Benzoin Condensation


The formation of carbon-carbon (C-C) bonds is a key process in benzoin condensation. It is accomplished by producing an acyl anion equivalent from 1 aldehyde molecule and then adding it to another. Usually, a cyanide ion catalyses the process. The 1$\mathrm{^{st}}$ intermediate is cyanohydrin anion, which is the precursor to the acyl anion equivalent. Plants contain cyanohydrins as glycosides. In our bodies, a process very similar to benzoin condensation occurs, although it does not include cyanohydrin intermediates and is not catalysed by cyanide ions. The thiazolium moiety of the coenzyme thiamine pyrophosphate catalyses it (TPP).

Definition and Meaning of Benzoin Condensation

Benzoin condensation reaction (BCR) is the condensation of aromatic aldehydes ($\mathrm{RCHO}$) in the presence of a catalyst to generate hydroxyl ketones that is benzoins. It must be noted that benzoin ($\mathrm{PhCH(OH)C(O)Ph}$) is synthesised from $\mathrm{C_{6}H_{5}CHO}$ in the existence of a catalyst. Stange confirmed the 1$\mathrm{^{st}}$ BCR was catalysed by cyanide ion in the year 1824, as well as it has been thoroughly researched by others since. Stange's interest in this condensation reaction is evident in the fact that $\mathrm{PhCH(OH)C(O)Ph}$ can be converted into 1,2-diphenyl amino ketones or 1,2-diphenyl amino alcohols, which have shown some vital functions, including tumour-necrotising tasks.

Thiamin (vitamin B1), and similar thiazolium salts have been recognised to catalyse the BCR in the existence of a moderate base since the year 1943. Other catalytic systems are now being established, such as N, N-disubstituted o-phenylenediamines, thiazolium cyclophane, or even enzymes. The BCR is generally conducted in a liquid solution, as well as the input of salt (LiCl,KCl) might accelerate the reaction rate; yet, the condensation can also be conducted in an organic solvent, such as anhydrous petroleum ether. Contrary to the salt effect in a liquid solution, adding salt ($\mathrm{LiClO_{4},LiCl}$) to organic solvents (ethylene glycol, formamide, as well as DMSO) causes the reaction rate to slow down. Unfortunately, a few aldehydes (RCHO) were discovered to not create $\mathrm{PhCH(OH)C(O)Ph}$ under the BCR condition, instead of forming ethylenediol but also ethanediol.

When catalysed by cyanide ion, this condensation reaction (BCR) is thought to proceed by cyanide addition to an aldehyde (RCHO), deprotonation to generate carbanion, and then carbanion addition to a 2$\mathrm{^{nd}}$ aldehyde group to form $\mathrm{PhCH(OH)C(O)Ph}$. When catalysed by thiazolium salt, the process is identical.

Mechanism of Benzoin Condensation Reaction

Step 1 − The nucleophilic addition of cyanide (CN-) to benzaldehyde ($\mathrm{C_{6}H_{5}CHO}$) results in the formation of cyanohydrin. The usual procedure begins with benzaldehyde being treated with a catalytic quantity of sodium cyanide in the existence of a base. The cyanide ion intermediates in the formation of a stable cyanohydrin.

Step 2 − Cyanohydrin condensation with a 2$\mathrm{^{nd}}$ benzaldehyde.

Step 3 − A rearrangement process takes place, as well as the elimination of cyanide ions, in the production of benzoin.

Application of Benzoin and Benzene Condensation Reaction

  • The benzoin condensation is used in a variety of chemical reactions including synthesises.

  • Benzoin is utilised in the hardening of various polymers utilising microemulsions.

  • It is employed in the manufacturing of deodorants due to its wonderful biological structure.

  • The reaction is significant in the synthesis of heterocyclic compounds as well as aliphatic aldehydes.

  • These reactions, like those employed in polymer chemistry, can be utilised to create polymers plus novel monomers.

  • In veterinary medicine, it is used as a topical antiseptic in the cure of skin ulcerations to promote healing. It is used in medicine in the manufacture of inhalants for the cure of bronchitis as well as oral expectorants.

  • It contributes to the production of organic molecules as a result of catalytic polymerization. It is an intermediary in the manufacture of oxime-benzoin, a metal analytical reagent.

Benzoin Condensation Reaction and Benzoin Users

  • Benzene is utilised to toughen the skin of athletes' parts.

  • Benzene is being used in complementary medicine.

  • The benzoin condensation reaction is employed in the synthesis of different chemical compounds.

  • This reaction is used to create heterocyclic compounds.

  • Benzoin is used to make benzoin tincture.

  • Benzoin is used to protect the skin against allergies.

  • Orthopedists employ benzoin beneath a cast.

  • Benzoic acid is utilized to treat asthma, bronchitis, as well as the common cold.

  • Benzoin is also utilised in the military to prevent skin loss.

  • It is employed in the extension of aliphatic aldehydes.

  • It has been shown that this essential benzoin Essential oil stimulates circulation. A positive effect on the neurological system, exhibited as anxiety but also stress alleviation, has also been recorded. It has also been shown to have an antibacterial effect on exposed wounds.


Condensation of benzoin can be done in a combination of two distinct aldehydes and also with an aldehyde as well as a ketone. In such combined benzoin condensation, the much more reactive aldehyde will eventually function as a nucleophile. Similarly, if you have an aldehyde but also a ketone combination, the aldehyde will always be a nucleophile. The benzene condensation reaction is also useful for producing cyclic compounds. Furthermore, by utilising chiral catalysts, we may produce stereoisomers with great stereoselectivity, which is critical for medicinal chemistry and indeed the production of physiologically active compounds. It should also be noted that benzoin condensation reaction is an equilibrium that may be overturned.


Q1. What exactly is benzoin gum?

Ans. Powdered Benzoin Gum, this resin, also known as gum Benjamin, is sourced from a rainforest tree that has a vanilla-like scent when cured. The substance has been used as a preservative in cosmetics products, as a fixative in incense and potpourri, as a flavouring in baked goods and other meals, so as for reducing abdominal pain, vomiting and to calm the mind.

Q2. Why then does benzaldehyde need the use of a catalyst to conduct a benzoin condensation reaction?

Ans. Often these, aldehydes slowly oxidise in air, creating carboxylic acids; however, introducing an acid into the benzoin reaction will protonate the negatively charged carbon of thiamine, killing the catalyst.

Q3. What happens when benzaldehyde is handled with KCN

Ans. When benzaldehyde reacts with an alcoholic solution of potassium cyanide, it produces benzoin. It exemplifies the Benzoin condensation reaction.

Q4. Which of the following does not experience benzoin condensation?

Ans. "Phenylethanal" doesn't condense with benzoin.

Q5. Is benzoin tincture safe to use?

Ans. Essentially, the danger of flask contamination is low, but precautions must be taken to reduce this little risk. Tincture of benzoin is a harmless, natural chemical that may be used to boost the efficacy but also longevity of medical tape and must be used anytime medical taping is required