Naphthalene and anthracene

Best-known and simplest of the condensed-ring hydrocarbons, naphthalene is a solid at room temperature. Like anthracene, also a solid at room temperature, it can be isolated from coal tar.

Products of both substances are used in the manufacture of dyestuffs and in the produc­tion of plastics and polyester resins. These res­ins are useful in the manufacture of paints, film, and synthetic fibers (polyester clothing). Certain compounds of naphthalene and an­thracene, however, have been banned in many countries. An impurity present during the pro­duction of these compounds has been found to cause cancer.

Further condensed hydrocarbons can be made by fusing rings together. They can be added together to form a chain of rings, or joined honeycomb-fashion. Many useful prod­ucts are derived from fusing rings together.

Coal carbonization is the major source of anthracene, naphthalene, and most other con­densed aromatics. In the absence of air, coal is heated to a temperature of about 1650° F. (900° C). This causes the coal to break down into three main products—coal gas, coal tar, and coke. The coke is used in steel manufac­ture, and the gas as fuel gas. The other frac­tion, coal tar, contains many organic com­pounds, among them the condensed hydrocarbons. The most important compounds—benzene, naphthalene, and anthracene—are extracted using a combina­tion of different techniques. Many other prod­ucts are also contained in the coal tar, al­though in much smaller amounts.

Today, coal gas as a domestic heating fuel has given way in many places to natural gas. And less coke is required to smelt iron ore be­cause blastfurnaces are more efficient. As a result, coal carbonization is declining. How­ever, other sources of condensed hydrocar-

Organic chemistry: Aromatic hydrocarbons 77

Naphthalene

Phenanthrene

Anthracen

Pyrene

Naphthacene

Benzapyrene

Condensed-ring aromatic compoundsconsist of two or more benzene rings joined together in chains of rings (top three examples to the left) or in honeycomb­like arrangements (bottom three examples to the left). These structures are simply represented with all the carbon-carbon bonds being the same length, as in ben­zene. In fact, the distances between adjacent carbon atoms are not equal.

bons are available. These include the exposing of gasoline to high temperatures.

Date: 2015-12-11; view: 1589