PROCESS FOR PREPARING STILBENE DIOLS

Abstract: Described is a process for preparing dihydroxy stilbene compounds which includes the steps of: (a) combining (i) at least one coumpound containing one phenolic hydroxyl group per molecule with (ii) a Lewis acid which may be mixed with the compound at a temperature above the melting point temperatures of (i) and (ii) to form a solution of (i) in (ii), which will remain in liquid form when the temperature of the solution is brought to a temperature in the range of from -30 DEG C to 10 DEG C, wherein (i) and (ii) were combined in amounts sufficient to provide a mole ratio of (ii):(i) of at least 0.3:1.0; (b) contacting (iii) at least one alpha-haloketone compound or the corresponding ketal or hemiketal, or at least one alpha-haloaldehyde compound or the corresponding acetal or hemiacetal with the solution obtained from step (a) under reaction conditions sufficient to form the corresponding halogen-containing bisphenol compound, wherein (iii) is employed in an amount of at least 10 mole percent of the molar amount of (i) present in the solution obtained from step (a); and (c) dehydrohalogenating the halogen-containing bisphenol compound under reaction conditions sufficient to form the corresponding dihydroxy stilbene compound. It has been discovered that the Lewis acid provides an effective solvent for the reaction between (i) and (ii) in step (a), thereby reducing or eliminating the need for using inert reaction solvents. A substantial absence of inert solvents in the reaction mixture results in a process that is relatively fast and selective to the desired product.

Description: PROCESS FOR PREPARING STILBENE DIOLS This invention relates to processes for preparing stilbene diols and, more particularly, to processes for preparing 4,4'-dihydroxy-alpha-alkylstilbenes. Processes for the preparation of 4,4'-dihydroxy-alpha-alkylstilbenes are known and are described, for example, by Zaheer et al. in Journal of the Chemical Society, Part 3, pp. 3360-3362 (1954) and by Percec et al., in Mol. Cryst. Liq. Cryst, Vol. 205, pp. 47-66 (1991). Such processes typically involve an acid-catalyzed reaction of phenol with chloroacetone at a molar ratio in excess of 2:1. However, such lab-scale processes are relatively unsuitable for commercial-scale reactions since the reaction mixture must be carefully controlled to prevent the formation of undesirable side products. Commercial-scale processes may require the use of a suitable reaction medium, such as a solvent. U.S. Patent 5,475,155 describes a process for preparing 4,4'-dihydroxy-alpha- alkylstilbenes and 4,4'-dihydroxy-alpha,alpha'-dialkylstilbenes which comprises reacting at a temperature of from -20°C to 20°C a mixture of at least one alpha-haloketone and at least one compound containing one phenolic hydroxyl group per molecule such that the mole ratio of phenolic compound to alpha-haloketone is no more than 1.85:1 to prepare an intermediate compound, which is subsequently dehydrohalogenated to produce the corresponding stilbene compound. The reference also teaches that carrying out this process in the presence of methylene chloride reduces the viscosity of the reaction mixture and allows for more effective heat transfer therein. However, the use of methylene chloride is disadvantageous because, while it effectively dissolves the reactants, it is not an effective solvent for the desired intermediate product of the reaction. Further, reactions carried out in the presence of large amounts of methylene chloride may be undesirably slow. In one aspect, this invention is a process for preparing dihydroxy stilbene compounds which comprises the sequential steps of: (a) combining (i) at least one compound containing one phenolic hydroxyl group per molecule with (ii) a Lewis acid which may be mixed with the compound at a temperature above the melting point temperatures of (i) and (ii) to form a solution of (i) in (ii), which will remain in liquid form when the temperature of the solution is brought to a temperature in the range of from -30°C to 10°C, wherein (i) and (ii) are combined in amounts sufficient to provide a mole ratio of (ii):(i) of at least 0.3:1.0; (b) contacting (iii) at least one alpha-haloketone compound or the corresponding ketal or hemiketal, or at least one alpha-haloaldehyde compound or the corresponding acetal, or hemiacetal, or a mixture thereof with the solution