METHOD OF ESTERIFYING DIHYDROXYBENZENES

Abstract: The present invention provides a method of esterifying dihydroxybenzene starting materials to synthesize un­ symmetrical diesters in high yield. Many of the resultant un­ symmetrical diesters are useful in dry bleaching com­ positions. The method can be practiced by selectively monoacylating a dihydroxybenzene starting material with an acid anhydride to form an intermediate monoester having the structure which is then acylated to form a diester reaction product hav­ ing the structure wherein R₁ is greater than R₃ (and both R₁ and R₃ are alkyl groups) and X is a substituent group which does not par­ ticipate in the esterification (or which can have a protecting group thereon).

Description: The present invention generally relates to a method for esterifying dihydroxybenzenes to synthesize unsymmetrical diesters therefrom via the selective formation of dihydroxybenzene monoesters. This application is related to EP-A-0185522 Peroxygen bleaching compounds are useful for bleaching fabrics, textiles and other materials, but are less effective than could be desired when bleaching temperatures less than 70°C are utilized. Thus, peroxygen bleaching compositions desirably include activators, particularly for monopersulfate and monoperphosphate systems generating hypochlorite, in order to provide effective concentration of the bleaching agent under cooler wash temperature conditions. In a technical service report dated February 1, 1970 by American Potash & Chemical Corporation, it was reported that certain ketones (i.e. acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone), activate persulfate bleaches in the presence of an alkaline buffer providing a pH of at least 8. U.S. Patent 3,822,114, inventor Montgomery, issued July 2, 1974 discloses peroxygen bleaching compositions which include a peroxygen bleaching compound, such as water-soluble monopersulfates and monoperoxy phosphates, and an aldehyde or ketone activator compound for the peroxygen compound. The aldehydes or ketones disclosed are said to activate the peroxygen compounds in aqueous solution having a pH of about 7 to about 12, and a preferred embodiment includes the optional addition of a water-soluble chloride salt to yield hypochlorite type bleaching. Dry bleaching compositions, particularly useful for low temperature applications, are described in U.S. Patent Application Serial No. 629,695, filed July 11, 1984, entitled "CONTROLLED GENERATION HYPOCHLORITE COMPOSITIONS AND METHOD," inventors Casella, et al., (EP-A-0 168253 in which generation of hypochlorite by reaction between a peroxygen bleaching agent and a chloride salt is promoted by an activator, preferably an aromatic diol in ester form having the structure illustrated below: wherein one of R₁ and R₂ is an alkyl group having at least one to about eight carbon atoms, the other is hydrogen or an alkyl group having at least one to about eight carbon atoms, and R₃, if present, may be a substituent such as sulfonate, carboxylate, alkyl ethoxylate, quarternary ammonium or lower alkyl (e.g., methyl, ethyl or butyl). As noted by D. Johnston, Chemistry & Industry 24 , 1000 (1982), attempts to mono-derivatize benzene diols usually lead to a mixture of the unreacted difunctional compounds, the mono-substituted product and the bis-derivatized by-product. Johnston describes a procedure giving good yields of hydroquinone monoacetate from hydroquinoine by reacting the hydroquinone with acetic anhydride in an equimolar ratio. However, attempts to adapt the Johnston method to resorcinol by reaction with longer chain acid anhydrides have been found to produce disappointing yields of monoester and have favored formation of symmetrical diesters. Summary of the Invention It is an object of the present invention to provide a method for the sequential esterification of dihydroxy benzenes to produce unsymmetrical diesters thereof in high yields. According to the present invention there is provided a method for the sequential esterification of dihydroxybenzenes to synthesize unsymmetrical diesters thereof