Improved process for the production of carbonate esters

Abstract: The invention relates to a process of producing carbonate esters wherein an alkyl chloroformate is reacted with a phenolsulfonate in an alkaline medium and discloses the improve­ ment whereby dialkylcarbonate formation is reduced by adding an acidifying agent to the reaction mixture after the reaction and before precipitation of the alkylsulfophenyl carbonate.

Description: The present invention relates to the production of unsymetrical alkylsulfophenyl carbonate esters wherein the carbonate ester product contains low levels of dialkylcarbonate impurities. The ability of certain materials to bleach is widely known and consequently these materials can be used to remove discolorations or stains from articles. Although the exact mechanism by which bleaching agents function is only partially understood, it is generally known that many stains and soils possess a series of alternating single and double bonds and that loss of color can occur if one of the double bonds is destroyed. Thus, a material which can eliminate a double bond may be an effective bleach. Categories of bleaches which are well known in the art include chlorine releasing components, inorganic oxygen bleaches and organic oxygen bleaches. Chlorine releasing compounds have certain disadvantages associated with their use such as, for example, their tendency to weaken or degrade fabrics, their tendency to react with other components of compositions in which they are present, their tendency to fade the colors of many dyed fabrics and to cause yellowing of certain synthetic or resin-treated fabrics. While inorganic oxygen bleaches overcome many of the disadvantages found with active chlorine releasing compounds, they have the disadvantage that they generally must be used at relatively high temperatures such as 85°C or higher. This drawback becomes significant in light of the modern trend towards using lower wash temperatures, which are generally less than about 60°C, in order to reduce energy cost and prolong the life of the fabric. However, it is possible to improve the low temperature performance of inorganic oxygen-releasing compounds through the addition of agents known as bleach activators. Generally, bleach activators react, in situ , with an inorganic oxygen bleach to generate a more reactive oxygen bleach such as peroxycarboxylic acid. An example of prior art teaching of alkylsulfophenyl carbonate esters is European Patent Application 202,698 to Nollet, et al. Consequently, there is a continuing need for an improved process for producing effective and skin-safe alkylsulfophenyl carbonate. SUMMARY OF THE INVENTION Among those compounds which can be used as bleach activators are alkylsulfophenyl carbonate esters. However, the prior art processes for production of this class of bleach activators yields products which have several significant disadvantages for use as commercial bleach activators. Typically, these alkylsulfophenyl carbonate esters have been synthesized in aqueous alkaline media via the reaction of alkyl chloroformate with the sodium salt of phenolsulfonic acid. While not being held to any theory, it is believed that on precipitation, a certain amount of the alkaline reaction medium is trapped in the crystalline product. Upon storage, the dry product undergoes a solid state reaction at a slow rate with the trapped alkalinity producing dialkylcarbonates. Thus, not only is the yield of alkylsulfophenyl carbonate reduced, which consequently will reduce bleach performance, but an impurity (dialkylcarbonate) is formed in the product which has very low water solubility and thus imparts a cloudiness to solutions of the product. More importantly, the dialkylcarbonates have been observed to be skin sensitizers as indicated by tests employing guinea pigs. Consequently, the presence of dialkylcarbonates as impurities in the sulfophenyl carbonate esters above certain levels make these impure esters potential skin sensitizers. In fact, alkylsulfophenyl carbonate esters produced by means of prior art processes have been observed as skin sensitizers in guinea pig tests at challenge levels of five percent or higher. In accordance with the present invention, there is provided an improved process for synthesizing alkylsulfophenyl carbonate esters by reacting an alkyl chloroformate with a salt of phenolsulfonic acid in an alkaline medium, wherein levels of dialkyl carbonate impurities are reduced to such a low level that the product is skin-safe. This invention relates to a process for synthesizing an alkylsulfophenyl carbonate having a straight or branched chain alkyl group containing from 6 to 12 carbon atoms or a cycloalkyl group containing 6 to 9 carbon atoms wherein an alkyl haloformate is reacted with