Among the ionic hydrides is the potassium hydride , formed by the direct combination of hydrogen in its molecular form and the alkaline metal potassium. Like all other hydrides of this type, potassium hydride is a solid compound, which has a high melting point as with all ionic molecules.
Hydrides are chemical compounds formed by hydrogen and one or more other elements, metallic or non-metallic in nature. Depending on their structure and characteristics, these substances can be of three types: ionic, covalent or interstitial hydrides.
By possessing the nature of an ionic compound, potassium hydride is constituted by an anion (in this case, the hydride ion H - ) and a cation (potassium ion K) + ). The hydride ion behaves like a strong Brønsted base; that is, it easily adopts the protons of a donor substance such as metallic potassium, which receives them.
Index
- 1 Structure
- 2 Training
- 3 Properties
- 3.1 Solubility
- 4 Applications
- 5 References
Structure
Potassium was first identified experimentally in the year 1807 by the British chemist Sir Humphry Davy, as well as other chemical elements (calcium, magnesium, boron, strontium and barium) by the technique of electrolysis.
It was also this scientist who discovered the chemical reaction that results in the formation of potassium hydride, which occurs in its pure form as a white solid, although the reagents that are commercially available are gray.
The structure of this binary hydride is characterized to be crystalline, specifically of the cubic type, that is to say, the unit cell of this crystal is a cube centered in the faces, as it is observed in the previous figure.
The reactions carried out by the metal hydrides occur in the crystalline surface, and this hydride has manifested to have the hydride radius and the optimum reticular energy for this type of reactions, even over the hydrides of other metals.
Training
Potassium hydride, whose formula is represented as KH, is an inorganic substance that is classified as an alkali metal hydride because it is formed by directly combining molecular hydrogen with potassium through the following reaction:
H 2 + 2K → 2KH
This reaction was discovered by the same scientist who identified potassium for the first time. He realized how this metal vaporized when exposed to a stream of hydrogen gas, when the temperature of the latter is increased below its boiling point.
A potassium hydride can also be produced that has a superior activity in a simple way, starting from a reaction of hydrogen and other compounds of a superbasic nature (such as potassium tert-butoxide, called t-BuOK-TMEDA), and being prepared in hexane.
Properties
Potassium hydride is not found spontaneously in nature. It is produced from the reaction described above and is found as a crystalline solid, which decomposes at a temperature around 400 ° C, before reaching its melting point.
This compound has a molar mass of approximately 40.106 g / mol due to the combination of the molar masses of its two components. In addition, its density is 1.43 g / cm 3 (taking as reference point the water in standard conditions, which is 1.00 g / cm 3 ).
In this sense, it is also known that this compound has pyrophoric properties; that is, it can ignite spontaneously in the presence of air, as well as oxidizing agents and certain gases.
For this reason it must be treated with caution and contained as a suspension in a mineral-type oil or even paraffin wax, thus reducing its pyrophoricity and facilitating its handling.
Solubility
As for its solubility, this hydride is considered soluble in molten hydroxides (such as fused sodium hydroxide), as well as in salt mixtures. On the other hand, it is insoluble in solvents of organic origin such as diethyl ether, benzene or carbon disulfide.
In the same way, it is considered a very corrosive substance, which also manifests a violent reaction when it comes in contact with compounds of an acid nature, interacting in quantitative relation.
This species also behaves as a"superbase"considered even stronger than the sodium hydride compound; in addition, it has the character of a hydride ion donor.
Applications
The potassium hydride that is commercially available, formed through the reaction of molecular hydrogen with elemental potassium, has a reactivity that is related to the impurities that it possesses (primarily potassium or its reaction products), which leads to Secondary reactions and yields that may vary.
Its nature of extreme basicity makes it very useful to carry out certain organic syntheses, as well as in processes of deprotonation of certain substances that possess carbonyl groups to give rise to enolate compounds.
Likewise, potassium hydride is used in the transformation of certain amines into their corresponding amides (amides with alkyl chains of the KNHR and KNR types) 2 ), by means of its deprotonation. In the same way, it carries out a rapid deprotonation in tertiary alcohols.
As it is an excellent desprotonador, this compound is also used in some reactions of elimination, cyclization-condensation and molecular rearrangement, and is an excellent reducing agent.
In another type of reactions, a crown ether can act as a phase transfer agent, although it can also act as a simple"pickling"agent (process to remove impurities) from the surface of potassium hydride, through the dissolution of the inorganic salts that are formed.
References
- Wikipedia. (2017). Retrieved from en.wikipedia.org
- Chang, R. (2007). Chemistry Mexico: McGraw-Hill
- Brown, C. A. (1974). Potassium hydride, highly active new hydride reagent. Reactivity, applications, and techniques in organic and organometallic reactions. Journal of Organic Chemistry.
- MacDiarmid, A. G. (2009). Inorganic Syntheses. Retrieved from books.google.co.ve
- Majewski, M., and Snieckus, V. (2014). Science of Synthesis: Houben-Weyl Methods of Molecular Transformations. Retrieved from books.google.co.ve