comprising: selectively acylating a dihydroxybenzene starting material with a first acid anhydride to form an intermediate monoester having the structure wherein R₁ is an alkyl of from 5 to 11 carbons and X is hydrogen or a substituent group the dihydroxybenzene starting material being in a molar ratio with respect to the first acid anhydride of at least 3:1; removing any carboxylic acid by-product and unreacted dihydroxybenzene starting material from the intermediate monoester; and, acylating the intermediate monoester to form an unsymmetrical diester reaction product having the structure wherein R₃ is an alkyl having less carbons than R₁. The removal of the carboxylic acid by-product may be effected by base extraction. Yields of the unsymmetrical diester reaction product of the order of 80% may be achieved. This invention generally relates to a method of making unsymmetrical diesters of hydroxy benzenes which are useful as peracid precursors from dihydroxybenzene starting materials, via an intermediate monoester of the dihydroxybenzene. Peracid precursors are usefully combined with a source of peroxygen (and optionally a halide salt) to promote good bleaching, particularly in wash temperatures below 70°C. The peracid precursors include phenylene diesters (having the general structure illustrated by Formula I, below). In the above formula R₁ is alkyl from 5 to 11 carbons and R₃ is alkyl with less carbons than R₁. The compounds are mixed (that is, are unsymmetrical) diesters when R₁ and R₃ are unequal. When either R₁ or R₃ is less than five carbons and the other greater, it is believed that both hydrophobic and hydrophilic peracids are generated. Therefore, if used in agueous media with a source of hydrogen peroxide (e.g., sodium perborate monohydrate), for example as an all-fabric bleach, two different oxidizing species appear to be present which then attach to hydrophilic soil, such as tea and wine, and oily soils, such as sebum. For example, it is believed that when one of the ester functionalities has an alkyl straight chain length of less than 5, e.g., wherein R₁ or R₃ is CH₃, and the other alkyl group's chain length is greater than 5 carbon atoms, peroxyacids which are, respectively, hydrophilic and hydrophobic are generated. It is believed that particulate soils and hydrophilic stains can be attacked with a hydrophilic peroxyacid bleach while oily soils can be attacked with a hydrophobic peroxyacid bleach. Different pre-formed hydrophobic and hydrophilic peroxyacid bleaches were combined in published European Patent Application EP68547, whose disclosure is incorporated herein by reference. Pre-formed peracids appear, however, to have storage stability problems and may lose significant amounts of active oxygen (A.O.) upon prolonged storage. The dihydroxybenzenes are weak acids with two disassociation constants. They are generally classified as antioxidant agents and are useful analytical reagents. Their structures, uses and chemistries are more thoroughly explored in Kirk-Othmer, Encyclopedia of Chemical Technology , 3rd Ed., Vol. 13, pages 39-69 (1981), which pages are incorporated herein by reference. Among the dihydroxybenzenes which are useful as starting materials in accordance with the present invention are hydroquinone, resorcinol and catechol. Hydroquinone (1,4-benzenediol; 1,4-dihydroxybenzene; p-dihydroxybenzene) is a white crystalline compound which can be obtained by dry distillation of guinic acid or by reduction of quinone. Resorcinol (1,3-benzenediol; 1,3-dihydroxybenzene; m-dihydroxybenzene) is a crystalline compound with a faint aromatic odor, and a sweet/bitter taste. It may be produced by the alkali fusion of galbanum and asafetida resins. Catechol (1,2-benzenediol; 1,2-dihydroxybenzene; o-dihydroxybenzene) is a crystalline compound with a phenolic odor and a sweet and bitter taste. It may be obtained by dried distillation of catechin which is found in the aqueous extract of catechu, which is an extract of an East Asian acacia plant. Useful dihydroxybenzene starting materials include those where the aromatic ring has substituents