Catalytic transfer phase

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Phase Transfer Catalysis is a method of conducting a chemical reaction involving anions and non-polar organic reagents.

The process is carried out in a heterophasic system (in two immiscible solvents). Anions are generated from moderately strong organic acids by the action of alkali metal hydroxide solutions or solid bases such as alkali metal hydroxides or carbonates. The concentration of the hydroxide used should be proportional to the strength of the acid used. Reactive "inorganic" anions can also be used in the form of salts. The transport of the reactants between the immiscible phases provides catalysts for phase transfer, most commonly quaternary ammonium salts.

Organic anions are produced at the interface. The catalyst enters into an ion exchange with the formed salt of the anion, resulting in an ionic pair that diffuses deep into the organic phase, where the anion can react with the electrophilic reactants present in the system. Depending on the structure of the anion and the electrophilic reagent, many types of reactions can be carried out in this system, such as alkylation and cycloalkylation, Darzens condensation, Michael reaction, etc. In this system, it is also possible to generate dihalocarbons by detaching the proton from the carbon atom connected to the halogen and subsequent cleavage of the halogen atom from the resulting α-halo-carboanion (α-elimination).

This method has several advantages compared to traditional methods. The necessity of using anhydrous reagents and solvents has been eliminated since concentrated base solutions have dehydration properties. Carboanides in the reaction medium exhibit higher nucleophilicity, as they are present in the form of tetraalkylammonium salts, where the cation-anion interaction is only electrostatic. The concentration of the produced carboanate does not exceed the concentration of the catalyst, so it is often not necessary to use solvents or they are used in small quantities.

PTC is very good in terms of green chemistry, due to the possibility of eliminating volatile organic solvents during the reaction.

Phase Transfer Catalysts

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