Extending the Hammett correlation to mechanochemical reactions

Abstract

The correlation between kinetics and Hammett constants in a model mechanochemical imine formation indicates that the mechanistic framework of physical–organic chemistry could be used to describe solid-state reactions conducted by ball milling.

Controlled alcohol oxidation reactions by supported non-noble metal nanoparticles on chitin-derived N-doped carbons

“…This indicates that 1) the substituent effect in the benzyl alcohol oxidation reaction, employing the Mo–N/C catalyst, is opposite to that of the Hammett standard reaction (ionization of substituted benzoic acids in water at 25 °C) and that 2) the non-linear relationship could be most likely attributed to the concomitant influence of two effects, namely the electron-withdrawing properties of Br together with the previously mentioned interactions of bromide with the metal nanoparticles. 56–59…”

“…This indicates that 1) the substituent effect in the benzyl alcohol oxidation reaction, employing the Mo-N/C catalyst, is opposite to that of the Hammett standard reaction (ionization of substituted benzoic acids in water at 25 °C) and that 2) the non-linear relationship could be most likely attributed to the concomitant influence of two effects, namely the electronwithdrawing properties of Br together with the previously mentioned interactions of bromide with the metal nanoparticles. [56][57][58][59] Beyond the scant reactivity expected for secondary versus primary hydroxyl groups, these results led us to hypothesize that stabilized aromatic species (e.g. radicals) of benzyl-/furyltype alcohols adsorbed on the catalyst surface were crucial for the oxidation step.…”

A kinetic study of mechanically activated atom exchange: the effect of milling frequency and ball mass

“…Consequently, mechanochemical reactions are a concoction of factors related to mechanical energy deposited during the impacts, mutual exposure of fresh surfaces of reactant phases and intrinsic chemical behaviour of reactant molecules as they come in contact. 11,12 Separating each of these contributions to the overall mechanochemical transformation has proved to be demanding. We have recently been able to study in macroscopic 13 and microscopic 14 detail a purely mechanically activated reaction that does not depend on mixing, but solely on the absorption of mechanical energy during impacts.…”

“…Consequently, mechanochemical reactions are a concoction of factors related to mechanical energy deposited during the impacts, mutual exposure of fresh surfaces of reactant phases and intrinsic chemical behaviour of reactant molecules as they come in contact [11,12]. Separating each of these contributions to the overall mechanochemical transformation has proved to be demanding.…”

Acid-Base Catalysis in the Mechanochemical Formation of a Reluctant Imine

“…[3,4] Previous work, [4][5][6][7][8][9][10][11] as well as our investigation of the mechanochemical imine formation from p-nitrobenzaldehyde (1) and differently substituted anilines, demonstrated facile preparation of imines by neat grinding. [12] However, imine formation from 1 and pnitroaniline (2) proved elusive, despite the presence of the favourable nitro group on the benzaldehyde partner, as the product did not form by neat grinding regardless of the milling conditions and the milling time. Surprisingly, a slow solid-state formation of our target imine (3) was previously T Scheme 1.…”