thereon, and substituted phenylene diesters have been found to be particularly effective in low temperature bleaching applications. Solubility and dispersibility (and hence performance) can be improved by the addition of solubilizing groups placed on the aromatic ring. Thus, X in Formula 1, can, represent a substituent group. Nitro groups can be substituted on the aromatic ring, for example, when the dihydroxybenzene is reacted with nitric acid in the presence of sulfuric acid. Sulfonate groups can be substituted when the dihydroxybenzene is reacted with concentrated sulfuric acid. Ammination will generally be produced by reacting a source of amino with the dihydroxybenzene in the presence of liquid ammonia. Sulfonate or carboxylate groups are especially preferred as solubilizing groups for the peracid precursors. A number of substituted dihydroxybenzenes are known and commercially available, and suitable dihydroxybenzene starting materials used in practice of the present invention have the structure already shown by Formula 1, wherein R₁ and R₃ are hydroxyl and X can be a wide variety of substituents such as sulfonate, halide, benzylamino, amino, alkyl ethoxylate, quarternary ammonium and carboxylate. For substituent groups which may be sensitive to acylation, such as amino substituents, it is generally desirable to utilize a protecting group during practice of the invention, whereby the protecting group can subsequently be removed. On an amine group, for example, bulky substituents such as alkyl chains could be present. The X substituent, if present, is preferably in the 5 position on the ring of resorcinol and in the 4 or 5 position on the ring of catechol. Ortho substituents, at the 2 position of the hydroquinone ring, at the 2 position of resorcinol or the 6 position of catechol are less desirable, particularly with bulky groups, as the acylation of the adjacent hydroxyl is inhibited. The peracid precursors containing unsymmetrical esters prepared according to the invention have been found to provide extremely good bleaching and can be incorporated into a liquid or solid matrix for use in liquid or solid detergent bleaches or laundry aids. These peracid precursors have the structure already shown by Formula 1. Particularly preferred peracid precursors are where one ester is an acetate (e.g., R₁ is -CH₃) and the other is an hexanoate, heptanoate, octanoate or nonanoate (e.g., R₃ is -(CH₂)₄CR₃ to -(CH₂)₇CR₃). In preferred bleaching composition embodiments, the total number of backbone carbons of R₁ plus R₃ should be in the range of 2-20, more preferably 5-20, most preferably 7-14. For example, a bleach composition is provided with a diester having the following ingredients: 15.5% Sodium Perborate Monohydrate 7.0% Resorcinol Octanoate Acetate 7.0% Nonionic Surfactant 15.0% Sodium Carbonate 55.5% Sodium Sulfate 100.0% The above composition including unsymmetrical diester is formulated to deliver, desirably, about 14 ppm A.O. at a pH of about 10.5. Other peroxygen sources, such as sodium perborate tertrahydrate or sodium percarbonate, are suitable in bleaching compositions utilizing peracid precursors made in accordance with the present invention. If a more detergent-type product is desired, the amount of filler can be increased and the precursor halved or further decreased. Unsymmetrical diesters from dihydroxybenzene starting materials could be used with a peroxygen bleaching agent and a chloride salt, in bleaching compositions such as are described in previously EP-A-0 168253 noted. The formation of hypochlorite is delayed in that the ester moieties of the dihydroxybenzene first hydrolyze to hydroxyl groups, but once hydrolyzed the resultant activator then promotes, or catalyzes, reaction between the peroxygen bleaching agent and chloride salt. However, by varying the amount and form of activator precursor, the amount of peroxygen bleaching agent, and the amount of chloride salt, a wide range of hypochlorite generation concentrations and delay profiles may be obtained, if desired. Suitable such bleaching compositions have from about 5 wt% to about 80 wt.