Aliquat cation

In recent years, a new class of ILs based on tricaprylammonium chloride (Ali-quat 336) has been investigated. By a simple replacement of the chloride anion, several new ILs have been generated and tested for their applicability, for instance, as extracting agents for heavy metals [641]. However, difficulties arise in the course of the analysis of Aliquat-based ILs as Aliquat 336 is a mixture of quaternary ammonium cations with different alkyl chain lengths rather than a well-defined pure compound. This property makes the quantification of the Aliquat cation and hence all of its products more comphcated. On the other hand, ILs based on quaternary phosphonium cations are already in use for a varietjr of applications. So far, no apphcable LC characterization and/or purity determination of these two classes of ILs was mentioned in literature. In 2008, Stojanovic et al. [642] introduced a reversed-phase liquid chromatographic method with serially coupled diode array detection (DAD) and charged aerosol detection for... 

It is worth mentioning at this point that according to Normant et al. (1975) simple polyamines such as tetramethylethylenediamine (TMEDA) are even more active than [2.2.2]-cryptand in the benzylation of acetates in acetonitrile under liquid-solid conditions. These authors suggested that the activity was due to salt solubilization by cation complexation and not to formation of a quaternary ammonium ion since the latter showed no activity. This statement, however, is not in line with the results of Cote and Bauer (1977), who were unable to detect any interaction between K+ and TMEDA in acetonitrile. Furthermore, Vander Zwan and Hartner (1978) found Aliquat 336 (tricaprylylmethylammonium chloride) to be almost as effective as TMEDA in this reaction (Table 30). It might well be, however, that in amine-catalysed benzylation reactions the quaternary salt formed in situ acts both as a reactant and as a phase-transfer catalyst, since Dou et al. (1977) have shown that the benzyltriethylammonium ion is a powerful benzylation agent. 

The interfacial mechanism provides an acceptable explanation for the effect of the more lipophilic quaternary ammonium salts, such as tetra-n-butylammonium salts, Aliquat 336 and Adogen 464, on the majority of base-initiated nucleophilic substitution reactions which require the initial deprotonation of the substrate. Subsequent to the interfacial deprotonation of the methylene system, for example the soft quaternary ammonium cation preferentially forms a stable ion-pair with the soft carbanion, rather than with the hard hydroxide anion (Scheme 1.8). Strong evidence for the competing interface mechanism comes from the observation that, even in the absence of a catalyst, phenylacetonitrile is alkylated under two-phase conditions using concentrated sodium hydroxide [51],... 

It is noteworthy that benzyltriethylammonium chloride is a slightly better catalyst than the more lipophilic Aliquat or tetra-n-butylammonium salts (Table 5.2). These observations obviously point to a mechanism in which deprotonation of the amine is not a key catalysed step. As an extension of the known ability of quaternary ammonium halides to form complex ion-pairs with halogen acids in dichloromethane [8], it has been proposed that a hydrogen-bonded ion-pair is formed between the catalyst and the amine of the type [Q+X—H-NRAr] [5]. Subsequent alkylation of this ion-pair, followed by release of the cationic alkylated species, ArRR NH4, from the ion-pair and its deprotonation at the phase boundary is compatible with all of the observed facts. 

Other applications of supported liquid membranes have been related to metal speciation. For example, recently a system for chromium speciation has been developed based on the selective extraction and enrichment of anionic Cr(VI) and cationic Cr(III) species in two SLM units connected in series. Aliquat 336 and DEHPA were used respectively as carriers for the two species and graphite furnace atomic absorption spectrometry used for final metal determination. With this process, it was possible to determine chromium in its different oxidation states [103]. 

The so-called "trapped sites" of classical mobile-site, liquid ion exchanger electrodes belong to a category of compounds known as ion association extractants. Examples are long-chain diesters of phosphoric acid and tricaprylylmethylammonium (Aliquat) ions. The latter cation was studied extensively by Freiser and co-workers (1-3 ) in the design of anion sensors. 

A carrier can be added to the membrane phase in several ways. A common compound is Aliquat-336 (methyltrioctyl-ammonium chloride). This is a tertiary ammonium ion, i.e., permanently positively charged in ion pair with chloride and can thus be added to a suitable membrane solvent. After addition of thiocyanate ions to the donor, a negatively charged metal-thiocyanate complex is formed in the donor and can be extracted as ion pair with the Ahquat-336 cation. It was used for extraction of Cu, Cd, Co, Zn [49] and for chromate [51]. The metal ion is subsequently trapped in the acceptor using DTPA as described above and shown in Figure 12.3b. 

