PREPARATION PROCESS OF BIPHENYL-4,4'-DICARBOXYLIC ACID

Abstract: Biphenyl-4,4′-dicarboxyl ic acid is prepared by oxidizing 4,4′-diisopropylbiphenyl or an oxidation intermediate thereof with molecular oxygen in the presence of an oxidation catalyst, which comprises a cobalt catalyst and/or manganese catalyst, in a solvent containing at least 50 wt.% of an aliphatic monocarboxylic acid having up to 3 carbon atoms.

Description: This invention relates to a process for preparing biphenyl-4,4'-dicarboxylic acid in which 4,4'-diisopropylbiphenyl or an oxidation intermediate thereof is oxidised with molecular oxygen. Biphenyl-4,4′-dicarboxylic acid is useful as a raw material for the production of high-performance polyesters and aramid resins having high heat resistance and strength. The following processes have heretofore been known as preparation processes of biphenyl-4,4'-dicarboxylic acid. (1) 4,4′-Diacetylbiphenyl, which has been obtained by acetylating biphenyl, is oxidized with a hypochlorite [Ukr, Khim Zh., 30, 938-941 (1964)]. (2) p-Bromotoluene is converted with magnesium into 4,4′-dimethylbiphenyl in ether, followed by oxidation with a cobalt catalyst and bromine catalyst in acetic acid [Zr, Prinkl, Khim, 40 , 935 (1967)]. (3) Using iron chloride or aluminum, chloride as a catalyst, biphenyl is reacted with a halogenated cyclohexane in nitrobenzene or carbon disulfide as a solvent to form 4,4′-dicyclohexylbiphenyl. It is then oxidized in the presence of a cobalt catalyst, manganese catalyst and bromine catalyst in acetic acid (Japanese Patent Laid-Open No. 16831/1982). (4) Using BF₃ as a catalyst, a 4-alkylbiphenyl is reacted with carbon monoxide in hydrogen fluoride as a solvent to form a 4-alkyl-4′-formylbiphenyl. It is then oxidized in the presence of a cobalt catalyst, manganese catalyst and bromine catalyst in acetic acid. (Japanese Patent Laid-Open No.174745/1985). These conventional processes are however accompanied by the following problems. The process (1) requires, as a catalyst for the acetylation, a great deal of aluminum chloride which is difficult to regenerate and is highly corrosive. In addition, the oxidation with the hypochlorite induces significant corrosion. It is hence difficult to practise this process industrially. The process (2) obtains the starting material, 4,4′-dimethylbiphenyl, by a Grignard reaction which consumes expensive magnesium. This process is thus impractical. The process (3) obtains the starting material, 4,4′-dicyclohexylbiphenyl by using iron chloride, aluminum chloride or the like, which is difficult to regenerate and is highly corrosive as a catalyst like the process (1) and by employing as a solvent nitrobenzene or carbon disulfide which is very dangerous due to its high inflammability and toxicity. Its industrial practice is therefore very troublesome. Moreover, oxidation of the starting material results in an oxidative loss of the expensive cyclohexyl groups. It is hence difficult to practise this process industrially. The process (4) makes use of hydrogen fluoride and BF₃, which are very corrosive, in order to obtain the starting material, i.e., the 4-alkyl-4′-formyl-biphenyl. It is therefore necessary to use an expensive and corrosion-resistant reactor. This process is accompanied by another drawback that the purification of the resulting product is cumbersome, since di-substituted derivatives other than 4,4′-derivative are also formed. The above-described processes, which have heretofore been proposed as processes for the preparation of biphenyl-4,4′-dicarboxylic acid, are accompanied by their own drawbacks. A great deal of efforts has been exercised to overcome such drawbacks. No satisfactory effects have however been achieved to date. Accordingly, the high price of biphenyl-4,4′-dicarboxylic acid still remains as an obstacle for the expansion of its application field. In a new process according to the invention biphenyl-4,4'-dicarboxylic acid is prepared by oxidising 4,4'-diisopropylbiphenyl or an oxidation intermediate using molecular oxygen under the following conditions: (a) in a solvent containing at least 50 wt.