Analytische Chemie
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Mechanaochemistry is an effective method to yield pure compounds within a short reaction time. Mechanochemical C-C bond forming reactions gained increasing interest in the past decade. Among those the Knoevenagel condensation is an important reaction for synthezing a,b-unsaturated compounds. The information on the underlying mechanisms of mechanochemical reactions are scarce. In situ investigations using Raman spectroscopy and synchroton XRD either alone or in combination address this challenge. We present the in situ results of a Knoevenagel condensation with p-nitrobenzaldehyde and malononitrile under neat grinding conditions.
Mechanaochemistry is an effective method to yield pure compounds within a short reaction time. Mechanochemical C-C bond forming reactions gained increasing interest in the past decade. Among those the Knoevenagel condensation is an important reaction for synthezing a,b-unsaturated compounds. The information on the underlying mechanisms of mechanochemical reactions are scarce. In situ investigations using Raman spectroscopy and synchroton XRD either alone or in combination address this challenge. We present the in situ results of a Knoevenagel condensation with p-nitrobenzaldehyde and malononitrile under neat grinding conditions.
Mechanochemistry is increasingly used for synthesizing soft matter materials including metal organic compounds and cocrystals. The ever-increasing interest in this method is contrasted by a limited mechanistic understanding of the mechanochemical reactivity and selectivity. Time-resolved in situ investigations of milling reactions provide direct insights in the underlying mechanisms. We recently introduced a setup enabling in situ investigation of mechanochemical reactions using synchrotron XRD combined with Raman spectroscopy. The specific combination allows to study milling processes comprehensively on the level of the molecular and crystalline structure and thus obtaining reliable data for mechanistic studies. In situ Raman spectroscopy coupled with thermography revealed a low temperature increase during milling reactions due to the mechanical impact and clear temperature increases because of the reaction heat.
Based on the data, temperature rises as postulated in the magma plasma and hot spot theory can be excluded for soft matter milling syntheses. Our results indicate that in situ investigation of milling reactions offer a new approach to tune and optimize mechanochemically synthesized compounds.
Mechanochemistry is increasingly used for synthesizing soft matter materials including metal organic compounds and cocrystals.1 The ever-increasing interest in this method is contrasted by a limited mechanistic understanding of the mechanochemical reactivity and selectivity. Time-resolved in situ investigations of milling reactions provide direct insights in the underlying mechanisms.2,3 We recently introduced a setup enabling in situ investigation of mechanochemical reactions using synchrotron XRD combined with Raman spectroscopy. The specific combination allows to study milling processes comprehensively on the level of the molecular and crystalline structure and thus obtaining reliable data for mechanistic studies. In this contribution, I will discuss our recent results investigating the formation of (polymorphic) cocrystals and metal phosphonates.4 First investigations of a mechanochemical synthesis under controlled temperature which allow determining the activation barrier are presented. Furthermore, in situ Raman spectroscopy coupled with thermography revealed a low temperature increase during milling reactions due to the mechanical impact and clear temperature increases as a result of the reaction heat.5 Our results indicate that in situ investigation of milling reactions offer a new approach to tune and optimize mechanochemically synthesized compounds.
Mechanochemistry is increasingly used for synthesizing soft matter materials including metal organic compounds and cocrystals.1,2 The ever-increasing interest in this method is contrasted by a limited mechanistic understanding of the mechanochemical reactivity and selectivity. Time-resolved in situ investigations of milling reactions provide direct insights in the underlying mechanisms.3,4 We recently introduced a setup enabling in situ investigation of mechanochemical reactions using synchrotron XRD combined with Raman spectroscopy (Fig.1a) The specific combination allows to study milling processes comprehensively on the level of the molecular and crystalline structure and thus obtaining reliable data for mechanistic studies. In this talk I will discuss our recent results investigating the formation of (polymorphic) cocrystals.6-7 First investigations of a mechanochemical synthesis under controlled temperature (Fig 2a) which allow determining the activation barrier are presented.8 Furthermore, in situ Raman spectroscopy coupled with thermography revealed a low temperature increase during milling reactions due to the mechanical impact and clear temperature increases as a result of the reaction heat.
Mechanochemistry is increasingly used for synthesizing soft matter materials including metal organic compounds and cocrystals.1,2 The ever-increasing interest in this method is contrasted by a limited mechanistic understanding of the mechanochemical reactivity and selectivity. Time-resolved in situ investigations of milling reactions provide direct insights in the underlying mechanisms.3,4 We recently introduced a setup enabling in situ investigation of mechanochemical reactions using synchrotron XRD combined with Raman spectroscopy (Fig.1a) The specific combination allows to study milling processes comprehensively on the level of the molecular and crystalline structure and thus obtaining reliable data for mechanistic studies. In this talk I will discuss our recent results investigating the formation of (polymorphic) cocrystals.
N−H bond activation of gaseous ammonia is achieved at room temperature in a reversible solvent-free reaction using a solid dicyclopalladated azobenzene complex. Monitoring of the gas−solid reaction in real-time by in situ solid-state Raman spectroscopy enabled a detailed insight into the stepwise activation pathway proceeding to the final amido complex via a stable diammine intermediate. Gas−solid synthesis allowed for isolation and subsequent structural characterization of the intermediate and the final amido product, which presents the first dipalladated complex with the PdII−(μ-NH2)−PdII bridge. Gas−solid reaction is readily followed via color changes associated with conformational switching of the palladated azobenzene backbone. The reaction proceeds analogously in solution and was characterized by UV−vis and NMR spectroscopies showing the same stepwise route to the amido complex. Combining the experimental data with density functional theory calculations we propose a stepwise mechanism of this heterolytic N−H bond activation assisted by exogenous ammonia.
A newly established in situ technique using Raman spectroscopy was employed for the detailed kinetic investigation of mechanochemical reaction pathways. This approach was applied for the systematic investigation of the direct influence of colliding balls on the reaction rate constants of a mechanochemical cocrystallization reaction. As a model reaction, the mechanochemical cocrystallization of felodipine and the coformer imidazole was investigated. Keeping the total ball mass constant by varying the number of milling balls, our study reveals that the impact of each single collision has a more significant influence on the reaction kinetics than expected.
We present a first direct measurement of the temperature during milling combined with in situ Raman spectroscopy monitoring. The data reveal a low temperature increase due to the mechanical impact and clear temperature increases as a consequence of the reaction heat. Based on the data, temperature rises as postulated in the magma plasma and hot spot theory can be excluded for soft matter milling syntheses.
Divalent metal phosphonates are promising hybrid materials with a broad field of application. The rich coordination chemistry of the phosphonate linkers enables the formation of structures with different dimensionalities ranging from isolated complexes and layered structures to porous frameworks incorporating various functionalities through the choice of the building blocks.
In brief, metal phosphonates offer an interesting opportunity for the design of multifunctional materials. Here, we provide a short review on the class of divalent metal phosphonates discussing their syntheses, structures, and applications. We present the advantages of the recently introduced mechanochemical pathway for the Synthesis of divalent phosphonates as a possibility to generate new, in certain cases metastable compounds. The benefits of in situ investigation of synthesis mechanisms as well as the implementation of sophisticated methods for the structure analysis of the resulting compounds are discussed.