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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.
The ageing of Fe-Cr model alloys in 0.5 % SO2 and 99.5 % Ar atmosphere was investigated to aim in a fundamental and systematic analysis of the combined oxidation and sulfidation mechanism. The crystallization and reaction paths for oxide and sulfide formation were followed in-situ by energy dispersive X-ray diffraction (EDXRD) in an early stage of corrosion (30 s – 24 h). For this technique, high energetic white synchrotron X-ray radiation (10-100 keV) was used as radiation source. Diffraction pattern were collected continuously in an early stage of corrosion up to 24 h during the complete ageing experiment.
The crystalline phases, growing on top of the coupons, were identified directly via their specific dhkl values. The evolution of the extracted integral intensities of specific reflections of the corrosion products as a function of time access direct information about the kinetics of the nucleation and growth. The results presented here show for iron with 2 wt% Cr wuestite formation first. Wuestite vanishes after 10 min of reaction only and magnetite and hematite appear. Magnetite formation proceeds simultaneously with sulfide formation. Sulfides growth proceeds after an incubation time, which differs for low alloyed (2 wt% Cr) and high alloyed (9 wt% Cr) material.
Mechanochemistry has become a valuable method for the synthesis of new materials, especially for pharmaceutical cocrystals. The Advantages of fast reactions in high purity and yield face a lack of understanding the underlying mechanism. Therefore, in situ setups to study mechanochemical reactions have been established. Herein, we present an in situ investigation of the mechanochemical cocrystal formation of pyrazinamide (PZA) with pimelic acid (PM) using synchrotron XRD. Two new polymorphs of PZA:PM (1:1) were synthesized by milling the starting materials in milling jars of different materials. While Form I is only obtained using a steel jar, Form II can be obtained purely in jars made of Perspex. In situ XRD experiments reveal a direct formation of Form II in Perspex and an intermediate formation of Form II in steel jars converting to Form I upon further grinding. Heating experiments and DFT calculations predict that Form II is the thermodynamically more stable polymorph. Therefore, the reaction progress in the steel jar contradicts Ostwald’s rules of stages as the more stable Form II converts into the metastable Form I. Hence, mechanochemistry offers the possibility to synthesize new materials that cannot be obtained using conventional methods.
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 this contribution, I will discuss our recent results investigating the formation of (polymorphic) cocrystals and metal phosphonates. 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. 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.
Polynuclear aluminium species (Al13 keggin cluster) find application in different areas like water purification, contaminant transport, and as pilling clays with high specific surface areas, due to their strong binding ability to aggregates and high positive charge.
In the present contribution, we report on the in situ investigation of the Al13 sulfate synthesis by synchrotron wide-angle X-ray scattering (WAXS). Al13 cluster were crystallized by precipitating hydrolyzed aluminum solutions by the addition of sodium sulfate. The measurements were performed using a custom-made acoustic levitator as sample holder. The study provides information about the intermediates during the crystallization process. From the data, a mechanism was derived indicating the influence of the crystallization process.