Naphthalene-2,7-dicarboxylic acid

Naphthalene-2,6-Dicarboxylic Acid. NDA is more compHcated to synthesize on an industrial scale. The preferred starting material is... 

The modification of PET with naphthalene-2,6-dicarboxylic acid and other additional comonomers is a common measure in bottle manufacturing. Copolyesters based on this compound show excellent barrier properties. Such materials can be produced by addition of the desired amount of comonomer during polymer processing or by blending PET with poly(ethylene naphthalate) (PEN). Additionally, PEN can also be modified by other comonomers such as isophthalic acid (IPA) to improve the flow properties and reduce the melting point. The high price of naphthalene dicarboxylic acid is the reason for its limited application. The overall cost may be reduced by using TPA or IPA as comonomers. 

Again, polyesters based on naphthalene-2,6-dicarboxylic acid can meet the desired properties, plus have other additional advantages. Food components containing double bonds or conjugated double bonds are extremely sensitive to light-induced reactions, such as photo-oxidation. The addition of UV stabilizers is therefore necessary to protect the content of PET bottles against UV irradiation. PET, in contrast to PEN, does not show intrinsic UV protection properties. 

Du Pont s Zenite range of LCPs have been reintroduced. These materials are also LCP polyesters based on HBA copolymers with, it is believed, various amounts of 4,4,-biphenol, terephthalic acid, and naphthalene-2,6-dicarboxylic acid (NDA) as comonomers. Their compositions are thus similar to those of XYDAR with added NDA to further reduce the melting point (235,236). 

Regioselective dialkylation of naphthalene is another reaction of considerable interest as 2,6-dialkylnaphthalenes can be oxidised to naphthalene-2,6-dicarboxylic acid, which is used in the synthesis of the commercially valuable polymer, poly(ethylene naphthalenedicarboxylate) (PEN).22 PEN has properties that are generally superior to those of polyethylene terephthalate) (PET) and has become the polymer of choice for a variety of applications such as in films, industrial fibres, packaging, liquid crystalline polymers, coatings, inks and adhesives. However, the high cost of naphthalenedicarboxylic acid has been a major hindrance to widespread application. 

Amoco chemicals have commercialised a procedure that uses o-xylene as starting material. However, this synthesis of naphthalene-2,6-dicarboxylic acid involves five steps, including isomerisation of 1,5-dimethylnaphthalene to 2,6-dimethylnaphthalene. The direct regioselective alkylation of naphthalene (9, Scheme 5) is therefore more attractive, and has been investigated by, amongst others, NKK, Chiyoda and Catalytica.22 Synthesis of 10 by this approach is complicated, however, by the possible formation of nine other dialkyl isomers, which can be difficult to separate from the 2,6-isomer. 

The most apparently desirable of the minor components is the 2,6-dimethyl naphthalene which can be used to make naphthalene-2,6-dicarboxylic acid, which in turn can be used to make special polyesters (3). Following oxidation of the alkylated naphthalenes (the alkyl groups do not necessarily have to be methyl, but the substitution pattern is important) the resulting dicarboxylic acids should be readily marketable. However, since the overall yields of naphthalene derivatives in the synthetic gasoline are low, this fraction is unlikely to be of commercial value in the near term. This is unfortunate, because these compounds are also unsuitable for gasoline as their boiling points lie outside the required specification. 

A new class of diamine spacer was synthesised from a,co-diaminoalkanes and 4-nitrophthalic anhydride the resulting a, -bis(4-aminophthalimido)alkanes were polycondensed with one of the following acid chlorides terephthaloylchlo-ride, 2-phenylthioterephthaloylchloride, naphthalene-2,6-dicarboxylic acid or 4,4 -biphenyldicarboxylic acid chloride [40]. Thermotropic behaviour was con-... 

Naphthalene-2,6-dicarboxylic acid. See 2,6-Naphthalene dicarboxylic acid... 

A further method for the synthesis of naphthalene-2,6-dicarboxylic acid is based on 2-methylnaphthalene or mixtures of l-/2-methylnaphthalene. The methylnaph-thalenes are oxidized to carboxylic acids subsequent Henkel rearrangement, which was carried out a number of years ago on a large scale in Japan Teijin) at 400 to 500 °C under CO2 pressure of around 100 bar, converts the monocarboxylic acid to dicarboxylic acid. 

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. 

Poly(butylene naphthalene-2,6-dicarboxylate), PBN, is prepared from naphthalene-2,6-dicarboxylic acid and 1,4-butsnediol. It exhibits a Tg of 78°C and... 

It is obtained by polycondensation between ethylene glycol and either naphthalene-2,6-dicarboxylic acid or its dimethyl ester. Its high thermomechanical characteristics and its excellent durability opened markets for it in the fields of electronics, industrial textiles, and food packaging (hot drinks and sparkling beverages). 

Figiire 8. Crystal structures of the aramid compounds naphthalene-2,6-dicarboxylic acid bis[4-(ethoxycarbonyl)phenylamide (top) and benzene-1,4-dicarboxylic acid bis(4-ethoxy-carbonyl)phenylamide (bottom) [58]... 

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