PROCESS FOR PREPARING BIS(3,5-DIALKYL-4-HYDROXYPHENYL) SULFONE

Abstract: An improved process for the production of bis(3,5-dialkyl-4-hydroxyphenyl) sulfone. The process involves: (a) forming a reaction solution of substantially stoichiometric amounts of sulfuric acid and 2,6-dialkyl phenol in an excess of inert organic liquid which forms an aqueous azeotrope having a boiling point above about 155<o>C.; (b) heating said solution to a temperature within the range of from 155<o> to 180<o>C and above the boiling point of said azeotrope; (c) maintaining said temperature of said solution for a time of reaction sufficient to produce solid bis(3,5-dialkyl-4-hydroxyphenyl) sulfone and remove by-product water; and (d) separating said solid sulfone from said organic liquid. The process produces exceptionally high product purity and yields of 60% and higher. Moreover, this may be accomplished under relatively mild conditions and shortened time of reaction.

Description: PROCESS FOR PREPARING BIS (3,5-Dialkyl-4-Hydroxyphenyl) SULFONE Background of the Invention Processes for the preparation of sulfones through reaction of dialkyl phenols with a sulfonating agent are known. These processes, however, suffer several draw¬ backs, the most important of which involve yield and purity of product. In, for example, U.S. Patent 3,383,421 of Fox et al, there is claimed a process yielding bis(3,5-dialkyl-4- hydroxyphenyl) sulfone. That process involves: (a) reaction of a 2,6-dialkyl phenol where each alkyl group has from 1 to 4 carbon atoms with sulfuric acid within a temperature range of 155 to 170°C. in the presence of an organic liquid capable of forming an azeotrope with the water of reaction, the azeotrope having a boiling point within the reaction temperature range; (b) recovering sulfone from reaction mixture; (c) dissolving said sulfone in aqueous solution of caustic soda or ammonia; (d) neutralizing the aqueous solution with acid to pH ranging between 4 and 6; and (e) collecting the sulfone in the form of white crystals. The disclosure of U.S. Patent 3,383,421 teaches the desirability of a mole ratio for phenol to sulfuric acid in excess of the stoichiometric 2:1 to avoid formation of such by-products as trifunctional sulfones. An initial amount of from 0.1 to 2 moles of liquid azeotrope former per mole of phenol may be used to regulate the reaction temperature. In U.S. Patent 4,162,270 of Ogata et al, there is described a similar process involving reaction of sulfuric acid with phenol having an unsubstituted ortho position to produce 4-4'dihydroxydiphenylsulfone. The reaction may commence in the presence of from about 0.1 to 5 parts of azeotrope-forming solvent by weight of the phenol. During reaction, however, essentially all the solvent is removed. The resultant condition leads to isomerization of by-product 2,4'-dihydroxydiphenylsulfone to the desired form of sulfone. Major drawbacks of the prior art processes involve the often related concerns of impurities and low product yield. Common impurities include partial reaction products such as phenol sulfonic acid and by-products of reaction such as quinone-type color bodies, sulfonic acid derivatives and sulfone isomers. Their production appears to be related to elevated reaction conditions employed in attempts to increase yield of diphenol sulfone product. Impurities are also particularly objectionable for the recent newer usages of diphenol sulfones as monomeric constituents. Whereas such impurities were often tolerable with such prior art utilities as plasticizers, wetting agents, agents for combating pests, auxiliary substances for use in canning, dyestuff and the like, they are very detrimental in the formation of high molecular weight polymers and copolymers. There they may additionally cause undesirable chain termination, branching and cross- linking as well as predispose the product to various degradation processes. Introduction to the Invention The present invention involves an improved process for the preparation of bis(3,5-dialkyl-4-hydroxyphenyl) sulfone. This process comprises the steps of: (a) forming a reaction solution of substantially stoichiometric amounts of sulfuric acid and 2,6-dialkyl phenol in an excess of inert organic liquid which forms an aqueous azeotrope having a boiling point above about 155°C. ; (b) heating said solution to a temperature within the range of from 155° to 180°C. and above the boiling point of said azeotrope; (c) maintaining said temperature of said solution fo. a time reaction sufficient to produce solid bis(3,5-dialkyl- 4-hydroxyphenyl) sulfone and remove by-product water; and (d) separating said solid sulfone from said organic liquid. This process results in unexpectedly high product purity and yields of, for example, in excess of 60%. Moreover, such yields may be obtained under relatively mild