obtained from step (a) under reaction conditions sufficient to form the corresponding halogen-containing bisphenol compound, wherein (iii) is employed in an amount of at least 10 mole percent of the molar amount of (i) present in the solution obtained from step (a); and (c) dehydrohalogenating the halogen-containing bisphenol compound under reaction conditions sufficient to form the corresponding dihydroxy stilbene compound. It has been discovered that the Lewis acid provides an effective solvent for the reaction between (i) and (ii) in step (a). Also, the substantial absence of inert solvents in the reaction mixture results in a process that is relatively fast and selective to the desired product. Further, highly hydrophobic reaction solvents (such as methylene chloride) tend to facilitate the formation of a separate aqueous phase in the reaction mixture, which further reduces the yield (since the acid will tend to go into the aqueous phase and therefore not remain in the same phase as the reactants). By contrast, if an acid is utilized as a substantial portion of the reaction medium, it tends to reduce this effect and keep the reactants together in a single organic phase. These and other advantages of the invention will be apparent from the description which follows. Suitable phenolic hydroxyl-containing compounds which can be employed herein include monohydric phenols or phenolic compounds represented by the following formula: wherein each R is independently hydrogen or a hydrocarbyl or hydrocarbyloxy group having from 1 to 12, preferably 1 to 6, most preferably 1 to 4, carbon atoms, a halogen atom, preferably chlorine, bromine or fluorine, or a nitro group. Examples of such compounds include phenol, 2,6-dimethylphenol, 2,6- diethylphenol, 2,6-dibromophenol, 2,6-dichlorophenol, 2,6-difluorophenol, 2,6-dimethoxy- phenol, 2,6-diethylphenol, 3,5-dimethylphenol, 2-nitrophenol, 2-cyanophenol, 2-methyl- phenol, 3-methylphenol, 2-phenylphenol, 2-cyclohexylphenol, 2-octylphenol, 2-methyl-6- chlorophenol, 2-methoxy-6-chlorophenol, and 2,3,5,6-tetramethylphenol. Phenol is most preferred as the phenolic hydroxyl-containing compound. Suitable atkoxy group-containing aromatic compound(s) which can be employed herein include those compounds represented by the following formula: wherein each R' is independently hydrogen or a hydrocarbyl group having from 1 to 12, preferably 1 to 6, most preferably 1 to 4, carbon atoms, a halogen atom, preferably chlorine, bromine or fluorine, or a nitro group; R 2 is a hydrocarbyl group having from 1 to 12, preferably 1 to 2, most preferably 1 , carbon atoms. Examples of such compounds include anisole, phenetole, 2,6-dimethylanisole, 2,6-diethylanisole, 2,6-dibromoanisole, 2,6-dichloroanisole, 2,6-difluoroanisole, 3,5-dimethylanisole, 2-nitroanisole, 2-methylanisole, 3-methylanisole, 2-phenylanisole, 2-cyclohexylanisole, 2-octylanisole, 2-methyl-6- chloroanisole, 2-methoxy-6-chloroanisole, and 2,3,5,6-tetramethylanisole. Anisole (methoxybenzene) is most preferred as the alkoxy group-containing aromatic compound. Suitable alpha-haloketones and alpha-haloaldehydes which can be employed herein include those represented by the following formula: R 4 — C— CH-R 3 wherein R 3 is hydrogen or a hydrocarbyl group having from 1 to 8, preferably 1 to 4, most preferably 1 to 2, carbon atoms; R 4 is hydrogen or a hydrocarbyl group having from 1 to 8, preferably 1 to 4, most preferably 1 carbon atom; and X is a halogen atom, preferably chlorine or bromine. When R 3 is other than hydrogen, the product produced will be a 4,4'-dihydroxy-alpha,alpha'-dialkylstilbene. When R 3 and R 4 are hydrogen, the product produced will be 4,4'-dihydroxystilbene. Examples of alpha-haloketones which can be employed herein to prepare dihydroxystilbenes include, for example, chloroacetone, bromoacetone, 4-methyl-1 - chloropentan-2-one, 1 -chlorooctan-2-one, 1 -bromobutan-2-one. 1-chlorobutan-2-one, 3- chlorobutan-2-one, 1-bromo-3-methylbutan-2-one, 1 -bromo-pentan-2-one, 1 -chloro-3- methylbutan-2-one, 1 -chloro-3-methylbutan-2-one, 1 -chloro-2-pentanone, 1 -bromo-hexan-2- one, 1 -bromo-3-methylpentan-2-one, 1 -bromo-4-methylpentan-2-one, 1 -chlorohexan-2-one, and 3-bromo-1 ,1 ,1 -trifluoroacetone, or any combination thereof. Chloroacetone is most preferred as the alpha-haloketone for preparing the 4,4'-dihydroxy-alpha-alkylstilbenes. Particularly suitable alpha-haloketones which can be employed herein to prepare the 4,4'-dihydroxy-alpha,alpha'-dialkylstilbenes include, for example, 3-chlorobutan- 2-one, 2-chloropentan-3-one, 3-chloro-pentan-2-one, 4-methyl-3-chloropentan-2-one, 4-methyl-2-chloropentan-3-one, 3-bromobutan-2-one, 2-bromopentan-3-one, 3-bromopentan-2-one, 2-chloro-3-pentanone, 3-bromo-hexan-2-one, 2-chlorohexan-3-one, or any combination thereof. 