Preparation of quaternary ammonium base and its application in dye synthesis

Abstract

The application provides a preparation method of quaternary ammonium base and application thereof in dye synthesis. Propylene oxide is added into trimethylamine, nucleophilic ring-opening addition reaction of trimethylamine to the epoxy group of propylene oxide is carried out, hydroxypropyltrimethylammonium hydroxide is obtained, then the hydroxypropyltrimethylammonium hydroxide is used to replace sodium hydroxide in the dye synthesis process, inorganic salt is not introduced into the reaction system, and after the reaction is completed, multiple water washing and salt removal are not needed, so that the wastewater amount and salt load can be obviously reduced.

Description

Technical Field

[0001] This application relates to the field of dye synthesis technology, specifically to a method for preparing a quaternary ammonium base and its application in dye synthesis. Background Technology

[0002] Direct dyes are a class of dyes that can directly color cellulosic fibers by heating and boiling in neutral or weakly alkaline media without the need for mordants. They bind to the fibers through hydrogen bonds and van der Waals forces and are widely used in cotton spinning, silk, leather, papermaking, knitting, yarn and ribbon, wool and linen industries. Direct dyes can be classified according to their chemical structure into azo and stilbene types, and according to their application performance into ordinary direct dyes, direct lightfast dyes, and direct azo dyes. Direct dyes have a complete color spectrum from yellow to black, and their production process is simple and cost-effective.

[0003] The traditional process for producing Direct Yellow R (Yellow 11) dye typically involves the self-condensation reaction of p-nitrotoluene-o-sulfonic acid in the presence of sodium hydroxide. After acidification, the condensation solution is then extracted with trialkylamine and back-extracted with diethanolamine to obtain the finished dye. This process is complex and generates a large amount of saline wastewater, which is difficult to treat and has a heavy environmental burden, making it difficult to meet current requirements for clean production and pollution control.

[0004] To reduce wastewater discharge, existing technologies (such as the invention patent with publication number CN 118638434 B) propose using choline hydroxide instead of sodium hydroxide in the synthesis of Direct Yellow 11 dye to reduce the introduction of inorganic salts. However, during the preparation and use of choline hydroxide, ethoxylated organic byproducts are easily generated. These byproducts are usually deep yellow, poorly soluble, and tend to precipitate or form precipitates during subsequent dye synthesis or finished product storage. This not only reduces the reaction yield but also affects the appearance quality, solution stability, and storage stability of the obtained Direct Yellow 11 dye.

[0005] Therefore, how to effectively reduce wastewater and pollution emissions while avoiding the introduction of unstable components that are prone to precipitation during storage during the preparation of direct dyes such as Direct Yellow 11, so as to obtain direct dye products with high yield, stable composition and suitable for a certain storage period, remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This application provides a method for preparing a quaternary ammonium base and its application in dye synthesis. The quaternary ammonium base has a high synthesis yield, no dark-colored byproducts, and is suitable for dye synthesis. The dye will not precipitate or settle after being stored for a long time.

[0007] In a first aspect, this application provides a method for preparing a quaternary ammonium base, the method comprising the following steps: Propylene oxide is added to trimethylamine, causing trimethylamine to undergo a ring-opening addition reaction with the epoxy group of propylene oxide, yielding hydroxypropyltrimethylamine hydroxide as a quaternary ammonium base.

