Alkylammonium ions, counterion

Foreign cations can increasingly lower the yield in the order Fe, Co " < Ca " < Mn < Pb " [22]. This is possibly due to the formation of oxide layers at the anode [42], Alkali and alkaline earth metal ions, alkylammonium ions and also zinc or nickel cations do not effect the Kolbe reaction [40] and are therefore the counterions of choice in preparative applications. Methanol is the best suited solvent for Kolbe electrolysis [7, 43]. Its oxidation is extensively inhibited by the formation of the carboxylate layer. The following electrolytes with methanol as solvent have been used MeOH-sodium carboxylate [44], MeOH—MeONa [45, 46], MeOH—NaOH [47], MeOH—EtsN-pyridine [48]. The yield of the Kolbe dimer decreases in media that contain more than 4% water. 

Whilst cations such as Fe +, Co +, Mn and Pb lower the yield in the Kolbe electrolysis, alkali and alkylammonium ions have no effect and are therefore preferably used as counterions for the carboxy-late. 

The mechanism is almost the same with nucleophiles like ammonia or amines with the only difference that a salt is formed and an extra step is needed to gain the free amine. For example, consider the reaction between ammonia and 1-iodopropane (Fig. G). Ammonia s nitrogen atom is the nucleophilic centre for this reaction and uses its lone pair of electrons to form a bond to the alkyl halide. Due to this, the nitrogen will effectively lose an electron and will gain a positive charge. The C-I bond is broken and an iodide ion is formed as a leaving group, which then acts as a counterion to the alkylammonium salt. 

Alkylammonium salts are typical cationic surfactants. The adsorption and the properties of the monolayers formed by these salts at water-air and water-oil interfaces have frequently been investigated [11, 24, 36, 37, 46, 63]. Mostly the adsorption of alkylammonium cations from the aqueous phase was studied. Special attention was paid to the relation between the structure of alkylammonium cations, their surface-active properties and the monolayer structure. Less attention was given to the influence of the anion nature of alkylammonium salt adsorption from the non-aqueous phase and competitive adsorption of counterions in cationic monolayers at the water-oil interface, although these problems are vital for understanding the mechanism of liquid ion-exchange extraction. 

The most detailed study of the interaction between inorganic ions and insoluble cationic monolayers was conducted by Goddard et al. [69-72]. A specific interaction was observed between anions and the monolayer of alkylammonium cations. Its value depends on the nature of the anion with the exception of the ion of fluorine. Only in the case when F is taken as a counterion, the dependence of the surface pressure on the area per molecule in the monolayer obeys the Davis equation of state for the charged monolayers. As the counterion radius decreases, the surface pressure on a given area... 

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