4- azobenzo

Attempts to obtain ring-expanded products by photolysis of azides in the presence of diethylamine were successful only for the 6-azido compound (Section III,C).193 4-Azidobenzo[i>]thiophene gave, inter alia, 4-amino-benzo[b]thiophene and 4,4 -azobenzo[f>]thiophene, probably via triplet nitrene.366 The-5-azido isomer gave 4-amino-5-diethylaminobenzo[h]thiophene, probably via an azirine intermediate, derived from singlet nitrene. Thermolysis of 4-azidobenzo[b]thiophene in PPA-AcOH gave 4-acetamido-... 

Somewhat different chromogenic procedures have involved preliminary reaction of phenols with 4>(S-fluoro-2,4-dinitro-l-phenyIazo)-iV,iV-dimethylaniline (130) and coupling with 4-benzoylamine-2,5-diethoxyaniline (Fast Blue salt BB) (131) followed in each case by separation of the azocompounds produced. Diazotized 4-nitroaniline, or the preferred reagent, anthraquinone-l-diazonium chloride (Fast Red salt AL) (131), have been reacted with phenol, the isomeric methylphenols, and dimethyl-phenols, and the colored azo products separated on silica gel G impregnated with potassium carbonate (86). Using this technique separations otherwise impossible with the free phenols have been achieved. A wide scope exists for quantification procedures with greatly improved sensitivity. 4-(A Af-dimethyl-aminophenyl)-4 -azobenzoates of various phenols have also been used (132). 

Dinitro-prp -azobenzoic Acid. See x,x -Dinitroazobenzene-4,4 -dicarboxylic Acid in Vol 1, p A651-L... 

Betaines 261 are stable crystalline compounds. Knowledge of their chemical reactions is still limited. Alkaline hydrolysis of aryl derivatives (261 R = Ar) gives the 2-azobenzoic acids 266 but the mechanism of this rearrangement is unknown. Reduction by tin and hydrochloric acid gives the hydrazides 267. Thermolysis of the p-tolyl compound (261 R = p-MeC6H4) (120 C at 0.1 mm Hg) gives the isomeric triazine (268 R = >-MeC6H4). Phosphorus pentasulfide converts the 2-methyl derivative (261 R = Me) into 2-methyl l,2,3-benzotriazinium-4-thiolate (272 R = Me) (Section in,B,15). 

Azobenzoic Acid Azodibenzoic Acid or Azobenzenedicarboxylic Acid, HOOO-C6H4-N N-CsH4-COOH, mw 270.24, N 10.37%. Three isomers 0,0 m,m - and p,p - are described in Beil 16, 228,232,233,236 (287). Of these only the para-isomer is of interest because its nitro- and dinitro- derivs form expl salts (see below)... 

Dinitro-p,p -azobenzoic acid see X,X -Dinitroazo-benzene4,4 -dicarboxylic acid 1 A651... 

The zinc-dust treatment serves to reduce and remove small amounts of azo compounds (notably o-azobenzoic acid) which always discolor the crude product. Attempts to purify the crude product by crystallization from 33 per cent alcohol invariably led to a darker colored product with the same melting point as the crude. The decolorizing carbon is not intended to decolorize the solution but to clarify the filtrate before the precipitation of the diphenic acid. 

Roholt, O.A., Friedenson, B., Radzimski, G., Pressman, D. (1973). A light chain tyrosyl sequence in the antibody site of a rabbit anti-p-azobenzoate antibody. J. Immunol. Ill, 1367-1375. 

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