In recent years, bioethanol is being probed as a sustainable alternative fuel (or fuel additive) to the conventional gasoline. However butanol offers a more viable option, due to its higher energy density and immiscibility with water. The project goal is to convert bio-ethanol selectively to butanol, using a tandem dehydrogenation/Aldol condensation/rehydrogenation route, the Guerbet process. Use of Cp*Ir(PhPyOH) (1) along with [Tp’Ni(OH)2] (2) or [IprCuOH] (3) has lead us to achieve &gt;99% selectivity with about 40% conversion. The second step, Aldol reaction is found to be key for the higher selectivity and the outstanding selectivity achieved by using [Tp’Ni(OH)2] & [IprCuOH] is certainly linked to their steric and electronic features. This work focuses on the mechanistic details of the Aldol reaction in order to understand the root of high-selectivity. In order to achieve better conversion while retaining the high selectivity different molecules with similar or modified structural and electronic facets as of [Tp’Ni(OH)2 ] & [IprCuOH] were employed in the Guerbet process under various reaction conditions and the results are documented here in. Replacement of precious metal catalysts in the Guerbet process with first-row metal complex catalysts is highly appreciated due to the economic and environmental benign. The manganese pincer complexes of the type [RPNPMnBr(CO)2] ( R = iPr, Cy, Ph or Ad) (4) are found to be excellent catalysts for upgrading of ethanol to 1-butanol. Under suitable reaction conditions and with an appropriate base about 32% of 1-butanol can be formed in higher selectivity. Here we present the detailed account on the effect of the temperature, solvent, nature and proportion of base used and the stereo-electronic effects of the ligand substituents on the catalytic activity of the catalysts. A plausible catalytic cycle is proposed as evident from the experimental observations.

Catalytic upgrading of ethanol to 1-butanol via Guerbet reaction

254th National Meeting (2017)

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