Using molecular spectroscopy to study reaction mechanisms | 3/5/2018 | Staff
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Gasoline, lubricants, and consumer products are improved by chemical additives. Making additives often involves a chemical reaction known as alkylation, the addition of a carbon chain to existing molecules. Chemists know acid catalysts are useful for alkylation, but how one of the most popular catalysts, acidic zeolites, perform alkylation in a condensed phase is not well understood.

Jian Zhi Hu, Zhenchao Zhao, **** Shi, Johannes Lercher, and their colleagues from Pacific Northwest National Laboratory identified a key reaction mechanism associated with zeolite-catalyzed alkylation of phenol with cyclohexanol. They made this discovery using in situ high-temperature and high-pressure magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy.

Scientists - Understanding - Activity - Mechanism - Reaction

Scientists now have an understanding of how the catalytic activity, mechanism, and reaction pathways depend on three factors. These factors are the concentration and strength of acid sites, the steric constraints for the reaction, and the identity of the alkylating agent.

Detailed kinetic and spectroscopy analyses showed that phenol alkylation with cyclohexanol does not appreciably occur before a majority of cyclohexanol has been dehydrated to cyclohexene. Alkylation reactions are slowed as long as the alcohol is present. In contrast, alkylation products are readily formed when the solution initially contains just phenol and cyclohexene.

Combination - MAS-NMR - Spectroscopy - Use - Isotope

A combination of in situ MAS-NMR spectroscopy and the use of carbon-13 isotope enriched phenol and cyclohexanol allowed the identification of the reaction pathway that is difficult to probe by other spectroscopy methods. The reaction sequence does not occur...
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