Theoretical values ​​(%): C: 48.00, H: 5.37, N: 9.33. Measured values ​​(%): C: 48.02, H: 5.36, N: 9.34.

[0053]

[0054] (III) Synthesis of barbituric acid derivatives containing carboxylic acid esters

[0055] In a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, 0.1 mol of 5,5-diacetate diethyl ester-2,4,6-trioxohexahydro pyrimidine, anhydrous K2CO3(0.1 mol), 1 g of tetrabutyl ammonium bromide and 80 mL of n-hexane were introduced, and 0.2 mol of ethyl chloroacetate was added dropwise. The reaction was carried out at reflux for 4 h, the stirring was stopped and the product was worked up to obtain 1,3,5,5-tetraacetate tetraethyl ester-2,4,6-trioxopyrimidine (C 20 H 28 N2O 11 ), mass 43.8 g, yield 92.8%, and the product had the following structure:

[0056]

[0057] NMR hydrogen spectrum (C 20 H 28 N2O 11 DMSO-d6)

[0058] 4.48 ppm (s, 4H, -NCH2COOC2H5), 4.15 ppm (q, 4H, -NCH2COOCH2CH3), 4.01 ppm (q, 4H, -CCH2COOCH2CH3), 2.71 ppm (s, 4H, -CCH2COO-), 1.21 ppm (t, 6H, -NCH2COOCH2CH3), 1.07 ppm (t, 6H, -CCH2COOCH2CH3).

[0059] NMR carbon spectrum (C 20 H 28 N2O 11 DMSO-d6)

[0060] 178.2 ppm, 170.4 ppm, 167.5 ppm, 150.7 ppm, 61.3 ppm, 61.0 ppm, 45.7 ppm, 41.8 ppm, 38.4 ppm, 14.1 ppm.

[0061] Elemental analysis (C 20 H 28 N2O 11 )

[0062] Theoretical values (%): C: 50.85, H: 5.97, N: 5.93. Found (%): C: 50.86, H: 5.95, N: 5.95.

[0063] (Hydrolysis of barbituric acid derivatives containing carboxylic acid esters

[0064] In a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, 0.1 mol of 1,3,5,5-tetraethyl-2,4,6-trioxopyrimidine tetraacetate was added, 150 mL of 20% sodium hydroxide solution was added, stirred at 60°C for 5 h, the pH was adjusted to 4-5 with acid, filtered, dried in a vacuum drying oven at 65°C for 4 h to obtain 1,3,5,5-tetraacetic acid-2,4,6-trioxopyrimidine (C 12 H 12 N2O 11 ), mass 32.3 g, yield 89.6%, the product structure is as follows:

[0065]

[0066] NMR hydrogen spectrum (C 12 H 12 N2O 11 DMSO-d6)

[0067] 13.51 ppm (s, 2H, -CCH2COOH), 13.03 ppm (s, 2H, -NCH2COOH), 4.46 ppm (s, 4H, -NCH2COOH), 2.69 ppm (s, 4H, -CCH2COOH).

[0068] NMR carbon spectrum (C 12 H 12 N2O 11 DMSO-d6)

[0069] 178.2 ppm, 177.3 ppm, 169.0 ppm, 150.7 ppm, 45.1 ppm, 41.2 ppm, 40.6 ppm.

[0070] Elemental analysis (C 12 H2N2O 11 )

[0071] Theoretical value (%): C: 40.01, H: 3.36, N: 7.78. Measured value (%): C: 40.02, H: 3.37, N: 7.76.

