PROCESS FOR PRODUCING 3,3-BIS-(4-DIMETHYLAMINOPHENYL)-6-DIMETHYLAMINOPHTHALIDE

Abstract: A process for producing 3,3-bis-­ (4-dimethylaminophenyl)-6-dimethylaminophthalide (crystal violet lactone) comprises oxidizing 2-{4,4′-bis-­ (dimethylamino)-benzhydryl]-5-dimethylaminobenzoic acid in an aqueous solution of a mineral acid having a pH of from 2.0 to 4.0 with air, oxygen or a gas containing oxygen in the presence of at least one catalyst selected from compounds of iron, copper, cobalt, nickel, chromium, vanadium and manganese.

Description: The present invention relates to a process for producing 3,3-bis-(4-dimethylaminophenyl)-6-dimethylaminophthalide(crystalviolet lactone, hereinafter referred to as CVL). Although CVL itself is colourless or nearly colourless, it has property of rapidly developing a blue-violet colour when brought into close contact with an electron-accepting substance, for instance, an organic acid, acid clay, phenol-formalin resin, metal salt of an aromatic carboxylic acid and bisphenol. A CVL is most widely used as a pigment in recording materials such as pressure-sensitive or heat-sensitive recording paper. Although many processes wherein 2-[4,4′-bis-(dimethylamino)-benzhydryl]-5-dimethylaminobenzoic acid(hereinafter referred to as LC) is oxidized into CVL are known, it is difficult to obtain CVL of high quality in a high yield because of the complexity of the production steps and the large amount of by-products produced by decomposition. For instance, in the process of oxidizing LC in an aqueous mineral acid solution with lead peroxide or potassium permanganate (refer to US-A-2,417,897), in the process of oxidizing LC in an organic solvent such as glacial acetic acid or chloroform, with oxygen in the presence of a metal complex [refer to JP-A-48-25730 (1973) (US-A-3828071)] and also in the process of oxidizing LC in a liquid mixture of a nonaqueous hydrocarbon solvent and water with hydrogen peroxide in the presence of an acid catalyst [refer to JP-A-52-78867 (1977)], large amounts of tarry by-products are formed, thereby substantially reducing the yield and quality of CVL, and such a process requires a complex step such as the recovery of the organic solvent. Furthermore, in the process of oxidizing LC with hydrogen peroxide in an aqueous solution or a water soluble organic solvent in the presence of an alkali [refer to JP-A-52-31384 (1977)] and also in the process of oxidizing LC with hydrogen perioxide, oxygen or air in an aqueous alkaline solution in the presence of a catalyst comprising a compound of cobalt or copper [refer to JP-B-59-19548 (1984) (US-A-4271075)] a large amount of the unreacted substance is contained in the reaction product, thereby forming a lumpy material. Thus the reaction hardly proceeds and the yield and quality of CVL are very poor. As a process for synthesizing LC as the intermediate for producing CVL, a process of reacting m-dimethylaminobenzoic acid(hereinafter referred to as DABA) with tetramethyl-4,4′-diaminobenzhydrol(hereinafter referred to an MH) in an aqueous solution of sulfuric acid (refer to US-A-3,842,103) and a process of dropping an aqueous sulfuric acid solution of MH into an aqueous sulfuric acid solution of DABA(refer to DE-C-2156648) have been known. However, in each of the two processes, the amount of by-products formed by decomposition is large and the yield and the quality of LC are extremely low. It has been known that the yield and quality of CVL synthesized by oxidation of LC are generally influenced by the quality of LC, and accordingly isolation and purification of LC are ordinarily carried out before subjecting LC to oxidation. For instance, although there is a method of treating LC in a mixture with an aromatic hydrocarbon or a water-insoluble alkane [refer to JP-A-53-115740 (1978) (CA-A-1087202)], there are the disadvantages that the recovery of the solvent is troublesome and that there is a large loss of LC the recovery treatment. Moreover, the process for producing CVL consists essentially of a first step of reacting DABA with MH to form LC and a second step of producing CVL by oxidizing the thus obtained LC. According to the conventional process, LC obtained in the first step is generally separated and purified and then the separated and purified LC is used as the starting material in the second step. However, since the loss of LC in the isolation and purification thereof is large, a method is also considered wherein the reaction mixture obtained in the first step is used as the starting material in the second step without separating and purifying, and the second step is carried out continuously