3-chlorobutan-2-one is most preferred as the alpha-haloketone for preparing the 4,4'-dihydroxy-alpha,alpha'-diaikylstilbenes. Particularly suitable alpha- haloaldehydes which can be employed herein to prepare 4,4'-dihydroxy-alpha-alkylstiibenes include, for example, 2-chloropropionaldehyde, 2-bromopropionaldehyde, 2-bromobutyraldehyde, and 2-chlorobutyraldehyde or any combination thereof. The corresponding ketals and acetals correspond to the formulas: R 4 -C(OR 5 )(OR 5 )-CH(X)-R 3 or R 4 -C(OR 6 O)-CH(X)-R 3 . The hemiketals and hemiacetals correspond to the formula: R*-CH(OR 5 )-CH(X)-R 3 wherein R 5 is independently in each occurrence a C, . , 0 hydrocarbyl group and R β is a C, . , 0 hydrocarbylene group. Such ketals, hemiketals, acetals, and hemiacetals may be prepared by reaching monol(s) or a diol with the acetone or aldehyde, or by any other suitable method. For example, a ketal may be prepared using ethylene glycol as the diol, wherein (OR β O) is -OCH 2 CH 2 O-. Examples of such compounds include: 2-chloromethyl[1 ,3]dioxolane, 2-bromomethyl[1 ,3]dioxolane, 2-chloro-1 ,1-di(ethyloxy)ethane, 2-bromo-1 ,1- di(ethyloxy)ethane, 2-bomo-1 ,1-di(methyloxy)ethane, 2-chloro-1 ,1-di(methyloxy)ethane, 1 -bromo-2,2-di(methyloxy)propane, and 1 -bromo-2,2-di(ethyloxy)propane. The phenolic hydroxyl-containing compound(s) or alkoxy group-containing aromatic compound(s) and the alpha-haloketone(s), the corresponding ketals or hemiketals, or alpha- haloaldehydes, corresponding acetals or hemiacetals (hereafter, collectively "halogen-containing reactants") are employed in an amount such that the mole ratio of the phenol or alkoxy group-containing aromatic compound:halogen-containing reactant is at least 0.1 :1 , more preferably at least 1 :1 , most preferably at least 2:1 ; but is preferably no greater than 30:1 , more preferably no greater than 20:1. These molar ratios refer to the relative quantities of these reactants which are utilized in the process, and do not necessarily refer to the molar ratio in the reaction mixture at any particular point in the process. Suitable Lewis acids which may be employed herein include, for example, sulfuric acid, sulfuric acid containing sulfur trioxide, hydrogen chloride, hydrogen fluoride, anhydrous aluminum chloride, tin tetrachloride, boron trifluoride, zinc chloride, boron trifluoride etherate, an alkanesulfonic acid such as methanesulfonic acid, ethanesulfonic acid, or propanesulfonic acid, or any combination thereof. Sulfuric acid and methanesulfonic acid are the most preferred acids. The acid must be sufficiently strong and present in amounts sufficient to promote the reaction between reactants (i) and (iii), either as a catalyst or a co-reactant which is consumed in stoichiometric amounts, depending on the particular acid. As the reaction proceeds, water is produced, thereby diluting the acid strength of the reaction mixture. Accordingly, the use of a strong acid such as methanesulfonic acid, or a dehydrating acid such as sulfuric acid, is preferred in order to facilitate the speed of the reaction. The acid is employed in an amount such that the mole ratio of phenolic hydroxyl-containing compound(s) or alkoxy group-containing aromatic compound(s):Lewis acid in the product of step (a) is at least 0.3:1.0. More preferably, the mole ratio is at least 1:1, and most preferably, is at least 2:1. In general, higher acid concentrations in the reaction mixture promote a faster reaction rate between (i) and (iii), but may make the process more expensive to run on a commercial scale due to the cost and processing requirements of the additional acid. In step (a) of the process of the present invention, the phenolic hydroxyl- containing compound(s) and the Lewis acid are combined together at a temperature at which both are liquid and the compound is soluble in the acid, and then brought to a temperature in the range of from -30°C to +10°C, preferably at least -20°C, more preferably at least -15°C; but preferably no greater than 0°C, more