JPS6232744B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides 1-amino-8-naphthol-3.
The present invention relates to an improved method for producing monoalkali metal 6-disulfonic acid salts. More specifically, the present invention converts 1-aminonaphthalene-3,6,8-trisulfonic acid or its alkali metal salt into 1-amino-8-naphthol-3. In the method of preparing a monoalkali metal 6-disulfonic acid salt, the alkali concentration at the start of the melt reaction (expressed as a weight percent of the total alkali weight relative to the sum of the total alkali weight and total water weight in the system) ) in the range of 20-29%, and the alkali concentration at the end of the reaction is 25-29%.
1- characterized in that the reaction is completed while regulating the alkali concentration during the reaction so that it becomes 35%.
This is a method for producing amino-8-naphthol-3,6-disulfonic acid monoalkali metal salt. 1-Amino-8-naphthol-3,6-disulfonic acid is usually called H acid and is an important compound with a particularly wide range of uses among dye intermediates. Conventional H-acid is used, for example, in "Dye Chemistry" (written by Yutaka Hosoda,
Gihodo), page 533, the stepwise sulfonation of naphthalene produces naphthalene-trisulfonic acid, which is then subjected to nitration and reduction steps to produce 1-aminonaphthalene-3,6,8-trisulfonic acid (also called kotsufoic acid). ), the sulfonic group at the 8-position is converted into a hydroxyl group by a melt reaction in the presence of an alkali, the subsequent acidification process produces a H acid monoalkali metal salt, and this is separated by filtration. . However, this production method requires a long number of steps and produces many by-products of isomers specific to naphthalene compounds, so the yield of H acid based on naphthalene as the raw material was extremely low at 42-50%. Therefore, although many improvement methods have been proposed for each process in the past, there is currently no known method that can significantly improve the yield. In particular, the melt reaction process, which is the subject of this study, has a low yield, along with the sulfonation process, and although many improvements have been made in the past, the yield from kotsufoic acid to H acid is still insufficient. Improvements were desired. According to the above-mentioned "Dye Chemistry", when caustic soda is used as an alkali source, the yield of H acid based on kotsufoic acid is as low as 75%. This yield is 94% for β-naphthalene sulfonic acid to β-naphthol, which is the same melt reaction of naphthalene sulfonic acid, and 94% for naphthalene-1,5-disulfonic acid to 1-naphthol-5-sulfonic acid. The yield was 92%, which is a very low level compared to the high yields of 90% or higher in all cases. The reason why the yield of the melt reaction from kotsufoic acid to H acid is lower than that of other similar compounds is due to the difficulty in suppressing side reactions during the melt reaction. One of the reasons for this is that, unlike β-naphthalene sulfonic acid, cottofoic acid has three sulfonic groups in one molecule, which have similar activity levels for melt reactions, and only one of these groups It is extremely difficult to react with high selectivity. For example, under normal known conditions, the sulfonic group at the 6-position of kotsufoic acid undergoes a melting reaction.
It is known that -amino-6-hydroxy-3,8-disulfonic acid (referred to as W acid) is produced, leading to a decrease in yield. Another cause is the hydrolysis reaction of the amino group, which is specific to the alkali melting reaction of aromatic sulfonic acid compounds having an amino group, such as cottofoic acid. In other words, even if H acid is generated by a melt reaction, under high-temperature conditions in the presence of alkali, the amino group is eliminated by hydrolysis and replaced with the hydroxyl group, and 1,8-dihydroxy-3,6-
Disulfonic acid (referred to as chromotropic acid)
This is due to the fact that there are reactions that change sequentially. Furthermore, among the byproducts, W acid has similar solubility characteristics to H acid, so the increase in this side reaction is not only due to a decrease in the yield in the reaction, but also due to the purification conditions in the acid precipitation step after melting. This results in a severe reduction in the yield of the H acid itself.
For example, according to the method described in "Dye Chemistry", pp. 535-536, the byproduct during the melt reaction is W acid.
