Alkylation, SCFs

The utility of SCFs for PTC was demonstrated for several model organic reactions - the nucleophilic displacement of benzyl chloride with bromide ion (26) and cyanide ion (27), which were chosen as model reversible and irreversible Sn2 reactions. The next two reactions reported were the alkylation and cycloalkylation of phenylacetonitrile (28,29). Catalyst solubility in the SCF was very limited, yet the rate of reaction increased linearly with the amount of catalyst present. Figure 5 shows data for the cyanide displacement of benzyl bromide, and the data followed pseudo-first order, irreversible kinetics. The catalyst amounts ranged from 0.06 (solubility limit) to 10% of the limiting reactant, benzyl chloride. 

A number of distonic halonium-based dications are also known and their properties are often superelectrophilic.81 The chemistiy of halonium ions was thoroughly reviewed, thus only a few aspects are described here. Alkylation of dihaloalkanes with methyl and ethyl fluoroantimonate (CHsF-SbFs-SCF and CHsCE F-SbFs-SCh) gives the monoalkylated halonium ions and/or the dialkylated dihalonium ions, depending on the reaction conditions. Iodine shows an unusual ability to stabilize positive... 

GC-MS (Hitachi M-80, Japan) was applied to determine the existing components in both alkylation products. Besides the main products ethylbenzene (EB) and diethylbenzene (DEB), triethylbenzene (TrEB) and tetraethylbenzene (TeEB) were found in the LP alkylation products. However, in the SCFP alkylation products, in addition to the LP alkylation products, 2-ethylbiphenyl (EBP), 2,2-biethylbiphenyl (BiEBP) and 1,5,6-trimethylanthracene (TMA) were found, as shown in Table 2. Benzene as a solvent was used to dissolve the deposited component on partially deactivated catalyst. Trace amounts of EBP, BiEBP and TMA were also found in the solution to evidence the presence of the precursors. The authors suppose that EBP, BiEBP and DMA may be the coke precursors of the reaction which can be leached out from the catalyst surface under the SCF conditions, while in the LP alkylation the deposited precursors mainly stay on the catalyst surface and thus can not be found in the products. 

The authors also suppose that EBP, BiEBP and TMA may be the coke precursors of the reaction that are leached out from the catalyst surface under the SCF alkylation condition, but... 

From computations with basis sets of the polarized 6-3IG type, at SCF and MP2 levels, the change from formic acid dimer to acetic acid dimer has only a very minor influence upon the energetics of binding . This conclusion is indeed verified by resonant laser photoacoustic spectroscopic measurements i 79,181,182 which find further that trifluoroacetic and propionic acid dimers have a very similar binding enthalpy to formic dimer. One may extrapolate that the formic acid dimer Fl-bond energy is probably applicable for most carboxylic acids with alkyl chains replacing the CH group. 

The effect of a progressively larger alkyl group replacing one of the hydrogens of water was probed by considering a series of alcohols . Study was restricted to cyclic trimcrs, at the SCF level with a 6-3IG basis set, and with no correction for superposition error. The... 

The effect of alkyl groups on the UV spectra of 1,2-dithiolium cations and the charge-transfer spectrum with iodide as donor have been compared with the results of SCF-LCI calculations. 

The photoelectron spectrum and ab initio SCF calculations of sulphur dichloride have been presented, and an assignment of observed states of the SCF radical cation was attempted.71 For the SC12 ground state the calculated dissociation energy, dipole moment, total atomic population, and total d -orbital population were given. The photolysis of sulphur monochloride with a series of saturated aliphatic hydrocarbons has been shown to yield alkyl chlorides, di- and poly-sulphides, hydrogen chloride, and elemental sulphur.72... 

It is necessary to use strong alkylating agents such as Merwein salts to alkylate l,2-dithiol-3-ones (60)110 (Eq. 3). A series of 3-ethoxy-1,2-dithio-lylium fluoborates was prepared and their visible spectra compared to data calculated by means of the SCF-PPP method.110... 

Carbon dioxide is not the only nonflammable, biocompatible, and widely available solvent. Let us not forget about water. In particular, supercritical water oxidation and related reactive processes have shown a tremendous capacity for reducing toxic chemicals to innocuous constituents. Akiya and Savage have authored a recent review. Of particular interest is the section on hydrolysis in SCF water. Numerous references are tabulated according to chemical family. With regard to the more toxic compounds, Klein et al. have been especially active for many years and Tester et al. have focused on alkyl halides. ... 

SCCO2 is largely used to process food (extraction or fractionation), but other applications, such as the fluoropolymer synthesis by DuPont, hydrogenation or alkylation by Thomas Swan, coatings by Union Carbide, and polyurethane processing by Crain Industries, are still in development [111]. The application of supercritical fluids (SCFs) as reaction media with homogeneous catalysts has been mainly investigated on a laboratory scale. 

Initial experiments performed at the INL compared different catalysts, fluids, and operating conditions to determine the effect of SCF on solid acid catalyst alkylation (5). Three sets of studies were performed a catalyst comparison using six different catalysts (i.e., two zeolites, two sulfated metal oxides, and two Nafion catalysts) with methane as a cosolvent an exploration of the effect of varying methane addition on alkylation using a USY zeolite catalyst and a study of the effect of seven cosolvents (i.e., three hydrocarbons, two fluorocarbons, carbon dioxide, and sulfur hexafluoride) at L, ML, NC-L, and SCF conditions on the USY catalyst performance. 

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