Terephthalic Acid: Para-Xylene Oxidised by Air with Manganese and Bromide

Terephthalic acid is the acid half of PET. Both methyl groups of para-xylene are burnt to acid groups by air under pressure in hot acetic acid, with a little manganese salt and bromide as catalyst: the Mid-Century process of Saffer and Barker (US 2,833,816, 1958). The acid does not dissolve, so it is simply filtered off. Example 24 of the patent, all parts by weight. The picture: our diagram of the reactor.