Quinone diimines, reaction with

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. 

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... 

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. 

With the exception of studies with o-quinone mono- and diimines,41-42 which exhibit accelerated participation in [4 + 2] cycloaddition reactions with electron-rich dienophiles (Table 9-III and Scheme 9-II42a), only two additional reports of [4 + 2] cycloaddition reactions of hetero-l-aza-1,3-butadienes have been detailed [Eqs. (19) and (20)].45-46... 

Oxidative coupling reactions of p-phenylenedia-mines with amines and phenols are widely used. As can be seen in Scheme 1 p-phenylene diamine is oxidized to its quinone diimine (QDI) by potassium hexacyanoferrate(III) or a similar oxidant in a weakly basic medium. In the rate-limiting step, QDI reacts with the amine or phenol to give leuco-indamines (indophenols), which are rapidly oxidized to colored indamines (indophenols) with the aid of a QDI molecule. This reaction is chiefly used for resolving a large variety of mixtures of aromatic amines, phenols, and chlorophenols. 

Other reactions of iodine studied include the oxidation of isopropanol (for which, at pH 9.18, the rate is independent of [I2] and involves a ratedetermining loss of a proton), and the oxidation of substituted p-phenylenedi-amines to quinone diimines in a mechanism involving a two-electron step, the iodine attacking the —NR2 group. This latter work was carried out with a stopped-flow apparatus having five mixing chambers to allow premixing of selected reactants and pH jumps. 

Ketenes participate as dienes as well as dienophiles in [4+2] cycloaddition reactions. For example, several ketenes with a suitable substituent in the a-positions readily participate in [4+2] cycloaddition reactions. The substituents include unsaturated groups, a-oxo, a-thio or a-imino groups. In their role as dienophiles, ketenes participate in the reaction with dienes, azadienes, diimines and o-quinones by addition across the C=C bonds, and sometimes the C=0 bonds. The [2+2+2] adducts obtained in the reaction of ketenes with C=N double-bonded substrates (see Section 4.1.4.2) are another example of [4+2] cycloaddition reactions of ketenes. 

Reaction of quinone diimines with phosphorous acid esters... 

Oxidation H ir Colorant. Color-forming reactions are accompHshed by primary intermediates, secondary intermediates, and oxidants. Primary intermediates include the so-called para dyes, -phenylenediamine, -toluenediamine, -aminodiphenylamine, and p- am in oph en o1, which form a quinone monoimine or diimine upon oxidation. The secondary intermediates, also known as couplers or modifiers, couple with the quinone imines to produce dyes. Secondary intermediates include y -diamines, y -aminophenols, polyhydroxyphenols, and naphthols. Some of the more important oxidation dye colors are given in Figure 1. An extensive listing is available (24,28). 

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