[10534-59-5] · C18H39NO2 · Tetra-n-butylammonium Acetate · (MW 301.58)
Physical Data: mp 114-115 °C (Alfa), 95-98 °C (Aldrich).
Solubility: sol most polar organic solvents (MeCN, acetone, CH2Cl2, EtOH); slightly sol benzene.
Form Supplied in: white crystalline solid; widely available.
Purification: recrystallization from a minimum amount of methanol (mp 114-115 °C) or, alternatively, filtration of a benzene solution through basic alumina (activity I) and recrystallization from 5:4:2 benzene-pentane-ethyl acetate at -25 °C (mp 95-98 °C).
Handling, Storage, and Precautions: irritant, hygroscopic; protect from moisture.
This reagent is an excellent source of nucleophilic acetate ion for SN2 substitution reactions. Tetraethylammonium acetate functions in a similar fashion. Equatorial steroidal tosylates are displaced to give axial acetates upon treatment with tetra-n-butylammonium acetate in refluxing acetone (eq 1).4 The use of benzene, instead of acetone, results in clean inversion of deuterated endo-norbornyl sulfonates without isotopic rearrangement5 (eq 2).1 This process may also be carried out in molten reagent (eq 3).6
3-Bromomethyl-2-thiacephem derivatives are converted to allylic acetates in excellent yield (eq 4).2 The use of AcOH as solvent prevents double bond isomerization for related D3-3-bromomethylcephems.7
The solubility of tetra-n-butylammonium acetate in organic solvents makes it an effective replacement for NaOAc. Tetra-n-butylammonium acetate is superior to NaOAc for the deoxygenation of aldehydes and ketones by reduction of the corresponding tosylhydrazones with catecholborane (eq 5).3
Use of tetra-n-butylammonium acetate in the electrochemical reduction of some o-bis(phenylsulfonyl)benzene derivatives affords good yields of dibenzothiophene 5,5-dioxides.8 Photolysis of 1,2,4,5-tetracyanobenzene in the presence of tetra-n-butylammonium acetate yields bis(2,4,5-tricyanophenyl)methane.9 The reaction between tetra-n-butylammonium carboxylates and p-Toluenesulfonyl Chloride produces mixed p-toluenesulfonic carboxylic anhydrides,10 an alternative to chloroformates.
Tetra-n-butylammonium acetate promotes an unexpected elimination of a bromohydrin acetate to produce an alkene.11 The reagent is also an effective catalyst for the phosphorylation of alcohols by cyclic enediol phosphates in aprotic solvents,12 as well as for anionic polymerization.13
Roberto Fernández de la Pradilla & Alma Viso
CSIC, Madrid, Spain