Zirconium(IV) Chloride as a New, Highly Efficient, and Reusable Catalyst for Acetylation of Phenols, Thiols, Amines, and Alcohols under Solvent-Free Conditions

Abstract

Zirconium(IV) chloride has been found to be a new, highly efficient, and reusable catalyst for acetylation of structurally diverse phenols, thiols, amines, and alcohols under solvent-free condtions. Acetylation of sterically hindered and electron deficient phenols is achieved in excellent yields with stoichiometric amounts of Ac 2 O at room temperature. Acid-sensitive alcohols undergo acetylation with excellent chemoselectivity without competitive side reactions such as dehydration or rearrangement. The mild Lewis acid property of the catalyst enables the acetylation to be carried out with optically active substrates without any detrimental effect on the optical purity.

Zirconyl triflate: A new, highly efficient and reusable catalyst for acetylation and benzoylation of alcohols, phenols, amines and thiols with acetic and benzoic anhydrides

“…In the case of benzylic alcohols, the nature of substituents had no significant effect on the acetylation yields. In comparison with other zirconium salts [22][23][24], ZrO(OTf) 2 was superior in product yields, catalyst amount and reaction times. Some of the above mentioned alcohols were subjected to benzoylation with benzoic anhydride, a less reactive anhydride, in the presence of 0.5 mol% of ZrO(OTf) 2 at 50 °C.…”

“…E-mail: moghadamm@sci.ui.ac.ir TaCl 5 [11], TMSOTf [12], [Cu(OTf) 2 ] [13], [In(OTf) 3 ] [14], magnesium bromide [15], bismuth(III) salts [16], ferric perchlorate adsorbed on silica-gel [17], RuCl 3 [18], InCl 3 [19], Ce(OTf) 3 [20], Mg(ClO 4 ) 2 [21], ZrCl 4 [22], Cp 2 ZrCl 2 [23], ZrOCl 2 .8H 2 O [24], Al(OTf) 3 [25], NaHSO 4 ·SiO 2 [26], La(NO 3 ) 3 .6H 2 O [27], NbCl 5 [28], Gd(OTf) 3 [29], Alumina supported MoO 3 [30] cerium polyoxometalate [31] Ce(OTf) 4 [32], (SiO 2 ) n -PCl 3-n [33], copper salts [34,35], AlPW 12 O 40 [36,37] and electron-deficient tin(IV) porphyrins [38][39][40]. However, some of the reported methods for the acetylation of alcohols suffer from one or more of the following disadvantages such as high temperature and drastic reaction conditions, formation of undesirable or toxic by-products, expensive reagents, hygroscopicity and thermal instability of the reagents, long reaction times, low yields of the desired products and bulk requirement of solid bed.…”

Some applications of zirconium(IV) tetrachloride (ZrCl4) and zirconium(IV) oxydichloride octahydrate (ZrOCl2.8H2O) as catalysts or reagents in organic synthesis

“…ZrCl 4 in the presence of Ac 2 O [41], and also ZrOCl 2 .8H 2 O in combination with acyl chloride [42], were used as highly…”

Zinc dust: An extremely active and reusable catalyst in acylation of phenols, thiophenol, amines and alcohols in a solvent-free system

“…Acylation with acids [8,9], acyl imidazoles [10], and acyl urea [11], are also known. Acid catalyzed acylation mainly requires polymeric acids [12,13]; and metal chlorides [14][15][16], metal triflates such as Sc(OTf)3/Bi(OTf)3/Li(OTf)3 [17][18][19], metal perchlorates (LiClO4 /BiOClO4) [20,21] have also been utilized as Lewis acid catalysts for acylation of alcohols. Other reagents such as I2 [22,23], [bmIm][dca] ionic liquid [24], solid supported reagents like HClO4-SiO2 [25], Py/basic alumina [26], neutral Al2O3 [27], Clay [28,29], ZrOCl2·8H2O [30] polyphosphate ester [31] and very recently ZnO [32], Sm [33] and Mg(NTf2)2 [34] have been employed for the same purpose.…”