Quinone diimines

Dye formation is complex because shading is achieved by employing several developers and several couplers in the same dye bath. The process is illustrated by -phenylenediamine, which is oxidized by the peroxide to a quinone diimine. This short-Hved intermediate can react, for example, with resorcinol to yield a brownish indoaniline. Table 17 provides some insight into the many interactions that exist from just a few components. Further shading is possible by including semipermanent colorants (see Table 16), especially nitroaniline derivatives. 

Q-Flex QDI Quinone Diimine Antidegradant—Improved Mixing Chemistry Resulting in a Better Balance of Productivity and Performance... 

Several studies characterizing the reactions of alkenyl radicals with quinone dumines and quino-neimines were published in the late 1970s. Quinone dumines react with allylic radicals yielding both the reduced PPD and the alkylated product. In these experiments 2-methyl-2-pentene served as a model olefin (model for NR). Samples of the olefin and quinoneimines or quinone diimine were heated to 140°C. Isolation and analysis of products demonstrated that 40%-70% of the imine or diimine was reduced to the corresponding PPD, while 20%-50% was isolated as the alkylated product. This alkylation reaction (via an allylic radical) represents the pathway to the formation of rubber-bound antidegradant. ... 

The results of the modeling smdy of the chain transfer chemistry have been published elsewhere. Quinone diimines are predicted to be more than two orders of magnimde more reactive toward free radicals than the corresponding PPD. The reactivity of a radical with another molecule should be related to the Lowest Unoccupied Molecular Orbital (LUMO) energy of that molecule. The reaction of a radical with a PPD differs from the reaction of a radical with QDI. 

RSS 2 was mixed with N-234 carbon black without additive or in the presence of quinonedihne, or with a peptizer (dibenzamidodiphenyl disulfide, activated with a metal chelate). In the case of the peptizer, rubber and carbon black were mixed for 30 s before the addition of carbon black. In the case of the quinone diimine, carbon black and QDI were added 15 s after addition of rubber to the mixer. 

Quinone diimines are capable of reacting rapidly with radicals formed during intensive mixing. The product, a polymer-bound PPD moiety, provides a polar functionality which is capable of improving polymer-filler interactions. In general the improvements can result in modest reductions in tangent delta (rolling resistance) and modest improvements in abrasion resistance. 

A-l,3-dimethylbutyl-A -phenyl quinone diimine (6QD1) has been introduced as a multifunctional additive for diene rubbers and provides an advantage in mixing characteristics (functions as peptizer and improves scorch safety) as well as improved performance (better antioxidant activity than paraphenylenediamine antidegradants) of the end products [36]. 

The bicyclic quinone diimine 10a exhibits the same product pattern in the reaction with excess GSH as the monocyclic quinonimine 9a. Reduction results in slow formation of... 

Let us now illustrate some significant examples of the redox propensity of related (but less widely studied61) quinone diimines. As happens for 1,2-dioxolenes, such ligands also exhibit the reversible electron transfer sequence o-benzoquinone diiminejo-benzosemiquinone diimine monoanion/ o-phenylendiamine dianion illustrated in Scheme 4. 

All the couplers used in colour photography contain an active centre, e.g. a methylene group, that can react with the quinone diimine to produce the azomethine dye as shown in Figure 2.31. The couplers need to remain anchored in their respective layers. The preferred method for meeting this requirement is to have medium-sized hydrophobic groups attached to the molecules. These hydrophobic couplers are introduced into the appropriate layer as oil-in-water dispersions. ... 

The half-wave potential for the electrochemical oxidation of NADH to NAD is ca. -bO.6 V vj. SCE at pH 7. The formal potential for the NADH/NAD couple, however, is only —0.56 V. The overpotential therefore is about 1.2 V. As NAD acts as coenzyme in many enzyme-catalyzed oxidations of practical importance, it would be of interest to regenerate NAD electrochemically. For this purpose it is necessary to find a mediator system which is able to lower the overpotential. Mediator systems accepting two electrons or a hydride atom are most effective. Therefore, dopaquinone electro-generated from dopamine 2" and quinone diimines derived from diaminobenzenes applied successfully. 

The intermediate responsible for the ring closure is probably the o-quinone diimine (44). 

In the reaction of ketones" and 1,4-quinones" " with bis(trimethylsilyl)carbodiimide in the presence of titanium tetrachloride reaction occurs across the C=0 bond to give cyanoimines. An example, is the reaction of the 1,4-quinone 37 with two equivalents of the carbodiimide in the presence of TCI4 to give the quinone diimines 38. 

The decomposition of 4-chloro- or 4-methylbenzenesulfenanilides with trifluoroacetic acid leads to the complete disappearance of the initially formed A -arylbis(benzenesulfen)amides with concomitant formation of phenazines, in yields of 4-35%. and/or 1,4-quinone diimines. Similar results are obtained using boron trifluoride-diethyl ether complex. ... 

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