[0072] Example 2

[0073] (I) Synthesis of tetraacetate

[0074] In a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, 0.1 mol of dimethyl malonate, anhydrous K2CO2(0.1 mol), 1 g of tetrabutyl ammonium bromide and 80 mL of n-hexane were introduced. 0.2 mol of ethyl chloroacetate was added dropwise and the reaction was carried out at reflux for 4 h. The stirring was stopped and the product was obtained after work-up. It was 3,3-dimethyl malonate-1,5-pentanedioic acid diethyl ester (C 13 H 20 O8, Mr = 304.12 g / mol), mass 27.8 g, yield 91.5%, product structure as follows:

[0075]

[0076] (ii) Synthesis of 2-thiobarbituric acid derivatives

[0077] In a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, 80 mL of ethanol, 0.1 mol of sodium ethoxide (6.8 g) were introduced. 0.11 mol of thiourea (8.4 g) and 0.1 mol of 3,3-dimethyl malonate-1,5-pentanedioic acid diethyl ester were added. The reaction was carried out at 80°C for 3 h. The reaction was quenched with saturated aqueous NaHC03solution and extracted with ethyl acetate. The organic phases were combined, washed with saturated brine, dried over anhydrous Na2S04, filtered and evaporated to give the product 5,5-diethyl acetate-2-thio-4,6-dioxohexahydro pyrimidine (C 12 H 16 N2O6S), mass 29.7 g, yield 93.8%, product structure as follows:

[0078]

[0079] NMR hydrogen spectrum (C 12 H 16 N2O6S, DMSO-d6)

[0080] 13.89 ppm (s, 2H, -NHC(S)NH-), 4.01 ppm (q, 4H, -CCH2COOCH2CH3), 2.71 ppm (s, 4H, -CCH2COOC2H5), 1.07 ppm (t, 6H, -CCH2COOCH2CH3).

[0081] NMR carbon spectrum (C 12 H 16 N2O6S, DMSO-d6)

[0082] 177.9 ppm, 176.0 ppm, 170.4 ppm, 61.3 ppm, 46.5 ppm, 37.8 ppm, 14.1 ppm.

[0083] Elemental analysis (C12 H 16 N2O6S)

[0084] Theoretical value (%): C: 49.17, H: 5.78, N: 5.73, S: 6.56. Found (%): C: 49.16, H: 5.79, N: 5.71, S: 6.57.

[0085] (III) Synthesis of 2-thiobarbituric acid derivatives containing carboxylic acid ester

[0086] In a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, 0.1 mol of 5,5-diethyl-2-thioxo-4,6-dioxohexahydropyrimidine, anhydrous K2CO3 (0.1 mol), 1 g of tetrabutylammonium bromide and 80 mL of n-hexane were added, and 0.2 mol of ethyl chloroacetate was added dropwise. The reaction was carried out under reflux for 4 h, the stirring was stopped, and the product was obtained by post-treatment. The yield was 44.7 g of 1,3,5,5-tetraethyl-2-thioxo-4,6-dioxopyrimidine (C20H28N2O10S) with a yield of 91.6%, and the structural formula of the product is as follows:

[0087]

[0088] NMR of hydrogen (C20H28N2O10S, DMSO-d6)

[0089] 4.77 ppm (s, 4H, -NCH2COOC2H5), 4.15 ppm (q, 4H, -NCH2COOCH2CH3), 4.01 ppm (q, 4H, -CCH2COOCH2CH3), 2.71 ppm (s, 4H, -CCH2COOCH2CH3), 1.21 ppm (t, 6H, -NCH2COOCH2CH3), 1.07 ppm (t, 6H, -CCH2COOCH2CH3).

[0090] NMR of carbon (C20H28N2O10S, DMSO-d6)

[0091] 180.2 ppm, 172.5 ppm, 170.4 ppm, 167.5 ppm, 61.3 ppm, 61.0 ppm, 50.8 ppm, 41.5 ppm, 38.4 ppm, 14.1 ppm.

[0092] Elemental analysis (C20H28N2O10S)

[0093] Theoretical value (%): C: 49.17, H: 5.78, N: 5.73, S: 6.56. Found (%): C: 49.16, H: 5.79, N: 5.71, S: 6.57.

