HF-catalyzed reaction

When the product of the HF-catalyzed reaction of benzene with l-dodecene, previously reported to be pure 2-phenyldodecane, was analyzed by gas chromatography, five evenly-spaced peaks of about the same size were observed, indicating the presence of five components, probably closely related in structure. What five compounds most likely make up this mixture, and how could you have anticipated their formation ... 

Finally, a word of caution when using [BF4] and [PF ]" ionic liquids - they are not stable and give off HF, particularly when heated in the presence of a proton source or a metal salt [21]. There are many examples of this in this chapter. An example of a HF-catalyzed reaction is ether formation from alcohols is a classic acid-catalyzed reaction. An ether formation reaction was found to occur in a range of [BF4] ionic liquids, with an example being the addition of methanol to ten-butanol to form methyl-tert-butyl ether (MTBE) [306]. The author is of the opinion that [Bp4] ionic liquids (even hydrophobic ones) can dehydrate alcohols to ether and refers to these ionic liquids as dehydrators. All that is happening here is a simple HF-catalyzed reaction. With many authors not aware of this phenomenon, they resort to all kinds of inappropriate explanations for what is occurring. 

Her advanced the hypothesis that the polymerization mechanism may involve the temporary expansion of the coordination number of silicon from four to five or six. just as in the case of OH" ion. It is not known whether the HF-catalyzed reaction is third order as in the H -catalyzed reaction in the absence of fluoride below pH 2. or... 

Regioselective Friedel-Crafts reaction with unsymmetrical alkynes was reported. A reaction of phenylacetylene with p-xylene afforded gem-diarylethylene (71) selectively (Equation 30) [35]. Zirconium triflate showed much higher catalytic activity than that of chloride. Hf-catalyzed reaction of benzene with 1-phenylpropane in ionic liquid produced 1,1-diphenylpropene (72) in excellent yield with excellent regioselectivity (Equation 31) [36]. 

My early work with acyl fluorides also involved formyl fluoride, ITCOF, the only stable acyl halide of formic acid, which was first made in 1933 by Nyesmeyanov, who did not, however, pursue its chemistry. 1 developed its use as a formylating agent and also explored formyla-tion reactions with CO and HF, catalyzed by BF3. 

As in the case of the base-catalyzed reaction, the thermodynamically most stable alkene is the one predominantly formed. However, the acid-catalyzed reaction is much less synthetically useful because carbocations give rise to many side products. If the substrate has several possible locations for a double bond, mixtures of all possible isomers are usually obtained. Isomerization of 1-decene, for example, gives a mixture that contains not only 1-decene and cis- and franj-2-decene but also the cis and trans isomers of 3-, 4-, and 5-decene as well as branched alkenes resulting from rearrangement of carbocations. It is true that the most stable alkenes predominate, but many of them have stabilities that are close together. Acid-catalyzed migration of triple bonds (with allene intermediates) can be accomplished if very strong acids (e.g., HF—PF5) are used. If the mechanism is the same as that for double bonds, vinyl cations are intermediates. 

Antimony pentachloride is a reactive Lewis acid that can be used for Friedel-Crafts reactions and some other Lewis-acid-catalyzed reactions. The HF-SbF5 system is known as magic acid, and carbocations are stabilized in this medium.353 By using the HF-SbF5 system, alkylation of acetophenone (a relatively unreactive aromatic compound) has been achieved (Scheme 87). 

Table III provides a comparison of alkylate compositions for both the liquid acid-catalyzed reactions with various feed alkenes. The data show that H2SO4 produces a better alkylate with 1-butene, whereas HF gives better results with propene or isobutylene. The products from 2-butene and also from pentenes (not shown in Table III) are nearly the same with either acid.

