[35638-41-6] · C16H36MnNO4 · Tetra-n-butylammonium Permanganate · (MW 361.47)
Physical Data: 98 °C (dec).5
Form Supplied in: purple solid.
Solubility: sol 0.417 M in CH2Cl2, 3.44 × 10-4 M in toluene, 2.96 × 10-5 M in CCl4, 2.10 × 10-3 M in H2O; dec CHCl3.5
Analysis of Reagent Purity: ε = 2530 ± 30 L mol-1 cm-1 at 526 nm.5 IR (KBr) 3420, 2970, 2870, 1470, 1370, 910 cm-1. NMR (CD2Cl2) d 0.35, 0.80, 2.70 ppm.
Preparative Methods: Potassium Permanganate (3.16 g, dissolved in a minimum of water) is added with stirring to tetra-n-butylammonium chloride (6.44 g, dissolved in 200 mL of water) and the purple precipitate collected and washed with water; yields 6.43 g (89%) after drying under vacuum in the presence of P2O5.6
Purification: recrystallize by dissolving the reagent in a 2:1 solution of CCl4 and CH2Cl2 and drawing a stream of dry air over the mixture to slowly evaporate the solvent. The crystalline product which forms is collected and washed with pentane. It decomposes with ignition at 101 °C when heated in a melting-point tube. The melting point obtained using thermal differential analysis is 98 °C. Highly purified material is not required for most synthetic procedures.
Handling, Storage, and Precautions: oxidant; small quantities may be stored in glass vessels at or below rt. One report states that a
violent ignition occurred when 2 g of tetra-n-butylammonium permanganate was being weighed onto a glassine paper.2 Precautions should, therefore, be taken when handling this reagent.
As illustrated by the following reactions, this reagent shows a substantial preference for the oxidation of tertiary C-H bonds to alcohols as compared to secondary C-H bonds to ketones (eq 1).1
The oxidation of benzylic methyl groups yields carboxylic acids (eq 2),2 while more elaborate side chains give alcohols or ketones, depending on the extent of substitution in the benzylic position (eqs 3 and 4).1
Alkenes are either cleaved2 or converted into 1,2-diols by tetra-n-butylammonium permanganate (eqs 5 and 6).
Primary alcohols are oxidized to carboxylic acids2 and secondary alcohols to ketones2,4 by this reagent (eqs 7-9).
Substituted benzaldehydes are oxidized to the corresponding benzoic acids in good yield.
Tetra-n-butylammonium permanganate has also been used as an oxidant in certain inorganic syntheses.7 The reactions of tetra-n-butylammonium permanganate are very similar to those of other quaternary ammonium and phosphonium permanganates such as Benzyltriethylammonium Permanganate and Methyltriphenylphosphonium Permanganate. Similar reactions can also be carried out more simply by use of phase-transfer processes which are described under Potassium Permanganate.
Donald G. Lee
University of Regina, Saskatchewan, Canada