Ziegler alcohol synthesis

What is Ziegler alcohol synthesis?

The Ziegler alcohol synthesis is an industrial method for producing higher and linear primary alcohols with an even number of carbon atoms. The process involves several steps, including the synthesis of triethylaluminum from aluminum, hydrogen, and ethylene, the chain growth reaction between triethylaluminum and ethylene, the oxidation of resulting trialkylaluminum to aluminum alkoxides, and the hydrolysis of aluminum alkoxides to aluminum hydroxide and the desired alcohols. This reaction was first reported by Ziegler in 1955 and is also known as the Ziegler higher alcohol synthesis or simply Ziegler synthesis.

Ziegler alcohol synthesis - general reaction scheme - Alfol process
Ziegler alcohol synthesis

The alcohols prepared by this process are generally referred to as Ziegler alcohols, and triethylaluminum is known as the Ziegler catalyst. In addition, because this process was first implemented by Sonoco in 1962 to produce a series of long-chain alcohols, the reaction is also termed as the Alfol process, and the alcohols are also named as Alfol 6, 8, 12, and so on.

The Ziegler alcohol synthesis has been used to produce alcohols with carbon atom distributions from C2 to beyond C26, and the molecular weight distribution follows the Poisson distribution. During the chain growth reaction, higher molecular weights of trialkylaluminum are formed at a relatively low temperature range, whereas at a higher temperature range, a thermal displacement reaction occurs, offering long-chain alpha-olefins. In the presence of nickel, cobalt, and platinum, the thermal displacement reaction occurs at a relatively lower temperature.

At the oxidation stage, the reaction is carried out stepwise by passing dried air through the mixture of trialkylaluminum while cooling. The by-product of this reaction, aluminum hydroxide, can be converted into alumina via dehydration, and the alumina is known as the Ziegler alumina. High purity alumina has high commercial value for the production of catalysts and for improving the economy of the Alfol process.

Applications

The versatility of Ziegler alcohol synthesis makes it a valuable tool in industrial settings, where it is utilized to synthesize long chain primary alcohols. These alcohols have diverse applications, such as in the production of cosmetics, and can also be converted into nonionic or anionic detergents.

References

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