% peroxygen bleaching agent, from about 10 wt.% to about 70 wt.% of the halide salt, and from about 0.1 wt.% to about 10 wt.% of the activator precursor. More preferably, the peroxygen bleaching agent is from about 25 wt.% to about 65 wt.%, the alkali halide salt from about 35 wt.% to about 45 wt.%, and the activator or activator precursor from about 0.5 wt.% to about 2 wt.%. A buffering agent is preferably present in an amount sufficient to maintain a pH within the range of from about 8 to about 11, more preferably from about 9 to about 10.5, when the compositions are dissolved in aqueous solutions. Such compositions may include other components for various purposes such as to aid in storage stability, to enhance or modify the solubilization rate of the activator precursor, in addition to including other well known laundry additives. Thus, a dihydroxybenzene, such as hydroquinone, resorcinol, or catechol, which may be substituted or unsubstituted, is initially provided as a starting material and is firstly monoesterified by reaction with an acid anhydride. The reaction mixture of the reacting step is mildly exothermic and although mild amounts of heat are acceptable, the reaction mixture should not be subjected to excessive heat which can lead to transacylation. Preferably, the reaction is conducted at about room temperature. It is very important that the dihydroxybenzene starting material be in a molar excess of at least 3:1. with respect to the acid anhydride. The reaction of dihydroxybenzene starting material with acid anhydride at the molar excess of dihydroxybenzene starting material monoacylates the starting material to form the monoester reaction product which is recoverable in yields of greater than about 50% (that is, the starting material is selectively monoacylated). A particularly preferred range of molar ratio for dihydroxybenzene starting material to acid anhydride is 3:1 to 6:1. The reaction may be acid or base catalyzed. Suitable acid catalysts include, for example, sulfuric acid, toluene sulfonic acid, methane sulfonic acid, trichloroacetic acid, and trifluoroacetic acid. Suitable basic catalysts include 4-dimethylaminopyridine, triethylamine, sodium carbonate, sodium bicarbonate, tetramethylpiperidine; generally, any tertiary amine or weakly basic catalyst can be used. The reaction may be conducted over (and catalyzed by) a basic or acidic ion exchange resin (well known to the art), such as one of the Dowex resins (available from Dow Chemical Company). The reaction mixture of the reacting step preferably is solubilized, or in liquid form. Suitable solvents for use to ensure that all reaction components are maintained in the liquid phase are non-nucleophilic to avoid interference with the course of the esterification reaction, and are preferably low molecular weight, volatile ketones (such as acetone) or halogenated hydrocarbons (such as chloroform). The intermediate monoester is then further esterified after removal of carboxylic acid by-product. For example octanoic anhydride is the acid anhydride used in the initial monoesterification then octanoic acid will results as an acid by-product. Removing any carboxylic acid by-product from the intermediate monoester may be done by base extraction (such as with sodium carbonate) and prevents the formation of a "mixed" anhydride in the reaction mixture. The presence of carboxylic acid by-product in the subsequent acylation step is undesirable, as it has been found to increase the amount of symmetrical diester formed. Thus, removal of carboxylic acid by-product is important for selectivity. Although some symmetrical diester is formed during the formation of intermediate monoester, the quantities formed are low (since the monoacylation is selective) and the small amount of symmetrical diester does not need to be removed in order to practice the second embodiment in obtaining high yields of unsymmetrical diester of dihydroxybenzene. Practice of the method according to the invention further continues with the intermediate monoester (from which any carboxylic acid by-product and