[0008] In existing technologies, choline hydroxide (hydroxyethyltrimethylammonium hydroxide) is typically synthesized from ethylene oxide and trimethylamine as a quaternary ammonium base. Ethylene oxide has a simple molecular structure, high symmetry, and large ring strain, resulting in extremely high reactivity. After undergoing a ring-opening quaternization reaction with trimethylamine to generate choline hydroxide, the hydroxyl groups in the product molecules still have strong nucleophilicity, easily attacking excess or residual ethylene oxide, thus causing continuous ethoxylation reactions and generating quaternary ammonium salt byproducts containing ethoxy groups. Such side reactions are difficult to avoid by adjusting the feed ratio or reaction conditions, leading to complex product structures, wide molecular weight distribution, darker color, and easy generation of insoluble impurities, directly affecting subsequent dye synthesis. Compared with the method of preparing choline hydroxide using ethylene oxide, this application uses the reaction of propylene oxide with trimethylamine to prepare hydroxypropyltrimethylamine hydroxide. In the reaction, the nitrogen atom of trimethylamine has a lone pair of electrons, which attacks the epoxy bond of propylene oxide, causing it to open the ring and forming a product with hydroxyl and quaternary ammonium structure - hydroxypropyltrimethylamine hydroxide. The introduction of methyl substituents on the carbon atom of the epoxy group reduces the electropositivity of the epoxy group and increases the steric hindrance, thus making its ring-opening quaternization reaction with trimethylamine more moderate. At the same time, the ortho-methyl substitution of the hydroxyl group in the generated hydroxypropyltrimethylamine hydroxide has a significant inhibitory effect on the nucleophilicity of the hydroxyl group, reducing its ability to further attack the remaining epoxy compound. From the reaction mechanism, this effectively inhibits the occurrence of continuous alkoxylation side reactions, thus significantly reducing the formation of by-products and obtaining a target product with a simpler structure and better stability.

[0009] In some embodiments, a method for preparing a quaternary ammonium base includes the following steps: The trimethylamine aqueous solution was cooled to 5°C, propylene oxide was added to the trimethylamine solution, the temperature was raised to 20-30°C, and the reaction was carried out for 3-6 hours to obtain hydroxypropyltrimethylamine hydroxide. The mass concentration of the trimethylamine aqueous solution was 30%-50%.

[0010] The above methods specifically illustrate the reaction conditions and dosage ratios for each step in the preparation of quaternary ammonium bases. Under these conditions, quaternary ammonium base hydroxypropyltrimethylamine can be obtained. In aqueous solutions of trimethylamine within this concentration range, trimethylamine is fully soluble in water in its molecular state, exhibiting high relative activity. This allows it to effectively attack propylene oxide, achieving a rapid and uniform ring-opening quaternization reaction. Simultaneously, water, as a continuous phase, can significantly absorb the exothermic reaction, reducing the risk of side reactions caused by local overheating and instantaneous high concentrations.

[0011] In some embodiments, the molar ratio of the trimethylamine to the propylene oxide is 1:1.03 to 1.05.

[0012] In some of the methods mentioned above, the molar ratio of trimethylamine to propylene oxide is controlled within the range of 1:1.03 to 1.05. The reason for the slight excess of propylene oxide is that trimethylamine, as a strong nucleophile, has a strong odor and is volatile. If it is in excess or not completely consumed, it is very easy to leave residues in the finished product and significantly affect the product's odor and safety. By making the propylene oxide slightly excess, it can be ensured that trimethylamine is quantitatively converted into a quaternary ammonium base, avoiding amine residues. Moreover, the main side reaction of propylene oxide is ring-opening hydrolysis with water in the system to generate propylene glycol. This process does not introduce new reactive functional groups and will not participate in subsequent quaternization or trigger continuous alkoxylation. Therefore, it has minimal impact on the product structure and stability.

[0013] Secondly, this application provides the application of the quaternary ammonium base prepared according to any embodiment of the first aspect in dye synthesis.

[0014] According to this application, hydroxypropyltrimethylamine hydroxide is used as a strong base in the synthesis process of direct dyes. In the production of anionic dyes, it can replace commonly used organic bases such as diethanolamine and triethanolamine. Although both are organic bases, hydroxypropyltrimethylamine hydroxide is a strong base, so the amount used will be less and the price will be lower. It can replace inorganic strong bases such as sodium hydroxide, potassium hydroxide, sodium ethoxide, and potassium ethoxide.

