Org. Synth. 1925, 4, 73
DOI: 10.15227/orgsyn.004.0073
[Benzoic acid, o-(p-toluyl)-]
Submitted by L. F. Fieser
Checked by Roger Adams and R. L. Shriner.
1. Procedure
A 2-l. round-bottomed flask is clamped to a ring stand and equipped with a rubber stopper carrying a glass stirrer with mercury seal, and a reflux condenser connected with a trap (Fig. 7 on p. 97) for removing the evolved hydrogen chloride.
One hundred grams (0.68 mole) of phthalic anhydride and 400 g. (462 cc., 4.35 moles) of toluene are placed in the flask, which is cooled in an ice bath while 200 g. (1.5 moles) of anhydrous aluminum chloride (Note 1) is being ground to a fine powder. The chloride is now added all at once (Note 2). Stirring is commenced at once, and the ice bath is removed. The mixture warms up considerably and becomes olive-green in color. When the evolution of hydrogen chloride begins to slacken (ten minutes) a water bath is put into place and heated to 90° in the course of forty-five minutes. The temperature of the bath is kept at 90° and vigorous stirring continued for two and one-half hours. At this point, the evolution of hydrogen chloride will have practically ceased and the reaction will have been completed. The hot water in the bath is replaced first by cold water and then by ice, while stirring is continued.
As soon as the flask is well cooled, it is disconnected and carried to the hood, and ice is slowly added, with shaking, until the dark mass is completely decomposed and the flask is about one-half filled with the mixture. After 150 cc. of crude concentrated hydrochloric acid has been added, the mass coagulates and the solution clears; the flask is then heated on the steam bath while preparations are being made for steam distillation.
This operation, which removes the excess of toluene, may be carried out in the same flask and loss by transfer thus avoided (Note 3). The aqueous solution of aluminum chloride and hydrochloric acid, after thorough cooling, is decanted through a suction filter, the residue washed with a little cold water, and that collected on the filter returned to the flask. This residue consists almost solely of p-toluyl-o-benzoic acid, partly crystalline, partly in oily lumps.
A previously prepared and heated solution of 50 g. of sodium carbonate in 1 l. of water is added, and steam is passed in to provide heat and agitation. With a rapid stream, the acid will go into solution in about ten minutes, leaving a small amount of brown, tarry material and a little alumina undissolved (Note 4). The solution is filtered while hot and transferred to a 2-l. beaker, and the acid precipitated by the addition of 65 cc. of concentrated hydrochloric acid. The acid separates as an oil, which soon crystallizes. The solution is cooled in ice and the acid filtered and washed.
The air-dried product is pure white and weighs 170 g. (Note 5). After drying at 100°, the anhydrous acid melts at 138–139° and weighs 157 g. (96 per cent of the theoretical amount). Air-dried material is suitable for the condensation to β-methylanthraquinone, p. 353. It may be recrystallized from toluene.
2. Notes
1. Although statements are found in the literature that quantitive yields may be obtained with smaller quantities of aluminum chloride, the ratio 1C6H4(CO)2O:2AlCl3 is essential.
2. Leakage of hydrogen chloride at any of the connections may be stopped with paraffin.
3. The steam distillation requires about fifteen minutes, and about 340–380 cc. of toluene is recovered.
4. If, in extracting the acid with sodium carbonate, more than 2–3 g. of material remains undissolved, the residue is treated with dilute hydrochloric acid to remove alumina, washed, and again extracted with a little carbonate solution. This extract is neutralized separately since some tar may separate with the p-toluyl-o-benzoic acid. In this event, it is filtered and extracted with cold carbonate solution, in which the tar is completely insoluble.
5. According to Limpricht,1 the acid may crystallize either in hydrated or in the anhydrous condition, but the transition temperature is not stated. The loss of water upon drying at 100° shows the compound obtained in this experiment to be the monohydrate.
3. Discussion
p-Toluyl-o-benzoic acid can be prepared by the action of aluminum chloride on phthalic anhydride and toluene.2
This preparation is referenced from:

References and Notes
  1. Limpricht, Ann. 299, 300 (1898).
  2. Friedel and Crafts, Bull. soc. chim. (2) 35, 505 (1881), Ann. chim. phys. (6) 14, 447 (1888); Limpricht, Ann. 299, 300 (1898); Heller and Schülke, Ber. 41, 3632 (1908); McMullen, J. Am. Chem. Soc. 43, 1965 (1921).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

p-Toluyl-o-benzoic acid

hydrogen chloride,
hydrochloric acid (7647-01-0)

sodium carbonate (497-19-8)

phthalic anhydride (85-44-9)

aluminum chloride (3495-54-3)

toluene (108-88-3)

β-Methylanthraquinone (84-54-8)

Benzoic acid, o-(p-toluyl)- (7148-03-0)