any unreacted dihydroxybenzene starting material have been removed) which is then acylated with a second acid anhydride to form an unsymmetrical diester reaction product. The unsymmetrical diester reaction product has the structure previously illustrated and described as Formula 1. In practice of the method according to the invention, the first acid anhydride chosen with which to monoacylate the dihydroxybenzene starting material preferably is where R₁ is 5 to 11 carbons, where the first acid anhydride has the structure The second acid anhydride has the structure where R₃ of the second anhydride is less than R₁ of the first anhydride, more preferably where R₃ is a carbon chain from 1 to 4 carbons. Initial formation of the longer chain ester has been found to be important in selectivity and hence yield. Yields of unsymmetrical diester reaction product greater than 80-85% may be obtained. Acylation of the second hydroxyl group on the intermediate monoester compound typically is conducted at about room temperature (albeit the reaction is mildly exothermic). As with preparation of the intermediate monoester, acylation, that is esterification, of the second hydroxyl group may be acid or base catalyzed and, if desired, conducted in suitable solvents. The following examples illustrate the invention. As illustrated by comparative Example I, below, resorcinol monooctanoate was synthesized by an adaption of the previously described Johnston method for comparison with practice of the first embodiment in accordance with the invention. In the comparative synthesis of Example I, yields of the desired monoester (i.e., resorcinol monooctanoate) were typically only about 40 wt. % whereas the symmetrical diester was coproduced in slightly larger amount. That is, the comparative synthesis was not a selective monoacylation. By contrast to the comparative synthesis, practice of the first step of the method according to the invention embodiment, as illustrated by Example II, below, provides yields of about 80-95 wt.% resorcinol monooctanoate Example III illustrates practice of the first step in accordance with the invention with another dihydroxybenzene starting material (i.e., catechol). Again, practice of this step according to the invention provides extremely high yields (90-95 wt. %) of the desired monoester. Example I Comparative Synthesis of Resorcinol Monooctanoate Resorcinol (2.75 g, 0.025 mole), 4-dimethylaminopyridine (0.3 g, 0.0025 mole), and triethylamine (2.5 g, 0.025 mole) were dissolved in 50 ml of ethyl acetate in a 100 ml round bottom flask equipped with a magnetic stir bar. Octanoic anhydride (6.76 g, 0.025 mole) was added dropwise, via an addition funnel, to the stirred solution over a 100 minute time period. The resulting solution was stirred for an additional 30 minutes, at which time the solvent was removed via rotary vacuum evaporation. The remaining oil was dissolved in 200 ml of ethyl ether and extracted with a 200 ml portion of 3% HCl to remove the 4-dimethylaminopyridine catalyst, and four 100 ml portions of 5% NaHCO₃ were used to remove the octanoic acid by-product. After drying the organic phase with 40 grams of Na₂SO₄, the ether was removed by rotary vacuum evaporation and the remaining oil was redissolved in 15 ml of chloroform. The sample was then chromatographed in a column on 200 grams of silica gel G with chloroform/petroleum ether (1:2 vol/vol ratio) and pure resorcinol monooctanoate (2.36 g) was collected. Yields of the desired monoester were typically only about 40% (wt.). Symmetrical diester, resorcinol dioctanoate, was co-produced in a slightly greater portion (about 50% (wt.)). Example II Inventive Synthesis of Resorcinol Monooctanoate First Step Resorcinol (13.76 g, 0.125 mole), 0.7 g 4-dimethylaminopyridine (0.68 g, 0.0057 mole), triethylamine (2.5 g, 0.025 mole) were dissolved in 50 ml of acetone in a 250 ml round bottom flask equipped with a magnetic stir bar. Octanoic anhydride (6.7 g, 0.025 mole) was dissolved in 15 ml of acetone and added dropwise, via an addition funnel, to the stirred solution over 10 minutes, the resulting