Potassium tert-butoxide

Potassium tert-butoxide

Names

IUPAC name

potassium 2-methylpropan-2-olate

Identifiers

CAS Number

865-47-4^Y

3D model (JSmol)

Interactive image

ChemSpider

63266^Y

ECHA InfoCard

100.011.583

PubChem CID

70077

InChI

InChI=1S/C4H9O.K/c1-4(2,3)5;/h1-3H3;/q-1;+1^Y

Key: LPNYRYFBWFDTMA-UHFFFAOYSA-N^Y
InChI=1/C4H9O.K/c1-4(2,3)5;/h1-3H3;/q-1;+1

Key: LPNYRYFBWFDTMA-UHFFFAOYAU

SMILES

[K+].[O-]C(C)(C)C

Properties

Chemical formula

C₄H₉KO

Molar mass

112.21 g mol⁻¹

Appearance

solid

Melting point

256 °C (493 °F; 529 K)

Solubility in diethyl ether

4.34 g/100 g (25-26 °C)

Solubility in Hexane

0.27 g/100 g (25-26 °C)

Solubility in Toluene

2.27 g/100 g (25-26 °C)

Solubility in THF

25.00 g/100 g (25-26 °C)

Hazards

Safety data sheet

Oxford MSDS

EU classification (DSD) (outdated)

Harmful (Xn), Corrosive (C)

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

(what is ^YN ?)

Infobox references

Potassium tert-butoxide is the chemical compound with the formula K⁺(CH₃)₃CO⁻. This colourless solid is a strong base (pKa of conjugate acid around 17), which is useful in organic synthesis. It exists as a tetrameric cubane-type cluster. It is often seen written in chemical literature as potassium t-butoxide. The compound is often depicted as a salt, and it often behaves as such, but it is not ionized in solution.

Potassium t-butoxide is commercially available as a solution and as a solid, but it is often generated in situ for laboratory use because samples are so sensitive and older samples are often of poor quality. It is prepared by the reaction of dry tert-butyl alcohol with potassium metal. The solid is obtained by evaporating these solutions followed by heating the solid. The solid can be purified by sublimation at 220 °C and 1 mmHg.

Potassium tert-butoxide crystallises from THF/pentane at −20 °C as [tBuOK·tBuOH]_∞, which consists of infinite one-dimensional chains linked by hydrogen bonding. Sublimation of [tBuOK·tBuOH]_∞ affords the tetramer [tBuOK]₄, which adopts a cubane-like structure. Mild Lewis basic solvents such as THF and diethyl ether do not break up the tetrameric structure, which persists in the solid, in solution and even in the gas phase.

The tert-butoxide species is itself useful as a strong, non-nucleophilic base in organic chemistry. 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 a Williamson ether synthesis or an S_N2 reaction. Substrates that are deprotonated by potassium t-butoxide include terminal acetylenes and active methylene compounds. It is useful in dehydrohalogenation reactions.

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