Preparation of YBa2Cu3O7−x precursors from a fused eutectic of sodium and potassium hydroxides

1989 ◽  
Vol 4 (6) ◽  
pp. 1307-1311 ◽  
Author(s):  
Nicholas Coppa ◽  
Daniel H. Nichols ◽  
John W. Schwegler ◽  
J. E. Crow ◽  
G. H. Myer ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Potassium Hydroxide ◽  
Product Formation ◽  
Mechanical Grinding ◽  
Reaction Conditions ◽  
Fine Powders ◽  
Yttrium Barium ◽  
Sodium And Potassium

A method for preparing YBa2Cu3O7−x from the simultaneous thermal decomposition of the nitrates of yttrium, barium, and copper in an anhydrous fused eutectic of sodium and potassium hydroxide is described. This method eliminates the need for any mechanical grinding or the introduction of carbon containing anions. Products formed are fine powders (∼1 μm) having mole ratios 1.00Y:2.00Ba:3.06Cu.X-ray diffraction analyses reveal that the initial products are Y(OH)3, BaO2, and CuO, which when air calcinated/oxygen annealed at 900–950 °C form the superconducting YBa2Cu3O7−x A mechanism is postulated for product formation as a function of reaction conditions.

Bu4N+-Controlled Addition and Olefination with Ethyl 2-(Trimethylsilyl)acetate via Silicon Activation

Synlett ◽  
2017 ◽  
Vol 28 (18) ◽  
pp. 2401-2406 ◽  
Author(s):  
Donal O’Shea ◽  
Manas Das ◽  
Atul Manvar ◽  
Ian Fox ◽  
Dilwyn Roberts
Keyword(s):  
Room Temperature ◽  
Product Formation ◽  
Unsaturated Ester ◽  
Reaction Conditions ◽  
Diverse Range ◽  
Inorganic Cation ◽  
Tetrabutyl Ammonium ◽  
Aldehydes And Ketones ◽  
Subsequent Elimination ◽  
Hydroxy Esters

Catalytic Bu4NOAc as silicon activator of ethyl 2-(trimethylsilyl)acetate, in THF, was utilized for the synthesis of β-hydroxy esters, whereas employing catalytic Bu4NOTMS gave α,β-unsaturated esters. The established reaction conditions were applicable to a diverse range of aromatic, heteroaromatic, aliphatic aldehydes and ketones. Reactions were achieved at room temperature without taking any of the specialized precautions that are in place for other organometallics. A stepwise olefination pathway via silylated β-hydroxy esters with subsequent elimination to form the α,β-unsaturated ester has been demonstrated. The key to selective product formation lies in use of the weaker acetate activator which suppresses subsequent elimination whereas stronger TMSO– activator (and base) facilitates both addition and elimination steps. The use of tetrabutyl ammonium salts for both acetate and trimethylsilyloxide activators provide enhanced silicon activation when compared to their inorganic cation counterparts.

Chlorination of Arylaldehyde-Derived Arylsulfonylhydrazones with N-Chlorosuccinimide Leading to 1,2,4,5-Tetrazine Derivatives

Synthesis ◽  
2019 ◽  
Vol 52 (01) ◽  
pp. 69-74
Author(s):  
Yuan-Zhao Ji ◽  
Hui-Jing Li ◽  
Ying Liu ◽  
Yan-Chao Wu
Keyword(s):  
Potassium Hydroxide ◽  
Reaction Conditions ◽  
Metal Free ◽  
Vinyl Halides

It has been reported previously that treatment of aryl­ketone-derived arylsulfonylhydrazones with NXS/(nBu)4NX affords exclusively vinyl halides. In contrast, we have found that treatment of aryl­aldehyde-derived arylsulfonylhydrazones with N-chlorosuccinimide in the presence of potassium hydroxide affords 1,2,4,5-tetrazine derivatives in good to excellent yields. The present reactions are carried out under metal-free and mild reaction conditions.

scholarly journals Use of an Asparaginyl Endopeptidase for Chemo-enzymatic Peptide and Protein Labeling

2020 ◽  
Author(s):  
Simon Tang ◽  
Davide Cardella ◽  
Alexander J. Lander ◽  
Xuefei Li ◽  
Yu-Hsuan Tsai ◽  
...  
Keyword(s):  
Phenylboronic Acid ◽  
Product Formation ◽  
Protein Labeling ◽  
Recognition Sequence ◽  
Reaction Conditions ◽  
Site Specific ◽  
Asparaginyl Endopeptidase ◽  
Coupling System ◽  
Labeling System ◽  
Specific Peptide

