HF/SbFs

Whereas superaeid (HF/BF3, HF/SbF, HF/TaF FS03FI/SbF3, etc.)-eatalyzed hydroearbon transformations were first explored in the liquid phase, subsequently, solid aeid eatalyst systems, sueh as those based on Nafion-H, longer-chain perfluorinated alkanesulfonic acids, fluorinated graphite intercalates, etc. were also developed and utilized for heterogeneous reactions. The strong acidic nature of zeolite catalysts was also successfully explored in cases such as FI-ZSM-5 at high temperatures. 

All lation with Alkanes. Superacids such as HF-SbF abstract hydride ion from alkanes to form carbocations at low temperatures. The... 

Superacids such as HF-SbF effect cyclo alkylation of aryl alkyl ketones to give tetralone derivatives (58). Tandem iatramolecular cyclo alkylatioas can be achieved when functional groups are located ia close proximity (59). 

Carbocations generated from alkanes using superacids react with carbon monoxide under mild conditions to form carboxyUc acid (188). In this process isomeric carboxyUc acids are produced as a mixture. However, when the reaction is mn with catalytic amounts of bromine (0.3 mmol eq) in HF-SbF solution, regio-selective carboxylation is obtained. / -Propane was converted almost exclusively to isobutyric acid under these conditions. 

Acid-cataly2ed hydroxylation of naphthalene with 90% hydrogen peroxide gives either 1-naphthol or 2-naphthiol at a 98% yield, depending on the acidity of the system and the solvent used. In anhydrous hydrogen fluoride or 70% HF—30% pyridine solution at — 10 to + 20°C, 1-naphthol is the product formed in > 98% selectivity. In contrast, 2-naphthol is obtained in hydroxylation in super acid (HF—BF, HF—SbF, HF—TaF, FSO H—SbF ) solution at — 60 to — 78°C in > 98% selectivity (57). Of the three commercial methods of manufacture, the pressure hydrolysis of 1-naphthaleneamine with aqueous sulfuric acid at 180°C has been abandoned, at least in the United States. The caustic fusion of sodium 1-naphthalenesulfonate with 50 wt % aqueous sodium hydroxide at ca 290°C followed by the neutralization gives 1-naphthalenol in a ca 90% yield. 

There has been considerable discussion about the extent of hydration of the proton and the hydroxide ion in aqueous solution. There is little doubt that this is variable (as for many other ions) and the hydration number derived depends both on the precise definition adopted for this quantity and on the experimental method used to determine it. H30" has definitely been detected by vibration spectroscopy, and by O nmr spectroscopy on a solution of HF/SbFs/Ha O in SO2 a quartet was observed at —15° which collapsed to a singlet on proton decoupling, 7( 0- H) 106 Hz. In crystalline hydrates there are a growing number of well-characterized hydrates of the series H3O+, H5O2+, H7O3+, H9O4+ and H13O6+, i.e. [H(0H2) ]+ n = 1-4, Thus... 

As a consequence, salts of H3O2" cannot be prepared from aqueous solutions but they have been obtained as white solids from the strongly acid solvent systems anhydrous HF/SbFs and HF/AsFj, e.g. ( 5)... 

Calculation of the second-order rate constant of carbonylation, kg, and the equilibrium constant, K = [t-C4H9CO+]/[t-C4H ][CO] = A c/fcD> requires knowledge of the concentration of CO. The constant a in Henry s law Pco = [CO] was determined to be 5-3 litre mole atm in HF—SbFs (equimolar) and 53 litre mole atm in FHSOs—SbFs (equimolar) at 20°C. From the ratio [t-C4HBCO+]/[t-C4HJ"] at a known CO pressure, values for k and K were obtained. The data are listed in Table 1, which includes the values for the rate and equilibrium constants of two other tertiary alkyl cations, namely the t-pentyl and the t-adamantyl ions (Hogeveen et al., 1970). 

The HF-SbFs system is known to be a superacid H34). The possible relevance of this to the intercalation process was pointed out by Vogel V12), who first reported on the extremely high electrical conductivity of graphite-SbFj measured normal to the crystallographic c-axis. The measured conductivity was approximately 40 times that of pristine graphite, and 50% greater than that of pure copper. Other workers... 

Figure 27. H-carbonium ion-like transition states for methane, ethane, propane and isobutane protonation by HF/SbFs.

Brouwer and Mackor (1964) found that concentrated and stable solutions of a series of tertiary alkyl cations can be prepared in HF-SbFs and their proton magnetic resonance spectra were recorded. The t-butyl, t-pentyl and t-hexyl cations were observed in this solvent system. The spectra were identical with those obtained previously in SbFs and FSOsH-SbFs solvent systems. 

Brouwer, D.M. (1968) HF-SbFs catalyzed isomerization of n-butane-1-13C. Recueil, 87. 

Fluorination of vinorelbine was thus performed in super acid medium (HF-SbFs). A super electrophilic agent, such as a chloromethyl or a Br+ cation is generated in s/fu from a chloromethane (CHCI3, CCI4) or from N-Bromo Succinimide (NBS). It is able to abstract a hydrogen from the protonated alkaloid, leading to a cation that can be trapped by an halide anion present in the medium [105,106], Difluorination remarkably occurs selectively at C-4 of the clavamine fragment (Fig. 37) [105]. 

Fluorination of cinchona alkaloids has also been investigated. For instance, fluorination of quinine acetate under similar superacidic conditions (HF—SbFs/CHCls) affords a mixture of difluorocompounds in the 10 position that are ephners in 3 (60% yield, 1 1 ratio). This reaction involves a mechanism similar to the one described earlier (protonation, isomerization of carbenium ions, and Cl— F exchange). Curiously, when the reaction is performed on quinine itself, fluorination does not occur and an unprecedented rearrangement takes place (Figure 4.51). ... 

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