Phase transfer reagents

It should be emphasized that ionic liquids are simply organic salts that happen to have the characteristic of a low melting point. Many ionic liquids have been widely investigated with regard to applications other than as liquid materials as electrolytes, phase-transfer reagents [12], surfactants [13], and fungicides and biocides [14, 15], for example. 

The use of tetraoctylammonium salt as phase transfer reagent has been introduced by Brust [199] for the preparation of gold colloids in the size domain of 1-3 nm. This one-step method consists of a two-phase reduction coupled with ion extraction and self-assembly using mono-layers of alkane thiols. The two-phase redox reaction controls the growth of the metallic nuclei via the simultaneous attachment of self-assembled thiol monolayers on the growing clusters. The overall reaction is summarized in Equation (5). 

Pt-catalyzed hydration of various aliphatic and aromatic alkynes under phase transfer conditions in (CH2C1)2/H20 in the presence of Aliquat 336 led to either a Markovnikov product, mixtures of two ketones, or ketones with the carbonyl group positioned away from the bulky side.72 In the absence of the phase transfer reagent, Aliquat 336, hardly any reaction took place. Recently, a hydrophobic, low-loading and alkylated polystyrene-supported sulfonic acid (LL-ALPS-SO3H) has also been developed for the hydration of terminal alkynes in pure water, leading to ketones as the product.73 Under microwave irradiation, the hydration of terminal arylalkynes was reported to proceed in superheated water (200°C) without any catalysts.74... 

Yordanov, A. T. Roundhill, D. M. Extraction of platinum from aqueous solution into chloroform using a 2-pyridylthio-N-oxide derivatized calix[4]arene as phase transfer reagent. Inorg. Chim. Acta 1997, 264, 309-311. 

Eugenol undergoes MW-assisted isomerization to isoeugenol under solvent-free condition in the presence of potassium tert-butoxide, t-BuOK, and a catalytic amount of phase transfer reagent [34]. 

Two phase reduction (Brust synthesis) This method is usually employed to make organic soluble quantum clusters [8]. This method consists of two steps. The first is the transfer of AuCLi from aqueous to the organic layer by a phase transfer reagent such as tetraoctyl ammonium bromide (TOABr). The next step is the subsequent reduction of AuCU in the presence of suitably selected ligands such as thiols, phosphines, etc. 

Addition of phase transfer reagents, i.e. phase transfer catalysis. 

Figure 8.1 A phosphine-substituted crown ether, used as ligand and phase transfer reagent...

Around 1980, Tabushi and coworkers used the lipophilized, DABCO-derived diammonium salt 52 as a phase transfer reagent for the transport of nucleotides in three-phase experiments (H2O-CHCI3-H2O) [75]. Whereas AMP was discriminated in a high degree, for ADP and ATP the acceleration rates were quite similar. The transport rates were significantly diminished for uracil and guanine nucleotides because of the low solubility of the resulting complexes. 

Notes A phase transfer reagent is a compound soluble in both an aqueous and organic phase. 

We also include crown ethers as phase transfer reagents. In these case the cation of the reactant is most likely coordinated. 

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