4- Toluic acid

Reaction.—p-Toluic Acid.—Boil up 10 grams tolylcyainidc with a mixture of 30 c.c. cone, sulphuric acid and 20 c.c. water, in i round flask with upright condenser until colourless crystals of toluic acid appear in the condenser tube (about half an hour). On cooling, the acid crystallises out, and is separated by filtration, washed with water, and recrystallised from liot water ni. p. i 79 . 

Preparation of p-Toluic Acid from the Nitrile (SECTION 551).—Hydrolyze the tolunitrile obtained in experiment 189, page 159, by heating it with sulphuric acid as follows For each gram of nitrile use 6 grams of concentrated sulphuric acid and 2 cc. of water. Heat on a sand-bath the mixture contained in a flask provided with a wide-bore reflux condenser, until the acid sublimes freely into the condenser. Cool, dilute with about 3 volumes of water, filter off the crystals, and wash them several times with cold water. Dissolve the toluic acid in hot alcohol, 

In a 5-I. flask, equipped with a mechanical stirrer, a reflux condenser and a separatory funnel, is placed 3 kg. of 75 per cent sulfuric acid (sp. gr. 1.67). The solution is heated to about 150°, the stirrer is started and r kg. (8.55 moles) of o-tolunitrile (Org. Syn. 4, 69) is added during the course of two hours. The temperature is maintained at 150-160° and the mixture is stirred for two hours after the addition of the nitrile is complete. The temperature is then raised to 190° and stirring is continued for another hour. Usually some crystalline material appears in the condenser at this stage. The reaction mixture is cooled, poured into ice water and filtered. The crude material is dissolved in an excess of 10 per cent sodium hydroxide solution (Note 1), filtered hot and the filtrate acidified with dilute sulfuric acid. The product is collected on a Buchner funnel, dried and recrystallized from about 3 1. of benzene (Note 2). The yield is 930-1030 g. (80-89 cent °f the theoretical amount) of a product which melts at 102-103° (Note 3). 

Any insoluble material which separates on conversion into the sodium salt is toluamide, which may be isolated. The appearance of this substance indicates too short a period of heating or too low a temperature. 

The reaction can be stopped readily so that a considerable quantity of the amide is produced. The crude amide is purified by recrystallization from water to give a product melting at r39 I4°°- 

An additional amount of pure o-toluic acid may be obtained by distilling the benzene mother liquor to a small volume and allowing to cool. 

p-Toluic acid (m.p. 178°) may be obtained from / -tolu-nitrile by the same process and in the same yields. This acid is less soluble in benzene and about 9 1. is needed for recrystallization. 

The best preparative method of obtaining terephthalic acid is to oxidise the sodium salt of p-toluic acid with permanganate at the temperature of the water bath. In the same way toluene can be converted into benzoic acid, and an important technical example of this reaction is the oxidation, of o-tolylsulphonamide to saccharin. 

By permanganate oxidation long side chains are broken down to carboxyl groups attached to the ring. The biological degradation of oj-aryl-fatty acids proceeds in accordance with the fi-oxidation rule (F. Knoop). 

Sandmeyer s Reaction.—The ready formation of iodobenzene in the above method is due to the spontaneous decomposition of the diazonium iodide into iodobenzene and nitrogen 

In the bromide and chloride, however, after the nitrogen has been eliminated, the halogen wanders only to a slight extent to the gap so left, and the formation of phenol predominates. 

In 1884, Sandmeyer, however, made the important discovery that in the presence of the corresponding cuprous salt chlorine and bromine are also directed to the nucleus. This catalytic action has not yet been explained. Perhaps a double salt is formed, or else a complex salt in which the halogen is more firmly bound than in the simple halide. According to Gattermann, the cuprous salt may be replaced by copper powder. In general, the decomposition of labile diazo-compounds, by elimination of elementary nitrogen, is accelerated by copper. 

