Phenolic Monoterpenes Conversion of Conobea scoparioides Essential Oil by Hydrotalcite Synthesized from Blast-Furnace Slag

TL;DR

This study shows how a catalyst made from industrial waste can convert plant oils from the Amazon into valuable antiseptic compounds like thymol.

Contribution

A hydrotalcite catalyst from blast-furnace slag effectively converts monoterpenes into high-value thymol derivatives.

Findings

The hydrotalcite catalyst increased thymol content in the oil from 41% to 95%.

The catalyst mimicked the plant's biosynthetic pathway, favoring hydroxylated derivatives.

The process offers an economically valuable method for producing antiseptic compounds from Amazonian plants.

Abstract

Conobea scoparioides (Plantaginaceae) is an herbaceous plant known as “pataqueira” that grows wild in seasonally wet areas of the Amazon region. It is used for aromatic baths and anti-protozoan remedies by the Brazilian Amazon native people. The main volatile compounds identified in the essential oil of “Pataqueira” were the phenolic monoterpenes thymol and thymol methyl ether and their precursors, the monoterpene hydrocarbons α-phellandrene and p-cymene. A hydrotalcite synthesized from blast-furnace slag exhibited a 3:2 (Mg/Al) molar ratio, and this layered double hydroxide (LDH) was evaluated as a catalyst in converting the main monoterpenes of the “Pataqueira” oil. This action significantly increased the thymol content, from 41% to 95%, associated with the percentual reduction in other main components, such as thymol methyl ether, α-phellandrene, and p-cymene. The LDH reaction showed a strong tendency towards producing hydroxylated derivatives, and its behavior was similar to the hypothetical plant biosynthetic pathway, which leads to the production of the monoterpenes of “Pataqueira” oil. Thymol and its derivatives are potent antiseptics applied in pharmaceutical and hygienic products as antibacterial, antifungal, and antioxidant properties, among others. The present work reports a natural source with a high thymol content in aromatic plants from the Amazon, with evident economic value.

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