Transpeptidases are ideal biocatalysts for site-specific peptide and protein labeling, whereas reactions that target N-terminus cysteine with commercially available reagents have become common practice. However, a versatile approach that allows bioconjugation at the terminus of choice (N or C), while avoiding the use of backbone-modified substrates (<i>e.g.</i> depsipeptide) or large excess of reagent, is highly desirable. Aiming to meet these benchmarks, we have combined the advantages of asparaginyl endopeptidase (AEP) catalysis with a N-terminal cysteine trapping reaction and created a chemo-enzymatic labeling system. In this approach, polypeptide with a Asn-Cys-Leu recognition sequence are ligated with a counterpart possessing an N-terminal Gly-Leu by AEP; the byproduct Cys-Leu is subsequently trapped by a stable and inexpensive scavenger, 2-formyl phenylboronic acid (FPBA), to yield an inert thiazolidine derivative, thereby driving the reaction forward to product formation. By carefully screening the reaction conditions for optimal compatibility and minimal hydrolysis, conversion to the ligated product in the model reaction resulted in excellent yields. The versatility of this AEP ligation/FPBA coupling system was further demonstrated by site-specific labeling the N- or C-termini of various proteins.

Benzo-Fused 1,4-Heterocycles via Dialkyl Carbonate Chemistry

Synthesis ◽  
2019 ◽  
Vol 51 (08) ◽  
pp. 1770-1778 ◽  
Author(s):  
Manuele Musolino ◽  
Fabio Aricò
Keyword(s):  
Dimethyl Carbonate ◽  
Ethylene Carbonate ◽  
Product Formation ◽  
Ring Closure ◽  
Organic Base ◽  
Reaction Conditions ◽  
Strong Base ◽  
Dialkyl Carbonates ◽  
Dialkyl Carbonate ◽  
Halogen Free

A novel halogen-free synthesis of benzo-fused six-membered 1,4-heterocycles through the chemistry of dialkyl carbonates is reported. Commercially available catechol, 2-aminophenol, and 2-amino­thiophenol were reacted first with ethylene carbonate in an autoclave to give O-hydroxyethyl, N-hydroxyethyl, and S-hydroxyethyl derivatives respectively, through a BAl2 mechanism. Then 2-(2-hydroxyethoxy)phenol and 2-(2-hydroxyethylamino)phenol were cyclized in excellent yields by reaction with dimethyl carbonate (DMC) and DABCO as a bi­cyclic organic base to give the corresponding benzodioxine and benzoxazine derivative, respectively. Moreover, 2-(2-aminophenylthio)ethanol afforded the benzothiazine derivative in good yield by reaction with DMC with an excess of a strong base such as NaH. The investigation on the cyclization reaction has highlighted that several equilibria are involved leading to the formation of carbonate and carbamate intermediates through BAc2 mechanisms. Depending on the reaction conditions employed, these intermediates may undergo either kinetic-controlled ring closure by a BAl2 mechanism or by-product formation.

The thermal and photochemical decompositions of succinic anhydride and 2,3-dimethyl succinic anhydride in the gas phase

1983 ◽  
Vol 61 (12) ◽  
pp. 2790-2794 ◽  
Author(s):  
S. Yamamoto ◽  
R. A. Back
Keyword(s):  
Thermal Decomposition ◽  
Succinic Anhydride ◽  
Product Formation ◽  
Radical Mechanism ◽  
Trans Isomers ◽  
Cis And Trans Isomers ◽  
Free Radical Mechanism ◽  
Trans Butene ◽  
Cis And Trans ◽  
Short Times