[0094] Hydrolysis of 2-thiobarbituric acid derivatives containing carboxylate ester

[0095] In a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, 0.1 mol of 1,3,5,5-tetraethyl-2-thioxo-4,6-dioxopyrimidine tetraacetate was added into 150 mL of 20% by mass sodium hydroxide solution, stirred at 60°C for 5 h, the pH was adjusted to 4-5 with acid, filtered to obtain 1,3,5,5-tetraacetic acid-2-thioxo-4,6-dioxopyrimidine (C12H12N2O10S), mass 34.2 g, yield 90.9%, the product structure is as follows:

[0096]

[0097] NMR of hydrogen (C12H12N2O10S, DMSO-d6)

[0098] 13.51 ppm (s, 2H, -CCH2COOH), 13.03 ppm (s, 2H, -NCH2COOH), 4.75 ppm (s, 4H, -NCH2COOH), 2.69 ppm (s, 4H, -CCH2COOH).

[0099] NMR of carbon (C12H12N2O10S, DMSO-d6)

[0100] 180.2 ppm, 177.3 ppm, 172.5 ppm, 169.0 ppm, 53.0 ppm, 40.9 ppm, 40.6 ppm.

[0101] Elemental analysis (C12H12N2O10S)

[0102] Theoretical value (%): C: 38.30, H: 3.21, N: 7.44, S: 8.52. Measured value (%): C: 38.32, H: 3.20, N: 7.43, S: 8.55.

[0103] Example 3

[0104] (I) Synthesis of tricarboxylic acid ester

[0105] In a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, 0.1 mol of 2-ethylmalonic acid dimethyl ester, anhydrous K2CO3 (0.1 mol), 1 g of tetrabutylammonium bromide and 80 mL of n-hexane were added, 0.105 mol of ethyl chloroacetate was added dropwise, and the reaction was carried out at reflux for 3 h, the stirring was stopped, and the product was obtained after work-up as 3,3-dimethyl-1-pentanoic acid ethyl ester (C 11 H 18O6), mass 23.0 g, yield 92.7%, product structure as follows:

[0106]

[0107] NMR hydrogen spectrum (CDC13, 300 MHz) 11 H 18 O6)

[0108] 4.01 ppm (q, 2H, -CCH2COOCH2CH3), 3.66 ppm (s, 6H, -CCOOCH3), 2.93 ppm (s, 2H, -CCH2COOC2H5), 2.25 ppm (q, 2H, -CCH2CH3), 1.07 ppm (t, 3H, -CCH2COOCH2CH3), 0.71 ppm (t, 3H, -CCH2CH3).

[0109] NMR carbon spectrum (CDC13, 75.5 MHz) 11 H 18 O6)

[0110] 171.1 ppm, 170.4 ppm, 61.3 ppm, 52.2 ppm, 50.2 ppm, 37.5 ppm, 28.2 ppm, 14.1 ppm, 8.2 ppm.

[0111] Elemental analysis (C 11 H 18 O6)

[0112] Theoretical value (%): C: 53.65, H: 7.37. Measured value (%): C: 53.63, H: 7.38.

[0113] (B) Synthesis of barbituric acid

[0114] In a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, 80 mL of ethanol, 0.1 mol of sodium ethoxide (6.8 g), 0.11 mol of urea (6.6 g), 0.1 mol of 3,3-dimethyl-1-pentane dicarboxylic acid dimethyl ester were added, and the reaction was carried out at 80°C for 6 h, cooled to room temperature, quenched with saturated aqueous sodium bicarbonate solution, extracted with ethyl acetate, the organic phases were combined, washed with saturated brine, dried over anhydrous sodium sulfate, filtered, and the ethyl acetate was removed by rotary evaporation to obtain the product 5-ethyl-5-ethyl acetate-2,4,6-trioxohexahydropyrimidine (C 10 H 14 N2O5), mass 23.0 g, yield 92.7%, product structure as follows:

[0115]

[0116] NMR hydrogen spectrum (CDC13, 300 MHz) 10H 14 N2O5, DMSO-d6)

[0117] 11.13 ppm (s, 2H, -NHC(O)NH-), 4.01 ppm (q, 2H, -CCH2COOCH2CH3), 2.71 ppm (s, 2H, -CCH2COOC2H5), 2.03 ppm (q, 2H, -CCH2CH3), 1.07 ppm (t, 3H, -CCH2COOCH2CH3), 0.71 ppm (t, 3H, -CCH2CH3).

