For my Advanced Higher Chemistry project (a piece of coursework in the last year of school) I'm trying to determine experimentally the identity of an unknown organic compound chosen by my teacher. It's a white odourless crystal.

It decolourises bromine so it's unsaturated (I know some saturated compounds may react with bromine but it will only require Chemistry that I've been taught). It doesn't contain a halogen or sulfur for the same reason. It burns with a smoky flame and is insoluble in water and HCl but dissolves in NaOH and forms bubbles (I haven't had time to set up lime water to check it's CO2) on addition to NaHCO3 so it's acidic.

It melts at approximately 132 degrees C.
I can't think of any compounds which fit the bill. I considered fumaric or maleic acid but my teacher made it clear that's wrong. He's also suggested there's a benzene ring, which fits with the smoky flame.
Any ideas?? Small Bio