6.2% and 7.3% of chromotropic acid and chromotropic acid were produced relative to kotsufoic acid, respectively, and it can be seen how their suppression greatly contributes to improving the yield of H acid. For example, as a method for improving the melt reaction,
Publication No. 19954 states that by-products are suppressed by the presence of aliphatic alcohols represented by methanol or their alcoholates in the reaction system, and when caustic soda is used as an alkali source, the yield of H acid is 77 to 82. It is stated that it improves by %. Furthermore, JP-A-54-19955 discloses that by coexisting additives such as nitrates and aromatic nitro compounds in the presence of alcohol or alcoholate, a yield of 77 to 81% can be obtained when using caustic soda. It is stated that. However, all of these methods that use organic solvents require an amount of solvent comparable to the total amount of water in the reaction mass, and equipment for solvent recovery,
There are disadvantages in that the cost is considerable and the production efficiency must be significantly reduced.
Regarding the method of using additives, the amount used is as high as 5.0 to 7.5 mol% per 1 mol of raw material cottufoic acid, and the increase in the cost of auxiliary raw materials due to these additives is These methods cannot be said to be advantageous since new problems such as increase in the number of children may arise. The present inventors have discovered that 1-aminonaphthalene-3.
As a result of a detailed study of the effects of various factors on the alkali melting reaction of 6,8-trisulfonic acid, such as the type of alkali source, the amount of alkali used, the alkali concentration, the reaction temperature, and the reaction time, we found that the alkali concentration was lower than the conventional one at the initial stage of the reaction. Either a method of starting from a concentration lower than that which has been adopted and adding alkali in portions during the preparation and after the start of the reaction, or a method of dehydration during the reaction, or a method of a combination of both. Therefore, the present invention was developed based on the knowledge that a method of regulating the alkali concentration during the reaction and setting the alkali concentration at the end of the reaction within a specific range suppresses by-products and brings extremely good results to the reaction yield. It was completed. That is, according to the method of the present invention, H acid containing only a very small amount of byproducts W acid and chromotropic acid can be obtained in high yield. Previously proposed improvement methods for melting reactions were only aimed at setting the preparation conditions at the initial stage of the reaction, but this method regulates the alkali concentration from the start of the reaction to the end of the reaction based on analysis of the reaction mechanism. This method is the first of its kind, and it is surprising that the yield can be greatly improved by this method, and the engineering value of the present invention is high. The method of the present invention will be explained in more detail below. In the present invention, the alkali concentration in the raw material composition at the start of the reaction must be 20-29%, and the alkali concentration during the reaction must be regulated so that the alkali concentration at the end of the reaction is 25-35%. It is necessary to carry out. Here, the alkali concentration is expressed as the total alkali weight percentage based on the sum of the total alkali weight and the total water weight in the reaction system. The alkali concentration after the start of the reaction due to the alkali concentration regulation may undergo any concentration change as long as the alkali concentration at the start and end of the reaction falls within the above range, but the upper limit of the alkali concentration during the reaction is
It is preferable to regulate it within a range of 35-45%, with a lower limit of 15-20%. The starting point for regulating alkali concentration can be any time after the point at which the alkali concentration in the reaction system begins to decrease as alkali is consumed by the reaction and water is produced as a by-product, and the internal temperature is at the reaction temperature (160-170℃). It is fine as long as it reaches . When regulating alkali concentration using the alkali split addition method, the split ratio of alkali, addition rate, addition timing, etc. should be selected in the optimal range depending on the alkali concentration at the start of the reaction and the temperature during incubation. However, any conditions may be adopted as long as the above-mentioned regulatory conditions for alkali concentration are satisfied. However, in general, it is done as follows. The alkali split ratio is
It is preferable to add 5 to 50%, preferably 10 to 35% of the total amount of alkali used in the melting reaction from 0 to 80 minutes after the start of the heat retention period, preferably from 5 to 60 minutes after the end of the heat retention time. . The concentration of the alkali to be added is preferably an aqueous alkali solution that is substantially higher than the alkali concentration in the reaction system, preferably 50 to 80%. The addition method may be one in which a predetermined amount of alkali in a solution state is continuously added into the autoclave at a constant rate using a pump, or in some cases, a method may be adopted in which the entire amount of alkali to be added is temporarily pressurized. can be done. When regulating the alkali concentration using the dehydration method, the optimal ranges for the amount of dehydration, dehydration rate, and dehydration time are selected depending on the alkali concentration at the start of the reaction and the temperature at which the reaction is maintained. Any dehydration method may be used as long as the conditions are met. Therefore, the dehydration rate may be determined by continuously removing a constant amount, or by intermittently removing water as the reaction progresses. The dehydration time may be any length as long as a predetermined amount of dehydration can be ensured, but preferably a time that can be carried out within the time of the temperature raising and heat retention steps is selected, and a range of 20 to 120 minutes is selected. Also, when should you start dehydrating?
