Benzyltriphenylphosphonium Peroxymonosulfate

Biographical Sketches

Purushotham Madupu was born in Tiruvuru, India in 1976. He received his B.Sc, degree in 1996 from Andhra Loyola College, ­Nagarjuna University (India) and his M.Sc, degree (Industrial Chemistry) in 1998 from SVKP & Dr. KS Raju Arts & Science College, Andhra University (India). He is currently working towards his Ph.D. under the supervision of Prof. C. Venkata Rao at Sri ­Venkateswara University, Tirupati (India). His research interest focuses on the development of new synthetic methodologies for bioactive heterocycles, especially by employing the principles of green chemistry.

Introduction

Benzyltriphenylphosphonium peroxymonosulfate ­(1, ­BTPPMS) is a mild, efficient, stable, and cheap reagent which displays its versatility in organic synthesis. It is a white solid and generally stored at room temperature. It is quite soluble in dichloromethane, chloroform, acetone, and acetonitrile but insoluble in non-polar solvents, such as carbon tetrachloride, n-hexane, and diethyl ether. It has been used for the oxidation of alcohols to aldehydes and ketones under aprotic solvent condition, [¹] oxidative deprotection of trimethylsilyl and tetrahydropyranyl ethers under non-aqueous conditions, [²] and selective oxidation of sulfides and thiols to the corresponding sulfoxides and disulfides under solvent-free conditions. [³] It was also found to be useful for the dethioacetalization of 1,3-dithio­lanes and 1,3-dithianes to the corresponding carbonyl compounds in the presence of bismuth chloride under aprotic conditions [4] and conversion of oximes and semicarbazones to carbonyl compounds using microwave irradiation to afford the carbonyl compounds. [5] Because of the mild conditions as well as the high yields, this reagent has wide acceptance in the area of synthetic chemistry.

Preparation

BTPPMS can be easily prepared [6] from commercially available reagents. To a solution of benzyltriphenylphosphonium chloride in water a solution of Oxone^® in water was added dropwise. After stirring for 1 h at room temperature, the resulting precipitate was filtered, washed with cooled distilled water and dried in a desiccator to afford a white powder which decomposed at 144-146 ˚C. The white solid was then titrated three times [7] to yield 99% of the active oxidizing agent (HSO₅).

Scheme 1

Abstracts

(A) Oxidation of Urazoles to Triazolinediones: A convenient practical method for the oxidation of urazoles 2a-f to their corresponding triazolinediones 3a-f in high yields (75-94%) and exceedingly short reaction times (10-15 min) has been developed. [8] The process involves the mixing of BTPPMS and urazoles 2a-f in the presence of AlCl3 in a mortar to afford corresponding triazolinediones 3a-f in high yields under solvent-free conditions.
(B) Oxidative Deprotection: BTPPMS and a catalytic amount of bismuth chloride (0.4 molar ratio) can be applied to the oxidative deprotection of primary and secondary trimethylsilyl ethers as well as tetrahydropyranyl ethers to their corresponding carbonyl compounds. Further, ethylene acetals can be transformed to the corresponding carbonyl compounds in high yields under microwave irradiation. [6b]
(C) Deoximation of Oximes: The conversion of oximes, phenylhydrazones, 2,4-dinitrophenyl­hydrazones and semicarbazones to the corresponding carbonyl compounds can be performed using BTPPMS in the presence of a catalytic amount of BiCl3. [6c]
(D) Deprotection of Acetals and Thioacetals: A variety of acetals and thioacetals are deprotected to the corresponding parent carbonyl compounds under solvent-free conditions [9] using BTPPMS in the presence of aluminum chloride in high yields.
(E) Selective Oxidation of Sulphides and Thiols: An efficient procedure for the selective oxidation of various aromatic and aliphatic sulphides and thiols to their corresponding sulfoxides and disulfides under non-aqueous and aprotic conditions without catalyst has been developed by Hajipour et al. [¹0]
(F) Regioselective Oxidative Bromination of Electron-Rich Aromatic Rings: The regioselective oxidative bromination of electron-rich aromatic rings has been studied using potassium bromide as a bromine source in the presence of BTPPMS as oxidant under nearly neutral reaction conditions. [¹¹] In most cases monobrominated derivatives have been obtained regioselectively in good to high yields without the aid of strong acids.
(G) Oxidative Aromatization of 4-Alkyl- or Aryl- and Heterocyclic-Substituted Derivatives: A convenient and efficient protocol for the oxidative aromatization of 4-alkyl-, aryl-, and heterocyclic-substituted derivatives of Hantzsch 1,4-dihydropyridines to the corresponding pyridine derivatives has been studied using BTPPMS in the presence of BiCl3 under nearly neutral reaction conditions. [¹²]
(H) Metal-Free Oxidative Dehydrogenation of Imidazolines and Pyrazolines: Oxidative dehydrogenation of 1,3,5-trisubstituted pyrazolines and 2-substituted imidazolines to their corresponding pyrazoles and imidazoles is carried out effectively by treatment with BTPPMS. [¹³]

References

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