Pinacol Pinacolone Rearrangement Process with FAQs

Q: Acetone can be converted into pinacol by-

Acetone can be converted into pinacol by Mg / Hg / H 2 O

Pinacol Pinacolone Rearrangement Process with FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:54 PM IST

Pinacol pinacolone rearrangement – Introduction

Before answering the question “what is pinacol pinacolone rearrangement?” We first need to understand the meaning of pinacol and pinacolone.

Pinacol – pinacol is a vicinal diol which has hydroxyl group (-OH) on vicinal carbon. It is a solid organic compound; white in color. It is produced when acetone undergoes pinacol coupling reaction. Because it is a vicinal diol, pinacol undergoes rearrangement when heated with sulfuric acid to form pinacolone. Pinacol reacts with boron and boron trichloride to give useful synthetic intermediates like pinacolborane, pinacol chloroborane and bis(pinacolato)diboron. Pinacol iupac name is 2,3-dimethylbutane-2,3-diol.

Pinacol structure

Figure.1. Pinacol structure

Pinacolone – pinacolone is a ketone which is a colorless liquid with a gentle peppermint-like or camphor-like smell. The IUPAC name of pinacolone is 3, 3-dimethyl-2-butanone. Pinacolone is an unsymmetrical ketone having an alpha methyl group which can participate in condensation reactions. Being a ketone, pinacolone also has a carbonyl carbon that can undergo nucleophilic addition reactions like hydrogenation etc. Pinacol undergoes protonation to form pinacolone. In industries, pinacolone is produced by hydrolyzing 4, 4, 5-trimethyl-1, 3-dioxane which is formed in Prins reaction. When pivalic acid and acetic acid (or acetone) are ketonized in presence of metal oxide catalyst they form pinacolone. Pinacolone is also formed by converting 2,3-dimethyl-2-butene. 2-methyl-2-butanol when reacted with C₅ alcohols produce pinacolone.

Pinacolone structure

Figure.2. Pinacolone structure

Also read -

Pinacol pinacolone rearrangement (or pinacol rearrangement)

In 1860, pinacol pinacolone reaction was first illustrated by Wilhelm Rudolph Fittig. The pinacol–pinacolone rearrangement involves conversion of a 1, 2-diol to a carbonyl compound via 1, 2-shift under acidic conditions. This reaction is called pinacol pinacolone rearrangement because 1,2-diol is called pinacol and the converted carbonyl group is called pinacolone (which is a ketone). In 1, 2-shift, a functional group present on the carbon atom or C₁ is relocated on the next carbon or C₂.

Pinacol pinacolone reaction

Pinacol pinacolone rearrangement mechanism

In pinacol pinacolone rearrangement, the reaction starts with protonation of one of the alcohols of vicinal diol or 1,2-diol or pinacol. This generates an oxonium ion which has a positive charge on a highly electronegative oxygen atom. Due to destabilized oxonium ion removal of water takes place from the carbon.

This process of removal of water generates carbocation as an intermediate. Carbon with positive charge is called carbocation. This carbocation undergoes a 1,2-methyl shift. 1,2-methyl shift involves relocation of methyl groups from one carbon to another. Due to this methyl shift, a new carbocation is formed. This newly formed carbocation is resonance stabilized. Since an oxygen atom has lone pairs of electrons, a pair of electrons is migrated on the electron deficient carbocation leading to the formation of pi bond between carbon and oxygen. This newly formed carbonyl compound or ketone is called pinacolone.

Pinacol pinacolone reaction is a regioselective reaction that means in pinacol pinacolone rearrangement, the major or single product is formed due to rearrangement of carbocation which is more stable.

Related Topics,

Pinacol pinacolone reaction

One of the important characteristics of pinacol pinacolone rearrangement is that the configuration of the migration group is retained or remains unchanged.

Migratory aptitude in pinacol pinacolone rearrangement

This process is not limited to 1,2-methyl shifts. A carbon can have different types of groups attached to it. Some of the group may rearrange more readily than others. Depending on the reaction conditions and on the nature of the substrate, it could be deduced which group might migrate.

