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The application of acid catalysts is very important in the chemical and refinery industries, and those technologies employing highly corrosive, hazardous and polluting conventional liquid acids and Lewis acids such as H2SO4, HCl, HF, HClO4, H3PO4, AlCl3, BF3, ZnCl2 and SbF5 are being replaced with solid acids such as clays, zeolites, heteropolyacids, ion exchange resins (Amberlyst and Nafion-H) and metal oxides. Some of these solid acids and superacids are characterized by various advantages which include easy handling, simplicity and versatility of process engineering, catalyst regeneration, decreasing reactor and plant corrosion problems and environmentally safe disposal [1-15]. Till date, a number of organic syntheses and transformation reactions have been conducted with solid acids leading to better rego- and stereo-selectivity/specificity which depend on the strength of the acid and type of acidity (Brønsted or Lewis). Over the past few decades, zirconia (ZrO2) based solid acids have received much attention, among other solid acids, due to their superior catalytic activity for hydrocarbon conversions at mild conditions [8,14-18]. Over the past few decades, zirconia (ZrO2) based solid acids have received much attention, among other solid acids, due to their superior catalytic activity for hydrocarbon conversions at mild conditions [8,14-18]. These catalysts are finding numerous applications in oil refinery and petrochemical industries. Among the promoted zirconia-based solid acid catalysts, the SO4 2− /ZrO2 (SZ) catalyst become more popular from 1979 when Arata and co-investigators [16,19] reported that zirconia, upon proper treatment with sulfuric acid or ammonium sulfate exhibits extremely strong acidity and is capable of catalyzing the isomerization of n-butane to isobutane at room temperature. Over the period of time the SZ catalyst has also been reported to be very active for various organic syntheses and transformation reactions including multi component reactions, isomerization, alkylation, acylation, esterification, glycosidation and some other commercially useful reactions [20-28]. 1-(2,6-dihydroxyphenyl)ethan-1-one compound which is an intermediate raw material for medicines, such as antitussive and expectorant, and used in many purpose to synthesize these molecules using green chemistry tool. Some of these solid acids and superacids are characterized by various advantages which include easy handling, simplicity and versatility of process engineering, catalyst regeneration, decreasing reactor and plant corrosionThese catalysts are finding numerous applications in oil refinery and petrochemical industries.with sulfuric acid or ammonium sulfate exhibits extremely strong acidity and is capable of catalyzing the isomerization of n-butane to isobutane at room temperature.

For instance, a method is known wherein resorcinol and ethyl acetoacetate are used as starting materials, as described in Organic Syntheses, Coll. Vol. 3, p. 281 (1965), but this method needs four steps. There are also known a method in which 2-acetyl-1 ,3-cyclohexanedione is chlorinated to provide 2-acetyl-2-chloro-1,3-cyclohexane dione, and then o the product is treated with hydrogen chloride in dimethylformamide, as described in as as https://www.mysciencework.com/patent/show/method-preparing-2acylresorcinols-EP0331422A2https://patentimages.storage.googleapis.com/d4/ff/d9/88050c5ba6f08c/EP0331422A2.pdf.Journal of Chemical Research 2020, Vol. 44(11-12) 660–666. In this paper, resorcin[4]arenes with an acetyl group at the ortho-position have been synthesized using sodium methoxide as the base under reflux conditions. doi.org/10.1177/1747519820915.

Synthetic scheme:

Experimental: Procedure for the preparation of the catalyst: The catalyst was prepared by treating a mixture of aqueous solutions of yttrium nitrate and zirconyl nitrate (molar ratio 16:84) with aqueous ammonia (28%) under vigorous stirring until a pH value of 8.5 was achieved and a precipitate was formed. Downloaded by: National University of Singapore. Copyrighted material. LETTER Yttria-Zirconia Based Lewis Acid 209 , Synlett 2001, No. 2, 206–209 ISSN 0936-5214 © Thieme Stuttgart • New York. Precipitate was washed with deionized water, dried at 110°C, treated with 2N sulfuric acid, dried again at 120°C for 24 h. The subsequent programmed calcination at 500°C for 3 h at a heating rate of 2°C min-1 resulted in a highly acidic material.

(a) 2,6- dihydroxyphenyl)ethane-1-one

Thus, when a resorcinol were treated with acid anhydrides in the presence of a catalytic amount of the new yttria-zirconia based catalyst, the corresponding acetates 1-(2,6- dihydroxyphenyl)ethane-1-one were obtained in excellent yields.

In a typical experimental procedure, acid anhydride (11 mmol; 1.1 equiv) and benze-1,3-diol (10 mmol) was added dropwise to a solution of neat reaction condition containing catalyst (20 % by weight), and the mixture was heated refluxed for 60-70 oC the indicated length of time (Table 1–3). The reaction was monitored by TLC. After completion of reaction, the catalyst was filtered and the filtrate was concentrated, diluted with water (15 ml) and extracted with CH2Cl2 (2 x 20 ml). The organic layer was separated, washed with 10 % aq. NaHCO3, brine, water and dried over Na2SO4. The solvent was removed and the crude product was chromatographed on a silica gel column to afford the pure product. After the reaction, the catalyst is recovered with retention of its catalytic activity. It can be further reactivated for reuse by heating it at 500 °C in the presence of air. The substrates examined in our studies and the results obtained are summarized in Table 1.

Product were characterized by1H NMR CDCl3 2.47 (3H, S), 6.38-6.40 (2H, dd), 7.22-7.26(2H, dd), 9.48 OH (bs) and IR in cm-1: ; C=O peaks 1715 cm-1, OH peak 2400 cm-1, Mass spectrum MS+1, (153) and its correspond to the authentic sample 28.

Table-1: Acid catalysed synthesis of 2,6- dihydroxyphenyl)ethane-1-one using Yttria-zirconia based lewis acid

 

a:Products were characterized by spectroscopic data and also by comparison with the authentic samples.

* a : Reaction performed in the absence of catalyst

**

b: Reaction performed in the with solvents (Acetonitrile) and catalyst

***

c: Reaction performed in the with without solvents/ neet reaction condition and catalyst.

Product were characterized by1H NMR CDCl3 2.47 (3H, S), 6.38-6.40 (2H, dd), 7.22-7.26(2H, dd), 9.48 OH (bs) and IR in cm^{-1: ;} C=O peaks 1715 cm-1, OH peak 2400 cm-1, Mass spectrum MS+1, (153) and its correspond to the authentic sample[ 28].

This prompted us to use this catalyst for acylation reactions as green chemistry application, and here we report that an yttria-zirconia based Lewis acid serves as an excellent catalyst for the selective acylation of benze-1,3-diol during synthesis of 1-(2,6-dihydroxyphenyl)ethan-1-one in without solvent (neat) reaction condition. 

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