PROCESS FOR THE PREPARATION OF A CARBOXYLIC ANHYDRIDE

Abstract: The present invention provides a colorless and transparent carboxylic anhydride with excellent stability in a liquid state at room temperature which is useful in uses such as a curing agent for epoxy resins, a liquid state encapsulant for semiconductors, and a liquid state encapsulant for light emission diodes. Said carboxylic anhydride which is a liquid at 20 DEG C containing a carboxylic anhydride not having carbon-carbon double bond such as 3-isobutyl-5,6-dimethylcyclohexane-1,2-dicarboxylic anhydride, 3-( beta -methylbutyl)-5-methylcyclohexane-1,2-dicarboxylic anhydride, and 4-isohexylcyclohexane-1,2-dicarboxylic anhydride is prepared by forming an acid anhydride compound having a cyclohexane ring by a Diels-Alder reaction of a diene-hydrocarbon or triene-hydrocarbon having a carbon number of 10 with maleic anhydride, followed by carrying out a stereo-isomerization in the presence of a catalyst, and further carrying out hydrogenation of said reaction product.

Description: PROCESS FOR THE PREPARATION OF A CARBOXYLIC ANHYDRIDE The present invention relates to a process for the preparation of a carboxylic anhydride. In particular, the present invention relates to a process for the preparation of a carboxylic anhydride having a cyclohexane ring which is a liquid at room temperature, which can be employed as a curing agent for epoxy resins, and which is useful in uses such as a liquid encapsulant for semiconductors, a liquid encapsulant for light emission diodes, and optical materials. Heretofore, most compounds are obtained as solid products by a Diels-Alder reaction of a diene- hydrocarbon or triene-hydrocarbon having a carbon number of 10 with maleic anhydride. For example, a carboxylic anhydride obtained from alloocimene which is one kind of dimethyl octatrienens, and maleic anhydride, is a solid having a melting point of 83 to 85 °C, and is troublesome in handling as a curing agent for epoxy resins. Therefore, in e.g. JP-A-54039048 , JP-A-55064581, and JP-A-55072184 there is proposed a process in which it is converted into a liquid state carboxylic anhydride by a catalytic isomerization. The carboxylic anhydrides obtained by the processes are liquids at room temperature, and those are excellent in handling. However, since said carboxylic anhydrides include unsaturated bonds, coloration is significant in a cured epoxy resin, they are unsuitable for using as a material such as optical materials which require the colorless and transparency. On the other hand, in e.g. British Patent No. 906017 there is also proposed a process in which a solid carboxylic anhydride obtained by a Diels-Alder reaction is liquefied by hydrogenation . In the carboxylic anhydride obtained by the process, coloration is slight, whereby, it can be employed as a curing agent for the preparation of a cured epoxy resin which can be utilized for the uses such as optical materials. However, a hydrogenated carboxylic anhydride in a high purity which is obtained by a recrystalliza- tion process is a solid having a melting point of 53 to 55 °C, and it is troublesome in handling as a curing agent for epoxy resins. Accordingly, a liquid state carboxylic anhydride is obtained as a mixture by controlling a ratio of hydrogenation in 70% or so. However, the process has a problem that a carboxylic anhydride obtained is yellow-colored because of comprising colored unhydrogenated compounds by 30% or so . Further, it also has another problem that a carboxylic anhydride in a high purity cannot be obtained because of side reactions in the case that the ratio of hydrogenation is increased by a severe hydrogenation condition. At the present time, there has not been obtained a liquid carboxylic anhydride which is colorless, transparent, and highly pure, with good stability by manufacturing from a hydrocarbon compound of a diene or triene having a carbon number of 10, and maleic anhydride . Therefore, in use of such optical materials which require colorless and transparent materials, there are employed