Kolbe reaction is one type of phenolic reaction in which, phenol is used as a main product and it gives salicylic acid.
Hello, reders welcome to anther fresh article, today, i m going to explain about kolbe reaction and it’s mechanism.
let’s get started,
What is kolbe reaction?
kolbe reaction is a type of phenol reaction. in which phenol is react with sodium hydroxide, phenoxide ion is generated. this is first step reaction and in second step reaction, phenoxide ion again react with CO2 and acidification (H+). then it give ortho hydroxy benzoic acid. this product is also know as salicylic acid.
kolbe reaction is a type of addition reaction or is a type of phenolic reaction. In which phenol is taken first, in this case phenol does not have a direct reaction.
the acidic hydrogen of phenol has to be removed. acidic hydrogen can be remove with the help of naoh (sodium hydroxide). this is shown in the reaction. and reaction is,
In this reaction, acidic hydrogen of phenol will be remove by naoh. and this reaction will form sodium phenoxide. Now, sodium phenoxide react with CO2 and also does acidification.
When sodium phenoxide react with CO2. and acidification (H+) after this reaction, hydroxyl group (COOH) comes to ortho position. this is called kolbe reaction.
Why sodium phenoxide react with CO2 then COOH comes to ortho position?
Resion is, intermolecular hydrogen bonding occur between oxygen and hydrogen. that’s why hydroxyl group attached on ortho position. this product is know as ortho hydroxyl benzoic acid. it is also called salicylic acid.
Kolbe Reaction Mechanism
We know that, kolbe’s reaction is a phenol reaction because phenol is used during reaction.
phenol is a acidic in nature. It is easy to remove hydrogen from phenol by using sodium hydroxide.
In kolbe reaction mechanism, there are 5 steps are required for kolbe’s reaction mechanism. and all step is given below.
1 steps : Phenol is taken first, and then naoh sodium hydroxide. when phenol is react with naoh (naoh gives OH-) then OH will donate electron to hydrogen. and h2o will be out. and phenoxide ion become.
2 steps: Oxygen has electron on the phenoxide ion, they will show resonance with the ring. donating electrons will bring the electrons to the carbon.
3 steps: Due to this, oxygen to form double bond. and electrons will shift to ortho position. causing, hydrogen bonding is formed between hydrogen and oxygen.
4 steps: Now, take CO2, CO2 is also In acidic in nature. and In this case the electrons of ortho position will be shifted on carbon. if electrons shift on carbon then pi electrons will break and both the electrons will shifted on oxygen. all steps is given in the mechanism, as shown in reaction.
Hydrogen are donated electrons for making Aromaticity if hydrogen donate electrons then oxygen will get – charge. it mean due to this, negative charge will come on oxygen.
After this, acidification is carryout to form final product. salicylic acid is formed as a final product.
Uses of kolbe reaction
• Kolbe’s reaction is used in chemical industry for chemical synthesis.
• it is windly use in chemical synthesis.
• it is used in medical industry.
• it is used in preparation of chemical and dyes.
• it is used in
Frequently Asked question
1. What is the main compound in kolbe’s reaction?
Phenol is the main compound in kolbe’s reaction because phenol is taken first, and then naoh is taken, after that phenol is react with naoh, then sodium phenoxide is formed and after that, sodium phenoxide react with CO2/H+, after this reaction it gives artho hydroxyl benzoic acid as a main product. this product is also know as salicylic acid.
therefore, we can say that phenol is main product in kolbe’s reaction.
2. Give the example of weak-acid and stronge-base in kolbe’s reaction?
When phenol is react with naoh, sodium hydroxide then it gives sodium phenoxide and h2 will out.
phenol – weak acid
NaoH – strong base
therefore, this is the best example of weak acid and strong base in kolbe’s reaction.
3. What is the main electrophile use in kolbe’s reaction?
Corbon dioxide – CO2
4. Give the main reaction of kolbe’s reaction and reimer – tiemann reaction?
kolb’s reaction – when phenol is react with naoh (sodium hydroxide) then it give sodium phenoxide and h2o will out. and then sodium phenoxide is react with CO2 after this reaction COOH group is attached on artho position of final product. this is called artho hydroxyl benzoic acid.
Reimer – Tiemann – when phenol is react with chloroform (chcl3) in the presence of naoh (sodium hydroxide). a -CHO group is attached on artho position of benzene ring.
5. What is the main synthesis of salicylic acid?
First synthesis – when phenol is treated with naoh then it give sodium phenoxide and h2o will out.
Second synthesis – when sodium phenoxide is treated with CO2/ acidification (H+) under pressure at 180° to 200°C. after this, it give salicylic acid as a final product. it is also know as artho hydroxyl benzoic acid.