Stainless Steel Ball Milling for Hydrogen Generation and its Application for Reduction

Direct Mechanocatalysis: Using Milling Balls as Catalysts

“…In their work they then proceeded to use pure metal powders with inert millingballs to elucidate the function of each of the metals present. [21] This shows nicely,h ow a metal can be catalytically active under mechanochemical condition, even if the catalyst ball only contains 8-20 %o ft he catalytic active metal.M oreover,w ew ant to highlight the possibility of conducting tandemr eactions having two active metals within one alloy.T he shape of the catalyst also plays a role. Usually round millingb alls with polished surface are utilized in mechanochemistry.D ifferent materials, however,a re either nots old as balls or hard to shape into balls in the first place.F or those cases it has been shown that even pellets and more rough geometries can be utilized as "milling balls", as demonstrated nicely in the work of the Mack group on the nickel-catalyzed [2 + 2 + 2 + 2] cycloaddition reaction( Fig- T he in situ formed hydrogenw as then used for ahydration of as ubstrate,u tilizing the nickel, which is also present in the alloy.…”

“…Here, Kwade and co‐workers established that approximately 30 % of the vessel volume needs to be occupied by the balls for an optimal energy input. In direct mechanocatalysis this rule is generally followed in planetary ball mills . The reactions in vibratory ball mills, however, usually only use one or two balls …”

“…It might also be the case that the higher energy input in planetary ball mills is the sole reason for this apparent acceleration of reactions. The Sawama group could demonstrate that for their reactions higher rotational speeds are beneficial (Figure A) …”

Mechanochemical, Water‐Assisted Asymmetric Transfer Hydrogenation of Ketones Using Ruthenium Catalyst

“…The mechanochemical reduction of various unsaturated compounds has been studied as well. [10][11][12][13][14][15][16] Thus, the solventfree reductive benzylation of malonitrile and 4-methylaniline by various aromatic aldehydes was carried out in a ball mill using Hantzsch ester as the reductant. [11] Sajiki et al used in situ generated hydrogen or deuterium for the saturation of various compounds, such as alkynes, alkenes, haloarenes, ketones, azides and nitroarenes.…”

“…The hydrogen (deuterium) was generated under milling conditions from water, alkanes or diethyl ether either by metals added to the reaction mixture or by the material of the stainless-steel grinding equipment. [12] Aldehydes and ketones were selectively transfer hydrogenated using tetrabutylammonium fluoride on silica catalyst and polymethylhydrosiloxane donor, [13] whereas, the reduction step in the preparation of fluoxetine, an active pharmaceutical ingredient, was carried out by NaBH 4 in mixer mills. [14] The efficiency of LAG was studied by Štrukil and co-workers in the catalytic transfer hydrogenation of aromatic nitro compounds on Pd/C catalyst and HCOONH 4 hydrogen donor.…”