Low-temperature selective ethanol upgrading to primary or secondary alcohols by homogeneous catalysis

Abstract

Ethanol is one of the most promising renewable resources for the production of key industrial commodities. Herein, we present the first direct and selective conversion of ethanol to either primary or secondary alcohols, or to hydrocarbons, using ruthenium PNP pincer complexes [(RPNP)RuHXCO] (R= iPr, Ph, Cy, tBu; X = Cl, H-BH3) as catalysts. Using phenyl substituted phosphines leads to the selective produc-tion of secondary alcohols. Hence, employing [(PhPNP)RuH(Cl)CO] (Ru-1) as a catalyst in ethanol, containing 20 mol% of NaOEt, at 115 ⁰C leads to 89% selective production of secondary alcohols over pri-mary alcohols. A yield of 12% of 2-butanol, and in total 22% of secondary alcohols, was achieved. In addition, minor amounts of 2 butenes/butane (≤5%) were observed in the gas phase. On the contrary, when using bulky phosphine substituents, such as t-butyl, the selectivity completely shifts toward primary alcohols. Thus, using [(tBuPNP)RuH(Cl)CO] (Ru 5) leads to >99% selectivity of 1 butanol (13% yield) over secondary alcohols at 115 ⁰C. In fact, the catalytic system is highly competitive for producing 1-butanol with 22% yield obtained at 130 ⁰C, a temperature significantly lower than previously re-ported systems. Our methodology unveils the potential for using bulk bio-alcohols to selectively produce primary or secondary alcohols and hydrocarbons under mild conditions.

Direct valorization of biomass waste to gamma-valerolactone

“…Notably, there exist relatively few examples of homogeneous catalytic hydrogenations under acidic conditions [18][19][20][21][22][23][24] . Furthermore, the Noyori-type PNP pincer complexes 25 , such as the Ru-MACHO complex 26 and analogs, have demonstrated excellent activity in both basic [27][28][29] and neutral media [30][31][32][33] , but to the best of our knowledge, never under Brønsted acid conditions.…”

“…(18) 13(29) https://doi.org/10.26434/chemrxiv-2023-kl7x8 ORCID: https://orcid.org/0000-0002-3170-1198 Content not peer-reviewed by ChemRxiv. License: CC BY 4.0…”