Mikkola J P, Virtanen P, Sjohohn R. Aliquat 336—a versatile and affordable cation source for an entirely new family of hydrophobic ionic liquids. Green Chem. 2006. 8, 250-255. 

Other results of extraction of proteins using different trialkylammonium salts differ somewhat from this tendency. Jolivalt (36) studied the solubilization of a-chymotrypsin in the Aliquat 336 system using isotridecanol as a cosurfactant. Alpha-chymotrypsin was most significantly extracted for pH above its isoelectric point but as the pH decreased below the pi, the extraction yield decreased very slowly and became negligible at 4 pH units below the pi. This means that a-chymotrypsin can be extracted in significant proportion by a cationic surfactant even when positively charged overall. 

Similar results are reported using cationic surfactants. The partition coefficient of a-chymotrypsin in Aliquat solutions decreased with increasing NaCl concentration (36). However, in order to interpret these results it is necessary to take into account that alkylmethyl ammonium salts are known to be involved in anion exchanges. Assuming an exchange equilibrium between the protein and chloride counterion, an increase of the chloride ion concentration should disfavor the extraction of the protein, following a mechanism of mass action law. 

Behr and Lehn (14) first demonstrated carrier-facilitated transport of amino acids through "liquid membranes" composed of a toluene layer floating on top of two isolated aqueous solutions. The carriers used were the quaternary ammonium salt Aliquat 336 (trioctylmethylammonium chloride) and the alkylated arylsulfonic acid dinonylnapthalenesulfonic acid. Amino acids were transported in the form of anions or cations, respectively, with the above carriers. The process is an ion-exchange process, as the carrier must exchange an ionized atom or molecule each time it forms a new ion pair (Figure 2). The net result of this type of carrier-facilitated transport process is that a solute ion is transported into the LM while an equal number of counterions are transported out of the LM. 

Niobium can be separated from Ta and other metals in HF or HCl media by extracting into CHCI3, CCI4, cyclohexane, 1,2-dichloroethane, or xylene the ion-associates, which are formed by Nb (and Ta) complexes with tetraphenylarsonium cation, TO A [8,9], DAM [10], or Aliquat 336 [11-13]. The thiocyanate complexes of Nb with triphenylphosphonium cation [14] or with amides [15] have also been extracted. 

Investigations clarified that the oxidation rate depends on the cation and anion of the ionic liquid, and among a range of ionic liquids, tetramethylammoifium hydroxide and Aliquat 336 showed the best results in the presence of Ru(PPh3)3Cl2. 

Figure 6.4 Elution curves for trivalent cations (Eu) and for Ta, Nb and Pa from Aliquat 336/Voltalef columns (1,6 x 8 mm2) in ARCA II. The activities are fed onto the column in 10 M HC1. Hus is followed by separate elutions of aTk fraction in 6 M HQ, of a Nb fraction in 4 M HQ and of a Pa fraction in 0.5 M HC1. Reproduced with permission from Paulus et al. (1999). 1999 R. Oldenbourg Verlag.

Experiments typically consisted of dispersing 70 milliliters of a 2 molar solution of sodium chloride (NaCl) in 100 milliliters of an oil phase. This oil phase consisted of a paraffinic solvent (Solvent 100 Neutral, Exxon Chemical Company), a nonionic emulsion-stabilizing surfactant (Paranox 100, Exxon Chemical Company), a cationic "carrier" - a tri-capryl quaternary ammonium salt (Aliquat 336,... 

Adogen TA 100 Aliquat 207 Ammonium, dimethyldioctadecyl-, chloride Ammonyx 2200P100 Arosurf TA 100 Arquad 218-100 Arquad 218-100P Arquad R 40 CA 3475 Cation DS Cedequat TD 75 Dehyquart DAM Dl-n-octadecyldimethylammonlum chloride Dimethyl dioctadecyl ammonium chloride ... 

Not only a wide range of cations complex with the catechol system of urushiol but the borate anion also undergoes quite strong association. Thus urushiol together with Aliquat 336 was valuable for the solvent extraction of this anion probably through the formation of 1 1 and 2 1 chelates (ref.293). 

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