Mono- and tri-ester hydrogenolysis using tandem catalysis. Scope and mechanism

Tracy L. Lohr, Zhi Li, Rajeev S. Assary, Larry A. Curtiss, Tobin J. Marks

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

The scope and mechanism of thermodynamically leveraged ester RC(O)O-R′ bond hydrogenolysis by tandem metal triflate + supported Pd catalysts are investigated both experimentally and theoretically by DFT and energy span analysis. This catalytic system has a broad scope, with relative cleavage rates scaling as, tertiary > secondary > primary ester at 1 bar H2, yielding alkanes and carboxylic acids with high conversion and selectivity. Benzylic and allylic esters display the highest activity. The rate law is ν = k[M(OTf)n]1[ester]0[H2]0 with an H/D kinetic isotope effect = 6.5 ± 0.5, implying turnover-limiting C-H scission following C-O cleavage, in agreement with theory. Intermediate alkene products are then rapidly hydrogenated. Applying this approach with the very active Hf(OTf)4 catalyst to bio-derived triglycerides affords near-quantitative yields of C3 hydrocarbons rather than glycerol. From model substrates, it is found that RC(O)O-R′ cleavage rates are very sensitive to steric congestion and metal triflate identity. For triglycerides, primary/external glyceryl CH2-O cleavage predominates over secondary/internal CH-O cleavage, with the latter favored by less acidic or smaller ionic radius metal triflates, raising the diester selectivity to as high as 48% with Ce(OTf)3.

Original languageEnglish
Pages (from-to)550-564
Number of pages15
JournalEnergy and Environmental Science
Volume9
Issue number2
DOIs
Publication statusPublished - Feb 1 2016

Fingerprint

Hydrogenolysis
catalysis
Catalysis
cleavage
ester
Esters
Metals
Triglycerides
metal
Alkanes
catalyst
Alkenes
Hydrocarbons
Carboxylic Acids
Glycerol
Carboxylic acids
Catalyst supports
Discrete Fourier transforms
Isotopes
Paraffins

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Environmental Chemistry
  • Pollution
  • Nuclear Energy and Engineering

Cite this

Mono- and tri-ester hydrogenolysis using tandem catalysis. Scope and mechanism. / Lohr, Tracy L.; Li, Zhi; Assary, Rajeev S.; Curtiss, Larry A.; Marks, Tobin J.

In: Energy and Environmental Science, Vol. 9, No. 2, 01.02.2016, p. 550-564.

Research output: Contribution to journalArticle

Lohr, Tracy L. ; Li, Zhi ; Assary, Rajeev S. ; Curtiss, Larry A. ; Marks, Tobin J. / Mono- and tri-ester hydrogenolysis using tandem catalysis. Scope and mechanism. In: Energy and Environmental Science. 2016 ; Vol. 9, No. 2. pp. 550-564.
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