pale yellow solution was stirred for an additional 1-3/4 hours, at which time the solvent was removed via rotary vacuum evaporation. The remaining oil was dissolved in 200 ml of ethyl ether and extracted one time with 200 ml of 3% HCl to remove the 4-dimethylaminopyridine catalyst and four times with 100 ml of 5% NaHCO₃ to remove octanoic acid. After drying the organic phase with 40 grams Na₂SO₄, the ether was removed by rotary vacuum evaporation and the oil redissolved in 100 ml of 1:1 (vol) of benzene/cyclohexane. Unreacted resorcinol was crystallized out after two hours at about 10°C which was then removed by filtration. After one more wash with 5% NaHCO₃, the solvent from the organic phase was removed by rotary vacuum evaporation to give 5.9 grams of resorcinol monooctanoate (90-95 wt. % yield). Example III Inventive Synthesis of Catechol Monooctanoate (First Step) To a 50 ml round bottom flask was added catechol (Aldrich, 3.3 g, 30 mmols), octanoic anhydride (5.4 gms, 20 mmols) and 5 mls of ethyl ether. After all the catechol was dissolved, one drop of methane sulfonic acid was added and the solution stirred for two hours at room temperature. 30 mls of petroleum ether was then added and the unreacted catechol was crystallized at 5-10°C for one hour. Greater than 95% of the unreacted catechol was recovered. After filtration, the organic solution was washed three times with 50 mls of 5% NaHCO₃ and the catechol monooctanoate (4.4 g) was isolated in 90-95 wt. % yield after rotary vacuum evaporation of the solvents. Example IV, below, illustrates practice of the two step method according to the the present invention. As can be seen in Example IV, the resultant unsymmetrical diester reaction product was obtained in a yield of 82.5%. Example IV Inventive Synthesis of Resorcinol Acetate Octanoate (A) Preparation of the monoester: Resorcinol (55.04 g, 0.50 mole), 4-dimethylaminopyridine (2.0 g, 0.016 mole) and triethylamine (10.1 g, 0.10 mole) were weighed into a 1 liter round bottom flask equipped with a magnetic stir bar and dissolved, with stirring, in 200 ml of acetone. Octanoic anhydride (27.0 g, 0.10 mole) was dissolved in 50 ml of acetone, placed in a 125 ml addition funnel and added dropwise to the stirred resorcinol/4-dimethylaminopyridine/triethylamine solution over 35 min. The reaction was then stirred an additional 1 hr. 40 min. The solvent was removed by rotary evaporation (40°C) leaving a thick oil. To this oil was added 150 ml of 40/60 (vol/vol) petroleum ether (bp.30-60°C)/dichloromethane. After vigorous shaking, two phases separated upon standing. The upper phase (solvent) was decanted, followed by three more extractions (150 ml each) of the lower phase with 40/60 petroleum ether/dichloromethane. The combined petroleum ether/dichloromethane extracts were themselves extracted with: 1x250 ml 5% aqueous hydrochloric acid, 4x250 ml 7% aqueous sodium bicarbonate, and 1x250 ml filtered saturated sodium chloride solution. The organic phase was dried over 63 g sodium sulfate (anhydrous), filtered and rotary/evaporated (40°C) to a light yellow oil. Drying in vacuo at room temperature yielded 22.8 g of oil containing resorcinol monooctanoate (82.5 wt. % yield) and a small amount of resorcinol dioctanoate (14.7 wt. %). Unreacted resorcinol was recovered from the lower phase of the petroleum ether/dichloromethane extraction by dissolving in 250 ml of 20/80 (vol/vol) benzene/petroleum ether, and this was then extracted with 4x250 ml of 5% aqueous sodium bicarbonate. The combined aqueous extracts were acidified to pH 2 of concentrated hydrochloric acid extracted with 4x300 ml dichloromethane. The combined organic extracts were dried over sodium sulfate, filtered, and rotary-evaporated to an oil (44 g) which crystallized upon standing. Filtration and washing with petroleum ether followed by drying yielded 37 g (about 87 wt. %) of recovered resorcinol. (B) Preparation of the unsymmetrical diester via the monoester: To 22.7 g of the resorcinol monooctanoate reaction product obtained in (A) above, was added acetic anhydride (20.3 g, 0.198 mole) and 