Prepare o-tolunitrile, b.p. 94-96°/20 mm., from o-toluidine following the method given in Section IV,66 under -Toluidine. Also prepare 600 g. of 75 per cent, sulphuric acid by adding 450 g, (245 ml.) of con- 

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The crude phthalic anhydride is heated and held at 260 C to allow some byproduct reactions to go to completion. Purification is by continuous distillation in two columns. In the first column, maleic anhydride and benzoic and toluic acids are removed overhead. In the second column, pure phthalic anhydride is removed overhead. High boiling residues are removed from the bottom of the second column. 

Hydrolysis of />-Tolunitrile. As in the case of benzonitrile, alkaline h> drolysis is preferable to hydrolysis by 70% sulphuric acid. Boil a mixture of 5 g. of p-tolunitrile, 75 ml. of 10% aqueous sodium hydroxide solution and 15 ml. of ethanol under a reflux water-condenser. The ethanol is added partly to increase the speed of the hydrolysis, but in particular to prevent the nitrile (which volatilises in the steam) from actually crystallising in the condenser. The solution becomes clear after about i hour s heating, but the boiling should be continued for a total period of 1-5 hours to ensure complete hydrolysis. Then precipitate and isolate the p-toluic acid, CH3CgH4COOH, in precisely the same way as the benzoic acid in the above hydrolysis of benzonitrile. Yield 5 5 g. (almost theoretical). The p-toluic acid has m.p. 178°, and may be recrystallised from a mixture of equal volumes of water and rectified spirit. 

The methyl group in p-toluic acid may be oxidised to a -COOH group forming p-phthalic (or tere-phthalic) acid, C H4(C.OOH), but the oxidation is usually slow. 

An additional useful test is to distil the acid or its sodium salt with soda lime. Heat 0.5 g. of the acid or its sodium salt with 0 2 g. of soda lime in an ignition tube to make certain that there is no explosion. Then grind together 0-5 g. of the acid with 3 g. of soda hme, place the mixture in a Pyrex test-tube and cover it with an equal bulk of soda hme. Fit a wide dehvery tube dipping into an empty test-tube. Clamp the tube near the mouth. Heat the soda lime first and then the mixture gradually to a dull-red heat. Examine the product this may consist of aromatic hydrocarbons or derivatives, e.g., phenol from sahcyUc acid, anisole from anisic acid, toluene from toluic acid, etc. 

For initial experience in the uae of Uthium, the preparation of either p-toluic acid or of a-napbtboic acid mcay be undertaken. For the former, p-bromotoluene is converted into the lithium derivative and the latter carbonated with soUd carbon dioxide ... 

C bol the solution of re-butyl-hthium to — 35° in a Dry Ice - acetone bath and add, whilst stirring vigorously, a solution of 48 g. of ni-chlorobromo-benzene (Section IV,62) in 75 ml. of anhydrous ether. Stir for 8-10 minutes and pour the mixture with stirring on to a large excess of sohd carbon dioxide in the form of a Dry Ice - ether slush contained in a -htre beaker. Isolate the acid as detailed above for p-Toluic acid and recrystal-lise it from hot water. The yield of ni-chlorobenzoic acid, m.p. 150-151°, is 27 g. 

The formation of an organosodium compound (p-tolyl-sodium) is well illustrated by the interaction of sodium sand or wire with p-chlorotoluene in light petroleum (b.p. 40-60°) at about 25°, for when the reaction mixture is added to excess of solid carbon dioxide pure/ -toluic acid is obtained directly in a yield exceeding 70 per cent. ... 

Ethylbenzene. Prepare a suspension of phenyl-sodium from 23 g. of sodium wire, 200 ml. of light petroleum (b.p. 40-60°) and 56 3 g. (50 9 ml.) of chlorobenzene as described above for p-Toluic acid. Add 43 -5 g. (30 ml.) of ethyl bromide during 30-45 minutes at 30° and stir the mixture for a further hour. Add water slowly to decompose the excess of sodium and work up the product as detailed for n-Butylbenzene. The yield of ethylbenzene, b.p. 135-136°, is 23 g. 

