2,6-Dimethylnaphthalene

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2,6-Dimethylnaphthalene
2,6-dimethylnaphthalene.svg
Names
Preferred IUPAC name
2,6-Dimethylnaphthalene
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.008.605 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
UNII
  • 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
  • Cc1ccc2cc(ccc2c1)C
Properties
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).

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]

Contents

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 2,6-DMN synthesis 1.png
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]

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1,8-Naphthalic anhydride is an organic compound with the formula C10H6(C2O3). It is one of three isomers of naphthalic anhydride, the other two being the 1,2- and the 2,3-derivatives. The 1,8-isomer is prepared by aerobic oxidation of acenaphthene. 2,6-naphthalenedicarboxylic acid can be prepared from this anhydride. 1,8-Naphthalic anhydride is a precursor to the 4-chloro and 4,5-dichloro derivatives. These chloride groups are susceptible to displacement by amines and alkoxides, giving rise, ultimately, to a large family of naphthalimides, which are used as optical brighteners.

References

  1. ↑ Collin, Gerd; Höke, Hartmut; Greim, Helmut (2003). "Naphthalene and Hydronaphthalenes". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_001.pub2.
  2. ↑ USpatent 5004853,Paul T. Barger, Timothy J. Barder, David Y. Lin, Simon H. Hobbs,"Continuous process for the production of 2,6-dimethylnaphthalene",issued April 2, 1991
  3. ↑ USpatent,Lawrence D. Lillwitz, Anne M. Karachewski,"Alkylation of alkylaromatics promoted by sonicated alkali metal",issued March 30, 1993
  4. ↑ Lillwitz, L. D. (2001). "Production of Dimethyl-2,6-Naphthalenedicarboxylate: Precursor to Polyethylene Naphthalate". Applied Catalysis A: General. 221 (1–2): 337–358. doi:10.1016/S0926-860X(01)00809-2.
  5. ↑ Pollak, Peter; Romeder, Gérard; Hagedorn, Ferdinand; Gelbke, Heinz-Peter (2000). "Nitriles". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_363.
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