Because the alkylation reaction is exothermic, a considerable amount of process heat has to be removed. As HF-catalyzed processes operate at temperatures between 289 and 313 K, the reactors can be cooled with water. H2S04-catalyzed processes operate at temperatures between 277 and 291 K (Table II) and therefore require more complex cooling systems, which typically utilize the processed hydrocarbon stream itself. 

Ionic liquids containing chloroaluminate ions are strong Lewis, Franklin and Bronsted acids. Protons present in [emim][AlCl4] have been shown to be superacidic with Hammett acidities up to —18. Such highly acidic ionic liquids are, nonetheless, easily handled and offer potential as non-volatile replacements for hazardous acids such as HF in several acid-catalyzed reactions. 

Liquid-phase fluorination of methyl-substituted benzene derivatives depends strongly on the structure and concentration of the substrate, its molar ratio to xenon difluoride and the catalyst used (Scheme 32). HF-catalyzed fluorination of 1,2,4,5-tetramethylbenzene with an equimolar amount of xenon difluoride gave a small amount of 1,4-difluoro product, while reaction with two equivalents of xenon difluoride also gave the demethylated product l-fluoro-2,4,5-trimethylbenzene, which was also formed by HF-catalyzed fluorination of 1,3,4-trimethylbenzene34. In contrast, trifluoroacetic acid catalyzed fluorination is much more complex, and forms the four products l-(trifluoromethyl)-2,3,5,6-tetrametylbenzene, 2,4,5-trimethylbenzyl trifluoroacetate, l-fluoro-2,3,5,6-tetramethyl-benzene and l-(trifluoromethyl)-2,3,4,5-tetramethylbenzene, the distribution depending on the amount of trifluoroacetic acid used. Similar results were also observed in the fluorination of 1,2,3-trimethylbenzene and 1,3,5-trimethylbenzene34. 

Some organic reactions, particularly fluorination reactions, can be carried out in HF solutions. Also, because nitration is an acid catalyzed reaction, such reactions can be accomplished in HF. There are numerous other aspects to the chemistry of liquid HF that will not be described in this survey. 

Carbon monoxide can undergo base-catalyzed reactions with, for example, alcohols or secondary amines, yielding formates HCO2R or formamides HCONR2. Also, acid-catalyzed reactions of CO are known, such as the carbonyl insertion in toluene to give / -toluylaldehyde (equation 2) in the presence of HF/BF3. 

The first calculation of the complete hydroformylation cycle with Rh-phosphine catalysts (substrate = ethylene, model ligand = PH3) was published in 1997 [3]. The QM methods used are HF and MP2, respectively (cf. Section 3.1.2.1). Hybrid DFT methods such as B3LYP [4], however, are more appropriate in terms of both accuracy and efficiency [5, 6] (cf. Section 3.1.2.1). Therefore, the same model system was recalculated [7] on the level B3LYP functional/DZVP basis set [8]/quasi-relativistic pseudopotentials on rhodium [9]. Since homologous Ir catalysts are interesting alternatives from an economic point of view [10], calculations with the central metal Ir were also made. This comparative treatment is supported by the experimental assumption of a common mechanism [11], which equals the Heck-Breslow mechanism of the cobalt-catalyzed reaction [12],... 

During the production of CFC-11 and CFC-12 from the antimony-catalyzed reaction of CCl with HF, the small amount of moisture in the commercial HF is converted into COClj by reaction with the tetrachloromethane (see Section 5.2.1.2). The accumulation of phosgene... 

An alternative means of technical-scale access to fluoroarenes is the fluoroformate method. Starting from the corresponding phenol a fluoroformate is generated by reaction with carbonyl chloride fluoride and subsequently catalytically decarboxy-lated to the aryl fluoride, in the gas phase, by contact with hot platinum [80] (Scheme 2.30). A newer, greener variant of the fluoroformate process has recently been introduced by Rhodia. In this the fluoroformate is formed by the (catalyzed) reaction of the phenol with COj in HF, and the expensive platinum catalyst is replaced by an aluminum-based material. 

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