Process for synthesizing hydroxymethyl-dihalo-dialkylphenol

Abstract: A hydroxymethyl-dihalo-dialkylphenol is synthesized by contacting a halomethyl-dihalo-­ dialkylphenol with a substantial excess of water in a water-miscible organic solvent at a temperature of less than 55°C. The obtained product can be used to form epoxy resins useful as electrical components.

Description: The present invention relates to the art of producing hydroxymethyl-dihalo-dialkylphenols. It relates more specifically to the art of hydrolyzing halogenated substituted phenols, particularly brominated mesitols. Halogenated dihydroxy aromatic compounds are useful intermediates and curing agents for flame retardant epoxy resins. See, e.g., Mendoza, Brominated Hydroxyaromatic Compounds , U.S. Patent 4,621,159 (November 4, 1986); Silvis et al., Brominated Epoxyaromatic Compounds , U.S. Patent 4,661,644 (April 28, 1987); Mendoza, Brominated Hydroxyaromatic Compounds , U.S. Patent 4,705,901 (November 10, 1987); Berman, Halogenated Epoxy Resins , U.S. Patent 4,727,119 (February 23, 1988); and Mendoza et al., Meta-Halo-Phenolic Alkylation Products and Epoxy Systems , U.S. Patent 4,731,423 (March 15, 1988). In particular, 4-hydroxymethyl-dihalo-dialkylphenols (hereinafter referred to as 4-hydroxymethylphenols) are preferred reagents for making cured epoxy resins. Mendoza et al., Meta-Halo-Phenolic Alkylation Products and Epoxy Systems , U.S. Patent 4,731,423 (March 15, 1988). 4-hydroxymethylphenols are prepared in a two-step process from 4-methyl-dialkylphenols, such as mesitol. First, the 4-methyl-dialkylphenol is halogenated with a halogenating agent such as molecular bromine to form a 4-halomethyl-dihalo-dialkylphenol (hereinafter referred to as 4-halomethylphenol), according to a process such as that described in Mendoza, Di-ortho-substituted Di-meta-halogenated Para-halomethylphenols , U.S. Patent 4,684,752 (August 4, 1987). Second, the 4-halomethylphenol undergoes hydrolysis to form the 4-hydroxymethylphenol according to the process described in Auwers, et al., "Anhydro-p-hydroxymesityl Alcohol and its Conversion Products", 302 Ann. Chem. 76 (1898) and Auwers, et al., "Ueber Dibrom-p-oxymesityl-alkohol," 32 Chem. Berichte 3309 (1899). In actual practice, the synthesis described above gives a mixture of products. First, halogenation of 4-methyl-2,6-dialkylphenols yield some 2-halogenated product. For instance, halogenation of mesitol with bromine, produces ortho- and para-tribromomesitol and tetrabromomesitol illustrated below. Second, hydrolysis of the halomethylphenol mixture permits further side reactions. In one side reaction hydroxymethylphenol product reacts with halomethylphenol reagent to form a bis-(4-hydroxy-2,6 dihalo-3,5-dialkylbenzylic) ether (hereinafter referred to as ether). In another side reaction, the halomethylphenol or hydroxymethylphenol can react with the solvent to form side products. For instance, hydrolysis of the previously described halogenated mesitol mixture in acetone yields ortho- and para-dibromomesitol benzyl alcohol (DBMBA), di-hydroxymethyl-dibromomesitol (DHDBM), dibromomesitylbenzyl ether (DBMBE) and side products, such as acetyl derivatives caused by reaction of ortho-DBMBA and DHDBM with acetone. The product mixture from the hydrolysis is illustrated below. All of the products which contain at least two hydroxyl groups can be used to make cured epoxy resins. Even acetyl derivatives and other side products, which do not form resins, do not seriously degrade the resins if in low concentrations. However, the most desirable properties are obtained from 4-hydroxymethylphenol in which the concentrations of ether and acetyl derivatives are minimized. Suitable reagent mixtures can be achieved following the processes of Auwers et al. and purifying the final product. Such purifications require extra steps and expenses in the epoxy resin synthesis. It would be preferable to form the hydroxymethylphenol in a process which holds the production of ether and side products down to a level which is acceptable for use without purification. The present invention is a process for synthesizing a hydroxymethyl-dihalo-dialkylphenol comprising the step of contacting a halomethyl-dihalo-dialkylphenol with a substantial excess of water in a water-miscible organic solvent at a temperature of less than 55°C under conditions such that a hydroxymethyl-dihalo-dialkylphenol is formed. The process of the present invention hydrolyzes the halomethyl-dihalo-dialkylphenol but holds the production of ether and acetyl derivatives or other side products down to a level acceptable for further use without purification. The hydroxymethyl-dihalo-dialkylphenols thus produced can be used to form useful epoxy resins as previously described