[Cooper]

Hello,

I was looking over the steps for the Friedel-Crafts acylation. I am confused on the last step. Why does it even occur? (See below) I know that the last step prevents ployacylation by making the ketone even more electron withdrawing, but I don't get why it would happen. In the first and second step (not shown) an acylium ion (C-C(triple bond)O+) is formed.

Thanks!

The image is from Organic Chemistry 10^th E. by Solomons (p. 687)

[Cooper]

EDIT: My professor explained to me why. It's because the AlCl₃ is such a strong Lewis acid that you need to add water so that it won't stick to your product.