Legal. From mechanism it can be seen that, to perform Claisen condensation reaction reactant should have alpha hydrogen, here as reactant (C H 3 ) 3 C C O O E t dont have any … Instead, an alkoxide version of the alcohol used to synthesize the ester is used to prevent transesterification side products. For this reason, the conjugate sodium alkoxide base of the alcohol formed (e.g. In mixed Claisen condensations, a non-nucleophilic base such as lithium diisopropylamide, or LDA, may be used, since only one compound is enolizable. a. During the reaction a new carbon-carbon bond is formed. Claisen condensations between different ester reactants are called Crossed Claisen reactions. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. Instead, an alkoxide version of the alcohol used to synthesize the ester is used to prevent transesterification side products. Because esters can contain alpha hydrogens, they can undergo a condensation reaction similar to the aldol reaction called a Claisen Condensation. Have questions or comments? The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. Prof. Steven Farmer (Sonoma State University). 22. Methyl and ethyl esters, which yield the methoxy and ethoxy leaving groups, respectively, are usually used. Claisen Condensation. A major difference with the aldol reaction is the fact that hydroxide cannot be used as a base because it could possibly react with the ester. Which cannot be used in a Claisen condensation? Which cannot be used in a Claisen condensation? It is named after Rainer Ludwig Claisen, who first published his work on the reaction in 1887. • The esters having active methylene group (- CH. The product is a β-keto ester. two esters, both with alpha hydrogens one ester with an alpha hydrogen and one ester without an alpha hy. A. Dr. Dietmar Kennepohl FCIC (Professor of Chemistry, Athabasca University), Prof. Steven Farmer (Sonoma State University). The Claisen condensation can be used as one step in the synthesis of ketones, as illustrated by this reaction sequence 1. The alkoxy portion of the ester must be a good leaving group. Because of this most Crossed Claisen reactions are usually not performed unless one reactant has no alpha hydrogens. 1. LDA cannot be used in the classic Claisen or Dieckmann condensations, since virtually all ester will be converted to ester enolate and condensation will not occur. As C 6 H 5 - COOC 2 H 5 has no α-hydrogen atom or active methylene group, so it cannot undergo Claisen- Condensation reaction. Cloudflare Ray ID: 5f7cbd09e8ca05ed In this case, the ring formed must not be strained, usually a 5- or 6-membered chain or ring. The alkoxy group leaves (resulting in regeneration of the alkoxide), and aqueous acid (e.g. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. At least one of the reagents must be enolizable (have an α-proton and be able to undergo deprotonation to form the enolate anion). A major difference with the aldol reaction is the fact that hydroxide cannot be used as a base because it could possibly react with the ester. • The esters having active methylene group (- CH 2 -), show Claisen Condensation reaction. Example 1: Claisen Condensation. Then, what kind of bases are used in Claisen condensation? Bases such as LDA (lithium diisopropylamide) and NaH (sodium hydroxide) are frequently used in the synthesis of enolates, not only in Claisen condensation but also in other processes. The Claisen condensation reactions of methyl acetate and methyl propanoate are shown as examples. A. two esters, both without alpha hydrogens B. one ester with an alpha hydrogen and one ester without an alpha hydrogen C. two esters, both with alpha hydrogens D. all of these E. none of these 23. Instead, an alkoxide version of the alcohol used to synthesize the ester is used to prevent transesterification side products. To use all the functions on Chemie.DE please activate JavaScript. With an accout for my.chemeurope.com you can always see everything at a glance – and you can configure your own website and individual newsletter. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. The Dieckmann condensation, where a molecule with two ester groups reacts intramolecularly, forming a cyclic β-keto ester. H3O+ OH, 26. Which one of the following compounds would favor the enol tautomer over the ketone tautomer? Then, the carbonyl carbon of the other ester undergoes nucleophilic attack by the α-carbon of the enolate. Eto Na 2. Find out more about the company LUMITOS and our team. The R group of the ester starting material, the alkoxide base, and the alcohol solvent are chosen to be the same to not end up with a mixture of products. Which of the following esters cannot give claisen Condensation in the presence of C2H5ONA. Claisen condensations between different ester reactants are called Crossed Claisen reactions. If you are at an office or shared network, you can ask the network administrator to run a scan across the network looking for misconfigured or infected devices. b. Draw the bond-line structures for the products of the following reactions. There are a number of different combinations of enolizable and nonenolizable carbonyl compounds that form a few different types of Claisen condensations. 19.15: A Claisen Condensation Forms a β-Keto Ester. It is named after Rainer Ludwig Claisen, who first published his work on the reaction in 1881. Which one of the following esters cannot undergo Claisen self-condensation? Watch the recordings here on Youtube! Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. Missed the LibreFest? Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE. Students (upto class 10+2) preparing for All Government Exams, CBSE Board Exam, ICSE Board Exam, State Board Exam, JEE (Mains+Advance) and NEET can ask questions from any subject and get quick answers by subject teachers/ experts/mentors/students. Self condensation of two moles of ethyl acetate in presence of sodium ethoxide yields. © 2003-2020 Chegg Inc. All rights reserved. You may need to download version 2.0 now from the Chrome Web Store. Claisen Condensation . For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. During the reaction a new carbon-carbon bond is formed; the product is a β-keto ester. 21.9: The Claisen Condensation Reactions of Esters, [ "article:topic", "showtoc:no", "transcluded:yes", "source-chem-45969" ], 21.8: The Aldol Reaction and Condensation of Ketones and Aldehydes, 21.10: Conjugate Additions: The Michael Reaction. The Dieckmann condensation, where a molecule with two ester groups reacts intramolecularly, forming a cyclic β-keto ester. A. two esters, both without alpha hydrogens B. one ester with an alpha hydrogen and one ester without an alpha hydrogen C. two esters, both with alpha hydrogens D. all of these E. none of these. In a fashion similar to the aldol, one ester acts as a nucleophile while a second ester acts as the electrophile. &

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