and can also be incorporated into polyesters. Halomethyl-dihalo-dialkylphenols hydrolyzed in the process of the present invention are phenols substituted with two halogen atoms, two alkyl groups, and one halomethyl group. The halogens present in the substituted phenolic compounds are preferably chlorine or bromine and more preferably bromine. The alkyl groups are preferably hexyl or smaller, more preferably ethyl or methyl and most preferably methyl. Preferably, the halogen atoms are meta to the phenolic hydroxyl group and the alkyl and halomethyl groups are ortho and para to the phenolic hydroxyl group. In its most preferred embodiments, the halomethyl-dihalo-dialkylphenol is para -tribromomesitol ( para -TBM). The preferred process for making halomethylphenol is that described in Mendoza, Di-ortho-substituted Di- - meta-halogenated Para-halomethylphenols , U.S. Patent 4,684,752 (August 4, 1987). In the process of Mendoza, preferred halomethylphenols are made by halogenation of a 4-methyl-2,6-dialkylphenol or a 4-methyl-3,5-dihalo-2,6-dialkylphenol (both groups hereinafter called methylphenols). The methylphenol is most preferably mesitol or dibromomesitol. The methylphenol is preferably contacted with a halogenating agent such as molecular bromine in an aprotic solvent such as bromochloromethane at a temperature between 25°C and 85°C for a period of 2 to 5 hours. Selectivity to para-halo-methylphenol, which is important to maximize yields of para-hydroxymethylphenol, is preferably at least 90 percent, more preferably at least 95 percent. Other known processes are described in Auwers and Allendorf, 302 Ann. Chemie 76 (1898); Auwers and Rapp, 302 Chemie , 153 (1898); Fries and Brandes, 542 Ann. Chemie 48 (1939); and Auwers and Traum, 302 Ann. Chemie 3309 (1899). Hydrolysis of the halomethylphenol involves several competing reactions. First, the halomethylphenol reacts with water to yield the corresponding hydroxymethylphenol and a molecule of hydrogen halide. Second, the hydroxymethylphenol reacts further with unreacted halomethylphenol to form hydroxybenzylic ether. Third, halo- and hydroxymethylphenols react with solvents and impurities to form further impurities, such as acetyl derivatives. The rate constant for the ether formation reaction is substantially faster than the rate constant for the hydrolysis reaction, and the difference between reaction rates widens with increasing temperature. It is therefore necessary to accelerate conversion of halomethylphenol and to keep temperatures as low as feasible to limit ether formation. Hydrolysis takes place in a substantial excess of water to accelerate the conversion of halomethylphenol. Water used in the present process is preferable no more than 0.2N acidic or basic. The water is more preferably neutral. More acidic or basic solutions generate substantial amounts of unidentified impurities and lower the yield of the desired hydroxymethylphenol. The molar ratio of water to halomethylphenol is preferably at least 30:1 and more preferably 40:1. When the halomethylphenol being hydrolyzed is tribromomesitol, the ratio by weight of water to tribromomesitol is preferably at most 4:1 and at least 2:1. Greater excesses of water provide a some improvement in selectivity but may reduce the efficiency of the process since the ratio of water permits only small amounts of halomethylphenol in the reactor at any one time. Hydrolysis takes place in a solvent which will dissolve the halomethylphenol compound and which is miscible with water. Preferred solvents comprise acetone, THF, dioxan, n-methylpyrrolidone, dimethylsulfoxide or dimethoxyethane. The most preferred solvent is acetone. Water and the solvent must be maintained in a single phase state since unidentified by-products are formed if aqueous and organic layers separate during the reaction. The amount of solvent should also be sufficient to dissolve not only the halomethylphenol but also substantial amounts of water. The amount of solvent is preferably at least 0.35 mole of solvent per mole of water. It is also preferably at least 10 moles of solvent per mole of halomethylphenol. When hydrolyzing tribromomesitol in acetone, the preferred weight ratio of acetone to water to tribromomesitol is 2.5+:2.0:1.0. The temperature of the hydrolysis is kept at less than 55°C, preferably as low as possible without the product binding up the stirrer. The temperature is preferably no more than 50°C and most preferably no more than 45°C. The temperature is preferably no less than 20°C and more preferably no less than 40°C. Most preferably, water is added at a temperature of 20°C, and the temperature is raised gradually to between 40°C and 45°C. The pressure of the reaction is preferably ambient pressure. Due to the lower reaction