[0118] NMR carbon spectrum (C 10 H 14 N2O5, DMSO-d6)

[0119] 174.0 ppm, 170.4 ppm, 150.4 ppm, 61.3 ppm, 53.9 ppm, 38.1 ppm, 28.8 ppm, 14.1 ppm, 7.4 ppm.

[0120] Elemental analysis (C 10 H 14 N2O5)

[0121] Theoretical value (%): C: 49.58, H: 5.83, N: 11.56. Measured value (%): C: 49.57, H: 5.84, N: 11.57.

[0122] (III) Synthesis of barbituric acid derivatives containing carboxylic acid ester

[0123] Into a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, 0.1 mol of 5-ethyl-5-ethyl acetate-2,4,6-trioxohexahydro pyrimidine, anhydrous K2CO3 (0.1 mol), 1 g of tetrabutylammonium bromide and 80 mL of n-hexane were added, and 0.2 mol of ethyl chloroacetate was added dropwise. The reaction was carried out under reflux for 4 h, the stirring was stopped, and the product was obtained after work-up. The product was 5-ethyl-1,3,5-triethyl acetate-2,4,6-trioxopyrimidine (C 18 H 26 N2O9, mass 37.7 g, yield 91.2%, and the product structure is as follows:

[0124]

[0125] NMR hydrogen spectrum (C 18 H 26 N2O9, DMSO-d6)

[0126] 4.48ppm (s, 4H, -NCH2COO-), 4.15ppm (q, 4H, -NCH2COOCH2CH3), 4.01ppm (q, 2H, -CCH2COOCH2CH3), 2.71ppm (s, 2H, -CCH2COOC2H5), 2.03ppm (q, 2H, -CCH2CH3), 1.21ppm (t, 6H, -NCH2COOCH2CH3), 1.07ppm (t, 3H, -CCH2COOCH2CH3), 0.71ppm (t, 3H, -CCH2CH3).

[0127] NMR carbon spectrum (C 18 H 26 N2O9, DMSO-d6)

[0128] 178.2ppm, 170.4ppm, 167.5ppm, 150.7ppm, 61.3ppm, 61.0ppm, 48.9ppm, 45.7ppm, 38.7ppm, 29.4ppm, 14.1ppm, 7.4ppm.

[0129] Elemental analysis (C 18 H 26 N2O9)

[0130] Theoretical value (%): C: 52.17, H: 6.32, N: 6.76. Measured value (%): C: 52.18, H: 6.30, N: 6.77.

[0131] (Four) Hydrolysis of barbituric acid derivatives containing carboxylate

[0132] In a 250 mL four-necked flask equipped with a stirrer, thermometer and reflux condenser, 0.1 mol of 5-ethyl-1, 3, 5-triethyl triethyl 2, 4, 6-trioxo pyrimidine acetate was added, 150 mL of 20% sodium hydroxide solution was added, stirred at 80°C for 5h, the pH was adjusted to 4-5 with acid, filtered to obtain 5-ethyl-1, 3, 5-triethyl 2, 4, 6-trioxo pyrimidine acetate (C 12 H 14 N2O9), mass 30.1 g, yield 91.3%, the product structure is as follows:

[0133]

[0134] NMR hydrogen spectrum (C 12 H 14 N2O9, DMSO-d6)

[0135] 13.51 ppm (s, 1H, -CCH2COOH), 13.03 ppm (s, 2H, -NCH2COOH), 4.46 ppm (s, 4H, -NCH2COOH), 2.69 ppm (s, 2H, -CCH2COOH), 2.03 ppm (q, 2H, -CCH2CH3), 0.71 ppm (t, 3H, -CCH2COOH).