[0015] In the synthesis process of direct dyes using hydroxypropyltrimethylamine hydroxide as a strong base, it exhibits superior overall performance in terms of reaction stability and system controllability compared to choline hydroxide (hydroxyethyltrimethylammonium hydroxide) used in existing technologies. Because hydroxypropyltrimethylamine hydroxide introduces steric hindrance through ortho-alkyl substitution of hydroxyl groups in its molecular structure, it is less prone to further alkoxylation, intramolecular rearrangement, or degradation reactions under alkaline conditions. Therefore, it generates fewer organic byproducts that can associate, complex, or slowly react with azo intermediates or finished dyes during dye synthesis. Compared to choline hydroxide, this difference results in a more homogeneous reaction system composition, significantly reducing the potential unstable components in the obtained direct dye. Consequently, it is less prone to precipitation or color shift problems caused by slow component changes during storage, exhibiting better solution and storage stability. This makes it particularly suitable for liquid or water-soluble Direct Yellow 11 dye products requiring a certain storage period.

[0016] In some embodiments, the quaternary ammonium base prepared according to any embodiment of the first aspect is used to prepare Direct Yellow 11 liquid dye. In the traditional production process, Yellow 11 is produced by the self-condensation of p-nitrotoluene o-sulfonic acid and sodium hydroxide. The condensate is then acidified, extracted with trialkylamine, and back-extracted with diethanolamine. This process generates a large amount of wastewater that is extremely difficult to treat. However, by using hydroxypropyltrimethylamine hydroxide and p-nitrotoluene o-sulfonic acid in a one-pot process to produce a stable solution of Yellow 11, no wastewater is generated, and the dye product has strong stability.

[0017] In some embodiments, the method for preparing Direct Yellow 11 dye using quaternary ammonium bases includes the following steps: When p-nitrotoluene-o-sulfonic acid is added to hydroxypropyltrimethylamine hydroxide, the nitro group and toluene side chain in the p-nitrotoluene-o-sulfonic acid molecule undergo a base-catalyzed self-condensation and oxidative coupling reaction to form a molecular skeleton with an azo bond and a stilbene conjugated structure. At the same time, the sulfonate group formed by deprotonation of the sulfonic acid group forms an ion association with the 2-hydroxypropyltrimethylammonium cation, resulting in a mixed solution containing Yellow 11 dye. Hydrochloric acid was added to the mixed solution containing Yellow 11 dye to adjust the pH value to 6-8, resulting in a yellow transparent solution containing Yellow 11 dye.

[0018] In some of the above methods, under alkaline conditions, p-nitrotoluene-o-sulfonic acid can undergo condensation and coupling reactions to gradually form dye molecules with long conjugated structures, thereby exhibiting the characteristic absorption of Direct Yellow 11. Through experiments, the inventors discovered that the reaction process is more stable in the presence of hydroxypropyltrimethylamine hydroxide, and the resulting dye is better dispersed in aqueous solution. At the same time, the generated sulfonic acid anion and quaternary ammonium cation can form a stable ionic interaction, which enables the dye to maintain good solubility and dispersion stability in the aqueous phase. Subsequently, by adjusting the pH of the system to the neutral range, the resulting dye solution can be further stabilized, making it transparent and suitable for direct use.

[0019] It should be noted that the above reaction pathway is the inventor's understanding and speculation based on experimental results, and does not constitute a limitation on the scope of protection of this application.

[0020] In some embodiments, the method for preparing Direct Yellow 11 dye using quaternary ammonium bases includes the following steps: p-Nitrotoluene-o-sulfonic acid was added to an aqueous solution of hydroxypropyltrimethylamine hydroxide and reacted at a temperature of 65-75℃ for 4-6 hours to obtain a mixed solution containing Yellow 11 dye. Hydrochloric acid was added to the mixed solution containing Yellow 11 dye to adjust the pH value to 6-8, resulting in a yellow transparent solution containing Yellow 11 dye. The mass concentration of the aqueous solution of hydroxypropyltrimethylamine hydroxide is 45%~55%.

[0021] The above methods specifically illustrate the reaction conditions and dosage ratios for each step in the dye preparation process. Under these conditions, a transparent solution of Direct Yellow 11 dye can be obtained. The mass concentration of the aqueous solution of hydroxypropyltrimethylamine hydroxide is controlled within the range of 45% to 55%. The alkalinity of the system is conducive to the condensation reaction of p-nitrotoluene-o-sulfonic acid. Simultaneously, the system viscosity is suitable, facilitating uniform contact of reactants and heat release, and avoiding localized over-alkalinity or side reactions. Subsequent standardization with water is all that is needed to obtain a commercially viable dye. The molecular structural formulas of the main components in the dye are as follows:

[0022] Where X is the hydroxypropyltrimethylamine hydroxide cation.

