Petroleum and the Hydrocarbons

One of the most important sources of organic compounds is petroleum (crude oil). Petroleum, which is obtained from underground deposits that have been tapped by drilling oil wells, is a dark-colored, viscous liquid that is in the main a mixture of hydrocarbons (compounds of hydrogen and carbon see Section 7-2). A very great amount of it, approximately one billion tons, is produced and used each year. Much of it is burned, for direct use as a fuel, but much is separated or converted into other materials. 

The residue from distillation is a black, tarry material called petroleum asphalt. It is used in making roads, for asphalt composition roofing materials, for stabilizing loose soil, and as a binder for coal dust in the manufacture of briquets for use as a fuel. A similar material, hitumen or rock asphalt, is found in Trinidad, Texas, Oklahoma, and other parts of the world, where it presumably has been formed as the residue from the slow distillation of pools of oil. 

It is thought that petroleum, like coal, is the result of the decomposition of the remains of plants that grew on the earth about 250 million years ago. 

Polymerization is also used to make gasoline from the lighter hydrocarbons containing double bonds. For example, two molecules of ethylene, C0H4 can react to form one molecule of butylene, QH (structural formula CHg—CH=CH—CH3). 

Some gasoline is also made by the hydrogenation (reaction with hydrogen) of petroleum and coal. Many organic chemicals are prepared in great quantities from these important raw materials. 

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