At 165–200 uC, in the presence of sodium-exchanged faujasites (NaX or NaY) as catalysts, the reaction of dimethyl carbonate with benzyl-, o- and p-methoxybenzyl-, p-hydroxybenzyl-, diphenylmethyl-, and triphenylmethyl-alcohols (1a, 2a,b, 3a, 4a, and 4c, respectively), produces the corresponding methyl ethers in up to 98% yields. A peculiar chemoselectivity is observed for hydroxybenzyl alcohols (compounds 3a and 3b, para- and ortho-isomers) whose etherification takes place without affecting the OH aromatic groups. Acid–base interactions of alcohols and DMC over the faujasite surface offer a plausible explanation for the catalytic effect of zeolites NaY and NaX, as well as for the trend of reactivity shown by the different alcohols (primary . secondary . tertiary). However, in the case of substrates with mobile protons in the b-position (i.e. 1-phenylethanol and 1,1-diphenylethanol), the dehydration reaction to olefins is the major, if not the exclusive, process.

The Methylation of Benzyl-type Alcohols with Dimethyl Carbonate in Presence of Y and X-Faujasites: Selective Synthesis of Methyl Ethers

SELVA, Maurizio;FABRIS, Massimo
2008-01-01

Abstract

At 165–200 uC, in the presence of sodium-exchanged faujasites (NaX or NaY) as catalysts, the reaction of dimethyl carbonate with benzyl-, o- and p-methoxybenzyl-, p-hydroxybenzyl-, diphenylmethyl-, and triphenylmethyl-alcohols (1a, 2a,b, 3a, 4a, and 4c, respectively), produces the corresponding methyl ethers in up to 98% yields. A peculiar chemoselectivity is observed for hydroxybenzyl alcohols (compounds 3a and 3b, para- and ortho-isomers) whose etherification takes place without affecting the OH aromatic groups. Acid–base interactions of alcohols and DMC over the faujasite surface offer a plausible explanation for the catalytic effect of zeolites NaY and NaX, as well as for the trend of reactivity shown by the different alcohols (primary . secondary . tertiary). However, in the case of substrates with mobile protons in the b-position (i.e. 1-phenylethanol and 1,1-diphenylethanol), the dehydration reaction to olefins is the major, if not the exclusive, process.
2008
9
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10278/3982
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