% of an aliphatic monocarboxylic acid having up to 3 carbon atoms; (b) in the presence of at least one oxidation catalyst selected from cobalt catalysts and manganese catalysts in an amount of 0.001-0.2 gram atom in terms of metal element per 100 g of the solvent; (c) in the presence of a bromine compound catalyst in an amount of 1 x 10̅⁴ to 4 x 102̅² gram atom in terms of bromine element per 100 g of the solvent; (d) at a reaction temperature in the range of from 100 to 240°C; (e) at an oxygen partial pressure in the range of from 1 x 10⁴ to 8 x 10⁵ Pa; and (f) at a feeding rate of the starting material to an oxidative reaction system, which has been controlled to 0.01 to 1.5 gram moles per hour and per kilogram of the total amount of the catalyst and solvent in an oxidation reactor. The starting biphenyl derivative is available readily and biphenyl 4,4'-dicarboxylic acid is obtained in a high yield and in a form permitting easy purification. According to the process of this invention, readily available 4,4'-diisopropylbiphenyl or an oxidation intermediate thereof can be used as a starting material. Moreover, biphenyl-4,4'-dicarboxylic acid can be obtained in a high yield with less formation of byproducts. The use of the heavy metal catalyst or catalysts in combination with a bromine catalyst activates the oxidative reaction. Certain features of the present invention will hereinafter be described in detail. (4,4'-diisopropylbiphenyl and its oxidation intermediates). The starting material useful in the practice of this invention, namely, 4,4'-diisopropylbiphenyl can for instance be easily obtained as a product of a purity as high as 99.8% or higher by distilling and separating diisopropylbiphenyls from a reaction mixture, which has been obtained by subjecting biphenyl to propylation and transalkylation by a method known per se in the art and has a high diisopropylbiphenyl content, and then crystallizing and isolating 4,4'-diisopropylbiphenyl alone from the diisopropylbiphenyls in accordance with differences in crystallinity. In the course of an investigation on the preparation of 4,4′-dialkyl-substituted biphenyls which can be derived at a low cost from biphenyl and can be separated easily from other isomers byproduced, the present inventors previously found that 4,4′-diisopropylbiphenyl can be obtained by reacting biphenyl and propylene in the presence of a silica-alumina catalyst. It has conventionally been impossible to isolate a 4,4′-dialkylbiphenyl alone from corresponding dialkylbiphenyls formed by introducing a corresponding lower alkyl group sucy as methyl or ethyl group through an alkylation reaction, because the boiling points of these isomers are too close to permit their separation by distillation and they have no substantial differences in crystallinity, thereby making it difficult to separate them by crystallization. When isopropyl group, an alkyl group having a branched structure, is introduced in biphenyl, substituted derivatives other than the 4,4′-di-substituted derivate are all poor in crystallinity due to steric hindrance and are each in an oily or low m.p. solid form. In contrast, 4,4′-diisopropylbiphenyl has little steric hindrance. Accordingly, its crystallinity is good and its melting point is as high as 64 - 65°C. It can therefore be separated easily from the reaction mixture. The above-described Japanese Patent Laid-Open No. 16831/1982 discloses that 4,4′-dicyclohexylbiphenyl is good in crystallinity and is hence convenient for separation. When biphenyl-4,4′-dicarboxylic acid is prepared by oxidizing this 4,4′-dicyclohexylbiphenyl, ten carbon atoms are however wasted per molecule of 4,4′-dicyclohexylbiphenyl in the course of the oxidative reaction. On the other hand, the present invention makes use of 4,4′-diisopropylbiphenyl as a starting material, thereby bringing about a merit that the loss of carbon atoms in the oxidative reaction has been reduced to only 4 carbon atoms per molecule of 4,4′-diisopropylbiphenyl. The term "oxidation intermediate of 4,4′-diisopropylbiphenyl" as used her ein means a derivative formed by oxidation of 4,4′-diisopropylbiphenyl. It is an oxidation derivative which affords biphenyl-4,4′-dicarboxylic acid upon further oxidation in the reaction system. As its preferable example, 4′-isopropylbiphenyl-4-carboxylic acid may be mentioned. 4′-Isopropylbiphenyl-4-carboxylic acid is a compound having a molecular weight of 240.3 and a melting point of 234.5 - 235.2°c, and is obtained by oxidizing 4,4′-diisopropylbiphenyl with molecular oxygen in the presence of a cobalt catalyst and/or manganese catalyst in a solvent of an aliphatic monocarboxylic acid having up to 3 carbon atoms. It has not previously been known to prepare biphenyl-4,4′-dicarboxylic acid by oxidizing 4,4′-diisopropylbiphenyl or an oxidation intermediate thereof with molecular oxygen. (Solvent) The solvent useful in the practice of this invention is a solvent containing at least 50 wt.