Potassium perchlorate

Crystal structure
	__ K + __ Cl 7+ __ O 2−
Crystal system	orthorhombic
Space group	Pnma (No. 62)
Lattice parameters	a = 8.834 Å , b = 5.65 Å, c = 7.24 Å
General
Surname	Potassium perchlorate
other names	Potassium perchlorate; Hyperchloric acid potassium;
Ratio formula	KClO 4
Brief description	white, odorless powder
External identifiers / databases
EC number	231-912-9
ECHA InfoCard	100.029.011
PubChem	516900
Wikidata	Q422434
Drug information
ATC code	H03 BC01
properties
Molar mass	138.55 g mol −1
Physical state	firmly
density	2.52 g cm −3
Melting point	Decomposition> 400 ° C
solubility	poor in water (17 g l −1 at 20 ° C)
safety instructions
	Please note the exemption from the labeling requirement for drugs, medical devices, cosmetics, food and animal feed
H and P phrases	H: 271-302
	P: 210-221
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Potassium perchlorate, micrograph with polarized light

Potassium perchlorate , the potassium salt of perchloric acid with the chemical formula KClO ₄ , is a white crystalline solid that has a strong fire-promoting effect and can form explosive mixtures with many oxidizable substances. In the case of potassium perchlorate, chlorine is in the + VII oxidation state , the highest it can take.

Manufacturing

Nowadays, potassium perchlorate is produced in perchlorate cells , in which aqueous solutions of sodium chlorate are electrolyzed. At the anode , chlorine trioxide or dichlorohexoxide is formed from the chlorate anions through anodic oxidation , which hydrolyzes to chlorate and perchlorate . The resulting sodium perchlorate , after the rest of the sodium chlorate with reducing agents such as hydrochloric acid or sodium sulfite was destroyed with potassium chloride added to give potassium perchlorate precipitates. Since chlorine trioxide decomposes to chlorine dioxide and oxygen at high temperatures , perchlorate cells, unlike chlorate cells, must be operated at low temperatures. Platinum , similar precious metals or chemically resistant, electrically conductive oxides such as manganese dioxide or lead dioxide are usually used as anode material in perchlorate cells .

Alternatively, potassium perchlorate can be obtained by chemical oxidation of potassium chlorate by adding strong oxidizing agents such as persulfates or permanganates and suitable catalysts to aqueous potassium chlorate solutions.

A third method for producing potassium perchlorate is the thermal disproportionation of potassium chlorate , whereby one mole of potassium chloride, one mole of potassium perchlorate and one mole of oxygen are formed from two moles of potassium chlorate .

properties

In its pure form, potassium perchlorate forms rhombic prisms that can be several centimeters in size. The crystal system is orthorhombic , space group Pnma (space group no. 62) with the lattice parameters a = 8.834 Å , b = 5.65 Å and c = 7.24 Å isotypic to barium sulfate . Even slightly impure potassium perchlorate only forms extremely fine crystal needles. It is sparingly soluble in cold water, is not hygroscopic and does not form hydrates . It is rather poorly soluble in polar organic solvents. Template: room group / 62

Solubility in various solvents at 25 ° C
solvent		water	Methanol	Ethanol	n-propanol	acetone	Ethyl acetate
solubility	in g / 100 g solvent	2.062	0.105	0.012	0.010	0.155	0.001

It also has a strong oxidizing effect, as the release of oxygen from potassium perchlorate is a weakly exothermic process. However, the energy released is very low and not sufficient to heat additional perchlorate above the decomposition temperature, which is why pure potassium perchlorate cannot decompose explosively.
In aqueous solution, on the other hand, potassium perchlorate has a much weaker oxidizing effect than its related, less oxidized chlorine-oxygen salts, such as potassium hypochlorite . Potassium perchlorate oxidizes even boiling hydrochloric acid only to a negligible extent, whereas potassium hypochlorite reacts with hydrochloric acid even at room temperature with strong foaming and violent release of chlorine .

use

Potassium perchlorate is often used in pyrotechnics because of its strong fire-promoting effect and its good storability, for example as an oxidizing agent in lightning bolt sentences .
It is only rarely used in rocket engines because it has been replaced by the related salt ammonium perchlorate .

safety instructions

Mixtures of potassium perchlorate with phosphorus , sulfur or metal powders can ignite even at low temperatures. You can u. U. can be violently exploded with a simple blow of a hammer . Therefore, when storing chlorates and perchlorates, it is important to ensure that there is as little contamination as possible in the storage container.

However, perchlorates are more stable compared to chlorates (due to the oxidation level of chlorine of + VII) and have therefore replaced the chlorates when used in pyrotechnic mixtures.

Individual evidence

↑ ^a ^b C. Gottfried, C. Schusterius: The structure of potassium and ammonium perchlorate . In: Zeitschrift für Kristallographie, Kristallgeometrie, Kristallphysik, Kristallchemie , 84, 1932, pp. 65-73, doi : 10.1524 / zkri.1933.84.1.65 .
↑ ^a ^b ^c ^d ^e ^f Entry on potassium perchlorate in the GESTIS substance database of the IFA , accessed on January 10, 2017(JavaScript required) .
↑ Entry on Potassium perchlorate 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 .
↑ ^a ^b Long, JR: Perchlorate safety: Reconciling inorganic and organic guidelines in Chem. Health Safety 9 (2002) 12-18, doi : 10.1016 / S1074-9098 (02) 00294-0 .
↑ Willard, HH; Smith, GF: The Perchlorates of the Alkali and Alkaline Earth Metals and Ammonium. Their Solubility in Water and Other Solvents in J. Am. Chem. Soc. 45 (1923) 286-297, doi : 10.1021 / ja01655a004 .

Web links

The Chlorates and Perchlorates - Production via electrolysis ( Memento of November 6, 2007 in the Internet Archive )

[Kristallstruktur-1] C. Gottfried, C. Schusterius: The structure of potassium and ammonium perchlorate . In: Zeitschrift für Kristallographie, Kristallgeometrie, Kristallphysik, Kristallchemie , 84, 1932, pp. 65-73, doi : 10.1524 / zkri.1933.84.1.65 .

[GESTIS-2] ↑ ^a ^b ^c ^d ^e ^f Entry on potassium perchlorate in the GESTIS substance database of the IFA , accessed on January 10, 2017(JavaScript required) .

[CLP_100.029.011-3] Entry on Potassium perchlorate 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 .

[Long-4] Long, JR: Perchlorate safety: Reconciling inorganic and organic guidelines in Chem. Health Safety 9 (2002) 12-18, doi : 10.1016 / S1074-9098 (02) 00294-0 .

[Willard-5] Willard, HH; Smith, GF: The Perchlorates of the Alkali and Alkaline Earth Metals and Ammonium. Their Solubility in Water and Other Solvents in J. Am. Chem. Soc. 45 (1923) 286-297, doi : 10.1021 / ja01655a004 .