after the first step. However, in such a method, not only do the remaining raw material, the decomposition products of the raw material and the by-products of reaction of the first step badly influence the yield of CVL in the second step but also, according to the conditions in the second step, the operations such as the separation of the tarry by-products and the recovery of the solvent accompanying the purification of the CVL are complex. Particularly, in the first step, large amounts of by-products other than LC are formed, and in consideration of only this point, the process of continuously carrying out the reaction of the first step and the reaction of the second step is inadequate. The present inventors have studied the defects of the conventional process for synthesizing CVL and have found that (1) LC of an extremely high quality can be obtained in a high yield and (2) CVL can be obtained in a continuous process from DABA and MH. The present invention provides a process for producing 3,3-bis-(4-dimethylaminophenyl)-6-dimethylaminophthalide (CVL), which process comprises oxidizing 2-[4,4'-bis-(dimethylamino)-benzhydryl]-5-dimethylaminobenzoic acid (LC) in the form of particles having a mean particle diameter not larger than 20 µm in an aqueous solution of sulfuric acid or hydrochloric acid having a pH of from 2.0 to 4.0 with air, oxygen or a gas containing molecular oxygen in the presence of at least one catalyst selected from compounds of iron, copper, cobalt, nickel, chromium, vanadium and manganese at a temperature of from 40 to 120°C. The present invention also provides a process for producing CVL, which process comprises adding tetramethyl-4, 4' -diaminobenzhydrol (MH) in the form of particles having a mean particle diameter of not larger than 50 µm to an aqueous sulfuric acid or hydrochloric acid solution having a pH of from 1.5 to 3.0 containing m-dimethylaminobenzoic acid (DABA) in the form of particles having a mean particle diameter of not larger than 30 µm at a temperature of from 50-100°C, thereby forming LC, adding a catalyst selected from compounds of iron, copper, cobalt, nickel, chromium, vanadium and manganese to the reaction mixture and oxidizing the LC in the resultant reaction mixture with air, oxygen or a gas containing molecular oxygen at a temperature of from 40 to 120°C. The mean particle diameter of DABA is preferably not larger than 5 µm. The mean particle diameter of MH is preferably not larger than 10 µm. The reaction of DABA and MH is preferably carried out at a temperature of from 60 to 80 °C, and it is advantageous to add the MH as slowly as possible. The addition of a surfactant, for instance polyoxyethylene alkyl ether, to the reaction system is effective for uniformly dispersing the reaction mixture. The reaction of DABA and MH proceeds under the most suitable reaction conditions at a pH of from 2.0 to 3.0, preferably in a sulfuric acid solution. The reaction is remarkably accelerated under these conditions and only small amounts of by-products are formed. LC formed in the above-mentioned pH range does not dissolve much in the reaction solution; on the other hand, DABA and MH dissolve well in the reaction solution. Accordingly, MH added rapidly thereto dissolves in the reaction solution and reacts with DABA. Furthermore, DABA suspended in the reaction solution dissolves rapidly with the separation of LC which is formed by the reaction; accordingly the pH of the reaction solution is kept within the above-mentioned range. As a result, LC is formed smoothly and the objective product is obtained in a high yield. Furthermore, since the impurities in DABA and MH and the by-products formed by decomposition dissolve well in the reaction solution in the above-mentioned pH range, such impurities and by-products can be compltely removed merely by filtering the thus separated LC after reaction and washing the thus filtered LC with water. Consequently LC of a high quality can be obtained. Examples of the catalyst used in the oxidation of LC are ferric chloride, ferrous sulfate, cupric chloride, copper sulfate, copper acetate, cobalt chloride, cobalt sulfate, cobalt acetate, manganese chloride, manganese sulfate, chromium sulfate, nickel sulfate and vanadium sulfate. It is preferable that the mean particle size of the LC used in the present invention is as minute as possible, preferably not larger than 10 µm. The oxidation of LC is advantageously carried at a temperature of from 80 to 100°C.It is preferable to introduce the air, oxygen or gas containing molecular oxygen as minute bubbles into the reaction mixture. The pressure of the reaction vessel in the