Assessment on the double role of the transition metal salts on the acetalization of furfural: Lewis and Bronsted acid catalysts

The conversion of biomass derived to more valuable compounds has attracted growing attention due to the economic and environmental reasons. In special, the furfural deserves highlight because it is a versatile biorefinery platform-molecule and has been used as feedstock to produce fuels and fine chemicals. In this work, we have developed a process to synthesize furfural acetals at room temperature in transition metal-catalyzed reactions using different alcohols. Among the transition metal catalysts, the FeCl3 provided the highest catalytic activity (ca. 90% conversion within 1 h reaction) and highest furfural acetal yield (ca. 94% of 2-(dimethoxymethyl)furan). Effects of main reaction parameters such as e.g. reaction time, catalyst concentration and pH of medium were assessed. Based on experimental results, we conclude that metal salts (i.e., mainly FeCl3 and NiCl2) act as Lewis and Bronsted acid catalysts on these reactions. The reaction scope was successfully extended to the different alcohols. A special attention was paid to assess the effects of catalyst nature on these processes.