Electrocatalytic hydrogenation of lignin models at Raney nickel and palladium-based electrodes

2000 ◽  
Vol 78 (3) ◽  
pp. 307-315 ◽  
Author(s):  
André Cyr ◽  
Florence Chiltz ◽  
Paul Jeanson ◽  
Anna Martel ◽  
Louis Brossard ◽  
...  
Keyword(s):  
Raney Nickel ◽  
Sodium Hydroxide Solution ◽  
Aqueous Sodium Hydroxide ◽  
Reaction Scheme ◽  
Constant Current ◽  
Electrocatalytic Hydrogenation ◽  
Hydroxymethyl Group ◽  
Lignin Model ◽  
Aryl Ethers ◽  
Methylene Group

The electrocatalytic hydrogenation (ECH) of β-O-4 lignin model compounds has been carried out at constant current at Raney nickel and palladium-based cathodes in aqueous sodium hydroxide solution at temperatures ranging from 25 to 75°C. It was found that the hydrogenolysis of phenolic β-arylethyl-aryl ethers with one β-O-4 linkage takes place at both types of electrodes to give a mixture of phenolic compounds. The ECH of 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-ethanol (model 1) at Raney nickel gives guaiacol (9), acetovanillone (11b), alpha-methylvanillyl alcohol (12b), and products derived from their further hydrogenation. The β-O-4 bond is more difficult to cleave upon replacing one hydrogen of the methylene group of 1 by a hydroxymethyl group (see 2). However, model 4 with two β-O-4 linkages obtained by the introduction of an α-methylvanillyl group at the phenolic position of 1 is hydrogenolysed at the same rate as 1 at Raney nickel. Only the C-O aryl bond attached to the hydroxyethylphenol moiety is cleaved. At palladium, the hydrogenolysis of 1 requires only half of the theoretical amount of electricity due to the generation of chemisorbed hydrogen by dehydrogenation of 1 followed by hydrogenolysis of the resulting ketone. A general reaction scheme is proposed for the ECH of model 1.Key words: Lignins, lignin models, electrocatalytic hydrogenation, Raney nickel electrodes, palladium electrodes.

The electrocatalytic hydrogenation of fused poly cyclic aromatic compounds at Raney nickel electrodes: the influence of catalyst activation and electrolysis conditions

1990 ◽  
Vol 68 (7) ◽  
pp. 1218-1227 ◽  
Author(s):  
Denis Robin ◽  
Michel Comtois ◽  
Anna Martel ◽  
René Lemieux ◽  
Amoy Kam Cheong ◽  
...  
Keyword(s):  
Raney Nickel ◽  
Supporting Electrolyte ◽  
Aqueous Sodium Hydroxide ◽  
Constant Current ◽  
Electrocatalytic Hydrogenation ◽  
Catalyst Activation ◽  
Nickel Electrodes ◽  
Initial Ph ◽  
Raney Ni ◽  
Tetrabutylammonium Chloride

The electrocatalytic hydrogenation (ECH) of phenanthrene, anthracene, and naphthalene has been investigated under constant current at Raney nickel electrodes in a mixed aqueous organic medium. The influence of various parameters on the efficiency of the process determined by the current efficiency (a measure of the competition between hydrogenation and hydrogen evolution, the only two electrochemical processes occurring), the extent of hydrogenation (yield of octahydro-derivatives), and the conversion rate was studied with phenanthrene. The best conditions were ethylene glycol or propylene glycol as cosolvent containing between 1.5 to 5% of water, a neutral or slightly acidic medium containing boric acid (0.1 M) as buffer (initial pH of 2.6, final pH of 6.0–6.2), sodium chloride or tetrabutylammonium chloride as supporting electrolyte, a temperature of 80° C, and a current density of 42 to 84 mA/cm2. The most active electrodes (consisting of Raney Ni particles dispersed in a nickel matrix and surrounded by a layer of porous nickel) were obtained by leaching the dispersed alloy particles at 75 °C for 7 h in 30% aqueous sodium hydroxide. The electrohydrogenation stopped at derivatives with a single aromatic ring, namely the octahydrophenanthrenes, octahydroanthracenes, and tetralin. In a non-buffered medium, tetrahydrophenanthrene could be obtained with selectivities of 80% or better. Keywords: electrocatalytic hydrogenation, Raney nickel electrodes, phenanthrene, anthracene, naphthalene.

Electrocatalytic hydrogenation of conjugated enones on nickel boride, nickel, and Raney nickel electrodes

1995 ◽  
Vol 73 (6) ◽  
pp. 846-852 ◽  
Author(s):  
Behzad Mahdavi ◽  
Philippe Chambrion ◽  
Julie Binette ◽  
Eric Martel ◽  
Jean Lessard
Keyword(s):  
Double Bond ◽  
Raney Nickel ◽  
Carbonyl Compounds ◽  
Constant Current ◽  
Electrocatalytic Hydrogenation ◽  
Aqueous Methanol ◽  
Nickel Boride ◽  
Unsaturated Ketones ◽  
Nickel Electrodes ◽  
Bond Hydrogenation

The selectivity of the electrocatalytic hydrogenation (ECH) of conjugated enones to the corresponding carbonyl compounds has been investigated in aqueous methanol under constant current at nickel boride, fractal nickel, and Raney nickel electrodes made of pressed powders. The influence of various parameters (water percentage, pH, concentration of substrate, and current density) on the selectivity of the carbon–carbon double bond hydrogenation was studied with cyclohex-2-en-1-one at nickel boride electrodes. Under given electrolysis conditions, fractal nickel electrodes were found to give the highest selectivity. The selectivity of the ECH of a variety of conjugated enones at fractal nickel electrodes was determined under electrolysis conditions that gave the best selectivity with cyclohexenone at nickel boride electrodes. Keywords: electrocatalytic hydrogenation, α,β-unsaturated ketones, selective hydrogenation, nickel based cathodes.

