It was demonstrated that ortho-substituted anilines are prone to undergo hydroamination reactions with diethyl acetylenedicarboxylate in a planetary ball mill. A sequential coupling of the intermolecular hydroamination reaction with intramolecular ring closure was utilized for the syntheses of benzooxazines, quinoxalines, and benzothiazines from readily available building blocks, that is, electrophilic alkynes and anilines with OH, NH, or SH groups in the ortho position. For the heterocycle formation, it was shown that several stress conditions were able to initiate the reaction in the solid state. Processing in a ball mill seemed to be advantageous over comminution with mortar and pestle with respect to process control. In the latter case, significant postreaction modification occurred during solid-state analysis. Cryogenic milling proved to have an adverse effect on the molecular transformation of the reagents.

The synthesis of nopinone from β-pinene is an interesting model reaction for the investigation of methods for the oxidative cleavage of C=C bonds. Nopinone is used as chiral component for the total synthesis of different ligands or natural compounds such as di- or sesquiterpenes, as well as for the production of pharmaceutically active components. The cleavage of the C(2)=C(10) bond in β-pinene by suitable oxidants leads to the replacement of the exo-methylene functionality by a carbonyl group, which is more suitable for subsequent synthetic steps and the construction of complex condensed ring systems. Oxidants such as ozone, potassium permanganate, or sodium periodate have been applied successfully for this reaction. Ozonolysis of the double bond follows the classical Criegee mechanism, after which the secondary intermediate is isolated and reductive workup yields the carbonyl products. Dihydroxylation of the double bond can be initiated by permanganate or periodate. Further oxidation leads to the same products known from ozonolysis. Periodate oxidations in particular can be supported by catalysts such as RuCl₃ or OsO₄, because the oxidant is generally too weak to dihydroxylate the double bond. OsO₄-catalyzed reactions, for example, can take advantage of a co-oxidant such as trimethylammonium N-oxide for the dihydroxylation step. Other oxidants such as hydrogen peroxide or dioxygen have also been tested but with minor success with respect to conversion or selectivity.

Kugelmühlen gehören zu einer Klasse von Apparaten, die für die Zerkleinerung und Vermischung fester Stoffe in der Verfahrenstechnik angewendet werden. Die Tatsache, dass bei der Bewegung von Kugeln in den Mahlbehältern Energie auf die Reaktionsmischung übertragen wird, lässt sich für die Initiierung chemischer Reaktionen ausnutzen. Zahlreiche Beispiele aus dem Gebiet der organischen Synthesechemie zeigen die allgemeine Anwendbarkeit dieser Technik aber auch die Herausforderungen, die damit einhergehen und Potenzial für zukünftige Entwicklungen bieten.

Ball mills are instruments for the comminution and particle refinement of solids as part of process engineering. Due to the movement of milling balls inside the milling chamber energy is transferred to the reaction mixture which can be utilized to initiate chemical reactions. Numerous examples from the field of organic synthesis prove the general applicability of this technology but also point out accompanied challenges with potential for future developments.

The use of modern microwave equipment affords an easy and safe handling in the laboratory routine. The described quartz reactor system was tested in different reaction types to show its versatile applications. Various liquid-phase hydrogenations were carried out successfully. The construction of the reactor allows the direct introduction of gases into the reaction mixture so that the reduction can be performed with gaseous hydrogen.

A method for the Glaser coupling reaction of alkynes by using a vibration ball mill has been developed. The procedure avoids the use of ligands and solvents during the reaction. Aryl- and alkyl-substituted terminal alkynes undergo homocoupling if coground with KF–Al₂O₃ and CuI as a milling auxiliary and catalyst. Furthermore, an alternative protocol has been developed incorporating 1,4-diazabicyclo[2.2.2]octane (DABCO) as an additional base allowing the use of KF–Al₂O₃ with a lower KF loading. Besides Cu salts, the homocoupling of phenylacetylene is also catalyzed by Ni or Co salts, as well as by PdCl₂. TMS-protected phenylacetylene could be directly converted into the homocoupling product after in situ deprotection of the alkyne by fluoride-initiated removal of the trimethylsilyl group.

The microwave-assisted hydrogenation of citral (3,7-dimethylocta-2,6-dienal) to citronellal with molecular hydrogen as the reducing agent was investigated. Several polar and non-polar solvents were screened and imidazolium-based ionic liquids were applied as modifiers for the palladium-containing porous glass catalysts (Pd/TP). The best results were obtained with N-ethyl-N’-methylimidazolium dicyanamide, N-ethyl-N’-methylimidazolium acetate, or N-ethyl-N’-methylimidazolium trifluoroacetate, which were used to prepare supported catalysts with an ionic liquid layer (SCILL) on Pd/TP by wet-impregnation. The influence of pressure and temperature when using these ionic liquid-containing catalysts, as well as their long-term stabilities, were examined. Working with microwave-assisted heating, high yields of citronellal were achieved under mild conditions within short reaction times. Catalyst characterization was carried out by means of BET measurements, X-ray photoelectron spectroscopy (XPS) and thermo-gravimetric analyses. The influences of the ionic liquid layer were derived from experiments carried out before and after the reactions.

A solvent-free method for the direct oxidation of anilines to the corresponding azo and azoxy homocoupling products by using a planetary ball mill was developed. Various oxidants and grinding auxiliaries were tested and a variety of substituted anilines were investigated. It was possible to form chemoselectively either azo, azoxy, or the nitro compounds from reaction of aromatic anilines. The selectivity of the solvent-free reaction is switchable by applying a combination of oxidant and grinding auxiliary. Furthermore, a comparison with other methods of energy input (microwave, classical heating, and ultrasound) highlighted the advantages of the ball mill approach and its high energy efficiency.

A new method for the oxidative cleavage of β-pinene (1) yielding nopinone (2) with potassium permanganate as oxidant under solvent-free conditions was established. The reaction was performed in a conventional ball mill with use of a grinding auxiliary. The auxiliary has the ability to sorb liquid reactants such as 1 on its surface to make liquid(s) accessible for mechanical impact. Different reaction parameters and technical variables were assessed concerning their influence on yield and selectivity of 2. Different chemical parameters such as oxidants, grinding auxiliaries, and quantities were investigated. Also tuning parameters including milling time, rotation frequency, and number of milling balls were explored.

The thermal conversions of monoterpenes and monoterpenoids are an interesting field of research with respect to mechanistic, kinetic, and theoretical issues. Since the beginning of the 20th century, these reactions have attracted the interest of many research groups, and even today there are sufficient problems and questions to deal with. This review covers the thermal isomerization chemistry of pinanes, pinenes, carenes, and thujenes over the past 70 years. Categorization of these compounds into groups, each of them being represented by a small parent molecule (cyclobutane, vinylcyclobutane, vinylcyclopropane), allows systematization of multitude of publications.