Nitrodiphenyl Sulfide

Tarbell, Todd, Paulson, Lindstrom, and Wystrach, J. Am. Chem. Soc., 70, 1384 (1948). 

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An alternative synthesis of 4-nitrodibenzothiophene involves heating 2-amino-2 -nitrodiphenyl sulfide in a sealed tube at 190° (20%). The reaction probably proceeds via homolytic cleavage of the derived diazonium ion which could have been formed from nitrous acid liberated during the formation of phenothiazines, which were also detected. Similarly, 2-methyl-4-nitrodibenzothiophene is formed from 2-amino-2 -nitro-4 -methyldiphenyl sulfide (10%), and in this case the intermediacy of the diazonium ion was further indicated in that the same material was obtained by pyrolysis of the separately prepared diazonium salt of the sulfide. Although yields are poor in this reaction, it nevertheless represents the only route to substituted dibenzothiophenes containing a nitro substituent in the 4-position and as such is worthy of further attention. 

Phenoxazines and phenothiazines 32 and 33 are also made by reductive cyclization of o-nitrodiphenyl ethers or o-nitrodiphenyl sulfides, respectively, with triethyl phosphite. 

Dapsone has been prepared by a number of procedures (1,48). One procedure employs the reaction of l-chloro-4-nitrobenzene with excess sodium sulfide to give the 4-amino-4 -nitrodiphenyl sulfide. This compound, after acetylation of the amino group, is oxidized with H2O2 to the sulfone. The nitro group is then reduced to amino, and hydrolysis of the acetyl gives the product. 

Among the more recent approaches to phenoxazines and phenothiazines the reductive cyclization of 2-nitrodiphenyl ethers and sulfides with trialkyl phosphites is the most interesting. Here too a spiro intermediate is involved, produced by attack of an initially formed aryl nitrene on the second aromatic ring. The sulfide (252), for example, reacts with triethyl phosphite to yield 1-methylphenothiazine (253) and it is clear that in this case ring opening of the spiro intermediate also proceeds with a rearrangement of the Smiles type (Scheme 113) (75JCS(P1)2396). 

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