respectively), affording for the highest ELev yield (up to 75 mol%, Table 2.2) [103]. Neither Y(OTf)3 nor H3PO4 can separately catalyze the conversion of MCC into ELev, and only their combination generates the active catalyst (Table 2.2). Hard Lewis acids, including In(OTf)3, show moderate activity in this process, which can be marginally improved in combination with p‐toluenesulfonic acid (TsOH), as was noted during the conversion of MCC in methanol (Table 2.2) [101]. Usefully, the conversion of wood‐derived cellulose, obtained after the processing of softwood chips in the biphasic system ChCl/oxalic acid/MIBK (Table 2.1), as disclosed earlier in the text, enabled similarly excellent conversion thereof into ELev in the presence of a combined acid catalyst Y(OTf)3/H3PO4 (Table 2.2) [57]. Such integrated methods that involve different catalytic processes, leading to a range of value‐added chemicals, have significant potential to become commercially viable. Meanwhile, engineering of (preferably) continuous processes requires further laboratory‐ and pilot‐scale research.
Table 2.2 Conditions and results of the acid‐catalyzed processing of cellulosic biomass into organic acids or estersa. Source: Bodachivskyi et al. [57,103].
| Substrate | Catalyst | T (°C) | t (h) | Yield LevA or alkyl levulinates (%) | Yield ForA (%) | Yield LacA or α‐hydroxy acid derivatives (%) | References |
|---|---|---|---|---|---|---|---|
| Paper pulp | H2SO4 | 205 185 | 15 (s) 0.42 | 61 (LevA) | 82 | — | [96] |
| MCC | TsOH | 180 | 5 | 20 (MLev) | — | — | [101] |
| In(OTf)3 | 42 (MLev) | — | — | ||||
| In(OTf)3/TsOH | 70 (MLev) | — | — | ||||
| In(OTf)3/NSA | 75 (MLev) | — | — | ||||
| MCC | H3PO4 | 160 | 4 | 0 (ELev) | — | — | [103] |
| TsOH | 0 (ELev) | — | — | ||||
| Y(OTf)3 | 0 (ELev) | — | — | ||||
| Y(OTf)3/H3PO4 | 68 (ELev) | — | — | ||||
| In(OTf)3 | 20 (ELev) | — | — | ||||
| In(OTf)3/TsOH | 45 (ELev) | — | — | ||||
| MCC | Y(OTf)3/H3PO4 | 180 | 2 | 75 (ELev) | — | — | |
| Pinus cellulose (unbleached)b | 75 (ELev) | — | — | ||||
| Pinus celluloseb | 73 (ELev) | — | — | ||||
| Softwood | 52 (ELev) | — | — | ||||
| Softwood cellulosec | 62 (ELev) |
|