preferably no greater than -10°C; at which temperature the solution remains in liquid form. In step (b) of the process, the halogen-containing reactant is then added to the product of step (a) at such a rate as to maintain the aforementioned temperatures for the reaction. The time required to complete the addition of the component (iii) depends upon the variables such as the reaction temperature, reactants employed, the heat transfer ability of the reactor employed, the addition time for the reactants. Higher temperatures require shorter periods of time whereas longer temperatures require longer periods of time. Generally, however, times of from 5fminutes to 30 hours are suitable. The reaction can be conducted at atmospheric, superatmospheric or subatmospheric pressures. The reaction can be performed as a batch process or continuous process. It is frequently of benefit to conduct the reaction under an inert atmosphere, such as nitrogen, especially if the particular equipment used can entrain air which contains moisture. In the process of the present invention, it is typically desirable to choose a reaction time and temperature profile which provides the greatest conversion and selectivity to the halogen-containing bisphenol intermediate compound and subsequently to the 4,4'- dihydroxy-alpha-alkylstilbene product. The term "halogen-containing bisphenol intermediate compound" as used herein refers to a reaction product of (i) and (iii) (which reaction is carried out in the presence of an acid) which, upon being dehydrohaiogenated, forms a dihydroxy stilbene compound. In step (b) of the process, it is desirable to avoid the formation of products other than the halogen-containing bisphenol intermediate compound. Thus, for example, subjecting phenol, chloroacetone and sulfuric acid to higher temperatures for prolonged periods of time, favors the formation of undesirable trisphenols, such as 1 ,2,2- tris(4-hydroxyphenyl)propane. Thus, it is frequently of value to conduct simple preliminary experiments over the range of reaction variables which can be employed in order to define an optimum reaction time and temperature profile which provides the greatest conversion and selectivity for the halogen-containing diphenol intermediate compound. Removal or neutralization of the Lewis acid and/or any acid-functional co- products formed during step (b) may be accomplished using any unit operations which will effectively remove the acid such as washing with water, buffering, neutralization over a suitable ion exchange resin, neutralization with a basic-acting substance, such as, for example, alkali metal carbonates, bicarbonates or hydroxides such as, for example, sodium bicarbonate, potassium bicarbonate, sodium hydroxide or any combination thereof. It is also suitable to utilize combinations of unit operations which will effectively neutralize the acid in the reaction product, such as initially washing with water, followed by washing with an aqueous solution of a basic-acting substance. Likewise, the equipment associated with the aforementioned unit operations is chosen to maximize processability. Thus, for example, a centrifuge can be used to rapidly separate aqueous and organic layers resulting from the washing. A static coalescer can be used to induce rapid resolution of emulsified aqueous and organic layers resulting from the washing. The acid removal or neutralization step reduces the amount of strong protonic acids or Lewis acids or combination thereof and/or the products resulting from said acids in the reaction product to an amount of less than 10,000 ppm. This acid removal or neutralization step of the process is preferably conducted at temperatures of from 25°C to 75°C, more preferably from 0°C to 10°C. At temperatures below -20°C, acid removal or neutralization can be hindered by freezing out of water if used for washing or as a solvent for the buffer or basic acting substance. Temperatures below -20°C also favor the formation and stabilization of emulsions, such as are formed in the washing process, thus making resolution of acid from the reaction product difficult. The dehydrohalogenation of the product of step (b) to the corresponding stilbene diol is preferably carried out by heating the washed reaction crude product from the acid removal step to a temperature of at least 30°C, more preferably at least 50°C, more preferably at least 60°C; but preferably