[yitzik]

hello!
in the lab we have made an experiment of: oxidation of benzoin to benzil with the use of oxidizing agent HNO3 (nitric acid).

in the TLC of the products i can see 3 differrent spots. none of them corresponds to spot of the starting material benzoin.
in the figure- the tlc plate: lane 1 is benzoin and lane 2 is benzil....

i'm sure that the most upper spot in lane 2 corresponds to benzil (it's more polar than benzoin due to the lack of alcoholic group hence going upper).
i have tried to figure out what can the two additional spots be. i don't think that those are impurities but rather some other type of product that was produced in the oxidation reaction. it should be more polar than benzil... but it's not benzoin...
can it be due to:
- some kind of  rearrangement of benzoin (in acidic conditions)?
-somehow cleavage of the aromatic rings?
-product of aromatic nitration of benzoin/benzil with HNO3?

any other idea?
thanks

[rolnor]

You need to isolate them and run NMR and mass-spectrometry. You can also run a sample in a LC-MS machine but NMR is more conclusive. Sometimes by-products are very small impurities and not much to isolate.