Potassium hydride
Encyclopedia
Potassium hydride, KH, is a chemical compound
of potassium
and hydrogen
. It is a hydride
of potassium. It reacts with water according to the reaction:
The reaction is so vigorous that often the hydrogen gas produced will, due to the heat of the reaction, ignite with the oxygen in the air, producing a lilac flame from the presence of potassium ions in the hydrogen fire. Potassium hydride also reacts violently with acids and ignites with oxygen, chlorine or fluorine. It is pyrophoric and requires careful handling. For this reason it is sold commercially as a slurry (~35%) in mineral oil
. In one study the compound was dispersed in paraffin
to allow for better dispensing.
Potassium hydride can be formed by direct combination of the metal and hydrogen. This reaction was discovered by Humphry Davy
soon after his 1807 discovery of potassium, when he noted that the metal would vaporize in a current of hydrogen when heated just below its boiling point.
Potassium hydride is a superbase
(more reactive than sodium hydride
), which can be used to deprotonate
organic molecules. As a strong oxidizer, it is used in preparation of other superbases, RNHK and ROK, where R is an alkyl group. Potassium hydride is soluble in fused hydroxides and salt mixtures, but not in organic solvents.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
of potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
. It is a hydride
Hydride
In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties. In compounds that are regarded as hydrides, hydrogen is bonded to a more electropositive element or group...
of potassium. It reacts with water according to the reaction:
- KH + H2O → KOH + H2
The reaction is so vigorous that often the hydrogen gas produced will, due to the heat of the reaction, ignite with the oxygen in the air, producing a lilac flame from the presence of potassium ions in the hydrogen fire. Potassium hydride also reacts violently with acids and ignites with oxygen, chlorine or fluorine. It is pyrophoric and requires careful handling. For this reason it is sold commercially as a slurry (~35%) in mineral oil
Mineral oil
A mineral oil is any of various colorless, odorless, light mixtures of alkanes in the C15 to C40 range from a non-vegetable source, particularly a distillate of petroleum....
. In one study the compound was dispersed in paraffin
Paraffin
In chemistry, paraffin is a term that can be used synonymously with "alkane", indicating hydrocarbons with the general formula CnH2n+2. Paraffin wax refers to a mixture of alkanes that falls within the 20 ≤ n ≤ 40 range; they are found in the solid state at room temperature and begin to enter the...
to allow for better dispensing.
Potassium hydride can be formed by direct combination of the metal and hydrogen. This reaction was discovered by Humphry Davy
Humphry Davy
Sir Humphry Davy, 1st Baronet FRS MRIA was a British chemist and inventor. He is probably best remembered today for his discoveries of several alkali and alkaline earth metals, as well as contributions to the discoveries of the elemental nature of chlorine and iodine...
soon after his 1807 discovery of potassium, when he noted that the metal would vaporize in a current of hydrogen when heated just below its boiling point.
Potassium hydride is a superbase
Superbase
In chemistry, a superbase is an extremely strong base, that is a compound that has a high affinity for protons. Hydroxide ion is the strongest base possible in aqueous solutions, but bases exist with pKb's well outside of the aqueous range. Such bases are valuable in organic synthesis and are...
(more reactive than sodium hydride
Sodium hydride
Sodium hydride is the chemical compound with the empirical formula NaH. It is primarily used as a strong base in organic synthesis. NaH is representative of the saline hydrides, meaning it is a salt-like hydride, composed of Na+ and H− ions, in contrast to the more molecular hydrides such as...
), which can be used to deprotonate
Deprotonation
Deprotonation is the removal of a proton from a molecule, forming the conjugate base.The relative ability of a molecule to give up a proton is measured by its pKa value. A low pKa value indicates that the compound is acidic and will easily give up its proton to a base...
organic molecules. As a strong oxidizer, it is used in preparation of other superbases, RNHK and ROK, where R is an alkyl group. Potassium hydride is soluble in fused hydroxides and salt mixtures, but not in organic solvents.