no greater than 200°C, more preferably no greater than 90°C, and most preferably no greater than 85°C. Once the desired temperature is achieved, it is maintained until completion of the dehydrohalogenation, typically for from 1 second to 24 hours, preferably less than 6 hours, more preferably less than 30 minutes, and most preferably less than 5 minutes. It is frequently desirable to monitor the course of the dehydrohalogenation via an analytical method, such as high pressure liquid chromatographic analysis. Additionally, it is frequently of value to conduct simple preliminary experiments over the range of reaction variables which can be employed in order to define an optimum reaction time and temperature profile which provides the greatest conversion and selectivity to the desired stilbene diol. It is also frequently of benefit to add water or another suitable diluent to the washed reaction crude prior to the dehydrohalogenation. Examples of suitable diluents are described in the copending patent application by A. P. Haag et al., "Process for the Preparation and Purification of 4,4'-Dihydroxy-alpha-substituted Stilbene," U.S. Serial No. 08/608,807, filed February 29, 1996. This diluent serves to dilute any hydrogen halide released during the dehydrohalogenation and not volatilized out of the product and additionally dilutes any traces of acid not removed from the reaction crude by the prior acid removal process, such as water washing. The amount of diluent added varies depending upon the amount of water retained in the washed reaction crude, the amount of residual acid present in the washed reaction crude, the amount of acid expected to be liberated from the dehydrohalogenation, and other such variables, but typically is used in an amount of from 5 to 98, preferably from 10 to 85, most preferably from 20 to 65 percent by weight of the combined weight of the reaction crude and diluent used. The diluent can also contain a neutralization agent, such as the aforementioned basic acting substance, however, care must be taken so that the amount of neutralization agent is not in an amount that causes the dehydrohalogenation reaction to be basic during the entire course of said reaction. During the dehydrohalogenation, stirring or mixing is desirable to assure even heating of the reaction crude and complete dispersion of the water, if added. Once the dehydrohalogenation is complete, the mixture is neutralized by the addition of base and concentrated by removal of the diluent (alcohol), thus crystallizing the product from the solution. If desired, crystallization of the mixture of the dehydrohalogenation product and water can be induced or accelerated via the addition of seed crystals of the particular stilbene diol being prepared; however, this is typically unnecessary. It is frequently of value to conduct simple preliminary experiments over the range of time and temperature at which the crystalline slurry can be held in order to define an optimum time and temperature profile which provides the greatest isolated yield of stilbene diol. The product is recovered from the crystalline slurry using any unit operations which effectively remove the crystals from said slurry, such as, for example, filtration or centrifugation. The recovered product can be dried, for example, in an oven under vacuum, or utilized as recovered, as a wet cake. When an alkoxy group-containing aromatic compound, such as anisole, is utilized in the process of the present invention, the resulting 4,4'-dialkoxy-stilbene compound can be converted to the corresponding stilbene diol using methods described at column 11 , lines 1-24 of U.S. Patent 5,475,155. The stilbene diol product can be further processed for the purpose of upgrading or otherwise modifying product purity by any of the techniques well known to the skilled artisan such as described, for example, at column 11 , lines 26-39 of U.S. Patent 5,475,155. The stilbene diol product is typically a mixture of cis- and trans- isomers with the fraπs-isomer being predominant. The high purity 4,4'-dihydroxy-alpha-alkylstilbene products of the present invention are useful for the advancement of epoxy resins, for the preparation of phenoxy resins, and for the preparation of epoxy resins. The following examples are exemplary of the invention but are not to be construed as to limiting the scope thereof in any manner. Example 1 - Preparation of 