H-Cube®system

This process could also be applied to the synthesis of tripeptides. A Cbz-protected dipeptide (Cbz-Ala-Gly-OEt) was deprotected in flow using the H-Cube system, and using the above procedure the tripeptide Cbz-Phe-Ala-Gly-OEt was obtained in 59% overall yield and in only 6-7 h, based on the longest linear sequence from glycine. 

The first report using the H-Cube system appeared in 2005. AThalesNano team reported the reduction of nitro compounds into the corresponding amines under flow conditions using a Pd/C cartridge [61]. They also demonstrated the flow reduction of a variety of functional groups (Scheme 7.15) [62]. 

The use of eontinuous-flow for rapid optimization followed by seale up was demonstrated by Steven Ley s group [66]. Imine reductions were performed in the presenee of Pd/C as eatalyst on the H-Cube flow hydrogenation system. After optimization of eonditions on small quantities, 1.0 g of desired product was synthesized within 70 min with quantitative yield and exeellent purity. Worth noting is that the reactions progressed quantitatively without the need for further purifieation. 

The sequence includes several synthetic steps over polymer-supported catalysts in directly coupled commercially available Omnifit glass reaction columns [41] using a Syrris Africa microreactor system [14], Thales H-Cube flow hydrogenator [32] and a microfluidic chip. The process affords the alkaloid in 90% purity after solvent evaporation, but in a moderate 40% yield. After a closer investigation it was concluded that this is due to the poor yield of 50% in the phenolic oxidation step. On condition that this is resolved with the use of a more effective supported agent, the route would provide satisfactory yields and purities of the product. 

Another concept of packed bed microreactor systems are the Thales Nano continuous-flow reactors [96]. They are meant for hydrogenation (H-cube) and ozonolysis (0-cube) reactions. The catalyst is packed inside the reactor in a form of... 

Cycloaddition reactions have been extensively studied in flow reactors because of the ease with which highly complex scaffolds can be prepared. Using a combination of flow reactors and the H-Cube continuous flow hydrogenation system (ThalesNano, Budapest, Hungary), Baumann and co-workers demonstrated the generation of azomethine ylides and their dipolar cycloaddition reaction (Scheme 6.5) to afford a series of 3-nitropyrrolidines 10, which were subsequently chemoselectively hydrogenated to the respective amines in high yield. ... 

Properties of the alkali fluorides.—The anhydrous alkali fluorides crystallize in the cubic system.8 Lithium fluoride forms regular optohedrons and nacreous plates sodium fluoride crystallizes in cubes, but in presence of sodium carbonate, the crystals are octohedrons. The cubic crystals are frequently en tremies. H. Schwendenwein has discussed the space lattice of the alkali fluorides, and K. Fajans and H. Grimm estimated the distance of the atoms apart in sodium and potassium fluorides to be respectively 2 34 X 10 8 and 2 67 X10-8 cm. and the respective lattice energies to be 210-4 and 192 2 Cals, per mol. The taste of potassium fluoride is acrid and salty. 

In 1784, Haiiy formulated the Law of Rational Indices, which states that all faces of a crystal can be described by Miller indices (hid), and for those faces that commonly occur, h, k, and l are all small integers. The eight faces of an octahedron are (111), (111), (ill), (111), (111), (111), (III), and (III). The form symbol that represents this set of eight faces is 111. The form symbol for the six faces of a cube is 100. Some examples in the cubic system are shown in Figs. 9.1.3. and 9.1.4. 

Martin101 has calculated the long-range dipole moment for systems of three identical atoms. For the H H H system he has used a pseudo-spectral perturbation method, while for He-"He "He he has used the closure approximation. These quantities could be experimentally accessible via a pressure-induced i.r. absorption whose intensity varied as the cube of the pressure. 

In the reciprocal space in three dimensions the zones, instead of line sections, become geometrical bodies determined by the values of the three integers h, k, and l instead of by m. They are just such polyhedra (Brillouin zones) in the reciprocal lattice as the faces of a crystal in ordinary space which correspond to the same hkl (e.g. 100 is the cube, 111 the octahedron, etc. in the cubic system). 

The various groups of planes arc identified using indices in three dimensions h. k, and /, related to the directions of axes defining the crystalline system. Thus, for example, in a cubic system, the (100) family, in this case equivalent by a 90 rotation to the (010) and (001) families, corresponds to the planes parallel to the edges of the cube. The notation (110) denotes planes on the diagonal, (111) corresponds to planes perpendicular to the major diagonal, etc. (sec Fig. 10.2). 

---