[0136] Carbon magnetic resonance spectrum (C 12 H 14 N2O9, DMSO-d6)

[0137] 178.2 ppm, 177.3 ppm, 169.0 ppm, 150.7 ppm, 48.6 ppm, 45.1 ppm, 40.9 ppm, 29.4 ppm, 7.4 ppm.

[0138] Elemental analysis (C 12 H 14 N2O9)

[0139] Theoretical value (%): C: 43.64, H: 4.27, N: 8.48. Measured value (%): C: 43.62, H: 4.28, N: 8.50.

[0140] Example 4

[0141] (I) Synthesis of Tricarboxylic Acid Ester

[0142] Into a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, 0.1 mol of 2-cyclohexylmalonic acid dimethyl ester, anhydrous K2CO3 (0.1 mol), 1 g of tetrabutylammonium bromide and 60 mL of n-hexane were added, and 0.105 mol of methyl chloroacetate was added dropwise. The reaction was carried out under reflux for 3 h, the stirring was stopped, and the product was obtained by post-treatment. The product was 2-cyclohexyl-2-methyl carboxylate-malonate (C 14 H 22 O6), product mass 26.6 g, yield 92.9%, and the reaction equation is as follows:

[0143]

[0144] Proton magnetic resonance spectrum (H 14 H 22 O6, CDC13)

[0145] 3.66ppm (s, 6H, -CCOOCH3), 3.61ppm (s, 3H, -CCH2COOCH3), 2.93ppm (s, 2H, -CCH2COOCH3), 2.60ppm (m, IH, cyclohexane), 1.62ppm (m, 2H, cyclohexane), 1.53ppm (m, 2H, cyclohexane), 1.46ppm (m, IH, cyclohexane), 1.44ppm (m, IH, cyclohexane), 1.43ppm (m, 2H, cyclohexane), 1.38ppm (m, 2H, cyclohexane).

[0146] NMR carbon spectrum (C 14 H 22 O6, CDCl3)

[0147] 171.1ppm, 170.4ppm, 61.3ppm, 52.9ppm, 52.2ppm, 36.6ppm, 35.6ppm, 26.0ppm, 25.8ppm, 14.1ppm.

[0148] Elemental analysis (C 14 H 22 O6)

[0149] Theoretical value (%): C: 58.73, H: 7.74. Measured value (%): C: 58.75, H: 7.76.

[0150] (B) Synthesis of barbituric acid

[0151] In a 250 mL four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, 80 mL of t-butyl alcohol was added, 0.1 mol of potassium t-butoxide (11.2 g) was added, 0.11 mol of urea (6.6 g) was added, 0.1 mol of 2-cyclohexyl-2-methyl formate-dimethyl succinate was added, and the reaction was carried out at 80°C for 3 h, and then cooled to room temperature. The reaction was quenched with saturated aqueous sodium bicarbonate solution, extracted with ethyl acetate, the organic phases were combined, washed with saturated brine, dried over anhydrous sodium sulfate, filtered, and rotary evaporated to obtain the product 5-cyclohexyl-5-methyl formate-2,4,6-trioxohexahydropyrimidine (C 11 H 18 N2O5), mass 25.9 g, yield 91.7%, and the product has the following structural formula:

[0152]

[0153] NMR hydrogen spectrum (C 13 H 18 N2O5, DMSO-d6)

[0154] 11.13 ppm (s, 2H, -NHC(O)NH-), 3.63 ppm (s, 3H, -CCH2COOCH3), 2.71 ppm (s, 2H, -CCH2COOCH3), 1.94 ppm (m, 1H, cyclohexane), 1.62 ppm (m, 2H, cyclohexane), 1.53 ppm (m, 2H, cyclohexane), 1.46 ppm (m, 1H, cyclohexane), 1.44 ppm (m, 1H, cyclohexane), 1.43 ppm (m, 2H, cyclohexane), 1.38 ppm (m, 2H, cyclohexane).

