Fluorine oxyacids

The halogens, except fluorine, can be oxidized to positive oxidation states. Most commonly you will encounter these positive oxidation states in a set of compounds called halogen oxyacids and their ions. 

In the case of fluorine, the only oxyacid known is HOF. For acids having the formula HX02 (or more accurately, HOXO), only HC102 is well characterized and even for that acid only aqueous solutions are known. Consequently, the discussion will be limited to chlorous acid and its salts. 

Carbon is the basis of organic chemistry there are more compounds of carbon than of any other element except hydrogen and possibly fluorine. However, most of the chemistry of carbon is the province of organic chemistry and thus not covered in this encyclopedia. The inorganic chemistry of carbon discussed in this article, which is an update of an excellent article written previously by professor R. Bruce King (University of Georgia, Athens), includes the allotropic forms of elemental carbon, simple molecular carbon halides and oxides, carbon oxyacids and oxyanions, carbon snlfur derivatives, simple cyano derivatives, and carbon-based molecnlar ladders. 

Fluorine forms only one oxyacid, hypofluorous acid (HOF), but it forms at least two oxides. When fluorine gas is bubbled into a dilute solution of sodium hydroxide, the compound oxygen difluoride (OF2) is formed ... 

Chlorine is 2s 2p s p — In contrast to fluorine, chlorine forms a series of oxides and oxyacids and exhibits a variable valency. The ion CIO2 has been shown to have a triangular structure which would suggest that the chlorine was in the singly charged positive, divalent state ... 

Emeleus, H.J., Haszeldine, R.N., and Paul, R.C., Organometallic and organometaUoidal fluorine compounds. Part 12. Bistrifluoromethylphosphinic acid and related phosphorus oxyacids, J. Chem. Soc, 563, 1955. 

HF b.p. 19°C HCl b.p. -85°C). Unlike the other halogens, fluorine does not form higher oxides or oxyacids oxygen difluoride in fact reacts with water to give hydrogen fluoride. 

Fluorine forms one oxyacid HOF. Because the electronegativity of fluorine is greater than diat of oxygen we must consider fluorine to be in a — 1 oxidation state and oxygen to be in the 0 oxidation state in this compound. 

Bromine(III) fluoride fluorinates everything which dissolves in it. Numerous oxides, halides and salts of oxyacids are converted into fluorides. Carbonates, nitrates and iodates are usually completely converted into the fluorides, while some of the metal oxides, such as BeO, MgO, ZnO or AI2O3 are only partly fluorinated by liquid bromine(III) fluoride. Sodium vanadate yields a mixture of tetrafluorooxovanadate and hexafluorovanadate i, potassium or silver dichromates give KCrOF4 and AgCrOF4 resp. i. Potassium permanganate is converted into KMnFs, potassium metaphosphate into potassium hexafluoro-phosphate and sodium borate into the tetrafluoroborate ... 

Fluorinated lactones in the ring-size from 10 to 14 were enantioselectively polyunerized using lipase catalyst (173). The lipase CA-catalyzed polymerization of lO-fluorodecan-9-olide (10-membered) produced the optically active polymer with positive rotation. Interestingly, the corresponding oxyacid gave an optically inactive polyester. 

The simplest oxyacid of fluorine, hypofluorous acid, the synthesis of which had been unsuccessful until the beginning of the 1970s, is available by passing fluorine over water. Despite the strong tendency to decompose into HF and O2 at room temperature, it may have a half-life of up to one hour. Only theoretically derived data are known for HO2F, HO3F, and HO4F. 

The only oxyacid of fluorine is HOF. Numerous oxyacids are known for the other halogens (Fig. 1), although most cannot be isolated pure and are stable only in aqueous solution or as salts. 

An acid is a distinct type of molecular compound. Most acids used in the laboratory can be classified as either binary acids or oxyacids. Binary acids are acids that consist of two elements, usually hydrogen and one of the halogens— fluorine, chlorine, bromine, iodine. Oxyacids are acids that contain hydrogen, oxygen, and a third element (usually a nonmetal). 

All the halogens except fluorine combine with various numbers of oxygen atoms to form a series of oxyacids, as shown in Table 20.10. The strengths of these acids vary in direct proportion to the number of oxygen atoms attached to the halogen, as we discussed in Section 14.9. 

There has been general agreement that bonds to fluorine, chlorine, methyl, or phenyl groups in hypervalent compounds should be described as single polar covalent bonds and that the central atoms therefore must acconunodate more than four electron pairs in its valence shell. But there has been a curious reluctance to accept that bonds from the central atom to terminal oxygen atoms in the oxides or oxyacids of the Group 15, 16, or 17 elements, such as SO2 SO3, or H2SO4, are best described as double (two electron pair) bonds and that the central atoms in these compounds also must accommodate more than four electron pairs in their valence shells. 

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