oxidation is not limited; the oxidation can be conducted under elevated pressure, normal pressure or reduced pressure. Furthermore, in order to uniformly disperse the reaction mixture, the addition of a surfactant, for instance, a polyoxyethylene alkyl ether, to the reaction system is preferable. The aqueous solution of sulfuric acid or hydrochloric acid , preferably sulfuric acid, used in the oxidation of LC, scarcely dissolves CVL at a pH of from 2.0 to 4.0, preferably from 2.0 to 3.0. On the other hand, it dissolves LC and the impurities contained in LC or the by-products of reaction very well. As a result, CVL formed by oxidation separates out from the reaction solution immediately. Consequently the formation of CVL is smoothly carried out to obtain a high yield thereof. Preferred catalysts are compounds of copper and cobalt since these show a high catalytic effect and accelerate the reaction remarkably as compared to the case where no such catalyst is used. Every one of these compounds is soluble in water. Since such a compound and the impurities and by-products simply by collecting the CVL, which is separated out after finishing the reaction, by filtration and washing the thus collected CVL, the production of CVL of a high quality is carried out extremely satisfactorily. In the process for continuously producing CVL from DABA and MH without separating LC, it is particularly necessary to add MH to the aqueous sulfuric acid or hydrochloric acid solution which contains DABA. In the case where MH is thus slowly added, the MH dissolves in the solution and at the same time reacts with the DABA dissolved in the solution to form LC. Almost all of the thus formed LC separates from the solution except for a small amount thereof. On the other hand, with the formation and separation of LC, DABA which has been in a non-dissolved state begins to dissolve, and finally all the DABA reacts with MH. After the addition of MH is finished, and the reaction of DABA and MH is completely finished, the reaction mixture is maybe filtered, and the thus obtained residue washed with water to neutrality and dried to obtain a dried crude product. As a result, a dried product containing an amount of LC corresponding to 90% of the theoretical amount is obtained. However, in the present invention, the reaction mixture containing LC maybe is used as the starting material of the next step. The pH of the reaction mixture containing LC obtained in the first step is preferably changed to 2.0 to 4.0. In this reaction mixture , LC 80 to 90 % separates; the remaining LC exists stably in a dissolved state. In the case when air, oxygen or a gas containing molecular oxygen is blown into the reaction mixture containing LC and oxidation of LC is carried out, part of the LC which is present in the reaction mixture containing LC in a dissolved state is oxidized into CVL and the thus formed CVL separates. At the same time, LC which has been in the non-dissolved state in the solution dissolves in the solution. The reaction proceeds in the same way as mentioned above. Thus, a reaction mixture containing CVL in an amount of more than 90 % of the theoretical amount is finally obtained. However, in the oxidation of LC, the yield of CVL depends largely on the presence or absence of the abovementioned catalyst. For instance, the yield of 90 % attained in the presence of the catalyst is reduced to some dozen percent when the catalyst is not added. In the continuous process without separating LC, it is preferable that the particle sizes of the DABA and MH are as minute as possible in order to advance the reaction of DABA and MH and to form and separate LC in the form of particles which are as minute as possible. The mean particle diameters of DABA is preferably not larger than 5 µm, and of MH is preferably not larger than 10 µm. MH in a powdery form or an aqueous dispersion containing a powdery form of MH may be slowly added to the aqueous mineral acid solution containing DABA. The latter method is particularly preferred since the dissolution of MH in the solution containing DABA can be carried out with favorable reproducibility without regard to the purity of MH. According to the process of the present invention for producing CVL by oxidation of LC, it is possible to obtain CVL of an extremely high quality in a high yield and in a short period. Accordingly the process of the present invention is excellent economically. According to the continuous process without separating LC according to the present invention, it is possible to effectively combine the LC-formation reaction from DABA and MH as the first step with the CVL-formation by