[0023] In some embodiments, the molar ratio of p-nitrotoluene-o-sulfonic acid to hydroxypropyltrimethylamine hydroxide is 1:1.3~1.4.

[0024] In some of the above methods, maintaining a moderate excess of quaternary ammonium base can continuously provide a stable and sufficient effective alkalinity throughout the reaction process, avoiding incomplete condensation and oxidative coupling reactions due to insufficient base. At the same time, it ensures that the generated sulfonate ions can be fully paired with quaternary ammonium cations to form a stable ion-associated structure, thereby improving the transparency and storage stability of the dye solution. In addition, this excess range will not trigger significant side reactions, and the excess base can be directly neutralized by mild acidification after the reaction, without introducing inorganic salts, which is beneficial for obtaining a Yellow 11 liquid dye product with stable composition and consistent hue.

[0025] In some embodiments, the quaternary ammonium base is used to prepare Direct Orange 15 dye.

[0026] According to this application, p-nitrotoluene-o-sulfonic acid is added to an aqueous solution of hydroxypropyltrimethylamine hydroxide to obtain a stable solution of Yellow 11. The stable solution of Yellow 11 is then reduced by glucose monohydrate or thiourea dioxide to obtain a stable solution of Direct Orange 15.

[0027] In some embodiments, the quaternary ammonium base is used to prepare Direct Orange 39 dye.

[0028] According to this application, p-aminoazobenzene-4-sulfonic acid and 4,4'-dinitrostilbene-2,2'-disulfonic acid are added to an aqueous solution of hydroxypropyltrimethylamine hydroxide, and after reduction with glucose monohydrate, a stable Orange 39 stable solution can be generated.

[0029] Compared with the prior art, the beneficial effects of this application are at least as follows: This application synthesizes hydroxypropyltrimethylamine hydroxide as a quaternary ammonium base, which, compared with choline hydroxide, effectively inhibits the occurrence of continuous alkoxylation side reactions from the reaction mechanism. Therefore, it can significantly reduce the formation of by-products and obtain the target product with a simple structure and better stability. In the process of synthesizing Direct Yellow 11 dye, the hydroxypropyltrimethylamine hydroxide used in this application has higher structural stability and is less likely to generate dark, insoluble or semi-soluble ethoxylated byproducts during the reaction and post-processing. Compared with the existing technology using choline hydroxide, it can effectively reduce the possibility of such byproducts remaining in the finished dye, so that the obtained Direct Yellow 11 dye is less likely to precipitate or settle during storage, and has better solution stability and color stability, making it more suitable for Direct Yellow 11 dye products that require a certain storage period. It should be understood that although commercially available high-purity choline hydroxide can avoid byproduct residues in the preparation process, in the industrial production of liquid dyes such as Direct Yellow 11, this product can obtain a high-purity aqueous solution in a one-step reaction using propylene oxide and trimethylamine as raw materials, without the need for purification steps such as ion exchange or recrystallization. The raw material cost and process energy consumption are significantly lower than purchasing commercially available high-purity choline hydroxide. At the same time, the methyl substituent at the ortho position of the hydroxyl group in the hydroxypropyltrimethylamine hydroxide molecule gives it higher thermal stability, making it less prone to degradation or decomposition under the long-term reaction conditions of 65-75°C required for dye synthesis. No free trimethylamine escapes during the reaction, and the alkalinity remains constant, which is beneficial for batch reproducibility and improves the operating environment. Therefore, the quaternary ammonium base described in this application is superior to directly purchasing high-purity choline hydroxide in terms of economy, process stability, and production friendliness, and is more suitable for large-scale preparation of liquid dyes such as Direct Yellow 11. Attached Figure Description

[0030] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0031] Figure 1 The liquid chromatogram of the reaction product of propylene oxide and trimethylamine in Preparation Example 1; Figure 2 The liquid chromatogram of trimethylamine is shown. Figure 3 This is the liquid chromatogram of propylene oxide; Figure 4 The images show a comparison of the appearance of the reaction products of Preparation Example 1 (left) and Comparative Preparation Example 1 (right). Detailed Implementation

