Potassium tert -butanolate
Structural formula | |||||||||||||||||||
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General | |||||||||||||||||||
Surname | Potassium tert -butanolate | ||||||||||||||||||
other names |
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Molecular formula | C 4 H 9 KO | ||||||||||||||||||
Brief description |
white to yellowish odorless solid |
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properties | |||||||||||||||||||
Molar mass | 112.21 g mol −1 | ||||||||||||||||||
Physical state |
firmly |
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Melting point |
256-258 ° C |
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pK s value | |||||||||||||||||||
solubility |
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safety instructions | |||||||||||||||||||
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As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . |
Potassium tert -butanolate is the alcoholate salt made from tert -butanol and potassium . It is a strong, non- nucleophilic base that is commercially available both in solution and as a solid.
presentation
Potassium tert -butanolate is prepared using the usual procedure for the production of alcoholates. It can be produced in the absence of water under protective gas by reacting elemental potassium with tert- butanol according to the following equation:
The resulting solution of potassium tert -butanolate in tert- butanol can either be used directly or the solvent can be removed.
As potassium tert- butanolate ages faster (recognizable by a yellowish discoloration), it is recommended that older batches be cleaned before use. This is done by sublimation at 220 ° C and a pressure of 1.3 h Pa .
properties
Potassium tert -butanolate is a white solid that reacts violently with water. It has an ignition temperature of 360 ° C and can be ignited even by brief exposure to flames. The flammability increases with a finer distribution of the substance.
The base can sometimes react violently with short-chain alcohols and ketones , esters , diethyl sulfate and air.
Potassium tert -butanolate has a higher basicity than the homologous alcoholates of 1-butanol , 2-butanol and isobutanol . This is due to the higher + I effect of the tert-butyl radical.
use
In organic synthesis , potassium tert- butoxide is used as a strong, non-nucleophilic base. The low nucleophilicity is a consequence of the high steric hindrance of the alcoholate by the sterically demanding tert-butyl radical . In contrast, it is suitable for deprotonating C, H-acidic compounds and for dehydrohalogenation .
In solution, potassium tert- butoxide forms complex structures, which leads to a reduction in its reactivity. These structures can be broken up by adding DMSO .
In a mixture with lithium alkyls , potassium tert -butanolate is called Schlosser's base , which increases the basicity.
Individual evidence
- ↑ a b c d e f g Entry on potassium tert-butoxide in the GESTIS substance database of the IFA , accessed on January 10, 2017(JavaScript required) .
- ↑ Joseph Hornback: Organic Chemistry. Cengage Learning, 2005, ISBN 978-0-534-38951-2 ( limited preview in Google Book Search), p. 131.
- ^ FG Bordwell: Bordwell pKa Table (Acidity in DMSO) .
- ↑ a b c d e f g D. Caine: Potassium tert -butoxide , in: Encyclopedia of Reagents in Organic Synthesis , John Wiley & Sons, New York, 2006; doi : 10.1002 / 047084289X.rp198.pub2 .