C. Graebe (Ann., 1869, 149, p. 22) orientated the ortho-compound or phthalic acid from its formation from naphthalene on oxidation; the meta-compound or isophthalic acid is orientated by its production from mesitylene, shown by A.
A historic example is that of the condensation of three molecules of acetone, CH 3 CO CH 3, in the presence of sulphuric acid, to s-trimethylbenzene or mesitylene, C 6 H 3 (CH 3) 3, first observed in 1837 by R.
When mesitylene is used, the reaction does not proceed beyond the aldehyde stage since hydrocarbon formation is prevented by the presence of a methyl group in the ortho-position to the -CHO group. Acids and alkalis are in general without action on nickel carbonyl.
On distillation with sulphuric acid, it is converted into mesitylene C 9 H 12 (symmetrical trimethyl benzene).
Metaor iso-xylene, the most important isomer, may be prepared by nucleus-synthetic reactions, or by distilling mesitylenic acid, C 6 H 3 (CH 3) 2 CO 2 H, an oxidation product of mesitylene, C 6 H 3 (CH 3) 3, which is produced on the condensation of acetone, with lime; this reaction is very important, for it orientates meta-compounds.
Uvitic acid, 5-methyl isopthalic acid, is obtained by oxidizing mesitylene or by condensing pyroracemic acid with baryta water.