temperature, the time for the hydrolysis to run to completion may be longer in the process of the present invention. Highest yields and selectivity are obtained by isolating the halomethylphenol after halogenation and before hydrolysis. For the purposes of industrial efficiency, however, it is often preferable to perform a one-pot synthesis from methylphenol to hydroxymethylphenol without isolating the intermediate halomethylphenol. In such cases, it is important to remove substantially all of the halogenation solvent before proceeding to hydrolysis. Solvents such as haloalkanes used in the halogenation step decrease the selectivity of the hydrolysis step toward the hydroxymethylphenol and increase the levels of ether formation. The affinity of the halomethylphenol for haloalkane solvents is high enough that those solvents cannot be removed simply by distillation or vacuum stripping. However, excess solvent is removed by vacuum stripping until a thick slurry forms. Thereafter, an excess of acetone is added and the remaining halogenation solvent is removed by codistillation with the acetone. The excess of acetone is preferably at least 1.5 moles for each mole of halomethylphenol. When the halomethylphenol is tribromomesitol, the weight ratio of acetone to halomethylphenol is preferably at least 0.25:1. It has surprisingly been discovered that, despite the low boiling point of acetone, the halogenation solvent can be removed in this manner, while the halomethylphenol remains in a thick slurry with acetone. Thereafter, more hydrolysis solvent is added to complete the hydrolysis step. When the reagent mixture comprises primarily halomethylphenol, the major product of the instant process is a hydroxymethyl-dihalo-dialkylphenol. Preferably, the product is a hydroxymethyl-dialkyl3,5-dihalophenol. More preferably, the product is a 4-hydroxymethyl-3,5-dihalo-2,6-dimethylphenol. Most preferably, the product is 4-hydroxymethyl-3,5-dibromo-2,6-dimethylphenol (dibromomesitol benzyl alcohol). The proportion of 4-hydroxymethylphenol with respect to 2-hydroxymethylphenol and 2,4-dihydroxymethylphenol in the product mixture is dependent upon the proportion of 4-halomethylphenol with respect to other halogenated phenols in the reagent mixture. Generally, acetyl derivatives are not formed in measurable amounts from purified 4-halomethylphenol from which other isomers have been removed, but when using unpurified halomethylphenol, hydrolysis conditions of the present invention can significantly reduce acetyl derivative formation. Likewise, ether formation is effected by the presence of other isomers or compounds, but reaction conditions of the present invention can significantly limit either formation. Using a process of the present invention, a composition can be formed which comprises no more than 20 percent ether, no more than 7 percent acetyl derivatives and other impurities and no less than 70 percent 4-hydroxymethylphenol. Preferably, the ether is no more than 13 molar percent of the total product. More preferably, it is no more than 10 percent and most preferably no more than 8 percent. In a process hydrolyzing unpurified halomethylphenol, the selectivity to hydroxymethylphenol is preferably at least 84 percent by mole; more preferably, at least 90 percent. The production of acetyl derivatives is preferably no more than 8 percent by mole; more preferably, no more than 6 percent; and most preferably, no more than 3 percent. Illustrative Examples The following examples are for illustrative purposes only. All ratios are proportions are by mole unless otherwise indicated. Example 1 - One-pot Synthesis of DBMBA A 5-liter, 3-necked, round-bottom flask was equipped with a Vigreaux distillation column, a mechanical stirrer, a dropping funnel, a thermometer and a heating mantle. Mesitol (99 percent, 252 g) was dissolved in 1233 g of bromochloromethane. Bromine (976 g) was added through the dropping funnel over a period of about 60 minutes. The temperature was increased from about 20°C to about 68°C at which reflux occurs. After about 5 1 / 2 hours at reflux, excess bromine was vacuum stripped and any residual bromine was neutralized using propylene. The slurry was cooled to about 20°C and the remaining bromochloromethane is removed by vacuum stripping, followed by codistillation with 750 g of acetone. At room temperature, 1600 g of acetone was added to the dissolved tribromomesitol and then 1375 g of water was added. The temperature was gradually increased from 25°C to 50°C and remains at 50°C for about 3 hours. The acetone was removed by vacuum stripping and the slurry was filtered. The solid was washed with water until the water wash becomes neutral and was subsequently washed with 300 ml of 1N sodium hydroxide. The product