Halogenated oxygen acids
Halogen oxo acids (also halogen oxo acids ) are a chemical group of inorganic acids that are composed of hydrogen H, a halogen "X" and oxygen O. The participation of oxygen in the chemical compound distinguishes it from the substance group of hydrogen halides , whose solutions in water are called hydrohalic acids.
Molecular formula, breakdown
Halo- oxygen acids have the general empirical formula HXO n (X = F , Cl , Br , I , At ; n = 1, 2, 3, 4). In the case of fluorine, there is only one halogenated oxygen acid with n = 1 ( hypofluoric acid ). In the case of iodine (and probably astatine as well ) there are other types of empirical formulas in the highest oxidation state +7, the “water-rich” orthopperiodic acid H 5 IO 6 is particularly important . The following table shows a division of the halogenated oxygen acids and their salts into subgroups based on the oxidation level of the halogen or (correspondingly) the type of empirical formula:
| Oxidation level of the halogen X |
Acids | Salts | ||
|---|---|---|---|---|
| Name (a) | Sum formula type |
Surname | Sum type of formula (b) |
|
| +1 (c) | Hypohalous acids Halogen (I) acids |
HXO |
Hypohalite Halogenate (I) |
MXO |
| +3 | Halogenous acids Halogen (III) acids |
HXO 2 | Halogenite Halogenate (III) |
MXO 2 |
| +5 | Halogen acids Halogen (V) acids |
HXO 3 | Halogenate Halogenate (V) |
MXO 3 |
| +7 | Perhalogenic acids halogen (VII) acids |
HXO 4 (d) | Perhalogenates halogenates (VII) |
MXO 4 (d) |
Occur
Only the hypofluoric acid HOF (at low temperatures), the perchloric acid HClO 4 , the iodic acid HIO 3 , the meta periodic acid HIO 4 and the orthoperiodic acid H 5 IO 6 could be isolated as pure substances so far ; a substance previously known as triperiodic acid H 7 I 3 O 14 is a cocrystallizate of the last two periodic acids (2 HIO 4 · H 5 IO 6 ). The other halogenated oxygen acids are only known in aqueous solution and / or in the form of their salts, and HClO, HClO 4 , HBrO, HBrO 4 , HIO 3 and HIO 4 also in the gas phase.
In the case of radioactive astatine , only tests with trace amounts are possible. Located in the periodic table in the halogen group (7th main group and 17 IUPAC group ) below of astatine in the seventh period standing element with the atomic number 117, Tennessee Ts, is known only since it was first artificial production in the year of 2010. So far it has only been generated / detected in quantities of a few atoms, which were also radioactive with very short half-lives , so that no reliable information is yet available on its chemistry.
Overview table
The following overview table lists the known or postulated halogenated oxygen acids and the corresponding derived salts / anions , arranged according to the halogens:
| Oxidation level of the halogen |
Acids | Salts | |||
|---|---|---|---|---|---|
| Surname | Sum formula |
Acid constant (p K S ) |
Surname | Molecular formula of the anion |
|
| Fluorous oxygen acids | |||||
| −1 | Hypofluoric acid (a) | COURT | ? | Hypofluorite (s) | FO - |
| Chloro-oxygen acids | |||||
| +1 | Hypochlorous acid (b) (c) | HClO | 7.54 | Hypochlorite (a) | ClO - |
| +3 | Chlorous acid (b) | HClO 2 | 1.97 | Chlorite (a) | ClO 2 - |
| +5 | Chloric acid (b) | HClO 3 | −2.7 | Chlorates (a) | ClO 3 - |
| +7 | Perchloric acid (a) (c) | HClO 4 | −10 | Perchlorate (a) | ClO 4 - |
| Bromine Acids | |||||
| +1 | Hypobromous acid (b) (c) | HBrO | 7.69 | Hypobromite (a) | BrO - |
| +3 | Bromous acid (b) | HBrO 2 | ? | Bromites (a) | BrO 2 - |
