Phenolic acids (PAs) are key compounds involved in the metabolism of plants and necessary building blocks for the biosynthetic pathways to lignins, coumarins, lignans, stilbenes and many other families of phenolic compounds. The industrial interest for PAs is increasing due to the emergence of ferulic- and sinapic acid-based functional additives (e.g., bisphenol A substitutes, antioxidants), anti-UV molecules (i.e., sinapoyl malate), and renewable polymers and resins. Therefore, encouraging works have been conducted for the biosourcing of PAs. However, extracting them from raw biomass remains complicated and rather expensive because of their low concentration in the biomass and the necessity to perform costly separation/purification steps.&lt;span style="font-size:10.8333px"&gt; &lt;/span&gt;Thereby, the main access to PAs consists in the condensation of malonic acid with phenolic aldehydes that are readily obtained from the oxidation of lignins. However, the common reaction conditions, involving pyridine as solvent and aniline or piperidine as catalyst, limit greatly their uses in industries such as the cosmetic or pharmaceutical sectors. To overcome these drawbacks, a microwave-assisted Knoevenagel-Doebner condensation process was developed. It presents both advantages to reduce the relatively considerable energy intake of classical thermic conditions and to substitute pyridine by a less toxic solvent, dimethylformamide (DMF). A design of experiment (DoE) was conducted in order to access the optimal conditions of temperature, time, equivalents of malonic acid and piperidine. The minimization of the unwanted formation of vinyl phenols was also considered. Results from the this DoE allowed us to propose a reliable procedure that converts biosourced p-hydroxybenzaldehydes into the corresponding PAs with 86-99% conversions and in 85-97% yields.

Microwave-assisted Knoevenagel-Doebner reaction: An efficient method for phenolic acids synhtesis

2019 Spring National Meeting

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