Thiophenes using phosphorus sulfides

The original Paal reactions involved heating succinic acid or derivatives neat with P4S10 in a clay vessel, followed by crushing the vessel and extracting the tars to isolate the thiophene derivatives. Yields tended to be low. It was later shown that salts of the acids gave better yields, especially when lower sulfides of phosphorus were used, thus producing... 

A mixture of hydrogen sulfide and hydrogen chloride effects cycli-zation of 2-propynylcyclohexanone (44) to 2-methyl-4,5,6,7-tetra-hydrobenzo[6]thiophene (45) (69%).260 Treatment of 46 with either hydrogen sulfide or carbon disulfide also affords 45, but in lower yields. A 5% yield of 45 is obtained, together with 10% 2-methyl-4,5,6,7-tetrahydrobenzofuran, when phosphorus pentasulfide is used to effect cyclization of 44. 

C.N.-4. Salts, oxides, sulfides, imines, and ylides of the parent. Here cyclic delocalization is not possible since the lone pair on phosphorus is used in a fourth bond. Most of the oxides and some of the other functions are unstable at or slightly above room temperature, forming Diels-Alder dimers in the manner of thiophene oxides. 

Gulkova and Zdrazil studied kinetics of the parallel HDS of thiophene and HDN of pyridine as model reactions for elucidating the effect of the Ni addition to W on AC. For this purpose, the fixed-bed continuous system was used at 2 MPa and 553 and 593 K. The rate constants from this study are summarized in Table 31. They confirmed the promoting effect of Ni on both HDS and HDN reactions. The rate constants shown in Table 29 for some noble-metal sulfides were determined under identical conditions. The effect of phosphorus on parallel HDS of thiophene and HDN of pyridine for catalysts in Table 7 was quantified by kinetic measurements conducted by Vasques et Some results from this study are shown in Table 32. 

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