4,4 -Hydroxy azoxybenzene

If the photochemical reactions are superimposed by thermal reactions, in some cases additional information on the nature of the partial reactions can be obtained. This can be demonstrated in the case of the photoisomerisation of fra 5-azoxybenzene (A) to ort/io-hydroxy-azoxybenzene (C) [145]. In methanolic solution this reaction does not proceed uniformly, cis-Azoxybenzene (B) is formed as an intermediate. Using EDQ-diagrams explained in the next section one can demonstrate that just two linear independent partial reactions take place. The reaction can either follow the mechanism ps,... 

In some way formally similar to the benzidine rearrangement is the Wallach rearrangement of azoxybenzene 23 to give 4-hydroxyazobenzene 24 in concentrated (typically 95%) H2SO4. The 2-hydroxy isomer is sometimes formed in low yield with some substituted azoxybenzenes, and it is the main product in the photochemically induced reaction. Much of what is known about the reaction has been covered in earlier review articles28-30. This contribution will report work published since 1981. 

The time dependence of the glass transition was studied by Sorai and Seki641 who estimated an activation enthalpy of 75 kJ/mol for N-(2-hydroxy-4-methoxy-benzylidene)-4 -butylaniline, a value not much different from the 2,3 2,5 and 4,3 isomers of the same compound which do not form mesophases. For the azoxybenzene LC-glasses of Table 3 little time dependence was suggested by a missing hysteresis 2.6). 

N 15.27% om-yel ndls (from ale), mp 195 can be prepd by treating 4,4 -dihydroxy-azoxybenzene with NaNO, in glacial acetic acid or by sapon of 3-nitro-4-hydroxy-4. -benzoylhydroxy-azoxybenzene with coned KOH soln... 

The intermediate is considered to be (303) which either reverts to starting material or yields the o -hydroxy compound (304) by either acid or base catalysis. Rates of reaction are very dependent on positions of the substituents and while the conversion of (305) to (306) is efficient, the corresponding process of (307) proceeds slowly. Introduction of dimethylamino substituents markedly reduces the photoreactivity of the azoxybenzene and products derived from intramolecular hydrogen abstraction and cleavage of N=N or C=N bonds become evident. The conversion of (305) to (307) is reported to be a general one-way process for these systems and the azoxy isomer formed is always that with the N-oxide function far from the arene moiety which has the stronger electron donating substituent. 

C14H10N2O5, Mr 286.24, yellow amorphous powder, mp. >360 °C. A. is isolated, together with 4 -(hydroxy-methyl)azoxybenzene-4-carboxylic acid [C,4H,2N204, Mr 272.26, yellow powder, mp. 251°C (decomp.)] from cultures of Entomophthora virulenta (Zygomycetes), a fungal parasite on insects. 4 -(Hydroxyme-thyl)azoxybenzene-4-carboxylic acid is responsible for the Insecticidal activity of the culture extract. 

Sulphone cleavage is involved in a number of otherwise unrelated observations 2-(hydroxyamino)aryl phenyl sulphones or bis-(2-hydroxy-amino)aryl sulphones disproportionate into arylsulphinate and 2-hydroxy-2 -(arylsulphonyl)azoxybenzene (135) in aq. NaOH at 20 while... 

Secondary nematic structure was found by Blumstein and co-workers during the x-ray investigation of polyester prepared from 4,4 -hydroxy(2,2 -methyl) azoxybenzene and dodecanedioic acid. The diffraction pattern of the nematic shows the development of enhanced order characteristic of smectic phase (Fig. 16) the first of the meridional arcs splits up into four sharp spots. This phenomenon is incompatible with the classical definition of the nematic phase and suggests an additional order of macromolecules within cybotactic groups for which a structural model is proposed. 

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