Reactions catalyzed by hydrogen fluoride

Tertiary alkyl halides undergo a series of reactions when treated with hydrogen fluoride. f-Amyl chloride by means of reactions catalyzed by hydrogen fluoride yielded a series of teritary chlorides including f-butyl chloride (Simons et al., 35). t-Butyl chloride gives the same series of... 

The powerful dehydrating property of hydrogen fluoride would cause it to be expected to assist in reactions in which water is a product. Such dehydration reactions would not in the true sense be catalytic. However, as the addition of water in the case of the hydrolysis of esters (Simons and Meunier, 66) has been shown to be catalyzed by hydrogen fluoride, the catalytic powers of hydrogen fluoride are probably involved in the reverse reaction, as a catalyst must necessarily accelerate the reverse reaction if it does so for the forward one. For this reason some of these reactions are included here. 

Fluorinated organometallics can be prepared by the direct addition of metal fluorides across the double bond of fluorinated alkenes. Additions of mercury(II) fluoride, ar-senic(III) fluoride " and silver(I) fluoride " " have been reported (sec Table 35). These reactions are catalyzed by hydrogen fluoride. arsenic(III) fluoride or antimony(V) fluoride. 

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). 

The hydrogen fluoride catalyzed fluorination of norbornene by xenon difluoride at room temperature leads to a mixture of at least seven components,39 but under milder conditions (— 78 to 26 C, 22 hours) the reaction affords a mixture of two main products 2-e,xo-5-cxo-difluoro-norbornane and 2-c-wfo-5- Yo-difluoronorbornane, ratio 2 1, in a total yield of 51-76%. If the same reaction is carried out in a limited temperature range between — 46 and — 39 C the yield of these products decreases, their ratio becomes equal, and the main product is 2-exo-l-ff //-difluoronorbornane (42 %).40 The structure dependence of the fluorination products of norbornene with xenon difluoride was studied. Solvent, temperature, reaction duration, catalyst (hydrogen fluoride, boron trifluoride, trifluoroacetic acid, pentafluorobenzenethiol) and the routes of product isomerization were analyzed.41-42... 

The reactions catalyzed by Lewis acids are conducted for 10-20 hours at — 20 C to give hypochlorites in almost quantitative yield.82 Chlorine monofluoride activated by hydrogen fluoride to enhance its electrophilicity transforms the carbonyl function in esters of carboxylic acids to a difluoromethyl group. The reactions are carried out by passing 2molar equivalents of chlorine monofluoride gas through a solution of the ester in an equal volume of hydrogen fluoride at - 70 to - 30°C.83... 

Pentafluorophenyl sulfone is highly reactive even at room temperature. The reaction is catalyzed by potassium fluoride. It activates the phenol group and acts as a base to absorb the hydrogen fluoride, which is a byproduct of the polycondensation. By adjusting the feed ratio of monomers, the refractive index and crosslinking density of the polymers can be readily controlled. ... 

Sulfur tetrafluoride [7783-60-0] SF, replaces halogen in haloalkanes, haloalkenes, and aryl chlorides, but is only effective (even at elevated temperatures) in the presence of a Lewis acid catalyst. The reagent is most often used in the replacement of carbonyl oxygen with fluorine (15,16). Aldehydes and ketones react readily, particularly if no alpha-hydrogen atoms are present (eg, benzal fluoride [455-31-2] from benzaldehyde), but acids, esters, acid chlorides, and anhydrides are very sluggish. However, these reactions can be catalyzed by Lewis acids (HP, BF, etc). 

Catalysis. Catalytic properties of the activated carbon surface are useful in both inorganic and organic synthesis. For example, the fumigant sulfuryl fluoride is made by reaction of sulfur dioxide with hydrogen fluoride and fluorine over activated carbon (114). Activated carbon also catalyzes the addition of halogens across a carbon—carbon double bond in the production of a variety of organic haUdes (85) and is used in the production of phosgene... 

Ben zotricbl oride is hydrolyzed to benzoic acid by hot water, concentrated sulfuric acid, or dilute aqueous alkaH. Benzoyl chloride [98-88-4] is produced by the reaction of benzotrichloride with an equimolar amount of water or an equivalent of benzoic acid. The reaction is catalyzed by Lewis acids such as ferric chloride and zinc chloride (25). Reaction of benzotrichloride with other organic acids or with anhydrides yields mixtures of benzoyl chloride and the acid chloride derived from the acid or anhydride (26). Benzo triflu oride [98-08-8] is formed by the reaction of benzotrichloride with anhydrous hydrogen fluoride under both Hquid- and vapor-phase reaction conditions. 

Elsewhere the author has published examples of the use of hydrogen fluoride to catalyze the alkylation of benzene using a variety of alkylating agents (Simons, 22, 23, 24). The breadth and scope of the catalytic power of hydrogen fluoride can be better obtained by a more complete examination of the alkylations now published using this catalyst. For reasons of organization, the subject is divided into aromatic and aliphatic reactions. 

The use of additional substances to increase the activity of a catalyst is a well known phenomenon. Hydrogen chloride or traces of water are known to promote aluminum chloride catalyzed reactions. In the same way the reaction of isoparaffins with olefins has been shown to be catalyzed by boron trifluoride in the presence of nickel powder and with water as the promoter (Ipatieff and Grosse, 76). Hydrogen fluoride can take the place of the water and thus serve as the promoter. 

Considerations of mechanism despite their difficulties are extremely valuable and productive. The discovery of the catalytic properties of hydrogen fluoride for condensation reactions came about from considering the mechanisms of certain organic reactions coupled with a knowledge of the chemical and physical properties of hydrogen fluoride. That fundamental acidity is involved in the catalytic properties of hydrogen fluoride is confirmed by the fact that hydrogen chloride under appropriate conditions can catalyze some of the same reactions (Simons and Hart, 81). 

Fortunately a hydrogen fluoride catalyzed reaction capable of being followed kinetically by precise quantitative measurements has been found. (Sprauer and Simons, 82.) The reaction of tertiary butyl chloride with toluene at 25°C. is quantitative within the precision of the measurements to yield p-f-butyltoluene when the toluene is in large... 

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