Patented Mar. 27, 1951 2,546,545

UNITED STATES PATENT OFFICE 2,546,545 PROCESS FOR THE SEPARASON OF SOMERC CLOROSENZOIC ACDS Jonas Kamiet, New York, N. Y., assignor to Ten aessee Products & Chemical Corporation, Nash ville, Tenn., a corporation of Tennessee No Drawing. Application December 22, 1950, Serial No. 202,397 Cain. (C. 260-525) 2 The present invention relates to a proceSS for virtue of their varying reactivities with annonia, the separation of isomeric chlorobenzoic acids and alkylamines (Mills, U. S. Patent 1,882,335 of and, more particularly, it relates to a simplified October 1, 1932). However, these methods of procedure for the separation of ortho-chloro Separation have proven to be suitable for benzoic acid and para-chicrobenzoic acid fron technical purposes. mixtures of these two isoners. It has for itS It is Well known that tolene can be chlorinated purpose to provide a simple and inexpensive in the ring in the presence of substitution cata neans for the Separation of Ortho-chlorobenzoic lysts, to yield a mixture of 55%-60% of ortho acid and para-chlorobenzoic acid so that these chlorotoluene and 40%-45% of para-chlorotol two valuable organic intermediates can be made O Ulene. This mixture of chlorototlene (freed of from cheap and readily available raw materials the catalyst by distillation) can then be chlorin (e.g., and chlorine) without the necessity ated in the Side-chain, in the scrupulous absence of submitting any of the intermediates of said of substitution catalysts and listially with the proceSS to an expensive and tedious separation catalytic assistance of ultraViolet irradiation, to by means of fractional distiliations or an equally 5 yield a mixture of ortho-chlorobenzotrichloride expensive and involved separation by chemical and para-chlorobenzotrichloride. The latter reactions. mixture can then be hydrolyzed (in one step or in Ortho- and para-chlorobenzoic acids are now two steps) to the corresponding mixture of o made by the Sequence of staps involved in: and p-chlorobenzoylchlorides and finally to a (d) Chlorinating toluene in the ring to yield a mixture of 55%-60% of orchiCrobenzoic acid and mixture of Ortho- and para-chlorotoluenes, 40%-45% of p-chlorobenzoic acid. (b) Separating the Ortho-chlorotoluene (B, Pt. The basis of the present invention is the dis 158.5° C. G. 760 mm.) and the para-chloroto covery that a good separation of o-chlorobenzoic uene (8. Pt. 162.0°-162.2° C. G.) 760 mm.) by frac acid and p-chlorobenzoic acid can be effected by tional distillation or by cheinical ineans, and 25 fractional Solution of the mixture of these isoners (C) Oxidizing each isomer individually to the in a selected from the group consisting corresponding chlorobenzoic acid by any coin of O-chlorotoluene, p-chlorotoluene and prefer Wenient means. Thus, p-chlorotoluene can be ably mixtures theireof, in which the o-chloroben oxidized to p-chlorobenzoic acid by reaction with Zoic acid is markedly more soluble than the SOdiin bichronate and sulfuric acid; o-chloro-. p-chlorobenzoic acid. An important features of toluene can be chlorinated in the side chain and this invention is its economy as well as efficiency the resultant o-chlorohenzotrichloride hydrolyzed in that the Solvent mixture of O-chlorotoluene to O-chlorobenzoic acid, etcetera. and p-chlorotoluene is recovered and oxidized to The separation of the issoneric O- and p-chloro. forts Q-chlorobeilzoic and p-chlorobenzoic acids. by fractional distillation is quite difficut, I have found that a good separation of o however, inaSnatch as they differ in boiling points chlorobenzoic acid and p-chlorohenzoic acid can by Only 3.5° C. It has also been proposed to be effected by agitating a mixture. Of these iso Alfonate the mixture of o- and p-chlorotoluene, inners With a quantity of the solvent sufficient to Whereby the ortho isoner is preferentially sufo dissolve all of the G-chlorobenzoic acid and only nated, separating the ortho-chlorotoluene, para a ninimum amount of the p-chlorobenzoic acid, Sulfonic acid from the unreacted para-chloro 40 preferably at a temperature above 20° C., and toluene, and regenerating the ortho-chloroto thereafter separating the solution of o-chloro uene from the former compound by distillation benzoic acid from the insoluble precipitate of With Superheated steain (Wahl, German Patent, p-chlorobenzoic acid (as e. g., hy filtration). On 376,634; Seelig, Annalen 237, 152 (1887)). How. CC0 ling the Solution, ?y-chlorobenzoic acid pre ever, this conplicated chemical separation is 45 cipitates out and may be recovered by filtration. uSulally Corsidered in practical aid has fold to As a Solvent, the cheapest, and most readily avail Widespread acceptance. It has also been pro able for use is the unseparated mixture of ortho i}osed to Separate the isomeric ortho- and para and para-chlorotoluenes obtained by the ring chlorobenzoic acids by virtue of their different chlorination of toluene and either pure or as Solubilities in various , such as Water, irecovered in the separation treatiment. To de , heptane, etc., by virtue of the different termine the composition of this mixture, the Water Solubilities of their calcium salts, and by crystallization point of the mixed chlorotoluenes

