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.
On distillation with sulphuric acid, it is converted into mesitylene C 9 H 12 (symmetrical trimethyl benzene).
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.
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.
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.