128 THE PATH OF SCIENCE 



syntheses built on compounds containing it became of 

 general importance in organic chemistry. These synthetic 

 methods were satisfactory to the organic chemists as long as 

 they were dealing with the compounds derived from benzene 

 or from the heterocyclic ring structures, which, to some ex- 

 tent, simulate the properties of benzene; that is, as long as 

 organic chemistry used as its base materials the oils derived 

 from coal tar. But after the first World War, the great oil- 

 refining and chemical companies of the United States started 

 to study the possibility of using petroleum products as the 

 base for new groups of organic compounds, and the attention 

 of the manufacturing chemists became concentrated on the 

 aliphatic organic compounds, those composed of chains of 

 carbon atoms and derived from acetylene, natural gas, or 

 the decomposition products of petroleum. With these com- 

 pounds, it was found that reactions could be produced in the 

 gas phase with gieat facility, using catalysts that might be 

 solids, liquids, or even gases. As a result, the classical ali- 

 phatic chemistry ceased to have any relation to manufactur- 

 ing processes. 



The standard method of preparing acetic anhydride, for 

 example, is by the treatment of acetyl chloride with sodium 

 acetate. The process for manufacturing acetic anhydride, 

 which is used on a large scale, however, bears little relation 

 to that classical reaction. In that process, acetic acid is cata- 

 lytically decomposed in the gas phase at a very high tempera- 

 ture to ketene (CH2CO), the inner anhydride of acetic acid; 

 and the ketene then reacts with the molecules of acetic acid 

 to form acetic anhydride. More and more reactions of this 

 type are taking the place of the classic organic syntheses and 

 are making available large quantities of substances that used 

 to be chemical curiosities. 



Many of these new chemicals have a double bond in their 

 structure; that is, two carbon atoms are united not by one 

 but by two bonds. These compounds polymerize easily be- 

 cause one of the bonds is sufficient to hold the carbon atoms 

 together, while the other can supply a connection to link the 