[0155] NMR carbon spectrum (C 13 H 18 N2O5, DMSO-d6)

[0156] 174.0 ppm, 170.4 ppm, 150.4 ppm, 61.3 ppm, 56.6 ppm, 37.2 ppm, 36.2 ppm, 26.0 ppm, 24.6 ppm, 14.1 ppm.

[0157] Elemental analysis (C 13 H 18 N2O5)

[0158] Theoretical value (%): C: 55.31, H: 6.43, N: 9.92. Measured value (%): C: 55.33, H: 6.42, N: 9.94.

[0159] (III) Synthesis of barbituric acid derivatives containing carboxylic acid ester

[0160] Into a 250 mL four-necked flask equipped with a stirrer, thermometer, reflux condenser, 0.1 mol of 5-cyclohexyl-5-methyl acetate-2,4,6-trioxohexahydro pyrimidine, anhydrous K2CO3 (0.1 mol), 1 g of tetrabutylammonium bromide and 80 mL of n-hexane were added, and 0.205 mol of methyl chloroacetate was added dropwise. The reaction was carried out under reflux for 4 h, the stirring was stopped, and the product was obtained after work-up. The product was 5-cyclohexyl-1,3,5-trimethyl acetate-2,4,6-trioxohexahydro pyrimidine (C 19 H 26 N2O9), mass 39.4 g, yield 92.4%, and the product had the following structural formula:

[0161]

[0162] NMR hydrogen spectrum (C 19 H 26 N2O9, DMSO-d6)

[0163] 4.15ppm (s, 4H, -NCH2COOCH3), 3.95ppm (s, 2H, -CCH2COOCH3), 3.67ppm (s, 6H, -NCH2COOCH3), 3.61ppm (s, 3H, -CCH2COOCH3), 1.94ppm (m, IH, cyclohexane), 1.62ppm (m, 2H, cyclohexane), 1.53ppm (m, 2H, cyclohexane), 1.46ppm (m, IH, cyclohexane), 1.44ppm (m, IH, cyclohexane), 1.43ppm (m, 2H, cyclohexane), 1.38ppm (m, 2H, cyclohexane).

[0164] NMR carbon spectrum (CDC13, 100MHz) 19 H 26 N2O9, DMSO-d6

[0165] 178.2ppm, 170.4ppm, 167.5ppm, 150.7ppm, 61.3ppm, 61.0ppm, 51.6ppm, 45.7ppm, 37.8ppm, 36.8ppm, 25.0ppm, 24.6ppm, 14.1ppm.

[0166] Elemental analysis (C 19 H 26 N2O9

[0167] Theoretical value (%): C: 53.52, H: 6.15, N: 6.57. Measured value (%): C: 53.55, H: 6.13, N: 6.59.

[0168] (IV) Hydrolysis of barbituric acid derivatives containing carboxylate

[0169] Into a 250ml four-necked flask equipped with a stirrer, thermometer and reflux condenser, 0.1mol of 5-cyclohexyl-1,3,5-trimethyl-2,4,6-trioxohexahydropyrimidine trimethyl carboxylate was added, 150ml of 20% sodium hydroxide solution was added, stirred at 85°C for 5h, the pH was adjusted to 4-5 with acid, filtered to obtain 5-cyclohexyl-1,3,5-tricarboxylic acid-2,4,6-trioxopyrimidine (C 16 H 20 N2O9), product mass 35.3g, yield 91.9%, product structure as follows:

[0170]

[0171] NMR hydrogen spectrum (CDC13, 400MHz) 16 H 20 N2O9, DMSO-d6

[0172] 13.51 ppm (s, 1H, -CCH2COOH), 13.03 ppm (s, 2H, -NCH2COOH), 4.46 ppm (s, 4H, -NCH2COOH), 2.69 ppm (s, 2H, -CCH2COOH), 1.94 ppm (m, 1H, cyclohexane), 1.62 ppm (m, 2H, cyclohexane), 1.53 ppm (m, 2H, cyclohexane), 1.46 ppm (m, 1H, cyclohexane), 1.44 ppm (m, 1H, cyclohexane), 1.43 ppm (m, 2H, cyclohexane), 1.38 ppm (m, 2H, cyclohexane).