| +5 | Bromic acid (b) | HBrO 3 | approx. 0 | Bromates (a) | BrO 3 - |
| +7 | Perbromic acid (b) (c) | HBrO 4 | ? | Perbromate (a) | BrO 4 - |
| Iodoic acids | |||||
| +1 | Hypoiodous acid (b) | HIO | 10.64 | Hypoiodite (b) | IO - |
| +3 | Iodic acid (b) | HIO 2 | ? | Iodite (b) | IO 2 - |
| +5 | Iodic acid (a) (c) | HIO 3 | 0.804 | Iodates (a) | IO 3 - |
| +7 | Meta periodic acid (a) (c) | HIO 4 | ? | Meta periodate (a) | IO 4 - |
| Meso periodic acid (d) | H 3 IO 5 | ? | Meso periodate (a) | IO 5 3− | |
| Ortho periods acid (a) | H 5 IO 6 | p K S 1 = 3.29 p K S 2 = 8.31 p K S 3 = 11.60 |
Ortho periodate (a) | H 5 − n IO 6 n− (n = 1, 2, 3, 5) |
|
| Metadi periodic acid (d) | H 4 I 2 O 9 | ? | Metadi periodate (a) | I 2 O 9 4− | |
| Mesodi periodic acid (d) | H 6 I 2 O 10 | ? | Mesodi periodate (a) | H 6 − n I 2 O 10 n− (n = 3, 4, 5, 6) |
|
| Orthodi periodic acid (s) | H 8 I 2 O 11 | ? | Orthodi periodate (e) | H 8 − n I 2 O 11 n− | |
| Astat Oxygen Acids | |||||
| +1 | Hypoastatige acid (f) | HAtO | ? | Hypoastatite ( noun ) | AtO - |
| +3 | Astatige acid (f) | HAtO 2 | ? | Astatite ( noun ) | AtO 2 - |
| +5 | Astatic acid ( noun ) | HAtO 3 | ? | Astatates ( noun ) | AtO 3 - |
| +7 | Perastatic acid ( noun ) | HAtO 4 / H 5 AtO 6 ? |
? | Perastatate ( noun ) | AtO 4 - / H 5 − n AtO 6 n− ? |
|
(a) Can be isolated as pure substances.
(c) Also known in the gas phase.
(e) Still unknown.
|
(b) Known in aqueous solution.
(d) Only known in the form of the salts.
(f)Only experiments with trace amounts; actually present species partly uncertain.
|
Structures
In the molecules of all halogenated oxygen acids, the hydrogen H , which can be dissociated as a proton, is not always bound directly, but rather via an oxygen atom O to the central halogen atom X, so that the empirical formula HXO n is occasionally modified to HOXO n − 1 in order to better express the molecular constitution bring. The H-O-X groupings are angled, for example the bond angles of the hypohalous acids are 97.2 ° (HOF), 103 ° (HOCl) and 110 ° (HOBr). In accordance with the VSEPR model , the O – X – O units in the halogenic acids / halites are also angled, the XO 3 units in the halogen acids / halogenates are trigonal-pyramidal and the XO 4 units in the perhalogenic acids / perhalates are tetrahedral . In fixed mesoperiod data there are square-pyramidal IO 5 units, in orthopperiodic acid / ortho periodic octahedral IO 6 units. Two IO 6 octahedra linked via a common surface, edge or corner are present in the fixed metadiperiodata, mesodiperiodata or (still hypothetical) orthodiperiodata. The solid metaperiodic acid HIO 4 has a polymer structure ("polyperiodic acid" (HIO 4 ) x ) made of distorted IO 6 octahedra, which are each edge-linked with two IO 6 neighboring octahedra and thus form chains.
Acid-base properties
The acid strength of the halogenated oxygen acids (HXO n → H + + XO n - ) shows the following trends: It increases with an increasing number n of oxygen atoms (for example, chlorous acid HClO 2 is a stronger acid than hypochlorous acid HClO) and from bottom to top in the Halogen group, i.e. from the heavier to the lighter halogens (for example the acid strength increases from iodic acid HIO 3 via bromic acid HBrO 3 to chloric acid HClO 3 ). Accordingly, the perchloric acid HClO 4 is the strongest acid. The basicity of the halogenated oxygen acids (HXO n + H + → H 2 XO n + ) follows an opposite trend, but is overall only very weak. Autoprotolysis (2 HXO n → H 2 XO n + + XO n - ) occurs to a lesser extent in the pure acids .
