Diphenylamine, reaction with chloroform

Phenoselenazines can be synthesized from diarylamines by direct reaction with diselenium dichloride in chloroform <70CCA6i > phenoselenazine itself (176) is obtained in this way from diphenylamine <59JOC37>. Y-Alkyl phenoselenazines can be prepared in a similar way from 7V-alkyldiphenylamines, or by A-alkylation of phenoselenazine (see Section 6.24.7.2.1). 

A mixture of A,A-diphenylamine (0.03 mol), 4-aminobenzoic acid (0.06 mol) was heated in 230 g of polyphosphoric acid at 200 °C for 15 min. The reaction mixture was then poured onto ice and filtered or decanted. Treatment of the solution with 25% NaOH (aq) solution caused the precipitation of a solid (while the solution was still acidic) presumed to be the phosphate salt of 9-(4-aminophenyl)acridine. After filtration the solution was made strongly basic with NaOH and extracted with chloroform. Concentration of the chloroform yielded only trace amoimts of 5. The phosphate salt was shaken with 25% NaOH (aq) and chloroform and the chloroform concentrated to give a 24% yield of 5. 

Perhaps the main disadvantage of the diphenylamine reaction for de-soxypentose is the lack of sensitivity. In addition, interference in the test by some substances has been shown by certain investigators (17,21,23,44). Three recently proposed methods deserve serious consideration. Cohen (23) has developed a color reaction with tryptophane, while Stumpf (98) has standardized the cysteine reaction originally proposed by Dische (40). Both methods are accurate in the range of 50-500 / g. of DNA. Ceriotti (21) has developed a micromethod (2.5-15 /xg. of DNA) using the reaction of indole with DNA, followed by extraction of the yellow pigment with chloroform. 

Intramolecular cyclization of diphenylamines to carbazoles is one of the most versatile and practical methods. This has been achieved photochemically, thermally in the presence of elemental iodine at 350°C, or with platinum at 450-540°C, via free radicals with benzoyl peroxide in chloroform, or by using activated metals such as Raney nickel or palladium on charcoal. Most of these methods suffer from low to moderate yields, and, in some cases, harsh reaction conditions (8,480). 

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