Sodium Chlorite as an Efficient Oxidant and Hydroxy Ion Pump in Osmium-Catalyzed Asymmetric Dihydroxylation

Sodium chlorite is an efficient stoichiometric oxidant in Sharpless asymmetric dihydroxylation. One sodium chlorite provides the reaction with the stoichiometric number of electrons and hydroxide ions needed to dihydroxylate two olefins without the consumption of any additional base. 100% conversion in sodium chlorite asymmetric dihydroxylation of styrene was achieved twice as fast as in the established Sharpless K3[Fe(CN)6] dihydroxylation. Even internal olefins were dihydroxylated fast with sodium chlorite without hydrolysis aids. Eight olefins were dihydroxylated to corresponding vicinal diols with yields and ees as good as those reported in the literature for other similar processes

On the Hydrolysis Step in Osmium Catalyzed Asymmetric Dihydroxylations

In order to obtain information about the most important features that affect the efficiency of osmium catalyzed asymmetric dihydroxylation, a series of substituted styrenes have been studied by using a Hammett type approach as well as solvent kinetic isotope effects. A concave shaped Hammett plot with a minimum at X = H revealed a change in the mechanism going from electron-donating to electron-withdrawing substituents for both NaClO2 and K3[Fe(CN)6] asymmetric dihydroxylations. The Hammett plot together with solvent isotope effect results indicates that osmium (mono)glycolates of styrenes with electron-withdrawing substituents are hydrolyzed by a stepwise attack of the nucleophile to the electrophilic osmium-center and subsequent protonation of the alkaline intermediate. Osmium (mono)glycolates in dihydroxylation, using NaClO2 as the stoichiometric oxidant of styrenes with electron-donating substituents, are hydrolyzed by specific acid catalysis. The rate-limiting step is an A1 type process. Differences in the ρ values in the Hammett plots for NaClO2 and K3[Fe(CN)6] asymmetric dihydroxylations indicate that in dihydroxylations with NaClO2 as the secondary oxidant, the reactive osmium(VI) mono(glycolate) is oxidized to osmium(VIII) mono(glycolate) prior to hydrolysis. The reaction rate was found to have an effect on the enantioselectivity in asymmetric dihydroxylation. If the hydrolysis step is slow enough, a competitive bis(glycolation) deteriorates the enantioselectivity in K3[Fe(CN)6] asymmetric dihydroxylations and even more so in NaClO2 asymmetric dihydroxylations

Enhancement of the Nanofibrillation of Wood Cellulose through Sequential Periodate–Chlorite Oxidation

Sequential regioselective periodate–chlorite oxidation was employed as a new and efficient pretreatment to enhance the nanofibrillation of hardwood cellulose pulp through homogenization. The oxidized celluloses with carboxyl contents ranging from 0.38 to 1.75 mmol/g could nanofibrillate to highly viscous and transparent gels with yields of 100–85% without clogging the homogenizer (one to four passes). On the basis of field-emission scanning electron microscopy images, the nanofibrils obtained were of typical widths of approximately 25 ± 6 nm. All of the nanofibrillar samples maintained their cellulose I crystalline structure according to wide-angle X-ray diffraction results, and the crystallinity index was approximately 40% for all samples

Strong, Self-Standing Oxygen Barrier Films from Nanocelluloses Modified with Regioselective Oxidative Treatments

In this work, three self-standing nanocellulose films were produced from birch pulp using regioselective oxidation and further derivatization treatments. The modified celluloses were synthesized using periodate oxidation, followed by chlorite oxidation, bisulfite addition, or reductive amination with amino acid taurine, which resulted in dicarboxylic acid cellulose (DCC), α-hydroxy sulfonic acid cellulose (HSAC), and taurine-modified cellulose (TC), respectively. The nanocelluloses were fabricated by mechanical disintegration using high-pressure homogenization. Mechanical and barrier properties of the nanocellulose films were characterized. Two (2,2,6,6-tetramethyl-piperidin-1-yl)­oxyl (TEMPO) oxidation-based nanocellulose films were also produced, and their properties were compared to the periodate-based nanocellulose films. All of the periodate-based nanocellulose films showed high tensile strength (130–163 MPa) and modulus (19–22 GPa). Oxygen barrier properties of the films were superior to many synthetic and composite materials; in particular, the nanofibrillated DCC films had oxygen permeability as low as 0.12 cm³ μm/(m² d kPa) at 50% relative humidity. Compared to films of TEMPO-oxidized nanocelluloses, all of the periodate-based nanocellulose films had similar or even better mechanical and barrier properties, demonstrating versatility of periodate oxidation to obtain nanocellulose films with adjustable properties. Also, for the first time, amino-acid-based cellulose modification was used in the production of nanocellulose

Synthesis of 4-Alkoxy-8-hydroxyquinolines^†

Quinolines with a hydroxyl group at the 8-position and an alkoxy group at the 4-position are rare compounds. In this paper the synthesis of five 4-alkoxy-8-hydroxyquinolines is reported. The key reaction in the synthetic route is a selective protection of the hydroxyl group at C-atom 8 in 4,8-dihydroxyquinoline with a tosyl group and the hydrolytic removal of the protective group after the alkylation. The tosyl group is stable during the alkylations with various alkylating agents in the presence of sodium hydride

Synthesis of Benzothiadiazole Derivatives by Applying C–C Cross‑Couplings

The benzothiadiazole moiety has been extensively exploited as a building block in the syntheses of efficient organic semiconducting materials during the past decade. In this paper, parallel synthetic routes to benzothiadiazole derivatives, inspired by previous computational findings, are reported. The results presented here show that various C–C cross-couplings of benzothiadiazole, thiophene, and thiazole derivatives can be efficiently performed by applying Xantphos as a ligand of the catalyst system. Moreover, improved and convenient methods to synthesize important chemical building blocks, e.g., 4,7-dibromo-2,1,3-benzothiadiazole, in good to quantitative yields are presented. Additionally, the feasibility of Suzuki–Miyaura and direct coupling methods are compared in the synthesis of target benzothiadiazole derivatives. The computational characterization of the prepared benzothiadiazole derivatives shows that these compounds have planar molecular backbones and the possibility of intramolecular charge transfer upon excitation. The experimental electrochemical and spectroscopic studies reveal that although the compounds have similar electronic and optical properties in solution, they behave differently in solid state due to the different alkyl side-group substitutions in the molecular backbone. These benzothiadiazole derivatives can be potentially used as building blocks in the construction of more advanced small molecule organic semiconductors with acceptor–donor–acceptor motifs