Synthetic phenol capacity in the United States was reported to be ca 1.6 x 10 t/yr in 1989 (206), almost completely based on the cumene process (see Cumene Phenol). Some synthetic phenol [108-95-2] is made from toluene by a process developed by The Dow Chemical Company (2,299—301). Toluene [108-88-3] is oxidized to benzoic acid in a conventional LPO process. Liquid-phase oxidative decarboxylation with a copper-containing catalyst gives phenol in high yield (2,299—304). The phenoHc hydroxyl group is located ortho to the position previously occupied by the carboxyl group of benzoic acid (2,299,301,305). This provides a means to produce meta-substituted phenols otherwise difficult to make (2,306). VPOs for the oxidative decarboxylation of benzoic acid have also been reported (2,307—309). Although the mechanism appears to be similar to the LPO scheme (309), the VPO reaction is reported not to work for toluic acids (310). 

Herm/es/Djnamit JS obe/Process. On a worldwide basis, the Hercules Inc./Dynamit Nobel AG process is the dorninant technology for the production of dimethyl terephthalate the chemistry was patented in the 1950s (67—69). Modifications in commercial practice have occurred over the years, with several variations being practiced commercially (70—72). The reaction to dimethyl terephthalate involves four steps, which alternate between liquid-phase oxidation and liquid-phase esterification. Two reactors are used. Eirst, -xylene is oxidized with air to -toluic acid in the oxidation reactor, and the contents are then sent to the second reactor for esterification with methanol to methyl -toluate. The toluate is isolated by distillation and returned to the first reactor where it is further oxidized to monomethyl terephthalate, which is then esterified in the second reactor to dimethyl terephthalate. 

Formylbenzoic acid and -toluic acid are deterrnined by high performance hquid chromatography or capillary electrophoresis. Gas chromatography can be used for the aldehyde ester content of dimethyl terephthalate, this being the counterpart of 4-form ylben zoic acid in terephthahc acid. 

Impurities in isophthahc acid from the oxidation process are analogous to those in terephthahc acid, eg, 3-formylbenzoic acid and y -toluic acid. 

Formylbenzoic acid and -toluic acid can be deterrnined by high performance hquid chromatography. In some cases, polarography is used for 3-formylbenzoic acid and esterification gas chromatography for the y -toluic acid content. 

The hydroxyl group of the resulting phenol is situated immediately adjacent to where the carboxyl group was previously located. This same Hquid-phase copper oxidation process chemistry has been suggested for the production of cresols by the oxidation of toluic acids. y -Cresol would be formed by the oxidation of either ortho or para toluic acids a mixture of 0- and -cresols would be produced from y -toluic acid (6). A process involving the vapor-phase catalytic oxidation of benzoic acid to phenol has been proposed, but no plants have ever been built utilizing this technology (27). 

Theoretical yields of ester obtainable with proportions of reactants are shown ia Figure 1 for four values of the equbibrium constant. Thus when K equals 10 (esters of -toluic acid with primary alcohols), with equivalent amounts of acid and alcohol, a yield of about 76% may be expected. 

Terephthalic acid has been obtained from a great many /)-disubstituted derivatives of benzene or cyclohexane by oxidation with permanganate, chromic acid, or nitric acid. The following routes appear to have preparative value from />-toluic acid, />-methylacetophenone,2 or dihydro-/)-tolualdehyde by oxidation with permanganate from f>-cymene by oxidation with sodium dichromate and sulfuric acid from />-dibromobenzene or from /i-chloro- or -bromobenzoic acid by heating at 250° with potassium and cuprous cyanides and from />-dibromo-benzene, butyllithium, and carbon dioxide. ... 

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