Continuous Flow Reduction of Artemisinic Acid Utilizing Multi‐Injection Strategies—Closing the Gap Towards a Fully Continuous Synthesis of Antimalarial Drugs

One of the rare alternative reagents for the reduction of carbon–carbon double bonds is diimide (HN?NH), which can be generated in situ from hydrazine hydrate (N₂H₄ ? H₂O) and O₂. Although this selective method is extremely clean and powerful, it is rarely used, as the rate‐determining oxidation of hydrazine in the absence of a catalyst is relatively slow using conventional batch protocols. A continuous high‐temperature/high‐pressure methodology dramatically enhances the initial oxidation step, at the same time allowing for a safe and scalable processing of the hazardous reaction mixture. Simple alkenes can be selectively reduced within 10–20 min at 100–120 °C and 20 bar O₂ pressure. The development of a multi‐injection reactor platform for the periodic addition of N₂H₄ ? H₂O enables the reduction of less reactive olefins even at lower reaction temperatures. This concept was utilized for the highly selective reduction of artemisinic acid to dihydroartemisinic acid, the precursor molecule for the semisynthesis of the antimalarial drug artemisinin. The industrially relevant reduction was achieved by using four consecutive liquid feeds (of N₂H₄ ? H₂O) and residence time units resulting in a highly selective reduction within approximately 40 min at 60 °C and 20 bar O₂ pressure, providing dihydroartemisinic acid in ≥93 % yield and ≥95 % selectivity.     

Microwave‐Assisted Functionalization of Carbon Nanostructures in Ionic Liquids

The effect of microwave (MW) irradiation and ionic liquids (IL) on the cycloaddition of azomethine ylides to [60]fullerene has been investigated by screening the reaction protocol with regard to the IL medium composition, the applied MW power, and the simultaneous cooling of the system. [60]Fullerene conversion up to 98 % is achieved in 2–10 min, by using a 1:3 mixture of the IL 1‐methyl‐3‐n‐octyl imidazolium tetrafluoroborate ([omim]BF₄) and o‐dichlorobenzene, and an applied power as low as 12 W. The mono‐ versus poly‐addition selectivity to [60]fullerene can be tuned as a function of fullerene concentration. The reaction scope includes aliphatic, aromatic, and fluorous‐tagged (FT) derivatives. MW irradiation of IL‐structured bucky gels is instrumental for the functionalization of single‐walled carbon nanotubes (SWNTs), yielding group coverages of up to one functional group per 60 carbon atoms of the SWNT network. An improved performance is obtained in low viscosity bucky gels, in the order [bmim]BF₄> [omim]BF₄> [hvim]TF₂N (bmim=1‐methyl‐3‐n‐butyl imidazolium; hvim=1‐vinyl‐3‐n‐hexadecyl imidazolium). With this protocol, the introduction of fluorous‐tagged pyrrolidine moieties onto the SWNT surface (1/108 functional coverage) yields novel FT‐CNS (carbon nanostructures) with high affinity for fluorinated phases.     

Unusual Temperature-Retention Dependences Observed for Several Benzodiazepines in RP-HPLC Using Different Mobile Phase Compositions

Non-linear van’t Hoff plots were observed for several benzodiazepines over the usual temperature interval used in RP-LC (10–60 °C), when acetonitrile was added in the mobile phase. Such deviation from linearity was not observed when methanol or isopropanol was added to the mobile phase. Polynomial regressions were applied to fit the experimental data when acetonitrile was used as organic additive in mobile phase. The second-order polynoms may allow finding out the maximum retention depending on temperature, which can be within or out of the normal temperature range used in RP mechanism. A thermodynamic model deriving from the partition of two or more tautomers of the same analyte was proposed to explain this deviation from linearity of van’t Hoff plots.

