Diazo compounds, light-sensitive

The 3(5)-diazopyrazoles are noticeably less stable than the 4-diazo compounds.31 Both are light-sensitive and both couple with phenols in organic solvents. The dyes so obtained form lakes with transition metal ions (cf. dyes from 2-diazopyrroles above, e.g., 40).13 The coupled product from 3-diazopyrazole and /9-naphthol is not in fact the simple azo dye but a condensation product derived from it.7... 

The light-sensitive properties of heterocyclic diazo compounds have been utilized for two different photoreproduction processes. The first... 

The diene arises through the diazo compound 4 via a retro-[3 -f 2] reaction and diazo compounds of this type have been detected or isolated in several photolyses of 2,3-di-azabicyclo[3.1.0]hex-2-enes. The workup procedure for this particular reaction involves selective removal of the diene by ozonolysis, a chemical method of separating the products which may have applications in related systems since chromatography often proves difficult. In some cases, the intermediate diazabicyclohexenes also prove very sensitive and difficult to handle, rearranging to pyridazines under the influence of acid, base " or light and sometimes, as in the synthesis of methyl 4,4-dimethyl-l,3-diphenylbicyclo[1.1.0]butane-2-carboxyl-... 

H. Zollinger, Diazo and Azo Compounds, Interscience, New York (1961) J. Kosar, Light Sensitive Systems, John Wiley Sons, Hoboken, NJ (1965). 

Like other diazo compounds, diazo ketones are sensitive to both heat and light. Upon exposure to either, nitrogen is lost and a carhene intermediate (p. 431), in this case, a ketocarbene, is formed (Rg. 18.65). 

The compounds with a quinonoid structure differ from those with a diazo structure by their darker colour and lower chemical stability. They are for example easily decomposed by light and concentrated acids they are less resistant to heat and show a higher sensitiveness to impact, friction and flame than compounds with a diazo structure. 

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