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Reimer-Tiemann and Kolbe are the two named reactions of phenol that students most often swap. Both use sodium hydroxide, both put a new carbon group next to the –OH, and both are asked as "write the equation" questions. This post separates them step by step, explains why both prefer the ortho position, and finishes with a yield calculation and a practice routine.
Which exams ask for these reactions?
The NCERT Class 12 unit on alcohols, phenols and ethers (Reprint 2026-27) covers both, and its Intext Question 7.9 asks you to write the equations for each. The JEE (Main) 2026 syllabus and the NEET (UG) 2026 syllabus list phenols' "electrophilic substitution reactions, halogenation, nitration and sulphonation, Reimer - Tiemann reaction". Neither names Kolbe's reaction. So for JEE Main and NEET-UG, Reimer-Tiemann is the named one. For CBSE boards, which follow NCERT, learn both. Check the current bulletin.
Why does phenol need sodium hydroxide first?
NCERT's key point is that the phenoxide ion, made by treating phenol with NaOH, "is even more reactive than phenol towards electrophilic aromatic substitution". The negative charge on oxygen spreads into the ring at the ortho and para carbons, so the ring can attack electrophiles too weak to react with benzene. Both reactions depend on this.
Reimer-Tiemann, step by step
Reagents: phenol, chloroform, aqueous NaOH, then acid.
Make the electrophile. Hydroxide pulls the proton off CHCl3, and the CCl3⁻ ion loses Cl⁻ to give dichlorocarbene, :CCl2. Jack Hine (1950) proposed this "carbon dichloride" as the intermediate when chloroform reacts with base.
Attack at ortho. The phenoxide ring attacks the electron-poor carbene carbon at a position next to the O⁻.
Hydrolysis. NCERT says the substituted benzal chloride (a –CHCl2 group on the ring) is hydrolysed in alkali, giving a –CHO group.
Acidify. The product is ortho-hydroxybenzaldehyde, salicylaldehyde.
Overall: C6H5OH + CHCl3 + 3NaOH → o-HOC6H4CHO + 3NaCl + 2H2O. Check the balance yourself: 7 C, 10 H, 4 O, 3 Na and 3 Cl on each side.
The reaction is named after Reimer and Tiemann, who reported the action of chloroform on alkaline phenolates in 1876.
Kolbe's reaction, step by step
Reagents: phenol, NaOH, carbon dioxide, then acid.
Make sodium phenoxide with NaOH.
Attack CO2. NCERT calls CO2 "a weak electrophile". Only the highly activated phenoxide ring is reactive enough to attack it.
Acidify. NCERT gives ortho-hydroxybenzoic acid, salicylic acid, as the main product.
Hermann Kolbe published a synthesis of salicylic acid in 1860, and R. Schmitt published a study of Kolbe's salicylic acid synthesis in 1885. Many books call the reaction the Kolbe-Schmitt reaction. NCERT also notes that acetylating salicylic acid gives aspirin, so this route leads to a familiar medicine.
Worked example: a yield calculation
Sample numbers for practice: 4.70 g of phenol is used in a Reimer-Tiemann reaction and 2.50 g of salicylaldehyde is isolated. What is the percentage yield? What mass of salicylic acid would the same phenol give at 100% in Kolbe's reaction?
Molar mass of phenol, C6H6O: 6(12.011) + 6(1.008) + 15.999 = 94.11 g/mol.
Moles of phenol: 4.70/94.11 = 0.0499 mol.
Salicylaldehyde, C7H6O2: 122.12 g/mol. Theoretical mass: 0.0499 × 122.12 = 6.10 g.
Percentage yield: 2.50/6.10 × 100 = 41%.
Salicylic acid, C7H6O3: 138.12 g/mol. Theoretical mass: 0.0499 × 138.12 = 6.90 g.
Both reactions are 1:1 in phenol, so the only change is the product's molar mass.
Common mistakes and how to avoid them
Swapping the products. Write the reagent next to the product in your notes: CHCl3 with CHO, CO2 with COOH.
Starting from phenol, not phenoxide. Without NaOH, CO2 does not react. Show the phenoxide step.
Confusing Kolbe's reaction with Kolbe electrolysis. Electrolysis of a carboxylate salt makes an alkane. Our guide to carboxylic acids and their derivatives covers that one.
Drawing the group para. NCERT gives ortho products for both.
Dichlorocarbene returns in the test for primary amines; see our post on the carbylamine test. If you can write the steps but cannot see why the ring attacks where it does, the Fermi Problem Library has worked problems with a step-by-step solver that explains the reasoning.
A practice routine
Write both reactions from phenol to final product, with every reagent, from memory.
Draw the resonance forms of phenoxide and circle the carbons that carry negative charge.
Redo the yield example with 9.41 g of phenol and 6.0 g of product.
Answer NCERT Intext Question 7.9 in full.
Tonight, write the two reagents and two products on one flashcard, side by side.