an alkali metal phenolsulfonate salt in an aqueous alkaline medium and contemplates the improvement comprising adding to the alkaline medium an acidic material after the formation of the alkylsulfophenyl carbonate ester but prior to its precipitation from solution. Such acid material may take the form of an acidic buffering agent or a suitable acid, either organic or inorganic. The amount of acidic material employed is that which is sufficient to lower the pH of the reaction mass containing the alkylsulfophenyl carbonate in solution to 7 or below. Typically the solution is neutralized. The process of this invention allows the synthesis of alkylsulfophenyl carbonate esters in an aqueous alkaline media environment but decreases the amount of alkylsulfophenyl carbonate ester product which decomposes with time to yield dialkylcarbonate impurities. In so doing, alkylsulfophenyl carbonate ester product produced by the process of this invention contains lower levels of dialkylcarbonate impurities, especially as compared to such carbonate esters produced by precipitation from an aqueous alkaline reaction medium. The storage stability of the alkyl-sulfophenyl carbonates produced in accordance with this invention is greatly improved because such carbonates may be stored at relatively high temperatures for extended periods of time with reduced amount of dialkylcarbonate formation. The amount of dialkylcarbonate formation is so low that skin sensitivity of the stored carbonates is no longer a problem. The product made by the process of the invention retains more of its bleach activator activity and has a substantially reduced tendency to cause cloudiness in aqueous solutions. DETAILED DESCRIPTION OF THE INVENTION Prior art processes for production of carbonate esters have done so by reacting an alkyl chloroformate and, preferably, sodium phenosulfonate salt in aqueous alkaline media. Unfortunately, because of the alkaline media, a certain percentage of the alkylsulfophenyl carbonate esters which are formed in this manner decompose to yield dialkylcarbonates which can cause skin sensitization and impart cloudiness to aqueous solutions of such products. The peroxygen bleach activator compounds to which the process of this invention is directed are represented by the formula: wherein R is a straight or branch chained alkyl group having from 6 to 12 carbon atoms and cycloalkyl groups having from 6 to 9 carbon atoms and X is a non-interfering cation such as sodium and mixtures thereof. These compounds are employed in combination with an inorganic peroxygen bleaching compound capable of yielding hydrogen peroxide in an aqueous solution to provide effective and safe fabric bleaching over a wide range of temperatures and conditions. Preferably the alkyl group R in the above structural formula will contain from about 8 to about 10 carbon atoms while linear C₉ derivatives have been found to be most preferred. Compositions of this invention may comprise mixtures of compounds described by the above structural formula. Such mixtures may contain compounds wherein R is C₇, C₉ and C₁₁ alkyl groups. Also, mixtures of compounds may be employed wherein R is C₇ and C₉ or preferably C₈ and C₁₀ alkyl groups. For example, compositions containing mixtures of compounds described by the above formula may contain, by weight, equal parts of compounds wherein R is C₇, C₉ and C₁₁ or the average carbon chain length present in the mixture may be adjusted by varying the amounts of and carbon chain lengths of the various compounds employed. A preferred mixture is one containing from 30/70 to 70/30 ratio by weight percent of C₈ and C₁₀ alkylsulfophenyl carbonates. The R groups of the above formula may contain substituents which are non-interfering with the bleach activator function of the compounds. Examples of non-interfering substituents are halides such as chlorine, bromine or iodine, nitro, cyano, sulfo, alkoxy, amino, carboxymethyl, etc. The term "cation" employed hereinabove with respect to X in the structural formula refers to any non-interfering cation. By non-interfering it is meant that the cation will not interfere with the operation of the activator in producing a functional bleach or interfere with detergent action of a detergent material if present. The most frequently employed cations are those of Group I of the Periodic Table, preferably sodium but encompassing also lithium and potassium, cesium and rubidium. Alkaline earth metal cations can also be employed as, for example, magnesium, calcium, strontium and barium, but in detergent applications the addition of calcium cations is not regarded as optimum. Ammonium and organic ammonium cations which can be prepared from low molecular weight organic amines, especially those having a molecular weight below 300, are