Generally, the order of migration of groups can be given as:

H > aryl > alkyl

If hydrogen is present as a migratory group, aldehydes can also be produced by undergoing 1,2-shift.

As observed, the more nucleophilic a group is, the more readily it will migrate. Order of migration in aryl groups can be given as:

p-anisyl > p-tolyl > phenyl > p –chlorophenyl

Also, students can refer,

NEET Highest Scoring Chapters & Topics

This ebook serves as a valuable study guide for NEET exams, specifically designed to assist students in light of recent changes and the removal of certain topics from the NEET exam.

Download EBook

Application of pinacol pinacolone rearrangement

There are various synthesis processes of pharmaceutical in which pinacolone; a product of pinacol pinacolone rearrangement is used:

widely used in large amounts for synthesis of pesticides, fungicides, and herbicides.
used in retrosynthetic analysis of vibunazole.
used in production of drugs like pinacidil and naminidil.
used in stritipenol; a drug used as an epilepsy medication.
used in synthesis of Diethylstilbestrol pinacolone; a nonsteroidal estrogen medication.
used in triadimefon; a fungicide used to treat fungal disease.
used in paclobutrazol; a triazole fungicide and plant growth retardant.

Also check-

NCERT Chemistry Notes:

Frequently Asked Questions (FAQs)

1. Acetone can be converted into pinacol by-

Acetone can be converted into pinacol by Mg / Hg / H₂O

2. What is pinacol?

pinacol is a vicinal diol which has hydroxyl group (-OH) on vicinal carbon. It is a solid organic compound; white in color. It is produced when acetone undergoes pinacol coupling reaction. Because it is a vicinal diol, pinacol undergoes rearrangement when heated with sulfuric acid to form pinacolone. Pinacol reacts with boron and boron trichloride to give useful synthetic intermediates like pinacolborane, pinacol chloroborane and bis(pinacolato)diboron. Pinacol iupac name is 2,3-dimethylbutane-2,3-diol.

3. What is pinacolone?

Pinacolone is a ketone which is a colorless liquid with a gentle peppermint-like or camphor-like smell. The IUPAC name of pinacolone is 3, 3-dimethyl-2-butanone. Pinacolone is an unsymmetrical ketone having an alpha methyl group which can participate in condensation reactions. Being a ketone, pinacolone also has a carbonyl carbon that can undergo nucleophilic addition reactions like hydrogenation etc. Pinacol undergoes protonation to form pinacolone. In industries, pinacolone is produced by hydrolyzing 4, 4, 5-trimethyl-1, 3-dioxane which is formed in Prins reaction. When pivalic acid and acetic acid (or acetone) are ketonized in presence of metal oxide catalyst they form pinacolone. Pinacolone is also formed by converting 2,3-dimethyl-2-butene. 2-methyl-2-butanol when reacted with C₅ alcohols produce pinacolone.

4. What is pinacol pinacolone rearrangement?

5. Why is the Pinacol-Pinacolone Rearrangement important in organic chemistry?

This rearrangement is important because it demonstrates the concept of carbocation stability and rearrangement, showcases the migration of alkyl groups, and provides a method for synthesizing valuable ketone products from diols.

6. What is the role of acid in the Pinacol-Pinacolone Rearrangement?

The acid acts as a catalyst in this reaction. It protonates one of the hydroxyl groups, making it a good leaving group (water) and facilitating the formation of a carbocation intermediate.

7. What is the key intermediate in the Pinacol-Pinacolone Rearrangement?

The key intermediate is a carbocation formed after the loss of water from the protonated diol.

8. What determines which alkyl group migrates in the Pinacol-Pinacolone Rearrangement?

The alkyl group that can best stabilize the positive charge (usually the more substituted group) tends to migrate preferentially.

9. How does the migrating group move in the Pinacol-Pinacolone Rearrangement?

The migrating group moves with its pair of electrons from one carbon to the adjacent carbon, shifting the positive charge in the process.

