Methyl group is ortho para directing so it should direct the second methyl group to ortho or para position giving rise to ortho or para xylene but how can meta xylene be formed?
- Friedel Crafts alkylation of toluene is far less regioselective than you might think.
- The meta-substituted products are thermodynamically favoured. At higher temperatures, the alkylation yields more 1,3-dialkyl substituted benzenes.
- On a larger scale, Dimethylbenzenes are typically not synthesized by alkylation of toluene, but stem from catalytic reforming processes using alkanes as feedstock.
I don't know about the practical issues, but theoretically benzoic acid can undergo Friedel-Crafts alkylation to form 3-methylbenzoic acid which can be reduced to m-cresol and further to m-xylene