[0173] NMR carbon spectrum (C 16 H 20 N2O9, DMSO-d6)

[0174] 178.2 ppm, 177.3 ppm, 169.0 ppm, 150.7 ppm, 51.3 ppm, 45.1 ppm, 39.0 ppm, 37.8 ppm, 26.0 ppm, 25.0 ppm, 24.6 ppm.

[0175] Elemental analysis (C 16 H 20 N2O9)

[0176] Theoretical value (%): C: 50.00, H: 5.25, N: 7.29. Measured value (%): C: 50.02, H: 5.28, N: 7.27.

[0177] Different raw materials were used to prepare multifunctional high-absorption chrome tanning auxiliaries containing barbituric acid structure. Examples 1-4 are summarized in Table 1.

[0178] Table 1 Multifunctional high-absorption chrome tanning auxiliaries containing barbituric acid structure

[0179]

Claims

1. A multifunctional, high-absorption chrome tanning agent containing a barbituric acid structure, characterized in that, The molecular structure of the adjuvant is as follows: Where X is O or S, R1 = H, CH3, C2H5, R2 = H, CH3, C2H5, C3H5, C3H7, C4H9, C5H9, C6H5, C6H 11 , C7H7, Cl, Br.

2. A method for preparing the multifunctional, high-absorption chromium tanning agent containing a barbituric acid structure as described in claim 1, characterized in that, Includes the following steps: (1) C-alkylation reaction Using malonate diester and halocarboxylic acid ester as raw materials, and an inorganic base as an alkali, the reaction was carried out in an organic solvent at 60-100℃ for 6-12 h under the condition of a phase transfer catalyst to obtain carboxylic acid ester compound A. The molar ratio of malonate diester to halocarboxylic acid ester was 1:(1.0-2.05), and the molar ratio of malonate diester to alkali and phase transfer catalyst was 1:(0.2-0.4):(0.02-0.06). (2) Cyclic reaction Using carboxylic acid ester compound A and urea or thiourea as raw materials, and catalyzed by an inorganic or organic base, the reaction is carried out in an organic solvent at 80-100℃ for 4-6 hours to obtain barbiturate derivatives or 2-thiobarbituric acid derivative B; the molar ratio of carboxylic acid ester compound A to urea or thiourea is 1:(0.95-1.05), and the molar ratio of carboxylic acid ester compound A to organic or inorganic base is 1:(0.1-0.3); (3) N-alkylation reaction Using barbituric acid derivatives or 2-thiobarbituric acid derivative B and halocarboxylic acid esters as raw materials, and an inorganic base as an alkali, the reaction is carried out in an organic solvent at 60-100℃ under the catalytic conditions of a phase transfer catalyst to prepare barbituric acid derivatives containing polycarboxylic acid esters or 2-thiobarbituric acid derivative C containing polycarboxylic acid esters; the molar ratio of barbituric acid derivatives or 2-thiobarbituric acid derivative B to halocarboxylic acid esters is 1:(1.0-2.05), and the molar ratio of barbituric acid derivatives or 2-thiobarbituric acid derivative B to alkali and phase transfer catalyst is 1:(0.5-1.2):(0.02-0.06); (4) Hydrolysis reaction A barbituric acid derivative containing a polycarboxylic acid ester or a 2-thiobarbituric acid derivative C containing a polycarboxylic acid ester is hydrolyzed at 70-100℃ for 4-12 hours under alkaline conditions, cooled to room temperature, and the pH is adjusted to 4-5 with acid to precipitate a solid. The solid is then filtered to obtain a high-absorption chrome tanning auxiliary agent. The alkaline solution used under the alkaline conditions is a 10%-20% sodium hydroxide or potassium hydroxide solution by mass. The acid is one of a 5%-15% hydrochloric acid solution, sulfuric acid solution, or phosphoric acid solution by mass.

