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Sustainable chemistry
Sustainable chemistry

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4.2.1 A greener way of making 2-phenyl propane

Industrially, 2‑phenylpropane is now synthesised by the reaction of benzene with propene using a catalyst (Figure 4.3).

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Figure 6 Alternative synthetic route to 2‑phenylpropane
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The figure illustrates a reaction depicting an alternative synthetic route to 2-phenylpropane. The reaction has two reactants and one product. The first reactant is benzene. The second reactant is 2-chloropropane. A reaction arrow labelled ‘catalyst’ leads to the product. The product is 2-phenylpropane.

The molecular structures of reactants and products are as follows:

Benzene: a benzene ring is in a vertical orientation with the carbon atoms labelled 1 to 6 for the purposes of this description and with C1 occupying the topmost vertex. The ring contains alternating double bonds between C2 and C3, C4 and C5, and C6 and C1. C1 is single bonded to H.

2-chloropropane has the following line structure: a central C atom is single bonded to H on the upper left, CH3 (where 3 is a subscript) on the lower left, and double bonded to CH2 (where 2 is a subscript) on the right.

2-phenylpropane: a benzene ring is in a vertical orientation with C1 occupying the topmost vertex. The ring contains alternating double bonds between C2 and C3, C4 and C5, and C6 and C1. C1 is single bonded to C. C is single bonded to CH3 on the upper left, H above and CH3 on the upper right. In both cases in CH3, the 3 is a subscript.

Figure 6 Alternative synthetic route to 2‑phenylpropane

The catalyst is an aluminosilicate (an oxide based on aluminium and silicon), which does not dissolve in the reaction mixture and so can be recovered and recycled.

Also, no by-products are formed in the reaction.

  • What is the atom economy of this reaction?

  • 100%; all atoms of the two reactants are incorporated into in the product. As the catalyst is recycled it is not considered.

At this point you will move away from chemical manufacture to take a look at the very building blocks of chemical compounds themselves, the elements, in particular problems around their availability and how can we use them in a more sustainable way.