Azophenols preparation

Dihydroxyazobenzene and Derivatives. See under Azophenol (Azodiphenol) in Vol 1, pp A657-A658. Its nitrated derivative Hexanitrodihydroxyazobenzene was examined during WWII from the point of view of its utilization as a military expl, but was found to be rather expensive to prepare Ref A.H. Blatt F.C. Whitmore, A Literature Survey of Explosives , OSRD Rept 1085 (1942)... 

A series of azophenol acerands 4 was prepared by condensation of crowned benzoquinones 10 with 2,4-dinitrophenylhydrazine in ethanol [7b], The quinone was derived from p-methoxyphenol (6) as shown in Scheme 1 [8]. By bis(hy-droxymethylation) (67% yield of 6, followed by methylation (92%) of the phenol group and Williamson-type reaction with ditosylates of oligoethyleneglycol in the presence of sodium hydride, crowned 1,4-dimethoxybenzene 9 was obtained in reasonable yields. Oxidative demethylation of 9 with ceric ammonium nitrate (CAN) in aqueous acetonitrile at 50 °C gave the desired crowned benzoquinones 10 in good yields. 

As described in the previous section, azophenol crown 4 (n = 1) shows a characteristic coloration only for Li+ ion among alkali metal ions. After extensive examinations in a number of solvent systems, lithium analytical conditions were determined as shown in Table 2 [18a]. The resulting reddish purple color is very stable and its absorbance is maintained for 10-90 min after developing color. The calibration curve for Li+, in other words, sensitivity is linear from 25-250 ppb. Na+ does not interfere, but K+, Rb+, Ca2+, Sr2+, Ba2+, and Mg2+ interfered in the determination with a similar coloration. This method was applied to the analysis of a commercial pharmaceutical preparation, a lithium carbonate tablet, since the Li2C03 tablet has been used for medical treatment of manic depressive illness [18 b]. On the other hand, the azophenol crown 4 (n = 1) is also useful as a reagent for colorimetric determination of Rb+ and Cs+ [19]. 

AA-CPA-Zn served as the test system for incorporation of Co(III) into azoproteins as outlined in Figure 3. It was therefore important to distinguish between Co(III) and Zn(II) bound to azophenols. For this purpose model Co(III) complexes of the azophenolate ligands shown in Figure 2 have been prepared and characterized. 

Recently, creativity in chromogenic macrocycle synthesis has expanded. New spherand species have been synthesized that act as highly preorganized chromogenic-specific indicators for Li+ and Na (Cram et al., 1985), and an azophenol dye has been prepared with perfect selectivity for Li (Kaneda et al., 1985). Many of these chromogenic macrocycles and more complicated species such as the hemispherands and cryptohemispherands have found commercial use for Na" and K assays in body fluids (see 41) (Helgeson et al., 1989 Czech et al., 1990). 

Naemura, K. Ogasahara. K. Hirose, K. Tobe. Y. Preparation of homochiral azophenolic crown ethers containing l-phenylethane-1.2-diol and 2,4-dimethyl-3-oxapentane-l,5-diol as a chiral subunit Enantiomer recognition behaviour towards chiral 2-aminoetlianol derivatives. Tetrahedron Asymmetry 1997. 8 (1). 19-22. 

Materials. Horseradish peroxidase (HRP) (EC 1.11.1.7) (200 unit/mg) was purchased from Sigma with RZ > 2.2. A stock solution of 10 mg/ml in O.IM phosphate buffer (PH = 6.0) was prepared. The para substituted azophenol monomers were synthesized following typical procedure. All other chemicals and solvents used were commercially available, of analytical grade dr better and used as received. 

Optical quality polymer film preparation. The H, CN, NO2, and CH3O substituted azophenol polymers were soluble in most polar organic solvents. 

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