METHOD OF MAKING MIXED ESTERS OF PHTHALIC ACID

Abstract: A method of making mixed esters of phthalic acid for use as plasticizers for vinyl plastics. The ester mixture is character­ ized by having a low volatility while at the same time having excellent solvency characteristics. In its preferred form, the mixed ester is made by first reacting butyl alcohol or a mixture of butyl and octyl alcohols with phthalic anhydride in a mole ratio of about 0.80 to about 1.5 moles of alcohol per mole of phthalic anhydride. Next, an octyl alcohol is added in a stoichiometric amount based on unreacted acid groups along with 20 to 100 percent of the stoichiometric amount of octyl alcohol as excess. An esterification catalyst is added and the reaction mixture heated under vacuum at a temperature less than about 150°C for a time period sufficient to carry the esterification to substantial completion.

Description: Method of making mixed esters of ohthalic acid This invention relates to a new method of preparing mixed esters of phthalic acid for use as plasticizers particularly for vinyl plastics and more specifically, mixed esters from phthalic anhydride, butyl alcohol, and octyl alcohol by sequential reaction. A plasticizer has been defined as a material incorporated in a plastic to increase its workability and its flexibility and distensibility. The addition of the plasticizer may lower the melt viscosity, the temperature of the second-order transition, or the elastic modulus of the plastic. A class of such plasticizers, which has been widely used, is the phthalic acid esters of monoalcohols produced by condensing aliphatic monoalcohols containing not more than 20 carbon atoms with phthalic anhydride to form neutral products. Dioctylphthalate, known as DOP, is the industry standard for a general purpose plasticizer for poly (vinyl chloride) (PVC) and accounts for approximately one-fourth of the total plasticizer production. Since plasticization of poly (vinyl chloride) takes an estimated 80 percent of plasticizer production, most plasticizers are compared to DOP for price/per formance relationships. The economic life of any other plasticizer depends upon its being less expensive than DOP or its doing some specific job better than DOP. The demand from the public in the last decade for high-quality products has resulted in continued growth of many different plasticizers with unique properties. Among the better known plasticizers for PVC are the co-esters of butanol and octanol with phthalic anhydride generally referred to as butyl octyl phthalate (BOP) which have been available in the U.S. market since the early 1950's and butyl benzyl phthalate (BBP). It must be understood that the products referred to on the market as butyl octyl phthalate are not necessarily completely butyl octyl phthalate. Generally, when made by the mixed ester route, the final product is a ternary mixture of dibutyl phthalate, butyl octyl phthalate and dioctyl phthalate. The ratio of these three components can vary widely, based not only upon the stoichiometry of the original reaction, but also upon the manufacturing procedure and catalyst employed. Generally, the prior art butyl octyl phthalate products tend to have around a 20/80 mole percent ratio of C4 to Cg alcohol residues. During the 1950's, butyl octyl phthalate and butyl benzyl phthalate sold at a price of about one-half cent a pound below that of DOP. As such, these two plasticizers represented low-priced replacements for DOP. In the mid 1960's, both butyl octyl phthalate and butyl benzyl phthalate took the form of specialty plasticizers and the price rose above that of DOP. The specialty aspect emphasized was high solvency. This characteristic is particularly valuable in the manufacture of products such as vinyl asbestos tile, carpet backing, plastisols and organosols, coatings and as process aids. The latter, particularly, involve the addition of plasticizers to formulations used in calendering and extrusion where the primary performance characteristic is to reduce apparent melt viscosity at