2,546,545 3 4. is determined and the composition interpolated para-chlorobenzoic acids heretofore obtained by from the following table: other and more complicated procedures. The composition of mixtures of Ortho- and para-chlorobenzoic acids may be determined by (Per Cent, Per Cent- Crystalliza melting the mixture and noting the tempera Para- Ortillo ture at Which the initial crystallization takes toleneCE. tolueneiii. Ition. Egint, place. The following table can be used for in terpolating the initial crystallization point as a 100 0. 7.3 90 O 2.0 function of the composition of the mixture: 80 20 -3.5 0 70 30 -9.5 60 40 -16.2 Per Celt Per Cent 50 50 -24. 4. Para- Ortho- Initial Crys 40 60 -34. O Chloro- Chloro- tallization 30 70 - 46.5 benzoic benzoic Point, C. 20 80 -49.0 Acid Acid O 90 -43.0 O 100 -37.0 5 ----- 0.0 100.0 142.0 10.0 90.0 135.6 4.8 85.2 1132. O The following example is given to define and 20. O 80.0 42.1 22.0 78.0 152.6 illustrate the present invention, but in no Way 25.0 75.0 160, to limit, it to reagents, proportions or conditions 20 28.0 72.0 164. 4 30.0 70.0 167.5 described therein. Obvious modifications and 35, 0. 65. O 175.0 in provements will occur to any person skilled 40.0 60.0 82.5 45. O 55.0 191.0 in the art. 50.0 50. 196.8 Eacample 60.0 40.0 203.7 70. O 30.0 23.2 A mixture of 55%-60% o-chlorobenzoic acid 25 80.0 20.0 228.4 and 40%-45% p-chlorobenzoic acid (obtained by 90.0 0.0 235.8 the ring chlorination of toluene to O- aid p 100.0 0.0 243.0 chlorotoluene, the further Side-chain chlorination of the latter to o- and p-chlorobenzotrichloride 1 Eutectic. and the hydrolysis of the latter to a nixture of 30 The eutectic point is 132.0° C., corresponding o- and p-chlorobenzoic acids) is ground to 100 to a mixture of 14.8% of para-chlorobenzoic acid mesh fineneSS. and 85.2% of ortho-chlorobenzoic acid. It will To 500 parts by weight of the ground, mixed be noted that compositions containing from chlorobenzoic acids, add 600 parts by Weight of 100% ortho/0% para, to 85.2% ortho/14.8% para nixed chlorotoluenes (55%-60% o- and 40%- 35 Solidify from 142.0° C. to 132.0° C. Whereas com 45% p-) and heat, with agitation, for two hours, positions containing from 85.2% ortho/14.8% at 100-105° C. Filter the mixture rapidly. Care para, to 80.2% ortho/19.8% para, Solidify from hist be taken to keep the receiver warm (over 32.0° C. to 142.0° C. 33 C.) to avoid premature precipitation of the Thus, if a Sample of unknown composition o-chlorobenzoic acid. 40 meits between 132.0° C. and 142.0° C. it is ad The residue on the filter is now added to an Visable to dissolve a Small amount of pure para other 600 parts by weight of mixed chlorotolu chlorobenzoic acid in a melt of the unknoWn enes and heated, with agitation, at 100°-105 C. composition, and determine the initial Solidifica for Oile hour. The mixture is again filtered rap tion point of the mixture. If the initial Solidi idly. The warn filtrate is combined with the 45 fication point of the mixture is lower than that fit frate from the first extraction, which has been of the original sample, the sample contains be kept warm in the interval. tween 100.0% ortho/0.0% para, and 85.2% On slowly cooling the mixed filtrates to 70 ortho/14.8% para, chlorobenzoic acids. If the C., a Sinail precipitate of mixed chlorobenzoic initial solidification point is higher than that of acids settles out. This is filtered off rapidly and 50 the original sample, the sample contains between added to the next batch of mixed chlorobenzoic 85.2% ortho-/14.8% para, and 80.2% ortho/19.8% acids for Separation. para, chlorobenzoic acids. The filtrate is then cooled slowly, to roorin tem This application is a continuation-in-part of perature, and the copious precipitate of o-chloro 55 my application Serial No. 84,736, filed March 31, benzoic acid which separates out is filtered off 949. and dried in a hot air oven at a temperature not I claim: in excess of iC C. The filtrate which is a Sol A process for the preparation of o-chloro vent mixture of the mixed toluenes, namely o benzoic acid and insoluble p-chlorobenzoic acid and p-chlorotoluenes, with traces of p-chloro 60 which comprises agitating a mixture of the acids benzoic acid and O-chlorobenzoic acid is returned with a solvent mixture of o-chlorotoluene and to the process for oxidation to o- and p-chloro p-chlorotoluene, selectively dissolving Substan benzoic acids or may be reused as the separa tially all of said o-chlorobenzoic acid, separating tion solvent. The process of this invention is, the resultant Solution of o-chlorobenzoic acid therefoie, highly efficient and economical. 65 from the insolubie p-chlorobenzoic acid, recover With credit for recovered mixed chlorobenzoic ing the o-chlorobenzoic acid from said Solution, acids, there is thus obtained from 500 parts of and returning the solvent mixture to the process ri)ixed chlorobenzoic acid, 292 parts of o-chloro for oxidation to o-chlorobenzoic acid and para benzoic acid melting at 137°-139° C. ( When pure-142° C.), and 188 parts of p chlorobenzoic acid. chlorobenzoic acid melting at 238 C-241 C. 70 JONAS KAMET. (neiting point when pure-243. C.). These coi respond in purity to the technical ortho- and . No references cited.