The conformations of dodecamethylcyclohexasilane Si6Me12 and undecamethylcyclohexasilane Si6Me11H have been investigated by ab initio calculations employing the B3LYP density functional with a 6-31+G(d) basis set. Local minima as well as transition structures were calculated with imposed symmetry constraints. For Si6Me12, three unique minima, which correspond to the chair, twist and boat conformations were located with relative zero-point-vibration-corrected energies of 0.0, 7.8 and 11.4 kJ mol(-1). A half-chair conformation with four coplanar silicon atoms connects the chair and twisted minima via an energy barrier of 16.0 and 8.2 kJ mol(-1), respectively. A second transition structure with a barrier of 3.9/0.3 kJ mol(-1) connects the twist with the boat structure. Solution Raman spectra of Si6(CH3)12 and Si6(CD3)12 fully corroborate these results. Below -40 degrees C, the symmetric SiSi ring breathing vibration is a single line, which develops a shoulder (originating from the twist conformer) at longer wavelengths whose intensity increases with increasing temperature. From a Van't Hoff plot, the chair/twist enthalpy difference is 6.6+/-1.5 kJ mol(-1) for Si6(CH3)12 and 6.0+/-1.5 kJ mol(-1) for Si6(CD3)12, which is in reasonable agreement with the ab initio results. Due to the low barrier, the boat conformation cannot be observed, because either the lowest torsional vibration level lies above it or a rapid interconversion between the twist and boat conformations occurs, resulting in averaged Raman spectra. For Si6Me11H, six local minima were located. The chair with the hydrogen atom in the axial position (axial chair) is the global minimum, followed by the equatorial chair (+1.9 kJ mol(-1)) and the three twist conformers (+5.3, +8.0 and +8.1 kJ mol(-1)). The highest local minimum (+11.9 kJ mol(-1)) is a C(s) symmetric boat with the hydrogen atom in the equatorial position. Two possible pathways for the chair-to-chair interconversion with barriers of 13.9 and 14.5 kJ mol(-1) have been investigated. The solution Raman spectra in the SiSi ring breathing region clearly show that below -50 degrees C only the axial and equatorial chairs are present, with an experimental deltaH-value of 0.46 kJ mol(-1). With increasing temperature a shoulder develops which is attributed to the combined twist conformers. The experimental deltaH-value is 6.9 kJ mol(-1), in good agreement with the ab initio results. Due to the low interconversion barriers, the various twist conformers cannot be detected separately.

Oxidative O 2 ‐dependent biotransformations are promising for chemical synthesis, but their development to an efficiency required in fine chemical manufacturing has proven difficult. General problem for process engineering of these systems is that thermodynamic and kinetic limitations on supplying O 2 to the enzymatic reaction combine to create a complex bottleneck on conversion efficiency. We show here that continuous‐flow microreactor technology offers a comprehensive solution. It does so by expanding the process window to the medium pressure range (here, ≤34 bar) and thus enables biotransformations to be conducted in a single liquid phase at boosted concentrations of the dissolved O 2 (here, up to 43 mM). We take reactions of glucose oxidase and d ‐amino acid oxidase as exemplary cases to demonstrate that the pressurized microreactor presents a powerful engineering tool uniquely apt to overcome restrictions inherent to the individual O 2 ‐dependent transformation considered. Using soluble enzymes in liquid flow, we show reaction rate enhancement (up to six‐fold) due to the effect of elevated O 2 concentrations on the oxidase kinetics. When additional catalase was used to recycle dissolved O 2 from the H 2 O 2 released in the oxidase reaction, product formation was doubled compared to the O 2 supplied, in the absence of transfer from a gas phase. A packed‐bed reactor containing oxidase and catalase coimmobilized on porous beads was implemented to demonstrate catalyst recyclability and operational stability during continuous high‐pressure conversion. Product concentrations of up to 80 mM were obtained at low residence times (1–4 min). Up to 360 reactor cycles were performed at constant product release and near‐theoretical utilization of the O 2 supplied. Therefore, we show that the pressurized microreactor is practical embodiment of a general reaction‐engineering concept for process intensification in enzymatic conversions requiring O 2 as the cosubstrate.

Although continuous flow technology can facilitate the scale-up of photochemical processes it is not yet routinely implemented on production scale in the fine chemical industries. This can be attributed to additional challenges compared to thermal processes, mostly in the homogeneous irradiation of the flow reactor. Here, we detail the process of bringing a previously developed photochemical benzylic bromination, utilizing in situ bromine generation, from lab to pilot scale. The process setup is discussed in detail, alongside a comprehensive risk assessment and discussion of problems encountered in the investigation of key reaction parameters. Ultimately, an assay yield of 88% was obtained in 22 s irradiated residence time, resulting in a productivity of 4.1 kg h–1 (space-time yield = 82 kg L–1 h–1) representing a 14-fold scale-up versus the lab-scale process.

Three new nortricyclic P 7 R 3 derivatives with R = (SiMe 3 ) 2 -MeSi-(2), (SiMe 3 ) 2 PhSi-(3), and cyclo-Si 6 Me 11 -(4) were synthesized from red phosphorus, sodium/potassium alloy, and a chlorooligosilane, and their structures were elucidated with X-ray diffraction. Reactions of 2 and 3 and of tri(hypersilyl)heptaphosphane 1 [hypersilyl = (SiMe 3 ) 3 Si-] with KOtBu and LiOtBu were performed, which led to different results depending on the size of the substituent. With KOtBu, Si-P bonds were cleaved in 2 and 3, and the mono-and dianions [ 18-crown-6]+ salt of 2b suitable for X-ray diffraction could be grown successfully. Compound 1 reacted in an unprecedented way with KOtBu at -60°C. An Si-Si bond was cleaved, and a transient silyl anion formed, which immediately rearranged into a transient heptaphosphanide anion [Hyp 2 P 7 ] -(1a) under expulsion of bis(trimethylsilyl)silylene.

The installation of a StarLam 3000 microreactor in an existing production plant is reported. The aim was to double the capacity of a running two step batch process. This was achieved by installing the microreactor for the first reaction step. A higher reaction rate made it possible to reach overall throughputs of 3.6 tons per hour. Additionally energy savings were achieved. The microreactor is running in production for more than a year now.