processing temperature and/or to provide improved surface gloss. However, both products have the drawback of high volatility. In the case of the butyl octyl phthalate, this is due primarily to the presence of dibutyl phthalate. Accordingly, it is desirable to produce a higher solvating plasticizer than DOP with reduced volatility compared to BBP or prior art butyloctylphthalate products by producing a butyloctylphthalate product having an improved BOP/DOP ratio and a minimum dibutylphthalate (DBP) content. A substantial improvement in this direction has been achieved by the invention set forth in U.S. Patent Application Serial No. 069,636, filed August 27, 1979. This application discloses reacting butyl alcohol with phthalic anhydride to provide a mixture containing the half-ester and unreacted phthalic anhydride. This first step requires initial heating but exotherms near 90"C and it is necessary to maintain the temperature below 1300C. This reaction generally requires about 50 to 60 minutes. The reaction mixture is then cooled and octylalcohol is added along with a catalyst. The mixture is then heated with agitation to a temperature of about 1600C at which point it refluxes. It is allowed to rise slowly to a temperature of about 200"C and is not permitted to exceed 210'C. The reaction is continued until the water ceases to separate in the distillate. While this is a substantial improvement over the prior art, it is a purpose of the present invention to effect a substantial further improvement in the production of a butyloctylphthalate product, i.e., to further and substantially improve the combination of BOP/DOP ratio and dibutylphthalate concentration. The present invention is directed to an improvement in the process for preparing butyloctylphthalate products which are mixed esters of phthalic acid for use as plasticizers characterized by improved solvating characteristics and reduced volatility. More specifically, the present invention is an improvement in the process of U.S. Patent Application Serial No. 069,636 wherein the second step reaction temperature is maintained at a maximum of about 1500C and preferably about 140 C, and wherein vacuum is applied in amounts sufficient to maintain reflux. It was found tnat butyloctylphthalate products having a greatly improved combination of BOP/DOP ratio and dibutylphthalate content was achieved. The present invention is directed to the process where an alcohol composition consisting of 100 to 80 mole percent butyl alcohol and 0 to 20 mole percent octyl alcohol is reacted with phthalic anhydride in a mole ratio of about 0.80 to 1.5 moles alcohol total, i.e., butyl alcohol plus octyl alcohol, per mole of phthalic anhydride. The butyl alcdhols that may be employed include isobutyl alcohol and n-butyl alcohol. The octyl alcohols that may be employed include isooctyl alcohol and 2-ethylhexyl alcohol. The alcohol-phthalic anhydride reaction requires initial heating, generally to about 80"C and exotherms near 90"C, and it is necessary to maintain the temperature below about 120go. The reaction generally requires about 0.25 to 3 hours. Octyl alcohol is then added in a stoichiometric amount based on unreacted acid groups plus 20 to 100 percent of the stoichiometric amount of octyl alcohol as excess along with a catalyst. The mixture is heated gradually with agitation to a maximum temperature of about 1500C, preferably about 140to. In general, the temperature should be at least about 120 C. Vacuum is applied to maintain boilup (as much as necessary, often < 10 millimeters Hg absolute pressure) and the reactor overheads are fractionated (in a column or partial condenser or suitably designed decanter) so as to reflux octanol back to the reactor while removing water of reaction together with liberated butanol. The reaction is continued until the water ceases to separate in the distillate. When the acid number drops to 2-3, the reaction is considered complete. The reaction time generally runs from about 1 to 10 hours depending on many factors such as the size of the reactor. When the reaction is complete, the mixture is cooled and the acid neutralized with an alkali such as sodium hydroxide in a sufficient amount determined by acid numbers to completely neutralize the acid plus 10 percent excess. The ester is washed by adding water and salt, stirred for about 10 to 40 minutes; allowed to settle and the aqueous layer drawn off. It is then rehashed with water and salt mixture. The systemis then closed and subjected to a vacuum from about 15 to 25 inches of mercury absolute after which the alcohol is distilled off. After most of the alcohol is boiled off, the ester is stripped with steam until the free octyl alcohol content is less than 150 parts per million. After stripping, the ester is further purified by adding powdered carbon, filter aid, attapulgus clay and filtering. Suitable catalysts which may be employed in the second step of the reaction, i.e., the reaction of the halfester mixture with the octyl alcohol, include tetra-n-butyl titanate, a tin-titanate blend, and strong mineral acids such as sulfuric. Other catalysts that may be employed are ptoluenesulfonic acid, methanesulfonic acid, stannous octoate, and orthophosphoric acid. Alkaline solutions which may be employed for neutralizing include aqueous sodium hydroxide, aqueous potassium hydroxide, sodium bicarbonate, and calcium hydroxide. The following examcles illustrate the invention. All parts are by weight and all temperatures are in degrees Celsius unless otherwise indicated. Example 1 A mixture of phthalic anhydride and n-butanol was prepared in a 2-liter round bottom flask fitted with a heating mantle, temperature controller, stripping column, Stark & Dean trap, vacuum gauge, vacuum pump and variable speed agitator, by mixing 385.1 grams (2.6 moles) phthalic anhydride with 192.7 grams (2.6 moles) butanol. The mixture was heated and maintained at 90 to 95"C for 2 hours. A second alcohol charge was then made consisting of 677.2 grams (5.2 moles) of 2-ethylhexanol. Catalyst was then added (2.1 grams p-toluenesulfonic acid dissolved in 2 milliliters distilled water) and the batch heated and maintained at 1200C for 3 hours under a total pressure of 100 millimeters of mercury absolute. None of the overhead vapor was returned to the pot as condensate. The batch was then heated and maintained at 140"C for an additional 2.5 hours under total pressure of 200 millimeters mercury. The resulting product analyzed as follows. Percent by Weigflt n-butanol 2.55 2-ethylhexanol 17.62 monobutylphthalate 0.31 mono-2-ethylhexylphthalate 1.51 dibutylphthalate 2.86 butyl-2-ethylhexylphthalate 45. 17 di-2-ethylhexylphthalate 29.78 The BOP/DOP weight ratio was 1.52 and the amount of dibutylphthalate as percent of total diester was 3.68. Example 2 A mixture of phthalic anhydride, n-butanol and 2-ethylhexanol was prepared in a 2-liter round bottom flask fitted with a heating mantle, temperature controller, stripping column, Stark & Dean trap, vacuum gauge, vacuum pump and variable speed agitator, by mixing 385.1 grams (2.6 moles) phthalic anhydride with 173.4 grams (2.34 moles) butanol, and 33.9 grams (0.26 moles) of 2-ethylhexanol. The mixture was heated and maintained at 90 to 95"C for 2 hours. A second alcohol charge was then made consisting of 609.5 grams (4.68 moles) of 2-ethylhexanol. Catalyst was then added (2.1 grams p-toluenesulfonic acid dissolved in 2 milliliters distilled water) and the batch heated and maintained at 130 to 1350C for 3 hours under a total pressure of 100 millimeters of mercury absolute. The resulting product analyzed as follows. Percent by Weight n-butanol 0.40 2-ethylhexanol 11.60 monobutylphthalate 0.28 mono-2-ethylhexylphthalate 5.77 dibutylphthalate 2.05 butyl-2-ethylhexylphthalate 42.61 d i-2-ethylhexyl phthalate 37.09 The BOP/DOP weight ratio was 1.15 and the amount of dibutylphthalate as percent of total diester was 2.51. Example 3 A mixture of phthalic anhydride, n-butanol and 2-ethylhexanol was prepared in a 2-liter round bottom flask fitted with a heating mantle, temperature controller, stripping column, Stark & Dean trap, vacuum gauge, vacuum pump and variable speed agitator, by mixing 370.3 grams (2.5 moles) phthalic anhydride with 166.8 grams (2.25 moles) butanol and 32.6 grams (0.25 moles) 2-ethylhexanol. The mixture was heated and maintained at 1100C for 35 minutes. A second alcohol charge was then made consisting of 520.9 grams (4.0 moles) 2-ethylhexanol. Catalyst was then added (2.0 grams p-toluenesulfonic acid dissolved in 2.0 milliliters distilled water) and the batch heated and maintained at 140"C for 5 hours. Total pressure decreased from 760 to 100 millimeters of mercury absolute during the reaction. The resulting product analyzed as follows on a mole basis: Percent by Weight n-butanol 0.30 2-ethylhexanol 9.09 monobutylphthalate 0.06 mono-2-ethylhexylphthalate 1.33 dibutylphthalate 4.93 butyl-2-ethylhexylphthalate 41.72 di-2-ethylhexylphthalate 42.38 The BOP/DOP weight ratio was 0.98 and the amount of dibutylphthalate as percent of total diester was 5.54. Example 4 A mixture of phthalic anhydride, n-butanol and 2-ethylhexanol was prepared in a 2-liter round bottom flask fitted with a heating mantle, temperature controller, stripping column, Stark & Dean trap, vacuum gauge, vacuum pump and variable speed agitator, by mixing 370.3 grams (2.5 moles) phthalic anhydride with 157.5 grams (2.12 moles) butanol and 48.8 grams (0.37 mole) 2-ethylhexanol. The mixture was heated and maintained at 100or for 1 hour. A second alcohol charge was then made consisting of 520.9 grams (4.0 moles) 2-ethylhexanol. Catalyst was then added (2 grams p-toluenesulfonic acid dissolved in 2 milliliters distilled water) and the batch heated and maintained at 135"C for 6 hours under a total pressure ranging from 760 to 100 millimeters of mercury absolute. The resulting product analyzed as follows on a mole basis: Percent by Weight n-butanol 0.20 2-ethylhexanol 8.56 monobutylphthalate 0.12 mono-2-ethylhexylphthalate 3. 68 d ibutylphthalate 3.07 butyl-2-ethylhexylphthalate 41.60 di-2-ethylhexylphthalate 42.57 The BOP,'DOP weight ratio was 0.98 and the amount of dibutylphthalate as percent of total diester was 3.52. Example 5 A mixture of phthalic anhydride, n-butanol and 2-ethylhexanol was prepared in a 2-liter round bottom flask fitted with a heating mantle, temperature controller, stripping column, Stark & Dean trap, vacuum gauge, vacuum pump and variable speed agitator, by mixing 370.3 grams (2.5 moles) phthalic anhydride with 157.5 grams (2.12 moles) butanol and 48.8 grams (0.37 moles) 2-ethylhexanol. The mixture was heated and maintained at 100"C for 1 hour. A second alcohol charge was then made consisting of 520.9 grams (4.0 moles) 2-ethylhexanol. Catalyst was then added (4 grams p-toluenesulfonic acid dissolved in 4 milliliters distilled water) and the batch heated and maintained at 135"C for 4.5 hours under total pressure of 120 millimeters of mercury absolute. The resulting product analyzed as follows on a mole basis: Percent by Weight n-butanol 0.23 2-ethylhexanol 10.90 monobutylphthalate 0.01 mono-2-ethylhexylphthalate 0.42 dibutylphthalate 2.20 butyl-2-ethylhexylphthalate 41.76 di-2-ethylhexylphthalate 44.08 The BOP/DOP weight ratio was 0.95 and the amount of dibutylphthalate as percent of total diester was 2.50. Example 6 A mixture of phthalic anhydride and n-butanol was prepared in a 2-liter round bottom flask fitted with a heating mantle, temperature controller, stripping column, Stark & Dean trap, vacuum gauge, vacuum pump and variable speed agitator, by mixing 385.1 grams (2.6 moles) phthalic anhydride with 192.7 grams (2.6 moles) butanol. The mixture was heated and maintained at 100 C for 1 hour. A second alcohol charge was then made consisting of 474.0 grams (3.6 moles) 2-ethylhexanol. Catalyst was then added (4.2 grams p-toluenesulfonic acid dissolved in 4 milliliters -distilled water) and the. batch heated and maintained at 135"C for 5.5 hours under a total pressure ranging from 150 to 40 millimeters of mercury absolute. The resulting product analyzed as follows on a mole basis: Percent by Weignt n-butanol 0.20 2-ethylhexanol 5.78 monobutylphthalate 0.09 mono-2-ethylhexylphthalate 1. 84 dibutylphthalate 5.59 butyl-2-ethylhexylphthalate 54.54 di-2-ethylhexylphthalate 31.55 The BOP/DOP weight ratio was 1.73 and the amount of dibutylphthalate as percent of total diester was 6.10. Example 7 A mixture of phthalic anhydride and n-butanol was prepared in a 2-liter round bottom flask fitted with a heating mantle, temperature controller, stripping column, Stark & Dean trap, vacuum gauge, vacuum pump and variable speed agitator, by mixing 385.1 grams (2.6 moles) phthalic anhydride with 192.7 grams (2.6 moles) butanol. The mixture was heated and maintained at 1OCOC for 1 hour. A second alcohol charge was then made consisting of 474.0 grams (3.64 moles) 2-ethylhexanol. Catalyst was then added (4.2 grams p-toluenesulfonic acid dissolved in 4 milliliters distilled water) and the batch heated and maintained at 135"C for 3 hours under a total pressure ranging from 580 to 100 millimeters of mercury absolute. The overhead vapor was partially condensed at 90"C and the condensate was returned to the pot. The resulting product analyzed as follows on a mole basis Percent by Weight n-butanol 0.00 2-ethylhexanol 0.00 monobutylphthalate 0.06 mono-2-ethylhexylphthalate 5.90 dibutylphthalate 4.39 butyl-2-ethylhexylphthalate 53.60 di-2-ethylhexylphthalate 35.95 The BOP/DOP weight ratio was 1.49 and the amount of dibutylphthalate as percent of total diester was 4.68. Example 8 A mixture of phthalic anhydride and n-butanol was prepared in a 2-liter round bottom flask fitted with a heating mantle, temperature controller, stripping column, Stark & Dean trap, vacuum gauge, vacuum pump and variable speed agitator, by mixing 385.1 grams (2.6 moles) phthalic anhydride with 192.7 grams (2.6 moles) butanol. The mixture was heated and maintained at 100µC for 1 hour. A second alcohol charge was then made consisting of 474.0 grams (3.64 moles) 2-ethylhexanol. Catalyst was then added (4.2 grams p-toluenesulfonic acid dissolved in 4 milliliters distilled water) and the batch heated and maintained at 1300C for 2 hours under a total pressure ranging from 360 to 20 millimeters of mercury absolute. The resulting product analyzed as follows on a mole basis: Percent by Weight n-butanol 0.03 2-ethylhexanol 1.95 monobutylphthalate 0.05 mono-2-ethylhexylphthalate 2.47 dibutylphthalate 3.73 butyl-2-ethylhexylphthalate 55.02 di-2-ethylhexylphthalate 36.34 The BOP/DOP weight ratio was 1.51 and the amount of dibutylphthalate as percent of total diester was 3.92. Example 9 A mixture of phthalic anhydride and n-butanol was prepared in a 2-liter round bottom flask fitted with a heating mantle, temperature controller, stripping column, Stark & Dean trap, vacuum gauge, vacuum pump and variable speed agitator, by mixing 385.1 grams (2.6 moles) phthalic anhydride with 192.7 grams (2.6 moles) butanol. The mixture was heated and maintained at 100"C for 15 minutes. A second alcohol charge was then made consisting of 474.0 grams (3.64 moles) 2-ethylhexanol Catalyst was then added (4.2 grams p-toluenesulfonic acid dissolved in 4 milliliters distilled water) and the batch heated and maintained at 1300C for 5.5 hours under a total pressure ranging from 360 to 20 millimeters of mercury absolute. The resulting product analyzed as follows on a mole basis: Percent by Weight n-butanol 0.00 2-ethylhexanol 0.78 monobutylphthalate 0.00 mono-2-ethylhexylphthalate 3.40 dibutylphthalate 5.39 butyl-2-ethylhexylphthalate SE. 12 di-2-ethylhexylphthalate 33.91 The BOP/DOP weight ratio was 1.65 and the amount of dibutylphthalate as percent of total diester was 5.65. Example 10 A mixture of phthalic anhydride and n-butanol was prepared in a 2-liter round bottom flask fitted with a heating mantle, temperature controller, stripping column, Stark & Dean trap, vacuum gauge, vacuum pump and variable speed agitator, by mixing 385.1 grams (2.6 moles) phthalic anhydride with 192.7 grams (2.6 moles) butanol. The mixture was heated and maintained at 110µC for 5 minutes. A second alcohol charge was then made consisting of 474.0 grams (3.64 moles) 2-ethylhexanol. Catalyst was then added (4.2 grams p-toluenesulfonic acid dissolved in 4 milliliters distilled water) and the batch heated and maintained at 1300C for 5 hours under a total pressure ranging from 760 to 140 millimeters of mercury absolute. The overhead vapor was partially condensed at 70"C and the condensate was returned to the pot. The resulting product analyzed as follows on a mole basis: Percent by Weight n-butanol 2.01 2-ethylhexanol 3.51 monobutylphthalate 0.00 mono-2-ethylhexylphthalate 1,45 dibutylphthalate 6.53 butyl-2-ethylhexylphthalate 45.95 di-2-ethylhexylphthalate 42.15 The BOP/DOP weight ratio was 1.09 and the amount of dibutylphthalate as percent of total diester was 6.90. Example 10 A mixture of phthalic anhydride, n-butanol and 2-ethylhexanol was prepared in a 2-liter round bottom flask fitted with a heating mantle, temperature controller, stripping column, Stark & Dean trap, vacuum gauge, vacuum pump and variable speed agitator, by mixing 370.3 grams (2.5 moles) phthalic anhydride with 157.5 grams (2.12 moles) butanol, and 48.8 grams (0.37 mole) 2-ethylhexanol. The mixture was heated and maintained at 95"C for 2 hours. A second alcohol charge was then made consisting of 520.9 grams (4.0 moles) 2-ethylhexanol. Catalyst was then added (2.0 grams p-toluenesulfonic acid dissolved in 2 milliliters distilled water) and the batch heated and maintained at 125"C for 1 hour under a total pressure ranging from 430 to 250 millimeters of mercury absolute. None of the overhead vapor was returned to the pot as condensate. The batch was then heated and maintained at 125"C for an additional 4.5 hours under total pressure of 50 to 100 millimeters mercury. The resulting product analyzed as follows on a mole basis: Percent by Weight n-butanol 0.20 2-ethylhexanol 10.44 monobutylphthalate 0.11 mono-2-ethylhexylphthalate 3.94 d ibutylphthalate 2.33 butyl-2-ethylhexylphthalate 42.91 di-2-ethylhexylphthalate 39.86 The BOP/DOP weight ratio was 1.08 and the amount of dibutylphthalate as percent of total diester was 2.73.

Claims: The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 1. A method of making a mixed ester plasticizer for vinyl plastics and the like comprising the steps of first reacting an alcohol composition consisting of 100 to 80 mole percent butyl alcohol and 0 to 20 mole percent octyl alcohol with phthalic anhydride in a mole ratio of about 0.80 to about 1.5 moles of alcohol total per mole of phthalic anhydride, adding an octyl alcohol in a stoichiometric amount based on unreacted acid groups along with 20 to 100 percent of the stoichiometric amount of octyl alcohol as excess, adding an esterification catalyst and heating the reaction mixture at a maximum temperature of about 1500C for a time period sufficient to carry the esterification to substantial completion. 2. The process of claim 1 wherein said alcoholphthalic anhydride reaction is at a temperature of about 80 to 1200C for a period of time of about 0.25 to 3 hours and the subsequent reaction with said octyl alcohol is at a temperature of about 120 to 140"C for a time of from about 1 to 10 hours. 3. The method of claim 2 wherein said butyl alcohol is n-butyl alcohol and said octyl alcohol is 2-ethylhexyl alcohol. 4. The method of claim 2 wherein said esterification catalyst is p-toluene sulfonic acid. 5. The method of claim 2 which includes the additional steps of neutralizing the unreacted acid with an aqueous alkaline solution capable of converting the acid to water-soluble salts, and purifying the resultant ester mixture by the removal of salt solution, excess alkaline solution, excess alcohol and catalyst. 6. The method of claim 5 wherein said butyl alcohol is n-butyl alcohol and said octyl alcohol is 2-ethylhexyl alcohol. 7. The method of claim 6 wherein said esterification catalyst is p-toluene sulfonic acid.

Inventors: DECK, CHARLES FRANCIS, EVANGELISTA, JOHN JOSEPH
Applicants: BASF WYANDOTTE CORPORATION
Application year: 1981
Main classification: C07C69
IPC codes: C07C69, C07C67