Fusion of the diaroylethanes with phosphorus pentasulfide produces the 2,5diarylthiophenes. By this method, Kapf and Paal (1) claimed the preparation of 2,5-diphenylthiophene in 60% yield. Holleman (2) also synthesized 2,5-di-ptolylthiophene by this procedure. The reaction is generally unsatisfactory, due to tarry products and unpredictable yields. Since phosphorus pentasulfide acts 1405
A number of metal chelates of the isoalloxazines, riboflavin and 6,7-dichloro-9-(l'-D-sorbityl)-isoalloxazine, have been prepared and isolated. Evidence for chelate formation is provided by a drop in pH during the formation, absence of metal ions in the solution, analyses of the purified products, production of characteristic colors, decreased solubility in alkaline solution and comparison with a true salt formation. The chelates show the same relative degree of insolubility as riboflavin(1) Abstracted from the M.
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