Hydrohalic acids fluoride

With hydrohalic acids as catalysts, the hydrolysis of 1,3,2-dioxathiolane 2-oxide (16) is considered to occur (partly or entirely) via a halosulfite intermediate, e.g. (138 X = C1). The marked acceleration of the aqueous hydrolysis of catechol cyclic sulfite by small amounts of fluoride ion is likewise attributed to a nucleophilic catalysis (76CRV747). The nucleophilic attack of (16) at carbon by halide ion on reaction with phenylmagnesium bromide has already been discussed in Section 4.33.3.3.4. 

The ease of ionization of binary protonic acids depends on both (1) the ease of breaking H—X bonds and (2) the stability of the resulting ions in solution. Let us consider the relative strengths of the Group VIIA hydrohalic acids. Hydrogen fluoride ionizes only slightly in dilute aqueous solutions. 

Small quantities of the hydrogen halides (their solutions are called hydrohalic acids) and other volatile acids are usually prepared by adding concentrated nonvolatile acids to the appropriate salts. (Sulfuric and phosphoric acids are classified as nonvolatile acids because they have much higher boiling points than other common acids.) The reactions of concentrated sulfuric acid with solid sodium fluoride and sodium chloride produce gaseous hydrogen fluoride and hydrogen chloride, respectively. 

Electrophilic addition of hydrohalic acids (hydrogen fluoride, hydrogen bromide, hydrogen chloride), carboxylic acids (e.g. acetic acid) and halogens (bromine, chlorine, iodine) to bicy-cloheptadiene gave a homoallyl cation which underwent rearrangement to nortricyclyl derivatives, i.e. 5-substituted tricyclo[2.2.1.0 ]heptanes. ... 

The products of hydrolysis of sulphonyl halides, i.e. sulphonic and hydrohalic acids, can be easily titrated with bases, which accelerate the hydrolysis as well. Thus Cundiff and Markunas titrated potentiometrically benzenesulphonyl chloride (and sulphuric acid) in pyridine with tetrabutylammonium hydroxide in benzene/methanol251. Jansseune and Janssen252 titrated sulphonyl fluorides in butylamine with potassium methoxide. Krivoruchko253 estimated 2-chloroethanesulphonyl chloride in air by hydrolysing it with alcoholic potassium hydroxide and determining the chloride ion colorimetrically or nephelometrically. Jansseune and Janssen252 also hydrolysed sulphonyl fluorides with alkali, acidified the mixture, distilled the HF and titrated it with alkali. 

The HF bond is also extremely strong (BDE 569 kJ/mol), which in part explains why, unlike the other hydrohalic acids, HF is a weak acid. Thus, a number of p-block element fluorides react with proton sources to yield HE... 

A hydrohalic acid ester of practical importance as a microbicide has been tributyltin fluoride. 

The hahdes and oxyhalides of some nonmetak hydrolyze (react with water) to produce two acids a (binary) hydrohalic acid and a (ternary) oxyicid of the nonmetal. Phosphorus trihalides react with water to produce the corresponding hydrohalic acids and phosphorous add, a weak diprotic acid, whereas phosphorus pentahahdes give phosphoric acid and the corresponding hydrohahc acid. The phosphorus fluorides are an exception to this reactivity trend. The P — F bonds are generahy too stable to react with water under mild to moderate conditions. 

Dehydration of the dehydrated trihalides is a final method for oxide conversion. The hydrated trichlorides, tribromides and triiodides, RXj- H20, are obtained by dissolution of the oxides in aqueous hydrohalic acid and condensation by warming and desiccation (Ashcroft and Mortimer, 1968 Brown et al., 1968). The hydrated trifluorides are prepared by dissolution of the oxide in HNO3 or HCl and precipitation with aqueous HF. The filtered trifluoride may be dehydrated by heating slowly to 600°C in an inert gas stream or in vacuum (Strizhkov et al., 1972). Products obtained by heating in air are contaminated with oxide fluoride (Batsanova, 1971). Thermal decomposition studies of the hydrated trichlorides, cf. section 5.1, have shown that the oxide chlorides are readily formed, but careful dehydration under N2 flow has apparently been successful for the chlorides (Ashcroft and Mortimer, 1968). Tribromides have also been prepared by careful vacuum dehydration, but the lutetium products were contaminated with oxide bromide (Brown et al., 1968). In general simple dehydration becomes increasingly difficult with increasing atomic number of both the lanthanide and the halide. 

The heavier phosphorus trihaUdes (PX3, X = Cl, Br, I) are prepared by direct halogenation. The trifluoride, on the other hand, is best synthesized by treating the trichloride with an ionic fluoride such as CaF2 or ZnF2- The arsenic, antimony, and bismuth trifluorides are prepared by adding hydrogen fluoride to the oxides. (If fluorine gas is used, the pentafluorides result.) The other trihalides of arsenic and antimony can be produced by direct halogenation of either the elements or the trioxides, while the bismuth trihalides are best produced by the action of aqueous hydrohalic acids on 61203. 

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