% of an aliphatic monocarboxylic acid having up to 3 carbon atoms. Illustrative examples of the aliphatic monocarboxylic acid having up to 3 carbon atoms include formic acid, acetic acid and propionic acid, with acetic acid being particularly preferred. The solvent to be used may be mixed with water, an aldehyde such as paraformaldehyde, or ketone such as methyl ethyl ketone as desired. When water is used, its proportion may preferably be 30 wt.% or lower. When an aldehyde or ketone is employed, it is preferable to limit its proportion to 10 wt.% or less. It is preferable to use the solvent in an amount of about 2 - 20 times by weight as much as the total amount of the starting material, i.e., 4,4′-di isopropylbiphenyl or an oxidation intermediate thereof and the resulting desired compound, i.e., biphenyl-4,4′-dicarboxylic acid. If the solvent should be used in an excessively small amount, the flowability of the reaction system will be reduced to hamper the smooth reaction. Even if the solvent should be used in any large amounts in excess of the upper limit on the contrary, the reaction itself will not be accelerated. It is hence not beneficial to use the solvent in such a large excess amount. (Oxidation catalysts) The cobalt catalyst and manganese catalyst useful in the practice of this invention may be either metals or compounds so long as they are in forms soluble in the oxidative reaction system. No particular limitation is imposed thereon. As specific examples, may be mentioned the inorganic salts of cobalt and manganese such as their oxides, hydroxides, carbonates, basic carbonates and halides, the salts of cobalt and manganese and organic carboxylic acids such as formic acid, acetic acid, propionic acid, fatty acids, naphthenic acid and aromatic carboxylic acids. Of these, their bromides and fatty acid salts are preferred with their acetates being particularly preferred. Although the cobalt catalyst and manganese catalyst may be used singly, they may be used in combination. The cobalt catalyst and/or manganese catalyst are used in a total amount of 0.001 gram atom or more in terms of metal element(s) per 100 gram of the solvent. The selectivity to biphenyl-4,4′-dicarbocylic acid and its oxidation intermediates is improved further as these oxidation catalysts are used in greater amounts. The upper limit to the total amount of the cobalt catalyst and/or manganese catalyst to be used varies depending on their solubilities to the solvent. No significant improvement is however observed to the selectivity even if the catalyst(s) are used in any total amount greater than 0.2 gram atom in terms of metal element(s) per 100 g of the solvent. It is hence economically disadvantageous to use the catalyst(s) in such an excess amount. The total selectivity to oxidation intermediates and biphenyl-4,4′-dicarboxylic acid is improved as mentioned above, for example, to 95% or higher when the total amount, namely, total concentration of the cobalt catalyst and/or manganese catalyst increases. On the other hand, a fact is observed that the velocity of formation of biphenyl-4,4′-dicarboxylic acid is rendered slower as that concentration increases. The present inventors have hence proceeded with a further investigation. As a result, it has also been found that biphenyl-4,4′-dicarboxylic acid can be formed at a high selectivity and a high formation velocity when a compound capable of yielding bromine ions is used as an additional oxidation catalyst in combination with the cobalt catalyst and/or manganese catalyst. As illustrative examples of the compound which can yield bromine ions and is employed as the additional oxidation catalyst, may be mentioned inorganic substances such as molecular bromine, hydrogen bromide metal bromides, ammonium bromide and hydrobromides as well as organic compounds such as ethyl bromide and bromoacetic acid. Although no particular limitation is imposed so long as the compound is dissolved in the oxidative reaction system to yield bromine ions, hydrogen bromide, potassium bromide and ammonium bromide are preferred. The above bromine compound may be added to the reaction system from the beginning. As an alternative, when 4,4′-diisopropylbiphenyl is used as a starting material, it may be added either at once or gradually to the reaction system after the formation of an oxidation intermediate. The bromine compound may be added in an amount of 1 x 10⁻⁴ gram atom to 4 x 10⁻² gram atom in terms of bromine element per 100 grams of the solvent. If the amount of the bromine compound should be smaller than 1 x 10⁻⁴ gram atom in terms of bromine element, the velocity of formation of biphenyl-4,4′-dicarboxylic acid by the oxidation reaction will be slow. On the other hand, any amounts greater than 4 x 10⁻² gram atom will result in an