Desulphurization, lead-acid

A recent modification in the use of Raney nickel may greatly enhance its utility. Industrial use of the standard procedure has been limited by the necessity to use such large quantities of the very expensive Raney nickel. It now appears that the use of the nickel-aluminium alloy itself in formic acid leads to very efficient desulphurizations with Ni/S ratios of only 0 2. High proportions of the aluminium seem to give the best results, apparently because of the ability of the aluminium to regenerate the active nickel catalyst. Similar results were obtained using nickel or cobalt salts in the presence of auxiliary metals such as aluminium or iron. 

Lithium reagents desulphurize /ra s-2,3-diphenylthiiran 1-oxide, but give about equal yields of cis-stilbene and the lithium salt of stilbene-cf-sulphenic acid with cis-2,3-diphenylthiiran 1-oxide. Decomposition of the trans-isomer in the presence of ylides (53) leads to small yields of sulphines. Pyridine iV-oxide is deoxygenated by SO. In all these cases, kinetic measurements show that decomposition of the thiiran 1-oxide occurs independently of the substrate. 

Thiazolidine rings are normally easy to prepare but this year a new reaction has appeared in which the ring system was produced during a thermally-induced intramolecular eliminative rearrangement. The azido-enones (364) were heated to 140 C leading to a mixture of the products (365) and (366) in equal proportions. The authors have determined that an intramolecular acid-catalysed Schmidt reaction is not involved, and have proposed the triazoline (367) as a reasonable intermediate. They have also shown that in certain cases rearrangement coupled with desulphurization provides a completely regioselective method for conversion of 2-cycloalkenones to the ene lactams (368). 

Reactions Leading to Destruction of the Thiophen Ring.—Raney-nickel desulphurization has been used for the synthesis of aliphatic compounds and for structure determination. From (158) and (159) aliphatic y-diketones and y-keto-carboxylic acids have been obtained. " c-Caprolactams and e-enantholactams such as (199) have been prepared by desulphurization and transformed to amino-... 

The reaction between 2-nitrothiophen and secondary aliphatic amines leads most probably to the ring-opened product (213). Raney-Nickel desulphurization continues to play an important role in the structure determination of thiophen derivatives, and for the synthesis of macrocyc-lic compounds, such as a-alkylcycloalkanones, amino-lactams of aliphatic diaminocarboxylic acids, and of dethiobiotin. The nickel boride catalyst (NiBo), prepared from nickel(ii) chloride and sodium borohydride in methanol, gives olefins in 50—55% yield. From (214) a mixture of methyl... 

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