[0032] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0033] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0034] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0035] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0036] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0037] Preparation Example 1 Preparation of Quaternary Ammonium Bases A 40% (w / w) aqueous solution of trimethylamine was added to a low-temperature reactor and cooled to 5°C. Then, propylene oxide was slowly added dropwise to the trimethylamine aqueous solution, and the reaction temperature was kept below 30°C during the addition process. After the addition was completed, the temperature was controlled to 25°C and kept at that temperature for 5 hours. Then, an appropriate amount of water was added to adjust the solution to obtain a 50% (w / w) aqueous solution of hydroxypropyltrimethylamine hydroxide as a quaternary ammonium alkali solution. The molar ratio of trimethylamine to propylene oxide was 1:1.04.

[0038] The reaction products of trimethylamine and propylene oxide were determined by high-performance liquid chromatography-evaporative light scattering (HPLC-ELISA). Figures 1 to 3It is known that propylene oxide and trimethylamine are both small-molecule, low-boiling-point volatile organic compounds. In the drift tube of the evaporative light scattering detector, which reaches a temperature of up to 90°C, they will be completely evaporated along with the mobile phase and cannot form non-volatile particles that can be detected by light scattering. Therefore, when propylene oxide and trimethylamine are measured alone, there are no peaks on the chromatogram and the integral result is 0. The product of the reaction between trimethylamine and propylene oxide is a quaternary ammonium base, which is a typical non-volatile substance. In the same 90°C drift tube, after the solvent is evaporated, it still exists in the form of solid particles. When these particles pass through the light beam of the detector, they will produce light scattering and be recorded by the detector as chromatographic peaks.

[0039] At the same time, such as Figure 4 As shown in the left part, the reaction product of propylene oxide and trimethylamine is very light in color, and no precipitate was observed.

[0040] Preparation Example 2 Preparation of Quaternary Ammonium Bases The preparation method is largely the same as in Example 1, except that the molar ratio of trimethylamine to propylene oxide is 1:1.02.

[0041] Preparation Example 3 Preparation of Quaternary Ammonium Bases The preparation method is largely the same as in Example 1, except that the molar ratio of trimethylamine to propylene oxide is 1:1.06.

[0042] Comparative Preparation Example 1 Preparation of Quaternary Ammonium Bases The preparation method is largely the same as in Example 1, except that propylene oxide is replaced with ethylene oxide to prepare a 50% choline hydroxide aqueous solution as a quaternary ammonium base aqueous solution.

[0043] like Figure 4 As shown in the right part, compared to the product obtained in Preparation Example 1 ( Figure 4 (Left part) The solution after propylene oxide reacts with trimethylamine to synthesize choline hydroxide is yellow, and dark yellow solid suspensions can be clearly observed. This is because an excess of ethylene oxide needs to be added in order to consume all the trimethylamine, and the excess ethylene oxide will react with choline hydroxide to form ethoxy byproducts.

[0044] Example 1 Preparation of Direct Yellow 11 dye The quaternary ammonium base aqueous solution obtained in Preparation Example 1 was added to a reaction vessel, and then p-nitrotoluene-o-sulfonic acid was added. The temperature was raised to 70°C and the reaction was carried out for 5 hours to obtain a mixed solution containing Yellow 11 dye. Then, hydrochloric acid was added to adjust the pH value to 7 to obtain a yellow solution containing Yellow 11 dye. The quaternary ammonium base aqueous solution was a 50% (w / w) aqueous solution of hydroxypropyltrimethylamine hydroxide, and the molar ratio of p-nitrotoluene-o-sulfonic acid to hydroxypropyltrimethylamine hydroxide was 1:1.4. Example 2 Preparation of Direct Yellow 11 dye The preparation was largely the same as in Example 1, except that the aqueous solution of hydroxypropyltrimethylamine hydroxide prepared in Example 2 was used as a quaternary ammonium alkali solution.