also considered non-interfering cations. Many other cations which do not interfere with the formation of bleach and its action in situ as well as other functions which may be desirable in conjunction with bleaching can also be employed such as sulfonium and sulfoxide cations. The alkylsulfophenyl carbonate esters are prepared by reacting an alkyl haloformate with a salt of phenol sulfonate in an alkaline aqueous medium. In such a reaction, the alkyl group of the haloformate corresponds to the desired R group of the formula set out earlier for the alkylsulfophenyl carbonate esters. Alkyl chloroformates are normally employed for the reaction and are preferred. The reaction occurs in an alkaline aqueous medium generally at a pH of from 10 to 12 and at a temperature of from 50°C to 100°C. The concentration of reactant and the duration of the reaction are easily within the skill of the art. Processes for the production of alkylsulfophenyl carbonate esters are disclosed in European Patent Application 202,698 which is incorporated herein by reference. According to this invention, the reaction is carried out in water. At the conclusion of the reaction, the reaction mass is acidified with a suitable acidic substance while the desired alkylsulfophenyl carbonate is in solution. Acidification is accomplished by adding an appropriate amount of material which provides hydrogen ions in solution thereby lowering the pH of the reaction mass to about 7 or below. Preferably the pH of the reaction mass containing the alkylsulfophenyl carbonate in solution is lowered to the range of from about 5 to about 7. Higher pH provides some opportunity for degradation of the desired carbonate to the dialkylcarbonate while lower pH does not provide further benefit and requires the unnecessary handling of acidic liquid. Alkaline pH is conducive to dialkylcarbonate formation particularly during drying operations and prolonged storage of the alkylsulfophenyl carbonate solid product. Typical acidic buffering agents include acidic salts such as bisulfates, such as sodium, potassium or ammonium, hydrogen and dihydrogen phosphates, alkali metal or alkaline earth metal phosphates, etc. Any suitable acid salt may be employed. Acids may also be employed but cautious addition is suggested so as not to over neutralize the solution thus producing unnecessarily low pH material. Any number of acids may be employed such as sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, acetic acid, butyric acid or fumaric acid. Other suitable acids and acidic buffering agents will occur to those interested in operating the reaction described herein to provide alkylsulfophenyl carbonates. The addition of the acidic material should be added as soon after the end of the reaction of the alkyl chloroformate as possible since prolonged exposure of the desired carbonate to the alkaline reaction mass causes hydrolysis of the desired carbonate. As noted earlier the acidic material is added to the reaction mass prior to the precipitation of the carbonate. Such precipitation may take place as is convenient since contact with neutral or slightly acidic solution does not harm or degrade the alkylsulfophenyl carbonate. Precipitation and separation procedures as practiced in the prior art are performed to obtain the solid product from solution. The above disclosure generally describes the present invention. A more complete understanding can be obtained by reference to the following specific examples which are provided herein for the purposes of illustration only and are not intended to limit the scope of the invention. Unless otherwise stated, all references to percent is percent by weight in the following examples. EXAMPLE 1 (Prior Art) A reactor having a capacity of 378 liters was purged with nitrogen and then protected with nitrogen while being charged with 86.2 kg of water. With agitation, 31.6 kg of sodium 4-phenolsulfonate were added. After 10 minutes of agitation 12.8 kg of 50% sodium hydroxide was added over a period of 15 minutes. To serve as an emulsifying agent, 90.7 g of product was added. The batch was heated to 50°C and a 50/50, by weight, mixture of n-octyl-chloroformate and n-decyl chloroformate were added, 32.1kg, over a 15 minute period. The batch heated to 65°C following addition of the chloroformate and was held at a temperature in the range of from 60°C-70°C for 30 minutes. The reaction mixture was diluted with 99.9 kg of water and cooled to a temperature of from 0-5°C. The product was filtered after a 1-hour holding period by means of a centrifuge and spun dry. After pan drying at 50°C with vacuum, approximately 45.4 kg of a 50/50, by weight, mixture of n-octyl sulfophenyl carbonate and n-decyl sulfophenyl carbonate was obtained. The product was found to contain 4.63 percent, by