Experimental Investigation of AGET ATRP Polymerization of Butyl Methacrylate in an Emulsion Stirred Tank Reactor

This study investigates ATRP emulsion polymerization of butyl methacrylate (BMA) in a 2-L stirred tank reactor using AGET as the initiation technique with ascorbic acid. The polymerization is performed in two step procedure using surfactant (Brij 98) in distilled water. The reaction is initiated by the catalyst CuBr2/dNbpy and initiator EBiB under a blanket of nitrogen to minimize air presence. An experimental design is performed to investigate the effects of the key variables: temperature, catalyst complex, surfactant and reducing agent. For reaction temperatures of 50°C, 60°C and 70°C, BMA conversion obtained is 63.9%, 70.2% and 85.8%, respectively. All other nine tests are done at 70°C for appropriate amounts of reactants. The results concluded that BMA conversion improves to 90% and the PDI increases slightly from 1.15 to 1.29 for more ascorbic acid. BMA conversion and PDI improve with less surfactant, but more ligand narrows MWD and reduces the catalyst activity.

Experimental Investigation of AGET ATRP Polymerization of Butyl Methacrylate in an Emulsion Stirred Tank Reactor

This study investigates ATRP emulsion polymerization of butyl methacrylate (BMA) in a 2-L stirred tank reactor using AGET as the initiation technique with ascorbic acid. The polymerization is performed in two step procedure using surfactant (Brij 98) in distilled water. The reaction is initiated by the catalyst CuBr2/dNbpy and initiator EBiB under a blanket of nitrogen to minimize air presence. An experimental design is performed to investigate the effects of the key variables: temperature, catalyst complex, surfactant and reducing agent. For reaction temperatures of 50°C, 60°C and 70°C, BMA conversion obtained is 63.9%, 70.2% and 85.8%, respectively. All other nine tests are done at 70°C for appropriate amounts of reactants. The results concluded that BMA conversion improves to 90% and the PDI increases slightly from 1.15 to 1.29 for more ascorbic acid. BMA conversion and PDI improve with less surfactant, but more ligand narrows MWD and reduces the catalyst activity.

Asymmetric Henry Reaction of Nitromethane with Substituted Aldehydes Catalyzed by Novel In Situ Generated Chiral Bis(β-Amino Alcohol-Cu(OAc)2·H2O Complex

Novel chiral thiophene-2,5-bis(β-amino alcohol) ligands (L1–L5) were designed and synthesized from thiophene-2,5-dicarbaldehyde (3) with chiral β-amino alcohols (4a–e) in 4 steps with overall 23% yields. An in situ generated L-Cu(OAc)2·H2O catalyst system was found to be highly capable catalyst for the asymmetric Henry reaction of nitromethane (7) with various substituted aromatic aldehydes (6a–m) producing chiral nitroaldols product (8a–m) with excellent enantiomeric purity (up to 94.6% ee) and up to >99% chemical yields. 20 mol% of L4-Cu(OAc)2 catalyst complex in EtOH was effective for the asymmetric Henry transformation in 24 h, at ambient temperature. Ease of ligand synthesis, use of green solvent, base free reaction, mild reaction conditions, high yields and excellent enantioselectivity are all key factors that make this catalytic system robust and highly desirable for the access of versatile building block β-nitro alcohol in practical catalytic usage via asymmetric Henry reaction.

MW-Promoted Cu(I)-Catalyzed P–C Coupling Reactions without the Addition of Conventional Ligands; an Experimental and a Theoretical Study

An experimental and a theoretical study on the so far less investigated Cu(I) salt-catalyzed Hirao reaction of iodobenzene and diarylphosphine oxides (DAPOs) revealed that Cu(I)Br or Cu(I)Cl is the most efficient catalyst under microwave irradiation. The optimum conditions included 165 °C and a 1:2 molar ratio for DAPOs and triethylamine. The possible ligations of Cu(I) were studied in detail. Bisligated P---Cu(I)---P (A), P---Cu(I)---N (B) and N---Cu(I)---N (C) complexes were considered as the catalysts. Calculations on the mechanism suggested that complexes A and B may catalyze the P–C coupling, but the latter one is more advantageous both according to experiments and calculations pointing out the Cu(I) ® Cu(III) conversion in the oxidative addition step. The P–C coupling cannot take place with PhBr, as in this case, the catalyst complex cannot be regenerated.

Cooligomers from morpholine-2,5-dione and para-dioxanone and catalyst complex SnOct2/2-hydroxyethyl sulfide

Complexes from catalysts and initiator can be used to insert a specific number of additional chemical functional groups in (co)polymers prepared by ring-opening polymerization (ROP) of lactones. We report on the synthesis of cooligomers from sec-butyl-morpholine-2,5-dione (SBMD) and para-dioxanone (PDX) by ROP with varied feed ratios in the bulk using the catalyst complex SnOct2/2-hydroxyethyl sulfide. Mn of the cooligomers (determined by GPC) decreased with decreasing SBMD feed ratio from 4200 ± 420 to 800 ± 80 g mol−1. When the feed ratio was reduced from 80 to 50 mol% the molar ratio of SBMD of the cooligomers (determined by 1H-NMR) remained nearly unchanged between 81 and 86 mol% and was attributed to a higher reactivity of SBMD. This assumption was confirmed by fractionation of GPC, in which an increase of SBMD with increasing molecular weight was observed. The catalyst/initiator system provides a high potential to create orthogonal building blocks by cleavage of the sulfide bond. Graphic abstract

