Waste-free solid-state syntheses with quantitative yield

Unusual piezochromic fluorescence of a distyrylpyrazine derivative crystals: phase transition through [2 + 2] photocycloaddition under UV irradiation

The piezochromic fluorescence (FL) of a distyrylpyrazine derivative, 2,3-diisocyano-5,6-distyrylpyrazine (DSP), was investigated in this study. Depending on the recrystallization method, DSP afforded two different crystals with green and orange FL emission. The orange color FL emission crystal (O-form) was easily converted to the green color FL emission one (G-form) by manual grinding. The G-form was also converted to a slightly different orange color FL emission crystal (RO-form) by a weak UV irradiation. When the RO-form was ground again, the G-form was regenerated. The FL colors changed between the G- and RO-forms over several ten times by repeated mechanical grinding and UV irradiation. The FL, UV-visible, ¹H-NMR and XRD results showed that the O (or RO)-to-G transformation induced by mechanical stress results from the change of degree of molecular stacking from dense molecular stacking structure to relatively loose molecular stacking structure, whereas the G-to-RO reconversion by UV irradiation results from return to dense molecular stacking structure again due to lattice movement (lattice slipping) allowed by photocycloaddition in solid-state.

A Green Synthesis and Antibacterial Activity of N-Arylsulfonylhydrazone Compounds

A green method has been developed for the synthesis of N-arylsulfonylhydrazones via a simple grindstone procedure. By grinding mixtures of benzensulfonyl hydrazides and a series of aryl aldehydes or ketones in the mortar using L-tyrosine as catalyst, 24 N-arylsulfonylhydrazones were synthesized in a few minutes with high yield. All compounds were screened for their antibacterial activities. Most of them exhibit some antibacterial activities especially for 3d, 3l and 3v showing high activity against Staphylococcus aureus and Escherichia coli.

Sustainable Synthesis of Co@NC Core Shell Nanostructures from Metal Organic Frameworks via Mechanochemical Coordination Self-Assembly: An Efficient Electrocatalyst for Oxygen Reduction Reaction

Herein, a new type of cobalt encapsulated nitrogen-doped carbon (Co@NC) nanostructure employing Zn_x Co_1-x (C₃ H₄ N₂ ) metal-organic framework (MOF) as precursor is developed, by a simple, ecofriendly, solvent-free approach that utilizes a mechanochemical coordination self-assembly strategy. Possible evolution of Zn_x Co_1-x (C₃ H₄ N₂ ) MOF structures and their conversion to Co@NC nanostructures is established from an X-ray diffraction technique and transmission electron microscopy analysis, which reveal that MOF-derived Co@NC core-shell nanostructures are well ordered and highly crystalline in nature. Co@NC-MOF core-shell nanostructures show excellent catalytic activity for the oxygen reduction reaction (ORR), with onset potential of 0.97 V and half-wave potential of 0.88 V versus relative hydrogen electrode in alkaline electrolyte, and excellent durability with zero degradation after 5000 potential cycles; whereas under similar experimental conditions, the commonly utilized Pt/C electrocatalyst degrades. The Co@NC-MOF electrocatalyst also shows excellent tolerance to methanol, unlike the Pt/C electrocatalyst. X-ray photoelectron spectroscopy (XPS) analysis shows the presence of ORR active pyridinic-N and graphitic-N species, along with CoN_x C_y and CoN_x ORR active (M-N-C) sites. Enhanced electron transfer kinetics from nitrogen-doped carbon shell to core Co nanoparticles, the existence of M-N-C active sites, and protective NC shells are responsible for high ORR activity and durability of the Co@NC-MOF electrocatalyst.

Cu2(BDC)2(BPY)–MOF: an efficient and reusable heterogeneous catalyst for the aerobic Chan–Lam coupling prepared via ball-milling strategy

Nanoporous Cu₂(BDC)₂(BPY)–MOF was used as efficient and reusable heterogeneous catalyst to effect the aerobic cross-coupling of aromatic amines and phenyl boronic acid (Chan–Lam Coupling).

Mechanochemical polymerization – controlling a polycondensation reaction between a diamine and a dialdehyde in a ball mill

Mechanochemical polymerization displays a sustainable alternative to classical solvent-based approaches while also offering faster kinetics and an increased conversion.

Will measuring mechanical properties help us understand solid-state reactions?

In the solid-state photodimerization of cinnamic acid polymorphs, can mechanical properties tell us whether Schmidt 'minimal molecular movement' or Kaupp 'molecular migration' is more important?

Scale-up of organic reactions in ball mills: process intensification with regard to energy efficiency and economy of scale

The scale-up of the Knoevenagel-condensation between vanillin and barbituric acid carried out in planetary ball mills is investigated from an engineering perspective. Generally, the reaction proceeded in the solid state without intermediate melting and afforded selectively only one product. The reaction has been used as a model to analyze the influence and relationship of different parameters related to operation in planetary ball mills. From the viewpoint of technological parameters the milling ball diameter, dMB, the filling degree with respect to the milling balls' packing, ΦMB,packing, and the filling degree of the substrates with respect to the void volume of the milling balls' packing, ΦGS, have been investigated at different reaction scales. It was found that milling balls with small dMB lead to higher yields within shorter reaction time, treaction, or lower rotation frequency, rpm. Thus, the lower limit is set considering the technology which is available for the separation of the milling balls from the product after the reaction. Regarding ΦMB,packing, results indicate that the optimal value is roughly 50% of the total milling beakers' volume, VB,total, independent of the reaction scale or reaction conditions. Thus, 30% of VB,total are taken by the milling balls. Increase of the initial batch sizes changes ΦGS significantly. However, within the investigated parameter range no negative influence on the yield was observed. Up to 50% of VB,total can be taken over by the substrates in addition to 30% for the total milling ball volume. Scale-up factors of 15 and 11 were realized considering the amount of substrates and the reactor volume, respectively. Beside technological parameters, variables which influence the process itself, treaction and rpm, were investigated also. Variation of those allowed to fine-tune the reaction conditions in order to maximize the yield and minimize the energy intensity.

Ex situ and in situ monitoring of the syntheses of thermochromic Schiff bases

This work presents in situ PXRD monitoring of the syntheses of thermochromic Schiff bases and a study of the mechanisms of their formation.

An efficient, mild and solvent-free synthesis of benzene ring acylated harmalines

A facile synthesis of a series of benzene ring acylated analogues of harmaline has been achieved by Friedel-Crafts acylation under solvent-free conditions at room temperature using acyl halides/acid anhydrides and AlCl₃. The reaction afforded 10- and 12-acyl analogues of harmaline in good yield, along with minor quantities of N-acyl-tryptamines and 8-acyl analogues of N-acyltryptamines.

A simple, rapid and mild one pot synthesis of benzene ring acylated and demethylated analogues of harmine under solvent-free conditions

A simple, rapid, solvent-free, room temperature one pot synthesis of benzene ring acylated and demethylated analogues of harmine using acyl halides/acid anhydrides and AlCl₃ has been developed. Eight different acyl halides/acid anhydrides were used in the synthesis. The resulting mixture of products was separated by column chromatography to afford 10- and 12-monoacyl analogues, along with 10,12-diacyl-11-hydroxy products. In five cases the corresponding 10-acyl-11-hydroxy analogues were also obtained. Yields from the eight syntheses (29 products in total) were in the 6-34% range and all compounds were fully characterized.