Perchloric acid

Structural formula
General
Surname	Perchloric acid
other names	Hydrogen tetraoxochlorate (−I); Chlorine (VII) acid; Superchloric acid;
Molecular formula	HClO 4
Brief description	colorless, oily, hygroscopic liquid that smokes in the air
External identifiers / databases
EC number	231-512-4
ECHA InfoCard	100,028,648
PubChem	24247
ChemSpider	22669
Wikidata	Q193956
properties
Molar mass	100.46 g mol −1
Physical state	liquid
density	1.77 g cm −3
Melting point	−112 ° C
boiling point	130 ° C
Vapor pressure	40 h Pa (20 ° C)
pK s value	−10
solubility	miscible with water, acetic acid , chloroform , nitromethane , benzene , dichloromethane , dichloroethene and acetonitrile
safety instructions
H and P phrases	H: 271-290-302-314-373
	P: 210-280-303 + 361 + 353-304 + 340-310-305 + 351 + 338-371 + 380 + 375
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Perchloric acid , HClO ₄ , is an oxygen acid of chlorine . Their salts are called perchlorates .

properties

Anhydrous perchloric acid has a strong oxidizing effect, smokes in the air and is hygroscopic and volatile. Perchloric acid is a so-called superacid , so an extremely strong acid ( pK _S : -10). It causes severe burns and is highly reactive. When heating, especially perchloric acid with a mass fraction of over 50 percent, there is a risk of explosion , as is the case when concentrating or concentrating with desiccants . Anhydrous perchloric acid can decompose spontaneously even at room temperature. Together with a large number of other substances, this can lead to strongly exothermic reactions, heat generation, ignition, explosion or the formation of explosive gases and vapors. Contact with flammable substances poses a fire hazard, as the acid is oxidising due to its high oxygen content .

anhydride

The anhydride of perchloric acid is dichloroheptoxide (Cl ₂ O ₇ ). It can be prepared by carefully reacting perchloric acid with phosphorus pentoxide followed by vacuum distillation. Dichloroheptoxide is highly explosive and reacts again with water to form perchloric acid.

Manufacturing

Perchloric acid is obtained by adding strong acids, e.g. B. sulfuric acid , from its salts, e.g. B. released potassium perchlorate . Potassium perchlorate can be produced by disproportionation from electrolytically produced potassium chlorate KClO ₃ when heated.
${\ displaystyle \ mathrm {4 \ KClO_ {3} \ longrightarrow \ KCl + 3 \ KClO_ {4}}}$

Perchloric acid is also produced from the reaction of sodium perchlorate and concentrated hydrochloric acid :

${\ displaystyle \ mathrm {\ NaClO_ {4} + \ HCl \ longrightarrow \ NaCl + \ HClO_ {4}}}$

use

Perchlorates are strong plant toxins and are therefore contained in weed control agents in addition to chlorates. Perchlorates are also used as oxidants in some explosives and rocket propellants .

In the analysis of heavy metals, a concentrated (> 60%) perchloric acid was used to break down solid inorganic samples due to its strong oxidizing effect . This generally happened at high temperatures. There is a risk that the acid will concentrate further with the evaporation of water. Due to the explosive nature of perchloric acid and its vapors, this method is no longer recommended today. Concentrated perchloric acid should never come into contact with organic material.

In analytical chemistry, perchloric acid is used in particular for anhydrous titrations ( amine number ). To do this, perchloric acid is dissolved in glacial acetic acid (concentrated acetic acid). This creates acidium ions :

{\ displaystyle \ mathrm {HClO_ {4} \ + \ CH_ {3} COOH \ \ longrightarrow \ ClO_ {4} ^ {-} \ + \ CH_ {3} COOH_ {2} ^ {+}}}

In biochemistry perchloric acid is used for precipitation of proteins used. In clinical chemistry , this effect is used to immediately deactivate enzymes when examining special metabolic parameters (e.g. pyruvate ).

safety instructions

Perchloric acid is very corrosive to the skin, respiratory tract and mucous membranes. It is able to destroy living tissue. As a strong oxidizing agent, it has a fire-promoting effect . Together with a large number of other substances, this can lead to strongly exothermic reactions, heat generation, ignition, explosion or the formation of explosive gases and vapors. Dilute perchloric acid solutions are less dangerous and more stable.

Individual evidence

↑ ^a ^b Entry on perchloric acid. In: Römpp Online . Georg Thieme Verlag, accessed on April 17, 2014.
↑ ^a ^b ^c ^d ^e Entry on perchloric acid in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .
^ ^A ^b A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 480.
^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 .
↑ Entry on Perchloric acid in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
↑ G. Brauer (Ed.), Handbook of Preparative Inorganic Chemistry 2nd ed., Vol. 1, Academic Press 1963, pp. 318-20.

[roempp-1] Entry on perchloric acid. In: Römpp Online . Georg Thieme Verlag, accessed on April 17, 2014.

[GESTIS-2] Entry on perchloric acid in the GESTIS substance database of the IFA , accessed on February 1, 2016(JavaScript required) .

[Holleman-3] A ^b A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 480.

[4] AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 .

[CLP_100.028.648-5] Entry on Perchloric acid in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .

[6] G. Brauer (Ed.), Handbook of Preparative Inorganic Chemistry 2nd ed., Vol. 1, Academic Press 1963, pp. 318-20.