Al(HSO4)3 as an efficient catalyst for acetalization of carbonyl compounds under heterogeneous or solvent -free conditions

Abstract

O ácido Al(HSO 4 ) 3 sólido foi usado na acetalização de compostos carbonílicos à temperatura ambiente, sem solvente, levando aos produtos desejados em excelentes rendimentos. A disponibilidade e baixo custo deste reagente, aliados a processo simples e fácil torna o método atraente para a síntese orgânica.Al(HSO 4 ) 3 as a solid acid was applied for acetalization of carbonyl compounds at room temperature and under solvent-free conditions with good to excellent yields. The cheapness and availability of this reagent with easy procedure and work-up make this method attractive for the organic synthesis.Keywords: acetalization, solvent-free, solid acid, Al(HSO 4 ) 3 , carbonyl compound, heterogeneous condition IntroductionRecently, some chemists found that many reactions proceed efficiently in the solid state. Indeed, in many cases, solid state organic reaction occurs more efficiently and more selectively than does its solution counterpart. The solvent-free reaction has many advantages such as reduced pollution, low cost, process simplicity and easier workup. These factors are especially important in industry.Acetals are not only the most widely used protecting groups but are also efficient chiral auxiliary groups for enantioselective synthesis. 1 The most convenient and practical method for acetalization is the reaction of carbonyl compounds with ethylene glycol in the presence of an appropriate catalyst, with removal of water formed. Tetrabutylammonium tribromide, 2 polymer bounded metal complexes, 3 SbCl 3 , 4 silica gel supported metallic sulfates, 5 DDQ, 6 NBS, 7 lithium triflate, 8 iodine, 9 titanium cationexchange montmorillonite 10 and polyaniline supported sulfuric acid salt 11 are usually utilized as catalysts.Solid acids have many advantages such as simplicity in handling, decreasing reactor and plant corrosion problems, and environmentally safe disposal. 12 Also, wastes and by-products can be minimized or avoided by developing cleaner synthesis routes. On the other hand, any reduction in the amount of sulfuric acid needed and/ or any simplification in handling procedures is required for risk reduction, economic advantage and environment protection.Very recently, we among many others have demonstrated that heterogeneous reagent systems have many advantages such as simple experimental procedures, mild reaction conditions and minimization of chemical wastes as compared to the liquid phase counterparts. 13 Thus, inorganic acidic salts such as Al(HSO 4 ) 3 14 or Mg(HSO 4 ) 2 15 could be recommended for the above mentioned purposes. Results and DiscussionAlthough there are a few reports on the application of inorganic acidic salts such as Mg(HSO 4 ) 2 or Al(HSO 4 ) 3 in synthetic methodology, recently more attention has been paid to the investigation of their potentials in organic synthesis. 14-17 These salts are stable and non-hygroscopic solid material, insoluble in most organic solvents. In continuation of our studies on the application of metallic hydrogensulfate salts in organic synthesis, now we wish 878 ...

H3PW12O40/SiO2: An Eco‐Friendly Alternative for the Stereo‐, Regio‐ and Chemoselective Claisen‐Schmidt Condensation

“…In continuation of our studies on the application of solid acids in organic synthesis [17][18][19][20][21][22] we report a simple, efficient and selective protocol for the Claisen-Schmidt condensation in the presence of (H 3 PW 12 O 40 ) or (PW). It is obvious that bulk PW has a low surface area.…”

Preparation of indolylmethanes catalyzed by metal hydrogen sulfates

“…In continuation of our studies on the application of heterogeneous systems [2][3][4][5][6][7] we were interested in using inorganic solid acids such as Oxone ® , silica sulfuric acid, and metal hydrogen sulfate acidic salts, including Ca(HSO 4 ) 2 , Zn(HSO 4 ) 2 , Mg(HSO 4 ) 2 , Al(HSO 4 ) 3 , as catalysts in the synthesis of bis(indolyl)methanes. This is a simple method for the effective synthesis of bis(indolyl)methanes, obtained from the reaction of indole and a carbonyl compound, under mild and heterogeneous conditions at room temperature, in ethanol as a solvent (Scheme 1).…”

“…E-mail: niknam@pgu.ac.ir heterogeneous conditions. Along this line, using Al(HSO 4 ) 3 [3], Fe(HSO 4 ) 3 [4], Mg(HSO 4 ) 2 [5], NaHSO 4 .H 2 O [6], and Oxone ® (2KHSO 5 .KHSO 4 .K 2 SO 4 ) [7], which are low in toxicity, highly stable toward humidity, recyclable and air stable have found more attention. In continuation of our studies on the use of inorganic hydrogen sulfate acidic salts in organic transformations [3][4][5][6][7], we have found that aluminum hydrogen sulfate is suitable for the direct synthesis of bis(indolyl)-and tetra(indolyl)methanes at room temperature.…”

Acetalization of hexanal with 2-ethyl hexanol catalyzed by solid acids

“…[1][2][3][4] Most of the acetalization process is the reaction of carbonyl compounds with ethylene glycol in the presence of an appropriate catalyst. 1,5 Acetal derived compounds have been used as a solvent in fragrance industries, cosmetics, food and beverage additives, pharmaceuticals, in the synthesis of enantiomerically pure compounds, and in polymer chemistry. 6,7 Acetals have been also used in motor oils, lubricating oils and hydraulic fluids.…”