weight, of mixed dialkylcarbonates (n-octyl/n-decyl) by analysis of a cyclohexane extract. EXAMPLE 2 The procedure of Example 1 was repeated with the exception that the pH of the reaction solution was adjusted with sodium acid sulfate to 6.0 immediately after completion of the reaction and prior to precipitation of the product. Analysis (gc) of a cyclohexane extract was found to indicate the product contained only .14% alkyl carbonate. EXAMPLE 3 Into a reactor as described in Example 1 and with similar procedure were charged 40.9 kg of water and, with agitation, 24.9 kg of sodium 4-phenolsulfonate. The mixture was stirred for 10 minutes and then 9.72 kg of 50 percent sodium hydroxide were added over a period of 15 minutes. There were then added 9.72 g of product and 68.18 kg of methyl ethyl ketone. After heating the reaction mixture to 50°C, there was added 24.5 kg of 50/50 mixture, by weight, of n-octyl chloroformate and n-decyl chloroformate over a period of 15 minutes. The reaction was carried out at a temperature in the range of from 65°C to 70°C for a period of 30 minutes. Afterward the reaction mass was cooled to below 50°C and agitation stopped to allow the mixture to settle. Two liquid phases formed. The organic layer, containing the desired mixture of alkylsulfophenyl carbonate was separated from the aqueous layer. The organic phase was extracted several times with aqueous sodium sulfate then pan dried with vacuum to provide about 45.45 kg of a 50/50 mixture, by weight, of n-octyl/n-decyl sulfophenyl carbonate. Analysis (gc) of a cyclohexane extract of the product indicated that it contained 1.67 percent of a mixture of the dialkylcarbonates comprising the n-octyl and n-decyl species. The above level of concentration of dialkylcarbonate in alkylsulphenyl carbonate has been shown not to be a skin sensitizer in tests. EXAMPLE 4 The procedure of Example 3 was repeated except that the pH of the solution of adjusted to about 6.0 with 5% hydrochloric acid solution prior to extraction of the organic liquid phase. The product was found to contain .13 percent, by weight, dialkylcarbonate by analysis (gc) of a cyclohexane extract. EXAMPLE 5 Into a reactor as described in Example 1 and with similar procedure there were charged 40.9 kg of water and, with agitation, 24.5 kg of sodium 4-phenolsulfonate. After an additional 10 minutes of agitation, there was added 9.7 kg of 50%, by weight, sodium hydroxide over a period of 15 minutes. There were then added 9.72 g of product and 68.1 kg of methylethyl ketone. After heating the mixture to 50°C there was added 19.5 kg of n-hexylchloroformate over a period of 15 minutes. During addition of the chloroformate the batch temperature increased to about 65°C and the reaction allowed to proceed with agitation for a period of 30 minutes at a temperature in the range of 65°C-70°C. After completion of the reaction the mixture was cooled to below 50°C and allowed to settle into two phases. The top organic layer containing n-hexylsulfophenyl carbonate was separated from the bottom saturated layer, and was washed with 22.72 kg of a 33 percent aqueous solution of sodium sulfate. After thorough mixing the mixture was allowed to settle. The top organic layer was separated from the bottom salt layer and the procedure with sodium sulfate repeated two more times. The organic layer was pan dried with vacuum. About 45.4 kg of n-hexyl sulfophenyl carbonate was obtained which contained 0.92 percent di-n-hexyl carbonate as indicated by analysis (gc) of a cyclohexane extract. EXAMPLE 6 The procedure of Example 5 was repeated with the exception that the pH of the final extraction mixture was adjusted with phosphoric acid to 5. The product was isolated and dried as in Example 5 and found to contain .02 percent, by weight, di-n-hexyl carbonate by gc. analysis of a cyclohexane extract. EXAMPLE 7 Delayed contact hypersensitivity studies (Buehler Assay) were conducted employing an aqueous solution of a 50/50, by weight, mixture of n-octyl n-decyl sulfophenyl carbonate product of Example 1. In this test Hartley albino guinea pigs were divided into four groups consisting of 4 males and 4 females (group 1), 10 males and 10 females (group 2) and 5 males and 5 females (groups 3 and 4). Group 1 was used to determine the appropriate concentrations of test material for use during the study phases. The animals of group 2 were treated at induction with a 5 percent concentration of the test material and later challenged with a 2.5 percent concentration of the test material. Rechallenge concentrations were 2.5 percent and 1 percent. Groups 3 and 4 were treated only during the challenge and rechallenge phases respectively, to act as irritation controls. The sample tested was applied in patches on test sites once a week for three