Esterification of Vanillin In Presence of Acid

topic posted Mon, July 21, 2008 - 1:06 AM by  James Jockson
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Not sure what happens here when vanillin reacts with acetic anhydride n the presence of an acid...

The NMR of the acid product shows peaks at - ppm (integration) -
2.1 (6.37)
2.3 (2.90)
3.8 (3.00)
7.1 (3.22)
7.6 (1.08)

im really bad at NMRs... so im not getting too far with this..

thanks!
posted by:
James Jockson
Chicago
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  • What is the multiplet of each of those peaks?... understand the multiplet relationships is what tells the structure on a primary level (peak splitting is needed for a deeper understanding).
    • 2.1 (6.37)
      2.3 (2.90)
      3.8 (3.00)
      7.1 (3.22)
      7.6 (1.08)

      they all look like singlets to me...
      • How did you purify the sample?

        In the aromatic region 7.6 is the proton between the formyl and methoxide groups. This is a singlet.

        7.1 is also aromatic protons, but should be a doublet and count 2 protons, not 3, so something is wrong with the integration.

        3.8 is the methoxide protons (3) and should be a singlet.

        2.3 were the hydroxyl group was converted into an acetate ester (3 protons and a singlet)

        ~10-11 is were the formyl proton should be, but these often don't show up well (a singlet of 1 proton).

        At 2.1, you have a singlet of 6 protons which matches the methyl protons on acetic acid or acetic anhydride. It is possible but unlikely that the formyl group was converted into a hemi-acetate (2 ester groups on the same carbon). I say unlikely because you normally need a strong electron withdrawing group (like CF3) also attached to the same carbon to stablize the hemi-acetate....

        Go to www.sigmaaldrich.com/spectra...1609.PDF to see a FT-NMR of vanillin (the top is a carbon FT-NMR). Use that as a point of comparison.

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