# Industrial Importance of Alkenes

## Industrial Importance of Propylene

### Polypropylene

The low-pressure polymerization of ethylene was developed in the early fifties . Shortly thereafterafter, in 1953, K. Ziegler and G. Natta were successful in developing the stereospecific polymerization of propylene to polypropylene using a special catalyst which is named after them . Compared to polyethylene, the predominantly polypropylene shows higher stability at high temperatures (up to 100°C) and higher stress-cracking resistance. However, because of its tertiary carbon atoms polypropylene has a lower oxidative stability than polyethylene . The oxidative degradation results in ageing and a deterioration of mechanical properties requiring the addition of antioxidants.

Because of its low density (0.9 to 0.91 $g cm-3$) polypropylene is one of the lightest . Since 1957 the large-scale production of polypropylene uses coordination polymerization with Ziegler-Natta catalysts.

Fig.1
Polymerization of propylene to polypropylene

### Hock process

Propylene and benzene are the starting materials of another important industrial synthesis. In the cumene hydroperoxide process (Hock process), phenol and acetone are formed by oxidation via several intermediates, such as cumene (2-phenylpropane, isopropylbenzene) and cumene hydroperoxide, for example.

Fig.2
Synthesis of acetone and phenol

The large-scale synthesis of butyric aldehyde is also based on propylene. Hydroformylation of propene is carried out with syngas (a mixture of carbon monoxide and hydrogen) and cobalt or rhodium catalysts. This process can also be used to synthesize other aldehydes.

Fig.3
Synthesis of butyric aldehyde
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