The guideline is when the internal temperature reaches the reaction start temperature, and it is possible to start dehydration from that point.
It is effective to start 0 to 80 minutes, preferably 5 to 60 minutes after warming is started. Dehydration is carried out by removing water vapor from the gas phase by opening and closing a valve attached to the part of the autoclave that is in contact with the gas phase. The water vapor extracted from the gas phase is condensed by passing through a condenser,
It is preferable to control the amount of dewatering by controlling the amount of condensed water in terms of operation and control. When the reaction is carried out in a closed system as in the method of the present invention,
Since the temperature, composition, and internal pressure in the system have a certain relationship, the alkali concentration in the system can be controlled by controlling the internal pressure, and this can also be used to control the amount of water removed. Usually, an autoclave-type reactor equipped with a jacket is used for the melting reaction of the present invention, but if it is difficult to supply heat from the outside during dehydration, a type equipped with a coil-type heating device can also be used. In short, any type of reactor may be used as long as it can supply a sufficient amount of heat necessary for reaction and dehydration. When regulating alkali concentration, the effect on the reaction is the same whether the alkali split addition method or the dehydration method is adopted, so it is important to select the appropriate method according to equipment costs and operational management options. Can be adopted. Additionally, both regulatory laws can be used together. As the alkali source used, caustic soda, caustic potash, or a mixture thereof is selected, and caustic soda is advantageous from a cost standpoint. The amount used may be as long as the required alkali concentration regulation can be carried out, but when using caustic soda, the amount used is 6.0 to 15.0 per mole of cotzfoic acid.
twice the molar amount, preferably 8.0 to 13.0 times the molar amount. For caustic potash, 3.0 to 8.0 times the mole, preferably 4.0
~7.0 times the molar amount. The raw material kotsufoic acid is one in which all sulfonic groups have been neutralized with alkali, or the free acid of sulfonic acid is used as it is or partially neutralized, and the alkali equivalent to neutralization is added to the amount necessary for the melting reaction. It can also be combined with an alkali component and subjected to the reaction. In addition, it is desirable that the raw material kotsufoic acid be of high purity, containing no isomers or other impurities, but 1-aminonaphthalene-3, 5, 7, which is a typical by-product produced in the process of producing kotsufoic acid, is desirable. -trisulfonic acid, 1-aminonaphthalene-4,6,8-trisulfonic acid, and alkali salts thereof may be included. The contamination of these by-products has no negative effect on the reaction itself, and there is no particular restriction on the amount of contamination, but an increase in the amount of contamination will lead to an increase in the amount of alkali used and will put a burden on the purification process after the reaction, so aminonaphthalene sulfonic acid It is preferably 35% or less, preferably 10% or less of the total amount. There are no particular restrictions on the amount of organic salt mixed in during the reaction, but in order to maintain good physical properties during the reaction, it should be 30% or less, more preferably 15% or less, based on the total amount of the raw material aminotrisulfonic acid alkali metal salt. % or less is preferable. The reaction is carried out by charging an alkali metal salt of cottofoic acid or a mixture thereof with water and a required amount of an alkali or an aqueous alkali solution into an autoclave, raising the temperature to a predetermined temperature, and then keeping it warm. During this time, the alkali concentration is regulated, but the temperature raising stage should be carried out in as short a time as possible, preferably within 60 minutes. For this reason, for example, it is possible to adopt a method in which the total amount of kotsufoic acid alkali salt, alkali, and water that make up the raw material composition is mixed and homogenized in advance, and the mixture is preheated to an insulating temperature, preferably 100 to 170°C, before being charged into an autoclave. ,
It is also possible to adopt a method in which individual raw material components or a partial mixture thereof are separately preheated and charged into an autoclave. The temperature during heat retention may be in the range of 170 to 240°C, but preferably in the range of 180 to 220°C. The optimal incubation time is selected depending on the alkali concentration at the start of the reaction, the temperature, and the method for regulating the alkali concentration, but in any case, it is necessary to select the minimum time for the reaction to complete. , prolonging the reaction time is undesirable because it leads to decomposition of the product. From these points, the heat retention time is 10~
110 minutes are chosen, preferably 20-90 minutes. Further, the pressure during the reaction may be any autogenous pressure corresponding to each reaction temperature, and even if additional pressure is applied in addition to the autogenous pressure, there will be no adverse effect on the reaction. Once the melting reaction is complete, the reaction mass is cooled as quickly as possible and drained into dilution water. There are no particular restrictions on the time and temperature at this time, but preferably 110℃
Cool within 20 minutes and drain into dilution water.