Instant Microwave Synthesis of Titania Nanoflowers for Application in DSSCs

2015 ◽  
Vol 1119 ◽  
pp. 14-18
Author(s):  
Sofia Javed ◽  
Muhammad Aftab Akram ◽  
Mohammad Mujahid
Keyword(s):  
Titanium Dioxide ◽  
Hydrofluoric Acid ◽  
Sodium Hydroxide Solution ◽  
Dye Sensitized Solar Cells ◽  
Aqueous Sodium Hydroxide ◽  
Environment Friendly ◽  
Aqueous Sodium Hydroxide Solution ◽  
Dye Sensitized ◽  
Aqueous Conditions ◽  
Sensitized Solar Cells

Nanoflowers are desirable in light driven applications like Dye Sensitized Solar Cells (DSSCs) due to their large surface area and greater light absorption capabilities. An instant, simple, cheap and environment friendly method of preparing titanium dioxide nanoflowers is presented. The nanoflowers are produced in a time as short as 5 minutes in aqueous conditions without the use of hazardous hydrofluoric acid or organic surfactants at 1 atm. pressure and low temperature of 100°C. Titanium dioxide commercial nanopowders are treated with microwaves in an aqueous sodium hydroxide solution for small durations. The resulting powders are annealed at 450°C in air and characterization is performed using XRD, SEM and Raman spectroscopy.

Cleavage Reactions of 5-Arylazo Derivatives of 1-Methyl-2-benzyl-2-imidazolin-4-ones

1975 ◽  
Vol 30 (7-8) ◽  
pp. 603-605 ◽  
Author(s):  
Nazmi Abdel Latif Kassab ◽  
Abdel Hamid Harhash ◽  
Sanna Osman Abd Allah
Keyword(s):  
Sodium Hydroxide Solution ◽  
Aqueous Sodium Hydroxide ◽  
The Other ◽  
Ring Cleavage ◽  
Prolonged Heating ◽  
Aqueous Sodium Hydroxide Solution ◽  
Aqueous Sodium ◽  
Triazine Derivatives ◽  
Cleavage Reactions ◽  
Derivatives Of

The 5-arylazo-1-methyl-2-benzyl-2-imidazolin-4-ones (1 a-c) undergo ring cleavage with 1% aqueous sodium hydroxide solution affording α-arylhydrazono-phenacetyl-sarcosine amide (2). Prolonged heating of 1 and 2 with the same reagent yields the cyanamide (3). On the other hand, when 1 a-c were refluxed with acetic acid the triazinones (4) were obtained. The latter adds one mole of Grignards reagent to yield the 5-hydroxy-1,2,4-triazine derivatives (5).

Reactions of Lignin Model ß-Aryl Ethers with Acetyl Bromide

Holzforschung ◽  
1996 ◽  
Vol 50 (4) ◽  
pp. 360-364 ◽  
Author(s):  
Fachuang Lu ◽  
John Ralph
Keyword(s):  
Acetyl Bromide ◽  
Lignin Model ◽  
Aryl Ethers

Equilibrium and Kinetics of the Extraction of Gallium(III) from Sodium Hydroxide Solutions with 7-Dodecenyl-8-quinolinol (Kelex 100)

1993 ◽  
Vol 58 (5) ◽  
pp. 1093-1102 ◽  
Author(s):  
Aleksandra A. Mitrovic ◽  
Slobodan K. Milonjic ◽  
Zoja E. Ilic ◽  
Radomir V. Stevanovic
Keyword(s):  
Sodium Hydroxide ◽  
Sodium Hydroxide Solution ◽  
Aqueous Sodium Hydroxide ◽  
Sodium Concentration ◽  
Extraction Kinetics ◽  
Aqueous Sodium Hydroxide Solution ◽  
Ph Values ◽  
Constant Ph ◽  
Equilibrium And Kinetics ◽  
Kinetics Of

The influence of hydroxide ions concentration of the aqueous sodium hydroxide solution, at constant sodium concentrations, on the gallium extraction with Kelex 100 was examined in the hydroxide concentration range from 0.02 to 0.5 mol dm-3. The percentage of extracted gallium increases from 51% to 98% within the investigated hydroxide concentration range. The influence of sodium concentrations (from 1 to 6 mol dm-3) on the gallium extraction was also studied at constant pH values. The decrease of extracted gallium is slight for the sodium concentration up to 3 mol dm-3, while for the higher ones it is pronounced. The extraction kinetics was studied using a mixer-type apparatus. The rate expression of the extraction reaction of gallium with Kellex 100, for both lower and higher hydroxide concentrations are ascertained.

Palladium-catalyzed synthesis of 4-cyclohexylmorpholines from reductive coupling of aryl ethers and lignin model compounds with morpholines

2021 ◽  
Author(s):  
Bingxiao Zheng ◽  
Jinliang Song ◽  
Haihong Wu ◽  
Shitao Han ◽  
Jianxin Zhai ◽  
...  
Keyword(s):  
Reductive Coupling ◽  
Model Compounds ◽  
Lignin Model Compounds ◽  
Palladium Catalyzed ◽  
Lignin Model ◽  
Aryl Ethers

4-Cyclohexylmorpholines could be efficiently synthesized from reductive coupling of aryl ethers (including the typical lignin model compounds) with morpholines over Pd/C without using any acidic additives.

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