scholarly journals 1,3-Dioxolan-4-Ones as Promising Monomers for Aliphatic Polyesters: Metal-Free, in Bulk Preparation of PLA

Polymers ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2396
Author(s):  
Stefano Gazzotti ◽  
Marco Aldo Ortenzi ◽  
Hermes Farina ◽  
Alessandra Silvani
Keyword(s):  
Molecular Weight ◽  
Thermal Properties ◽  
Acid Catalyst ◽  
Monomer Conversion ◽  
Reaction Conditions ◽  
Aliphatic Polyesters ◽  
Metal Free ◽  
Weight Growth ◽  
Double Activation

The first example of solvent-free, organocatalyzed, polymerization of 1,3-dioxolan-4-ones, used as easily accessible monomers for the synthesis of polylactic acid (PLA), is described here. An optimization of reaction conditions was carried out, with p-toluensulfonic acid emerging as the most efficient Brønsted acid catalyst. The reactivity of the monomers in the tested conditions was studied following the monomer conversion by 1H NMR and the molecular weight growth by SEC analysis. A double activation polymerization mechanism was proposed, pointing out the key role of the acid catalyst. The formation of acetal bridges was demonstrated, to different extents depending on the nature of the aldehyde or ketone employed for lactic acid protection. The polymer shows complete retention of stereochemistry, as well as good thermal properties and good polydispersity, albeit modest molecular weight.

The role of alkoxy radicals in the heterogeneous reaction of two structural isomers of dimethylsuccinic acid

2015 ◽  
Vol 17 (38) ◽  
pp. 25309-25321 ◽  
Author(s):  
Chiu Tung Cheng ◽  
Man Nin Chan ◽  
Kevin R. Wilson
Keyword(s):  
Molecular Weight ◽  
Hydroxyl Radicals ◽  
Heterogeneous Reaction ◽  
Methyl Groups ◽  
Structural Isomers ◽  
Alkoxy Radicals ◽  
Weight Growth ◽  
Bond Scission

The heterogeneous reaction of hydroxyl radicals with two isomers of dimethylsuccinic acid is used to explore how the location of branched methyl groups controls C–C bond scission and molecular weight growth reactions.

scholarly journals The Mechanism of Rhodium Catalyzed Allylic C–H Amination

2019 ◽  
Author(s):  
Robert Harris ◽  
Jiyong Park ◽  
Taylor Nelson ◽  
Nafees Iqbal ◽  
Daniel Salgueiro ◽  
...  
Keyword(s):  
Acid Catalyst ◽  
Reductive Elimination ◽  
Quantum Mechanical ◽  
Allylic Amination ◽  
Reaction Conditions ◽  
Allyl Complex ◽  
Acetate Ligand ◽  
Amination Reaction ◽  
Lewis Acid Catalyst

The mechanism of catalytic allylic C–H amination reactions promoted by Cp*Rh complexes is reported. Reaction kinetics experiments, stoichiometric studies, and DFT calculations demonstrate that allylic C–H activation to generate a Cp*Rh(π-allyl) complex is viable under mild reaction conditions. The role of external oxidant in the catalytic cycle is elucidated. Quantum mechanical calculations, stoichiometric reactions, and cyclic voltammetry<b></b>experiments support an oxidatively induced reductive elimination process of the allyl fragment with an acetate ligand. Lastly, evidences supporting the amination of an allylic acetate intermediate is presented. Both nucleophilic substitution catalyzed by Ag<sup>+</sup>that behaves as a Lewis acid catalyst and an inner-sphere amination catalyzed by Cp*Rh are shown to be viable for the last step of the allylic amination reaction.

Novel unsaturated ε-caprolactone polymerizable by ringopening and ring-opening metathesis mechanisms

e-Polymers ◽  
2002 ◽  
Vol 2 (1) ◽  
Author(s):  
Xudong Lou ◽  
Christophe Detrembleur ◽  
Philippe Lecomte ◽  
Robert Jérôme
Keyword(s):  
Molecular Weight ◽  
Ring Opening ◽  
Unsaturated Polyester ◽  
Side Reaction ◽  
Monomer Conversion ◽  
Ring Opening Metathesis Polymerization ◽  
Aliphatic Polyesters ◽  
Metathesis Polymerization ◽  
Insertion Mechanism ◽  
Alternative Routes