increase to the formation of byproducts having one or more bromine atoms bonded on the biphenyl ring, so that the purification of biphenyl-4,4′-dicarboxylic acid from the reaction mixture will be rendered difficult. (Reaction conditions) Although the starting material, namely, 4,4′-diisopropylbiphenyl may be added to at once the oxidative reaction system containing the solvent and oxidation catalyst(s), still better results may be obtained when it is added gradually at a predetermined feeding rate. Since the tertiary hydrogen atoms in the two isopropyl groups of 4,4′-diisopropylbiphenyl are active, the hydrogen abstraction reaction as the first stage of the oxidative reaction proceeds easily. The velocity of the abstraction reaction of the tertiary hydrogen atoms in the two isopropyl groups of 4,4′-diisopropylbiphenyl is faster than the velocity of formation of the desired compound, i.e., biphenyl-4,4′-dicarboxylic acid. If the feeding rate of 4,4′-diisopropylbiphenyl to the oxidative reaction system is too high, it is estimated that the concentrations of reaction products in some intermediate stages of the oxidation would increase and when their concentrations exceed certain levels, a side reaction would be induced to form a polycondensation product and the yield of the desired compound would be lowered correspondingly. The existence of an important causal relation is therefore recognized between the feeding rate of 4,4′-diisopropylbiphenyl to the oxidative reaction system and the yield of biphenyl-4,4′-dicarboxylic acid. The feeding rate of 4,4′-diisopropylbiphenyl to the oxidative reaction system is in a range from of 0.01 gram mole to 1.5 gram moles per hour and per kg of the total weight of the catalyst(s) and solvent in the reactor. Any feeding rates smaller than 0.01 gram mole per hour are impractical because a large reactor is required. On the other hand, any feeding rates greater than 1.5 gram moles per hour result in an increase of the formation of byproducts due to side reactions, thereby lowering the yield of the desired compound. The reaction temperature is in the range from 100°C to 240°C. Any temperatures lower than the lower limit result in a slow reaction velocity, while any temperatures higher than the upper limit lead to more oxidative decomposition of the solvent. It is hence not preferable to use any reaction temperature outside the above range. The pressure of the oxidative reaction system may be at any level, so long as the solvent is allowed to remain in a liquid phase at the reaction temperature. As the oxygen partial pressure, 0.1 - 8 kg/cm²-abs. (1x10⁴ - 8x10⁵Pa absolute pressure) is sufficient. In the case of molecular oxygen diluted with an inert gas, for example, air, a range of 0 - 30 kg/cm² (0-3x10⁶Pa gauge-pressure) is sufficient as its total pressure. The process of this invention for the preparation of biphenyl-4,4′-dicarboxylic acid is superior in that it has both of the following merits: (1) The preparation of its starting material, i.e., 4,4′-diisopropylbiphenyl or its oxidation intermediate is easy; and (2) The reaction product is practically free of biphenyldicarboxylic acids other than the 4,4′-derivative and the purification of the intended compound is easy. The preparation process of this invention is therefore useful in the industry. The present invention will hereinafter be described in detail by the following Examples. It should however be borne in mind that the present invention is not necessarily limited to the following Examples. Example 1(comparative): Five experiments were conducted separately by varying the kind and amount of the catalyst and reaction time as shown in Table 1. In each experiment, 10 g of 4,4′-diisopropylbiphenyl, 100 g of glacial acetic acid and the corresponding amounts(s) of the corresponding catalyst(s) were charged in a 200 ml autoclave made of titanium. The contents were stirred vigorously at 180°C while maintaining the pressure at 15kg/cm²-G (1.5x10⁶Pa gauge pressure). Air was fed at a rate of 24 1 (STP-standard reference conditions) per hour. After proceeding with the reaction for a predetermined period of time, the reaction mixture was cooled. Biphenyl-4,4′-dicarboxylic acid which had crystallized out was collected by filtration and washed with hot acetic acid and then with water, whereby biphenyl-4,4′-dicarboxylic acid was isolated. The filtered cake and filtrate were also analyzed to obtain results shown in Table 1. From Table 1, it is appreciated that the total selectivity to 4′-isopropylbiphenyl-4-carboxylic acid, an oxidation intermediate, and biphenyl-4,4′-dicarboxylic acid reaches as high