hexahydrophthalic anhydride and methylhexa- hydrophthalic anhydride which are obtained from maleic anhydride and dienes having a carbon number of 4 to 5. However, the acid anhydrides themselves are highly hygroscopic, whereby, they have a problem of readily forming acids and also have a problem that the cured products of epoxy resin cured with the carboxylic anhydrides is hygroscopic, and thus unsuitable for the use which require a low water absorption property. The present invention, by which the aforementioned problems are solved, aims at providing a process for readily preparing a carboxylic anhydride having a high purity from a hydrocarbon compound of a diene or triene having a carbon number of 10 and maleic anhydride, which has low water absorption property, and is excellent in the colorless and transparency, and a liquid at room temperature. Also, the present invention aims at providing a carboxylic anhydride which is low hygroscopic, excellent in colorless and transparency and a liquid at room temperature and thus is useful for uses such as a curing agent for epoxy resins, a liquid encapsulant for semiconductors, a liquid encapsulant for light emission diodes, and optical materials. As a result of extensive research and experimentation such a process aimed could be found. Accordingly the present invention relates to a process for the preparation of a carboxylic anhydride which is a liquid at 20 °C containing a carboxylic anhydride not having carbon-carbon double bond by forming a carboxylic anhydride having a cyclohexene ring by a Diels-Alder reaction of a diene- or triene- hydrocarbon compound, having a carbon number of 10, with maleic anhydride, followed by carrying out a stereo-isomerization reaction in the presence of a catalyst to prepare a reaction product liquefied, successively by carrying out a hydrogenation of said reaction product. A preferred embodiment of the present invention relates to a process for the preparation of the aforementioned carboxylic anhydride, in which dimethyloctatriene is employed. More preferably alloocimene is employed as the aforementioned dimethyloctatriene . According to still another one of the most preferred embodiments of the process, the afore- mentioned stereo-isomerization reaction is carried out in a temperature range of 100 to 250 °C, and preferably from 175-225 °C,and the catalyst for an isomerization is employed under conditions within a range of 0.005 to 5 parts by weight based on 100 parts by weight of the carboxylic anhydride. Furthermore, the present invention relates to a process for the preparation of the aforementioned carboxylic anhydride, in which the aforementioned hydrogenation reaction is carried out until a carboxylic anhydride not having carbon-carbon double bond attains to not less than 90% by weight. As the diene- or triene-hydrocarbon compound to be employed in the present invention, for example, there are exemplified alloocimene, ocimene, myrcene, 2 , 7-dimethyl-l, 3, 7-octatriene, and 2, 6-dimethyl-l, 3, 6- octatriene, etc. Among the diene- or triene-compound, alloocimene is particularly preferred from a viewpoint of the ready availability and liquid state stability of the obtained carboxylic anhydride. Further, although alloocimene can be employed as a mixture with other diene- or triene-compounds, alloocimene is preferably employed in a proportion of not less than 50% in the mixture. The catalyst for stereo isomerization to be employed in the present invention is a compound or a mixture of more than two kinds of compounds selected from a compound having nitrogen atom (s), a phosphine compound, a salt of an alkaline metal, and a salt of thiocyanic acid. As the compound having nitrogen atom (s), there are employed tertiary amines, salts of tertiary amines, imidazoles, salts of imidazoles, and salts of quaternary ammonium. As the tertiary amines, for example, there are employed aliphatic tertiary amines such as triethylamine, tri-n-propylamine, tri-n- butylamine, tri-2-ethylhexylamine, trilaurylamine, and triethanolamine, cycloaliphatic tertiary