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Heterogeneous catalytic acylation of aromatic compound was investigated using solid Lewis acids consisting of yttrium zircon based Levis acid. The nature of the transition metal ions introduced in the mesoporous clay plays an important role in the activity of the catalysts. Yttria zirconia shows the best catalytic properties and could suit for selective practical preparation purposes 1-(2,6-dihydroxyphenyl)ethan-1-one was produced with 90 % yield under optimal conditions.

As part of a research program aimed at developing a new solid catalyst and its subsequent application in green chemistry for various organic transformations, the Yttria-zirconia based Lewis acid was found to be an extremely efficient catalyst for the DielsAlder 22-28 reaction and transesterification 23-28 of b-keto esters 24. 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. However, the reaction of benze-1,3-diol with acetic anhydride is found to be sluggish with solvent and catalyst (Table 1, entries 2) and reaction without solvent and catalyst (20 mol %) gives better yield and selectivity of the product. (Table 1, entries 3)

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. 

Promoted yttria zirconia catalysts have shown good catalytic activity or sometimes better for the synthesis of 1-(2,6-dihydroxyphenyl)ethan-1-one . Catalytic activity of these catalysts depends on the method of preparation, precursors used, nature of promoting agents, calcination temperature etc. These solid acid catalysts having strong incentives to which one can replace the unfriendly H2SO4 and HF acids in many industrial processes, and in this direction, there is a lot of scope and advantage to work., but still there is tremendous scope to study and exploit these catalysts for numerous reactions as a green chemistry.

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