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On treating phenol with chloroform in the presence of sodium hydroxide, a $\ce{-CHO}$ group is introduced at the ortho position of the hydroxy group. Why is this so? Why is 4-hydroxybenzaldehyde not obtained?

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    $\begingroup$ I know this might seem unrelated, but do you know about the selectivity in the Kolbe-Schmitt reaction? Treatment of phenol with NaOH and carbon dioxide also gives the ortho product, salicylic acid, exclusively. $\endgroup$ – orthocresol Oct 30 '15 at 19:14
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    $\begingroup$ The Reimer-Tiemann reaction generally proceeds in poor yield. In the case of phenol, both the ortho and para products are formed in the expected statistical ratio of 2:1 respectively (20% : 10% isolated yield). See this earlier question and the link provided in my answer. $\endgroup$ – ron Oct 30 '15 at 19:30