Ion-pair mediated derivatization

Extractive alkylation processes utilizing ion-pair distribution have been used in organic synthesis [61], as well as in derivatization for gas chromatographic assay. The technique is suitable for organic compounds containing active hydrogen, which are particularly reactive as ion-pairs in non-polar solvents. 

Carboxylic acids can be reacted with pentafluoro-benzyl bromide after extraction as ion-pairs with symmetrical quaternary ammonium ions at pH 7-9 [62,63]. The same process can be applied to phenols extracted at more alkaline pH values [26,27]. Xanthine derivatives 

When the extractive alkylation is carried out from a strongly alkaline aqueous phase, the counter-ion, a quaternary ammonium ion, is extracted into the organic phase as well, as a hydroxide ion-pair. This may improve the reactivtiy of the analyte but sometimes decreases the stability of the alkylated reaction product. The hydroxide will also react with the chloroalkane solvent used [67]. 

The size and extraction capability of the counter-ion will, as in other kinds of ion-pair extraction, govern the extent of extraction and in many instances the reaction rate and the recovery [65]. This is of particular importance when side reactions occur and the reaction time is critical owing to the limited stability of the alkylating agent [67]. In many instances a low ion-pair distribution ratio is sufficient, since alkylated acid molecules are continuously replaced by the distribution of new ones from the aqueous phase in order to maintain equilibrium. 

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