[0045] Example 3 Preparation of Direct Yellow 11 dye Similar to Example 1, except that the aqueous solution of hydroxypropyltrimethylamine hydroxide prepared in Example 3 was used as a quaternary ammonium base solution.

[0046] Example 4 Preparation of Direct Orange 15 dye The quaternary ammonium base aqueous solution obtained in Preparation Example 1 was added to a reaction vessel, and then p-nitrotoluene o-sulfonic acid was added, wherein the molar ratio of p-nitrotoluene o-sulfonic acid to the hydroxypropyltrimethylamine hydroxide was 1:1.4. The temperature was raised to 70°C and the reaction was carried out for 5 hours to obtain a mixed solution containing Yellow 11 dye. Continue to add reducing agent (glucose monohydrate or thiourea dioxide) to the reaction system, control the molar ratio of reducing agent to p-nitrotoluene-o-sulfonic acid to be 1.2:1, heat to 90℃ and reflux for 3 hours to reduce and transform the chromophore in the Yellow 11 molecule, and generate dye molecules with the chromophore system of Direct Orange 15. After the reduction reaction is complete, hydrochloric acid is added to the system to adjust the pH value to 7, thus obtaining a stable and transparent Direct Orange 15 liquid dye product.

[0047] Example 5 Preparation of Direct Orange 39 dye p-Aminoazobenzene-4-sulfonic acid, 4,4'-dinitrostilbene-2,2'-disulfonic acid, and the quaternary ammonium base aqueous solution obtained in Preparation Example 1 were added to a reaction vessel in a molar ratio of 1:1:1.3. The mixture was heated to 100°C and refluxed for 3 hours under stirring. Then, a reducing agent (glucose monohydrate) was added, and the molar ratio of the reducing agent to p-nitrotoluene-o-sulfonic acid was controlled at 1.2:1. The mixture was then refluxed for another 2 hours. After reduction, hydrochloric acid is added to adjust the pH to 7, thus obtaining a transparent and stable Orange 39 liquid dye product.

[0048] Comparative Example 1 Preparation of Direct Yellow 11 dye It is largely the same as Example 1, except that the molar ratio of p-nitrotoluene-o-sulfonic acid to hydroxypropyltrimethylamine hydroxide is 1:1.2.

[0049] Comparative Example 2 Preparation of Direct Yellow 11 dye It is largely the same as Example 1, except that the molar ratio of p-nitrotoluene-o-sulfonic acid to hydroxypropyltrimethylamine hydroxide is 1:1.5.

[0050] Comparative Example 3 Preparation of Direct Yellow 11 dye The method is largely the same as in Example 1, except that the aqueous solution of hydroxypropyltrimethylamine hydroxide in Example 1 is replaced with the aqueous solution of choline hydroxide prepared in Comparative Preparation Example 1.

[0051] Comparative Example 4 Preparation of Direct Yellow 11 dye Deionized water was added to the reaction vessel, followed by p-nitrotoluene-o-sulfonic acid, and then a 50% sodium hydroxide aqueous solution was added, wherein the molar ratio of p-nitrotoluene-o-sulfonic acid to sodium hydroxide was 1:1.3. The temperature was raised to 70 °C and the reaction was carried out for 5 h to allow p-nitrotoluene-o-sulfonic acid to undergo self-condensation and oxidative coupling reactions under alkaline conditions, resulting in a condensation solution containing sodium salt of Yellow 11 dye. After cooling the above condensate, hydrochloric acid was added to adjust the pH value to 5, so that the Yellow 11 dye was converted from sodium salt form to free acid form; then trialkylamine extractant was added to the system for liquid-liquid extraction, so that the Yellow 11 dye entered the organic phase, wherein the molar ratio of p-nitrotoluene o-sulfonic acid to trialkylamine was 1:1. The obtained organic phase was contacted with a 25% diethanolamine aqueous solution for back-extraction, which transferred the Yellow 11 dye to the aqueous phase. The molar ratio of p-nitrotoluene-o-sulfonic acid to diethanolamine was 1:1. After back-extraction, the obtained aqueous phase was washed four times with deionized water to remove residual inorganic salts and impurities in the system, and finally the Yellow 11 dye aqueous solution was obtained.