The dilution water may be sufficient as long as it can melt the inorganic salt precipitated in the molten reaction mass, and is preferably selected in an amount in the range of 0.4 to 2.5 times the weight of the molten reaction product. The diluted molten mass thus obtained is dropped into an aqueous mineral acid solution, typically sulfuric acid or hydrochloric acid, and is acidified by a neutralization reaction to precipitate H acid crystals. The amount of mineral acid used is such that the remaining alkali of the molten reactant, the total amount of acid-consuming components such as sulfites are neutralized, and the pH of the diluted molten mass and the total amount of mineral acid is preferably 3.0 or less.
The concentration of the mineral acid used may be selected from any range as long as it is in an amount sufficient to make it 1.0 or less. Furthermore, the acid used is not limited to mineral acids, and for example, free acids such as naphthalene sulfonic acid and derivatives thereof can also be used in combination. The H acid monoalkali salt precipitates as hydrated crystals under this acidic condition. The amount of water in the acidified mass is adjusted to the amount that allows this H-acid slurry to be stirred uniformly, according to the amount of water in the dilution mass and mineral acid aqueous solution, but preferably the total amount of acid is equal to the weight of the H-acid monoalkali salt. A range is selected such that the proportion of the weight of the analyzed mass is 3 to 30%, preferably 6 to 25%.
The acidification treatment is preferably carried out by dropping a water-diluted mass of the molten reactant into an aqueous acid solution maintained at 60 to 90°C, and the dropping is usually carried out over a period of 30 minutes to 2 hours. After the dropping is completed, the acidified mass is kept warm under high temperature conditions in order to discharge the generated sulfur dioxide gas out of the system.
The higher the heat retention temperature, the better the efficiency, and preferably the reflux temperature is employed, and the heat retention is continued until most of the sulfur dioxide gas is removed. The temperature is usually kept for 1 to 5 hours, preferably 2 to 4 hours. At this time, in order to proceed with degassing more efficiently, it is also possible to maintain the temperature under reduced pressure. After heat retention and degassing, the mixture is cooled to 50 DEG C. or below, preferably 30 DEG to 40 DEG C., for 1 to 9 hours, more preferably 2 to 4 hours, with stirring, and the precipitated H acid monoalkali salt is separated by filtration. The resulting wet cake is washed with cold water.
The amount of washing water used is based on the total weight of the wet cake.