Redox properties
The redox potentials of the halogenated oxygen acids or their corresponding oxo anions are dependent on the pH value : In acidic solution they consistently show high positive values (→ strong oxidizing agents ); Perbromic acid and perastatic acid have the highest normal potentials at pH = 0 with ≥ +1.85 V (based on a reduction to the level of bromic acid or astatic acid). The redox potentials decrease with increasing pH, but are still positive even in a strongly alkaline solution at pH = 14, so that there is still an oxidizing effect here. At the same time, however, the halogenated oxygen acids or their corresponding oxo anions - if the oxidation state of the halogen is less than +7 - are in principle redoxamphoters , that is, they can also occur as reducing agents compared to stronger oxidizing agents . Therefore, depending on the pH, disproportionation reactions or comproportionation reactions are also possible.
presentation
There are various ways of representing the halogenated oxygen acids or their salts, including:
- Disproportionation reactions, for example the disproportionation of elemental halogens (oxidation level 0) in aqueous solution to form hydrohalic acids / halides (oxidation level −1) and hypohalous acids / hypohalites (oxidation level +1) Mercury (II) oxide HgO made. The generated hypohalous acids / hypohalites (oxidation level +1) can for their part disproportionate (favored by a temperature increase) to form hydrohalic acids / halides (oxidation level −1) and halogen acids / halogenates (oxidation level +5).
- Comproportionation reactions, for example from bromide Br - (oxidation state −1) and bromate BrO 3 - (oxidation state +5) to bromite BrO 2 - (oxidation state +3) in the form of a solid-state reaction of the lithium salts at elevated temperature.
- Oxidations or reductions of halides, halogens, other halogenated oxygen acids or their corresponding oxo anions and halogen oxides with chemical oxidizing or reducing agents or electrolytically , for example the reduction of chlorine dioxide ClO 2 (oxidation level +4) with hydrogen peroxide H 2 O 2 in alkaline solution Chlorites (oxidation level +3) or the anodic oxidation of chlorates (oxidation level +5) to perchlorates (oxidation level +7).
- Hydrolysis of halogen oxides, for example dichloromonoxide Cl 2 O, to form hypochlorous acid / hypochlorites .
- Hydrolysis of interhalogen compounds , for example bromine fluoride BrF to hypobromous acid / hypobromites and hydrofluoric acid / fluorides .
- Preparation of pure solutions of halogenated oxygen acids by reacting their barium salts with sulfuric acid ( barium sulfate by-product precipitates as a solid which is almost insoluble in water and can therefore be easily separated).
Important technical products are primarily aqueous solutions of hypochlorous acid HClO and perchloric acid HClO 4 as well as hypochlorites , chlorites , chlorates , perchlorates , bromates and periodates as solid salts.
literature
- M. Binnewies , M. Jäckel, H. Willner, G. Rayner-Canham: General and Inorganic Chemistry . 2nd Edition. Spektrum Akademischer Verlag, Heidelberg 2011, ISBN 978-3-8274-2533-1 .
Web links
Individual evidence
- ↑ a b c d e f g h i A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. De Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 458, 461, 463–478 ( limited preview of the 101st edition in Google Book Search).
- ^ A b c d e NN Greenwood, A. Earnshaw: Chemistry of the Elements . 2nd Edition. Elsevier Butterworth-Heinemann, Oxford [a. a.] 2005, ISBN 0-7506-3365-4 , pp. 853–875, 885–887 ( limited preview in Google Book Search - first edition: 1997).
- ^ A b c A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. De Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 454–455 ( limited preview in Google Book search).
- ^ A b c JE Huheey, EA Keiter, RL Keiter: Inorganic chemistry: principles of structure and reactivity . 3. Edition. De Gruyter, Berlin 2003, ISBN 3-11-017903-2 , p. 995–996 ( limited preview in Google Book Search - American English: Inorganic Chemistry - Principles of Structure and Reactivity . 1993. Translated by R. Steudel).
- ↑ a b c GK Schweitzer, LL Pesterfield: The Aqueous Chemistry of the Elements . Oxford University Press, Oxford [u. a.] 2010, ISBN 978-0-19-539335-4 , pp. 258–260 ( limited preview in Google Book search; limited preview in Google Book search).
- ↑ a b HK Kugler, C. Keller (ed.): Gmelin Handbook of Inorganic Chemistry , System Number 8 a, At Astatine . 8th edition. Springer, Berlin / Heidelberg 1985, ISBN 3-662-05868-5 , doi : 10.1007 / 978-3-662-05868-8 ( limited preview in the Google book search).