Potassium tetrachloro , isomers

Dichlorodibenzo-p-dioxin was prepared from isotopic potassium 2,4-dichlorophenate uniformly labeled with Ullman conditions gave a 20.5% yield. Small amounts of dichlorophenoxy chlorophenol were removed from the product by extraction with sodium hydroxide before purification by fractional sublimation and recrystallization from anisole. Chlorination of 2,7-dichlorodibenzo-p-dioxin in chloroform solution containing trace amounts of FeCls and 12 yielded a mixture of tri-, tetra-, and pentachloro substitution products. Purification by digestion in boiling chloroform, fractional sublimation, and recrystallization from anisole was effective in refining this product to 92% 2,3,7,8-tetrachloro isomer, which also contained 7% of the tri- and 1% of the penta-substituted dibenzo-p-dioxin. Mass spectroscopy was used exclusively to monitor the quality of the products during the synthesis. 

A solution of 4.15 g. (0.01 mol) of potassium tetrachloro-platinate(II) in 50 ml. of water is shaken vigorously in a 250-ml., glass-stoppered Erlenmeyer flask with 4.31 ml. (3.61 g. = 0.04 mol) of diethyl sulfide (density, 0.837) until the originally deep red supernatant liquid has become colorless (ca. 15 minutes). The mixture is allowed to remain in the stoppered flask for about 24 hours, whereupon the yellow precipitate of trans isomer initially formed above dissolves. The resulting clear yellow solution is filtered if necessary, transferred to an evaporating dish, and evaporated to dryness at room temperature, f Caution. A hood should be used. This evaporation can be accomplished in about 10 to 20 hours if a constant flow of air is maintained above the dish. 

A solution of 4.15 g. (0.01 mol) of potassium tetrachloro-platinate(II) in 50 ml. of water is shaken vigorously in a stoppered 250-ml. wide-mouth container with 4.99 ml. (4.05 g. 0.02 mol) of freshly distilled tri-n-butylphosphine (density, 0.8118 g./ml.) until no further lightening of the color of the supernatant liquid occurs (about 3 hours).f The resulting waxy salmon-colored mass, containing predominantly cis isomer but also some trans isomer, is scraped from the sides of the container, washed with several 10-ml. portions of water, and dried in a vacuum oven at 30° for about one hour. Complete removal of occluded potassium chloride and tetrachloroplatinate(II) from the isomer mixture is difficult because of its waxy nature, but is effected by subsequent purification steps. 

Methods of synthesis of 3-chloro- and 3,4-dichloro-thiophenes have usually involved tedious procedures in which tri- and tetra-chloro derivatives are dechlorinated by reductive or other methods. Gthanolic potassium hydroxide converted 2,3,4,5-tetrachlorothiophene into a 50 50 mixture of 2,4- and 3,4-dichlorothiophenes direct heating of the same tetrachloro substrate gave a mixture of 2,3- and 2,4-dichloro isomers (48JA1158). 3,4,5-Trichlorothiophene was readily prepared by the reaction of 1,1,2,3-tetrachloro-l,3-butadiene with sulfur (82JOU348). 

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