19. The Simple Compounds
                                   of Carbon
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      Reactions of Hydrocarbons

The main reactions that saturated hydrocarbons do undergo are dehydrogenation and cracking, combustion (with F2 or 02), and halogenation (especially with Cl and Br).

If the temperature is raised high enough to surmount the activation barrier, or if catalysts are used to bypass it with an alternative mechanism, then hydrogen atoms may be removed to form unsaturated compounds (dehydrogenation),or a long molecule may be broken into smaller pieces (cracking).

  • Dehydrogenation: CH3CH2CH2CH3 -----> CH3CH2=CH2 + H2
  • Cracking: CH3CH2CH2CH3 -----> CH3CH=CH2 + CH4

These processes are important in the petroleum industry as a means of converting oils and kerosenes into the more salable gasolines. Dehydrogenation and cracking usually are rather nonspecific processes that lead to a mixture of products.

The selection of the right catalyst (often finely divided metals or metal oxides) and right temperature and pressure to maximize the yield of the desired product is one of the black arts of the petroleum chemist.
Combustion or oxidation by 02 or F2 is a destructive attack by very electronegative atoms, which results in the complete fragmentation of the molecule (see page 15).

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