Heteropoly Acids as Heterogeneous Catalysts for Thioacetalization and Transthioacetalization Reactions

Abstract

Heteropoly acids are effective solid catalysts for the thioacetalization of carbonyl compounds. Tungstophosphoric acid (H 3 PW 12 O 40), was found to be an effective and a highly selective catalyst for the thioacetalization of aldehydes, ketones and for the transthioacetalization of acetals, acylals and O,S-acetals which proceeded in excellent yields in the absence of solvent. The catalyst has also been successfully applied to the chemoselective conversion of aor b-diketones and a b-keto ester into the corresponding dithioacetals. Sterically hindered carbonyl compounds such as camphor and benzophenone were also converted to their corresponding thioacetals in refluxing petroleum ether in 89-94% yields. Surprisingly, anthrone was reduced to anthracene in 91% yield.

Study on Catalysed Oxidation of Some Aliphatic Hydroxy Acids by N-chlorosuccinimide in Aqueous Acetic Acid Medium

“…Its high acidity and thermal stability in acetic acid shows that the three protons dissociate independently rather than sequentially. The PTA catalysed [4] oxidation of amines [5] , alcohols [ 6,7] , have already been acclaimed by few researchers.…”

Metal-Free Oxidation of Alcohols to Their Corresponding Carbonyl Compounds Using NH4NO3/Silica Sulfuric Acid

“…14 Additionally, metal nitrates supported on inorganic supports have been used as oxidizing reagents. Iron (III) nitrate supported on silica gel (Silfen), 15 iron (III) nitrate or copper (II) nitrate supported on K10-clay (Clayfen or Claycop), 16 iron (III) nitrate mixed with HZSM-5 zeolite (Zeofen) 17 and ferric nitrate activated by heteropoly acids 18 are the reagents employed for the oxidation processes. However, the use of harmful transition metals and the stability of these reagents face problems.…”

“…For example, Clayfen should be kept under n-pentane. 18 Thus, the search for environmentally friendly as well as economical oxidation processes continues. On the other hand; recent rapidly growing environmental concerns need much greener transition-metal-free oxidation protocols.…”

Efficient catalytic synthesis of 2-imidazolines and bis-imidazolines with silica supported tungstosilicic acid

“…Some advantages of HPAs are non-corrosivity, environmentally friendly because of its reusability, economically feasible solid acid catalysts compared to conventional homogeneous acids, high flexibility in modification of the acid strength, ease of handling, nontoxicity and experimental simplicity. From a synthetically point of view, a variety of useful transformations such as oxidation of alcohols, 4 Friedel-Crafts 5 and Mannich reactions, 6 cyanosilylation, 7 ring-opening of epoxides, 8 and dehydration, 9 have been developed using HPAs as catalysts.…”