4,4'-Dihydroxy-alpha-methylstilbene Using a 4:1 Molar Ratio of Phenol hloroacetone Methanesulfonic acid (192.2 g, 2 mol) and phenol (107.55 g, 1.14 mol) were weighed and transferred into a jacketed flask, and rinsed with 10 g of methylene chloride. The flask was fitted with a nitrogen inlet and outlet, an addition funnel, thermometer and an overhead stirrer. Stirring was started and the speed was adjusted to approximately 200 rpm (± 10 rpm). The mixture was cooled to less than -15°C and the chloroacetone (27.83 g, 0.2857 mol) was added dropwise, rinsing with 2 mL of methylene chloride. The temperature was then adjusted to maintain at -10°C to -12°C and the mixture was stirred until GC analysis showed the chloroacetone peak to be much less than the 1 ,1-dichloroacetone peak. The mixture was chilled to -15°C, then quenched by the addition of 100 g of cold (less than -20°C) methylene chloride, followed by the addition of 283 g of chilled water. The mixture was agitated until the temperature returned to 0°C, then the lower organic layer was drained off and poured into the preheated (65°C) solvent in the dehydrochlorination reactor (716.4 g of isopropanol and 358.2 g of water). The aqueous phase of the condensation reaction was washed with an additional 50 mL of methylene chloride which was drained off and added to the dehydrochlorination reaction. The dehydrochlorination reaction was heated and stirred under nitrogen at 65°C for 3.5 hours. After completion, the mixture was neutralized (observation of color change to bright yellow) by the addition of 40 g of 30 percent NaOH (aqueous). The mixture was concentrated by rotary evaporation to remove essentially all of the isopropanol, causing the precipitation of the product as large crystals. The mixture was allowed to sit overnight and then filtered. The crystals were washed with 200 mL of methylene chloride followed by 200 mL of hot (greater 80°C) water. The crystals were transferred to a crystallizing dish and dried in a vacuum oven at 60°C to 80°C overnight. Yield = 50.45 g (78 percent). Purity = 99.23 percent, 0.06 percent tris, 0.32 percent dimerl , 0.04 percent cis, 002 percent dimer2. Example 2 - Reaction Using Three Equivalents of Phenol with Azeotropic Workup Methanesulfonic acid (192.2 g, 2 mol) and phenol (80.68 g, 0.857 mol) were weighed and transferred into a jacketed flask, rinsing with 150 g of methylene chloride. The flask was fitted with a nitrogen inlet and outlet, an addition funnel, thermometer, and an overhead stirrer. Stirring was started and the speed was adjusted to approximately 200 rpm (± 10 rpm). The mixture was cooled to less than -15°C and the chloroacetone (27.83 g, 0.2857 mol) was added dropwise. The temperature was then adjusted and maintained at -10°C to -12°C and the mixture was stirred until GC analysis showed the chloroacetone peak to be much less than the dichloroacetone peak. The mixture was chilled to -15°C, then quenched by the addition of 100 g of cold (-20°C) methylene chloride followed by 283 g of chilled water. The mixture was agitated until the temperature returned to 0°C, then the lower organic layer was drained off and poured into the preheated (65°C) solvent in the dehydrochlorination reactor (727.6 g of isopropanol and 363.8 g of water). The aqueous phase of the condensation reaction was washed with an additional 50 mL of methylene chloride which was drained off and added to the dehydrochlorination reaction. The dehydrochlorination reaction was heated and stirred under nitrogen at 65°C for 3.5 hours. After completion, the mixture was neutralized (observation of color change to bright yellow) by the addition of 23.77 g of 50 percent NaOH (aqueous) to pH 8.5. Water was added (421 g) to azeotrope the excess phenol. The mixture was concentrated by rotary evaporation to remove essentially all of the isopropanol and phenol, which caused large crystals of the product to precipitate. The mixture was allowed to cool and then filtered. The crude crystals were 86 percent DHAMS with 2.6 percent phenol (dry weight = 69.53 g). The crystals were washed twice with 198.63 g of methylene chloride and twice with 198.63 g of hot water (greater than 80°C). The crystals were transferred to a crystallizing dish and dried in a vacuum oven at 60°C to 80°C overnight. Yield = 64.38 g (99.58 percent). Purity = 94. percent, 1.16 percent tris, 0.47 percent dimerl , 0.06 percent cis, 0.44 percent dimer2.

