The Diazo Group

Diazomethane is a linear molecule with the structure CH2=N=N and absorbs at 2101 cm . The assignment of this to the stretching 

The high frequency of this absorption is typical of X=X=X structures, and it cannot therefore always be readily differentiated from wocyanates and similar materials. However, the recognition of this band in the spectrum of the naturally occurring azaserine has led to its successful synthesis [65]. 

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The diazonium salts usually decompose when warmed with water to give a phenol and nitrogen. When treated with CuCl, CuBr, KI, the diazo group is replaced by chlorine, bromine or iodine respectively (Sandmeyer reaction). A diazonium sulphate and hydroxyl-amine give an azoimide. The diazonium salt of anthranilic acid (2-aminobenzoic acid) decomposes to give benzyne. ... 

When a solution of a diazonium salt is heated, the diazo group is replaced by hydroxyl and nitrogen is evolved ... 

Diazo compoimds are partieularly easy to make with the diazo group next to a carbonyl group by this reaction ... 

Diazoindazole (51) is one of the few heterocyclic diazo compounds whose structure has been determined (78AX(B)293). The diazo group shows a substantial carbanionic character (51b). 

B (11— 12— 14). Examination of a more recent study suggests the von Richter reaction probably involves simultaneous attack of the triple bond on the diazo group accompanied by attack by a halide ion but not by a water molecule. The halocinnoline 13 is then hydrolyzed under the von Richter reaction conditions to furnish the 4-hydroxycinnoline derivative 14 (11 - 12- 13 14, pathway A). 

In general, it is diffieult to prediet the outeome of eyelizations of alkynylpyrazole diazonium salts, even with elosely related arrangements of funetional groups, sinee reaetion ean oeeur at both the a- and /3-earbon atoms of the aeetylenie substituent. Moreover, it is known that the eleetrophilieity of the diazo group and the nueleophilieity of a triple bond markedly depend on their positions in the pyrazole ring and that this ean affeet both the eourse and ease of eyelization and even its viability (83IZV688). 

Methyl-1,2,4-benzotriazm-3(4//)-one 1-oxide 122 can be obtained in good yield by the diazotization of 121 to give 3-diazo-7-methyl-l,2,4-benzotriazine 1-oxide followed by the substitution of the diazo group with water (82JHC497). 

Itishould be noticed that the similarity between the osmophore theory and Witt s chromophore colour theory does not extand much beyond the initial conception and there seems to be no connection between the odour and the colour of a body, it is indeed quite the exception for a body to have both a strong odour and a strong colour. Two prolific sources of colour, viz. the diazo group and a large molecule have no counterpart as regards odour, and it is probably only by chance that quinone and chroman both have pronounced odours and are the sources of colour. 

This diazotization is typical of many aminoazoles the diazonium ions formed are relatively strong acids. The pATa values of five di-, tri-, and tetrazolediazonium ions are reported to be between 3 and 4, i. e., about 10 units lower (more acidic) than those of the respective unsubstituted heterocycles (Vilarrasa et al., 1974). Therefore, deprotonation of the diazonium ion is easy and, depending on reaction conditions, yields either the diazonium salt or its conjugate base, the diazo compound. The electrophilic reactivity of the P nitrogen atom in the diazo group of the base is lower than the reactivity of the diazonio group of the cation (Diener and Zollinger, 1986 see Sec. 12.2). 

Quinone diazides can also be obtained by the diazo group transfer reaction of 4-tosyl azide. For example, 9-diazo-10-anthrone (2.55) is formed from anthrone (2.54) if the reaction is carried out in an ethanol-piperidine mixture. On the other hand, if ethanol is replaced by pyridine, dimerization with loss of molecular nitrogen takes place and the azine 2.56 is isolated (Scheme 2-32 Regitz, 1964 Cauquis et al., 1965). In the preceding discussion tosyl azide was shown to be an electrophilic reagent. It therefore seems likely that it is not the anthrone 2.54 but its conjugate base which reacts with tosyl azide. 

This is, however, a weak electrophile compared with species such as N02 and will normally only attack highly reactive aromatic compounds such as phenols and amines it is thus without effect on the otherwise highly reactive PhOMe. Introduction of electron-withdrawing groups into the o- or p-positions of the diazonium cation enhances its electrophilic character, however, by increasing the positive charge on the diazo group ... 

The presence of 9-diazofluorene groups in kinamycin antitumor natural products would lead one to think of an active role for the diazo group. The hypothesis may be substantiated by the fact that one of the precursors in kinamycin biosynthesis, kinafluorenone 10 [44], which lacks the diazo moiety, shows no antibiotic activity against B. subtilis ATCC 6633, known to be very sensitive to the kinamycins. However, prekinamycin (9) [49], which is similar to kinafluorenone but retains the diazo group, shows activity to-... 

These mechanistic possibilities, which give such an active role for the diazo group, are summarized in Fig. 20 using the model compound 9-diazo-fluorene 18. 

Patai S (ed) (1972) Chemistry of the diazo groups. Chemistry of the functional groups. Interscience, New York... 

Instead of by alkali stannite the diazo-group can be exchanged for hydrogen by prolonged boiling of the diazonium salt in alcohol, which is thereby oxidised to aldehyde. 

The simplest azo-dye—devoid of technical importance, however— is forded from phenyl diazotate and phenol the diazo-group takes up the p-position—in the case of j8-naphthol the adjacent a- or o-position. 

It has been reported that thermolysis of the bis(diazomethyl)phosphines lo leads to the formation of the diazaphospholes 64. This can be explained by either an intramolecular [2 + 3] cycloaddition process involving the diazo group, or a diazo-carbene coupling reaction. 

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