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Problems and solutions
Major Disadvantages

The process generates more effluent than product. This is clear when we look at the atom economy of the reaction we have considered.

The relative masses of all the reagents are given below,


and the relative masses of the products are



But it is even worse than this. Before disposal the HCl must be neutralised with alkali, so the final result looks like

Question

Using the relative masses given work out what percentage by mass of atoms end up in the desired product.

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This is unfortunately typical of Friedel-Crafts acylations where 1 tanker of product leads to 2 tankers of waste.

There are advantages: the raw materials are relatively cheap and AlCl3 is very active.

The solution

A catalytic process, with high atom efficiency.

A wish list for a new process
  • It is truly catalytic
  • The catalyst does not form a strong complex with the product
  • The catalyst can be recycled
  • The reagents used are acids, esters or anhydrides rather than halogen compounds
  • Solvents are not needed or those used are not halogenated
Some alternatives

It looks like a single catalyst of high activity which can work on all acylation reactions may not be found. Different catalytic systems work on different reactions

Some of the suggestions are

Click to learn more about these.

Question

Assume the reaction gives a 100% yield calculate the mass of waste for every
134 g (I mole) of product ketone.

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