Oxidative degradation of the organometallic iron(II) complex [Fe{bis[3-(pyridin-2-yl)-1H-imidazol-1-yl]methane}(MeCN)(PMe3)](PF6)2: structure of the ligand decomposition product trappedviacoordination to iron(II)

2015 ◽  
Vol 71 (12) ◽  
pp. 1096-1099
Author(s):  
Stefan Haslinger ◽  
Alexander Pöthig ◽  
Mirza Cokoja ◽  
Fritz E. Kühn
Keyword(s):  
Decomposition Product ◽  
Oxidative Degradation ◽  
Structural Features ◽  
Heterocyclic Carbenes ◽  
Axial Position ◽  
Decomposition Products ◽  
Low Toxicity ◽  
The Stability ◽  
Harsh Conditions ◽  
Organic Decomposition

Iron is of interest as a catalyst because of its established use in the Haber–Bosch process and because of its high abundance and low toxicity. Nitrogen-heterocyclic carbenes (NHC) are important ligands in homogeneous catalysis and iron–NHC complexes have attracted increasing attention in recent years but still face problems in terms of stability under oxidative conditions. The structure of the iron(II) complex [1,1′-bis(pyridin-2-yl)-2,2-bi(1H-imidazole)-κN3][3,3′-bis(pyridin-2-yl-κN)-1,1′-methanediylbi(1H-imidazol-2-yl-κC2)](trimethylphosphane-κP)iron(II) bis(hexafluoridophosphate), [Fe(C17H14N6)(C16H12N6)(C3H9P)](PF6)2, features coordination by an organic decomposition product of a tetradentate NHC ligand in an axial position. The decomposition product, a C—C-coupled biimidazole, is trapped by coordination to still-intact iron(II) complexes. Insights into the structural features of the organic decomposition products might help to improve the stability of oxidation catalysts under harsh conditions.

Application of Nitrogen Heterocyclic Carbenes in Organocatalysis

2020 ◽  
Vol 09 ◽  
Author(s):  
Minita Ojha ◽  
R. K. Bansal
Keyword(s):  
Asymmetric Catalysis ◽  
Building Blocks ◽  
Structural Features ◽  
Heterocyclic Carbenes ◽  
Stetter Reaction ◽  
Metal Pollutants ◽  
Synthetic Strategy ◽  
Wide Range ◽  
Benzoin Condensation ◽  
Nitrogen Heterocyclic

Background: During the last two decades, horizon of research in the field of Nitrogen Heterocyclic Carbenes (NHC) has widened remarkably. NHCs have emerged as ubiquitous species having applications in a broad range of fields, including organocatalysis and organometallic chemistry. The NHC-induced non-asymmetric catalysis has turned out to be a really fruitful area of research in recent years. Methods: By manipulating structural features and selecting appropriate substituent groups, it has been possible to control the kinetic and thermodynamic stability of a wide range of NHCs, which can be tolerant to a variety of functional groups and can be used under mild conditions. NHCs are produced by different methods, such as deprotonation of Nalkylhetrocyclic salt, transmetallation, decarboxylation and electrochemical reduction. Results: The NHCs have been used successfully as catalysts for a wide range of reactions making a large number of building blocks and other useful compounds accessible. Some of these reactions are: benzoin condensation, Stetter reaction, Michael reaction, esterification, activation of esters, activation of isocyanides, polymerization, different cycloaddition reactions, isomerization, etc. The present review includes all these examples published during the last 10 years, i.e. from 2010 till date. Conclusion: The NHCs have emerged as versatile and powerful organocatalysts in synthetic organic chemistry. They provide the synthetic strategy which does not burden the environment with metal pollutants and thus fit in the Green Chemistry.

A review of lignin hydrogen peroxide oxidation chemistry with emphasis on aromatic aldehydes and acids

Holzforschung ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Ajinkya More ◽  
Thomas Elder ◽  
Zhihua Jiang
Keyword(s):  
Hydrogen Peroxide ◽  
Oxidative Degradation ◽  
Reaction Medium ◽  
Dicarboxylic Acids ◽  
Aromatic Aldehydes ◽  
Product Distribution ◽  
Reaction Conditions ◽  
Alkaline Conditions ◽  
The Stability ◽  
Oxidation Chemistry

Abstract This review discusses the main factors that govern the oxidation processes of lignins into aromatic aldehydes and acids using hydrogen peroxide. Aromatic aldehydes and acids are produced in the oxidative degradation of lignin whereas mono and dicarboxylic acids are the main products. The stability of hydrogen peroxide under the reaction conditions is an important factor that needs to be addressed for selectively improving the yield of aromatic aldehydes. Hydrogen peroxide in the presence of heavy metal ions readily decomposes, leading to minor degradation of lignin. This degradation results in quinones which are highly reactive towards peroxide. Under these reaction conditions, the pH of the reaction medium defines the reaction mechanism and the product distribution. Under acidic conditions, hydrogen peroxide reacts electrophilically with electron rich aromatic and olefinic structures at comparatively higher temperatures. In contrast, under alkaline conditions it reacts nucleophilically with electron deficient carbonyl and conjugated carbonyl structures in lignin. The reaction pattern in the oxidation of lignin usually involves cleavage of the aromatic ring, the aliphatic side chain or other linkages which will be discussed in this review.

