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The reaction: (a) m-hydroxyphenol + aq. $\ce{NaHCO3}$/boil; (b) workup with $\ce{H3O+/H2O}$

I know that $\ce{CO2}$ will be formed by boiling aq. $\ce{NaHCO3}$, and so the reaction will be like Kolbe-Schmitt type, i.e. $\ce{COOH}$ group will be attached on the benzene ring.

But I have a doubt that where will the addition of $\ce{COOH}$ group take place,

(1) ortho-position w.r.t. both hydroxy groups $$\text{or}$$

(2) ortho-position w.r.t. one hydroxy group and para-position w.r.t. the other group.

So, Which will be the major product and why?

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The major product (proportions dependent on conditions) is option 2 (beta-resorcylic acid) according to these papers$\ce{^{[1]} ^{[2]}}$. The relatively low proportion of option 1 (gamma-resorcylic acid) is attributed to steric hindrance$\ce{^{[3]}}$.

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References

  1. The carboxylation of resorcinol and the separation of β-and γ-resorcylic acid by ion-exchange chromatography by D. K. Hale, Audrey R. Hawdon, J. Idris Jones and D. I. Packham. DOI: https://pubs.rsc.org/en/content/articlelanding/1952/JR/JR9520003503#!divCitation
  2. The chemistry of resorcinol carboxylation and its possible application to the CO2 removal from exhaust gases by Vincenzo Barbarossa, Francesco Barzagli, Fabrizio Mani, Sarah LaicGiuseppina Vangaa DOI:https://doi.org/10.1016/j.jcou.2015.04.004 (picture source)
  3. https://www.studocu.com/en-us/document/university-of-north-carolina-at-charlotte/organic-chemistry-2/assignments/lab-report-4-carboxylation-of-resorcinol/2141490/view
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  • $\begingroup$ Isn't OH a small group? Can it contribute to steric hinderence so much so as to change the major product? $\endgroup$ – Meet Patel Apr 25 '20 at 10:42
  • $\begingroup$ Apparently so. This is the accepted explanation $\endgroup$ – Waylander Apr 25 '20 at 10:43
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These are a few points I'd like to add in addition to Waylander's answer for readers' benefits:

It is true that $\beta$-resorcylic acid (2,4-dihydroxybenzoic acid) is the major product of this reaction (option 2),a significant amount of $\gamma$-resorcylic acid (2,6-dihydroxybenzoic acid) would also form (option 1). For example, heating resocinol (1,3-dihydroxybenzene) with excess $\ce{KHCO3}$ or $\ce{NaHCO3}$ in water had afforded $\beta$-resorcylic acid exclusively, and $\ce{KHCO3}$ had given higher yield (Ref.1). As Waylander pointed out, the proportions are dependent on conditions, specifically by excessive heating (Ref.1). According to the authors, about 80% $\gamma$-resorcylic acid tends to be decarboxylated. And also, with 20% sodium hydroxide solution, it afforded some $\gamma$-resorcylic acid but considerable decarboxylation occurred simultaneously. This effect on base to give more $\gamma$-resorcylic acid is evident in Ref.2, which speculate formation of dianion would be the reason.

Further, $\beta$-resorcylic acid also tends to be decarboxylated in organic solvents above $\pu{150 ^\circ C}$ to give resocinol (First order kinetics; Ref.3 & Ref.4).

References:

  1. D. K. Hale, Audrey R. Hawdon, J. Idris Jones, D. I. Packham, "The carboxylation of resorcinol and the separation of β-and γ-resorcylic acid by ion-exchange chromatography," J. Chem. Soc. 1952, 3503-3509 (https://doi.org/10.1039/JR9520003503).
  2. Vincenzo Barbarossa, Francesco Barzagli, Fabrizio Mani, Sarah Lai, Giuseppina Vanga, "The chemistry of resorcinol carboxylation and its possible application to the $\ce{CO2}$ removal from exhaust gases," Journal of $\ce{CO2}$ Utilization 2015, 10, 50-59 (https://doi.org/10.1016/j.jcou.2015.04.004).
  3. Louis Watts Clark, "The kinetics of the decarboxylation of β-resorcylic acid in amines and glycols," J. Phys. Chem. 1963, 67(12),2831-2833 (https://doi.org/10.1021/j100806a078).
  4. M. A. Haleem, M. A. Hakeem, "The kinetics of the decarboxylation of β-resorcylic acid in catechol," Australian Journal of Chemistry 1976, 29(2),443-446 (https://doi.org/10.1071/CH9760443).
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