     

Copolymerization and Copolymers of 2,4,5-Tribromostyrene with Styrene and Acrylonitrile

Abstract

2,4,5-Tribromostyrene (TBSt) was copolymerized with styrene (St) or acrylonitrile (AN) in toluene solution using 2,2′-azobisisobutyronitrile as free radical initiator. The copolymerization reactivity ratios were found to be for the system TBSt/St r ₁ = 1.035 ± 0.164 (TBSt) and r ₂ = 0.150 ± 0.057 (St), and for the system TBSt/AN r ₁ = 2.445 ± 0.270 (TBSt) and r ₂ = 0.133 ± 0.054 (AN). The e and Q values were also calculated. The initial copolymerization rate, R _p, for both systems linearly increases as the content of TBSt in the monomer mixture increases. However, these values are somewhat higher when AN was used as a comonomer. A similar behavior has also been established for the course of the copolymerization reactions to high conversion. The resulting copolymers and TBSt-homopolymer show similar thermal stabilities of polystyrene. However, the glass transition temperature increases markedly with increasing TBSt content.     

Reaction of Dimethyl Acetylene-Dicarobxylate With Triazinone

Abstract

The addition of dimethyl acetylenedicarboxylate (DMAD) to 6-menthy-1, 2,4-triazlne-3(2H)thione-5(4H)-one afforded 2-methoxylcarboxy-7-methyl-1,3-thiazino[3,2-b][1,2,4]triazine-4,8-dione.     

Influence of the pH on the Formation of the Catanionic n-Tetradecylammonium Cholate Surfactant Salt

The catanionic n-tetradecylammonium cholates, with the 1:1 and 1:2 cationic:anionic surfactant molar ratio, have been synthesized by reaction of tetradecylammonium chloride and sodium cholate. The stoichiometry of the compounds formed is strongly dependent on pH of the aqueous reaction solution. In the neutral and slightly acidic medium the isolated surfactant was detected as 1:1, at acidic medium (pH ≈ 3) as 1:2, while the cholic acid alone precipitated from the strong acidic solution (pH ≈ 2). The catanionic surfactants have been characterized by elemental and spectroscopic (IR, ¹H, and ¹³C NMR) analyses, and microscopic observations. The mole fractions of individual components in precipitate present in the heterogeneous aqueous system have been determined as a function of pH. The data interpretation in the pH regions where two different kinds of precipitates coexist pointed to the complex equilibrium in the examined systems. The evaluation of the relevant equilibrium constants was solved by the nonlinear regression analysis. In the acidic region where cholic acid and 1:2 precipitate coexisted the equilibrium constants of dissolution were K ₁ = 8.4 × 10^?10 and K ₄ = 3.7 × 10^?27, respectively. In the region where 1:2 and 1:1 precipitate coexisted the equilibrium constant of dissolution of 1:1 tetradecylammonium cholate was K ₂ = 4.2 × 10^?20.     

Thermodynamic Study of Cadmium Chloride in Aqueous Mixtures of 2-Butanol from Potential Difference Measurements

The standard molal potential differences (E_m∘) have been determined for the cell: CdHg_x(two phase) | CdCl₂(m), H₂O(1 − w), 2-butanol (w) | AgCl(s) | Ag(s) in aqueous mixtures of low mass fraction of 2-butanol (w_2-butanol = 0.05, 0.10, and 0.15) by using the literature data for the stability constants of the chlorocadmium complexes and the present potentiometric data for this cell at five temperatures from (293.15 to 313.15) K and at 10 molalities of CdCl₂ from (0.002 to 0.02) mol-kg⁻¹. The resulting values of E∘_m have been used to calculate the standard thermodynamic quantities (Δ_rG^∘, Δ_rH^∘, and Δ_rS^∘) for the cell reaction, the stoichiometric mean molal activity coefficients (γ_±) of CdCl₂, and the standard thermodynamic functions for CdCl₂ transfer (Δ_t G∘, Δ_t H∘, and Δ_t S∘) from water to the examined aqueous mixtures of 2-butanol. The values obtained have been compared with the analogous literature data for aqueous mixtures of 2-butanone; standard thermodynamic quantities for transfer of CdCl₂ and HBr from water to mixtures containing the same mass fraction of 2-butanol have also been compared. For both electrolytes, these quantities show analogous trends with the alcohol content. This transfer process is nonspontaneous and endothermic. Enthalpy and entropy are evidently influenced by structural changes.