[0052] Test section For each embodiment and comparative example, 200 ml of the clear intermediate layer of the Yellow 11 dye aqueous solution from the reaction vessel was placed in a transparent beaker, the mouth of the beaker was sealed with plastic film, and the beaker was placed at 25°C and 50% humidity for 7 days. Clarity observation: In each example and comparative example, observe whether the solution in the beaker after standing for 0 days and 7 days is cloudy or crystallized. The observation results are shown in Table 1.

[0053] Spectrophotometric detection: Under an indoor environment of 25℃ and 50% humidity, samples of the liquid yellow 11 dye to be tested were taken and diluted with deionized water to a mass concentration of 0.02 g / L. The diluted samples were then filtered through a 0.45 μm microporous membrane before use. Using deionized water as a blank, the samples were scanned using a UV-Vis spectrophotometer at room temperature. The scanning wavelength range was set to 350–550 nm, and the optical path of the cuvette was 1 cm. The maximum absorption wavelength (λmax) and corresponding absorbance value in the visible light region were recorded. Samples stored for 0 days and 7 days after sealing were tested, and the changes in their absorbance characteristics were compared under the same test conditions to evaluate the structural stability of the liquid yellow 11 dye during storage. The test results are shown in Table 1.

[0054]

[0055] Comparing Examples 1 and 2-3, it can be seen that in the process of preparing liquid yellow 11 dye using hydroxypropyltrimethylamine hydroxide as a quaternary ammonium base, the molar ratio of trimethylamine to propylene oxide during the synthesis of the quaternary ammonium base has a certain influence on the storage stability and optical properties of the obtained liquid yellow 11. When the molar ratio of trimethylamine to propylene oxide is 1:1.04, the resulting quaternary ammonium base has a uniform composition, and the yellow 11 dye formed after reacting with p-nitrotoluene-o-sulfonic acid exhibits the best dispersion in the aqueous phase. During storage, precipitation or attenuation of absorbance is less likely to occur, resulting in a clear and stable liquid yellow 11 dye. In contrast, when the molar ratio of trimethylamine to propylene oxide is too low or too high, the effective basicity of the quaternary ammonium base is insufficient or the impurity content increases, leading to uneven ionization or trace aggregation of dye molecules, which easily results in a decrease in absorbance during storage.

[0056] Comparing Example 1 and Comparative Examples 1-2, it can be seen that in the preparation of liquid Yellow 11 dye using hydroxypropyltrimethylamine hydroxide as the quaternary ammonium base, when the molar ratio of the quaternary ammonium base to p-nitrotoluene-o-sulfonic acid deviates from the optimal value, it affects the dispersion state of dye molecules and the formation of ion pairs in the aqueous phase. When the molar ratio is too low (Comparative Example 1), the effective basicity of the system is insufficient, and Yellow 11 dye molecules cannot fully form stable ion pairs, resulting in a decrease in absorbance and slight precipitation during storage. When the molar ratio is too high (Comparative Example 2), the basicity of the system is too strong, and some dye molecules undergo non-ideal aggregation, which also leads to a decrease in absorbance and slight precipitation.

[0057] Comparing Example 1 and Comparative Example 3, it can be seen that after long-term storage in solution, the maximum absorption wavelength (λmax) and corresponding absorbance value of Comparative Example 3 both decreased. The reason may be that in the preparation of liquid Yellow 11 dye, when choline hydroxide is used as the quaternary ammonium base, ethoxylation byproducts are inevitably generated during the synthesis process. These byproducts enter the Yellow 11 synthesis system, and the presence of trace amounts of continuous ethoxylation byproducts in the solution causes uneven ionization of dye molecules, forming micro-aggregates, which leads to slight precipitation or a decrease in absorbance during storage. In contrast, Example 1 uses hydroxypropyltrimethylamine hydroxide as the quaternary ammonium base, which has a uniform composition and low impurity content. The Yellow 11 dye is stable in dispersion in the aqueous phase and is not easily precipitated during storage.