Linking Chemical Reaction Intermediates of the Click Reaction to Their Molecular Diffusivity

Bipolar reactions have been provoked by reports of boosted diffusion during chemical and enzymatic reactions. To some, it is intuitively reasonable that relaxation to truly Brownian motion after passing an activation barrier can be slow, but to others the notion is so intuitively unphysical that they suspect the supporting experiments to be artifact. Here we study a chemical reaction according to whose mechanism some intermediate species should speed up while others slow down in predictable ways, if the boosted diffusion interpretation holds. Experimental artifacts would do not know organic chemistry mechanism, however. Accordingly, we scrutinize the absolute diffusion coefficient (D) during intermediate stages of the CuAAC reaction (coppercatalyzed azide-alkyne cycloaddition click reaction), using proton pulsed field-gradient nuclear magnetic resonance (PFG-NMR) to discriminate between the diffusion of various reaction intermediates. For the azide reactant, its D increases during reaction, peaks at the same time as peak reaction rate, then returns to its initial value. For the alkyne reagent, its D decreases consistent with presence of the intermediate large complexes formed from copper catalyst and its ligand, except for the 2Cu-alk complex whose more rapid D may signify that this species is the real reactive complex. For the product of this reaction, its D increases slowly as it detaches from the triazolide catalyst complex. These examples of enhanced diffusion for some molecular species and depressed diffusion for others causes us to conclude that diffusion coefficients during these elementary reactions are influenced by two components: hydrodynamic radius increase from complex formation, which slows diffusion, and energy release rate during the chemical reaction, which speeds it up. We discuss possible mechanisms and highlight that too little is yet understood about slow solvent reorganization during chemical reactions.<br>

Linking Chemical Reaction Intermediates of the Click Reaction to Their Molecular Diffusivity

Bipolar reactions have been provoked by reports of boosted diffusion during chemical and enzymatic reactions. To some, it is intuitively reasonable that relaxation to truly Brownian motion after passing an activation barrier can be slow, but to others the notion is so intuitively unphysical that they suspect the supporting experiments to be artifact. Here we study a chemical reaction according to whose mechanism some intermediate species should speed up while others slow down in predictable ways, if the boosted diffusion interpretation holds. Experimental artifacts would do not know organic chemistry mechanism, however. Accordingly, we scrutinize the absolute diffusion coefficient (D) during intermediate stages of the CuAAC reaction (coppercatalyzed azide-alkyne cycloaddition click reaction), using proton pulsed field-gradient nuclear magnetic resonance (PFG-NMR) to discriminate between the diffusion of various reaction intermediates. For the azide reactant, its D increases during reaction, peaks at the same time as peak reaction rate, then returns to its initial value. For the alkyne reagent, its D decreases consistent with presence of the intermediate large complexes formed from copper catalyst and its ligand, except for the 2Cu-alk complex whose more rapid D may signify that this species is the real reactive complex. For the product of this reaction, its D increases slowly as it detaches from the triazolide catalyst complex. These examples of enhanced diffusion for some molecular species and depressed diffusion for others causes us to conclude that diffusion coefficients during these elementary reactions are influenced by two components: hydrodynamic radius increase from complex formation, which slows diffusion, and energy release rate during the chemical reaction, which speeds it up. We discuss possible mechanisms and highlight that too little is yet understood about slow solvent reorganization during chemical reactions.<br>

Experimental Investigation of Emulsion AGET ATRP of MMA in a Stirred Tank Reactor

This study investigates the emulsion AGET ATRP of MMA in a 2-L reactor using the reactants: surfactant (Brij 98), catalyst complex (CuBr2/dNbpy), initiator (EBiB) and reducing agent (ascorbic acid). Preliminary trials demonstrate that the two-step procedure preserves the ATRP living features much better than the single-step procedure. An experimental design and statistical analysis were performed to investigate the main effects and two-factor interaction effects of temperature, surfactant, catalyst complex, initiator and reducing agent on the monomer conversion, average molecular weights and polydispersity index of the polymer. The input-output model predictions agree with experimental data. The results revealed that the temperature was the most influential factor for all three-process responses with 71.34%, 32.78% and 27.76 % contribution. However, the initiator was the least influential factor for both conversion and PDI with 0.035% and 0.13% contribution, whereas the surfactant was the least influential factor for molecular weight with 0.068% contribution

Experimental Investigation of Emulsion AGET ATRP of MMA in a Stirred Tank Reactor

This study investigates the emulsion AGET ATRP of MMA in a 2-L reactor using the reactants: surfactant (Brij 98), catalyst complex (CuBr2/dNbpy), initiator (EBiB) and reducing agent (ascorbic acid). Preliminary trials demonstrate that the two-step procedure preserves the ATRP living features much better than the single-step procedure. An experimental design and statistical analysis were performed to investigate the main effects and two-factor interaction effects of temperature, surfactant, catalyst complex, initiator and reducing agent on the monomer conversion, average molecular weights and polydispersity index of the polymer. The input-output model predictions agree with experimental data. The results revealed that the temperature was the most influential factor for all three-process responses with 71.34%, 32.78% and 27.76 % contribution. However, the initiator was the least influential factor for both conversion and PDI with 0.035% and 0.13% contribution, whereas the surfactant was the least influential factor for molecular weight with 0.068% contribution