why we cannot have two reimer tiemann substitutions on the same phenol as CHO- group is electron withdrawing it wont disturb electron concentration at its meta which is phenol's ortho- product
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$\begingroup$ But it deactivates the system overall $\endgroup$ – Waylander Apr 24 '18 at 16:11
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$\begingroup$ If you look at the electron flow, you'd see the electron density on $\ce{O}$ in $\ce{Ar-OH}$ is not completely available after the first substitution. $\endgroup$ – Mathew Mahindaratne Apr 24 '18 at 16:22
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$\begingroup$ why am i getting down votes? you guys find it difficult to help $\endgroup$ – amish dua Apr 25 '18 at 7:08
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There are some literature evidence that shows to have two Reimer–Tiemann substitutions on same phenol ring could be possible. For example, salicilic acid is a Reimer–Tiemann product from phenol and carbon tetrachloride. Yet, it had undergone another Reimer–Tiemann reaction to give 5-formyl-2-hydroxybenzoic acid with $17\%$ yield (para-substitution) but no 3-formyl-2-hydroxybenzoic acid (ortho-substitution) when chloroform was replaced by trichloroacetic acid (J. Chem. Soc., 1933, 496-500).
For more examples: Read, Chem. Rev., 1960, 60(2), 169–184.
answered Apr 24 '18 at 17:16
