Tetrabutylammonium Hydrogen Sulfate

Introduction

Tetrabutylammonium hydrogen sulfate (TBAHS, 1), is a stable, hygroscopic, white solid (mp 169–171 °C). It is widely used in various fields of chemistry as phase-transfer catalyst (PTC) and ion-pairing reagent as mobile phase additive in HPLC. It has been also used in a variety of organic transformations some of which include the syntheses of triarylpyridines,[ ¹ ] N-monosubstituted α-keto amides,[ ² ] cyclic and acyclic β-disubstituted, α,β-unsaturated ketones,[ ³ ] 3-alkylated indoles,[ ⁴ ] benzopyran-annulated pyrano[2,3-c]pyrazoles,[ ⁵ ] N1-alkylated 3,4-dihydropyrimidine-2(1H)-ones,[ ⁶ ] 2-O-deacetylated glucosyl hydroxamates,[ ⁷ ] 1,2,3-triazoles,[ ⁸ ] 1,8-dioxooctahydroxanthenes,[ ⁹ ] β- and γ-amino ethers, morpholines and their higher homologues,[ ¹⁰ ] etc.

Although TBAHS is commercially available and inexpensive, it can be prepared from tetrabutylammonium azide[ ¹¹ ] by treating it with potassium hydrogen sulfate and 10% aqueous sulfuric acid in aqueous medium (Scheme [1], eq. 1) or from tetrabutylammonium thiocyanate[ ¹² ] by treating it with relatively concentrated sulfuric acid (70%) at 75 °C (Scheme [1], eq. 2).

Scheme 1 Synthesis of tetrabutylammonium hydrogen sulfate (TBAHS, 1)

• References

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