PRODUCTION OF 2-METHYLNAPHTHALENE FROM COAL SOURCES

摘要

Coal tar is a source of 2-methylnaphthalene, a raw material for making drugs, dyes, plasticizers, and wetting agents. For the synthesis of derivatives, the 2-methylnaphthalene should contain not less than 98 percent of the basic substance. Methods described in the literature [1-3] for isolating 2-methylnaphthalene are devised also for coal sources. In the first stage of any method, one obtains a narrow fraction containing not only 2-methylnaphthalene but also in considerable amounts its isomer 1-methylnaphthalene. The boiling points of 1-methylnaphthalene and 2-methylnaphthalene are very similar (correspondingly 244.8 and 241.1 deg C), and rectification gives only a mixture of isomers. There is an adverse effect on the rectification from phenols, bases, and indole, which form azeotropes with minimum boiling points with the homologs of naphthalene and diphenyl. The following methods have been proposed for the next stage in separating the isomers:1) freezing the 2-methylnaphthalene; 2) sulfonating the isomer mixture with concentrated sulfuric acid and desulfurization, whose rate is higher for the 1-methylnaphthalene derivative; 3) alkylation with a tertiary olefm, with fractional distillation or crystallization of the products and dealkylation; and 4) fractional distillation with a azeotropic agent, e.g., diethylene glycol monoethyl ether, and so on. Sulfonation, alkylation, and azeotropic fractionation are either multistage complicated processes with large amounts of waste difficult to utilize, or else processes requiring expensive reagents not produced by the industry. The simplest method is freezing the 2-methylnaphthalene, but it requires considerable energy to produce the low temperature.