was dried at 70°C for 24 hours. The process yielded 562 g of product. The product contained 1.5 percent 3,5-dibromo-4,6-dimethyl-2-hydroxymethylphenol, 1.6 percent acetyl derivatives of tribromomesitol, 4.3 percent 2,4-bis-hydroxymethyl-3,5-dibromo-6-methylphenol, 12.2 percent 2,6-dibromo-3,5 dimethyl-4-hydroxybenzyl ether and 80.4 percent 3,5-dibromo-2,6-dimethyl-4-hydroxymethylphenol. Example 2 - Comparative Synthesis of DBMBA Using Unpurified TBM Mesitol ( 150 g) was dissolved in 370 ml of bromochloromethane in a 3-liter, three-neck round-bottom flask equipped with a reflux condenser, a mechanical agitator, a dropping funnel and a heating mantle. The solution was heated to reflux over about 1 hour (about 68°C to 74°C) while 581 g of bromine was added through the dropping funnel. Reflux was maintained for about 5 hours and then the solution was cooled to about 60°C. Hexene (20 g) was added to neutralize excess bromine and the solvent was removed under reduced pressure in a rotary evaporator. When the product was in solid form, 100 ml of acetone was added and removal of the solvent was continued. Addition of acetone and removal of the solvent was repeated three more times. Then the solid was transferred to a dish and dried in a vacuum oven at 40°C for 18 hours. A light yellow solid (429 g) was recovered. The product (20 g) was dissolved in 120 ml of acetone. Water (80 ml) was added at room temperature and then the temperature of the reaction was increased through a range of 24°C to 34°C. The high temperature was maintained until GLC analysis showed that the reaction was essentially complete after about 320 minutes. The products were analyzed by GLC, which showed the proportions of products set out in Table I. The process was repeated three more times using the reagents and reaction conditions set out in Table I. Sample TBM (g) Acetone (ml) Water (ml) Temp (°C) Time (min) DBMBA (%) DBMBE (%) Other (%) 1 20 120 80 24-34 320 92.27 5.01 2.72 2 40 120 80 21-38 320 83.93 8.47 7.61 3 20 120 80 58-64 90 87.19 4.80 8.01 4 40 120 80 58-64 90 79.46 11.04 9.50 The results show that the process of the present invention minimized the total proportions of ether and side products and maximizes the proportions of DBMBA in the product mixture. Example 3 - Comparative Hydrolysis of Purified TBM At least 99 percent pur para-TBM (20 g) was dissolved in 120 ml of acetone. Water (80 ml) was added at room temperature and then the temperature of the reaction was increased through a range of 24°C to 47°C. The high temperature was maintained until GLC analysis showed that the reaction was essentially complete after about 120 minutes. The products were analyzed by GLC, which showed the proportions of products set out in Table II. The process was repeated five more times using the reagents and reaction conditions set out in Table II. Sample TBM (g) Acetone (ml) Water (ml) Temp (°C) Time (min) DBMBA (%) DBMBE (%) 5 20 120 80 24-47 120 93.55 6.45 6 20 120 80 27 320 94.39 5.61 7 20 120 80 58-64 90 91.66 8.34 8 40 120 80 24-47 120 90.58 9.42 9 40 120 80 27 320 94.56 5.44 10 40 120 80 58-64 90 86.33 13.67 The results show that the selectivity to DBMBA and away from DBMBE was greater for the process of the present invention than for the process under prior art conditions.

Claims: A process for synthesizing a hydroxymethyl-dihalo-dialkylphenol comprising the step of contacting a halomethyl-dihalo-dialkylphenol with a substantial excess of water in a water-miscible organic solvent at a temperature of less than 55°C under conditions such that a hydroxymethyl-dihalo-dialkylphenol is formed. A process of Claim 1, wherein the reaction mixture comprises at least 30 moles of water per mole of halomethyl-dihalo-dialkylphenol and the amount of solvent is sufficient to prevent formation of separate aqueous and organic phases. A process of Claim 2, wherein the reaction mixture comprises at least 0.35 mole of solvent per mole of water. A process of Claim 3, wherein each halogen on the halomethyl-dihalo-dialkylphenol and the hydroxymethyl-dihalo-dialkylphenol is independently chlorine or bromine and wherein the temperature of the reaction is no more than 50°C. A process of Claim 4, wherein the halomethyl-dihalo-dialkylphenol is tribromomesitol and the hydroxymethyl-dihalo-dialkylphenol is dibromomesitol benzyl alcohol. A process of Claim 5, wherein the solvent comprises acetone, THF, n-methylpyrrolidone, dimethylsulfoxide, dioxan or dimethoxyethane. A process of Claim 6, wherein the solvent is acetone. A process of Claim 7, wherein the temperature of the process is at least 20°C.

Inventors: LIU MING-BIANN, LIU, MING-BIANN
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1989
Main classification: C07C37
IPC codes: C07C67, C07C39, C07C37, C07C27