as 95% or even higher when the cobalt and manganese catalysts are used in large amounts. It is also understood that the unreacted starting material and the oxidation intermediate are eliminated and are converted into biphenyl-4,4′-dicarboxylic acid in a short period of time by an addition of a bromine compound. Example 2(comparative): Charged in a 5ℓ autoclave made of titanium were 2,380 g of glacial acetic acid, 12 g of cobalt acetate tetrahydrate and 24 g of manganese acetate tetrahydrate. While stirring the contents vigorously, air was fed at 190°C and 15kg/cm²-G (1.5x10⁶Pa gauge pressure) at a rate of 600 1 (STP-standard reference conditions) per hour. Into the autoclave, 238 g of 4,4′-diisopropylbiphenyl was fed in the course of 3 hours. After the feeding of the starting material, air was introduced at the same temperature and pressure for additional 2 hours. At that time, the feeding rate of 4,4′-diisopropylbiphenyl was 0.14 gram mole per hour and per kg of the total weight of the catalysts and acetic acid in the autoclave. After the reaction, the reaction mixture was cooled and filtered. The filtered cake was washed with hot acetic acid and then with water, thereby obtaining 190 g of crude biphenyl-4,4′-dicarboxylic acid whose purity was 93.6%. The yield was 73.5%. Here, 36 g of 4′-isopropylbiphenyl-4-carboxylic acid was contained in total in the filtrate and washing. Example 3 Charged in a 5ℓ autoclave made of titanium were 1,190 g of glacial acetic acid, 76 g of cobalt acetate tetrahydrate, 225 g of manganese acetate tetrahydrate and 12 g of ammonium bromide. While stirring the contents vigorously, air was fed at 180°C and 9kg/cm²-G (9x10⁵Pa gauge presssure) at a rate of 1,200 1 (STP-standard reference conditions) per hour. Into the autoclave, 238 g of 4,4′-diisopropylbiphenyl was fed in the course of 1 hour. After the feeding of the starting material, air was introduced at the same temperature and pressure for additional 2 hours. At that time, the feeding rate of 4,4′-diisopropylbiphenyl was 0.67 gram mole per hour and per kg of the total weight of the catalysts and acetic acid in the autoclave. After the reaction, the reaction mixture was cooled down to 100°C and filtered. The filtered cake was washed with hot acetic acid and then with water, thereby obtaining 230 g of crude biphenyl-4,4′-dicarboxylic acid whose purity was 95%. The yield was 90.3%.

Claims: A process for the preparation of biphenyl4,4'-dicarboxylic acid, which comprises oxidizing 4,4'-diisopropylbiphenyl or an oxidation intermediate thereof with molecular oxygen, under the following conditions: (a) in a solvent containing at least 50 wt.% of an aliphatic monocarboxylic acid having up to 3 carbon atoms; (b) in the presence of at least one oxidation catalyst selected from cobalt catalysts and manganese catalysts in an amount of 0.001-0.2 gram atom in terms of metal element per 100 g of the solvent; (c) in the presence of a bromine compound catalyst in an amount of 1 x 10̅⁴ to 4 x 10̅² gram atom in terms of bromine element per 100 g of the solvent; (d) at a reaction temperature in the range of from 100 to 240°C; (e) at an oxygen partial pressure in the range of from 1 x 10⁴ to 8 x 10⁵ Pa; and (f) at a feeding rate of the starting material to an oxidative reaction system, which has been controlled to 0.01 to 1.5 gram moles per hour and per kilogram of the total amount of the catalyst and solvent in an oxidation reactor. The process as claimed in claim 1 wherein the bromine compound catalyst is selected from molecular bromine, hydrogen bromide, metal bromides, hydrobromides, ammonium bromide, ethyl bromide and bromoacetic acid. The process as claimed in claim 1 or 2 in which the cobalt catalyst and/or manganese catalyst comprise the salts of inorganic or organic acids or oxides or hydroxides. The process as claimed in claim 3 in which the cobalt and/or manganese catalyst comprise the acetates or bromides. The process as claimed in any of the preceding claims in which the solvent also comprises water, preferably in an amount of less than 30% by weight of the solvent. The process as claimed in any of claims 1 to 4 in which the solvent also comprises an aldehyde or a ketone preferably in an amount of less than 10% by weight of the solvent. The process as claimed in any of the preceding claims in which the aliphatic monocarboxylic acid is acetic acid.

Inventors: HAYASHI, SHOICHIRO, KONAI, YUTAKA, MATSUDA, TOSHIHARU, NAKAMURA, TADASHI, SASAKAWA, ATSUSHI
Applicants: KUREHA KAGAKU KOGYO KABUSHIKI KAISHA
Application year: 1987
Main classification: C07C63
IPC codes: C07C51, B01J31, C07B61, C07C63, C07C67