amines such as N, N ' -dimethylpiperazine, N, N ' -bis [ (2-hydroxy) - propyl] piperazine, N-alkylmorpholine, 1,4-diazabi- cyclo [2.2.2] octane, N, N ' -dimethylcyclohexylamine, and N-alkylpyrrolidine, unsaturated cyclic tertiary amines such as pyridine, α-picoline, 3, 5-lutidine, and diazabicycloalkenes . As the imidazoles, for example, there are employed 2-methylimidazole, 2-ethyl-4- methylimidazole, 2-undecylimidazole, 2-phenylimidazole, l-benzyl-2-methylimidazole, and l-cyanoethyl-2- methylimidazole . As the salts of the tertiary amines and the salts of imidazoles, for example, there are employed salts of a mineral acid such as a chloric acid salt and a sulfuric acid salt of tertiary amines and imidazoles, salts of an organic carboxylic acid such as salts of an acetic acid and salts of 2-ethylhexyl acid, and salts of a phenol such as salts of a bisphenol and salts of hydroquinone . As the salts of quaternary ammonium, for example, there are employed tetramethylammonium chloride, tetraethyl ammonium chloride, tetraethyl- ammonium bromide, tetraethylammonium iodide, tetra- butylammoniu bromide, lauryltrimethylammonium chloride, and benzyltrimethylammonium chloride. As the salts of the phosphine compounds, there are employed trialkyl phosphines, triphenylphosphines, or salts of quaternary phosphonium, etc. As the trialkyl- phosphines, for example, there are employed tri- methylphosphine, triethylphosphine, triisopropyl phosphine, tri-n-butylphosphine, trioctylphosphine, and tricyclohexylphosphine . As the triphenylphosphines, for example, there are employed triphenylphosphine, tri- tolyl phosphine, and tris (2, 6-dimethoxyphenyl) - phosphine. As the salts of quaternary phosphonium, for example, there are employed tetramethyl phosphonium chloride, tetraethyl phosphonium chloride, tetraethylphosphonium bromide, tetraethylphosphonium iodide, tetrabutyl phosphonium bromide, lauryltrimethyl phosphonium chloride, and benzyltrimethyl phosphonium chloride, ethyltriphenyl phosphonium iodide, tetraphenyl phosphonium chloride, and tetraphenyl phosphonium bromide . As the salts of an alkaline metal, for example, there are employed halogenated alkaline metals, salts of alkaline metal of an inorganic acid, or salts of an alkaline metal of an organic acid. As the halogenated alkaline metals, for example, there are employed lithium chloride, lithium bromide, sodium chloride, sodium bromide, sodium iodide, potassium chloride, potassium bromide, potassium iodide, and cesium chloride. Examples of the salts of an alkaline metal of an inorganic acid, are lithium sulfate, lithium nitrate, lithium phosphate, lithium carbonate, sodium sulfate, sodium nitrate, sodium phosphate, sodium carbonate, potassium sulfate, potassium nitrate, potassium phosphate, and potassium carbonate. Lithium salts are the preferred ones. Examples of the salts of an alkaline metal of an organic acid, are lithium acetate, lithium oxalate, lithium octylate, lithium salicylate, sodium acetate, sodium benzoate, potassium acetate, potassium oleate, and potassium lactate. Examples of the salts of the thiocyanic acid are salts of an alkaline metal of thiocyanic acid, salts of an alkaline earth metal of thiocyanic acid, or a salt of ammonium thiocyanate. As the salts of an alkaline metal of thiocyanic acid, there are exemplified sodium thiocyanate and potassium thiocyanate, and as the salts of an alkaline earth metal of thiocyanic acid, there are exemplified magnesium thiocyanate and calcium thiocyanate . The isomerization is a stereo-isomerization of an acid anhydride compound having a cyclohexene ring which is a product in a Diels-Alder reaction. The isomeriza- tion is preferably carried out in a temperature range of 100 to 250 °C and more preferably in a temperature range of from 175-225 °C. In the case that the temperature in the isomerization is less than 100 °C, the reaction does not readily proceed, and in the case that it exceeds 250 °C, side reactions occur, unpreferably resulting in a yield decrease. The catalysts in the isomerization are employed in an amount