Potassium tert-butoxide

Description

Potassium t-butoxide (t-BuOK) is a strong, non-nucleophilic base. The pKa of its conjugate acid is about 17. Similar bases include sodium t-butoxide (t-BuONa) and lithium t-butoxide (t-BuOLi).

Chemical properties

white crystalline powder

The Uses of Potassium tert-butoxide

Potassium tert-Butoxide is used in the synthesis of many organic compounds primarily as a strong base. In particular, it is used as a reagent in the base- catalyzed carbonylation of amines for the synthesis of N-Formamides.

The Uses of Potassium tert-butoxide

To a suspension of methyl triphenylphosphonium bromide (2.4 g, 6.6 mmol) in THF was added tBuOK (1M in THF, 7.1 mmol) at RT. After stirring for 90 min, a solution of the SM (1.25 g, 3.35 mmol) in dry THF was added. The resulting mixture was stirred at RT for 18 h, after which time it was partitioned between saturated NH4Cl and MTBE. The org layer was dried (Na2SO4), concentrated, and purified by flash chromatography (25-30% EtOAc/hexane) to provide the product as a colorless oil. [0.3 g, 24%] [UK Pat App GB2463151A, page 141]

The Uses of Potassium tert-butoxide

Usually used for greener amidation of esters.

Synthesis

Potassium tert-butoxide is produced by reacting tert-butanol with potassium metal.

What are the applications of Application

Potassium tert-butoxide has been used as a strong base in the enantioselective synthesis of amines by transfer hydrogenation of N-(tertbutylsulfinyl)imines. It can also be used:
To synthesize aliphatic and aromatic amides from corresponding esters and amines.
As a base in the intramolecular cyclization of aryl ethers, amines, and amides.
As a catalyst to prepare styrene derivatives from aryl halides and alkenes by Mizoroki-Heck reaction.

Hazard

Potassium tert-butoxide is unstable and reactive; Reacts violently with water; Self-heating in large quantities, may catch fire; Causes burns; Inhalation may cause corrosive injuries to upper respiratory tract and lungs;

General Description

This product has been enhanced for catalytic efficiency.

Fire Hazard

Potassium tert-butoxide is a flammable solid. It ignites on heating. Being very strongly basic, its reactions with acids are highly exothermic. Contact of solid powder with drops of sulfuric acid and vapors of acetic acid caused ignition after an induction period of 0.5 and 3 minutes, respectively (Manwaring 1973). Ignition occurs upon reactions with many common solvents of the type ketone, lower alcohols, esters, and halogenated hydrocarbons. Such solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, n-propanol, isopropanol, ethyl acetate, n-propyl formate, n-butyl acetate, chloroform, methylene chloride, carbon tetrachloride, epichlorohydrin, dimethyl carbonate, and diethyl sulfate (NFPA 1997). Such ignition may arise from accidental contact of the alkoxide with these solvents and may be attributed to sudden release of energy from exothermic reactions. However, slow mixing of the powder with excess solvent will dissipate the heat. It reacts violently with water, producing tert-butanol and potassium hydroxide, as follows:
K―OC―(C4H9)3＋H2O → tert-C4H9OH +KOH
The addition of potassium tert-butoxide to the solvent dimethyl sulfoxide can cause ignition of the latter (Bretherick 1995).

Flammability and Explosibility

Flammable

Purification Methods

It sublimes at 220o/1mm. The last traces of tert-BuOH are removed by heating at 150-160o/2mm for 1hour. It is best prepared afresh as likely impurities are tert-BuOH, KOH and K2CO3 depending on its exposure to air. Its solubility at 25-26o in hexane, toluene, Et2O, and THF is 0.27%, 2.27%, 4.34% and 25.0%, respectively. [Feuer et.al. J Am Chem Soc 78 4364, Doering & Urban J Am Chem Soc 78 5938 1956, Beilstein 1 IV 1612.]