Three-stage catalytic converters

Only two examples of the synthesis pyrimidoazocines have been described. In Ref. 82JHC1257, a three-stage synthesis of a new heterocycle system, pyrimido[5,4-c]benz[l]azocine, has been proposed. Condensation of 4-methyl-2-phenyl-5-pyrimidincarboxylate (112) with 3,4-dimethoxy-6-nitrobenzaldehyde (113) led to the substituted alkene 114, which, after catalytic hydrogenation of the nitro group on Raney nickel and subsequent intramolecular cyclization of product 115, was converted into pyrimidobenz[l]azocine 116 (Scheme 32). 

The Claus process is the most widely used to convert hydrogen sulfide to sulfur. The process, developed by C. F. Claus in 1883, was significantly modified in the late 1930s by I. G. Farbenindustrie AG, but did not become widely used until the 1950s. Figure 5 illustrates the basic process scheme. A Claus sulfur recovery unit consists of a combustion furnace, waste heat boiler, sulfur condenser, and a series of catalytic stages each of which employs reheat, catalyst bed, and sulfur condenser. Typically, two or three catalytic stages are employed. 

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