[Arait]

Hi!

For my most recent lab we had to determine the identity of an unknown carboxylic acid.  I think I've figured out the identity: 2-bromobenzoic acid.  Now, we're supposed to write out the reaction for this experiment so we can calculate the percent yield.  I'm not exactly sure how to figure this out since it is a two step reaction.  I'm not even sure what exactly is the first step and what is the second.  Here's what we did:

1. Combined maleic anhydride and water and boiled the solution.
2. Added zinc, let it dissolve, then added HCL.  
3. Heated again, filtered ,crystallized, yada, yada, yada.

So, my question is what are the two reaction steps.  They give us this in the book,

Zn + 2HCl --> H2 + ZnCl2

But that's all...  Is that a separate reaction step itself, or no?

Also, one of the post-lab exercises asks us to write the balanced equations of the reactions of maleic acid with water, cyclohexanol, aniline, and isoprene.

I got the reaction with water figured out, but not some of the others.  When cyclohexanol and aniline reaction with maleic acid, does the compound not break apart like it would with acetic anhydride because the compound is cyclic?  Also, I'm really not sure how isoprene reacts at all...

Any help would really be appreciated!

[mschelthoff]

Well when you boil the maleic anhydride with water, consider the sites on the anhydride that might be susceptible to the nucleophillic water molecules.

Also, you mention maleic acid "breaking apart" when reacting with an alcohol/amine, yet maleic acid isn't an anhydride or cylic as you state.

Regarding isoprene, notice how both maleic acid and isoprene contain double bonds, in a specific configuration. Consider reactions where two molecules are joined through multiple pi-bond interactions. Also note the electron-withdrawing effects of two carbonyl groups on maleic.

And on the HCl/Zn, H2 gas is formed, which would imply a hydrogenation, but as far as I know a non-catalytic hydrogenation of maleic acid at rt isn't possible, so I have no clue on that. Furthermore, HCl can cause maleic acid to isomerize to fumaric acid, complicating matters.

Good luck.

[Arait]

Thanks!

For the second part (the reactions), I did mean maleic anhydride.  I typed the wrong name!  So, that might be where some of the confusion was caused.