Claims: CLAIMS: 1. A process for preparing dihydroxy stilbene compounds which comprises the sequential steps of: (a) combining (i) at least one compound containing one phenolic hydroxyl group per molecule with (ii) a Lewis acid which may be mixed with the compound at a temperature above the melting point temperatures of (i) and (ii) to form a solution of (i) in (ii), which will remain in liquid form when the temperature of the solution is brought to a temperature in the range of from -30°C to 10°C, in an amount sufficient to provide a molar ratio of (ii):(i) of at least 0.3:1.0; (b) contacting (iii) at least one alpha-haloketone compound, or the corresponding aldehyde or ketal, therewith under reaction conditions sufficient to form the corresponding halogen-containing bisphenol compound, wherein (iii) is employed in an amount of at least 10 mole percent of the molar amount of (i) present in the solution obtained from step (a); and (c) dehydrohalogenating the halogen-containing bisphenol compound under conditions sufficient to form the corresponding dihydroxy stilbene compound. 2. The process of Claim 1 wherein the Lewis acid is sulfuric acid. 3. The process of Claim 1 wherein the Lewis acid is hydrogen fluoride. 4. The process of Claim 1 wherein component (i) is phenol and component (iii) is monochloroacetone. 5. The process of Claim 1 wherein the molar ratio of component (i) to (iii) in step (b) is at least 2:1. 6. A process for preparing dihydroxy stilbene compounds which comprises the sequential steps of: (a) combining (i) at least one compound containing one phenolic hydroxyl group per molecule with (ii) methanesulfonic acid, in an amount sufficient to provide a molar ratio of (ii):(i) of at least 0.3:1.0; (b) contacting (iii) at least one alpha-haloketone compound, or the corresponding aldehyde or ketal, therewith under reaction conditions sufficient to form the corresponding halogen-containing bisphenol compound, wherein (iii) is employed in an amount of at least 10 mole percent of the molar amount of (i) present in the solution obtained from step (a); and (c) dehydrohalogenating the halogen-containing bisphenol compound under conditions sufficient to form the corresponding dihydroxy stilbene compound. 7. The process of Claim 6 wherein component (i) is phenol and component (iii) is monochloroacetone. 8. The process of Claim 6 wherein the molar ratio of component (i) to (iii) in step (b) is at least 2:1. 9. A process for preparing dihydroxy stilbene compounds which comprise the sequential steps of: (a) combining (i) phenol with (ii) methanesulfonic acid, in an amount sufficient to provide a molar ratio of (ii):(i) of at least 0.3:1.0; (b) contacting (iii) monochloroacetone therewith under reaction conditions sufficient to form the corresponding halogen-containing bisphenol compound, wherein (iii) is employed in an amount of at least 10 mole percent of the molar amount of (i) present in the solution obtained from step (a); and (c) dehydrohalogenating the halogen-containing bisphenol compound under conditions sufficient to form the corresponding dihydroxy stilbene compound. 10. The process of Claim 9 wherein the molar ratio of component (i) to (iii) in step (b) is at least 2:1.

Inventors: CLEMENT KATHERINE S, TASSET EMMETT L, WALKER LOUIS L, CLEMENT, KATHERINE, S., TASSET, EMMETT, L., WALKER, LOUIS, L.
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1997
Main classification: C07C37
IPC codes: C07B61, C07C37, C07C39