Quaternary ammonium salts with weakly basic cationics

2 Quaternary ammonium salts with weakly basic cationics 

Several approaches are possible. Complications arise if the quat contains 

Titrate with SDS in acid and alkaline solution, or with NaTPB at pH 3 and 10 or 13. The weak base titrates in the acid but not in the alkaline medium. 

Dissolve in neutral ethanol or titrate with ethanolic hydrochloric acid, either potentiometrically or to bromophenol blue, to determine the weak base. 

Extract the weak base with diethyl ether (caution flammable) from alkaline 33% ethanol. To minimise the risk of decomposing labile quats, make the solution just alkaline to phenolphthalein. If desired, titrate the quat in the aqueous layer with SDS, and weigh the extracted weak base and titrate it with acid. 

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The catalytic effect of quaternary ammonium salts in the basic liquid liquid two-phase alkylation of amines [1-3] is somewhat unexpected in view of the low acidity of most amines (pKfl>30). Aqueous sodium hydroxide is not a sufficiently strong base to deprotonate non-activated amines in aqueous solution and the hydroxide ion is not readily transferred into the organic phase to facilitate the homogeneous alkylation (see Chapter 1). Additionally, it is known that ion-pairs of quaternary ammonium cations with deprotonated amines are decomposed extremely rapidly by traces of water [4]. However, under solidrliquid two-phase conditions, the addition of a quaternary ammonium salt has been found to increase the rate of alkylation of non-activated amines by a factor of ca. 3-4 [5]. Similarly, the alkylation of aromatic amines is accelerated by the addition of the quaternary ammonium salt the reaction is accelerated even in the absence of an inorganic base, although under such conditions the amine is deactivated by the formation of the hydrohalide salt, and the rate of the reaction gradually decreases. Hence, the addition of even a weak base, such as... 

The ability of the sodium salts of weakly acidic cation exchangers to retain quaternary ammonium salts has not been fully confirmed, and neither has the ability of the same resins in the acid form to retain weak bases, although there is some experimental evidence for both. The ability of free weakly acidic and basic resins to retain free bases and acids respectively is in any case of limited use, because once some of the resin has done this it is in salt form, and able to undergo ion exchange with other salts. For this reason such resins must be placed last in any multicolumn system. 

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