Oxygen on charcoal

MAGNETIC SUSCEPTIBILITY. Pinnick (58) has correlated the magnetic susceptibility of synthetic graphite with the a-dimension of the lattice plane. There is a sharp increase in susceptibility as a grows from 50 to 150 A., and the susceptibility remains constant thereafter to 1000 A. Juza (39) has shown that the adsorption of oxygen on charcoal at room temperature is molecular, as magnetic susceptibility does not change. 

When chemical action enters into the picture, in other words when chemisorption can also take place, more forces come into action, as in the above-mentioned adsorption of water molecules. We shall discuss the chemisorption of hydrogen and of oxygen on charcoal and on metal surfaces in subsequent sections. 

The simpler isotherms are used when interactions between neighboring molecules at the solid surface are relatively minor. Heats of adsorption are then as low as 5-10 kcal mol , of the same order as the heat of vaporization. Therefore, the gas molecules are considered to be bonded physically to the surface by the van der Waals force. Other cases have heats of adsorption of 10-100 kcal mol . Molecules dissociate to atoms and adhere to the solid surface by sharing some outer-shell electrons. This phenomenon is known as chemisorption, and it is of great importance in catalytic reactions. The adsorption of oxygen on charcoal is an example of chemisorption. 

Simple l,2,3,4-tetrahydro-)3-carbolines have been aromatized in this manner. Palladium black at 160-170° or at higher temperature, palladium-maleic acid in aqueous solution, and platinum/oxygen have been used for the purpose. Palladium-on-charcoal in a high-boiling solvent has been used also to aromatize 5,6,7,8-tetrahydro-j3-carbohnes and 6,7,8,9-tetrahydro-3-carbo-hne. ... 

Physical adsorption is a readily reversible process, and alternate adsorption and desorption stages can be carried out repeatedly without changing the character of the surface or the adsorbate. Chemisorption may or may not be reversible. Often one species may be adsorbed and a second desorbed. Oxygen adsorbed on charcoal at room temperature is held very strongly, and high temperatures are necessary to accomplish the desorption. CO and/or C02 are the species that are removed from the surface. Chemical changes like these are prima facie evidence that chemisorption has occurred. 

Adsorption of perchloryl fluoride on charcoal can, like liquid oxygen, produce a powerful Sprengel explosive. 

Boron reacts with sulfur at 600°C becoming incandescent [1]. Mixtures of sulfur with lamp black or freshly calcined charcoal ignite spontaneously, probably owing to adsorbed oxygen on the catalytic surface [2], Mixtures of yellow phosphorus and sulfur ignite and/or explode on heating [3], Ignition of an intimate mixture of red phosphorus and sulfur causes a violent exothermic reaction [4],... 

Wasserman et al.9T> irradiated a methanolic solution of 41 a in the presence of oxygen and methylene blue for 18 h at 25 °C. After hydrogenation of the reaction mixture over palladium on charcoal for 24 h they were able to isolate three products 120 (26%), 121 (11%), and 5% of a substance which was assigned structure 122 on the basis of spectroscopic and X-ray crystallographic data. The mechanism of formation of this polycycle probably involves an epoxide of type 123... 

At 0° to 100° C. part of the oxygen adsorbed on charcoal is endowed with catalytic properties, thus it will readily oxidise oxalic acid, amino acids, cystein and other similar compounds, whilst we would anticipate similar reactions if the oxygen molecule were now adsorbed in such a way as to cause a breakage of one of the two bonds 0=0 —> 0—0. At high temperatures, as is well known. 

The selective oxidation of a 50% aqueous solution of glycerol was performed at 50 °C with an oxygen/glycerol ratio of 2, in a continuous fixed bed process using a Pt-Bi catalyst supported on charcoal. Here, a DHA selectivity of 80% at a conversion of 80% was obtained. 

Nitroform, Methanol, Hydrazine Nitroform, Diethyl ether, Hydrazine Nitroform, Methyl acetate, SUver-I oxide, 1,4-Dibromobutyne-2, Chloroform Glyoxal, Benzylamine, Formic acid, Acetonitrile, Acetic anhydride. Palladium on charcoal, Bromobenzene, Chloroform, Sulfolane, Nitrosonium tetrafluoroborate. Ethyl acetate TNT, DMSO, Oxygen gas. Sodium benzoate. Hydrochloric acid. Methanol, Acetone... 

Heterogeneous palladium catalysts proved to be active in the conversion of simple alkenes to the corresponding allylic acetates, carbonyl compounds, and carboxylic acids.694 704 Allyl acetate or acrylic acid from propylene was selectively produced on a palladium on charcoal catalyst depending on catalyst pretreatment and reaction conditions.694 Allylic oxidation with singlet oxygen to yield allylic hydroperoxides is discussed in Section 9.2.2. 

It is generally accepted that the oxidative power of charcoal is due to the chemisorbed layer of oxygen on its surface.1 This oxygen layer appears to be important also in other ways T. W. J. Taylor s studies on the interconversion of stereoisomeric oximes and sulphoxides show that oxygen is necessary for this reaction. The mechanism appears to be an exchange of the active, adsorbed oxygens on the surface of the carbon, with the molecules of the substances undergoing isomerization in solution. The nature of the layers adsorbed on charcoal influences, naturally, its behaviour as an electrode, and the kind of ions which it sends into solution ... 

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