This article reported the synthesis of different sulfonyl chloride of polynuclear heterocyclic compounds which are very important intermediates to form different derivatives like sulfonates. Unfortunately, this paper is lacking a complete isolation and purification procedure of all these sulfonyl chlorides. During my investigation, I found it is more convenient to isolate and purify sulfonyl chlorides than doing purification after making their derivatives. The following sulfonyl chlorides have been tried to regenerate.
Synthesis of Dibenzofuran-2,4,8-trisulfonyl chloride: The article did not confirm (Page 158) if they were successful to isolate dibenzofuran-2,4,8-trisulfonyl chloride. My investigation found that only a specific reaction condition resulted in trisulfonyl chloride. The mixture of dibenzofuran and a large excess of chlorosulfonic (20 mol equivalents) was heated at 120 °C for 45 minutes to yield Dibenzofuran-2,4,8-trisulfonyl chloride. The crude sulfonylchloride was chromatographed on silica gel, eluting with 50% dichloromenthane in hexane to give dibenzofuran-2,4,8-trisulfonylchloride with other minor impurities, crystallization from dichloromethane gave pure dibenzofuran-2,4,8-trisulfonylchloride.
Synthesis of Fluorene-2,4,7-trisulfonyl chloride (51) (Page 169): I found that the reported procedure at room temperature did not work on forming trisulfonyl chloride rather resulted in fluorene-2,7-disulfonyl chloride. However, their alternative procedure carried out at 100 °C (page 166) worked as mentioned.
Synthesis of Dibenzothiophen-2-sulfonyl chloride (21) (Page 167): The reported procedure required 10 days to complete the reaction. My experiment showed, the similar yield can be achieved if the reaction mixture is heated under reflux at 100 °C for 2.5 h.
Purification of Carbazole-1,3,6,8-tetrasulfonyl chloride (46) (Page 168):
The reaction mixture was gradually added to crush ice. The resulting precipitate was filtered by gravity filtration and dried by squeezing with paper towel. The solid was dissolved in a desired amount of ethyl acetate containing equivalent amount of norit and refluxed for 15 minutes, passed through a pad of silica. The filtrate was concentrated in vacuo and yellow solid was precipitated out from crystallization in a mixture of 10% ethyl acetate in hexane. The solid was filtered and dried under vacuum.
Purification of Dibenzofuran-2,4,6,8-tetrasulfonyl chloride (18) (Page 167)
The reaction mixture was gradually added to crush ice. The resulting precipitate was filtered by gravity filtration and dried in air. The crude sulfonylchloride was chromatographed on silica gel, eluting with 10% ethylacetate in hexane. Crystallization from 50% dichloromethane in hexane gave pure dibenzofuran-2,4,6,8-tetrasulfonylchloride.