Homogeneous Ethanol to Butanol Catalysis—Guerbet Renewed

Abstract

The catalytic conversion of (bio)ethanol into butanol is an attractive route to upgrade the modest fuel characteristics of this widely available bioderived substrate into a molecule that has properties much closer to conventional gasoline. The Guerbet reaction, known for more than 100 years, provides an ideal mechanism for this transformation. However, despite the apparently simple nature of this reaction for ethanol, it provides formidable challenges, especially in terms of achieving high selectivity. There have been advances in both heterogeneous and homogeneous catalysis in this regard, and this Perspective focuses on the very recent reports of homogeneous catalysts that describe encouraging results in terms of achieving high selectivity, mechanistic understanding, and widening scope.

Transfer Hydrogenation of Carbon Dioxide to Methanol Using a Molecular Ruthenium‐Phosphine Catalyst

“…Furthermore, these experiments clearly corroborate the stability of the catalytic system and pave the way to an efficient process concept. In details running the reaction in higher boiling alcohols like n BuOH and could clearly facilitate the isolation of volatile MeOH . The hydrogenation of ethyl acetate was not further optimized as already intensive investigations on ester reduction with similar ruthenium catalyst systems are reported …”

Glycidol, a Valuable Substrate for the Synthesis of Monoalkyl Glyceryl Ethers: A Simplified Life Cycle Approach

“…As am atter of fact, to compare the sustainability of the proposed reaction pathwayw ith datar eported previously,r egarding the conversion of glycerolt on-butanoxyg lyceryl ether using Bi(OTf) 3 as homogeneous catalyst, [14] we focused our investigation on the etherification of glycidol with n-butanol using Bi III triflates.A lso, n-butanol was recently recognized as as ustainable feedstock obtained by the catalytic coupling of bioethanol through the well-known Guerbet reaction. [28] As is shown in Figure 2, we performedakinetic study under the optimized reaction conditions already described (80 8C, 0.01 mol %c atalyst, alcohol/glycidol molar ratio 9:1). Remarkably,B i(OTf) 3 was shown to promote the total conversion of glycidol with high selectivity (90 %) to monobutoxy glyceryl ether [b] These valuesa re calculated on the basis of the reactiont imeof3 0 minutes.…”

The Role of Copper in the Upgrading of Bioalcohols

“…The presence of both adehydrogenationand af inal hydrogenation step makes homogeneous "hydrogen-borrowing" catalysts very good candidates for this reaction (Figure 2). Ru complexes show very high activity and selectivity for this reaction, [6][7][8] reachingu pt o1 8209 TON and 86 %s electivity.R ecently,a non-noblem etal catalyst, aM nc omplex with aP NP pincer ligand in the presence of EtONa, has shown an excellent activity in the upgradingo fe thanolt ob utanol for the first time, with aT ON > 110000 and 92 %s electivity at 11 %c onversion. [9] However,asignificant amount of research is devoted to the heterogenization of the catalytic systems, mixing an heterogeneous catalystw ith dehydrogenation-hydrogenation activity with ah omogeneous base or moving towards purely heterogeneous,b ifunctional materials.…”

“…The presence of both a dehydrogenation and a final hydrogenation step makes homogeneous “hydrogen‐borrowing” catalysts very good candidates for this reaction (Figure ). Ru complexes show very high activity and selectivity for this reaction, reaching up to 18 209 TON and 86 % selectivity. Recently, a non‐noble metal catalyst, a Mn complex with a PNP pincer ligand in the presence of EtONa, has shown an excellent activity in the upgrading of ethanol to butanol for the first time, with a TON >110 000 and 92 % selectivity at 11 % conversion …”