Reactive depletion

Many aromatic compounds are sufficiently basic to be appreciably protonated in concentrated sulphuric acid. If nitration occurs substantially through the free base, then the reactivity of the conjugate acid will be negligible. Therefore, increasii the acidity of the medium will, by depleting the concentration of the free base, reduce the rateof reaction. This probably accounts for the particularly marked fall in rate which occurs in the nitration of anthraquinone, benzoic acid, benzenesulphonic acid, and some nitroanilines (see table 2.4). 

Chemical shim control is effected by adjusting the concentration of boric acid dissolved ia the coolant water to compensate for slowly changing reactivity caused by slow temperature changes and fuel depletion. Eixed burnable poison rods are placed ia the core to compensate for fuel depletion. 

The advantages claimed for organotin polymer-based antifouling paints include constant toxicant deHvery vs time, erosion rate and toxicant deHvery are controUable, no depleted paint residue to remove and dispose, 100% utilization of toxicant, polishing at high erosion rates, surface is self-cleaning, and function is continuously reactivated. 

Naphthyridines are (just as pyridines) characterized as 7r-deficient systems. Introduction of an electron-withdrawing group such as the nitro group further depletes the ring of its 7r-electrons and lowers its electron density. On account of this low electron density, nitronaphthyridines show a high reactivity to nucleophilic reagents and low reactivity to electrophiles several characterictic examples of this behavior are shown in this chapter. 

A small amount of sodium dithionite added to an aqueous medium depletes oxygen almost instantly. Due to the acidity of the reagent, a sufficiently strong buffer must be included in the medium. However, the use of dithionite is not recommended in the stages of extraction and purification because the reagent and its decomposition products are highly reactive and can cause undesirable reactions. 

Diffusion as referred to here is molecular diffusion in interstitial water. During early diagenesis the chemical transformation in a sediment depends on the reactivity and concentration of the components taking part in the reaction. Chemical transformations deplete the original concentration of these compounds, thereby setting up a gradient in the interstitial water. This gradient drives molecular diffusion. Diffusional transport and the kinetics of the transformation reactions determine the net effectiveness of the chemical reaction. 

Redispersion of gas compensates for coalescence and pressure effects negligible depletion of the reactive component or else a high level of inerts are present in the gas phase... 

Figure 5.10 In these glasses, the main phase is depleted in calcium and fluoride, which reduces Its reactivity. Acid attack occurs selectively at the phase-separated droplets which are rich in calcium and fluoride (Hill Wilson, 1988a).

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