ranging from 0.005 to 5 parts by weight, preferably from 0.01 to 3 parts by weight based on 100 parts by weight of the carboxylic anhydride . In the case that the amount of the catalysts for the isomerization is less than 0.005 part by weight, the reaction does not readily proceed, and in the case that it exceeds 5 parts by weight, side reactions readily occur, and color hue of the carboxylic anhydride obtained becomes worse. The hydrogenation reaction in the present invention is a hydrogenation to carbon-carbon double bond. A usual catalytic reduction can be employed for the reaction methods. The reaction is carried out at a temperature of 30 to 200 °C, and preferably 50 to 150 °C under a pressure of not less than 10 kg/cm^, and preferably not less than 60 kg/cm^, and for a reaction time of 0.5 to 20 hours in the presence of hydrogen and a catalyst. As the catalyst, there can be employed a nickel- based catalyst such as a Raney-nickel or nickel- diatomaceous, and platinum group catalysts such as platinum, a palladium black rhodium, and ruthenium, etc . In the above-mentioned reaction conditions, the hydrogenation is carried out until a carboxylic anhydride not having carbon-carbon double bond attains to not less than 90% by weight, and preferably not less than 95% by weight. In the case that the carboxylic anhydride not having the double bond is less than 90% by weight, coloration increases, unpreferably resulting in that it cannot be employed for uses such as optical materials . The reaction in order to obtain a desired carboxylic anhydride is carried out by a Diels-Alder reaction method in which a diene or triene is added dropwise in a range of 0.8 to 1.2 mol and preferably in the range of 0.9 to 1.1 mol of a carboxylic anhydride based on 1 mol of the diene-or triene-hydrocarbon compound having a carbon number of 10, while maintaining the reaction temperature in a range of 50 to 180 °C, and preferably 70 to 150 °C . After the completion of the dropwise addition, a solid carboxylic anhydride is obtained by carrying out a reaction for aging for 0.5 to 3 hours while maintaining the temperatures . Subsequently, the aforementioned catalyst for isomerization is added, and the isomerization is carried out for 0.1 to 10 hours, preferably 0.5 to 4 hours while maintaining the temperature in a range of 100 to 250 °C and preferably from 175 to 225 °C, to obtain a liquid state carboxylic anhydride. Subsequently, a hydrogenation reaction of the liquid state carboxylic anhydride obtained in the aforementioned conditions followed by a distillation refining, or a distillation refining followed by a hydrogenation gives a carboxylic anhydride having a cyclohexane ring which is liquid state at 20°C. There is described below a reaction formula showing a process for the preparation of a liquid carboxylic anhydride from alloocimene and maleic anhydride as starting materials. (trans form) According to the present invention, there can be_ readily manufactured in a high yield a hydrogenated carboxylic anhydride with excellent colorless transparency and liquid state stability from a hydrocarbon compound of a diene or triene having a carbon number of 10. Also, the liquid carboxylic anhydride obtained has an excellent property as a curing agent for epoxy resins, and it can be employed in extensive uses such as a liquid encapsulant for semiconductors, a liquid state encapsulant for emission diodes, and optical materials . Hereinafter, the present invention is illustrated in more detail based on Examples and Comparative Examples. Example 1 A 1-liter four-necked flask equipped with an agitator, a thermometer, a condenser, and a dropwise funnel was charged with 245 g (2.5 mol) of maleic anhydride, and then 357 g (2.625 mol) of alloocimene was added dropwise over 1 hour while maintaining a temperature in a system at 80 °C and agitating. After the completion of the dropwise addition, aging was further carried out at the temperature of 80 °C for 1 hour to complete Diels-Alder reaction. After the completion of the reaction, 0.6 g of lithium bromide was