[Darkstar]

Benzaldehyde + acetyl anhydride in the presence of NaOAc. What kind of reaction is this? Just a common carbonyl alpha-substitution or something else? What do we get?

[movies]

It's not an alpha substitution, there are no alpha protons in benzaldehyde.  I think that those are acylation conditions.  Sort of like Friedel-Crafts, but without a metal Lewis acid.  I think that you would get 3-formyl acetophenone.

[falcon]

 
It`s classic Perkin condensation! Synthesis  of cinnamic (3-phenyl-2-propenoic) acids. Acetate anion
tears off the proton from acetic anhydride, this anion attack carbonyl group in benzaldehyde, further follows migration negative charge, leading to cinnamic acid.

[Darkstar]

That's right... thanks, I see now.

[movies]

Really?  But the acetate anion isn't nearly a strong enough base to remove that proton!

[movies]

I stand corrected.  Falcon was right on.  Here is a link with some references if anyone is interested:

http://themerckindex.cambridgesoft.com/TheMerckIndex/NameReactions/ONR300.htm