Phenol → Alpha-Methylstyrene

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Reaction Steps

Phenol is manufactured via air oxidation of cumene to cumene hydroperoxide (CHP), followed by acid-catalyzed cleavage of the latter to phenol and acetone, and is known as CHP decomposition. CHP decomposition is a very exothermic reaction which is normally carried out on a commercial scale in continuous stirred or back-mixed reactors. In such reactors only a small fraction of CHP is unreacted at any given time and the reaction medium consists essentially of the products of decomposition of CHP, i.e., phenol and acetone, plus any solvent (e.g., cumene) and other materials added with CHP to the reactor. During cumene oxidation small amounts of dimethyl phenyl carbinol (DMPC) and acetophenone are also formed. In the presence of acid catalyst, DMPC dehydrates to alphamethylstyrene (AMS), a useful by-product. Very high yields of AMS can be obtained from pure DMPC, e.g., 98% yield upon dehydration over acidic silica at 300° C. In the presence of phenol, however, and more specifically in a phenol/acetone/cumene mixture which is a solvent in the decomposition of CHP/DMPC mixtures, the ultimate AMS yield is normally about 50–60 mol % of the DMPC. Main by-products are AMS dimers and cumylphenol which have no commercial value. Formation of cumylphenol also reduces the phenol yield.

Provenance & Evidence