Competitive recrystallization

Entry 22-24 shows competitive recrystallization from 1 1 mixtures of xylene isomers [34], In contrast to mono-alkylbenzenes, m-xylene and //-xylene were exclusively included in CA cavities from mixtures of o- and m-xylene, o- and p-xylene, respectively, i.e. //-xylene acts as a solvent and is not included in the CA host cavity at all. Recrystallization from a 1 1 mixture of m-xylene and //-xylene yielded a crystal that included both guest components in a similar guest ratio... 

Table 6 Competitive recrystallizations of CA with various compounds".

Table 8 Competitive recrystallizations of DCA with monosubstituted benzenes".

Chevron Chemical Co. began commercial production of isophthahc acid in 1956. The sulfur-based oxidation of / -xylene in aqueous ammonia at about 320°C and 7,000—14,000 kPa produced the amide. This amide was then hydrolyzed with sulfuric acid to produce isophthahc acid at about 98% purity. Arco Chemical Co. began production in 1970 using air oxidation in acetic acid catalyzed by a cobalt salt and promoted by acetaldehyde at 100—150°C and 1400—2800 kPa (14—28 atm). The cmde isophthahc acid was dissolved and recrystallized to yield a product exceeding 99% purity. The Arco technology was not competitive and the plant was shut down in 1974. 

The Dynamit Nobel process produces dimethyl terephthalate (DMT) by a complicated series of oxidation and esterification stages (equation 241).83,84,86 In the oxidation section, p-xylene is oxidized at 150°C and 6 atm without solvent and in the presence of cobalt octoate to TPA and p-toluic acid. These oxidation products are sent to another reactor for esterification by methanol at 250 °C and 30 atm. Fiber grade DMT is purified by several recrystallizations, and monoesters are recycled to the oxidation reactor. The overall yield in DMT is about 80%, which is lower than in the Amoco process. However, this process is competitive because it is not corrosive and requires lower investments. It provides high-quality fiber-grade dimethyl terephthalate. 

In order for the composites to become conductive, the TCNQ salt, initially dissolved in DMF solution before casting, should subsequently recrystall ze as pure microcrystals. To realize this condition with NMP TCNQ7, two approaches are possible one is to reduce the association through choosing weak donor polymers as matrices, and another is to dope the system with TCNQ so that TCNQ salt association with the polymer should be reduced through a competitive reaction with TCNQ, thereby facilitating salt crystallization. 

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