Tris-azo compounds

Brown FK (E 154, Cl Food Brown) is a mixture of six mono, bis, and tris azo compounds. 

This, again, may be diazotized and then coupled with a new ring yielding a compound containing three azo groups and termed a tris-azo compound. 

Tri-azo Compounds.—As phenyl hydrazine is both a primary and a secondary amine the (NH) group reacts with nitrous acid yielding a nitroso amine compound. This compound is very unstable, readily losing water, and forming a compound in which the ring is linked to a three nitrogen group. It is known consequently as a tri-azo compound, also as a diazo imide. 

Eupe and Majewski attempted to determine by experiment the influence of the relative positions of osmophores on each other in the same molecule. In the case of the three methyl tri-azo-benzoates no great difference in the type of odour exists, only a difference in the strengths, the para compound being the strongest and the ortho the weakest. Of the three methoxy-acetophenones, as another example, the meta isomer is almost odourless in comparison with the ortho and para. 

The multifunctional initiators may be di- and tri-, azo- or peroxy-compounds of defined structure (c.g. 20256) or they may be polymeric azo- or peroxy-compounds where the radical generating functions may be present as side chains 57 or as part of the polymer backbone."58"261 Thus, amphiphilic block copolymers were synthesized using the polymeric initiator 21 formed from the reaction between an a,to-diol and AIBN (Scheme 7.22).26 Some further examples of multifunctional initiators were mentioned in Section 3.3.3.2. It is also possible to produce less well-defined multifunctional initiators containing peroxide functionality from a polymer substrate by autoxidalion or by ozonolysis.-0... 

It must be concluded, therefore, that the ligands do not become completely detached from the metal ion in isomerization reactions. Comparable results have been observed in the isomerization95 of potassium diaquodioxalatochromium(III) and the racemization96 of optically active potassium tris(oxalato)chromium(III) when no exchange with free ligand in solution occurs. Thus, although it is not practicable to take advantage of the desirable properties of individual isomers of 2 1 chromium and cobalt complexes of tridentate azo compounds because of the facility with which such compounds isomerize in solution, the technically important unsymmetrical 2 1 complexes are capable of practical application because they show little or no tendency to disproportionate in solution. 

In general, metal complexes of bidentate formazans have low stability towards acids and, following the comparable work on metal complexes of azo compounds, Wizinger116 was prompted to investigate tri- and tetra-dentate formazans in an endeavour to obtain metal complexes having enhanced stability. 

Both di-amino and tri-amino azo compounds are known. In these compounds in which two amino groups are in the same ring the azo group cannot be para to both and it is found that the most common form is the one in which one amino group is ortho and the other para. 

The important tri-amino azo compound is the one in which two amino groups are in one ring, ortho and para to the azo group and one amino group meta to the azo group in the other ring. The constitution of the compound is proven by its preparation from meta-phenylene di-amine, we/a-di-amino benzene. This is diazotized so that only one... 

Bismarck Brown.—The dis-azo compound obtained meta-diamino benzene dis-azo benzene meta-di-amino benzene is a dye known as Bismark brown, though the dye is probably a mixture of the dis-azo compound and tri-amino azo benzene. With the exception of aniline yellow or amino azo benzene it was the first azo dye to be made. It was first prepared by Martins in 1864, and first made as a dye in 1866. 

Not only mono-sulphonic acids but also di- and tri-sulphonic acids are known. These all undergo the general reactions of the class as discussed under the sulphonic acid derivatives of benzene (p. 519). On fusion with potassium hydroxide they yield hydroxyl derivatives and similar fusion with potassium cyanide converts them into acid nitriles. They are characterized as soluble compounds and are readily coupled with diazo compounds yielding azo compounds many of which are dyes. ... 

A phosphorus analog of aliphatic azo compounds, bis[tris-(trimethylsilyl)methyl]di-phosphene, (Me3Si)3C-P=P-CSiMe3, shows a rapid reversible one-electron reduction to its radical anion at a mercury-coated platinum electrode in DME, MeCN [85], or THF [86]. The arseneous analog is reduced similarly [86] at a potential about 0.5V less negative the anion radical is less stable than that of the phosphorus compound. 

Aromatic primary amines react with lead tetraacetate to give symmetrical azo compounds in varying yields, via hydrazo intermediates." " However, in the case of 2,4,6-tri-tert-butylaniline, reaction with lead tetraacetate in benzene at 5°C led to a mixture of three products, the formation of which can be explained by a ligand coupling process. (Scheme 7.2)... 

The main classes of initiators based on photofragmentation (scission of covalent bonds) are limited to UV applications, and they include peroxides, azo compounds, benzoin derivatives, acetophenone derivatives, ketoxime esters of benzoin, tri-azines, etc. On photolysis, these classes of initiators, depending on their wavelength of sensitivity, are able to initiate the polymerization of monomers such as methyl methacrylate in negative-tone lithographic imaging. 

Pyrroles.—Formation. A general synthesis of 2-aryl-pyrroles (112) is by cycliz-ation of the esters (111), which are obtained from unsaturated aldehydes and methyl azidoacetate. Thermolysis of the acetylene (113 Ar = p-MeC6H4) gives Al-(p-tolyl)pyrrole with the elimination of p-thiocresol. The pyrrole derivative (115) is the product of the action of benzylamine on tri-(t-butylthio)cyclopropenylium perchlorate (114). Azoalkenes combine with fi-dicarbonyl compounds or with enamines to yield derivatives of Al-aminopyrrole thus the ester (116) and ethyl acetoacetate form (117). The base-catalysed addition of methyl propiolate to toluene-p-sulphonylmethyl isocyanide, T0SCH2NC, gives the ester (118). The dipolar cyclo-adduct (120) of piperidinocyclopentene to the azo-compound (119) forms the A-(tosyl-amino)pyrrole derivative (121) and piperidine on heating. ... 

The oxidation of 4-aminoazobenzene with the UHP-acetic acid system was also investigated and the corresponding tri-azobenzene compound was formed. It appears as though the oxidative coupling reaction of the amino group preferentially occurs in contrast to the oxidation of the azo-moiety to produce the corresponding azoxy compound. Further experiments are needed to determine the facility of the azoxy formation by varying the stoichiometry of the oxidation... 

The discovery of the antibacterial action of Prontosil prompted a flurry of research activity. At the Pasteur Institute, between July and November 1935, Jacques and Therese Trefouel synthesized 44 azo compounds, of which 18 were sulfonamides Daniel Bovet and Frederic Nitti conducted animal studies on 80 compounds. On November 6, 1935, Bovet and Nitti were doing a study of seven new compounds and had an extra group of mice. They tried p-aminobenzenesulfonamide, which contained the functionality present in the other molecules being tested. They found the white compound to be active, which resulted in a breakthrough in the research that had previously been focused on dyes. In 1937, p-aminobenzenesulfonamide, by now called sulfanilamide in the United States, went on the market. ... 

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