Efficient formation of angelica lactones in a vapor-phase conversion of levulinic acid

Abstract

Vapor-phase lactonization of levulinic acid to produce angelica lactones, which include α-, β-and γform isomers, was performed in fixed-bed down-flow glass reactors over various oxide catalysts. SiO 2 and SiO 2-Al 2 O 3 showed relatively high catalytic activity. The lactonization of levulinic acid to angelica lactones was found to be an endothermic equilibrium reaction, and the pressure equilibrium constant was calculated to be 0.2 atm at 275 o C. High temperatures and reduced pressures were efficient for shifting the equilibrium from levulinic acid to angelica lactones, while the suitable reaction temperature was estimated to be 275 o C because temperatures higher than 275 o C decreased the selectivity to angelica lactones. The highest angelica lactones yield of 87.5% was achieved at a levulinic acid conversion of 95.3% over SiO 2 under reduced pressure conditions of ca. 5 kPa at 275 o C. IR, NH 3-TPD and TG analyses were performed for characterizing the catalysts used after the reactions together with a silylated SiO 2 prepared for studying the active species on SiO 2. The silanol groups of SiO 2 with weak acidity were proposed to be the active species.

Angelica Lactones: From Biomass‐Derived Platform Chemicals to Value‐Added Products

“…By this path, in 2016 Sun et al reported the preparation am esoporous silica type catalysta nd its use in the vapor-phase conversion of LA into a-AL. [21] The authors propose that the low acidity of the catalyst contributes to inhibiting the formation of oligomerization products,acommon drawback of this type of approach, and the ALs are furnishedi n8 7.5 %y ield at 275 8Cu nder reduced pressure conditions. Whereas this approach effectively reduces the formation of oligomerization products, it requires high temperatures and relies on an oncommercial catalyst.…”

A Facile Direct Route to N‐(Un)substituted Lactams by Cycloamination of Oxocarboxylic Acids without External Hydrogen

“…First, LA can be directly cyclized to form angelica lactones (ALs) by dehydration. [16] Second, H 2 NCHO can be hydrolyzed in water with conversions up to around7 0% after 1.5 ha t1 60 8Ca nd were then constant upon prolonged reactiont o4h. These findings demonstrate that water obtained by LA dehydration can in principle promote the hydrolysis of H 2 NCHO and relevant N-formyl intermediates to releaseH COOH.…”

“…The formation of GVL ( Figures 1B and S3), which can be obtained from ALs by hydrogenation with HCOOH, [19] suggests that ALs could be the intermediates leading to the N-heterocycles MDPY and MPD. To explore this possibility, a-AL was thermally treated with H 2 NCHO in water or neat conditions, where-by 44 %a nd < 6% MPD yields together with MDPY in roughly 8% and < 1% yields,r espectively,w ere obtained after heating at 160 8Cf or 1h.T hese differences can be attributedt ot he reversibility of the reaction between LA and ALs, [16] with the presence of water shiftingt he equilibrium to the LA side. LA is the speciest hat reacts to form MPD andM DPY.Akinetic study of the conversion of LA into MPD with normal and deuterated water reveals as econdary hydrogen isotope effect with k H /k D = 0.94 ( Figure S6).…”

Effects of Solid Acid Supports on the Bifunctional Catalysis of Levulinic Acid to γ‐Valerolactone: Catalytic Activity and Stability

“…Empirically in an aqueous solvent system, the hydrogenation process would occur first at lower temperatures to promote the conversion of LA to 4‐hydroxyvaleric acid (4‐HVA), which could then be dehydrated to generate GVL . At higher temperatures, an angelica lactone (AL) would be formed through the dehydration process of LA, and then be hydrogenated to generate GVL . The Al‐oriented pathway generally prevailed particularly under vapor phase conditions .…”