10. What is the Pinacol-Pinacolone Rearrangement?

The Pinacol-Pinacolone Rearrangement is an acid-catalyzed rearrangement reaction where a vicinal diol (pinacol) is converted into an α,α-disubstituted ketone (pinacolone). This reaction involves the migration of an alkyl group and the loss of water.

11. What type of compounds undergo the Pinacol-Pinacolone Rearrangement?

Vicinal diols, also known as 1,2-diols or glycols, undergo this rearrangement. The most common example is 2,3-dimethyl-2,3-butanediol (pinacol).

12. How does the mechanism of the Pinacol-Pinacolone Rearrangement begin?

The mechanism begins with the protonation of one of the hydroxyl groups by the acid catalyst, converting it into a good leaving group (water).

13. What is the driving force for the Pinacol-Pinacolone Rearrangement?

The driving force is the formation of a more stable carbocation intermediate and ultimately a more stable ketone product.

14. Can the Pinacol-Pinacolone Rearrangement occur in basic conditions?

No, this rearrangement specifically requires acidic conditions to proceed. Basic conditions would not facilitate the necessary carbocation formation.

15. Can the Pinacol-Pinacolone Rearrangement be reversed?

No, the Pinacol-Pinacolone Rearrangement is not reversible under normal conditions due to the stability of the ketone product and the loss of water.

16. Can cyclic diols undergo the Pinacol-Pinacolone Rearrangement?

Yes, cyclic diols can undergo this rearrangement, often leading to ring expansion or contraction depending on the migrating group.

17. How does the presence of different substituents on the diol affect the rate of the Pinacol-Pinacolone Rearrangement?

Electron-donating substituents generally increase the rate by stabilizing the carbocation intermediate, while electron-withdrawing groups tend to slow the reaction.

18. How does solvent choice affect the Pinacol-Pinacolone Rearrangement?

Polar protic solvents like water or alcohols can facilitate the reaction by stabilizing charged intermediates. However, the choice of solvent can also affect the rate and sometimes the product distribution.

19. Can the Pinacol-Pinacolone Rearrangement occur intramolecularly?

Yes, if a molecule contains two hydroxyl groups in the appropriate position, it can undergo an intramolecular Pinacol-Pinacolone Rearrangement.

20. How does the Pinacol-Pinacolone Rearrangement demonstrate the principle of microscopic reversibility?

The principle of microscopic reversibility suggests that the mechanism for the forward reaction (diol to ketone) should be the reverse of the backward reaction (if it were possible). This helps in understanding and predicting the reaction pathway.

21. Can the Pinacol-Pinacolone Rearrangement occur with other functional groups besides diols?

While the classic reaction involves diols, similar rearrangements can occur with other functional groups that can form carbocation intermediates, such as certain ethers or alkenes under acidic conditions.

22. What are some common side reactions in the Pinacol-Pinacolone Rearrangement?

Common side reactions include elimination to form alkenes, especially if heating is involved, or the formation of ether products if the reaction is carried out in alcoholic solvents.

23. What is the effect of temperature on the Pinacol-Pinacolone Rearrangement?

Higher temperatures generally increase the rate of the reaction but can also lead to side products. Lower temperatures may improve selectivity but slow down the reaction.

24. What are some experimental techniques used to study the mechanism of the Pinacol-Pinacolone Rearrangement?

Techniques include isotope labeling to track atom movement, kinetic studies to determine rate laws, and computational modeling to understand energy profiles and transition states.

25. How does the presence of aromatic groups affect the Pinacol-Pinacolone Rearrangement?

Aromatic groups can participate in the rearrangement, often migrating preferentially due to their ability to stabilize positive charge through resonance.

26. How does the Pinacol-Pinacolone Rearrangement relate to the concept of carbocation rearrangements in biological systems?

While not identical, this rearrangement shares similarities with certain enzyme-catalyzed rearrangements in biological systems, particularly those involving carbocation intermediates.

27. What are some strategies to control the regioselectivity of the Pinacol-Pinacolone Rearrangement?

Regioselectivity can be influenced by using bulky substituents to hinder migration of certain groups, or by introducing electron-donating or withdrawing groups to affect carbocation stability.

