|Acetaldehyde can be oxidised to acetic anhydride using Cu(I) acetate catalyst.The mechanism is complicated. A radical abstracts H from acetaldehyde forming an acetyl radical which is oxidised to the acetyl cation by a Cu2+ ion. The acetyl cation reacts with acetic acid to give acetic anhydride. At the same time, peracetic acid is formed which oxidises Cu+ to Cu2+.
Industrial Organic Chemistry, 3rd. Ed. K. Weissermel, H.-J. Arpe, VCH (1997)|