oxidation of LC as the second step. Accordingly, it is possible to produce an amount of CVL of not less than 90 % of the theoretical amount without carrying out isolation and purification of LC. In the final reaction mixture the unreacted DABA and MH, the impurities in the raw materials, i.e. DABA and MH, and the by-products of the reactions dissolve well, and only CVL separates substantially in an undissolved state. Accordingly, it is possible to easily obtain CVL of a high quality merely by filtering the thus separated CVL and washing the thus collected CVL with water. The present invention is explained in more detail in the following Examples. EXAMPLE 1 : Into 500 ml of an aqueous 4.9 % by weight solution of sulfuric acid, 177 g of DABA (containing 173 g of pure DABA in particles having a mean particle diameter of not larger than 30 µm) were added and after further adding 1 g of SCOUROL® #100 (made of KAO-ATLAS CO.) to the thus formed mixture, a mixture of 284 g of MH (containing 270 g of pure MH in particles having a mean particle diameter of not larger than 50 µm) and 500 ml of water was added to the mixture within 10 hours at 70°C under agitation. After the reaction was over, the reaction mixture was subjected to filtration and the residue was washed with water to the neutral point to obtain 391 g of the dried crude product (containing an amount of LC corresponding to 92 % of the theoretical amount). EXAMPLE 2 : In the same manner as in Example 1 except for using 310 g of MH (containing 270 g of pure MH in particles having a mean particle diameter of not larger than 10 µm) instead of the 284 g of MH used in Example 1, 387 g of the dried crude product (containing an amount of LC corresponding to 90 % of the theoretical amount) were obtained. EXAMPLE 3 : In the same manner as in Example 1 except for adding MH within 5 hours, 390 g of the dried crude product (containing an amount of LC corresponding to 90 % of the theoretical amount) were obtained. EXAMPLE 4 : In the same manner as in Example 1 except for using an aqueous 9.8 % by weight solution of sulfuric acid instead of the aqueous solution of sulfuric acid in Example 1, 387 g of the dried crude product (containing an amount of LC corresponding to 88 % of the theoretical amount) were obtained. EXAMPLE 5 : Into 46.3 g of industrial LC (containing 41.7 g of pure LC in particles having a particle diameter of from 10 to 20 µm), 250 g of an aqueous 1 % weight solution of sulfuric acid, 0.05 g of copper sulfate and 0.1 g of SCOUROL® #100 (made by KAO-ATLAS Co.) were added, and air was introduced into the thus formed mixture at a rate of 100 ml/min for 10 hours at 90°C under agitation. After the reaction was over, the reaction mixture was subjected to filtration and the residue was washed with water to neutrality to obtain 41.1 g of the dried crude product (containing an amount of CVL corresponding to 97 % of the theoretical amount) of a melting point of from 172 to 175°C. COMPARATIVE EXAMPLE : In the same manner as in Example 5 except for not adding copper sulfate, 37.5 g of the dried crude product (containing an amount of CVL corresponding to 12 % of the theoretical amount) were obtained. EXAMPLE 6 : In the same manner as in Example 5 except for adding 0.1 g of cobalt chloride instead of the copper sulfate , 40.5 g of the dried crude product of a melting point of from 171 to 175°C (containing an amount of CVL corresponding to 95.6 % of the theoretical amount) were obtained. EXAMPLE 7 : In the same manner as in Example 5 except for introducing oxygen at ordinary pressure into the reaction solution for 5 hours until the solution was saturated instead of air, 40.8 g of the dried crude product of a melting point of from 172 to 175°C (containing an amount of CVL corresponding to 97 % of the theoretical amount) were obtained. EXAMPLE 8 : Into 500 ml of an aqueous 4.9 by weight solution of sulfuric acid, 177 g of DABA (containing 173 g of pure DABA in particles having a mean particle diameter not larger than 30 µm ) were added and after adding 1 g of SCOUROL® #100 (made by KAO-ATLAS Co.) into the thus formed mixture, a mixture of 500 ml of water and 284 g of MH (containing 270 g of pure MH in particles having a mean particle diameter not larger than 50 µm ) was added to the thus formed mixture at 70°C within 10 hours under agitation. After 2 hours of the addition, 1500 ml of water and 0.5 g of copper sulfate were added to the mixture, and air was introduced to the mixture at a rate of 100 ml/min for 10 hours at 90°C under agitation. After the reaction was over, the reaction mixture was subjected to filtration and the residue was washed with