28. What is the stereochemistry of the Pinacol-Pinacolone Rearrangement?

The rearrangement proceeds with retention of configuration at the migrating carbon center. However, the overall stereochemistry can be complex depending on the starting material.

29. How does the structure of the starting diol affect the product of the Pinacol-Pinacolone Rearrangement?

The structure of the starting diol determines which alkyl group is more likely to migrate, influencing the structure of the final ketone product.

30. What happens to the carbon-oxygen double bond in the product of the Pinacol-Pinacolone Rearrangement?

A new carbon-oxygen double bond (C=O) is formed in the product, creating a ketone functional group.

31. What is the difference between a pinacol and a pinacolone?

A pinacol is a vicinal diol (two adjacent hydroxyl groups), while a pinacolone is an α,α-disubstituted ketone produced from the rearrangement of a pinacol.

32. How does the Pinacol-Pinacolone Rearrangement demonstrate the concept of carbocation stability?

The rearrangement showcases how carbocations can be stabilized through alkyl group migration, leading to more stable intermediates and products.

33. What type of reaction is the Pinacol-Pinacolone Rearrangement classified as?

It is classified as a rearrangement reaction, specifically a 1,2-rearrangement or shift.

34. What is the significance of the 1,2-shift in the Pinacol-Pinacolone Rearrangement?

The 1,2-shift allows for the formation of a more stable carbocation intermediate and ultimately leads to the ketone product. It demonstrates how molecules can rearrange to achieve greater stability.

35. What is the role of water in the Pinacol-Pinacolone Rearrangement?

Water acts as both a byproduct (leaving group) and a proton source in the reaction. It is eliminated from the diol during carbocation formation and can participate in proton transfer steps.

36. How does the Pinacol-Pinacolone Rearrangement compare to other carbonyl-forming reactions?

Unlike many carbonyl-forming reactions that involve oxidation, the Pinacol-Pinacolone Rearrangement forms a ketone through rearrangement without changing the overall oxidation state of the molecule.

37. What are some industrial applications of the Pinacol-Pinacolone Rearrangement?

This rearrangement is used in the synthesis of various fragrances, pharmaceuticals, and other organic compounds where α,α-disubstituted ketones are desired.

38. How does the energy profile of the Pinacol-Pinacolone Rearrangement look?

The energy profile typically shows an initial increase in energy as the carbocation intermediate forms, followed by a decrease as the more stable ketone product is formed. The overall reaction is usually exothermic.

39. How does the Pinacol-Pinacolone Rearrangement relate to other rearrangement reactions in organic chemistry?

It is similar to other carbocation rearrangements like the Wagner-Meerwein rearrangement or benzilic acid rearrangement, all of which involve the migration of alkyl groups to stabilize carbocation intermediates.

40. How can you predict the major product in a Pinacol-Pinacolone Rearrangement?

Predict the major product by identifying which alkyl group is most likely to migrate (usually the more substituted one) and considering the stability of the resulting carbocation intermediate.

41. What is the importance of orbital overlap in the Pinacol-Pinacolone Rearrangement?

Proper orbital overlap between the migrating group and the carbocation center is crucial for the rearrangement to occur. This overlap allows for the smooth transfer of electrons during the migration step.

42. How does the Pinacol-Pinacolone Rearrangement showcase the concept of neighboring group participation?

The rearrangement demonstrates neighboring group participation as the adjacent alkyl group actively participates in stabilizing the reaction intermediate by migrating to the carbocation center.

43. Can the Pinacol-Pinacolone Rearrangement be used in retrosynthetic analysis?

Yes, synthetic chemists can use this rearrangement in retrosynthetic analysis to envision how certain α,α-disubstituted ketones might be synthesized from simpler diol precursors.

44. What is the significance of the semi-pinacol rearrangement?

The semi-pinacol rearrangement is a related reaction where only one hydroxyl group is present. It showcases how similar rearrangements can occur with slight variations in the starting material.