Sauro Passeri

A comparison of the reaction mechanism in acid-and in basic-catalysed gas-phase methylation of phenol

This paper compares the reaction of gas-phase methylation of phenol with methanol in basic and in acid catalysis, with the aim of investigating how the transformations occurring on methanol affect the catalytic performance and the reaction mechanism. It was found that with the basic catalyst Mg/Fe/O, the true alkylating agent is formaldehyde, obtained by dehydrogenation of methanol. Formaldehyde reacted with phenol to yield salicylic alcohol, which rapidly dehydrogenated to salicylic aldehyde. The latter was isolated in tests made by variation of the residence time, and in tests made by feeding a formalin/phenol aqueous solution. Salicylic aldehyde then transformed to o-cresol, the main product of the basic-catalyzed methylation of phenol, by means of an intermolecular H-transfer. With an H-mordenite catalyst, instead, the activated methanol reacted with phenol to generate anisole, cresols and polyalkylated phenols.

A Two-Step Process for the Synthesis of Hydroxytyrosol

A new process for the synthesis of hydroxytyrosol (3,4-dihydroxyphenylethanol), the most powerful natural antioxidant currently known, by means of a two-step approach is reported. Catechol is first reacted with 2,2-dimethoxyacetaldehyde in basic aqueous medium to produce the corresponding mandelic derivative with >90 % conversion of the limiting reactant and about 70 % selectivity to the desired para-hydroxyalkylated compound. Thereafter, the intermediate is hydrogenated to hydroxytyrosol by using a Pd/C catalyst, with total conversion of the mandelic derivative and 68 % selectivity. This two-step process is the first example of a synthetic pathway for hydroxytyrosol that does not involve the use of halogenated components or reduction methodologies that produce stoichiometric waste. It also avoids the complex procedure currently used for hydroxytyrosol purification when it is extracted from wastewater of olive oil production.