2,6-Dimethylnaphthalene

2,6-Dimethylnaphthalene is a polycyclic aromatic hydrocarbon. It is one of the ten dimethylnaphthalene isomers, which are derived from naphthalene by the addition of two methyl groups.

Synthesis

Alkylated naphthalenes are found in low concentrations in crude oil and coal tar. Separation is difficult, expensive, and requires a number of operations such as selective crystallization and adsorption, in addition to any isomerization reactions. Alternative routes to 2,6-DMN remains of interest.
In the "alkenylation process" butadiene, o-xylene, and sodium–potassium alloy are used, which react to form 5-pent-2-ene. OTP is subsequently cyclized to 1,5-dimethyltetraline. Dehydrogenation then provides 1,5-dimethylnaphthalene. Finally, 1,5-DMN is isomerized to 2,6-DMN. In the final step, other mono-, di-, and tri-methylnaphthalenes are formed. More work is therefore required in separation of the mixture, which is done by selective crystallization.

2,6-Dimethylnaphthalene is mainly used for the preparation of 2,6-naphthalenedicarboxylic acid by oxidation of 2,6-dimethylnaphthalene in the liquid phase. 2,6-Naphthalenedicarboxylic acid is a monomer for the production of high-performance polymers, in particular poly or shorter polyethylene naphthalate. That polyester is stronger and has a higher thermal resistance than the more frequently used polyethylene terephthalate.
2,6-Dimethylnaphthalene undergoes ammoxidation to give the 2,6-dicyanonaphthalene, which can be hydrogenated to bisnaphthalene, a precursor to dyes.