Diazo oxide

In alkaline solution, diazonium ions are converted to diazoate anions, which are in equilibrium with diazo oxides.84... 

Diazonium salts can also be converted to halides by processes involving aryl free radicals. In basic solutions, aryl diazonium ions are converted to radicals via the diazo oxide.102... 

In the classical procedure, base is added to a two-phase mixture of the aqueous diazonium salt and an excess of the aromatic that is to be substituted. Improved yields can be obtained by using polyethers or phase transfer catalysts with solid aryl diazonium tetrafluoroborate salts in an excess of the aromatic reactant.177 Another source of aryl radicals is A-nitrosoacetanilides, which rearrange to diazonium acetates and give rise to aryl radicals via diazo oxides.178... 

Recently from a comparison of the infra-red absorption spectrum of this compound with that of o-benzoquinone Glowiak [10] came to the conclusion that dinitro-benzenediazo-oxide has a quinonoid structure. Both substances show the presence of the strong absorption band of the carbonyl group 1666 cm-1 for dinitrobenzene-diazo-oxide and 1680 cm-1 for o-benzoquinone. In addition dinitrobenzenediazo-oxide gives a band with a frequency of 2190 cm-1, characteristic of a double bond between nitrogen atoms. (Some derivatives of this compound may also have the diazo structure (Ha), which is discussed later on.)... 

T. Urbanski, Szyc-Lewanska et al. [18] have recently found that dinitrobenzene-diazo-oxide can be prepared by oxidation of picramic acid with chromium trioxide in the presence of sulphuric acid at 55-60°C. One part of picramic acid is fully oxidized by chromic acid to yield gaseous products CO, C02, N02, NH3 and H20. Nitrogen dioxide acts further as a diazotizing agent on undecomposed picramic acid to yield the diazo compound. The yield of this reaction does not exceed 31% of theoretical calculated on the picramic acid used. 

Dinitrobenzene diazo-oxide reacts with hydrazine hydrate to yield 2,4-dinitro-6-[tetrazene-(l)]-phenolhydrazine salt (XIV)... 

Diozo Oxides. Diazo oxides are obtd irom substituted aminophenols amino-naphthols. They are also obtd from amino-phenolcarboxylic acids with the amino group either ortho or para to the hydroxyl group. 

In comparison with diazonium salts (qv), diazo oxides are, more stable, more deeply colored, less soluble and less reactive. They do not readily couple to give azo colors except in strongly alkaline solns. Although diazo oxides are generally stable, some (such as 4,6-Dinitrobenzene-2-diazo- 1-oxide, Vol 2, p B59-L) are used as detonating expls Refs 1) G.T. Morgan J.W. Porter, JCS 107 I, 645-59 (Constitution of internal diazo oxides) 2) G.T. Morgan H.P. Tomlins,... 

No structural assignments were made to the diazo oxides because of the uncertain positions of the labilized fluorine atoms Refs 1) Beil - not found 2) G.C. Finger et al, JACS 73, 148(1951) CA 45, 7034 (1951)... 

Replacement of the diazo group by hydrogen has been reported for a number of diazo oxides. For example, the diazo oxide from 2-nitro-4-aminophenol yields o-nitrophenol in 53% yield,42 - 43 and that from 1-amino-2-hydroxy-6-bromonaphthalene-4-sulfonic acid gives XV in approximately 50% yield.44... 

For a discussion of the structure of the diazo oxides (diazophenols) see Sidgwick, "The Organic Chemistry of Nitrogen, revised by Taylor and Baker, pp. 422-423, Oxford University Press, 1937. For convenience, the first of the two resonance structures (XIII, XIV) will be used in this chapter. 

With 3,5-dinitro-4-methoxyaniline rapid and complete conversion to the diazo oxide occurs upon diazotization with sulfuric or hydrochloric... 

In consequence of hydrolytic cleavage, a diazo oxide also is obtained from the isomeric l,8-dinitronaphthylamine-2. Here, however, elimination of the nitro group is a comparatively slow reaction so that treatment with ethanol gives, a satisfactory yield of 1,8-dinitronaphtha-. lene.63-64 ... 

A dearth of quantitative information about the rate of diazo oxide formation makes it impossible to generalize about the importance which is to be attached to this side reaction. However, it appears that in many instances the reaction is a comparatively slow one, so that anhydrous conditions are unnecessary. In this connection it is significant that diazotized picramide, which is reported to be very unstable in the presence of water,61- 62 is converted to trinitrobenzene in 60-65% yield upon treatment with 50% aqueous hypophosphorous acid. -... 

There is a substantial group of diazonium salts to which the alkaline formaldehyde method, or any other deamination process requiring alkaline conditions, should not be applied, inasmuch as they are unstable in the presence of alkali. This instability is merely an extension of the hydrolytic cleavage reaction previously noted (pp. 274-276). Comparatively few diazonium salts are converted to the diazo oxides in aqueous mineral acid. As the acidity of the solution is decreased, however, diazo oxide formation is facilitated, and finally on the alkaline side many diazo compounds that are stable in acid media undergo hydrolytic cleavage.96 96 Thus, while 2,4-dinitrobenzenediazonium acid sulfate is stable to dilute aqueous sulfuric acid, in neutral or slightly alkaline solution it readily yields the diazo oxide.6 The reaction is not quantitative a poorly defined insoluble product is also formed in 14 to 20% yields. 

Symmetrical tribromo- and trichloro-benzenediazonium salts are rapidly transformed into the diazo oxides by ice-cold aqueous sodium hydroxide.97- 98... 

The para halogen atoms are less labile than those in the ortho positions about 20% of the molecules that yield diazo oxides lose an atom of bromine from the para position, whereas approximately 80% lose an ortho bromine.9 The more highly halogenated diazonium salts are more likely to undergo hydrolytic cleavage.109... 

It is reported that alkaline sodium hydrotulfite (Na2S204) is effective -in converting certain diazo compounds to the hydrocarbons,119 a statement supported solely by reference to the work of Grandmougin.130 Actually he obtained only a small yield of benzene from benzenediazonium salts but suggested that on further study the process might prove to be useful. Upon reduction with hydrosulfite, the diazo oxide XXIV is converted to the phenol XXV in 95% yield (crude product.)131... 

Diazo oxides when treated with phosphorus pentasulfide also form benzothiadiazoles (equatio/T34) (b-61MI42400>. 

Certain nuclear substituents ortho to a newly formed diazonium group may interact to form a cyclic structure with or without retention of the nitrogen atoms. Such is the case in the diazotization of o-phenylene-diamine in aqueous solution, the product being 1,2,3-benzotriazole (81%). If the ortho substituent is an activated methyl group, an indazole is formed. Hydroxyl groups ortho or para to the diazonium group may interact to form internal condensation products called diazo oxides. These compounds may also form in the reaction of halo- and nitro-substituted aminophenols. 

Reactivity with Diazo Oxides and Azides. Diazo oxides, e.g. 2,6-di-f0rf-butyl-4-diazo-2,5-cyclohexadiene-l-one (184, R = terr-butyl) or 2,6-diphenyl-4-diazo-2,5-cyclohexadiene-l-one (184, R = phenyl) are thermolabile and photolabile. Car-benes 185 are formed from 184 as reactive intermediates. The process proceeds in a one-step mechanism in which the carbene species reacts in the singlet state [238], The attachement of 185 to saturated hydrocarbon chains proceeds via insertion in C—H bond during processing. LDPE and PP were modified in this way [239, 240]. Poly(oxymethylene) was modified similarly. 

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