added into a reaction solution, and the temperature in the system was elevated to 200°C, followed by agitating at the temperature for 1 hour to carry out an isomerization reaction. Subsequently, a single-stage distillation was carried out under the reduced pressure of 0.9 mmHg, and distillates at 150 to 165 °C were collected to obtain 536 g (a yield of 91.6%) of yellowish liquid of a carboxylic anhydride. After the completion of the distillation, a 1-liter autoclave was charged with 500 g of the carboxylic anhydride obtained and 2.5 g of 5%-palladium black as a catalyst, and then a reduction reaction was carried out for 7 hour while maintaining conditions of the hydrogen pressure of 100 kg/cm2, the temperature of 90 °C, and agitating speed of 500 to 800 rpm. After the completion of the reaction, the catalyst was filtered to obtain 490 g (a yield of 96.4%) of 3-isobutyl-5, 6-dimethylcyclohexane-l, 2-dicarboxylic anhydride which is a colorless and transparent liquid. The carboxylic anhydride showed APHA of 20, viscosity of 540 cps at 20 °C, and purity of 98.2% by GPC and GC analyses. And, the carboxylic anhydride showed excellent stability of a liquid state which did not solidify even being stored at the temperature of 5 °C for 3 months after adding 1% by weight of crystal nuclei of a solid maleic anhydride-alloocimene adduct . Comparative Example 1 Diels-Alder reaction by the same conditions as in Example 1 was carried out, and a single-stage distillation of an obtained carboxylic anhydride was carried out under the reduced pressure of 0.9 mmHg and collecting distillates at 150 to 165 °C gave 545 g (a yield of 93.2%) of a brownish yellow solid of a carboxylic anhydride. After the completion of the distillation, a solid of the carboxylic anhydride was reduced under the same conditions as in Example 1 to obtain 492 g (a yield of 96.8%) of a yellow liquid of 3-isobutyl-5, 6-dimethyl- cyclohexane-1, 2-dicarboxylic anhydride. The carboxylic anhydride showed purity of 86.2% by GPC and GC analysis through which polymeric impurities were identified. And it showed APHA of 100, and viscosity of 1020 cps at 20 °C. Comparative Example 2 Diels-Alder reaction was carried out under the same conditions as in Comparative Example 1, and a 1-liter autoclave was charged with 250 g of the carboxylic anhydride obtained by a single-stage distillation, 250 g of ethyl acetate, and 5 g of Raney-nickel as a catalyst, and then a reducing reaction was carried out for 8 hour while maintaining the conditions of hydrogen pressure of 80 kg/cm 2 , temperature of 90 °C, and agitating speed of 500 to 800 rpm. After the completion of the reaction, the catalyst was filtered and ethyl acetate was removed by a distillation at 70 °C and 5 mmHg to obtain 243 g (a yield of 95.4%) of 3- isobutyl-5, 6-dimethylcyclohexane-l, 2-dicarboxylic anhydride which is a yellow liquid. The carboxylic anhydride showed APHA of not less than 300, viscosity of 450 cps at 20 °C, and purity of 71.2% by GPC and GC analysis, and it was identified that unhydrogenated compound was remained in a large amount. Still further, the carboxylic anhydride was solidified by being stored at the temperature of 5 °C for 1 month after the addition of 1% by weight of a crystal nucleus of a solid maleic anhydride-alloocimene adduct . Example 2 Diels-Alder reaction and isomerization reaction were carried out under the same conditions as in Example 1. A 1-liter autoclave was charged with all amount of a reaction solution which is not distilled and 2.5 g of 5%-paradium black as a catalyst, and then a reducing reaction was carried out for 7 hour while maintaining the conditions of the hydrogen pressure of 100 kg/cm 2 , the temperature of 90 °C, and agitating speed of 500 to 800 rpm. After the completion of the reactions, the catalyst was filtered, subsequently, a single-stage distillation was carried out at the reduced pressure of 0.9 mmHg to obtain 529 g (a yield of 88.9%) of 3-isobutyl-5, 6-dimethylcyclohexane-l, 2- dicarboxylic anhydride which is a colorless and transparent liquid by collecting