weeks (3 exposures). After a two week rest period, animals were treated at new sites with the challenge concentrations noted above. Rechallenges were carried out one week after the primary challenge. Scores of 1 or greater in the test group are indicative of sensitization provided scores of less than 1 were present in the irritation control groups (groups 3 and 4). If grades of 1 or greater are found in the irritation control group, then the test group must have reactions exceeding those of the control group to be considered sensitized. The test sample of the 50/50 mixture of n-octyl sulfophenyl carbonate and n-decyl sulfophenyl carbonate caused slight patchy erythema in one animal after the second induction and in 10 animals after the third induction. After the first challenge one animal had a score of 1 at both 24 and 48 hours, while 9 animals at 24 hours and 10 animals at 48 hours had scores of ± (slight patchy erythema). The rechallenge at 2.5 percent concentration produced a score of 1 in one animal and a score of ± at 48 hours in 9 animals. Rechallenge at 1 percent produced slight patchy erythemia in two animals at 48 hours. None of the irritation control animals responded to either concentration of the sample material. The results indicate that sensitization occurred at 2.5 percent challenge and rechallenge while the slight response at 1 percent concentration is equivocal. EXAMPLE 8 A delayed contact hypersensitivity study as described in Example 7 was repeated by employing samples of alkylsulfophenyl carbonates. The first sample was the product produced in accordance with the procedure of Example 1 which was purified by extraction with cyclohexane to remove dialkylcarbonates. The second sample was the purified product of Example 1 to which was added 4.63 percent, by weight, of a 50/50 mixture of di-n-octyl and di-n-decyl carbonates. The concentration of the challenge solution was 10 percent, by weight, of total carbonate. On the basis of a screen for primary irritation, an induction solution of the product at a 10%, by weight, concentration was employed. During induction, the test material was applied on patches to the same site once a week for three weeks. Two weeks after the last induction, the guinea pigs were challenged at new sites with two materials. Scores of 1 or greater indicated sensitization in the absence of a similar response in control animals. In this test, the purified sample, having the dialkylcarbonate removed, produced no scores of 1 or greater in the test group. When the dialkylcarbonates were added to the purified sample, scores of 1 in two of 20 animals were observed while none of the controls responded. The results indicate that the dialkylcarbonates were responsible for the sensitization response produced by the contaminated product.

Claims: A process for synthesizing an alkylsulfophenyl carbonate having a straight or branched chain alkyl group containing from 6 to 12 carbon atoms or a cycloalkyl group containing from 6 to 9 carbon atoms wherein an alkyl chloroformate is reacted with a phenolsulfonate in an aqueous alkaline medium, characterized by adding to said alkaline medium an acidifying agent whereby the reaction mass is neutralized to a pH of 7 or below after formation of the carbonate but before recovery of the alkylsufophenyl carbonate. The process of Claim 1, wherein said acidifying agent is an acidic buffering agent or an acid. The process of Claim 2, wherein said acidifying agent is an acidic buffering agent selected from the group consisting of bisulfate salts, alkali metal and alkaline earth metal phosphate salts and hydrogen and dihydrogen phosphate salts, and the acid is selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, acetic acid, butyric acid and fumaric acid. The process of Claim 1, wherein the phenolsulfonate is an alkali metal phenolsulfonate, wherein the alkyl group contains from 8 to 11 carbon atoms. The process of Claim 4, wherein the alkyl chloroformate is a mixture comprising octyl and decyl chloroformate, hexyl chloroformate, n-decylchloroformate or n-octylchloroformate. The process of Claim 3 wherein the acidic buffering agent is selected from sodium bisulfate, sodium dihydrogen phosphate, and sodium monohydrogen phosphate. The process in accordance with Claim 1 wherein a miscible organic solvent is added to aqueous alkaline medium. The process of Claim 1 wherein the alkylchloroformate is selected from n-hexylchloroformate, mixtures of n-octyl and n-decyl chloroformate, and 2-ethylhexyl chloroformate.

Inventors: JAKSE FRANK PETER, MORRIS DONALD EUGENE, VANDERLINDE WILLIAM, JAKSE, FRANK PETER, MORRIS, DONALD EUGENE, VANDERLINDE, WILLIAM
Applicants: MONSANTO CO, MONSANTO COMPANY
Application year: 1990
Main classification: C07C309
IPC codes: C11D7, C07C309, C07C303