Synthesis of 5-methylisophthalic acid

Preparation of 5-methylisophthalic acid

20 g of mesitylene are refluxed with 80 g of 30% nitric acid in a 250-ml round-bottomed flask, on a sand bath in a fume cupboard for 18 hours. The white residue is filtered off on cooling, washed with cold water, dissolved in sodium carbonate solution, unattacked mesitylene and nitromesitylene separated, and the mixed acids reprecipitated by acidification with dilute hydrochloric acid. The white precipitate is filtered off, washed with cold water, and heated on a water bath with tin and excess of strong hydrochloric acid for 2 hours with constant shaking in a capacious flask (caution! hydrogen evolved). Nitromesitylenic acid, a by-product in the reaction, is thus reduced and brought into solution. On cooling, the undissolved portion is filtered off, washed with cold water, dissolved in dilute caustic soda, and reprecipitated from the hot filtered solution with dilute hydrochloric acid. The precipitate is a mixture of 3,5-dimethylbenzoic acid and 5-methylisophthalic acid. It is filtered off, washed with cold water and distilled in steam, till after several hours no further trace of 3,5-dimethylbenzoic acid appears in the condenser, and the distillate ceases to have an acid reaction. The greater portion of the 3,5-dimethylbenzoic acid, free from 5-methylisophthalic acid, is suspended in the distillate. It is filtered off and the filtrate neutralised with sodium hydroxide solution, evaporated to small bulk, acidified with dilute hydrochloric acid, and the usually somewhat yellow-coloured acid thus obtained united to the first portion. The whole is redissolved in sodium hydroxide solution, filtered boiling hot, precipitated by addition of dilute hydrochloric acid, washed with cold water, and recrystallised from alcohol. It is then pure 3,5-dimethylbenzoic acid. 5-Methylisophthalic acid containing slight traces of 3,5-dimethylbenzoic acid separates from the residual liquid in the distilling flask on cooling. It is recrystallised from hot alcohol, after precipitation by acid from alkaline solution. Yield 3,5-dimethylbenzoic acid 50% theoretical, 5-methylisophthalic acid acid 40% theoretical. 3,5-Dimethylbenzoic acid forms colourless monoclinic crystals; difficultly soluble in hot water; easily soluble in cold alcohol; m.p. 166° C. 5-Methylisophthalic acid forms colourless fine needles; insoluble in cold and hot water; readily soluble in alcohol and ether; m.p. 287-288° C.

Systematic organic chemistry, by W. M. Cumming, 245-246, 1937.


5-methylbenzene-1,3-dicarboxylic acid



InChI Key


Canonical SMILES


Depositor-Supplied Synonyms

5-Methylisophthalic acid, 499-49-0, UVITIC ACID, 5-methylbenzene-1,3-dicarboxylic acid, 5-Methyl-1,3-benzenedicarboxylic acid, Isophthalic acid, 5-methyl-, PMZBHPUNQNKBOA-UHFFFAOYSA-N, SBB008429, 3,5-Dicarboxytoluene, AC1Q5TMY, ACMC-209kj2, SCHEMBL40661, KSC237E4T, toluene-3,5-dicarboxylic acid, 641383_ALDRICH, CTK1D7249, MolPort-001-759-807, AC1L2941, ACN-S004165, NSC41436, ZINC1672687, EINECS 207-881-2, ANW-30876, AR-1L8097, CM-195, NSC-41436, AKOS015891094, FR-2039, MCULE-1116314925, PS-3522, RTR-033584, TRA0127676, VZ30493, 1,3-Benzenedicarboxylicacid, 5-methyl-, 1,3-Benzenedicarboxylic acid, 5-methyl-, AJ-29257, AK-73016, AN-25563, BR-73016, OR002801, OR120984, SY005375, AB0008661, AB1003131, DB-051706, ST2412102, TR-033584, AM20060639, FT-0620641, M1903, ST50825152, M-2620, I01-8330, 3B1-005622, 3B3-004240, 5-Methylbenzene-1,3-dicarboxylic acid; 5-Methyl-1,3-benzoic acid; 5-Methyl-1,3-benzenedicarboxylic acid; 2,4-Toluenedicarboxylic acid; 4-Methylisophthalic acid

Removed Synonyms

1, 5-methyl-, CID68137, 3347-99-7, 51895-55-7

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