Direct Mechanocatalysis: Using Milling Balls as Catalysts

Abstract

Direct mechanocatalysis describes catalytic reactions under the involvement of mechanical energy with the distinct feature of milling equipment itself being the catalyst. This novel type of catalysis features no solubility challenges of the catalysts nor the substrate and on top offering most facile way of separation.

Keywords: ball milling; cross coupling; heterogeneous catalysis; mechanochemistry; reactive milling.

Figure 1

C−C coupling reactions using either palladium or copper balls or vials as catalyst species. We propose to combine the symbol for mechanochemical reactions introduced by Hanusa in addition with the catalytic element inside the milling balls as a symbol for direct mechanocatalysis. A: Sonogashira reaction with the replacement of the Copper co‐catalyst by the Mack group.11 B: Oxidative coupling catalyzed by copper balls by the Jiang group.8a C: Suzuki polymerization by Vogt et al.9

Figure 2

Cycloaddition reactions by Mack et al. A: Ni‐pellet catalyzed cycloaddition of alkyne derivatives leading to a mixture of cyclooctatetraene and benzene derivatives.6 B: Copper and silver‐catalyzed [2+1] cycloaddition. A competing reaction was set up to test the selectivity of the used metals.8b C: In situ generation and cycloaddition of an azide compound.8c

Figure 3

Dehydrogenation/hydrogenation reaction performed by the Sawama group. A: Water or deuterium oxide were dehydrated by the alloyed chromium. The in situ formed hydrogen was then used for a hydration of a substrate, utilizing the nickel, which is also present in the alloy.17 B: The described dehydrogenation/hydrogenation reaction using an alkane as hydrogen source.

Figure 4

Milling vessels lined with copper and silver foil demonstrated by the Mack group.8b Published by The Royal Society of Chemistry.

Figure 5

A: Influence of the rotational speed on the hydrogen evolution (pressure increase) from water in a planetary ball mill (P7). Copied from [17b] with permission of The Society of Synthetic Organic Chemistry, Japan. B: Influence of the rotational frequency on the time to reach 97 % yield of the Knoevenagel condensation of vanillin and barbituric acid in a planetary ball mil (P6) in a 250 mL steel beaker. Printed with permission from [19a]. Copyright 2015 American Chemical Society.