1 3
Topics in Current Chemistry (2019) 377:1
of the catalytic bed at 160 °C under atmospheric pressure [107]. Similarly, Vac‑
caro and colleagues studied the continuous flow synthesis of alkyl levulinates
using various sulfonic acid‑based resins (Fig. 36) [108]. Among the various
acidic catalysts tested, the best results were obtained over Aquivion mP98, which
bears –CF 2 CF 2 SO 3 H functional groups, partially because its nonporous structure
prevents water adsorption. Preliminary attempts were performed in batch with
1‑pentanol (61) as a reagent, and various other alcohols were then assessed too.
Conversions in the 50–84% range were obtained. Finally, the process was tested
under continuous‑flow conditions, affording a productivity of 4.8 g/h for 62 and
quantitative 8 conversion under optimized conditions.
Alkyl esters of valeric (pentanoic) acid, commonly called “valeric biofuels”,
can be blended at high volume percentages with both gasoline and diesel, lead‑
ing to satisfactory fuel properties. Lange et al. studied the preparation and per‑
formance of such biofuels over a successful 250,000 km road trial [109]. Valeric
biofuels are typically prepared in a three‑step process from levulinic acid (8),
including hydrogenation to γ‑valerolactone (21, see Sect. 2.1.4), hydrogenation
of 21 to valeric acid (63), and a final esterification to give alkyl valerates. Li and
colleagues developed a cascade process featuring a single bifunctional Ni‑K/
HZSM‑5 catalyst for the direct conversion of 8 into a mixture of valeric acid (63)
and ethyl valerate (64, Fig. 37) [110]. Potassium doping of the Ni/HZSM‑5 cata‑
lyst improved its performance in terms of yield and stability through acidity regu‑
lation. Optimized process conditions consisted of co‑feeding an EtOH solution
of 8 and hydrogen over a fixed‑bed reactor operated at 240 °C under 30 bar of
Fig. 36 Esterification of n‑pentanol (61) with levulinic acid (8) in a fixed‑bed flow reactor
Fig. 37 Continuous flow cascade process for the upgrading of levulinic acid (8) to valeric biofuels
137
Reprinted from the journal
Topics in Current Chemistry (2019) 377:1
of the catalytic bed at 160 °C under atmospheric pressure [107]. Similarly, Vac‑
caro and colleagues studied the continuous flow synthesis of alkyl levulinates
using various sulfonic acid‑based resins (Fig. 36) [108]. Among the various
acidic catalysts tested, the best results were obtained over Aquivion mP98, which
bears –CF 2 CF 2 SO 3 H functional groups, partially because its nonporous structure
prevents water adsorption. Preliminary attempts were performed in batch with
1‑pentanol (61) as a reagent, and various other alcohols were then assessed too.
Conversions in the 50–84% range were obtained. Finally, the process was tested
under continuous‑flow conditions, affording a productivity of 4.8 g/h for 62 and
quantitative 8 conversion under optimized conditions.
Alkyl esters of valeric (pentanoic) acid, commonly called “valeric biofuels”,
can be blended at high volume percentages with both gasoline and diesel, lead‑
ing to satisfactory fuel properties. Lange et al. studied the preparation and per‑
formance of such biofuels over a successful 250,000 km road trial [109]. Valeric
biofuels are typically prepared in a three‑step process from levulinic acid (8),
including hydrogenation to γ‑valerolactone (21, see Sect. 2.1.4), hydrogenation
of 21 to valeric acid (63), and a final esterification to give alkyl valerates. Li and
colleagues developed a cascade process featuring a single bifunctional Ni‑K/
HZSM‑5 catalyst for the direct conversion of 8 into a mixture of valeric acid (63)
and ethyl valerate (64, Fig. 37) [110]. Potassium doping of the Ni/HZSM‑5 cata‑
lyst improved its performance in terms of yield and stability through acidity regu‑
lation. Optimized process conditions consisted of co‑feeding an EtOH solution
of 8 and hydrogen over a fixed‑bed reactor operated at 240 °C under 30 bar of
Fig. 36 Esterification of n‑pentanol (61) with levulinic acid (8) in a fixed‑bed flow reactor
Fig. 37 Continuous flow cascade process for the upgrading of levulinic acid (8) to valeric biofuels
137
Reprinted from the journal