Acetalization of ss-citronellal Over a Renewable Carbon Catalyst Obtained from Bio-Oil Sulfonation: A Green Route to Obtain Valuable Feedstocks

In this work, an efficient renewable carbon catalyst obtained by bio-oil sulfonation was used for the first time to produce terpene acetals by condensation of ss-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/ g. catalyst, for the catalyst obtained with reactions 120 and 240 min. These catalysts were used for ss-citronellal condensation with alkyl alcohols to acetals with conversion and selectivity higher than 90%, at room temperature, using a 3.96 wt.% catalyst and 2 h reaction time. 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. The use of renewable origin solid catalysts, recyclable, and active in acetalization reactions at room temperature are positive aspects of this process.

Automated summary

In this study, an efficient renewable carbon catalyst obtained from bio-oil sulfonation was used for the first time to produce terpene acetals at room temperature. The catalyst was obtained by reacting bio-oil with sulfuric acid and showed very strong acid sites. The condensation reactions of ss-citronellal and alkyl alcohols achieved high conversion and selectivity, and the catalyst could be reused four times without significant activity loss. The use of renewable solid catalysts with recyclability and activity at room temperature is a positive aspect of this process.