Isopropylbenzene , cumene synthesis

The most widely used industrial synthesis of phenol is based on isopropylbenzene (cumene) as the starting material and is shown m the third entry of Table 24 3 The eco nomically attractive features of this process are its use of cheap reagents (oxygen and sulfuric acid) and the fact that it yields two high volume industrial chemicals phenol and acetone The mechanism of this novel synthesis forms the basis of Problem 24 29 at the end of this chapter... 

An increasingly important process for the synthesis of phenol starts with cumene, isopropylbenzene. Cumene is converted by air oxidation into cumene hydroperoxide, which is converted by aqueous acid into phenol and acetone. 

For many years, phenol was manufactured b the Dow process, in which chlorobenzene reacts with NaOH at high temperature and pressure (Section 16.9). Now, however, an alternative synthesis from isopropylbenzene (cumene) is used. Cumene reacts with air at high temperature by a radical mechanism to form cumene hydroperoxide, which is converted into phenol and acetone by treatment with acid. This is a particularly efficient process because two valuable chemicals are prepared at the same time. 

Propene is used as a starting material for the synthesis of acetone, cumene (isopropylbenzene), and polypropylene (PP). 

The related manufacture of cumene (isopropylbenzene) through the alkylation of benzene with propylene is a further industrially important process, since cumene is used in the synthesis of phenol and acetone. Alkylation with propylene occurs more readily (at lower temperature) with catalysts (but also with hydrogen fluoride and acidic resins) similar to those used with ethylene, as well as with weaker acids, such as supported phosphoric acid (see further discussion in Section 5.5.3). 

Autoxidation is one of the key steps in the industrial synthesis of phenol and acetone from benzene and propylene. In the second step of this synthesis, cumene (isopropylbenzene) is autoxidized to give cumyl hydroperoxide. 

The key stage is the alkylation of cumene. From its reaction in the liquid phase at 300°C in the presence of a silica/alumina catalyst with 3 moles of propene the 1,4-isomer required for hydroquinone is separated by fractionation (ref.30) and the mixture of 1,2- and 1,3-di-isopropylbenzenes together with the tri-isopropyl isomer equilibrated with benzene at 270°C with the same catalyst to enrich the proportion of the 1,3-compound required for the synthesis of resorcinol. The sequence of steps for hydroquinone is shown. By-product 4-isopropylphenol is mostly reoxidised and recycled giving a total yield of 71% based on di-isopropylbenzene (ref.31). 

Synthesis of Cumene (Isopropylbenzene) from Diisopropylbenzenes in the presence of Benzene using Triflic acid as catalyst at room temperature... 

From Cumene Hydroperoxide. This process illustrates industrial chemistry at its best. Overall, it is a method for converting two relatively inexpensive organic compounds— benzene and propene—into two more valuable ones—phenol and acetone. The only other substance consumed in the process is oxygen from air. Most of the worldwide production of phenol is now based on this method. The synthesis begins with the Friedel-Crafts alkylation of benzene with propene to produce cumene (isopropylbenzene) ... 

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