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I was given some data to determine what the unknown compound was and figured out that it was cinnamaldehyde. After reviewing the classification test given to me by my professor, I was a bit confused as to why it would pass the ferric chloride test as well as pass a Lucas test but yet show no reaction.

Can someone explain to me why that is possible?

Also, in terms of solubility, why would cinnamaldehyde be soluble in sulfuric acid only and not both sulfuric acid and $\ce{NaHCO3}?$

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    $\begingroup$ The ferric chloride test is generally for phenols and enols, i. e., acetoacetic ester (purple color. $\ce{FeCl3}$ is also an oxidant which may cause a change in color. $\endgroup$
    – user55119
    Commented Mar 30, 2020 at 1:11

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I think the cinnamaldehyde gives $\ce{FeCl3}$ test due the similar reason why acetic acid can give $\ce{FeCl3}$ test as $\ce{Fe^3+}$ can act as oxidizing agent.

As in case of acetic acid $\ce{Fe(CH3COO)3}$ (red colour) is formed, a similar complex may be produced.

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  • $\begingroup$ The formation of ferric acetate is not an oxidation. $\endgroup$
    – user55119
    Commented Apr 8, 2020 at 20:08
  • $\begingroup$ Ferric ion may oxidize the aldehyde group to carboxylic acid group $\endgroup$ Commented Apr 10, 2020 at 5:23
  • $\begingroup$ True enough but that doesn't account for a necessary, definitive color change. $\endgroup$
    – user55119
    Commented Apr 10, 2020 at 15:36

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