Quinones, applications kinetics

INTERMOLECULAR APPLICATIONS OF 0-QUINONE METHIDES (o-QMs) ANIONICALLY GENERATED AT LOW TEMPERATURES KINETIC CONDITIONS... 

A further application of flash photolysis is illustrated by the reactions of a quinone (Q). The kinetic scheme in ethanol (RH) and water is made up of a number of elementary steps, which are given in Figure 10.12. 

In chapter 7, special emphasis has been placed on the synthesis of representative polycyclic quinones and their photochromic behavior, including the spectral, kinetic, and fatigue characteristics of such systems. Potential applications are focused on recording and multiplication of images, optical memories, and gradation masking. 

An analysis of the kinetic characteristics of photochromic quinones showed that the photochromic transformations of methylnaphthoquinone, alkyl- and acyloxyan-thraquinones in solution at room temperature were observed in the microsecond range. As a consequence, these compounds may be of theoretical interest in the future. The photochromic aryloxyanthraquinones are characterized by a lifetime of the photoinduced form that reaches several minutes in solution and several hours in polymer films at room temperature, which makes them acceptable for a number of applications. In this regard, of special interest are photochromic naphthacenequi-... 

The application of the CIDEP technique to the kinetic isotope effect in the photoreduction of quinones was made by Adeleke and Wan (2). Photolyses of naphthaquinone in isopropanol and in isopropanol-dg were carried out under identical experimental conditions. Analysis of the polarization data indicates that the ratio kjj/kj = 2.6. However, in a separate series of experiments in which the naphthaquinone was photoreduced by substituted phenol and phenol-O,, the kinetic isotope effect drops to a value of kjj/kj = 1.6. 

The reaction has a wide applicability but is subject to certain interferences. In general, any material that will react with iodine in the reagent mixture will cause an interference. Common organic interferences are active carbonyl compounds, ascorbic acid, quinone, mercaptans, and diacyl peroxides (Mitchell, 1961). Several of these interferences can be eliminated or minimized by appropriate modifications to the method such as prereaction to remove interfering materials and extrapolation of the observed endpoint to the true endpoint based on kinetically slow interfering reactions. Care must also be taken to avoid introducing extraneous moisture from the atmosphere and to be sure that the reaction has reached completion. 

A comprehensive study of the free radical polymerization of methyl methacrylate (MMA) photoinitiated by anthraquinone and 2-tert-butyl anthraquinone in tetrahydrofuran has been completed by Ledwith, Ndaalio and Taylor (78). 2-tert-butyl anthraquinone is frequently used in applications (72—76) on account of its greater solubility and com-patihty with solvents and polymers but detailed kinetic and mechanism studies (78) show that anthraquinone and 2-tert-butyl anthraquinone behave in an almost identical manner. Consequently results for the former quinone only are considered here. 

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