Question

Using your knowledge of chemical migration, outline the two most possible chemical migration pathways for non-polar C9H12 that has been spilled onto an open field on a warm spring day.

Answer 1

Mesitylene is prepared by equilibration of xylene (or simple methyl alkylation of it) over solid acid catalyst:

2 C₆H₄(CH₃)₂ ⇌ C₆H₃(CH₃)₃ + C₆H₅CH₃

C₆H₄(CH₃)₂ + CH₃OH → C₆H₃(CH₃)₃ + H₂O

Although impractical, it could be prepared by trimerization of propyne, also requiring an acid catalyst, affords a mixture of 1,3,5- and 1,2,4-trimethylbenzenes. Catalyzing and dehydrating by sulfuric acid, trimerization of acetone via aldol condensation also affords mesitylene.

The three aromatic hydrogen atoms of mesitylene are in identical chemical shift environments. Therefore, they only give a single peak near 6.8 ppm in the 1H NMR spectrum. For this reason, mesitylene is sometimes used as an internal standard in NMR samples that contain aromatic protons.