AbstractRing-opening polymerization (ROP) and ring-opening metathesis polymerization (ROMP) of an unsaturated ε-caprolactone, 6,7-dihydro-2(3H)-oxepinone (DHO2), are alternative routes to produce unsaturated aliphatic polyesters with the same molecular structure. Polymerization of DHO2 initiated by Al isopropoxide in toluene at room temperature or at 0°C proceeds by a coordination-insertion mechanism, although intramolecular transesterification takes place beyond complete monomer conversion. The molecular weight distribution is narrow as long as monomer conversion does not exceed 90%. Ring-opening metathesis polymerization of DHO2 initiated by Schrock’s Mo-based catalyst, 1, at 60°C allows higher molecular weight unsaturated polyester to be prepared, even though an intramolecular side reaction also operates. The structure of poly(DHO2) synthesized by ROP and ROMP is the same, as confirmed by 1H, 13C NMR, and FT-IR spectra. Copolymers of DHO2 with norbornene, cis-cyclooctene, and 1,5-cyclooctadiene have been successfully prepared.

scholarly journals Halogenations of 3-aryl-1H-pyrazol-5-amines

2021 ◽  
Author(s):  
Jing He ◽  
Yueting Wei ◽  
Yijiao Feng ◽  
Chuntian Li ◽  
Bin Dai ◽  
...  
Keyword(s):  
Room Temperature ◽  
Dual Role ◽  
Pyrazole Derivatives ◽  
Reaction Conditions ◽  
Metal Free

A direct C-H halogenation of 3-aryl-1H-pyrazol-5-amines with NXS (X = Br, I, Cl) as cheap and safe halogenating reagents at room temperature has been developed. This transformation provides an effective metal-free protocol towards the synthesis of novel 4-halogenated pyrazole derivatives with moderate to excellent yields. The method represents simple and mild reaction conditions, broad substrate scope as well as gram-scale synthesis. The utility of this procedure is established by further transformations of the 4-halogenated products. Mechanism studies show that DMSO plays a dual role of catalyst and solvent.

Role of the Kidney in the Production of a Low Molecular Weight Growth Factor (MW < 1000 Da): Experimental Study in the Pig

Renal Failure ◽  
1995 ◽  
Vol 17 (4) ◽  
pp. 339-347 ◽  
Author(s):  
C. Jacob ◽  
J. Hubert ◽  
F. Maachi ◽  
A. Punga-Maole ◽  
B. Dousset ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Experimental Study ◽  
Growth Factor ◽  
Low Molecular Weight ◽  
Weight Growth

scholarly journals The Role of the Mechanical, Structural, and Thermal Properties of Poly(l-lactide-co-glycolide-co-trimethylene carbonate) in the Development of Rods with Aripiprazole

Polymers ◽  
2021 ◽  
Vol 13 (20) ◽  
pp. 3556
Author(s):  
Artur Turek ◽  
Jakub Rech ◽  
Aleksandra Borecka ◽  
Justyna Wilińska ◽  
Magdalena Kobielarz ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Weight Loss ◽  
Thermal Properties ◽  
Pore Formation ◽  
Tensile Tests ◽  
Mechanical Tests ◽  
Lag Phase ◽  
Trimethylene Carbonate ◽  
Hot Melt

In this work, we aimed to determine the role of the mechanical, structural, and thermal properties of poly(l-lactide-co-glycolide-co-trimethylene carbonate) (P(l-LA:GA:TMC)) with shape memory in the formulation of implantable and biodegradable rods with aripiprazole (ARP). Hot melt extrusion (HME) and electron beam (EB) irradiation were applied in the formulation process of blank rods and rods with ARP. Rod degradation was carried out in a PBS solution. HPLC; NMR; DSC; compression and tensile tests; molecular weight (Mn); water uptake (WU); and weight loss (WL) analyses; and SEM were used in this study. HME and EB irradiation did not influence the structure of ARP. The mechanical tests indicated that the rods may be safely implanted using a pre-filled syringe. During degradation, no unfavorable changes in terpolymer content were observed. A decrease in the glass transition temperature and the Mn, and an increase in the WU and the WL were revealed. The loading of ARP and EB irradiation induced earlier pore formation and more intense WU and WL changes. ARP was released in a tri-phasic model with the lag phase; therefore, the proposed formulation may be administered as a delayed-release system. EB irradiation was found to accelerate ARP release.

scholarly journals Influence of Co-Catalysts and Polymerization Conditions on Properties of Poly(anhydride-alt-epoxide)s from ROCOP Using Salen Complexes with Different Metals

Polymers ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1222 ◽  
Author(s):  
Proverbio ◽  
Galotto ◽  
Losio ◽  
Tritto ◽  
Boggioni
Keyword(s):  
Molecular Weight ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Reaction Conditions ◽  
Aliphatic Polyesters ◽  
Co Catalyst ◽  
Co Catalysts ◽  
Salen Complexes ◽  
Polymerization Conditions