A weight ratio of 0.3 to 2.5, preferably 0.5 to 2.0 is used, and the amount of washing water is selected to be the minimum amount depending on the washing efficiency of the washing method. The wet cake after washing is dried at a temperature of 100°C or less under normal pressure or reduced pressure to obtain a dry cake of H acid monoalkali salt. EXAMPLES The present invention will be specifically explained below using Examples, but the present invention is not limited to these Examples. Example 1 16.4 kg of an aminonaphthalene trisulfonate mixture containing 15.0 kg of chusfoic acid trisodium salt was obtained by a known method, ie, naphthalene sulfonation, nitration, and reduction steps. This mixture contained 0.2 kg of aminonaphthalene trisulfonic acid isomer other than cottofoic acid, and the rest contained mirabilite and water. 16.4Kg of the above raw materials, 16.8Kg of 70% caustic soda solution, water
A molten raw material weighing 27.0 kg was sufficiently kneaded to obtain a uniform molten raw material. On the other hand, the temperature of the heat medium in 50 cast steel autoclaves equipped with an anchor type stirrer and a heat medium circulation device was set in advance at 150°C, and the molten raw material was press-injected into these autoclaves in a short time. The alkali concentration in the raw material at this point was 27.0%. After the preparation was completed, the temperature of the heat medium in the autoclave jacket was raised and the temperature started to rise. Internal temperature reaches 195℃ in 30 minutes
It turned on to keep warm at the same temperature. When 20 minutes had elapsed from the start of the incubation, 4.8 kg of a 70% caustic soda aqueous solution kept at 150°C was added to the autoclave at a constant rate over a period of 35 minutes using a pump, while keeping the autoclave at 195°C. The alkaline concentration at the end of the heat retention was 27.0%. At the same time as the addition of caustic soda was completed, the heating was stopped and the internal temperature was cooled to 120°C in 20 minutes, and the reaction mass was discharged into 30 kg of cold water to dissolve the inorganic salts that had precipitated after the reaction. Dilute the resulting lysate at 80%
The mixture was poured into 39 kg of 50% sulfuric acid kept at ℃ over 1 hour, and acid precipitation was performed under stirring. After the entire amount was injected, the internal temperature was raised to 100 to 105°C, and the temperature was kept for 2 hours to remove the generated sulfur dioxide gas. The pH of the acid-precipitated mass solution after the completion of the incubation was 1.0 or less. The mass was cooled to 40° C. over 4 hours, the precipitated H acid monosodium salt was separated, and the resulting cake was washed with 10.0 kg of cold water. The amount of wet cake obtained was 18.1Kg, and the amount of dry cake after drying was 11.3Kg. The content of H acid monosodium salt in the dry cake is
The concentrations of W acid and monosodium salt of chromotropic acid were 0.6% and 0.6% by weight, respectively. Moreover, the yield of H acid to kotsufoic acid was 83.0%. In addition, the reaction yield of each component with respect to cotzfoic acid at the stage where the melting reaction is completed is 86.8% for H acid and 2.7% for W acid.
%, and chromotropic acid 3.3%. Example 2 To 16.4 kg of aminonaphthalene sulfonate mixture having the same composition as in Example 1, 16.8 kg of 70% caustic soda,
After adding 32.3 kg of water, the mixture was sufficiently kneaded to obtain a uniform molten raw material. This raw material was press-fitted into a 50-liter autoclave in the same manner as in Example 1. The alkali concentration in the raw material at this point was 24.0%. After the preparation was completed, the temperature was started to increase. The internal temperature reached 200°C in 35 minutes, and the device entered heat retention at the same temperature. At the same time as heating started, 7.9 kg of 70% caustic soda solution at 150℃ was added for 30 minutes.
Incubation at 200°C was continued while adding the mixture into the autoclave at a constant rate by a pump in minutes. After the alkali addition was completed, the mixture was kept warm at the same temperature for another 20 minutes to complete the heat retention. The alkaline concentration at the end of insulation is
It was 26.0%. Thereafter, cooling and discharging were performed in the same manner as in Example 1, and the obtained molten mass solution was
Acid precipitation was carried out by pouring it into 44 kg of 50% sulfuric acid kept at ℃ over 1 hour. After acid precipitation, 19.0 kg of wet cake was obtained through filtration and washing. The amount of dry cake after drying was 11.6 kg. The content of H acid monosodium salt in the dry cake is
The concentrations of W acid and monosodium salt of chromotropic acid were 0.5% and 0.7% by weight, respectively. In addition, the yield of H acid to kotsufoic acid is 83.5%,
At the stage where the melting reaction was completed, the reaction yields of each component with respect to chufoic acid were 87.3% for H acid, 2.5% for W acid, and 3.8% for chromotropic acid. Example 3 16.4Kg of aminonaphthalene trisulfonate mixture with the same composition as Example 1, 11.8Kg of caustic soda, and water
After thoroughly mixing 32.0Kg of molten raw materials, 50
The mixture was placed in a cast steel autoclave equipped with an anchor-type stirrer and heated to 130°C while stirring. On the other hand, the temperature of the heat medium in a cast steel autoclave equipped with a heat medium circulation device was set at 150℃ in advance, and the molten raw material was pressurized into the autoclave for 5 minutes.The alkali concentration at the start of the reaction was 27%. After the preparation was completed, the temperature of the heating medium in the autoclave jacket was increased to begin raising the temperature. Internal temperature in 35 minutes
The temperature reached 195℃, and I started keeping warm at the same temperature. The internal pressure at this point was 7.5Kg/cm ² G. After 20 minutes had passed from the start of heat retention, the needle valve attached to the top of the autoclave was opened to remove water vapor from the gas phase and dehydrate the autoclave. The water vapor extracted from the needle valve is condensed through a condenser, and then stored in a storage tank and measured. Dehydration was performed intermittently at 5-minute intervals, and the valves were automatically opened and closed in conjunction with a timer. The total dehydration amount was 7.7Kg, and the time required for dehydration was 40 minutes. The heating medium temperature was controlled so that the internal temperature could be maintained at a warm temperature even during dehydration. Stop keeping warm as soon as dehydration is completed, and allow the internal temperature to rise within 20 minutes.
