Organic chemistry is a vast field. Almost every day, new and newer discoveries are being made, and new rules are being formed. Though these rules have their importance, have separate meanings, and have their respective applications as well, sometimes, these rules might sound or seem similar to each other. Hofmann and Zaitsev are two such people who introduced the Hofmann rule and the Zaitsev rule respectively.
Hofmann vs Zaitsev
The main difference between the Hofmann rule and the Zaitsev rule is that the Hofmann rule states that in a chemical reaction, the product which was least substituted during the process is the most stable. On the other hand, the Zaitsev rule states that in a chemical reaction, the product which was most substituted during the process is the most stable.
The full name of Zaitsev is Alexander Zaitsev. He was a Russian scientist who had made major contributions in the field of organic chemistry. He pursued his early studies at the University of Kazan where he gained a degree in economics, however, he was always interested in chemistry. While he was studying at the university, he used to study chemistry and observe chemical reactions.
Hofmann was a german chemist who was born on April 8, 1818, and died on May 5, 1892. He had made major contributions in the field of chemistry. His research work on the compound aniline played a major role in the production of aniline dye. Among all his contributions, one of the major contributions was the Hofmann rule.
Comparison Table Between Hofmann and Zaitsev
What is Hofmann?
Hofmann’s rule is also known as the elimination rule. The reason behind that is that the Hofmann rule is implied in the elimination type of reactions. More specifically, the Hofmann elimination reaction is when tertiary amines and alkenes are produced from quaternary ammonium. This reaction is also known as an exhaustive methylation reaction.
The Hofmann elimination reaction includes three different steps. In step 1, when an amine is treated along with either a beta-hydrogen or quaternary ammonium in the presence of excess methyl iodide, then the ammonium iodide salt is formed. In the second step, the iodide is reacted with silver oxide, which is followed by deprotonation of the water atom by the ion of the silver oxide, then the product which is yielded is the substituted iodide ion by the hydroxide ion.
In the last step, is step 3, the mixture which was yielded in step 2 is heated. Due to the heating, the elimination process occurs, which consequently results in the desired product. One of the most common examples of the Hofmann elimination reaction is the synthesis reaction of the trans-cyclooctene.
What is Zaitsev?
As mentioned before in the article as well, Zaitsev was very interested in the field of chemistry. Later in the time, Zaitsev introduced a rule in the field of organic chemistry, which is known as the Zaitsev rule, or also known as saytzeff rule. The rule made a major contribution in the field and became highly recognizable in the 18th and 19th centuries. Zaitsev received several different awards for his contribution to the field of organic chemistry.
Zaitsev rule is an empirical rule which is used to identify what the final product of a chemical reaction would be depending upon what product is the most substituted. The zaitsev rule is most prominent in the case of an elimination type of reaction where an alkene is supposed to be the final product. From the zaitsev rule, it is supposed that the alkene which corresponds to the removal of the hydrogen atom from the alpha carbon would be the type of alkene that will be formed in the highest amount in that particular chemical reaction.
One of the most common examples in which the zaitsev rule is followed is that when the compound 2-iodobutane is reacted in the presence of alcoholic potassium hydroxide, then 2 different products will be formed, which are, 2-butene and 1-butene. According to the Zaitsev rule, 2-butene will be the major product formed and 1-butene will be the minor product.
Main Differences Between Hofmann and Zaitsev
- Hoffman’s rule was introduced by August Wilhelm Von Hofmann. Whereas, the Zaitsev rule was introduced by Alexander Zaitsev.
- Hofmann’s rule states that the least substituted product is the most stable. On the other hand, the Zaitsev rule states that the most substituted product is the most stable.
- In Hofmann’s rule, elimination is done from the beta carbon which has the least hydrogen substitutes available. On the contrary, in the zaitsev rule, elimination is done from the alpha carbon which has the most hydrogen substitutes available.
- The Hofmann rule was introduced in 1851. The Zaitsev rule was introduced in 1875.
- An example of the Hofmann reaction is when alkene is formed from a tertiary amine that has the most substituted carbon atoms in a double bond. Whereas, one example of the Zaitsev rule is when 2-butene is formed as a major product from 2-iodobutane.
Conclusion
Though both types of reactions, that is, the Hofmann rule and the Zaitsev rule are two different rules. The statements of both these rules are applied in different cases. The major difference between the two rules lies in their statement, their meaning, and their application as well. Though both the statements might seem similar, it is important to have a clear understanding of both the rules to understand their applications, and consequently, their differences.
References
- https://link.springer.com/article/10.1007/s10608-012-9476-1
- https://www.sciencedirect.com/science/article/pii/0012821X8890132X