Hydrogen fluoride catalytic effect

Stability toward reduction makes hydrogen fluoride a good medium for different hydrogenation processes [1, 2] It is a useful solvent for the hydrogenation of benzene in the presence of Lewis acids [f ] Anhydrous hydrofluonc acid has pronounced catalytic effect on the hydrogenations of various aromatic compounds, aliphatic ketones, acids, esters, and anhydrides in the presence of platinum dioxide [2] (equations 1-3)... 

Bradfield and Stickland [40,41] determined molybdenum in plant tissue by its catalytic effect on the liberation of iodine from the reaction between potassium iodide and hydrogen peroxide. The detection limit is 0.003 pg/ml of molybdenum. Interference from iron and tungsten can be overcome by addition of ammonium fluoride, but for the greatest precision and accuracy a preliminary separation of molybdenum as its benzoin a-monoxime complex is recommended. 

The catalytic activity of hydrogen chloride was found by Tarbell and Kincaid 34g). Continuing this work, Tarbell et al. 36) showed that certain acids and bases affect the yields of urethanes obtained from a-naphthyl isocyanate and phenols. Thus, catalytic effects were observed with sodium carbonate and acetate, pyridine, triethylamine, acetic acid, trichloroacetic acid, zinc chloride, hydrogen chloride, and boron fluoride etherate. The latter catalyst and triethylamine were found to be the most effective acidic and basic catalysts, respectively. 

Materials of Construction. In a great many cases, steel is suitable for the construction of alkylating equipment, even in the presence of the strong acid catalysts, as their corrosive effect is greatly lessened by the formation of esters as catalytic intermediate products. In the petroleum industry, sulfuric acid and hydrogen fluoride are employed on a very large scale as alkylation catalysts however, these must be substantially anhydrous to be effective so steel equipment is satisfactory. Where conditions are not anhydrous, lead-lined, Monel-lined, or enamel-lined equipment is satisfactory. In a few cases, copper or tinned copper is still used, as in the manufacture of pharmaceutical and photographic products, to lessen contamination with metals. 

The alkylation of phenol with tert-butyl alcohol was carried out in the ionic liquids [BMIM][Pp6] [48], [OMIM][Bp4], and [HMIM][BF4], Comparative studies on the catalytic properties of ionic liquids, H3PO4 and some solid acidic catalysts were carried out under identical reaction conditions, and the solvent effects were studied. The use of ionic liquids was found to enhance the catalytic properties of the catalysts used [49]. However, the claim that [BMIM][PP6] alone can catalyze this reaction is uncertain, and, is probably due to the presence of traces of hydrogen fluoride in the ionic liquid [45, 46]. Dy(OTf)3 dissolved in various [BF4] and [PFg]" ionic... 

The modern industrial-scale synthesis of ibuprofen has very high atom efficiency, and it has been modified from the original synthesis to be both more environmentally friendly and more cost effective. The original method involved six synthetic steps but used stoichiometric (as opposed to catalytic) quantities of reagents, had lower atom efficiency, and produced undesirable quantities of waste. The modern alternative, on the other hand, requires just three steps, each of which is catalytic in nature. The first step employs a recyclable catalyst (hydrogen fluoride, HF) and produces almost no waste. The second and third steps each achieve 100% atom efficiency (wow ). This process truly represents an idetd benchmark for excellence in green synthesis on the industrial scale. 

Fluoride is generally determined by forming a complex with the reagents it sometimes acts as a catalyst or inhibits chemical reactions. Example, fluoride ions form stable complexes with Fe(III), thus reducing its catalytic effect in the oxidation of 2,4-diaminophenol by hydrogen peroxide. In the other case, ternary complexes can be used for fluoride determination, such as that based on La(III)-E -alizarin complexone (ALC). 

Finally, we shall consider some special problems connected with the catalytic effect of hydrogen fluoride and related species. The acid HF has a pK of 3.23, so that the species HF and F" should act as acid and basic catalysts respectively in suitable reactions. The fluoride ion does, however, differ from most basic anions in being monatomic, and the process of... 

Traces of fluoride ion have a marked catalytic effect at low pH where it is mainly present as HF. Her (87) found that, whereas the polymerization reaction is catalyzed above about pH 2 by hydroxyl ions as reported by others, at lower pH the polymerization is catalyzed by hydrogen fluoride, or more specifically the rate is proportional to the concentrations of hydrogen ions and fluoride ions (Figure 3.14). 

Water vapour formed in the reactions (7) and (8) obviously exerted a catalytic effect on the chemical transformations occurring in the blends (Simons, 1950 Prodan et al., 1976 Tret yakov, 1978). The hydrogen fluoride HF released in the reaction (12) facilitated the decomposition of initial minerals and products of thermal treatment of mining rocks, e.g. metaserpentine, forsterite, enstatite, amorphous Si02, and intermediate compounds (Ryss, 1956 Butt et al., 1965 Kogarko and Krigman, 1981). The possible interactions are summarized in the reactions (14)-(17). 

Hydrogen fluoride has been reported as having a strong catalytic effect on sulfonation and nitration reactions. ... 

The preparation of thiols by nucleophilic displacement reactions using aqueous potassium or sodium hydrogen sulphide under catalytic conditions is not particularly effective. A limited number of simple alkane thiols have been obtained under mild and neutral conditions in moderate yield (70-80%) from the reaction of bis(n-butyltin) sulphide with bromoalkanes in the presence of a ca. twofold amount of tetra-n-butylammonium fluoride [1], but there has been no exploitation of this procedure. 

Like vinyl fluorides, vinyl chlorides suffer hydrogenolysis during catalytic hydrogenation. Rhodium is claimed to effect addition of hydrogen rather than hydrogenolysis of vinylic chlorides. However, hy-... 

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