Sodium tert-butoxide

Description

Sodium t-butoxide (t-BuONa) is a strong, non-nucleophilic base. The pKa of its conjugate acid (t-butanol) is about 17. Similar bases include potassium t-butoxide (t-BuOK) and lithium t-butoxide (t-BuOLi). Sodium t-butoxide is the preferred base over t-BuOK and t-BuOLi for palladium catalyzed Buchwald reactions.

Chemical properties

white to light tan crystalline powder

The Uses of Sodium tert-butoxide

Sodium tert-butoxide is used as a strong base and a non-nucleophilic base. In organic synthesis, it serves as an intermediate in various reactions like condensation, rearrangement and ring-opening. Further, it finds use in agrochemicals, pharmaceuticals, colorants, aroma chemicals, detergents and biodiesel. It acts as a catalyst in polymerization and isomerization reactions.

Reactions

Sodium tert-butoxide is used to prepare tert-butoxide complexes. For example hexa(tert-butoxy)ditungsten(III) is thus obtained by the salt metathesis reaction from a ditungsten heptachloride:

NaW2Cl7(THF)5 + 6 NaOBu-t → W2(OBu-t)6 + 7 NaCl + 5 THF

Synthesis

A mixture of the chloride (25 g, 168 mmol), the amine (40 g, 168 mmol), Pd(OAc)2 (1.5 g, 6.72 mmol), (+-) BINAP (4.18 g, 6.72 mmol), and Cs2CO3 (76.7 g, 235.2 mmol) in toluene (800 mL) was stirred at 90 C under N2 for 23 h. The mixture was filtered through a pad of celite and washed with EtOAc. The filtrate was concentrated in vacuo and purified by silica gel flash chromatography (1:5 EtOAc/petroleum ether) to provide the product as a red solid. [22.4 g, 37%]

Preparation

Sodium tert-butoxide can be produced by treating tert-butyl alcohol with sodium hydride.

Safety

Sodium t-butoxide (t-BuONa) is a strong alkoxide base. It is a hygroscopic powder that should be stored and handled under an inert atmosphere.

Flammability and Explosibility

Highly flammable

Purification Methods

Its solubility in tert-BuOH is 0.208M at 30.2o and 0.382M at 60o, and it is quite soluble in tetrahydrofuran (32g/100g). It should not be used if it has a brown colour. [Feuer J Am Chem Soc 78 4364 1956, Hurd Inorg Synth I 87 1939, IR: Seubold J Org Chem 21 156 1956, Beilstein 1 IV 1609.]