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I want to react the following molecule with conc. sulfuric acid in the presence of methanol at room temperature:

enter image description here

If I am right, this would make a methyl ester to be formed on the carboxyl.

The aim afterwards is to let it react with vanillin (in the presence of left over sulfuric acid) at 90°C, so it will give a coloured derivative.

Below is the structure of vanillin. As you can see, this has an aldehyde group and a hydroxy group.

enter image description here

Is it possible to let an aldehyde and ester react at higher temperatures?

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  • $\begingroup$ What do you hope to get as a result of this reaction? (Also, I'm not sure the first reaction would give you the ester in good yield - there are a number of -OH that can easily be protonated, and then leave to form a carbocation, and do a number of things from there. For instance, that allylic hydroxyl looks particularly tasty for concentration sulfuric acid.) $\endgroup$
    – kosyumote
    Jul 3 '16 at 23:49
  • $\begingroup$ I found these steps in a post-column derivatization reaction in HPLC. It gives a coloured molecule, but I don't know how this would look like. I would like to know the principle, so I could use this for similar reactions in the future. $\endgroup$ Jul 4 '16 at 6:39
  • $\begingroup$ I just checked chemaxon, and it seems that the hydroxy groups have pka's that are in the range of -3 ; 12.7. So it seems that these groups will not be protonated with conc. sulfuric acid as this is only a semi-strong acid. $\endgroup$ Jul 4 '16 at 6:43
  • $\begingroup$ Regarding your first comment: do you have a link to a paper describing this? It might provide some more insight. $\endgroup$
    – kosyumote
    Jul 4 '16 at 7:05
  • $\begingroup$ I don't really understand your second comment. What is the "semi-strong acid" you refer to? Sulfuric acid has a Hammett acidity of around -12 if I remember correctly - thus making it a very very strong acid. Depending on how concentrated the sulfuric acid is, it can also produce species such as pyrosulfuric acid, which is even MORE acidic. The question isn't whether or not the hydroxyls will get protonated - it's whether something else will happen faster, and lead to a more useful product. $\endgroup$
    – kosyumote
    Jul 4 '16 at 7:11

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