2,4-dinitrophenylpyridinium chloride

Dinitrochlorobenzene (95) reacts with pyridine to form 2,4-dinitrophenylpyridinium chloride (103), a reactive intermediate which readily reacts with a variety of nucleophiles. The reaction of (103) with hydrogen sulfide yields 2,2, 4,4 -tetranitrodiphenylsulfide (104), which on nitration-oxidation with fuming nitric acid, yields 2,2, 4,4, 6,6 -hexanitrodiphenylsulfoxide (105). The sulfide (104) is also formed from the reaction of two equivalents of 2,4-dinitrochlorobenzene (95) with sodium thiosulfate or sodium disulfide in aqueous ethanol. ... 

Treatment of N-2,4-dinitrophenylpyridinium chloride (778) with phenyl-hydrazine in acetic acid causes reductive cyclization to yield the pyrido[l,2-ajimidazole (779). 3-Aminocrotononitrile, MeC(NH2)=CHCN, condenses with quinoline 1-oxide and isoquinoline 2-oxide to form the tricyclic compounds (780) and (781), respectively." The imidazo[5,l-a]isoquinoline derivative (783) is obtained by the action of phenyl isothiocyanate on the sodium salt of the Reissert compound (782)." ° Triethyl phosphite reduces the o-nitrophenyldipyr-rolylmethane (784 R=N02) to the nitrene (784 R = N), which forms the pyrrolo[3,2-6]quinoline derivative (785) by an intramolecular insertion reac-tion." 3-Amino-177-isoindole (786) reacts with acetylacetone in the presence of perchloric acid to yield the pyrimidoisoindolium salt (787). ... 

Indole has been separated from carbazole and diphenylamine on silica gel, copper sulphate-impregnated silica gel, on alumina and on cellulose with aqueous and non-aqueous systems (212). The color reactions with six different spray reagents following two-dimensional separations on silica gel H have been studied (213) for a wide range of indoles and skatole on cellulose detected by its fluorescence with 2,4-dinitrophenylpyridinium chloride (213a). Indole and oxindole alkaloids have been separated in 10 neutral and 10 alkaline solvents (214). 

Chlorodinitrobenzene reacts with pyridine to form dinitrophenylpyridinium chloride (Vongerichten [19]) ... 

This compound, first prepared by Wedekind [33], is even more reactive than dinitrophenylpyridinium chloride (p. 454). Bielig and Reidies [23] described a reaction after Zincke and Weisspfennig s work [22] which resulted in the formation of hexanitrodiphenyl sulphide (picryl sulphide) (p. 553). 

Examples have been mentioned in which various nucleophiles produced 4-substituted pyridines from 4-pyridylpyridinium chloride hydrochloride, rather than causing ring opening (pp. 210, 239, 251), and it is interesting to notice that dinitrophenylpyridinium salts can imdergo nucleophilic attack... 

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