Sustainable synthesis of acetals from glycerol as potential additives for biofuels under solvent-free conditions

Acetals formed from glycerol find applications in several areas, their use as fuel additives being the most promising, since it results in total integration in the biodiesel chain and eliminates one of the obstacles to its production. In order to convert glycerol into acetals, the use of p-sulfonic acid calix[4]arene supported on silica (CX4SO3HSi(n)) and microwave-assisted heating was proposed, and quantitative analysis was performed by 1H NMR. The effects of the main reaction parameters were evaluated, such as temperature, reaction time and the amount of heterogeneous catalyst, using benzaldehyde and glycerol as model substrates. From the optimized conditions (0.5 mmol of glycerol, 0.5 mmol of benzaldehyde, 5 wt% of the catalyst CX4SO3HSi(n), at 110 °C in 20 min), the generality of the reaction was evaluated, obtaining twelve products with yields ranging from 6 to 99%. The important aspects of this protocol are the following: solvent-free reaction, water as the sole waste, being metal-free, and shorter reaction times.