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| Names | |||
|---|---|---|---|
| Preferred IUPAC name Potassiumtert-butoxide | |||
| Other names KOt-Bu, potassiumt-butoxide. | |||
| Identifiers | |||
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3D model (JSmol) | |||
| ChemSpider |
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| ECHA InfoCard | 100.011.583 | ||
| UNII | |||
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| Properties | |||
| C4H9KO | |||
| Molar mass | 112.21 g mol−1 | ||
| Appearance | colourless solid | ||
| Melting point | 256 °C (493 °F; 529 K) | ||
| Boiling point | sublimes at 220 °C (1 mmHg) or at 140 °C (0.01 hPa) | ||
| Reacts with water | |||
| Solubility indiethyl ether | 4.34 g/100 g (25-26 °C)[1] | ||
| Solubility inHexane | 0.27 g/100 g (25-26 °C)[1] | ||
| Solubility inToluene | 2.27 g/100 g (25-26 °C)[1] | ||
| Solubility inTHF | 25.00 g/100 g (25-26 °C)[1] | ||
| Hazards | |||
| GHS labelling:[2] | |||
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| Danger | |||
| H228,H252,H314 | |||
| P405 | |||
| Safety data sheet (SDS) | Oxford MSDS | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Potassiumtert-butoxide (orpotassiumt-butoxide) is achemical compound with theformula [(CH3)3COK]n (abbr. KOtBu). This colourless solid is a strongbase (pKa of conjugate acid is 17 in H2O),[3] which is useful inorganic synthesis. The compound is often depicted as a salt, and it often behaves as such, but its ionization depends on the solvent.[1]
Potassiumt-butoxide is commercially available as a solution and as a solid, but it is often generatedin situ for laboratory use because samples are so moisture-sensitive and older samples are often of low purity. It is prepared by the reaction of drytert-butyl alcohol withpotassium metal.[4] The solid is obtained by evaporating these solutions followed by heating the solid. The solid can be purified by sublimation.
It crystallizes as a tetramericcubane-type cluster. It crystallises fromtetrahydrofuran/pentane at −20 °C as [tBuOK·tBuOH]∞, which consists of straight chains linked byhydrogen bonding. Sublimation of [tBuOK·tBuOH]∞ affords the tetramer [tBuOK]4, which adopts a cubane-like structure. MildlyLewis basic solvents such as THF anddiethyl ether do not break up the tetrameric structure, which persists in the solid, in solution and even in the gas phase.[5]
Many modifications have been reported that influence the reactivity of thisreagent. The compound adopts a complex cluster structure (the adjacent picture is a simplified cartoon), and additives that modify the cluster affect the reactivity of the reagent. For example,DMF,DMSO,hexamethylphosphoramide (HMPA), and18-crown-6 interact with the potassium center, yielding solvent separated ion pairs such as K(DMSO)x+ andtert-BuO−. Whereas in benzene, on the other hand, the compound remains as a cluster structure, which is less basic.[1] Even in polar solvents, it is not as strong as amide bases, e.g.,lithium diisopropylamide, but stronger than potassium hydroxide. Its steric bulk inhibits the group from participating in nucleophilic addition, such as in aWilliamson ether synthesis or relatedSN2 reactions.[citation needed]
Substrates that are deprotonated by potassiumt-butoxide include terminal acetylenes andactive methylene compounds. It is useful indehydrohalogenation reactions. Illustrating the latter behavior, potassiumtert-butoxide reacts with chloroform yieldingdichlorocarbene, which is useful for dichlorocyclopropanations.[6][7] Potassiumtert-butoxide can abstract a beta-proton from alkylammonium cations, leading to the Hofmann product via anelimination reaction.
Potassiumtert-butoxidecatalyzes the reaction ofhydrosilanes and heterocyclic compounds to give the silyl derivatives, with release of H2.[8]
Potassiumtert-butoxide is a very strong base that rapidly attacks living tissue.
Potassiumtert-butoxide forms explosive mixtures when treated withdichloromethane.[9][10]
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