scholarly journals EFFECT OF COCAINE ON THE GROWTH OF LUPINUS ALBUS. A CONTRIBUTION TO THE COMPARATIVE PHARMACOLOGY OF ANIMAL AND PLANT PROTOPLASM

1922 ◽  
Vol 4 (5) ◽  
pp. 573-584 ◽  
Author(s):  
David I. Macht ◽  
Marguerite B. Livingston
Keyword(s):  
Sodium Benzoate ◽  
Lupinus Albus ◽  
The Other ◽  
Plant Roots ◽  
Animal Tissues ◽  
Decomposition Products ◽  
Other Hand ◽  
Low Toxicity

1. The effects of cocaine and its decomposition products were studied on the growth of the young roots of Lupinus albus. 2. The results obtained were compared with similar experiments on animal tissues. 3. It was found that, while cocaine is the most toxic of these compounds studied for animal tissues, it was of comparatively low toxicity in respect to its effect on the growth of roots. On the other hand, sodium benzoate, being practically non-toxic for animals, was the most toxic of the compounds studied for the plant roots.

scholarly journals Genipin as An Emergent Tool in the Design of Biocatalysts: Mechanism of Reaction and Applications

Catalysts ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 1035 ◽  
Author(s):  
Veymar G. Tacias-Pascacio ◽  
Esmeralda García-Parra ◽  
Gilber Vela-Gutiérrez ◽  
Jose J. Virgen-Ortiz ◽  
Ángel Berenguer-Murcia ◽  
...  
Keyword(s):  
Drug Delivery ◽  
Controlled Drug Delivery ◽  
Medical Applications ◽  
Fruit Extract ◽  
Biological Scaffolds ◽  
Gardenia Jasminoides ◽  
Mechanism Of Reaction ◽  
Low Toxicity ◽  
Activating Agent ◽  
The Stability

Genipin is a reagent isolated from the Gardenia jasminoides fruit extract, and whose low toxicity and good crosslinking properties have converted it into a reactive whose popularity is increasing by the day. These properties have made it widely used in many medical applications, mainly in the production of chitosan materials (crosslinked by this reactive), biological scaffolds for tissue engineering, and nanoparticles of chitosan and nanogels of proteins for controlled drug delivery, the genipin crosslinking being a key point to strengthen the stability of these materials. This review is focused on the mechanism of reaction of this reagent and its use in the design of biocatalysts, where genipin plays a double role, as a support activating agent and as inter- or intramolecular crosslinker. Its low toxicity makes this compound an ideal alterative to glutaraldehyde in these processes. Moreover, in some cases the features of the biocatalysts prepared using genipin surpassed those of the biocatalysts prepared using other standard crosslinkers, even disregarding toxicity. In this way, genipin is a very promising reagent in the design of biocatalysts.

Stability of dronabinol capsules when stored frozen, refrigerated, or at room temperature

2016 ◽  
Vol 73 (14) ◽  
pp. 1088-1092 ◽  
Author(s):  
Michael F. Wempe ◽  
Alan Oldland ◽  
Nancy Stolpman ◽  
Tyree H. Kiser
Keyword(s):  
High Performance ◽  
Room Temperature ◽  
Oxidative Degradation ◽  
Storage Condition ◽  
Sesame Oil ◽  
Forced Degradation ◽  
Product Packaging ◽  
Time Points ◽  
The Stability ◽  
Minimal Reduction

Abstract Purpose Results of a study to determine the 90-day stability of dronabinol capsules stored under various temperature conditions are reported. Methods High-performance liquid chromatography (HPLC) with ultraviolet (UV) detection was used to assess the stability of dronabinol capsules (synthetic delta-9-tetrahydrocannabinol [Δ9-THC] mixed with high-grade sesame oil and other inactive ingredients and encapsulated as soft gelatin capsules) that were frozen, refrigerated, or kept at room temperature for three months. The dronabinol capsules remained in the original foil-sealed blister packs until preparation for HPLC–UV assessment. The primary endpoint was the percentage of the initial Δ9-THC concentration remaining at multiple designated time points. The secondary aim was to perform forced-degradation studies under acidic conditions to demonstrate that the HPLC–UV method used was stability indicating. Results The appearance of the dronabinol capsules remained unaltered during frozen, cold, or room-temperature storage. Regardless of storage condition, the percentage of the initial Δ9-THC content remaining was greater than 97% for all evaluated samples at all time points over the three-month study. These experimental data indicate that the product packaging and the sesame oil used to formulate dronabinol capsules efficiently protect Δ9-THC from oxidative degradation to cannabinol; this suggests that pharmacies can store dronabinol capsules in nonrefrigerated automated dispensing systems, with a capsule expiration date of 90 days after removal from the refrigerator. Conclusion Dronabinol capsules may be stored at room temperature in their original packaging for up to three months without compromising capsule appearance and with minimal reduction in Δ9-THC concentration.

