What is it about?

The reactivity of organic acids on titania is important for many green chemistry applications. So, the behaviour of formic acid on titania surfaces has been intensely studied, but its acid proton has escaped the most accurate experiments so far. Now we show that the formic acid proton is shared between one oxygen from the formic acid molecule and one oxygen of the titania surface. At very low temperature, this is due to quantum effects, while, at room temperature, the proton is shuttling between the molecule and the surface. In both cases, proton sharing makes the acid proton "invisible" to experiments.

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Why is it important?

We show that the surface of titania acts like a protecting group for the formic acid proton. How does this work? Because the proton is shared with the surface, it is difficult for other molecules to take it away! This protecting role of the surface could explain, for example, why carboxylic acids on titania, upon addition of amines, give high-value products (amides) at low costs for the environment.

Perspectives

Discovering the fate of the invisible proton could be an important step for applications, because it is just the acid proton that makes carboxylic acids on titania so relevant in many sustainable chemical processes. On a more personal note, my feeling is that our work has unveiled just a little part of the wonderful things that molecules can do on surfaces. Next step would be to study this process on different surfaces of titanium dioxide. This could help us to understand the role of surface defects in the reactivity of the acid proton.

Gloria Tabacchi
university of insubria

Read the Original

This page is a summary of: The Case of Formic Acid on Anatase TiO2 (101): Where is the Acid Proton?, Angewandte Chemie International Edition, August 2019, Wiley,
DOI: 10.1002/anie.201906709.
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