Findings of new oscillations in BR reaction
The Briggs Rauscher reaction, i. e., BR reaction, which is one of the oscillation reactions, produces iodide ion and iodine repeatedly. Continual color changes of the solution from colorless to deep blue, and vice versa, are observed during the reaction due to the so-called “iodine test” reaction. In this work, we studied the effects of the presence of the redox active indicators on the oscillation behavior of the BR reaction. To the reaction mixture of KIO3, H2SO4, H2O2, C3H4O4, MnSO4, and starch, which are used for the general BR reaction as added a redox active reagent (indicator). Then, the changes in color and voltage of the reaction solution were recorded by a photosensor of the LEGO MINDSTORMS and a voltmeter using Pt electrodes. Under general reaction conditions, the oscillation reaction continued for ca. 5 minutes, including 18 times of oscillations. When an indicator, such as BTB, was added instead of starch to the reaction solution, splits of the voltage wave were observed, which should be a kind of new oscillation. Moreover, we found that the addition of K3[Fe(CN)6], which exhibits high redox activity, in the reaction solution instead of starch made the life-time and the numbers of the oscillation in the reaction greater by 3 times (14 min.) in time and more than 4 times (81 times) in the frequency. It’s also a kind of new oscillation. These results suggested that the oxidation-reduction reactions by the addition of ferricyanate ion effectively promotes the redox process of iodine and iodide ion. The experiments we wrote above were conducted without starch. Thus, as a reference, we conducted the same experiments under the presence of starch and got interesting results. We also studied the effects of K4[Fe(CN)6], suggeting that not only redox reaction between ferricyanide and ferrocyanide ion, but also the redox reaction with BR solution should occur in these reactions.
The change in NaCl crystals from cubic to octahedral～Sodium polyacrylate stabilizes the {111} face of Miller indices～
When adding 2% or 4% sodium polyacrylate as habit modifier, standard milky-white octahedral NaCl crystals grew gradually in saturated NaCl solution on the bottom of the container. [1] [2] Sodium polyacrylate is well known as a highly water-absorbable polymer with many carboxylate anions. In the case of low concentration (0.01%, 0.02%, 0.05%, 0.1% and 0.5%) sodium polyacrylate many small or microscopic crystals whose shapes were nearly octahedrons and had {111} faces were observed with an optical microscope on the bottoms of the solution containers. In low concentration sodium polyacrylate, octahedral NaCl crystals made up of electrostatically unstable {111} faces grew similarly to crystals in high concentrations of 2% or 4% NaCl. Therefore, by adding sodium polyacrylate to saturated NaCl solution, cleaved rock salt crystals in this sol were observed to find out whether or not a change in crystal morphology from cuboids of {100} faces to octahedrons of {111} faces would occur. Regardless of the sodium polyacrylate concentrations of 0.01%, 0.02%, 0.05%, 0.1%, 0.5% and 2%, all cuboid crystals changed into a pyramidal shape in which four of the side surfaces formed an equilateral triangle. When one side of each equilateral triangle face was rotated so the square face of the crystal was soaked in the NaCl sol, all crystals grew into octahedrons of high transparency. Sodium polyacrylate, even under a low concentration, caused morphological change in the NaCl crystals. Many carboxylate anions in the sodium polyacrylate attracted sodium ions and the repulsive force between the carboxylate anions became weak, excluding the water in the internal space of the polymer. We considered that the stabilizing {111} faces of gathered sodium ions attached to carboxylate anions. Chloride and sodium ions coordinated continuously to minimize the NaCl surface area, growing into an octahedral and lowering the surface energy of the NaCl crystal. [3]
Direct reductive amination of camphor
Terpenoids are an irreplaceable class of natural products. The camphoryl group is an important moiety in the structure of chiral ligands for asymmetric synthesis catalysis or it can be used as an auxiliary group in asymmetric synthesis.[1] The usage of fenchone based molecules for asymmetric catalysis and synthesis is less common because of the difficulty of fenchone modifications due to steric hindrance. Camphor is a readily available starting molecule for the preparation of different compounds with biological activity. For example, camphor diimines demonstrate antiviral activity.[2] Fenchonyl amine-based molecules are potential therapeutic agents for the treatment of Alzheimer’s disease. Amines are a crucial class of organic compounds with multiple academic and industrial applications. There are a plethora of synthetic approaches towards amines synthesis and modifications, reductive amination being one of the most powerful and useful methods. However, the reductive amination of camphor and fenchone remains a challenge. A standard approach to reductive amination with amines other than ammonia and methylamine includes two steps: preparation of azomethines or Schiff bases in the presence of strong Lewis acids and their reduction with more or less conventional reducing agents. The synthesis of fenchonyl amines is even more challenging. There is no universal approach, and almost every manuscript reports some particular protocol different from others. In most cases, the first stage of this process requires quite harsh conditions. For example, the preparation of a Schiff base from camphor and 1-phenylethylamine requires 5-10 days of heating at 150°C.[3] Schiff bases of other primary amines could be prepared under similarly harsh conditions. Preparation of enamines is possible using titanium tetrachloride as a catalyst. The reduction also might be challenging. Sodium borohydride or sodium cyanoborohydride was described as suitable for this goal in several reports.[4] To the best of our knowledge, no papers describe any general approach for the direct reductive amination of camphor or fenchone. There is only one example of camphor direct reductive amination without an external hydrogen source using carbon monoxide as a reducing agent. This protocol is very efficient but its application is limited by the necessity of carbon monoxide and high-pressure equipment for the reaction setup.