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. Claisen condensations between different ester reactants are called Crossed Claisen reactions. HCl, H2O NaOH, H20 Heat HCI, H2O Heat compoun da compound b-: compound c (C5H8O) Work out this synthesis on a separate sheet of … Example 1: Claisen Condensation. 22. The Claisen condensation can be used as one step in the synthesis of ketones, as illustrated by this reaction sequence 1. Predict the product for the following reaction. Which of the following will not undergo aldol condensation? The Claisen condensation (not to be confused with the Claisen rearrangement) is a carbon-carbon bond forming reaction that occurs between two esters or one ester and another carbonyl compound in the presence of a strong base, resulting in a β-keto ester or a β-diketone. Cloudflare Ray ID: 5f7cbd09e8ca05ed Which one of the following compounds would favor the enol tautomer over the ketone tautomer? It is named after Rainer Ludwig Claisen, who first published his work on the reaction in 1887. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Eto Na 2. Dr. Dietmar Kennepohl FCIC (Professor of Chemistry, Athabasca University), Prof. Steven Farmer (Sonoma State University). Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE. An interamolecular Claisen condensation is called a _____. Find out more about the company LUMITOS and our team. Draw the bond-line structures for the products of the following reactions. Legal. Which cannot be used in a Claisen condensation? Predict the product for the following reaction. 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. 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 of the following compounds cannot serve as a Michael acceptor? Claisen Condensation . Which of the following esters cannot give claisen Condensation in the presence of C2H5ONA. Watch the recordings here on Youtube! CH3CH2Br C. D. IV E. V. 22. 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. Then, what kind of bases are used in Claisen condensation? LDA is a bulky base, as shown below. Which Cannot Be Used In A Claisen Condensation? condensation? • Why is it important to use NaOCH 3 and not NaOCH 2 CH 3 ? Which cannot be used in a Claisen condensation? A diester can undergo an intramolecular reaction called a Dieckmann condensation. To use all the functions on Chemie.DE please activate JavaScript. 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. identify the product formed in a given Claisen condensation reaction. Methyl and ethyl esters, which yield the methoxy and ethoxy leaving groups, respectively, are usually used. The esters having active methylene group (- CH 2 -), show Claisen Condensation reaction. Missed the LibreFest? sodium ethoxide if ethanol is formed) is often used, since the alkoxide is regenerated. 19.15: A Claisen Condensation Forms a β-Keto Ester. NaH is also … Crossed Claisen reactions in which both reactants can serve as donors and acceptors generally give complex mixtures. The mixed (or "crossed") Claisen condensation, where one enolizable ester or ketone and one nonenolizable ester are used. Instead, an alkoxide version of the alcohol used to synthesize the ester is used to prevent transesterification side products. 13. Privacy 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. Which one of the following esters cannot undergo Claisen self-condensation? b. Predict the final product for the following reaction sequence. If you are on a personal connection, like at home, you can run an anti-virus scan on your device to make sure it is not infected with malware. | Your browser does not support JavaScript. 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 base used must not interfere with the reaction by undergoing nucleophilic substitution or addition with a carbonyl carbon. Legal. Have questions or comments? Because of this most Crossed Claisen reactions are usually not performed unless one reactant has no alpha hydrogens. 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. There are a number of different combinations of enolizable and nonenolizable carbonyl compounds that form a few different types of Claisen condensations. For this reason, the conjugate sodium alkoxide base of the alcohol formed (e.g. LDA, -78°c 2. If a Claisen condensation reaction is run using methyl propanoate as the reactant, NaOCH 3 is the ideal base. The Claisen condensation reactions of methyl acetate and methyl propanoate are shown as examples. Due to its large steric hindrance, LDA has almost no nucleophilic properties and acts only as a base. Then, the carbonyl carbon of the other ester undergoes nucleophilic attack by the α-carbon of the enolate. Which one of the following is a major product in a Claisen condensation? It is named after Rainer Ludwig Claisen, who first published his work on the reaction in 1881. Instead, an alkoxide version of the alcohol used to synthesize the ester is used to prevent transesterification side products. In this case, the ring formed must not be strained, usually a 5- or 6-membered ring. 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. Have questions or comments? • Which of the following cannot be used in a Claisen condensation? Basic reaction. As C6H5- COOC2H5 has no α-hydrogen atom or active methylene group, so it cannot undergo Claisen- Condensation reaction. 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. © 1997-2020 LUMITOS AG, All rights reserved, https://www.chemeurope.com/en/encyclopedia/Claisen_condensation.html, Your browser is not current. 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. Transesterfication can occur when esters react, and this transesterfication would result in a mixture of products. Claisen condensations between different ester reactants are called Crossed Claisen reactions. Because esters can contain alpha hydrogens, they can undergo a condensation reaction similar to the aldol reaction called a Claisen Condensation. Self condensation of two moles of ethyl acetate in presence of sodium ethoxide yields. The esters having active methylene group (- CH. A. α-keto ester B. γ-hydroxy ester C. β-diketone D. β-keto ester E. β-hydroxy ester.
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