The absorption spectrum of succinic anhydride shows a broad maximum near 220 nm, attributed to the lowest π*–n− transition. Photolysis in this region (220–270 nm) gives CO2, CO, and C2H4, but not in the equimolar quantities expected from a simple molecular dissociation. Production of CO also shows a time dependence, increasing with time, and a free-radical mechanism is tentatively suggested to account for this. The thermal decomposition of succinic anhydride at 625–775 K yields the same products, but is more complex, with larger deviations from the simple stoichiometry, and product formation non-linear with time and pressure. At short times, production of CO, the most abundant product, is described by first-order Arrhenius parameters of log A (s−1) = 11.6 and E = 53 kcal/mol, apparently independent of surface.The photolysis of the cis and trans isomers of 2,3-dimethylsuccinic anhydride at 250 and 230 nm is simpler than that of succinic anhydride, giving equimolar CO and CO2, but with butene-2 still falling short of a stoichiometric yield by from 10 to 40%. Both cis- and trans-butene-2 were produced, with the latter always in excess and with no retention of the configuration of the original anhydride. The thermal decomposition of 2,3-dimethylsuccinic anhydride is more complex than the photolysis, with much less butene-2 produced (again with no retention of cis–trans configuration) and methane an important product. Activation energies for CO formation were about 48 and 45 kcal/mol and log A (s−1) was 10.4 and 9.5 for the cis and trans isomers, respectively.

The thermal decomposition of diethyl ether. II. Analytical survey of the reaction products as a function of reaction conditions

1958 ◽  
Vol 245 (1240) ◽  
pp. 40-48 ◽  
Keyword(s):  
Thermal Decomposition ◽  
Rate Constants ◽  
Vapour Phase ◽  
Mass Spectrometric ◽  
Spectrometric Analysis ◽  
Reaction Products ◽  
Reaction Conditions ◽  
True Rate ◽  
Carbon Tetrafluoride ◽  
Pressure Changes

By mass-spectrometric analysis combined with vapour-phase chromatography the reaction products from the thermal decomposition of ether have been determined at various stages of the reaction (uninhibited and inhibited by nitric oxide) for initial ether pressures of 80 to 1000 mm. The effects of added hydrogen and of carbon tetrafluoride on the composition of the products have also been examined. No major changes in the chemistry of the reaction occur with these variations in conditions. Factors are given for calculating true rate constants from pressure changes accompanying the reaction. Corrected values of rate constants vary with the conditions in the same way as the values derived from uncorrected pressure changes, the correspondence being close for the uninhibited reaction.

Synthesis of intermetallic NiAl and Ni3Al fine powders through organometallic precursors

1991 ◽  
Vol 6 (5) ◽  
pp. 928-934 ◽  
Author(s):  
Osami Abe ◽  
Akira Tsuge
Keyword(s):  
Heat Treatment ◽  
Thermal Decomposition ◽  
Particle Size ◽  
Aqueous Solutions ◽  
Single Phase ◽  
Initial Step ◽  
The Other ◽  
Fine Powders ◽  
Organometallic Precursors ◽  
Step Heat Treatment

Fine powders of intermetallic NiAl and Ni3Al were synthesized through organometallic precursors, which were coprecipitated from aqueous solutions of NiCl2 and AlCl3 by the addition of ammonium benzoate and hydradinium monochloride as precipitants. Ni3Al and NiAl were synthesized by a two-step heat treatment of the precursors. The initial step was the thermal decomposition of organic groups to form homogeneous mixtures of Ni3C, amorphous Al2O3, and free C below 1000 °C. The other step was the reaction above 1300 °C to form the intermetallics. Single phase powders of NiAl and Ni3Al with the particle size less than 3 μm were obtained above 1300 and 1400 °C, respectively.

scholarly journals Cluster Evolution in Thermal Decomposition of CL-20/TNT Co-Crystal in Compressed State:A ReaxFF Reactive Molecular Dynamics Simulation Study

2021 ◽  
Author(s):  
Yan Li ◽  
Wen-li Yu ◽  
Huang Huang ◽  
Min Zhu
Keyword(s):  
Molecular Dynamics ◽  
Thermal Decomposition ◽  
Atmospheric Pressure ◽  
Product Formation ◽  
Decomposition Process ◽  
Dynamics Simulation ◽  
Thermal Decomposition Process ◽  
Reactive Molecular Dynamics ◽  
Cluster Evolution ◽  
Dynamics Method

Abstract The thermal decomposition process of CL-20/TNT co-crystal in different compression states is simulated by ReaxFF reactive molecular dynamics method. Co-crystals models with different degrees of compression are obtained under four pressures of atmospheric pressure, 4.6GPa, 9.2GPa and 18.4GPa. The potential energy evolution, product formation and cluster evolution in the process are analyzed. We find that the formation of clusters is the key to the decomposition process. When the system is compressed, there will be more clusters which can bind the free atoms, resulting in the reaction to be inhibited. Other evolution information conforms this.

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