Isopropylbenzene synthesis from benzene

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. 

Isopropylbenzene is an imp>ortant intermediate for the production of phenol. There are two main industrial methods for the synthesis of isopropylbenzene from benzene and propylene. One is the liquid-phase process using sulfuric acid as catalyst and the other is the vapor-phase process using phosphoric acid (or PiOs) supported on silica or kieselguhr, the content of P2O5 and SiOi being 62 — 65% and 25%, respectively. In the latter process, UOP process,the reaction is carried out at 570 — 640 K and 17 — 30 bar with a benzene-to-propylene ratio of 5 — 7. Isopropylbenzene yield of 96 — 97% of the theoretical value based on benzene and 91—92% based on propylene is typical. The formation of isopropylbenzene in the alkylated products is more than 90%. This process has also been applied to the alkylation of benzene with ethylene. 

Design a synthesis of -propylbenzene from benzene. Hint A one-step synthesis using CH3CH2CH2Br and AlBrs yields a large amount of isopropylbenzene. 

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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