water to neutrality to obtain 410 g of the dried crude product of a melting point of from 172 to 175°C (containing an amount of CVL corresponding to 94 % of the theoretical amount). EXAMPLE 9 : In the same manner as in Example 8 except for adding 310 g of MH (containing 270 g of pure MH in the form of particles having a mean particle diameter of not larger than 10 µm ) instead of the 284 g of MH , 415 g of the dried crude product of a melting point of from 171 to 178°C (containing an amount of CVL corresponding to 92 % of the theoretical amount) were obtained. EXAMPLE 10 : In the same manner as in Example 8 except for adding the same amount of the same MH within 5 hours instead of 10 hours, 412 g of the dried crude product of a melting point of from 172 to 175°C (containing an amount of CVL corresponding to 93 % of the theoretical amount) were obtained. EXAMPLE 11 : In the same manner as in Example 8 except for using 500 ml of an aqueous 9.8 % by weight solution of sulfuric acid instead of the aqueous solution of sulfuric acid used in Example 8, 395 g of the dried crude product of a melting point of from 170 to 178°C (containing an amount of CVL corresponding to 90 % of the theoretical amount) were obtained. EXAMPLE 12 : In the same manner as in Example 8 except for using 1 g of cobalt chloride instead of 0.5 g of copper sulfate , 406 g of the dried crude product of a melting point of from 172 to 175°C (containing an amount of CVL corresponding to 93 % of the theoretical amount) were obtained. EXAMPLE 13 : In the same manner as in Example 8 except for introducing oxygen at ordinary pressure to the reaction solution for 5 hours until the solution was saturated by oxygen instead of introducing air , 412 g of the dried crude product of a melting point of from 172 to 175°C (containing an amount of CVL corresponding to 93 % of the theoretical amount) were obtained.

Claims: A process for producing 3,3-bis-(4-dimethylaminophenyl)-6-dimethylaminophthalide (CVL), which process comprises oxidizing 2-[4,4'-bis-(dimethylamino)-benzhydryl]-5-dimethyl-aminobenzoic acid (LC) in the form of particles having a mean particle diameter not larger than 20 µm in an aqueous solution of sulfuric acid or hydrochloric acid having a pH of from 2.0 to 4.0 with air, oxygen or a gas containing molecular oxygen in the presence of at least one catalyst selected from compounds of iron, copper, cobalt, nickel, chromium, vanadium and manganese at a temperature of from 40 to 120⁰C. A process for producing CVL, which process comprises adding tetramethyl-4,4'-diaminobenzhydrol (MH) in the form of particles having a mean particle diameter of not larger than 50 µm to an aqueous sulfuric acid or hydrochloric acid solution having a pH of from 1.5 to 3.0 containing m-dimethylaminobenzoic acid (DABA) in the form of particles having a mean particle diameter of not larger than 30 µm at a temperature of from 50 to 100°C, thereby forming LC, adding a catalyst selected from compounds of iron, copper, cobalt, nickel, chromium, vanadium and manganese to the reaction mixture and oxidizing the LC in the resultant reaction mixture with air, oxygen or a gas containing molecular oxygen at a temperature of from 40 to l20⁰C. A process according to claim 2, wherein said DABA is in the form of particles having a mean particle diameter of not larger than 5 µm. A process according to claim 2, wherein said MH is in the form of particles having a mean particle diameter of not larger than 10 µm. A process according to claim 2 wherein the reaction of DABA and MH is carried out at a temperature of from 60 to 80°C. A process according to claim 2 , wherein said LC is in the form of particles having a mean particle diameter of not larger than 20 µm. A process according to claim 1, wherein said LC is in the form of particles having a mean particle diameter of not larger than 10 µm. A process according to claims 1 or 2 wherein the catalyst is ferric chloride, ferrous sulfate, cupric chloride, copper sulfate, copper acetate, cobalt chloride, cobalt sulfate, cobalt acetate, manganese chloride, manganese sulfate, chromium sulfate, nickel sulfate or vanadium sulfate. A process according to claims 1 or 2, wherein the pH of the solution used in the oxidation of LG is from 2.0 to 3.0. A process according to claims 1 or 2, wherein a surfactant is added to the reaction system between the MH and DABA or to the reaction system used in the oxidation of LC.

Inventors: FUJINO, YOSHIHARU, KAWAI, HAJIME, TSUNEMITSU, KATUSHIKO
Applicants: YAMADA CHEMICAL CO., LTD.
Application year: 1987
Main classification: C07D307
IPC codes: C09B11, C07D307, B41M5, B01J27, C07B61, C07C227