Hydroquinone experimental concentrations

FIG. 9 Experimental concentration profile of hydroquinone (HQ) above a hair follicle in hairless mouse skin. The experiment corresponds to diffusion of HQ through the hair follicle. (Donor solution 0.2 M HQ and 0.2 M NaCl receptor solution 0.2 M NaCl.) The solid fine corresponds to the best fit of Eq. (10) to the data. (From Ref. 27.)... 

Thus, the available evidence indicates that little or no adsorption of hydroquinone by silver occurs. Rabinovich s data are unacceptable because of the large experimental errors involved. The possible amount of adsorption indicated by the data of Perry, Ballard, and Sheppard does not exceed the limits of error in their analytical determination of hydroquinone and could not under any circumstances cover more than a small fraction of the silver surface. The kinetics of the reaction between hydroquinone and silver ions do not indicate adsorption of the reducing agent, although the first-order dependence of rate on concentration is not incompatible with weak adsorption. It seems unlikely, accordingly, that adsorption of hydroquinone by silver plays a role of any consequence in the silver catalysis of the reaction between hydroquinone and silver ion. 

In the case of semiconductor assisted photocatalysis organic compounds are eventually mineralized to carbon dioxide, water, and in the case of chlorinated compounds, chloride ions. It is not unusual to encounter reports with detection of different intermediates in different laboratories have been observed. For example, in the degradation of 4-CP the most abundant intermediate detected in some reports was hydroquinone (HQ) [114,115,123], while in other studies 4-chloro-catechol, 4-CC (3,4-dihydroxychlorobenzene) was most abundant [14,116-118, 121,163]. The controversy in the reaction intermediate identification stems mainly from the surface and hydroxyl radical mediated oxidation processes. Moreover, experimental parameters such as concentration of the photocatalyst, light intensity, and concentration of oxygen also contribute in guiding the course of reaction pathway. The photocatalytic degradation of 4-CP in Ti02 slurries and thin films... 

Fig. 31. Packing density of hydroquinone versus HQ concentration at polycrystalline Pt electrodes. Experimental conditions electrode potential, 0.2 V (vs. Ag/AgCl) at pH = 0 or - 0.2 V at pH = 7 (F only) electrolyte was 1 M HC104 or 1 M NaC104 (F only) temperature was 23 1°C. Reprinted from ref. 63.

The semiquinone radicals are produced by base-induced oxidation of 1,4-dihydroxy-benzene (hydroquinone) or 1,2-dihydroxybenzene (catechol) by molecular oxygen, present in dissolved form. Radical concentration will increase over a period of time as the oxidation reaction proceeds and then decay as radical-radical reaction and other processes destroy the anions. Rates for these processes will depend on temperature, concentration of the dihydroxybenzene, and other parameters, so some experimentation may be necessary to obtain optimal spectra. 

Figure 7. Decay of electron donor concentration as measured at pH 4.8 and as calculated by numerical simulation with dependence on n. Experimental signal-same conditions as in Figure 4. Because the concentration of silver ions after the puke is smaller than that of hydroquinone, the ordinate of the experimental plot is (OD-OD j/ODt=o- Numbers next to simulation curves correspond to n. The value of Is 2.25 X JO mol The best adjustment unth numerical simula-...

Fig. 20.1. Concentration trends during phenol electrolysis on a BDD anode ( ) phenol, (A) benzoquinone, (0) hydroquinone, (O) catechol, and (x) total organic carbon (TOC). The experimental conditions were electrolyte, 1 M HCIO4 initial phenol concentration, 20 mM temperature, 25°C current density, 5 mA cm 2 anode potential, 2.5 0.1 V vs. SHE.

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