[0058] Comparing Example 1 and Comparative Example 4, it can be seen that after long-term storage in solution, the maximum absorption wavelength (λmax) and corresponding absorbance value of Comparative Example 4 decreased significantly. This may be because, in the preparation of liquid Yellow 11 dye, although sodium hydroxide was used as the alkali solution and multiple water washings were performed (generating a large amount of wastewater), a small amount of sodium ions still existed in the system, weakening the dispersibility of dye molecules. Simultaneously, the preparation process involved multiple steps such as acidification, trialkylamine extraction, diethanolamine back-extraction, and multiple water washings, causing the system to experience multiple pH fluctuations and solvent changes, increasing the risk of dye molecule aggregation or precipitation, thus leading to a decrease in absorbance or slight precipitation during storage. In contrast, Example 1 used hydroxypropyltrimethylamine hydroxide as the quaternary ammonium base and prepared the dye in a one-pot process. The system had uniform alkalinity, low impurity content, and a mild ionic environment, resulting in uniform dispersion and stable storage of Yellow 11 dye, with performance significantly superior to Comparative Example 4.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a quaternary ammonium base, characterized in that, Includes the following steps: Propylene oxide is added to trimethylamine, causing trimethylamine to undergo a ring-opening addition reaction with the epoxy group of propylene oxide, yielding hydroxypropyltrimethylamine hydroxide as a quaternary ammonium base.

2. The preparation method according to claim 1, characterized in that, Includes the following steps: Propylene oxide is added to a trimethylamine aqueous solution at 0-10°C, the temperature is raised to 20-30°C, and the reaction is carried out for 3-6 hours to obtain hydroxypropyltrimethylamine hydroxide. The mass concentration of the trimethylamine aqueous solution is 30%-50%.

3. The preparation method according to claim 2, characterized in that, The molar ratio of the trimethylamine to the propylene oxide is 1:1.03~1.

05.

4. The application of the quaternary ammonium base prepared by the preparation method according to any one of claims 1 to 3 in dye synthesis.

5. The application according to claim 4, characterized in that, The quaternary ammonium base is used to prepare Direct Yellow 11 liquid dye.

6. The application according to claim 5, characterized in that, The method for preparing Direct Yellow 11 dye using the quaternary ammonium base includes the following steps: Adding p-nitrotoluene o-sulfonic acid to hydroxypropyltrimethylamine hydroxide causes the nitro group and toluene side chain in the p-nitrotoluene o-sulfonic acid molecule to undergo base-catalyzed self-condensation and oxidative coupling reactions, forming a molecular skeleton with azo bonds and a stilbene conjugated structure. At the same time, the sulfonate group formed by deprotonation of the sulfonic acid group forms an ion association with the 2-hydroxypropyltrimethylammonium cation, resulting in a mixed solution containing Yellow 11 dye. Hydrochloric acid was added to the mixed solution containing Yellow 11 dye to adjust the pH value to 6-8, thus obtaining Direct Yellow 11 liquid dye.

7. The application of a quaternary ammonium base in dye synthesis according to claim 6, characterized in that, The method for preparing Direct Yellow 11 dye using the quaternary ammonium base includes the following steps: p-Nitrotoluene-o-sulfonic acid was added to an aqueous solution of hydroxypropyltrimethylamine hydroxide and reacted at a temperature of 65-75℃ for 4-6 hours to obtain a mixed solution containing Yellow 11 dye. Hydrochloric acid was added to the mixed solution containing Yellow 11 dye to adjust the pH value to 6-8, thereby obtaining Direct Yellow 11 liquid dye; The mass concentration of the aqueous solution of hydroxypropyltrimethylamine hydroxide is 45%~55%.

8. The application of a quaternary ammonium base in dye synthesis according to claim 7, characterized in that, The molar ratio of p-nitrotoluene-o-sulfonic acid to hydroxypropyltrimethylamine hydroxide is 1:1.3~1.

4.

9. The application of a quaternary ammonium base in dye synthesis according to claim 4, characterized in that, The quaternary ammonium base is used to prepare Direct Orange 15 liquid dye.

10. The application of a quaternary ammonium base according to claim 4 in dye synthesis, characterized in that, The quaternary ammonium base is used to prepare Direct Orange 39 liquid dye.

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