Carbon nanotube/PTFE as a hybrid platform for lipase-assisted transformation of α-angelica lactone to alkyl levulinates

In this work the enzymatic method for the synthesis of alkyl levulinates from α-angelica lactone has been reported for the first time. Candida antarctica lipase B was immobilised on the surface of hybrid support, consisting of commercially available multi-walled carbon nanotubes (MWCNT) and polytetrafluoroethylene (PTFE). CALB/MWCNT-PTFE(0.10 wt.%) biocatalyst with 22.5 wt. % CALB loading was determined as the most active one in model synthesis of the n-butyl levulinate in toluene. n-Butyl levulinate was obtained quantitively after 120 min of reaction under the selected reaction conditions (2-fold molar excess of n-butanol, 0.150 g of biocatalyst per 1 mmol of α-angelica lactone, 20 °C). The yield of n-butyl levulinate was found as higher than in the presence of accurate amount of sulfuric acid or Novozyme-435. Additionally, a unique stability of developed biocatalyst was presented in 6 reaction cycles at 20 °C as well as in 3 reaction cycles at 60 °C. The essence of proposed approach lies in possibility to overcome the equilibrium limitations occurring in the conventional Fisher esterification. Application of the elaborated hybrid biocatalyst of enhanced stability in the reactions non-specific for lipases is a clear proof for versality of the novel system.