2.3- Dimethylnaphthalene, oxidation acids

An autoclave (Note 1) is charged with 200 g. (1.28 moles) of 2,3-dimethylnaphthalene (Note 2), 940 g. (3.14 moles, 23% excess) of sodium dichromate dihydrate, and 1.8 1. of water. The autoclave is closed, heated to 250°, and shaken continuously at this temperature for 18 hours. The autoclave is cooled with continued agitation (Note 3), the pressure is released, and the autoclave is opened. The contents are transferred to a large vessel (Note 4). To effect complete transfer, the autoclave is rinsed with several 500-ml. portions of hot water. Green hydrated chromium oxide in the reaction mixture is separated on a large Buchner funnel and washed with warm water until the filtrate is colorless. The combined filtrates (7-8 1.) are acidified with 1.3 1. of 6N hydrochloric acid. The acidified mixture is allowed to... 

Although the superior properties of PEN have been known for many years, the unavailability of the naphthalate monomer has delayed the development of commercial markets, until relatively recently (1995) when the Amoco Chemical Company offered high purity naphthalene-2,6-dimethyl dicarboxylate (NDC) in amounts of up to 60 million pounds per year. This diester is produced by a five-step synthetic route, starting from the readily available compounds, o-xylene and 1,4-butadiene [3], Prior to this, the NDC diester was obtained by extraction of 2,6-dimethylnaphthalene (DMN) from petroleum streams, where it was present in relatively low abundance. Oxidation of DMN to crude 2,6-naphthalene dixcarboxylic (NDA) is conducted by a similar process to that used for conversion of p-xylcnc to purified terephthalic acid (TA), crude NDA is esterified with methanol, and is then distilled to yield high purity NDC. Other companies (e.g. the Mitsubishi Gas Chemical Company) followed Amoco s introduction with lesser amounts of NDC. Teijin [4] has manufactured PEN for many years for its own captive uses in films. 

Similar regiospecific syntheses employing PMBs and dialkylnaphthalene have been used to prepare 2,6-dimethylnaphthalene [581-42-0] which is oxidized to the corresponding 2,6-naphthalenedicarboxylic acid [1141-58-4]y also used as a monomer for liquid crystal polymers. 

Homologues of naphthalene are oxidized to naphthalenecarboxylic acids on heating in an autoclave at 250 °C for 18 h with an aqueous solution of sodium dichromate. p-Methylnaphthalene affords (3-naphthoic acid in 93% yield [633], and 2,3-dimethylnaphthalene, 2,3-naphthalenedicar-boxylic acid in 87-93% yield [1130]. Methylanthracenes and methylphen-anthrenes are similarly converted into the corresponding carboxylic acids in yields well over 90% [633]. 

Naphthalenedicarboxylic acid is a precursor to polyethylene naphthalate (PEN), which is used to improve the properties of polyester bottle resins (see also problem E.1.6). It can be made by the liquid phase oxidation of 2,6-dimethylnaphthalene as described in U.S. 6,114,575, assigned to BP Amoco. Estimate the cost of production for a plant that produces 250,000 metric tons per year (250 kMTA). 

In water at 250°. A highly efficient oxidation procedure first described in the patent literature and developed further by Friedman " is illustrated by Friedman s procedure for the oxidation of 2,3-dimethylnaphthalene to naphthalene-2,3-dicar-boxylic acid. An autoclave charged with the reagents indicated is shaken con-... 

A combination of sc carbon dioxide and light has been used in flow reactors to make some metal complexes not possible by other methods, for example, cyclopentadi-enylMn(CO)2(H2) and Cr(CO)s(ethylene).179 A man ganese hydride has been added to olefins in carbon dioxide.180 A zeolite in sc carbon dioxide selectively adsorbs 2,7-dimethylnaphthalene so that it can be separated from the desired 2,6-dimethylnaphthalene.181 The latter is oxidized to the dicarboxylic acid for conversion to a highermelting analogue of poly(ethylene terephthalate). A pillared clay made in supercritical carbon dioxide had a higher... 

Sulfur, and derivatives of sulfur in a low oxidation state, can also be applied for oxidation of methylated aromatic compounds. Thus, under the conditions of a modified Willgerodt reaction, dimethylnaphthalenes can be converted into methylnaphthoic acids (ca. 40%) and naphthalenedicarboxylic acids (ca. 60%) (molar ratios of Hydrocarbon S NH3 H20 = 1 7 5.6 65 ... 

TMLA is produced by the oxidation of one of the rings of the 2,6-dimethylnaphthalene molecule. 2-Formyl-6-naphthoic acid results from the incomplete oxidation of one of the methyl groups of the 2,6-dimethylnaphthalene molecule [6]. 

Among the di-substituted alkylnaphthalene derivatives, 2,6-dimethylnaphtha-lene is important as it can also be used as a base material for the production of naphthalene-2,6-dicarboxylic acid. It is produced from the coal tar fraction boiling between 255 and 265 °C, by redistillation and crystallization. Oxidation of 2,6-dimethylnaphthalene is carried out in the same way as the oxidation of p-xylene, in the liquid phase with Co/Br-catalysts. Naphthalene-2,6-dicarboxylic acid, or its acid chloride and ester, are components in the production of high-value polymer films and fibers, with high temperature resistance these polymers can display liquid-crystalline character in the molten state. 

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