Azoxy-compounds, table

TABLE 108. AZO AND AZOXY COMPOUNDS TABLE 108. AZO AND AZOXY COMPOUNDS... 

Table 14. Crystal data and phase sequences of mesogenic azo and azoxy compounds (see Fig. 23)... 

The reaction is generally carried out by refluxing a stirred mixture of 0.014 mole of the nitro compound and 0.042 mole (8.5 gm) of thallium in 75 ml of ethanol for the periods shown in Table I. The cooled solution is decanted to remove unreacted thallium, 8 gm of potassium iodide is added, and the mixture is stirred for 1 hr at room temperature. The precipitated thallium iodide is filtered, and the filtrate concentrated under reduced pressure. The residue is dissolved in chloroform and then filtered through an alumina column (4 x 1 in.) to remove traces of inorganic salts. Chloroform is used as the eluent, and the resulting solution is concentrated under reduced pressure to afford the solid azoxy compounds. 

Tables II and III give the physical properties of a selected list of azoxy compounds.

Oxidative reactions of organonitrogen species that do not involve molecular oxygen are rather limited. The only case for which the evidence is at all convincing is the oxidation of arylhydroxylamines to arylnitroso species (Table 2). This reaction resembles the first half of the hydroxylamine oxidoreductase reaction found in nitrifying bacteria. The key difference is that the aryl nitroso compound is stable (although condensation with the arylhydroxy-lamine can occur to produce the azoxy compound, ArN(O)NAr), while the inorganic analog is nitroxyl, HNO, which if released from the enzyme would rapidly dimerize and dehydrate to form N2O. Consequently, HAO does not release the HNO or NO intermediate, but instead oxidizes it to nitrite before any substrate-derived species are released. 

The oxidation of aromatic hydroxylamines has been widely used in the preparation of nitrosobenzenes. Among the methods described in the literature for this transformation, the most common procedure involves heterogeneous oxidation using iron(III) chloride [140]. This oxidation is normally slow, which can lead to the formation of the corresponding azoxy derivatives through coupling of the formed nitroso compound with the unreacted hydroxylamine. In addition, low yields are sometimes obtained due to the partial instability of the starting hydroxylamine and/ or nitroso product. Illustrative examples of this transformation are shown in Table 3.2 [141]. 

The other nitrogen-oxygen linkages which exhibit weak bands due to n -> rr transitions are alkyl nitrites12 14, alkyl nitrates12, nitroso compounds14-18 and azoxy compounds19. The absorption maxima and extinction coefficients of a few typical compounds have been summarized in Table 3.6. 

---