Diazophenols

Diazophenols, ie, o-hydroxyaryldiazonium salts, couple to 1-naphthol in weaMy basic solution primarily in the para position, but as the hydroxyl ion concentration is increased, formation of the ortho isomer is favored and is frequentiy the sole product. Pyridine and pyridine derivatives, urea, and acetate, etc, used as buffers can also catalyze azo coupling reactions (28). l-amino-2-naphthol-4-sulfonic acid [116-63-2] (1,2,4-acid) and 1-naphthol yield the important Eriochrome Black A [3564-14-5] (18a, R = H) (Cl Mordant Black 3 Cl 14640) which is reportedly (20) a mixture of ortho and para isomers. 

Dihydroxynaphthalene [83-56-7] behaves similarly to 1-naphthol coupling takes place mainly in the 4-position by simple diazonium compounds, and in the 2-position with diazophenols. Diazotized 2-arninophenol-4-sulfonic acid [98-37-3] couples with 1,5-dihydroxynaphthalene to produce the important mordant dye Diamond Black PV [2052-25-7] (see stmcture 53) (Cl Mordant Black 9 Cl 16500). 

Nitro-l-diazo-2-naphthol-4-sulfonic acid prefers the 2-position in spite of the nitro group, and increasing alkalinity favors ortho coupling with diazophenols. 1-Naphthalenesulfamic acid [24344-19-2] (ArNHSO H) and N-nitro-1-naphthylamine [4323-69-7] (ArNHNO ) couple exclusively in the para position. The substitution of resorcinol [108-46-3] and y -phenylenediamine [108-45-2] is compHcated and has been discussed (29,30). The first azo dyes from aniline, eg. Aniline Yellow [60-09-3] (19) (Cl Solvent Yellow 1 Cl 11000) were manufactured in 1861 and Bismark Brown [10114-58-6] (20) (Cl Basic Brown 1 Cl 21000) appeared in 1863. The reaction is as follows ... 

Originally, 2-diazophenols were used as diazo components. Nowadays the most important compound is 2,5-diethoxy-4-morpholinobenzenediazonium tetrafluoro-borate. Typical coupling components are acetoacetic anilide, l-phenyl-3-carbamido-... 

Lowe-Ma, Ch., Robin, A. N. und William, S. W. Diazophenols-Their Structure and Explosive Properties, Naval Weapons Center, China Lake, CA 9355 -6001 Rept.-Nr. WC TP 6810 (1987). 

A number of bases, with pyridine heading the list, act as proton acceptors in the electrophilic coupling reaction. Their contribution is particularly useful if voluminous substituents exist in ortho or peri position relative to the coupling location of the intermediate they may also facilitate coupling with diazonium ions of low electrophilicity (e.g., diazophenols). 

Under certain conditions the first products of the reaction, in the case of nitrophenols, are diazophenol ethers (diazohydroxy-compounds), which then very easily undergo rearrangement... 

Reaction mixtures containing an arylnitramine with an o-nitro group require careful work-up because the formation of diazophenols is often a facile and sometimes spontaneous process. The... 

Diazophenol formation is most competitive when a nitramine substrate contains an electron-withdrawing nitro group ortho to the nitro group being displaced and hence meta to the nitramine functionality, assumedly because that site is then activated towards nucleophilic aromatic substitution. Heating nitramines in inert chlorinated solvents also favours diazophenol formation but this is suppressed by using urea or sulfamic acid as additives. 

The course of a reaction involving At-nitration of an aromatic amine is very dependent on both the substrate and the reaction conditions, i.e. nitrating agent, temperature, work-up etc. The nitration of 3-amino-2,5-dinitrotoluene with mixed acid in glacial acetic acid at 0 °C yields the corresponding diazophenol with no trace of the intermediate nitramine. In contrast, nitration of the same substrate at ambient temperature with mixed acid composed of 90 % nitric acid and 96 % sulfuric acid yields the corresponding nitramine. ... 

Glowiak studied the stability of the four diazophenols (59-62), which he prepared from the diazotization of the corresponding aminophenols. It was noted that (61) and (62) show higher chemical stability than (59) and (60) the latter compounds were postulated to have a quinonoid structure rather than a zwitterionic diazophenol structure. 

The nitration of both 4-methyl- and 4-chloro-2,6-dinitrotoluenes (66 and 67) with mixed acid in acetic acid at subambient temperature allows the isolation of the nitramines, (68) and (69), respectively. Thermolysis of (68) and (69) in refluxing methylene chloride yields the corresponding diazophenols, (70) and (71), respectively. Scilly and co-workers isolated 2-diazo-4,6-dinitrophenol (DINOL) (53) from the thermolysis of fV,2,3,5-tetranitroaniline (73) in ethyl acetate at 60 °C. 

Unsymmetrical arylnitramines with two nitro groups positioned ortho to the nitramino functionality can yield two isomeric diazophenol products. The diazophenols (76) and (77) were isolated in a 4 1 ratio from the nitration of 3-amino-2,6-dinitrotoluene (74) with mixed acid, the reaction proceeding via the intermediate nitramine (75). ... 

Chemists at the Naval Air Warfare Center (NAWC), China Lake, have conducted much research into the nitration of various substituted anilines as an indirect route to highly nitrated arylene hydrocarbons (Section 4.5). On numerous occasions these chemists found that diazophenols are formed as by-products and sometimes as the main or only product of a reaction. During these studies the diazophenols (65) and (78-81) ° were isolated and characterized. These diazophenols were screened for use as explosive components of both percussion and stab-sensitive primary explosive compositions. ... 

Other groups, including azide, peroxide, diazophenols, and nitrogen-rich compounds derived from guanidine derivatives. 

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