distillates at distilling temperatures of 150 to 165 °C . The carboxylic anhydride showed APHA of 30, viscosity of 530 cps at 20 °C, and purity of 97.7% by GPC and GC analysis. Further, the carboxylic anhydride did not solidify even being stored at the temperature of 5 °C for 3 months after the addition of 1% by weight of a crystal nucleus of a solid maleic anhydride-alloocimene adduct, and it was excellent in stability in a liquid state . Examples 3 to 10 The same operations were carried out as in Example 1, except that the diene or triene, catalysts for isomerization, and conditions for isomerization were changed as described in Table 1 to obtain carboxylic anhydrides which are a colorless and transparent liquid. Results are shown in Table 1. [Table 1 1) 2, 6-dimethyl-l, 3, 6-octatriene 2 ) 3-isobutyl-5, 6-dimethyleyelohexane-1 , 2- dicarboxylic anhydride 3) a mixture composed of 3-isobutyl-5, 6- dimethylcyclohexane-1, 2-dicarboxylic anhydride and 3- (β-methylbutyl) -5-methylcyclohexane-l, 2-dicarboxylic anhydride 4) a mixture composed of 3-isobutyl-5, 6- dimethylcyclohexane-1, 2-dicarboxylic anhydride and 4-isohexylcyclohexane-l, 2-dicarboxylic anhydride

Claims: C L A I M S 1. A process for the preparation of a carboxylic anhydride which is a liquid at 20 °C containing a carboxylic anhydride not having carbon-carbon double bond by forming an acid anhydride compound having a cyclohexene ring by a Diels-Alder reaction of a diene- hydrocarbon or triene-hydrocarbon having a carbon number of 10 with maleic anhydride, followed by carrying out a stereo-isomerization reaction in the presence of a catalyst to prepare a reaction product, and further carrying out a hydrogenation of said reaction product. 2. A process for the preparation of a carboxylic anhydride as claimed in claim 1, wherein said diene- hydrocarbon or triene-hydrocarbon having a carbon number of 10 is dimethyloctatriene. 3. A process for the preparation of a carboxylic anhydride as claimed in claim 2, wherein said dimethyl octatriene is alloocimene. 4. A process for the preparation of a carboxylic anhydride as claimed in claim 1, wherein said catalyst for a stereo-isomerization is at least one compound selected from a compound having nitrogen atom (s), a phosphine compound, a salt of an alkaline metal, and a salt of thiocyanic acid. 5. A process for the preparation of a carboxylic anhydride as claimed in claim 4, wherein said compound having nitrogen atom (s) is at least one compound selected from tertiary amines, salts of tertiary amines, imidazoles, salts of imidazoles, and salts of quaternary ammonium. 6. A process for the preparation of a carboxylic anhydride as claimed in claim 4, wherein said phosphine compound is trialkyl phosphines, triphenyl phosphines, or salts of quaternary phosphonium. 7. A process for the preparation of a carboxylic anhydride as claimed in claim 4, wherein said salts of an alkaline metal are salts of a halogenated alkaline metal, alkaline metal salts of an inorganic acid, or alkaline metal salts of an organic acid. 8. A process for the preparation of a carboxylic anhydride as claimed in claim 4, wherein said salt of thiocyanic acid is alkaline metal salts of thiocyanic acid, alkaline earth metal salts of thiocyanic acid, or ammonium salt of thiocyanic acid. 9. A process for the preparation of a carboxylic anhydride as claimed in claim 1, wherein said stereo- isomerization reaction is carried out at a temperature range of 100 to 250 °C, and said catalyst for the stereo-isomerization reaction is employed in a range of 0.005 to 5 parts by weight based on 100 parts by weight of said carboxylic anhydride. 10. A process for the preparation of a carboxylic anhydride as claimed in claim 1, wherein said hydrogenation reaction is carried out until said carboxylic anhydride not having carbon-carbon double bond attains to not less than 90% by weight.

Inventors: MIURA MAREKI, OHNUMA YOSHINOBU, MIURA, MAREKI, OHNUMA, YOSHINOBU
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1998
Main classification: C07D307
IPC codes: C07B61, C07C51, C07D307