3 drops methane sulfonic acid in a 500 ml round bottom flask with a magnetic stir bar. A slight warming was noted, and a color change from yellow to orange and back to yellow occurred within 1/2 hr. The reaction was stirred 2 hrs., then diluted with 400 ml 50/50 (vol/vol) pentane/ethyl ether and extracted with 4x250 ml of 7% aqueous sodium bicarbonate and 1x25 ml saturated sodium chloride solution. The organic phase was dried over 60 g sodium sulfate, filtered and rotary-evaporated to a light yellow oil. Vacuum drying gave 26.0 g of product which was determined to be resorcinol acetate octanoate (yield of 82.5 wt. %) and 14.7 wt. % resorcinol dioctanoate as by-product. Examples V and VI, below, also illustrate practice of the two step method according to the invention. The "x" substituent of the Example V dihydroxybenzene starting material is carboxymethyl and of the Example VI starting material is chloride. Yields of the resultant unsymmetrical diester reaction products were about 71% and 75%, respectively. Example V (A) 16.81 g (.10 mole) 3,5-dihydroxymethyl Benzoate, 0.4 g (.003 mole) 4-DimethylaminoPyridine (DMAP), 2.02 g (.02 mole) Triethyl Amine (TEA) and 60 ml acetone were combined in a 250 ml round bottom flask equipped with a magnetic stir bar and addition funnel. This was stirred until complete solution was obtained. 5.4 g (.02 mole) octanoic anhydride was placed in the addition funnel and added dropwise to the stirred phenol/amine solution over 1/2 hr. The reaction was stirred an additional 2-1/2 hrs., then the solvent was stripped by rotary evaporation. The thick residual oil was extracted with 4x100 ml of 10% dichloromethane in hexane (vol/vol), with the last extraction going overnight. The combined extracts were themselves extracted with. 4x200 ml 5% HCl and 8x200 ml 5% NaHCO₃, dried over Na₂SO₄, and rotary evaporated to an oil which crystallized upon standing. Wt = 6.0 g (5.9 g theoretical) IR ( OH at 3420 cm⁻¹, C=0 at 1765 cm⁻¹ and 1722 cm⁻¹) and TLC (CH₂Cl₂ on silica GF, R f about 0.18) indicates substantially one product as the desired intermediate, illustrated below. There was a minor amount of higher R f material, presumably the dioctanoate ester. (B) The 6.0 g of oil from step (A) of the reaction was dissolved in 20 ml of diethyl ether. 3.0 g (.029 mole) acetic anhydride and 3 drops methane sulfonic acid were added and the reaction was stirred for 3 hrs. At this time 250 ml diethyl ether was added and the reaction was washed with 4x100 ml of 5% NaHCO₃. The ether layer was dried over Na₂SO₄, filtered, and rotary evaporated to an oil (wt = 5.5 g, 82% theo.). This material was shown by G.C. to be about 87% mixed ester (illustrated below) and 10% dioctanoate ester. IR and ¹³C-NMR confirm the structure of the compound as 3-acetoxy-5-octanoyl oxy-methyl benzoate. Example VI (A) 14.75 g (.10 mole) 4-Chloro resorcinol, 2.02 g (.02 mole) Triethylamine, and 0.4 g 4-dimethylaminopyridine (DMAP, .003 mole) were weighted into a 250 ml round bottom flask equipped with addition funnel and magnetic stir bar and dissolved in 60 ml of acetone. 5.4 g (.02 mole) Octanoic anhydride in 5 ml of acetone was added dropwise over 1/2 hr. to the stirred resorcinol/amine solution. The reaction was stirred an additional 2 hrs. and the solvent rotary evaporated. The oily residue was extracted with 2x150 ml 10% dichloromethane in hexane (vol/vol) and 1x75 ml Hexane. The combined organic extracts were washed with 3x200 ml of 5% NaHCO₃, 2x150 ml 5% HCl and 1x200 ml H₂O. After drying over sodium sulfate, and filtration, the solvent was rotary evaporated leaving a light yellow oil (wt = 5.9 g, 5.4 g theoretical). IR (ν OH at 3420 cm⁻¹,ν C=0 at 1740 cm⁻¹ and 1760 cm⁻¹ and TLC (20% CH₂Cl₂ in Hexane on silica gel GF) indicate the two products, illustrated below, with R f 's of .08 and .17 along with a minor amount of the di-octanoyl oxy Resorcinol. (B) To 5.9 g of product oil from step A of the reaction was added 3.08 (.029 mole) acetic anhydride and 2 drops of methanesulfonic acid. This was stirred for 2 hrs., then diluted with 160 ml hexane and extracted with 5x100 