Hydrogen fluoride constants

The relative basicities of aromatic hydrocarbons, as represented by the equilibrium constants for their protonation in mixtures of hydrogen fluoride and boron trifluoride, have been measured. The effects of substituents upon these basicities resemble their effects upon the rates of electrophilic substitutions a linear relationship exists between the logarithms of the relative basicities and the logarithms of the relative rate constants for various substitutions, such as chlorination and... 

Because of the small size of the fluoride ion, F participates in coordination stmctures of high rank. Tantalum and niobium form stable hexafluorotantalate and hexafluoroniobate ions and hydrogen fluoride attacks these usually acid-resistant metals. Hydrogen fluoride in water is a weak acid. Two dissociation constants are... 

It is known that the order of acidity of hydrogen halides (HX, where X = F, Cl, Br, I) in the gas phase can be successfully predicted by quantum chemical considerations, namely, F < Cl < Br < I. However, in aqueous solution, whereas hydrogen chloride, bromide, and iodide completely dissociate in aqueous solutions, hydrogen fluoride shows a small dissociation constant. This phenomenon is explained by studying free energy changes associated with the chemical equilibrium HX + H2O + HjO in the solu-... 

The number of fluorine equivalents (to toluene) was varied the gas and liquid flow velocities were kept constant to maintain the same flow pattern for all experiments. Liquid products were collected in an ice-cooled roimd-bottomed glass flask containing sodium fluoride to trap the hydrogen fluoride. The flask is connected to a cooling condenser to recover the solvent. Samples were typically collected for 1 h. Waste gases were scrubbed in aqueous 15% potassium hydroxide solution. Samples were degassed with nitrogen and filtered before analysis. 

A violent explosion followed the use of magnesium perchlorate to dry wet fluo-robutane. The latter was presumed to have hydrolysed to give hydrogen fluoride which had liberated perchloric acid, explosively unstable when anhydrous. (This explanation seems unlikely in view of the large disparity between dissociation constants of the two acids). Magnesium perchlorate is unsuitable for drying acidic or flammable materials calcium sulfate would be suitable. 

Before fluorination, the dielectric constant ofpoly(bisbenzocyclobutene) was 2.8, and this value was reduced to 2.1 after plasma treatment. No data were reported in the paper on characterization of structure or properties, except for the dielectric constant of the modified poly(bisbenzocyclobutene). The authors did report that the thermal stability offluorinatedpoly(vinylidenefluoride) was inferior to the original poly(vinylidenefluoride) when treated in a similar way. One of the probable reasons for the low thermal stability is that the NF3 plasma degraded the polymer. According to their results, the thickness of fluorinated poly(bisbenzo-cyclobutene) was reduced by 30%. The same phenomenon was observed for other hydrocarbon polymers subjected to the NF3 plasma process. A remaining question is whether plasma treatment can modify more than a thin surface layer of the cured polymer Additionally, one of the side products generated was hydrogen fluoride, which is a serious drawback to this approach. 

The only measured enthalpy of vaporization is for n-butyl lithium, 107.1 2.9 kJmoU, from which the constant b(Li) in equation 4 is derived as 85 kJmoU. This is a hefty value compared to fc(OH) = 29, b(—S(0)2—) = 53 and b(CY) = 11 kJmoU. However, the oligomeric states of the organolithium liquid and gas phases are not known with certainty. This is reminiscent of problems for hydrogen-bonded species such as carboxylic acids and hydrogen fluoride. 

Apparent photosynthetic rates in plants subjected to SO2 or NO exposures with constant pollutant concentrations, as illustrated in Figure 1, characteristically dropped rapidly upon initiation of treatment to new depressed equilibrium levels which could be maintained for several ho irs. Hydrogen fluoride, conversely, caused CO2 uptake rates to decline more gradually during fumigation. Chlorine, O3 and NO2 exposures induced inhibition rate responses which were intermediate between these... 

In a later publication [ 129], using the same equipment, Liu et al. describe process improvements in the electrochemical fluorination of octanoyl chloride in which formation of polymeric tar at the anode surface was limited by addition of a mercaptan (1-methyl-1-propanethiol), and by constant current density operation (7 mA cm-2). Continuous operation was achieved by frequent additions of a solution of reactant in hydrogen fluoride. Conversion of reactant to perfluori-nated products was increased to 80%, with good selectivity. 

Computed coupling constants show moderate to large sensitivity to basis set, and accurate predictions require very llexible bases (see, for example, the hydrogen fluoride (HF) data in Table 9.7). In addition, DFT is much more robust than HF theory for predicting coupling constants, and the latter level of theory simply should not be used for this purpose. 

A. A. Bineau9 found that during the boiling of a cone. aq. soln. of hydrofluoric acid an excess of hydrogen fluoride escapes until there remains a soln. with a constant b.p., 130°, and a constant composition corresponding with about 36 per cent. HF. In an analogous way, if dil. soln. are distilled, the first fractions are particularly rich in water, this continues until there remains an acid with the same constant b. temp, and the same constant composition. Similarly, if the cone, or dil. acid is allowed to stand over slaked lime, the former becomes more dil. and the latter more cone. 

The acidity scale in anhydrous hydrogen fluoride has been the subject of electrochemical investigations by Tremillon and coworkers48 and is presented in Figure 1.9. The figure also indicates the acidity constants of various Lewis acids allowed to buffer the medium to a pH value as calculated by Eq. (1.33), or in dilute solution by Eq. (1.34). 

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