After cooling to 110°C, the reaction mass was discharged into 30 kg of cold water to dissolve the inorganic salts precipitated by the reaction. Pour the obtained solution into 30 kg of 50% sulfuric acid kept at 80℃.
The mixture was injected over a period of time, and acid precipitation was performed under stirring. After the entire amount was injected, the internal temperature was raised to 100 to 105°C, and the temperature was kept for 2 hours until the generated sulfur dioxide gas was removed. The liquid pH of the acid-precipitated mass after the completion of the incubation was 1.0 or less. The mass was cooled to 40° C. over 4 hours, the precipitated H acid monosodium salt was separated, and the resulting cake was washed with 10.0 kg of cold water. The amount of wet cake obtained was 18.5 kg, and the amount of dry cake after drying was 11.2 kg. The content of H acid monosodium salt in the dry cake is
The concentrations of W acid and monosodium salt of chromotropic acid were 0.7% and 0.6% by weight, respectively. Moreover, the yield of H acid to kotsufoic acid was 83.5%. In addition, the reaction yield of each component with respect to cotzfoic acid at the stage where the melting reaction is completed is 87.0% for H acid and 87.0% for W acid.
2.5% and chromotropic acid 3.5%. Example 4 A reaction was carried out according to the method of Example 1, except that the operating conditions and reaction factors shown in Table 1 below were changed. The reaction results are shown in Table-2.

【table】

[Table] *Each component is expressed as monosodium salt.
Example 5 23.4 kg of an aminonaphthalene trisulfonate mixture containing 15.0 kg of chufoic acid trisodium salt was obtained by a known method. This mixture contains 1 aminonaphthalene trisulfonic acid other than cotfoic acid.
Contains 2.7Kg of -amino-naphthalene-3,5,7-trisulfonic acid trisodium salt, 2.4Kg of 1-aminonaphthalene-4,6,8-trisulfonic acid trisodium salt, and also contains mirabilite. It contained a total of 3.3 kg of water. Above raw materials 23.4Kg, caustic soda 16.0Kg, water 42.0Kg
A dehydration melting reaction was carried out under the same conditions as in Example 3 using a material consisting of Kg as a molten raw material. The alkali concentration of the molten raw material is 27.0%, the alkali concentration after dehydration is 26.0%, and the time required for dehydration is 50%.
It was hot in minutes. After cooling the reaction mass to 110°C for 20 minutes, it is discharged into 35 kg of cold water to dissolve the inorganic salts precipitated by the reaction. The resulting solution was kept at 80°C while stirring.
Injected into 46kg of 50% sulfuric acid over 1 hour, then
Raise the internal temperature to 100℃ and keep it warm for 2 hours until the generated sulfur dioxide gas is completely removed. After heating, the mixture was cooled to 35°C over 4 hours with stirring, and the precipitated H acid monosodium salt was separated and washed with 10.0 kg of cold water. The amount of wet cake obtained was 17.8 kg, and the amount of dry cake after drying was 11.0 kg. In the dry cake, the content of monosodium salt of H acid was 83.3% by weight, and the content of monosodium salts of chromonoropic acid and W acid was 0.7% and 0.8% by weight, respectively, and no other components were found to be mixed in. Ta. Moreover, the yield of H acid to kotsufoic acid was 81.0%. Example 6 60.2 kg of molten raw material with the same composition as in Example 3 was press-fitted in a short time into a 50° autoclave equipped with a stirrer whose jacket heat medium temperature was preset at 150°C.
