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revised on 10.09.2019 and posted on 10.09.2019by Nikola Cindro, Martina Tireli, Tomislav Mrla, Krunoslav Uzarevic
reactions gained a lot of attention lately as a green and highly efficient path
towards various relevant materials. The control over the fundamental reaction
parameters in milling procedure, such as temperature and pressure of the reactor,
is still in infancy and the vast majority of milling reactions is done with
controlling just the basic parameters such as frequency and milling media
weight. We demonstrate here how the milling under controlled, prolonged and
variable heating programs accomplished in a new milling reactor introduces a new
level of mechanochemical reactivity beyond what can be achieved by conventional
mechanochemical or solution procedures, and also reduces the time and energy costs
of the milling process. The methodology is demonstrated on four varied systems:
C–C bond forming Knoevenagel condensation, selective C–N bond formation for
amide/urea synthesis, selective double-imine condensation, and solid-state
formation of an archetypal open metal-organic framework, MOF-74. The potential
of this methodology is best demonstrated on the one-pot selective synthesis of
four complex products containing combinations of amide, amine or urea
functionalities from the same and simple acyl azide and diamine reactants.
Principal control over this enhanced reactivity and selectivity stemmed from
the application of specific heating regimes to mechanochemical processing
accomplished by a new, in-house developed mechanochemical reactor. As even the
moderate increase in temperature strongly affects the selectivity and the rate
of mechanochemical reactions, the results presented are in line with recent
challenges of the accepted theories of mechanochemical reactivity.