Tetraheptylammonium

The mechanism for the nucleophilic displacement reaction of benzyl chloride with potassium cyanide has also been studied under multiphasic conditions, i.e., an scC02 phase and a solid salt phase with a tetraheptylammonium salt as the phase-transfer catalyst (PTC) (Scheme 3.8). The kinetic data and catalyst solubility measurements indicate that the reaction pathway involves a catalyst-rich third phase on the surface of solid salt phase. 

The breadth of the eompounds available ean be gauged from Table 5.40. Some of the remarkable properties of these compounds are exhibited in Tables 5.41 to 5.43, taken here from the pioneering work of Jones and Blomgren in 1989. Melting points go down as the complexity increases. Tetraheptylammonium ehloride melts at 264 K However, the more complex salts have high viscosity and low conductivity. Conductivity is reduced by the presence of aryl groups. Mixed with AlClj, liquid eutectics at 198 K can be obtained. 

Chloromethylated polystyrene-DVB (2.5 g) (1.23 meq/g) and 2 g of thiourea were refluxed with a mixture of THF ethanol (2 1) for 48 hr. The resin was then washed with water, followed by THF and benzene, to remove all excess soluble reagents and byproducts. The resin was then suspended in a 50 ml of benzene and 0.1 g of tetraheptylammonium chloride and 2 g of sodium hydroxyde in 10 ml of deionized and degassed water were added. The three-phase mixture was refluxed under N2 for 48 hr. After filtration, washings with THF, water, THF 6N HC1 (3 1), water, THF, acetone, methylene chloride, and finally methanol were carried out. The resulting resin was dried under vacuum. 

Mobile phase MeCN 6.5 mM tetraheptylammonium bromide 100 mM pH 7.0 phospihate buffer 100 mM pH 5.0 citrate buffer 40 55.2 4.4 0.4 Flow rate 1 Iqjection volume 20 Detector UV 271... 

Most reactions that have been investigated using PTC in supercritical fluids have been solid-SCF systems, not liquid-SCF. The first published example of PTC in an SCF is the displacement reaction of benzyl chloride 1 with potassium bromide in supercritical carbon dioxide (SCCO2) with 5 mol % acetone, in the presence of tetraheptylammonium bromide (THAB) [19-20] (Scheme 4.10-1) to yield benzyl bromide 2. The effects on reaction rate of traditional PTC parameters, such as agitation, catalyst type, temperature, pressure, and catalyst concentration were investigated. The experimental technique is described below. PTC appeared to occur between an SCF phase and a solid salt phase, and in the absence of a catalyst the reaction did not occur. With an excess of inorganic salt, the reaction was shown to follow pseudo-first order kinetics. 

This reaction is catalyzed by tetraheptylammonium chloride. The solvent is supercritical carbon dioxide, with acetone as a cosolvent. 

The 300 mL stainless steel reactor was loaded in a glovebox under a nitrogen atmosphere to exclude atmospheric water. Placed in the reactor were 5.09 g of KCN, 0.175 g of tetraheptylammonium chloride, and 9.75 mL of acetone. These quantities correspond to a salt amount equal to five times that of the benzyl chloride on a molar basis, a catalyst amount of 2.5 mol % of the benzyl chloride, and 5 mol % acetone based on the solvent. The reactor was then sealed, and the contents were stirred overnight at 200 rpm at 35 °C and atmospheric pressure. 

The nucleophilic displacement of benzyl chloride with solid potassium bromide [54] or potassium cyanide [55] has been carried out with tetraheptylammonium salts as catalysts. The kinetic data together with the determination of catalyst solubility clearly indicate that the reaction proceeds through formation of a catalyst-rich third phase on the surface of the solid salt phase, where the reaction occurs. The low solubilities of traditional PTC catalysts in the CO2 phase do not hamper the process but facilitate catalyst removal and recovery. 

HCO4) and that this species will perform epoxidations of hydrophilic alkenes in the presence of base [46]. To reduce transport limitations between the hydrophobic alkenes in CO2 and the reactant formed in situ in the aqueous layer, phase-transfer catalysts such as tetraheptylammonium bromide may be used and increase the reaction rate. Similarly to what has been found for conventional SCCO2/H2O systems, it is also possible to increase the interfacial area by addition of fluorinated surfactants. 

Other strategies to cope with hydrophobic compounds include the addition of neutral surfactants or neutral CDs to SDS micelle systems, use of bile salts, and by exploring solvophobic association with tetrahexyl- or tetraheptylammonium ions (added as perchlorate salt [THxAP] or bromide salt [THpAB]) or dioctylsulfosuccinate (DOSS). 

The first reported example of a PTC reaction carried out in a supercritical fluid was the nucleophilic displacement of benzyl chloride with solid potassium bromide, in the presence of tetraheptylammonium bromide (THAB) or 18-crown-6 as catalysts.Supercritical CO2 (SCCO2) was used as a bulk solvent, with variable amounts of acetone added in order to increase the solubility of the catalyst. The kinetics of the nucleophilic displacement was studied, and the reaction was found to follow first-order, reversible kinehcs in the case of THAB and zero-order kinetics for reactions catalyzed by 18-crown-6. 

Li and Fritz [30] studied the effect of some surfactants [i.e., tetraheptylammonium bromide (THP A), CTAB, SDS, dioctylsulfosuccinate. 

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