Quinonediimine

Quinone Diels—Alder chemistry, regioselectivity in, 21 255 Quinonediimine (QDI), 19 249, 251 in chromogenic chemistry, 19 245—246... 

According to a general rule, not only dihydric phenols, but also those diamines of the p-series which still contain one hydrogen atom attached to each nitrogen, are dehydrogenated to quinone or quinonediimine with great ease. Hence in the oxidation solution emeraldine is also immediately converted into the doubly quinonoid chain... 

Aniline black which is thus obtained is hydrolysed by acids like all derivatives of quinonediimine and like the indamines, to which aniline black belongs. 

If this cleavage principle is applied to the molecule of aniline black it will be found that from it four molecules of quinone, three molecules of p-phenylenediamine, and one molecule each of aniline and ammonia arise. Since an excess of chromic acid is present, the p-phenylene-diamine is readily dehydrogenated to quinonediimine, which is hydrolytically decomposed into quinone and ammonia. The single molecule of aniline begins the cycle anew. 

The typical transformation of all p-phenylenediamine derivatives by oxidising agents in acid solution consists in a change into a salt of the quinonediimine series. The dye just observed, so called Wurster s red , was long regarded as a simple quinonimonium salt ... 

This, however, already appeared improbable when the (colourless) chloride of the simple quinonediimine became known (Willstatter). 

At this point the oxidation stage of quinonediimine has been fully reached its (very unstable) salts have scarcely any colour. The production of colour only takes place when quinonoid and benzenoid systems are present together. The molecular union of the two substances at different stages of oxidation produces the intense absorption which is a prerequisite for the formation of a dye (Willstatter and Piccard). This union need not take place in the proportion 1 1, which obtains in the present case. The relations between quinhydrone and quinone-quinol are quite similar (p. 314). 

The p-quinonediimines are the parent substances of the indamine dyes and of the tricyclic quinonoid salts of the phenazine, phenthiazine, and phenoxazine groups which are related to them. (Detailed information on this subject is to be found in special works, e.g. of Nietzki-Mayer and of Bucherer.)... 

The main dye prodncing system nsed in hair coloration involves the oxidation of a primary intermediate in the presence of a colonr coupler to produce the coloured molecule. The primary intermediates are 1,4-phenylenediamines or 1,4-aminophe-nols and the colonr conplers are 1,3-phenylenediamines or 1,3-aminophenols. The primary intermediates are oxidised by peroxides to give the colonred benzo-quinonediimines or monoimines, which react with the couplers to give indoamines or indophenols, e.g. (2.52) and (2.53), depending on the natnre and ratio of the reactants, as shown schematically in Fignre 2.20. ... 

K. T. Finley u. L. K.J. Tong, Quinonediimines and Related Compounds, in S. Patai, The Chemistry of the Carbon-Nitrogen Double Bond, S. 663-729, Interscience Publishers, New York 1970. 

The first nitrenium ion to be examined using any flash photolysis method was the 4-dimethylaminophenylnitrenium ion (131). However, the workers who carried out these experiments apparently did not consider this species to be a nitrenium ion. It was generated by pulsed Xe lamp photolysis from the corresponding azide (132, Fig. 13.64), and was detected through its absorption at 325 nm. As the resonance structure 131 implies, this nitrenium ion (or quinonediimine) is especially stable. In fact, its lifetime exceeds 100 ms at neutral pH, and it decays through hydrolysis of the C=N bond to give iminoquinone (133). 

Oxidation. A primary intermediate, i.e., a para-substituted aromatic compound such as a derivative of 1,4-diaminobenzene or of 4-aminophenol, is oxidized to a quinonediimine or quinonemonoimine, respectively. The imine then reacts with a secondary intermediate (coupler), which is a meta-substituted compound such as as a derivative of 1,3-diaminobenzene, 3-aminophenol, or resorcinol. Another oxidation step yields an indo, phenazine, or oxazine dye which is three times the size of the precursors. The mechanism of this coupling reaction is shown in Scheme 5.1. 

A limited set of phenylenediamine color developers are used. Kodak s CD-3, CD-4, and CD-6 (26-28) are the principle color developers used today [31], They are directly incorporated into the alkaline processing fluid. The methyl group in the 2-position is important for preventing side reactions and enhancing the formation of the desired dye. The phenylenediamine undergoes a two-electron oxidation to quinonediimine, which then reacts with the color couplers to form the desired chromophores [32],... 

The effects of micellization on reactivity have been investigated for a wide variety of ionic organic reactions other than those discussed previously in Sections IV and V, e.g. the Cannizzaro reaction, racemiza-tion, acid catalyzed enolization, base catalyzed hydrolysis of a,]8-un-saturated ketones, and coupling of quinonediimines with phenols. In the case of the Cannizzaro reaction of benzaldehyde (equation 43), the cationic surfactants eicosanyltrimethylammonium bromide and octa-decyltrimethylammonium bromide increased and the anionic surfactant... 

The quinonediimine (QDI) is an important species in color development since it is this that forms dye on reaction with a coupler molecule and transforms a black-and-white image into color (see Section 1.2.3). 

The reactions of quinonediimine are reviewed by Brown [33]. The quinonedii-mine (QDI) is susceptible to hydroxide ion attack and forms the quinonemonoimine (QMI) according to the mechanism shown in Eq. (23) [34]. 

Azo dyes can be formed by the self-condensation of a quinonediimine and a p-phenylenediamine [35]. The rate dependence has been found to be given by Eq. (24),... 

Scheme 1. Suggested mechanism for formation of azo dye from a quinonediimine and a p-phenylendiimine. RDS, rate determining step.

Leucoemeraldine is the formal hydrogenation product of emeraldine. As shown in reaction 12, each tetramer unit contains one reducible quinonediimine moiety. 

There are two related hydrogenation reactions for which there are requisite enthalpy of formation data p-benzoquinone to hydroquinone and p-xylylene to p-xylene. For the former reaction, the enthalpies of hydrogenation are —179 kJmol-1 (s) and —142 kJ moL1 (g). For the latter62, the gas-phase hydrogenation enthalpy is ca —192 kJmol-1. An interpolated gas-phase hydrogenation enthalpy for p-quinonediimine is ca — 167 kJ mol-1. Based on the benzoquinone/hydroquinone example, the solid-phase value presumably would be more negative. The enthalpy of formation of solid emeraldine thus would be at least 534 kJmol-1. 

---