Wolff-Kishner Reduction Mechanism

Aldehydes and ketones are converted to alkanes in an organic reaction known as the percent. Carbonyl compounds that are stable under strongly basic conditions can be quickly reduced to alkanes (The carbon-oxygen double bond converts into two carbon-hydrogen single bonds). While the process usually begins with the condensation of hydrazine to form hydrazone, using a preformed hydrazone may have advantages such as faster reaction times, room-temperature reactions, or extremely mild reaction conditions. The preformed hydrazone substrates that can be used in this reduction require different solvents and reaction temperatures.

The Wolff–Kishner reduction reaction is used in organic chemistry to convert carbonyl functionalities to methylene groups. Because it necessitates extremely simple conditions, the Wolff–Kishner reduction is incompatible with base-sensitive substrates. In some cases, sterically hindered carbonyl groups will fail to form the required hydrazone, preventing the reaction from taking place. This approach may be superior to the associated Clemmensen reduction for compounds with acid-sensitive functional groups, such as pyrroles, and for high-molecular-weight compounds.

In 1911 and 1912, N. Kishner and Ludwig Wolff independently discovered the Wolff Kishner reaction. When pre-formed hydrazone was added to hot potassium hydroxide with crushed platinized porous plate, Kishner discovered that the corresponding hydrocarbon was formed.

Mechanism of the Wolff-Kishner Reduction Reaction

Step 1: Szmant and colleagues looked into the Wolff–Kishner reduction’s mechanism. According to Szmant’s research, the first step in this reaction is the formation of a hydrazone anion 1 by deprotonation of the terminal nitrogen by MOH. Semicarbazones are converted into the corresponding hydrazone before being deprotonated because they are used as substrates. According to a variety of mechanistic results, the formation of a new carbon-hydrogen bond at the carbon terminal in the delocalized hydrazone anion appears to be the rate-determining step.

Step 2: The terminal nitrogen atom is deprotonated, and the nitrogen atom next to it forms a double bond. In the basic environment, the proton that has been released binds to the hydroxide ion to form water.

Step 3: The water molecule protonates the carbon, because oxygen withdraws more electrons than carbon.

Step 4: The terminal nitrogen is once again deprotonated, forming a triple bond with the nitrogen atom next to it. The carbanion is formed when the two triple-bonded nitrogens are released as nitrogen dioxide. Similar to phase 2, the ejected proton reacts with the basic atmosphere to form water.

Step 5: Water protonates the carbon, resulting in the formation of the desired hydrocarbon product as shown, similar to step 3 of the Wolff Kishner reduction process. The aldehyde or ketone is transformed into an alkane as a result.

The rate-determining step in this reaction is the formation of a bond between the terminal carbon and hydrogen (in the hydrazone anion). Substitutes that are mildly electron-withdrawing aid in the formation of carbon-hydrogen bonds. Highly electron-withdrawing substituents reduce the negative charge of the terminal nitrogen, making it more difficult to split the N-H bond. Many techniques have been adapted from the Wolff Kishner reduction, each with its own set of benefits and drawbacks. The Huang Minlon modification, for example (which uses the carbonyl compound, 85 percent hydrazine, and potassium hydroxide as the reagent) allows for faster reaction times and higher temperatures, but it requires distillation.

Did You Know?

Clemmensen reduction is a chemical reaction that uses zinc amalgam and concentrated hydrochloric acid to convert ketones (or aldehydes) to alkanes. This reaction was inspired by Danish chemist Erik Christian Clemmensen. The original Clemmensen reduction conditions react well with aryl-alkyl ketones, such as those produced in a Friedel-Crafts acylation. A two-step sequence of Friedel-Crafts acylation followed by Clemmensen reduction is a classic method for primary alkylation of arenes. With aliphatic or cyclic ketones, modified Clemmensen conditions using activated zinc dust in an anhydrous solution of hydrogen chloride in diethyl ether or acetic anhydride are much more successful.

Clemmensen Reduction vs. Wolff-Kishner Reaction: What’s the Difference?

By reducing the functional groups, both Clemmensen Reduction and Wolff-Kishner processes work. As a result, for the process to work properly, both reactions must meet specific conditions and catalysts. Clemmensen Reduction and Wolff-Kishner Reactions differ in the following ways: We try to convert ketones and aldehydes into an alkane using the Clemmensen reduction reaction. The Wolff-Kishner reaction, on the other hand, is used to convert a carbon functional group into a methylene group.

We use amalgamated zinc as a catalyst in the Clemmensen reduction process. The Wolff-Kishner Reduction, on the other hand, does not require the use of a catalyst.

Clemmensen and Wolff-Kishner Reactions differ in that the former works under highly acidic conditions, making it unsuitable for acid-sensitive substrates. The Wolff Kishner reduction reaction, on the other hand, uses basic conditions, making it incompatible with base-sensitive substrates.

Wolff-Kishner Reduction Mechanism’s advantages

You will benefit greatly from learning the Wolff-Kishner Reduction Mechanism. It is one of the most important concepts in chemistry, which is why you should understand it thoroughly. Before you begin working with the Wolff-Kishner Reduction Mechanism, go over the textbook explanations of the concept. It will give you a better understanding of the concept and why it is important in Chemistry. Additionally, you should use the exercise questions to test your knowledge and see if you understand the Wolff-Kishner Reduction Mechanism. Some of the benefits of learning the Wolff-Kishner Reduction Mechanism are listed below:

You’ll learn how to convert a carbon functional group into a methylene functional group using the Wolff-Kishner Reduction Mechanism.

You can improve your knowledge of organic chemistry, which is an important part of the Chemistry curriculum, by understanding the Wolff-Kishner Reduction Mechanism.

You won’t have to go over the entire chapter again during your revisions and exam preparations once you’ve learned the Wolff-Kishner Reduction Mechanism.

The Wolff-Kishner Reduction Mechanism is a crucial concept in chemistry, with a significant weighting in the final exam. As a result, if you improve your understanding of the Wolff-Kishner Reduction Mechanism, you will do well on your exams.

You’ll be able to tell the difference between this organic reaction and the Clemmensen reduction reaction after thoroughly studying the Wolff-Kishner Reduction Mechanism.

Conclusion

The Wolff Kishner reduction has been modified into several techniques, each with its own set of benefits and drawbacks. For example, the Huang Minlon modification (which uses the carbonyl compound, 85 percent hydrazine, and potassium hydroxide as the reagent) allows for a faster reaction time and higher temperatures, but it necessitates distillation. It is one of the most important concepts in chemistry, which is why you should understand it thoroughly. Before you begin working with the Wolff-Kishner Reduction Mechanism, go over the textbook explanations of the concept. It will give you a better understanding of the concept and why it is important in Chemistry.