reaction conditions and a shortened time of reaction. Description ' of the Invention The phenol starting materials of the present invention are so-called "2-6-dialkyl phenols". They have the formula: wherein R and R are each alkyl groups, most preferably having from 1 to 4 carbons. The preferred phenol in accordance with the present invention is 2,6-xylenol. The 2,6-dialkyl phenol and sulfuric acid reagents will react at a temperature in excess of about 155°C. to produce the desired diphenol sulfone product. Below this temperature, the primary reaction product is phenol sulfonic acid intermediate. These two reagents of phenol and sulfuric acid should be combined for reaction in essentially stoichiometric proportions of about 2:1, respectively. Variation of less than 2% from this ratio is preferred. Significantly, the prior art has often avoided this ratio for varying different reasons. In accordance with the present process, however, this ratio leads to maximized yield and minimized impurities. To effect their reaction, the phenol and sulfuric acid should first be dissolved in an inert organic liquid. The manner or sequence of their addition is relatively unimportant. In a preferred embodiment, however, the sulfonating agent is added after the phenol has been dissolved in the organic liquid. In addition to being an Inert solvent, the organic liquid is also employed to remove water formed during the sulfonating process. To satisfy this function it should be capable of forming an aqueous azeotrope which will vaporize during the reaction. Accordingly, the organic liquid should be one which forms an azeotrope having a boiling point of above about 155°C. The boiling point must also be below that employed in the reaction. Suitable organic liquids for the present process include hydrocarbons and halohydrocarbons, nonane, decane, dichloro- benzene and, preferably, nonane are representative of such liquids. The amount of organic liquid employed in accordance with _ the present process should be in excess of that required simply to perform its primary functions of dissolution and azeotropic removal of water. It has been discovered that an excess of this solvent enhances both the yield and purity of product diphenyl sulfone. Consequently, a weight ratio of organic liquid to phenol which is at least 0.7:1 to 10:1 desirably at least 1:1 is preferred. The solution of phenol and sulfuric acid in the organic liquid must as previously indicated, be heated to a temper¬ ature in excess of about 155°C. to commence production of bis(3,5-dialkyl-4-hydroxyρhenyl) sulfone . . This temperature should also be above the boiling point of the aqueous azeotrope to ensure removal of water formed during the reaction. Due to the possibility of adverse side- reactions, a maximum temperature of 180°C more preferably 170°C should also be observed for the reaction. Although a fixed reaction temperature may be employed in the present process, this is not necessary. A gradually increasing temperature has the advantage of allowi greater control over the reaction rate. That temperature may even commence well below 155°C, so long as it rises to the temperature discussed above and is there maintained for at least a limited period of time. Such a graduated and successive temperature increase forms a preferred embodiment of this process. In accordance therewith, the solution of phenol to which the sulfuric acid is to be added is first heated to from about 40 to 80°C. After the acid is added, the reaction medium is heated quick to above the boiling point of the aqueous azeotrope of organic liquid. Thereafter, further heating to higher temperature is performed in an essentially step-wise manner to maintain a desirable reaction rate. At the beginning of the reaction, the rate may well be above 30%, often 40% by weight of phenol per hour even with little increase in temperature. Subsequently, as the rate drops, higher temperatures are employed until the maximum desired temperature is reached. The latter temperature increases are usually made as the rate of consumption of phenol falls below about 3%, preferably 5% per hour. A significant advantage of the present process is that the reaction medium need not be maintained at a temperature in excess of 155°C. for an extruded period of time. In contrast to many prior art processes, yields of over 60% of diphenol sulfone are quickly achieved with minimal exposure to high temperature. This is particularly true where the foregoing embodiment of graduate temperature increases Is employed. In less than about 6 hours, for example, a yield in excess of about 85% may be obtained. Bis(3,5-dialkyl-4-hydroxyphenyl) sulfone formed pursuant to the present process is insoluble in the organic liquid. It therefore precipitates as a solid. Consequently, when the desired yield has been obtained, it