ml 5% NaHCO₃ and 1x200 ml water. The organic layer was dried over sodium sulfate, filtered and rotary evaporated to an oil wt = 5.0 g (80% wt). This oil was substantially one component by GLC (94%) with IR and ¹³C-NMR confirming the 4-Chloro resorcinol, acetate/octanoate mixed esters having the structures illustrated below. As previously described, molar ratio, temperature, the relative chain length of R₁ and R₃ for the first and second acid anhydrides, and the removal of carboxylic acid by-product are all believed to affect selectivity of the inventive method. This is illustrated by the following example. Comparative Example VII, below, illustrates the loss of selectivity in the two step method when the shorter chain acid anhydride is first used, rather than the longer, and the molar ratio of dihydroxybenzene starting material with respect to the first acid anhydride is about 1:1. Thus, yield of the unsymmetrical mixed ester (1-acetoxy-3-octanoyloxybenzene) was only about 47%. Comparative Example VII To 5.5 g (50 mmole) of resorcinol in 100 ml of ethyl acetate was added 0.3 g (2.5 mmole) of 4-dimethylaminopyridine catalyst at room temperature. To this solution was added 5.1 g (50 mmole) of acetic anhydride while keeping the solution at 21°C with an ice bath. The mixture was stirred for 60 min. and this was followed by the addition of 13.5 g (50 mmole) of octanoic anhydride. The solution was stirred for an additional 2 hrs. at room temperature, and then the solvent was removed under reduced pressure. The residue was redissolved in diethyl ether (100 ml) and washed three times with 50 ml of 5% sodium carbonate. The organic layer was separated, dried over sodium sulfate, filtered, and the solvent was then removed by rotary vacuum evaporation. The residue was then separated by chromatography on silica gel with chloroform/petroleum ether (1/1, V/V) to yield 6.6 g (47% yield) of the unsymmetrical mixed ester (I) and 3.75 g of resorcinol diacetate II. During practice of the invention, the solvents, unreacted (and excess) dihydroxybenzene starting materials and carboxylic acid by-products are all recoverable and can be recycled. The course of the reactions, particularly the formation of diester reaction product in practice of the second embodiment, may be monitored by gas chromatography.

Claims: A method for the sequential esterification of dihydroxybenzenes to synthesize unsymmetrical diesters thereof comprising: selectively acylating a dihydroxybenzene starting material with a first acid anhydride to form an intermediate monoester having the structure wherein R₁ is an alkyl of from 5 to 11 carbons and X is hydrogen or a substituent group the dihydroxybenzene starting material being in a molar ratio with respect to the first acid anhydride of at least 3:1; removing any carboxylic acid by-product and unreacted dihydroxybenzene starting material from the intermediate monoester; and, acylating the intermediate monoester to form an unsymmetrical diester reaction product having the structure wherein R₃ is an alkyl having less carbons than R₁. A method as claimed in claim 1 characterised in that the molar ratio of the dihydroxybenzene starting material with respect to the first acid anhydride is within the range of 3:1 to 6:1. A method as claimed in claim 1 or claim 2 characterised in that the carboxylic acid by-product is removed by base extraction. A method as claimed in any of claims 1 to 3 characterised in that the selective acylation of the dihydroxybenzene starting material is conducted at ambient temperature. A method as claimed in any of claims 1 to 4 characterised in that the selective acylation of the dihydroxybenzene starting material is conducted in the presence of an acidic or a basic catalyst. A method as claimed in any of claims 1 to 5 characterised in that the dihydroxybenzene material is hydroquinone, substituted hydroquinone, catechol, substituted catechol, resorcinol or substituted resorcinol.

Inventors: FONG, RONALD A., ROWLAND, RICHARD R.
Applicants: THE CLOROX COMPANY
Application year: 1987
Main classification: C07C69
IPC codes: C07C67