scholarly journals Buffer Additives and Packaging Differentially Influence the Stability of Dyes Commonly Used in Chromovitrectomy

2016 ◽  
Vol 1 (3) ◽  
pp. 1-10
Author(s):  
Begoña Parrado Aliod ◽  
Wilfried Kugler ◽  
Tim Häring
Keyword(s):  
Polyethylene Glycol ◽  
Chemical Stability ◽  
Deuterium Oxide ◽  
Oxidative Degradation ◽  
Bromophenol Blue ◽  
Physiological Range ◽  
Vis Spectroscopy ◽  
The Stability ◽  
Acid Violet ◽  
Dye Solutions

Purpose: This study was performed to investigate the chemical stability of different dyes used in chromovitrectomy and the influence of various product parameters on it. Methods: Buffered dye solutions were prepared containing 1.5 g/L acid violet 17, 0.25 g/L brilliant blue G, 1.3 g/L bromophenol blue, and 1.5 g/L trypan blue, combined with deuterium oxide, polyethylene glycol 3350, and D-mannitol as additives. For accelerated storage testing, samples were incubated for 400 h at 80°C corresponding to 2 years according to the Van ‘t Hoff equation. After different incubation times samples were taken for UV/Vis spectroscopy, pH measurement, and osmometry. Results: Depending on dye, additive, and packaging, different solutions exhibit differences in chemical stability and hence shelf life. Packaging in syringes instead of vials increases dye stability. Additives may negatively influence important parameters, e.g. polyethylene glycol 3350 increases osmolality beyond the physiological range. Notably, acid violet 17 is chemically unstable except in D-mannitol-containing buffer, packed in syringes. However, simultaneously, D-mannitol leads to a pH shift below 7.0. Conclusion: In summary, dye solutions filled in syringes should be preferred to vials to slow down oxidative degradation. Especially acid violet 17 solutions should be used with caution because the addition of D-mannitol may contribute to pH values beyond the physiological range.

FABRICATION OF NANOPOROUS CHITOSAN MEMBRANES

NANO ◽  
2010 ◽  
Vol 05 (01) ◽  
pp. 53-60 ◽  
Author(s):  
XIAOLIANG WANG ◽  
XIANG LI ◽  
ELEANOR STRIDE ◽  
MOHAN EDIRISINGHE
Keyword(s):  
Low Frequency ◽  
Drug Carriers ◽  
Structural Features ◽  
Wound Dressings ◽  
Ftir Analysis ◽  
Tissue Engineering Scaffolds ◽  
Nanoscale Structures ◽  
Low Frequency Ultrasound ◽  
Chitosan Membranes ◽  
The Stability

Naturally derived biopolymers have been widely used for biomedical applications such as drug carriers, wound dressings, and tissue engineering scaffolds. Chitosan is a typical polysaccharide of great interest due to its biocompatibility and film-formability. Chitosan membranes with controllable porous structures also have significant potential in membrane chromatography. Thus, the processing of membranes with porous nanoscale structures is of great importance, but it is also challenging and this has limited the application of these membranes to date. In this study, with the aid of a carefully selected surfactant, polyethyleneglycol stearate-40, chitosan membranes with a well controlled nanoscale structure were successfully prepared. Additional control over the membrane structure was obtained by exposing the suspension to high intensity, low frequency ultrasound. It was found that the concentration of chitosan/surfactant ratio and the ultrasound exposure conditions affect the structural features of the membranes. The stability of nanopores in the membrane was improved by intensive ultrasonication. Furthermore, the stability of the blended suspensions and the intermolecular interactions between chitosan and the surfactant were investigated using scanning electron microscope and Fourier transform infrared spectroscopy (FTIR) analysis, respectively. Hydrogen bonds and possible reaction sites for molecular interactions in the two polymers were also confirmed by FTIR analysis.

Explosive Thermal Decomposition Mechanism of NTO

1995 ◽  
Vol 418 ◽  
Author(s):  
David J. Beardall ◽  
Tod R. Botcher ◽  
Charles A. Wight
Keyword(s):  
Thin Films ◽  
Thermal Decomposition ◽  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
Condensed Phase ◽  
Decomposition Product ◽  
Rapid Heating ◽  
Initial Step ◽  
Thermal Decomposition Mechanism ◽  
Decomposition Products

AbstractThe initial step of the thermal decomposition of NTO (5-nitro-2,4-dihydro-3H-1,2,4- triazol-3-one) is determined by pulsed infrared laser pyrolysis of thin films. Rapid heating of the film and quenching to 77 K allows one to trap the initial decomposition products in the condensed phase and analyze them using transmission Fourier-transform infrared spectroscopy. The initial decomposition product is CO2; NO2 and HONO are not observed. We propose a new mechanism for NTO decomposition in which CO2 is formed.

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