may readily be separated (normally after first cooling to below 100°C.) by filtration or similar physical means. The separated, bis(3,5-dialkyl-4-hydroxyphenyl) sulfone may evidence contamination by impurities such as color bodies In accordance with the present invention, however, it has been found that this product is easily purified. The crude diphenyl sulfone may simply be washed with an alcohol such as methanol, ethanol, propanol or, preferably, isopropyl alcohol. These alcohols are desirably of neutral pH. The alcohol selectively dissolves impurities from the solid sulfone, leaving a refined product. The following examples are given by way of illustration only and are not intended as a limitation on the scope of this invention. Many variations are possible without departing from its spirit and scope. Unless otherwise specified herein, all proportions are provided on a weight basis. EXAMPLE I Both 720 grams of 2,6-xylenol (5.90 moles) and 70 ml of hydrocarbon solvent (ISOPAR-H produced by Exxon, Inc.) are added to a 2 liter 4-necked flask equipped with a mechanical stirrer, Vigreux column (30cm)-Dean-Stark trap thermometer, and nitrogen inlet. This mixture is heated to 50° - 60°C. and 258 grams of concentrated sulfuric acid (2.50 moles: 95% H^SO,) are added slowly. The temperature is then raised. At a pot temperature of 140°C. water collects in _ _ the trap. The time-temperature-water removal profile is shown below. T Tiimmee ((hhoouurrss)) % % HH.0 Pot Temperature (°C) 0.75 36 148 1.25 58 158 1.75 67 161 3 .25 86 163 5 5..0000 9 933 165 6 .00 97 167 During the course of the reaction, the sulfone falls out of solution to produce a particulate slurry. At the end of 6 hours the reaction mixture is cooled to below 100°C. and filtered. The crude solid product has a deep red color. This material is washed with isopropyl alcohol to give 650 grams (85% yield) of a light-tan solid product. High pressure liquid chromotography, HPLC, analysis of this bis(3,5-dimethyl-4-hydroxyphenyl) sulfone product indicates about 99% purity with less than 1% xylenol sulfonic acid contaminant. EXAMPLE 2 In a one liter flask equipped with a thermometer, mechanical stirrer and Dean-Start trap/condenser is charged 136 g (1.115 moles) of xylenol and 240 ml of n- octane/dodencane (40/60) . The flask is heated to 50° - 60°C and 0.507 moles of concentrated sulfuric acid are added over a period of 5 minutes. Thereafter the reaction vessel is heated such that the water of reaction is removed continuously as formed by azeotropic distillation. The time-temperature extent of reaction (as measured by water removal) is shown below: Time (Hours) Temperature (°O) Extent of Reaction (%) .25 122 33 1.00 125 41 1.67 140 55 2.16 145 66 3.00 150 77 3.50 160 82 3.67 160 88 4.00 162 93 EXAMPLE 3 In a one liter flask equipped with a thermometer, mechanical stirrer and a Dean-Start trap/condenser was charged 178 g (1.46 moles) of xylenol and 200 ml of o-dichlorobenzene. The flask is heated to 50° - 60°C. and 0.610 moles of concentrated sulfuric acid are added over a period of.5 minutes. Thereafter the reaction vessel is heated such that the water of reaction is removed continuously as formed by azeotropic distillation. The time-temperature extent of reaction (as measured by water removal) is shown below: Time (Hours) Temperature (°C) Extent of Reaction (%) 0.50 145 23 1.00 156 36 1 1..5500 1 15588 55 2.00 164 68 2.83 172 82 3.67 178 86 4.00 179 91 4 4..5588 1 17788 96 E EXXAAMMPPLLEE 44 In a five liter flask equipped with a thermometer, mechanical stirrer and a Dean-Start trap/condenser is charge 1112 g (9.11 moles) of xylenol and 1000 ml of Mineral Spirits (Rule 66 produced by Ashland Chemical Co.) . The flask is heated to 50° - 60°C. and 3.91 moles of concentrated sulfuric acid are added over a period of 15 minutes. Thereafter the reaction vessel is heated such that the water of reaction is removed continuously as formed by azeotropic distillation. The time-temperature extent of reaction (as measured by water removal) is shown below: Time (Hours) Temperature (°C) Extent Of Reaction (%) 0.17 148 17 - 0.67 156 35 1.83 167 62 2.67 173 73 4.67 177 85 EXAMPLE 5 In a one liter flask equipped with a thermometer, mechanical stirrer and a Dean-Start trap/condenser is MP charged 590 gm (4.83 moles) of xylenol and 600 ml of ISOPAR-H. The flask is heated to 50° - 60°C. and 2.38 moles of concentrated sulfuric acid are added over a period of 5 minutes. Thereafter the reaction vessel is heated such that the water of reaction is removed continuously as formed by azeotropic distillation. The time-temperature extent of reaction (as measured by water removal) is shown below: Time (Hours) Temperature (°C) ' Extent of Reaction (%) ..3333 151 10 .50 159 27 .75 165 45 1 .00 170 63 1. .58 172 76 22.. .0000 172 89 EXAMPLE 6 In a one liter flask