2,6-Dimethylnaphthalene

2,6-Dimethylnaphthalene (2,6-DMN) 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.^[1]

2,6-Dimethylnaphthalene

Names
Preferred IUPAC name 2,6-Dimethylnaphthalene
Identifiers
CAS Number	581-42-0 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:34251
ChemSpider	10909
ECHA InfoCard	100.008.605
PubChem CID	11387
UNII	76U29QW3FM Y
CompTox Dashboard (EPA)	DTXSID0029187
InChI InChI=1S/C12H12/c1-9-3-5-12-8-10(2)4-6-11(12)7-9/h3-8H,1-2H3 Key: YGYNBBAUIYTWBF-UHFFFAOYSA-N InChI=1/C12H12/c1-9-3-5-12-8-10(2)4-6-11(12)7-9/h3-8H,1-2H3 Key: YGYNBBAUIYTWBF-UHFFFAOYAZ
SMILES Cc1ccc2cc(ccc2c1)C
Properties
Chemical formula	C12H12
Molar mass	156.228 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Synthesis

Alkylated naphthalenes (methyl-, dimethyl-, and poly-methyl naphthalenes, thus including 2,6-DMN) 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.^[2]

In the "alkenylation process" butadiene (1), o-xylene (2), and sodium-potassium alloy (3) are used, which react to form 5-(ortho-tolyl)pent-2-ene (OTP, 3).^[3] OTP is subsequently cyclized to 1,5-dimethyltetraline (4). Dehydrogenation then provides 1,5-dimethylnaphthalene (1,5-DMN, 5). Finally, 1,5-DMN is isomerized to 2,6-DMN (6). 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.

Synthesis of 2,6-dimethylnaphthalene by the alkenylation process

Applications

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 (ethylene-2,6-naphthalene dicarboxylate) or shorter polyethylene naphthalate (PEN).^[4] That polyester is stronger and has a higher thermal resistance than the more frequently used polyethylene terephthalate (PET).

2,6-Dimethylnaphthalene undergoes ammoxidation to give the 2,6-dicyanonaphthalene, which can be hydrogenated to bis(aminomethyl)naphthalene, a precursor to dyes.^[5]