3. The method for preparing the barbituric acid-containing multifunctional high-absorption chromium tanning aid according to claim 2, characterized in that: In step (1), the malonate diester compound is dimethyl malonate, 2-methyl dimethyl malonate, 2-propyl dimethyl malonate, 2-butyl dimethyl malonate, 2-isobutyl dimethyl malonate, 2-allyl dimethyl malonate, 2-cyclopentyl dimethyl malonate, 2-fluoromalonate, 2-chloromalonate, 2-bromomalonate, diethyl malonate, 2-methyl diethyl malonate, 2- One of the following: diethyl propyl malonate, diethyl 2-butyl malonate, diethyl 2-isobutyl malonate, diethyl 2-allyl malonate, diethyl 2-cyclopentyl malonate, diethyl 2-fluoromalonate, diethyl 2-chloromalonate, diethyl 2-bromomalonate, dipropyl malonate, diisopropyl malonate, dibutyl malonate, di-tert-butyl malonate, dihexyl malonate, diethyl phenyl malonate, and diethyl benzyl malonate.

4. The method for preparing the multifunctional, high-absorption chromium tanning agent containing a barbituric acid structure according to claim 2, characterized in that: In step (1), the halocarboxylic acid ester is one of methyl chloroacetate, ethyl chloroacetate, butyl chloroacetate, tert-butyl chloroacetate, ethyl bromoacetate, butyl bromoacetate, tert-butyl bromoacetate, methyl 2-chloropropionate, ethyl 2-chloropropionate, methyl 2-bromopropionate, ethyl 2-bromopropionate, methyl 2-chlorobutyrate, ethyl 2-chlorobutyrate, methyl 2-bromobutyrate, and ethyl 2-bromobutyrate; the inorganic base is one of anhydrous potassium carbonate, anhydrous sodium carbonate, potassium phosphate, and sodium phosphate; the phase transfer catalyst is one of tetrabutylammonium bromide, tetrabutylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, and tetradecyltrimethylammonium bromide; and the organic solvent is one of petroleum ether, cyclohexane, n-hexane, ethyl acetate, and 1,4-dioxane.

5. The method for preparing the barbituric acid-containing multifunctional high-absorption chromium tanning aid according to claim 2, characterized in that: In step (2), the inorganic base is one of sodium hydroxide or potassium hydroxide; the organic base is one of sodium ethoxide, sodium methoxide, sodium tert-butoxide, or potassium tert-butoxide; and the organic solvent is one of methanol, ethanol, isopropanol, n-butanol, or tert-butanol.

6. The method for preparing the multifunctional, high-absorption chromium tanning aid containing a barbituric acid structure according to claim 2, characterized in that: In step (3), the halocarboxylic acid ester is one of methyl chloroacetate, ethyl chloroacetate, butyl chloroacetate, tert-butyl chloroacetate, ethyl bromoacetate, butyl bromoacetate, tert-butyl bromoacetate, methyl 2-chloropropionate, ethyl 2-chloropropionate, methyl 2-bromopropionate, ethyl 2-bromopropionate, methyl 2-chlorobutyrate, ethyl 2-chlorobutyrate, methyl 2-bromobutyrate, and ethyl 2-bromobutyrate; the inorganic base is one of anhydrous potassium carbonate, anhydrous sodium carbonate, potassium phosphate, and sodium phosphate; the phase transfer catalyst is one of tetrabutylammonium bromide, tetrabutylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, and tetradecyltrimethylammonium bromide; and the organic solvent is one of ethyl acetate, 1,4-dioxane, methanol, ethanol, and n-butanol.

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