equipped with a thermometer, mechanical stirrer and a Dean-Stark trap/condenser was charged 390 gm (3.19 moles) of xylenol and 300 ml of I -DRI (produced by Ashland Chemical Co.). The flask is heated to 50° -60°C. and 1.58 moles of concentrated sulfuric acid are added over a period of 5 minutes. Thereafter the reaction vessel is heated such that the water of reaction is removed continuously as formed by azeotropic distillation. The time-temperature extent of reaction (as measured by water removal) is shown below: Time (Hours) Temperature (°C) Extent of Reaction (%) 0.25 148 23 0.50 158 41 1.10 163 64 1.40 165 72 2.00 165 79 2.25 165 87 3.80 165 95 EXAMPLE 7 Two comparative processes utilizing the high phenol to sulfonating agent and low organic azeotropic liquid ratios of the prior art are performed. For each, a one liter flask equipped with a thermometer, mechanical . stirrer and a Dean-Stark trap/condenser is charged 516 g (4.22 moles) of xylenol and 80 ml of heptane. The flask is heated to 50° - 60°C. and 1.05 moles of concentrated sulfuric acid are added over a period of 5 minutes. Thereafter the .reaction vessel is heated such that the water of reaction is removed continuously as formed by azeotropic distillation. The time-temperature extent of reactions (as measured by water removal) for each are shown below: Process A Time (Hours) Temperature (°C) Extent of Reaction ' (%) 0.16 146 14 0.42 149 18 0.67 154 26 1.00 164 38 1.25 172 49 2.00 180 61 2.50 180 62 3.00 179 64 4.00 180 65 5.00 180 66 6.25 180 67 7.00 180 67 Proicess B Time (Hours) Tempisrature (°C) Extent of Reaction ' (%) 0.20 147 16 0.83 160 34 1.16 170 43 1.25 172 50 1.83 180 59 2.50 182 64 O Time (Hours) Tempisratur ' e (°C) ' Extent of Reaction (%) 3.33 185 71 4.00 187 75 4.58 195 81 5.00 197 83 5.42 197 87 6.00 197 89 In comparing the respective results of this example with those of Examples 1-6, many of the advantages of the present inention become more evident. In Example 7, the profiles for both process A and B show a quick peaking and decline of reaction rate with time. Moreover, after only a low degree of reaction (even where high temperature is employed) little further reaction occurs. In contrast, the processes of the present invention (Examples 1-6) show more sustained rates of reaction. This is true even at much lower temperatures of reaction. As a result, substantially higher yields are obtained and under more mild conditions and shorter reaction times which correspondingly reduce the side-production of impurities. All of the foregoing patents and/or publications are incorporated herein by reference. Obviously, other modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that changes may be made in the particular embodiments of the invention described which are within the full intended scope of the invention as defined by the appended claims.

Claims: CLAIMS 1. A process for the preparation of bis(3,5-dialkyl- 4-hydroxyphenyl) sulfone, said process comprising the steps of: (a) forming a reaction solution of substantially stoichiometric amounts of sulfuric acid and 2,6-dialkyl phenol in an excess of inert organic liquid which forms an aqueous azeotrope having a boiling point above about 155°C. ; (b) heating said solution to a temperature within the range of from 155° to 180°C. and above the boiling point of said azeotrope; (c) maintaining said temperature of said solution for a time of reaction sufficient to produce solid bis(3,5-dialkyl-4-hydroxyphenyl) sulfone and remove by-product water; and (d) separating said solid sulfone from said organic liquid. 2. The process of Claim 1, wherein the weight ratio of organic liquid to 2,6-dialkyl phenol in the reaction solution is at least about 0.7:1. 3. The process of Claim 2, wherein the time of reaction is sufficient to produce a yield of at least 60% of bis(3,5-dialkyl-4-hydroxyphenol) sulfone. 4. The process of Claim 3, wherein the separated bis(3,5-dialkyl-4-hydroxyphenyl) sulfone is purified by washing with alcohol. 5. The process of Claim 4 wherein the temperature gradually Increases within the range to maintain the rate of reaction. 6. The process of Claim 5, wherein the alkyl radicals of the phenol have from 1 to 4 carbons. 7. The process of Claim 6, wherein organic liquid is a hydrocarbon or halogenated hydrocarbon. 8. The process of Claim 6, wherein the time of reaction is less than about 6 hours and the yield in excess of about 85%. 9. The process of Claim 8, wherein the weight ratio of organic liquid to 2,6-dialkyl phenol in the reaction solution is at. least about 10:1. 10. The process of Claim 9, wherein the 2,6-dialkyl phenol is xylenol.

Inventors: PETERS EDWARD NORMAN, SMITH GARY FRANCIS, STURGES JOHN STEELE
Applicants: GEN ELECTRIC, GENERAL ELECTRIC CO
Application year: 1982
Main classification: C07C147
IPC codes: C07C67, C07C313, C07C317