Sodium bromide surface conditions

A verification of the interpretation of the surface of sodium bromide, when prepared under usual conditions, as a dual distribution is again provided by a new preparation under anhydrous conditions of a sample of the sublimed crystals, which when used as an adsorbent shows evidence of type 2 surface only. The... 

Sodium cyanide does not dissolve in butyl bromide. The two reactants contact each other-only at the surface of the solid sodium cyanide, and the rate of reaction under these conditions is too slow to be of synthetic value. Dissolving the sodium cyanide in water is of little help because butyl bromide is not soluble in water and reaction can occur only at the interface between the two phases. Adding a small fflnount of benzyltrimethyl-fflnmonium chloride, however, causes pentanenitrile to form rapidly even at room temperature. The quaternary ammonium salt is acting as a catalyst it increases the reaction rate. How ... 

Chemical kinetics deductions are, in some circumstances, possible from a reaction system using a dispersed solid. If the solid is entirely insoluble, for example a supported catalyst, true surface kinetics can be obtained provided (i) it can be shown that the chemical reaction on the surface is much slower than the associated mass transfer, and (ii) the surface area of the solid can be obtained. These conditions applied in the case of the oxidation of an aqueous solution of hydrazine using a dispersion of insoluble barium chromate [16]. Another case is where it can be shown that an increase in the amount of the solid component does not increase the reaction rate. In this case, exemplified by the formation of benzyl acetate from benzyl bromide and solid sodium acetate in toluene solvent, it is likely that the reaction occurs in the solution phase and that the reaction is proceeding at the saturation concentration of the solid reactant in the liquid phase [17]. 

Several solvent-free N-alkylation reactions have been reported which involve use of tetrabutylammonium bromide (TBAB), as a phase-transfer agent, under micro-wave irradiation conditions, an approach that is developed in Chapter 6 [36]. An experimentally simple microwave-assisted solvent-free N-arylation of primary amines with sodium tetraphenylborate or arylboronic acids, promoted by inexpensive cupric acetate on the surface of KF-alumina, has been reported. The reaction is selective for mono-N-arylation and a variety of functional groups are tolerated in the process (Scheme 8.4) [37]. 

Temperature can also alter wettability by affecting either the surfactant or the surfactant-surface adsorption characteristics. Ziegler et al. [69] reported that the adsorption of a nonionic (nonylphenoxypolyethanol) decreased with temperature increase for low concentrations, whereas the opposite was true for high concentrations. Noll et al. [66] reported adsorption calorimetry results that indicated an increase in temperature decreased adsorption for sodium dodecylsuUate (anionic) and decyltrimethy-lammonium bromide (cationic) surfactants regardless of surface wettability. Similar results were reported for nonionic commercial surfactant (Triton X-100) except for adsorption on an oil-wet surface. These trends were eonsistent with an increase in adsorption associated with conditions that caused a decrease in surfactant solubility in solution. 

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