The temperature was raised in 30 minutes until the internal temperature reached 195°C. After the temperature was raised, the mixture was kept at the same temperature for 20 minutes and dehydrated in the same manner as in Example 3 to obtain 4.8 kg of condensed water in 25 minutes. Upon completion of dehydration, 3.7 kg of 70% caustic soda solution at 150℃ was injected for 10 minutes, and then at 195℃.
The melting reaction was completed by keeping warm for 15 minutes. The alkali concentration at the end of the melting reaction was 29%. From cooling to removal of H acid, the same method as in Example 3 was followed except that the amount of sulfuric acid during acidification treatment was 35 kg. As a result, 11.6 kg of dry cake was obtained after drying H acid, and the analysis revealed that the content of H acid monosodium salt was 82.6.
The weight percentages of W acid and monosodium salt of chromotropic acid were 0.8 weight percent and 0.4 weight percent, respectively.
Further, the yield of H acid to kotsufoic acid was 84.2%. Comparative Example 1 The same molten raw material as in Example 1 was heated to 50% by the same operation.
The mixture was placed in an autoclave and heated to 195°C over 40 minutes. At the same temperature, the melting reaction was completed by keeping it warm for 60 minutes without controlling the alkali concentration such as adding alkali. Alkali concentration at the start of reaction is 27.0%
and decreased to 22.1% at the end of the reaction. After heating, cool to 110°C over 20 minutes and repeat the same procedure as in Example 1 to prepare a dry cake.
Obtained 10.6Kg. The content of H-acid monosodium salt in the dry cake is
The monosodium salts of W acid and chromotropic acid were 1.5 and 3.0% by weight, respectively, and the yield of H acid to kotsufoic acid was 73.5%. In addition, the dry cake contained 1.1% by weight of the raw material disodium cottofoic acid salt, and cottofoic acid was also detected in the liquid separated from the H-acid cake. From this value, under the conditions of this example, the conversion rate of kotsufoic acid did not reach 100%. Comparative Example 2 A melting reaction was carried out under exactly the same conditions as Comparative Example 1 (no regulation of alkali concentration) except that only the amount of water at the time of preparation was changed to 24.0 kg. Under these preparation conditions, the alkali concentration at the start of the reaction is
It was 33.0% and decreased to 26.8% at the end of the reaction. Acid treatment, filtration and washing were carried out under the same conditions as in Example 1 to obtain 10.8 kg of a dry cake of H acid. The content of H acid monosodium salt in the dry cake is
81.0% by weight, and the monosodium salts of W acid and chromotropic acid each accounted for 3.5% by weight.
It was 3.0% by weight. The yield of H acid versus kotsufoic acid is
It was 76.8%. In addition, only trace amounts of kotsufoic acid were confirmed in the H acid cake.

Claims (1)

[Scope of Claims] 1. 1-Aminonaphthalene-3,6,8-trisulfonic acid or its alkali metal salt is subjected to a melting reaction with an alkali and a subsequent acidification treatment to produce 1.
- In the method of preparing amino-8-naphthol-3,6-disulfonic acid monoalkali metal salt, the alkali concentration at the start of the melting reaction is set in the range of 20-29%, and the alkali concentration at the end of the reaction is 1. A method for producing a monoalkali metal salt of 1-amino-8-naphthol-3,6-disulfonic acid, which comprises completing the reaction while controlling the alkali concentration during the reaction so that the concentration is 25-35%. 2. As a method of controlling the alkali concentration during the alkali melting reaction, a method is adopted in which the total amount of alkali used in the melting reaction is added in divided amounts at the time of preparation and after the start of the reaction, and/or a method in which the reaction is carried out under dehydration. A method according to claim 1, characterized in that: