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Terephthaloyl Dichloride Synthesis Essay

1. Field of the Invention

This invention relates to a process for preparing a poly(paraphenylene terephthalamide) fibrous gel composition comprising an amide solvent, an alkaline earth metal salt and N-methylpyrrolidine or its hydrochloride and a process to prepare wholly poly(paraphenylene terephthalamide) papers using the composition as a binder.

2. Description of the Prior Art

The preparation of poly(paraphenylene terephthalamide) such as taught by U.S. Pat. No. 3,869,429 issued to Blades is generally described by reacting terephthaloyl chloride with para-phenylenediamine in a stirred solution of an alkaline earth metal salt and an amide solvent such as N-methylpyrrolidone. The result is a dry, crumb-like product devoid of fiber structure and too coarse for fiber or paper uses. To make fibers, the polymer component must be isolated from the reaction product by, for example, washing and drying, then dissolving the polymer in an appropriate solvent such as sulfuric acid and spinning the solution through an air gap into a coagulation bath.

Poly(paraphenylene terephthalamide) pulp is generally prepared from such spun filaments which are washed and dried before mechanical abrasion into pulp. It is also generally necessary to use specialized fiber cutting equipment to cut the spun continuous filaments into uniform short lengths before abrasion into pulp.

Obtaining poly(paraphenylene terephthalamide) polymers useful as a pulp directly from the polymerization system without first spinning a fiber is disclosed in U.S. application Ser. No. 07/213,741 filed June 30, 1988. Briefly, that process for producing para-aramid pulp includes forming an actively polymerizing solution containing para-aramid polymer chains by contacting an aromatic diacid halide and an aromatic diamine in a solvent and subjecting the solution to orienting flow. When the solution has a viscosity sufficient to maintain the orientation of the polymer chains, the solution is incubated until it gels. The gel is cut and the pulp is isolated from the gel.

The use of an acid acceptor in a polymerization system is known. As examples, U.S. Pat. No. 4,011,203 issued Mar. 8, 1977 and U.S. Pat. No. 4,072,664 issued on Feb. 7, 1978 disclose processes to prepare copolymers of two aromatic polyamides optionally using an acid acceptor as a polymerizing additive. Suitable acid acceptors for polymerizing the aromatic polyamides produced from one of piperazine, p-phenylene diamine, terephthaloyl halide or N,N'-bis(p-aminobenzoyl) ethylene diamine may include N-methylpyrrolidine and N-methylmorpholine present in an amount of not more than 10% by volume based on the volume of the solvent in the polymerization system.

Aromatic tertiary amines, such as pyridine are disclosed in references teaching the preparation of aromatic polyamides. For example, Japanese Pat. Application No. 52-124099 published Oct. 18, 1977 discloses a method of preparing aromatic polyamides using as polymerizing additives only aromatic tertiary amines. U.S. Pat. No. 4,511,623 issued Apr.16, 1985 discloses poly(paraphenylene terephthalamide) short fibers directly prepared during polymerization of the components of the polymer. Only heterocyclic aromatic tertiary amines such as pyridine, are taught as suitable additives to achieve the desired chain growth. Similarly, U.S. Pat. No. 4,579,895 issued Apr.1, 1986 to Cuidard, et al. discloses a process to prepare poly(paraphenylene terephthalamide) using tertiary amines with a pKa equal to, at most, 6.60 such as pyridine. Cuidard et al. discloses that the use of an amine with a higher pKa forms a sparingly soluble complex between the tertiary amine and the terephthaloyl chloride, totally or partially preventing the terephthaloyl chloride from reacting with the para-phenylenediamine.

There is provided by this invention, a process for preparing a poly(paraphenylene terephthalamide) fibrous gel composition comprising the steps of placing substantially stoichiometric amounts of terephthaloyl chloride in reactive contact with para-phenylenediamine in a solution, under agitation, of: (a) at least one amide solvent, preferably N-methylpyrrolidone, in an amount sufficient to produce a final concentration of poly(paraphenylene terephthalamide) in the range from about 3 to about 7 percent by weight of the solvent; (b) at least 1.5 moles of an alkaline earth metal salt per mole of para-phenylenediamine, preferably calcium chloride; (c) and N-methylpyrrolidine present in the range from 1.0 to 2.0 moles per mole of para-phenylenediamine and preferably 1.5 to 1.8 moles per mole of para-phenylenediamine or N-methylpyrrolidine hydrochloride present in the range from 1.5 to 4.0 moles per mole of para-phenylenediamine.

Papers of wholly poly(paraphenylene terephthalamide) are produced by combining, under agitation to yield a slurry, the poly(paraphenylene terephthalamide) fibrous gel composition of this invention; poly(paraphenylene terephthalamide) fiber; and a liquid precipitating medium. The slurry is poured onto a screen to form a sheet, which is washed, pressed and dried.

Surprisingly, it has now been found, by the process of this invention, that the addition of the aliphatic heterocyclic tertiary amine, N-methylpyrrolidine (pKa 10.46) or its hydrochloride to the polymerizing mixture of para-phenylenediamine and terephthaloyl chloride results in a poly(paraphenylene terephthalamide) fibrous gel composition useful in the preparation of poly(paraphenylene terephthalamide) fiber, pulp and binder fiber.

In accordance with this invention, the poly(paraphenylene terephthalamide) fibrous gel composition is prepared by placing substantially stoichiometric amounts of terephthaloyl chloride in reactive contact with para-phenylenediamine in a solution under agitation of at least one amide solvent, an alkaline earth metal salt and N-methylpyrrolidine or N-methylpyrrolidine hydrochloride.

Quantities of terephthaloyl chloride and para-phenylenediamine are employed which result in a final concentration of poly(paraphenylene terephthalamide) in the range from about 3 to about 7% by weight of the amide solvent. Polymer concentrations in excess of 11% by weight of the amide solvent result in the formation of a dry crumb-like product without the fibrous structure necessary for pulp-type uses.

The para-phenylenediamine and the terephthaloyl chloride are reacted in an amide solvent system similar to that disclosed in Kwolek, et al., U.S. Pat. No.3,063,966. The disclosures of U.S. Pat. No. 3,063,966 is hereby incorporated by reference. Suitable amide solvents, or mixtures of such solvents, include N-methylpyrrolidone, tetramethylurea, N,N-dimethylacetamide. In the preferred form of this invention, N-methylpyrrolidone is the amide solvent.

The presence of at least 1.5 moles of an anhydrous alkaline earth metal salt per mole of para-phenylenediamine in the polymerization system is critical for the preparation of the fibrous gel composition of this invention. Salts which can be used include calcium chloride, lithium chloride and the like. Calcium chloride is conveniently the preferred salt. Without the salt, only a low molecular weight crumb-like product is produced.

In accordance with the invention, the aliphatic heterocyclic tertiary amine, N-methylpyrrolidine or N-methylpyrrolidine hydrochloride, is added to the polymerization mixture of N-methylpyrrolidone, alkaline earth metal salt and para-phenylenediamine and results in the formation of the poly(paraphenylene terephthalamide) fibrous gel composition of this invention on the addition of the terephthaloyl chloride. The N-methylpyrrolidine must be present in the range from 1.0 to 2.0 moles per mole of para-phenylenediamine to achieve the desired fibrous gel composition. The preferred amount of N-methylpyrrolidine is 1.5 to 1.8 moles per mole of para-phenylenediamine. The N-methylpyrrolidine hydrochloride may be used in place of the N-methylpyrrolidine to yield the fibrous gel composition of this invention. N-methylpyrrolidine hydrochloride can be added in the range from 1.5 to 4.0 moles per mole of para-phenylenediamine. Amounts of N-methylpyrrolidine or its hydrochloride added to the system below 1.0, or 1.5 if the hydrochloride is used, yield a reaction product that is crumb-like and similar to the reaction product made in the absence of N-methylpyrrolidine. Amounts of N-methylpyrrolidine added to the system beyond 2.0 moles per mole of para-phenylenediamine limits the molecular weight of the polymer and results in a product with limited utility.

The typical fibrous gel composition of this invention contains fibers of poly(paraphenylene terephthalamide) with lengths in the range of 20 to 500 microns. The inherent viscosity of the polymer isolated from the composition is about 4 to about 6, or higher. The composition is gel-like and non-pourable. When stored as long as two years, the polymer inherent viscosity remains in the same range as the inherent viscosity of freshly isolated polymer. In addition, the composition shows substantially no change on storage for periods up to 2 years, shows no tendency to become brittle or to crumb and retains its utility as a source of fiber, pulp or binder fiber.

Once the fibrous gel composition is obtained, the fibers contained therein can be isolated by further dispersing the composition by dilution in a vigorously stirred precipitating medium comprising a non-solvent for the polymer. The precipitating medium is conveniently water, but can include a variety of polar liquids such as alcohols, amines, amides, N-methylpyrrolidone and mixtures thereof. The fibers produced by the process in accordance with the invention are short fibrillated pulp fibers of poly(paraphenylene terephthalamide). The length of the fibers isolated from the composition of this invention are about 400 to 1000 microns. Since the method does not involve spinning from a sulfuric acid solution, the fibers are free of sulfonic acid groups. The fibers that are isolated from the gel-like composition of this invention can be employed in typical poly(paraphenylene terephthalamide) pulp-type end-use applications such as friction products and gaskets.

The fibrous gel composition can also be used directly as a binder in paper. A wholly poly(paraphenylene terephthalamide) paper can be conveniently prepared by diluting the composition with an amide solvent, preferably N-methylpyrrolidone; and then mixing the diluted gel composition with a slurry of poly(paraphenylene terephthalamide) fiber in water or another suitable precipitation medium. Suitable poly(paraphenylene terephthalamide) fibers for use with the composition are fibers of 0.25 inch or less, "floc", such as sold by the E.I. du Pont de Nemours and Co., Wilmington, Delaware under the trade designation "Kevlar" T-679. The mixture is then filtered to form a sheet structure which is washed, pressed and dried to form a paper sheet.

Longer fibers have been produced from the fibrous gel composition of this invention by press extruding the composition at 90° C. through a spinneret into a water quench. Fibers of up to 12 inches in length were obtained. Tensile properties were T/E/Mi (gpd/%/gpd)=1.4/8/15 as dried and 1.9/5/43 after heating to 250° C.

In the following Examples, as well as in other passages of this specification, parts and percentages are by weight unless otherwise indicated. The Examples which follow illustrate the invention employing the following test methods:

Inherent viscosity (IV) is defined by the equation:

IV=1n(ηrel)/c

where c is the concentration (0.5 gram of polymer in 100 ml of solvent) of the polymer solution and η rel (relative viscosity) is the ratio between the flow times of the polymer solution and the solvent as measured at 30° C. in a capillary viscometer. The inherent viscosity values reported and specified herein are determined using concentrated sulfuric acid (96% H2 SO4).

The fiber lengths are measured directly from optical microscopic photographs, corrected for the magnification.

The characteristics referred to herein for the sheet in Example 4 are measured by the following methods. In the description of the methods, ASTM refers to the American Society of Testing Materials and TAPPI refers to the Technical Association of Paper and Pulp Industry. TAPPI--403 and uses a 2×2.5 inch sample. Aluminum foil is used as the burst control.

Tongue tear is measured by ASTM method D 2261 and is based on using a 2.0×2.5 inch sample. A one inch slit is cut lengthwise in each specimen. Nominal gauge length is set at one inch and a crosshead speed of 2.0 inch per minute is used.

Strip tensile strength, modulus strain and toughness are calculated from ASTM D-828 and were run using a 0.5×2 inch gauge length sample.

This example describes the preparation of a 6% composition of poly(paraphenylene terephthalamide) by weight of N-methylpyrrolidone solvent with 2.8 moles of calcium chloride per mole of para-phenylenediamine and 1.46 moles of N-methylpyrrolidine per mole of para-phenylenediamine.

A resin kettle equipped with a basket stirrer, a nitrogen inlet, and an outlet to which drying tubes were attached, was flamed under a stream of nitrogen to remove adsorbed moisture. 15.6 (0.14 moles) grams of anhydrous calcium chloride dried at 400° C. was added to 200 grams of dried distilled N-methylpyrrolidone in the dried kettle. The mixture was stirred and heated to approximately 100° C. until the calcium chloride was substantially dissolved. The solution was then cooled with an external ice bath and 5.4 grams (0.05 moles) para-phenylenediamine was added and stirred until dissolved. 6.2 grams (0.073 moles) N-methylpyrrolidine was added and the mixture was stirred for several seconds. 10.2 grams(0.05 moles) powdered terephthaloyl chloride was added at once, and rinsed in with 20cc of N-methylpyrrolidone. Immediately, the mixture was rapidly stirred. The cooling bath was removed after about one minute. The stirring was continued for an hour and a half. The solution changed to a thick fibrous gel composition and remained that way throughout the reaction. A sample of the gel was removed at the end of the reaction, and after diluting 5x times with N-methylpyrrolidone, was examined under a polarizing microscope and showed clumps of fibers and individual fibers about 60 microns in length. A sample of the gel was thoroughly extracted with water in a blender, filtered and then dried yielding a fibrous pulpy material. The inherent viscosity of a 0.5% solution in 98% sulfuric acid at 30° C. was 5.03 dl/g.

This example was carried out as in Example 1 except that 7.5g (0.088 mole (1.76 moles per mole of para-phenylenediamine)) of N-methylpyrrolidine was used. A thick fibrous gel composition also resulted. A sample of the gel diluted 5x with N-methylpyrrolidone and examined under a polarizing microscope showed clumps of fibers some of which individually exceeded 500 microns in length. Most of the fibers however were 20-60 microns in length. Inherent viscosity of fibrous pulpy material isolated from the gel composition was 4.4 at 0.5% concentration in 98% sulfuric acid.

Example 1 was repeated except that the N-methylpyrrolidine was replaced by 24g of N-methylpyrrolidine hydrochloride (3.9 moles per mole of para-phenylenediamine). Polymerization took place rapidly as evidenced by increase in viscosity. The polymer remained in solution through 30 minutes giving a very viscous golden solution. At 39 minutes the solution became a thick gel that balled up on the stirrer. Polymerization was continued for 1.5 hours. The product was then a thick gel, like that seen in Example 1. Examination under the optical microscope showed the gel to contain an oriented fibrous structure. Dilution of the gel 5x with N-methylpyrrolidone and examination under the optical microscope at 100x magnification revealed a fiber and film structure exceeding 500 microns in length. On aqueous work-up, a very fibrous pulpy material was obtained.

For a control, Example 1 was repeated except that no N-methylpyrrolidine was added. The polymer solution did not remain as a gel but broke up into a damp sawdust-like crumb after stirring for 13 minutes. Stirring however was continued for a total reaction time of 90 minutes. A sample of the polymer mixture was diluted 5x with N-methylpyrrolidone and examined under a polarizing microscope. This showed the polymer as chunks and not as discrete fibers. Inherent viscosity at 0.5% concentration in 98% sulfuric acid was 4.48.

As a comparison, Example 1 was repeated except 14.2g(0.16moles (3.2 moles per mole of para-phenylenediamine)) N-methylpyrrolidine was used. The resultant product was slightly viscous and when precipitated into water in a blender, a powdery, chunky polymer resulted. The inherent viscosity of the isolated polymer was 0.74.

As a comparison, Example 1 was repeated except that the N-methylpyrrolidine was replaced with 6.9g (0.087 moles (1.74 moles per mole of para-phenylenediamine)) of pyridine. A gel structure resulted. A sample of the gel was diluted 5x with N-methylpyrrolidone and on examination under a polarizing microscope showed small clumps of fibers which individually were in the 100 micron range. Polymer inherent viscosity at 0.5% concentration in 98% sulfuric acid was 4.7.

As a comparison, Example 1 was repeated except that the N-methylpyrrolidine was replaced with 7.6g (0.075 mole (1.5 moles per mole of para-phenylenediamine)) triethylamine. the product was a soft yellow semi-dry gel that solidified after standing overnight. A sample of the product was diluted 5x with N-methylpyrrolidone and on examination under a polarizing microscope showed discrete tiny particles generally less than 15 microns in length. These particles showed little tendency to agglomerate or entangle, as required for paper or binder uses. The polymer inherent viscosity was 3.4.

As a comparison, Example 2 was repeated except that the N-methylpyrrolidine was replaced with 8.8g (0.087 moles (1.74 moles per mole of para-phenylenediamine) N-methylmorpholine. Polymerization was rapid on addition of the acid chloride and a dry crumb formed after about 3 minutes. Polymerization was continued for 90 minutes. The dry crumb was examined under a polarizing microscope after dilution 5x with N-methylpyrrolidone and showed polymer chunks interdispersed with small fibers. The inherent viscosity of the isolated polymer was 6.2.

As a comparison, Example 1 was repeated except that the polymer solution concentration was increased 2x i.e. 7.8g calcium chloride and 100g N-methylpyrrolidone were used instead of 15.6 and 200 g, respectively. A viscous solution formed immediately on addition of the acid chloride and a dry crumb formed after about 1 minute. The final product, after water extraction, was a non-fibrous powder. Inherent viscosity at 0.5% in 98% sulfuric acid was 3.6.

As a comparison, Example F was repeated except that 200 g of N-methylpyrrolidone was used. The polymer again precipitated as a crumb. The inherent viscosity of the product was 4.48.

The fibrous gel composition made using N-methylpyrrolidine in the polymerization reaction as described in Example 1 was used as a binder to make a paper with poly(paraphenylene terephthalamide) fibers of 0.25 inch or less (hereinafter "floc") sold by the E.I. du Pont de Nemours and Co., Wilmington, Delaware under the trade designation "Kevlar" T-679. 40g of the gel composition was diluted in a Waring Blendor with 150cc of N-methylpyrrolidone. This yielded a diluted gel. In a separate vessel, 10g of 0.25 inch floc was slurried by hand in 500 cc water to get uniform dispersion. This was then added to the diluted gel and stirred rapidly for 5 minutes in the blender and filtered through a 12×12 inch hand sheet mold using 100 mesh screen. The sheet was washed several times with water. The poly(paraphenylene terephthalamide) paper sheet was removed from the screen without breakage and dried 100° C. under a canvas screen at low pressure. The sheet contained 16-17% binder fiber from the fibrous gel composition. Measured properties on the sheet were: Burst 1.38psi/oz/sq.yd.; Tongue Tear: 0.38 g./g./sq. meter,; Strip Tensile strength 0.34 lb/in/oz/sq.yd., Modulus 14.2 lb/in/oz/sq.yd., Strain 4.9%, Toughness 0.0121b/oz/sq.yd. A paper made in the same way from floc without binder had no integrity and negligible useful properties.

United States Patent O 3,833,652 PREPARATION OF TETRACHLOROTEREPH- THALOYL CHLORIDE FROM CHLORINA- TION OF TEREPHTHALOYL CHLORIDE OR TEREPHTHALIC ACID IN A SOLUTION F CHLOROSULFONIC ACID James O. Knobloch, Naperville, Ill., assignor to Standard Oil Company, Chicago, Ill. No Drawing. Filed Dec. 29, 1972, Ser. No. 319,502 Int. Cl. C07c 63/30 US. Cl. 260544 M 6 Claims ABSTRACT OF THE DISCLOSURE Tetrachloroterephthaloyl chloride is prepared from terephthaloyl chloride or terephthalic acid in a single step by chlorinating terephthaloyl chloride or terephthalic acid in solution in chlorosulfonic acid containing sulfur trioxide and employing an iodine catalyst. The reaction is carried out under mild conditions. The product, tetrachloroterephthaloyl chloride is recoverable by extraction with an inert solvent or by low temperature crystallization. Adhering chlorosulfonic acid is flashed from the recovered solid tetrachloroterephthaloyl chloride which is then so limed or recrystallized. Chlorosulfonic acid is formed as a by-product of the chlorination reaction.

BACKGROUND OF INVENTION The recent growth in the use of flammable materials has increased the incidences of damage and personal injury by fire. Concern for public safety has prompted government agencies to impose stricter flammability standards for those applications where synthetic materials are used. As a result, the use of halogen containing compounds as additives or as an integral part of a finished polymer to impart fire retardant properties to polymeric materials is a rapidly growing industry of great commercial importance. Such compositions can be utilized in those areas of application where fire is likely to occur and to prevent substantial danger or hazard to individuals or property. Examples of such applications are use of polymeric material in household appliances, building materials, the auto industry, the aircraft industry, and others. The seriousness of the potential danger from combustible materials has spurred activity on the part of various government regulatory bodies. Thus, several government agencies are setting flammability standards for autos, aircraft, carpets and other articles made from synthetic polymeric materials. In response to these pressures, makers of synthetic polymeric materials are increasing their efforts to impart flame retardant properties to their products.

An object of this invention is to provide an intermediate compound containing chlorine that may be used to form fire retardant polymeric products. Such products would include synthetic polyesters that may find use in a variety of applications where a high degree of flame retardancy or where self-extinguishing properties are desirable or necessary.

My invention relates to the preparation of tetrachloroterephthaloyl chloride, a valuable intermediate to be used to form flame retardant polymers, wherein terephthaloyl chloride or terephthalic acid is reacted with chlorosulfonic acid containing sulfur trioxide in the presence of an iodine catalyst.

Current methods for preparing tetrachlorinated intermediates, such as dimethyl tetrachloroterephthalate, requires a four step process wherein paraxylene is chlorinated to para-di (trichloromethyl) benzene. The para-di (trichloromethyl benzene, is then reacted in equimolar quantities, with terephthalic acid, forming two moles of terephthaloyl chloride. The resulting terephthaloyl chloice ride is then chlorinated to tetrachloroterephthaloyl chloride by heating the terephthaloyl chloride neat, in the presence of an iron catalyst and introducingchlorine to the mixture. This process requires high temperatures, 175 C. or greater, provides a yield of tetrachloroterephthaloyl chloride of about to and results in the formation of an excessive amount of hexachlorobenzene, an undesirable byproduct because it is diflicult to separate from the tetrachloroterephthaloyl chloride. In addition, the aromatic ring chlorination requires excessive reaction time, a reported time being about 50 hours. Finally the tetrachloroterephthaloyl chloride is reached with methanol to form dimethyl tetrachloroterephthalate.

According to another method tetrachloroterephthalic acid is made by tetrachlorination of paraxylene on the ring and then oxidation of the resulting compound in a sealed tube in the presence of potassium permanganate and nitric acid to form tetrachloroterephthalic acid.

Another method, consisted of chlorinating terephthalic acid in oleum in the presence of an iodine catalyst. However, the reaction temperatures were extremely high, extending to 180 C. and the resulting tetrachloroterephthalic acid product was accompanied by much hexachlorobenzene and abundant quantities of partially chlorinated acid. Further chlorination of the partially chlorinated acid was made diflicult due to the ease with which the terephthal-ic acids decarboxylate at these high temperatures with the formation of hexachlorobenzene.

In a German patent, No. 1,078,563, a process for the preparation of tetrachloroterephthalic acid is disclosed wherein terephthalic acid is chlorinated in oleum held at 40 to C. and 7 atmospheres of pressure in the presence of an iodine catalyst. The process provides a yield of 70 mole percent tetrachloroterephthalic acid product.

In an earlier patent, US. Pat. 1,997,226, certain organic compounds dissolved in oleum were chlorinated by applying chlorine gas to the mixtures under pressure and allowing the reactants to react until the pressure is reduced to one atmosphere.

The use of oleum during the chlorination process, as disclosed in the German and US. patents, produces a chlorinated product in the form of a free acid or, in the case of phthalic anhydride, the easily formed anhydride. The product, tetrachloroterephthalic acid, is unreactive and therefore not a desirable product, under ordinary esterification conditions. The product produced from my novel process, tetrachloroterephthaloyl chloride, is however, a compound that is chemically reactive and therefore a more desirable chlorinated compounds than the free acid.

Tetrachloroterephthaloyl chloride has been produced by certain classical reactions. Thus for example, tetrachloroterephthalic acid may be reacted with phosphorous pentachloride to give a reasonable yield of tetrachloroterephthaloyl chloride. However, phosphorous pentachloride is a commercially expensive reagent and hence this method is not desirable.

Tetrachloroterephthaloyl chloride has been synthesized from terephthaloyl chloride by neat chlorination at elevated temperatures of 175 C. in the presence of an iron catalyst. The product contains from 10 to 20% hexachlorobenzene, an undesirable by-product because it is hard to remove from the diacid chloride. Also, where terephthaloyl chloride is used as the starting material, it must be obtained and purified by commercially expensive routes from terephthalic acid.

My novel process consists of the chlorination of terephthalic acid or terephthaloyl chloride in chlorosulfonic acid in the presence of an iodine catalyst. The reaction temperature is moderate, being in the range of 50 to C. In addition the yields of tetrachloroterephthaloyl chloride is extremely high, yields as high as 81 mole percent having been realized. In addition, the tetrachloroterephthaloyl chloride produced is 97 to 99% pure and contains less than 1% hexachlorobenzene.

My novel process allows terephthalic acid to be used as the starting material directly, producing high yields of tetrachloroterephthaloyl chloride, containing low impurities, in a one step process, and forming little hexachlorobenzene, as an undesirable lay-product.

SUMMARY OF INVENTION My new process consists of chlorinating terephthaiic acid or terephthaloyl chloride in a solution of chlorosulfonic acid containing sulfur trioxide, in the presence of an iodine catalyst, at moderate temperatures in the range of from about 50 to about 120 C., the preferred temperature range being from about 85 to about 95 C. The reaction proceeds rapidly producing a high yield of tetrachloroterephthaloyl chloride over a period of from 1 to 4 hours. Chlorine gas is passed through the solution of oleum held at atmospheric pressure, to produce the diacid chloride as well as additional chlorosulfonic acid, a valuable by-product.

According to my novel process, terephthaloyl chloride may be chlorinated to form tetrachloroterephthaloyl chloride. The reaction occurring can be represented by the following equation:

I2 C1 C1 4012 48 4CISO3H ClSOaH 01 C1 Alternatively, my novel invention provides that terephthalic acid may be chlorinated directly to tetrachloroterephthaloyl chloride. The reaction occurring according to this novel process may be represented by the following equation.

coin co 21 c1 or 4012 4S0. 20130311 2 4 JOzH coc'n This process obviates the expensive isolation and purification of terephthaloyl chloride; the reaction proceeds to form directly the tetrachloroterephthaloyl chloride, in a single step process.

The product of my novel process tetrachloroterephthaloyl chloride, may be recovered from the reaction mixture by either solvent extraction or low temperature precipitation. Chlorosulfonic acid may then be distilled from the mother liquor. If the chlorosulfonic acid is distilled before removing the tetrachloroterephthaloyl chloride, unfavorable equilibria will reduce the tetrachloroterephthaloyl chloride yield by the formation of insoluble polymeric anhydride and free tetrachloroterephthalic acid. The tetrachloroterephthaloyl product may be isolated by flash distilling the solvent and any accompanying chlorosulfonic acid from the solvent extraction step, and then purifying this product by subliming or recrystallizing the residual tetrachloroterephthaloyl chloride.

The product obtained by my novel process melts in the temperature range of 144 to 146 C. (uncorrected). The literature shows that tetrachloroterephthaloyl chloride has a melting point of 147.Sl48 C. This product may be further purified by recrystallization from a suitable solvent such as n-octane or carbon tetrachloride.

My novel process may be further illustrated by the following examples:

4 PREPARATION OF TE'IRACHLOROT-EREPHTHAL- OYL CHLORIDE FROM CHLORINATION OF TEREPHTHALOYL CHLORIDE IN CHLOROSUL- FONIC ACID Example .1

Chlorination without sulfur trioxide in solvent.-Apparatus consisting of a 1 liter, 4-neck creased flask equipped with a fritted glass gas sparger, a thermometer in the liquid phase, a stirrer, a condenser, and a heating mantle (the flask being shielded from the light With an aluminum foil cover) was mounted on a solution balance so that weight uptake could be monitored. Terephthaloyl chloride was freshly distilled into the reaction flask. The chlorosulfonic acid and iodine were then added. The charge was: Freshly distilled terephthaloyl chloride 77.6 g. (0.382 moles), chlorosulfonic acid 699.4 g. (6.00 moles), and resublimed iodine 1.007 g. Chlorine was passed into the light-shielded flask at 64 C., the temperature rose to C. in ten minutes and was manitained in the 9096 /2 C. range for 70 minutes longer. The Weight of the solution increased approximately 30' grams over a period of 60 minutes. The reaction was much less vigorous than when free was charged. Chlorination was stopped when the Weight became constant. The solution was clear. Overnight the cooled solution deposited solids. These were filtered on an M porosity Biichner funnel in a dry box. The filter cake (hereinafter called Insoluble Product A) weighed 67.3 g. (acid wet). The filtrate (730.4 g.) was vacuum distilled to strip off excess chlorosulfonic acid (598.4 g.) at 5-7 mm. Hg and 6074 C. distilling head temperature. The residue, a thick syrupy material, Weighed 80.8 g. (hereinafter called Residue B).

Aliquots of insoluble Product A and Residue B were worked up by several routes. In each case the results are reported on the total run basis, as if all of each product had been handled by each method.

Insoluble Product A and Residue B were reacted with sodium methoxide in absolute methanol thereby converting tetrachloroterephthaloyl chloride to the dimethyl ester. On evaporating the methanol, suspending the alkaline residue in water, filtering and washing until the filtrate was neutral, the dimethyl esters were recovered. The dried esters had the weights and analyses as shown in Table I.

TABLE I [Ester formed by reacting tetrachloruterephthaloyl chloride with sodium methoxide in absolute methanol] Insoluble Source Product A Residue B Weight, 31. 0 38. 6 Melting point, C 156 Gas chromatographic analysis (wt. percent):

Dimethyl terephthalate 0. 70 Dimethyl ehloroterephthalate 0. 84 Dimethyl dichloroterephthalate- 61. 1 Unknown- 4. 66 Dimethyl trichloroterephthalate'. 0. 68 20. 4 Dimet-hyl tetraehloroterephthalate. 94. 7 9. 50

Total. 96.7 97.2

1 85-110 0. (most) to 284 C. (small amount).

The analyses of Table I corresponds to the following mole percent yields based on terephthaloyl chloride charged to chlorination:

Insoluble The yields are based on the assumption that the diacid chlorides were converted to dimethyl esters. Insoluble Product A was also worked up by vacuum distillation of residual chlorosulfonic acid and sublimation of the residue, under vacuum. Sublimate amounted to 35.2 g. The gas chromotographic analysis for tetrachloroterephthaloyl chloride symbolically denoted as (C14TACl) was 89.5 wt. percent. This corresponds to a 24.2 mole percent yield of tetrachloroterephthaloyl chloride in the original filter cake. This yield was confirmed by a gas chromatographic analysis of a carbon tetrachloride solution of Insoluble Product A.

In the next example (Example 2), the solvent used was chlorosulfonic acid. A 4.58 to 1 mole ratio of sulfur trioxide to terephthaloyl chloride was provided by adding liquid sulfur trioxide. Monitored weight uptake during chlorination showed 99% of the weight increase expected from theoretical calculations.

Example 3 illustrates a realized yield of 45.6 mole percent of product is obtainable if all of the chlorosulfonic acid is distilled from the total chlorination effluent and the tetrachloroterephthaloyl chloride product is sublimed.

When the total chlorination efiluent from Example 2 was extracted with carbon tetrachloride, and the extracts distilled under vacuum to remove the carbon tetrachlo ride and any residual chlorosulfonic acid, the product, after sublimation, represents a 79.5 mole percent yield of tetrachloroterephthaloyl chloride. This is illustrated in Example 4.

Example 5 illustrates the same results where carbon disulfide is used as the extracting solvent. Here an 81.0 mole percent yield of tetrachloroterephthaloyl chloride is realized.

Example 2 Chlorination was S0 in solvent-The apparatus of Example 1 was employed. The charge was 72.2 grams of (.356 moles) freshly distilled terephthaloyl chloride, 664.3 grams of chlorsulfonic acid, 130.7 grams of liquid sulfur trioxide (1.63 moles) and 1.005 grams of iodine. Chlorine was introduced at 35 C. Weight intake indicating chlorination began at about 75 C. The weight of the solution increased approximately 98 grams during a period of about 70 minutes. The temperature inside the flask was maintained in the 9098 C. range by intermittent use of an ice bath. After 82 minutes of chlorination the reaction was stopped. The clear effluent (weighing 9525 grams) was divided into four weight aliquots for separate study.

Example 3 A 217.0 gram aliquot of the chlorosulfonic acid solution from Example 2 was vacuum distilled using an 8 inch knockback tube and a vacuum jacketed distillation head. Under 2 /z3 mm. Hg absolute pressure distillate was taken over (at a 54 /z-59 /2" C. head temperature) until the final bottoms temperature reached 81 C. Distillate of 145.6 grams was collected. Additional overhead product was collected in the vacuum trap but was not measured. The bottom product weighed 28.9 grams. An analysis of the bottoms product by gas chromatography employing an internal standard revealed it to consist of 41.6 wt. percent of tetrachloroterephthaloyl chloride and .416 wt. percent hexachlorobenzene. This is equivalent to a 43.4 mole percent yield of tetrachloroterephthaloyl chloride on a total run basis.

A 5.1 gram sample of the bottoms was sublimed using a Kontes 85550 Sublimator at less than 1 mm. Hg absolute pressure and an oil bath temperature of 130-236' /2 C. (Steam was passed through the sublimators condenser until the bath temperature reached 130 C., to drive over any chlorosulfonic acid present in the charge; cooling water was then turned on in place of steam.) The cold receiver collected 0.4 grams. The sublimate amounted to 2.5 grams and the bottoms product was 2.0 grams. Gas chromatographic analysis of the bottoms product showed only trace amounts of hexachlorobenzene and tetrachloroterephthaloyl chloride. The subliminate consisted of 89.4 wt. percent tetrachloroterephthaloyl chloride and 1.53 wt. percent hexachlorobenzene. This is equivalent to a 45.6

mole percent yield of tetrachloroterephthaloyl chloride on a total run basis.

Example 4 A 223.4 gram aliquot of the chlorosulfonic acid solution from Example 2 was extracted successively with dry carbon tetrachloride in 500 ml. separatory funnels, first with 250 cc. of carbon tetrachloride and then followed by three successive extractions with 170 cc. of carbon tetrachloride each. The final solution of chlorosulfonic acid weighed 205.8 grams. The four extracts weighed: 241.3 grams, 254.1 grams, 314.2 grams and 300.7 grams respectively.

The chlorosulfonic acid solution was then stripped of the carbon tetrachloride in an oil bath held at 98 to 106 C. by distillation. The distillate held at 77 C. consisted of 63.9 grams of amber liquid.

The bottom was held at l06 C. (oil bath temp.) in an attempt to obtain equilibration. After cooling 132.6 grams of the remaining liquid solution was further extracted in two 500 ml. separatory funnels, first with 150 cc. of carbon tetrachloride and then with 110 cc. of carbon tetrachloride leaving behind 154.8 grams of chlorosulfonic acid. The first extract weighed 191.6 grams and the second extract weighed 200.7 grams.

All six extracts were analyzed by gas chromotography. The results are shown in Table II. The 20.30 grams of tetrachloroterephthaloyl chloride found in the extracts represented a 71.4 mole percent yield based on terephthaloyl chloride charged to the reaction. The tetrachloroterephthaloyl chloride was recovered from the extract by evaporation of the carbon tetrachloride solvent under vacuum.

The residual chlorosulfonic acid was removed by vacuum distillation and then the tetrachloroterephthaloyl chloride was purified by sublimation. The sublimate consisted of 22.62 grams of pure tetrachloroterephthaloyl chloride representing a 79.5 mole percent yield.

TABLE II [Extraction of ClSOaH solution with OCH and recovery of Cl4TACl] Wt. of CMTACI A 278.9 gram aliquot of the chlorosulfonic acid solution from Example 2 was extracted successively with dry carbon disulfied in a 500 cc. separatory funnel. First 225 cc. of carbon disulfide then followed by three successive extractions with 200 cc. of carbon disulfide each. The final solution of chlorosulfonic acid weighed 255.0 grams. The four extracts weighed 256.0 grams, 263 grams, 258.5 grams and 252.4, grams, respectively.

The four extracts were hazy. Upon allowing them to stand overnight they became clear and a small yellow underlayer separated. A gas chromotograph analysis was performed on the clear upper layer. Both the upper layer and the smaller heavy under layer were combined and evaporated under vacuum to remove solvent. Extract and sublimate analyses are shown in Table IH. The 22.7 grams of tetrachloroterephthaloyl chloride recovered in the extract represented a 63.8 mole percent yield of tetrachloroterephthaloyl chloride based on the terephthaloyl chloride charged to chlorination. The 28.8 grams of pure tetrachloroterephthaloyl chloride found in the sublimate represented an 81.0 mole percent yield on the same basis.

Recovery of tetrachloroterephthaloyl chloride by cooling chlorinated solution.-A 231.4 g. aliquot from another chlorination was cooled in a special stirred 500 ml. cylindrical vessel having a fritted glass disc as a bottom, a draw-off line beneath it and protected from outside moisture. The vessel was then immersed in a Dewar flask. A small flow of dry nitrogen was passed upward through the M porosity filter. The aliquot was cooled to 4l C. (bath temperature) over a one-hour period with stirring. After holding at 40 to 41 C. for 75 minutes, the charge was pressure filtered into a suction flask using 3 p.s.i.g. nitgoen pressure on the vessel side and house vacuum on the receiver. Filtration was slow and in the to 20 hours required the batch temperature rose from 4l to -l6 C.

To remove the filter cake from the vessel a total of 600 ml. of carbon tetrachloride was used as a transfer solvent not as an extractive solvent. The recovered filter cake was completely dissolved in a 957.3 grams solution of carbon tetrachloride. A 195.9 gram aliquot was vacuum evaporated to remove the solvent and left a 11.4 gram solvent moist residue. Upon sublimation, 5.5 grams of chlorosulfonic acid was collected in the cold trap, 0.36 grams of solids remained as bottoms and 4.0 grams of sublimate was obtained. Analysis revealed the sublimate to be 90.8 wt. percent tetrachloroterephthaloyl chloride and 3.38% hexachlorobenzene. This represented a 62.5 mole percent yield of tetrachloroterephthaloyl chloride based on the terephthaloyl chloride charged to the chlorosulfonic acid solution for chlorination.

Example 7 The apparatus consisted of a l-liter, 4-neck round bottomed, creased flask equipped with a fritted glass sparger, a stirrer, a reflux condenser, and a thermometer immersed in the liquid phase. The chlorine inlet line to the spargcr was a Tygon tube which was shielded from light by an outer black rubber hose. To observe the gas flow the vent was passed from the reflux condenser to a Gilman trap containing concentrated sulfuric acid. The reaction flask was sealed from the light by aluminum foil and was heated by a mantle. The chlorination apparatus rested on a solution balance so that the increase in weight could be suitably monitored. The heating mantle was lowered on a jack and an ice bath was raised to control the temperature during the exothermic part of the reaction.

A 59.8 gram (.360 mole) charge of terephthalic acid was dissolved in 666.2 grams of chlorosulfonic acid. The solution was clear and was held at 48-51 C. for three hours. The next day 129.3 grams (1.62 moles) of sulfur trioxide (Sultan) was added followed by 1.13 grams of iodine. Addition of chlorine was started at 30 C. and was continued for 100 minutes. The temperature of the solution rose quickly after about 10 minutes to 85-95 C. and remained in this range. The solution began to gain weight minutes later and continued for the remainder of the 100 minutes, slowing to a negligible amount after 90 minutes. The apparent weight increase was approximately 9l grams. After the weight increases became negligible, indicating that the reaction was complete, the flask contents were divided among four separate tarred flasks for further processing.

One aliquot (241:9 grams) was extracted successively with one 300 and five 200 ml. portions of dry carbon tetrachloride. The combined extracts were evaporated under vacuum on a rotating flask evaporator to a maximum fina'l) temperature of 25 C. No heat was applied during evaporation. The residue contained both the desired tetrachloroterephthaloyl chloride and chlorosulfonic acid that had been dissolved in the carbon tetrachlorde. The chlorosulfonic acid was taken overhead under a vacuum of 11 to 2 mm. Hg in an oil bath at a temperature of 47 /z99 C. leaving a residue of 23.9 g. A 5.0 gram sample of this residue was sublimed. The sublimation was carried out in a Kontes Sublimator (Catalog No. 85550) to which a ball joint and glass transfer line were added to make the system all glass through the cold receiver. The sublimation was done at 0.5 mm. Hg. Steam was passed through the condenser so that any residual solvent or chlorosulfonic acid would be carried over to the cold receiver. When solids began to appear on the walls (usually at to C. bath temperature) the steam was turned oflt and cooling water was passed through the condenser jacket. Tetrachloroterephthaloyl chloride sublimes readily and completely at a bath temperature of C. The 30 mm. (inside diameter) by 75 mm. high pot can be charged with a maximum of about 12 grams of tetrachloroterephthaloyl chloride. Sublimate adheres well to the condenser walls and pot can be removed (gently) without having any sublimate fall back into the pot. The following results were observed:

Anal. (wt. percent) Hexaehlo Wt. g. ChTACl benzene Cold trap contents 0.1 (probably ClSOsH) ..c Sublimate:

Top of deposit 0.1 (trace of yellow) 51. 1 8. 1

Main deposit 4.5 (dead white) 98. 0 48 The main sublimate had a melting point of 144146 C.

To see if the chlorosulfonic acid solution that had been extracted contained any more tetrachloroterephthaloyl chloride it was further extracted with two 250 ml. portions of carbon tetrachloride. Each extract was analyzed in the same manner as the sublimate.

Weight of Cl TA Cl found by analysis, g.

Seventh extract 1.03 Eighth extract .76

Complete recovery of product had still not been realized. However, the product seen represents mole percent yields of tetrachloroterephthaloyl chloride on terephthalic acid charged as follows:

Mole percent 1st six extracts (main sublimate) 68.2 Top portion of sublimate .83 Seventh extraction 3.3 Eighth extraction 2.4

Total 74.7

With terephthaloyl chloride as the starting material there is no free sulfuric acid in the chlorosulfonic acid solvent and carbon disulfide is as efiicient as carbon tetrachloride in recovering the product. Other suitable solvents include the fully halogenated alkanes, such as 1,2,2-t1'ichloro-l,1,2-trifluoroethane which is even more stable than CCl and is a good solvent for the diacid chloride.

What I claim is:

l. A process for the preparation of tetrachloroterephthaloyl chloride by chlorinating terephthaloyl chloride in a solution of chlorosulfonic acid in the presence of an iodine catalyst in the absence of light at a temperature in the range of 50-1l0 C., by reacting with chlorine and recovering the tetrachloroterephthaloyl chloride.

2. A process as set forth in claim 1 wherein sulfur trioxide is charged to the solution.

3. A process as set forth in claim 1 where the preferred temperature range of the reaction is 8595 C.

4. A process for the preparation of tetrachloroterephthaloyl chloride by chlorination of terephthalic acid in a solution of chlorosulfonic acid in the presence of iodine as a catalyst where the reaction temperature may vary from 45-100" C. under a pressure of one atmosphere or greater, and recovering the tetrachloroterephthaloyl chloride.

5. A process for the preparation of tetrachloroterephthaloyl chloride as set forth in claim 4 wherein sulfur trioxide is charged to the reaction mixture.

6. A process for the preparation of tetrachloroterephthaloyl chloride as set forth in claim 4 wherein the reaction temperature is 85-95 C.

References Cited Yakobsen: Zh Obshch. Khim., 34(9), 2953-8 (1964). Profit: Arch. Pharm., 299(7), 577-88 (1966).

LORRAINE A. WEINBERGER, Primary Examiner R. D. KELLY, Assistant Examiner