Acetalization of β-citronellal over a renewable carbon catalyst obtained from bio-oil sulfonation: a green route to obtain valuable feedstocks

Abstract

In this work, an efficient renewable carbon catalyst obtained by sulfonation of bio-oil was used for the first time to produce terpene acetals by condensation of β-citronellal with alkyl alcohols (methyl, ethyl, propyl, butyl, isopropyl) at room temperature. The catalyst was obtained by a simple bio-oil reaction with sulfuric acid at 393 K for different times (15, 30, 60, 90, 120, and 240 min). Potentiometric titrations and FT-IR analyses showed the formation of very strong acid sites, likely -SO3H, with surface concentrations reaching 0.35 and 0.50 mmol/ gcatal, for the catalyst obtained with reactions 120 and 240 min. These catalysts were used in the β-citronellal condensation with alkyl alcohols to acetals with conversion and selectivity higher than 0 %, at room temperature using 3.96 wt.% catalyst, and 2 h reaction. The effects of temperature, time, different alcohols, and catalyst load were evaluated. The catalyst can be recovered and reused four times without significant activity loss.