Cyclohexene oxide (CHO) and phthalic anhydride (PA) have been reacted in the presence of commercial salen–type complexes with different metals Cr (1), Al (2), and Mn (3) in combination with 4-(dimethylamino) pyridine (DMAP), bis-(triphenylphosphorydine) ammonium chloride (PPNCl) and bis-(triphenylphosphoranylidene)ammonium azide (PPNN3) as co-catalysts to obtain alternating poly(PA-alt-CHO)s by ring-opening copolymerization (ROCOP). The effect of different reaction conditions (pre-contact between catalyst and co-catalyst, polymerization time) on the productivity, molecular weight and glass transition temperature has been evaluated. By using a 24 h pre-contact, the aliphatic polyesters obtained were characterized by high molecular weight (Mn > 15 kg/mol) and glass transition temperature (Tg) up to 146 °C; the more sustainable metals Al and Mn in the presence of PPNCl give comparable results to Cr. Moreover, biodegradability data of these polyesters and the study of the microstructure reveal that the biodegradability is influenced more by the type of chain linkages rather than by the molecular weight of the polyesters.

Role of graphene oxide as a heterogeneous acid catalyst and benign oxidant for synthesis of benzimidazoles and benzothiazoles

RSC Advances ◽  
2016 ◽  
Vol 6 (10) ◽  
pp. 8164-8172 ◽  
Author(s):  
Kiran B. Dhopte ◽  
Rahul S. Zambare ◽  
Anand V. Patwardhan ◽  
Parag R. Nemade
Keyword(s):  
Graphene Oxide ◽  
Reduced Graphene Oxide ◽  
Free Acid ◽  
Acid Catalyst ◽  
Dual Role ◽  
Metal Free ◽  
Active Metal ◽  
Reduced Graphene ◽  
Heterogeneous Acid Catalyst

Graphene oxide plays a dual role as active metal-free acid catalyst and as non-toxic oxidant for benzothiazole and benzimidazole synthesis. Isolated partially reduced graphene oxide was re-oxidized to regenerate the catalyst and restore its activity.

Halogenations of 3-aryl-1H-pyrazol-5-amines

Synthesis ◽  
2021 ◽  
Author(s):  
Jing He ◽  
Yueting Wei ◽  
Yijiao Feng ◽  
Chuntian Li ◽  
Bin Dai ◽  
...  
Keyword(s):  
Room Temperature ◽  
Dual Role ◽  
Pyrazole Derivatives ◽  
Reaction Conditions ◽  
Metal Free

A direct C-H halogenation of 3-aryl-1H-pyrazol-5-amines with NXS (X = Br, I, Cl) as cheap and safe halogenating reagents at room temperature has been developed. This transformation provides an effective metal-free protocol towards the synthesis of novel 4-halogenated pyrazole derivatives with moderate to excellent yields. The method represents simple and mild reaction conditions, broad substrate scope as well as gram-scale synthesis. The utility of this procedure is established by further transformations of the 4-halogenated products. Mechanism studies show that DMSO plays a dual role of catalyst and solvent.

scholarly journals The Mechanism of Rhodium Catalyzed Allylic C–H Amination

2019 ◽  
Author(s):  
Robert Harris ◽  
Jiyong Park ◽  
Taylor Nelson ◽  
Nafees Iqbal ◽  
Daniel Salgueiro ◽  
...  
Keyword(s):  
Acid Catalyst ◽  
Reductive Elimination ◽  
Quantum Mechanical ◽  
Allylic Amination ◽  
Reaction Conditions ◽  
Allyl Complex ◽  
Acetate Ligand ◽  
Amination Reaction ◽  
Lewis Acid Catalyst

The mechanism of catalytic allylic C–H amination reactions promoted by Cp*Rh complexes is reported. Reaction kinetics experiments, stoichiometric studies, and DFT calculations demonstrate that allylic C–H activation to generate a Cp*Rh(π-allyl) complex is viable under mild reaction conditions. The role of external oxidant in the catalytic cycle is elucidated. Quantum mechanical calculations, stoichiometric reactions, and cyclic voltammetry<b></b>experiments support an oxidatively induced reductive elimination process of the allyl fragment with an acetate ligand. Lastly, evidences supporting the amination of an allylic acetate intermediate is presented. Both nucleophilic substitution catalyzed by Ag<sup>+</sup>that behaves as a Lewis acid catalyst and an inner-sphere amination catalyzed by Cp*Rh are shown to be viable for the last step of the allylic amination reaction.

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