Yu. A. Serguchev, I. I. Chernobaev, L. F. Lur'e, and V. N. KalininAnionic and cationic complexes of ferric chloride with crown polyethers were synthesized. We studied the effect of complexes of various structure and nature on the rate and selectivity of the chlorination of aromatic compounds. In comparison with the catalytic action of ferric chloride, the para selectivity in the chlorination of toluene and chlorobenzene is enhanced, while the reaction rate is reduced in the presence of the complexes studied.The catalytic liquid-phase chlorination of toluene and chlorobenzene is an important chemical reaction leading to many valuable products [1,2]. The chlorination of toluene derivatives is used in the manufacture of agricultural, medicinal, and other chemical products. The chlorination of toluene in the presence of ferric chloride leads to the predominant formation of ortho-chlorotoluene (o-CT) although the demand for para-chlorotoluene (p-CT) is greater.Use has been found for para-dichlorobenzene (p-DCB) as an insecticide, deodorant, and starting material for the manufacture of polyphenylene sulfides; p-DCB is produced in larger amounts than ortho-dichlorobenzene, which is employed as a solvent, purifying agent for metals, and heat exchange liquid.There have been two major approaches in the attempt to increase the para/ortho ratio for the isomer products in the catalytic chlorination of aromatic compounds. In early studies, organic and inorganic sulfur compounds were added as cocatalysts to the major ferric chloride catalyst to obtain reaction mixtures with a higher content of the para isomers of chlorotoluene and dichlorobenzene. In this case, the para/ortho ratio of the dichlorobenzene products is usually enhanced from 1.5 to 3.3 [1, 3] or higher [4,5], while the para/ortho ratio for chlorotoluene products is enhanced from 0.46-0.56 to 1.0 [2,3,6].In recent years, a high content of para isomer products has been obtained in the chlorination of aromatic compounds using zeolites as catalysts [3,7,8] but the catalytic activity of zeolites decreases over time due to the absorption of water present in the substrate, polychlorides, and tarry substances, while the chlorination rates in the presence of zeolites are only slight. A solution to these problems requires the use of special techniques and, thus, large capital expenditures. Therefore, the search for new catalytic systems affecting the positional selectivity in the chlorination of aromatic compounds has both practical and theoretical importance.Various ferric chloride complexes are formed in the substituent chlorination of aromatic compounds in the presence of FeCl 3 , electron-donor compounds, and hydrogen chloride released in the reaction: anionic tetrachloroferrates H + FeCl 4 − [9], 116 0040-5760/08/4402-0116
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