Organic substances, hydrogenation

Combustion of alkanes is an example of oxidation-reduction Although It IS possible to calculate oxidation numbers of carbon m organic mole cules It IS more convenient to regard oxidation of an organic substance as an increase m its oxygen content or a decrease m its hydrogen content... 

Alkali metal peroxides are stable under ambient conditions in the absence of water. They dissolve vigorously in water, forming hydrogen peroxide and the metal hydroxide. They are strong oxidizing agents and can react violendy with organic substances. Only lithium peroxide and sodium peroxide have been commercialized. 

Reactions of organic substances at the dropping electrode usually involve hydrogen ions a typical reaction can be represented by the equation... 

Fig. 8. Relationship between relative reactivities S and the ratios of the initial reaction rates rj°/VA° of alkylphenols to phenol in the hydrogenation on Ni-catalyst containing 8.4% (wt.) AUOa at 160°C and initial molar ratio of hydrogen to organic substances G = 19. Alkyl substituents in phenols Me—methyl, Et—ethyl, Pr—n-propyl, i-Pr— isopropyl, s-Bu—sec-butyl, t-Bu—terc-butyl.

Both these conversion processes involve the addition of electrons to the toxic substances. The trichloroethylene molecule is electrically neutral and must gain electrons in reactions that generate negatively charged chloride anions, hi addition, water or hydronium ions must supply hydrogen atoms that replace the chlorine atoms in the organic substance. The detailed reaction is complicated, but the net reaction is relatively simple CI2 C I CHCl + 3 H3 + 6 H2 C CH2 + 3 Cr + 3 H2 O... 

Hydrogen does not appear free in the atmosphere except at levels below 1 ppm, since rapid diffusivity enables molecules to escape the earth s gravitational field and it is continuously lost from the atmosphere. It is present in the earth s crust at about 0.87% in combination with oxygen in water and with carbon and other elements in organic substances. It is prepared commercially on a small scale by action of sulphuric acid on zinc ... 

In the past it had been a popular belief that the electrochemical reduction of any inorganic or organic substance involves the primary electrochemical formation of a special, active form of hydrogen in the nascent state (in statu nascendi) and subsequent chemical reaction of this hydrogen with the substrate. However, for many reduction reactions a mechanism of direct electron transfer from the electrode to the substrate could be demonstrated. It is only in individual cases involving electrodes with superior hydrogen adsorption that the mechanism above with an intermediate formation of adsorbed atomic hydrogen is possible. 

For the cathodic reduction of organic substances, electrodes of two types are used the platinum and the mercury type. Those of the first type (platinum metals, and in alkaline solutions nickel) exfiibit low polarization in hydrogen evolution their potential can be pushed in the negative direction no further than to -0.3 V (RHE). Hydrogen readily adsorbs on these electrodes, which is favorable for reduction... 

A process involving water electrolysis is the production of heavy water. During cathodic polarization the relative rates of deuterium discharge and evolution are lower than those of the normal hydrogen isotope. Hence, during electrolysis the solution is enriched in heavy water. When the process is performed repeatedly, water with a D2O content of up to 99.7% can be produced. Electrochemical methods are also used widely in the manufacture of a variety of other inorganic and organic substances. 

It is very well known that Pt is one of the best metal catalysts for hydrogen as well as for organic oxidations. Nevertheless, a comparison of the electrochemical behavior of hydrogen and any of these organic substances shows large differences. While hydrogen establishes its reversible thermodynamic potential with platinum in an aqueous acidic solution very quickly, the reversible potential of the other fuels could never be experimentally observed. 

The Babylonians and Assyrians cemented stone slabs as well as bricks with bitumen (which is sometimes also referred to as asphalt), a mixture of a black or brown natural organic material with a pitchy luster and comminuted mineral. Bitumen is a thermoplastic solid material when heated above 50°C, it softens and becomes a thick, viscous liquid that reverts to a solid on cooling. It is composed of a natural mixture of hydrocarbons (organic substances composed of carbon, hydrogen, and oxygen) that occurs in natural... 

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