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The overall reaction of the classic Claisen 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[1]. The Claisen rearrangement is a powerful Carbon -carbon bond -forming Chemical reaction discovered by Rainer Ludwig Claisen. A carbon-carbon bond is a Covalent bond between two Carbon Atoms. Organic reactions are Chemical reactions involving Organic compounds The basic Organic chemistry reaction types are Addition reactions Elimination Esters are a class of Chemical compounds and Functional groups Esters consist of an inorganic or organic Acid in which at least In Organic chemistry, a carbonyl group is a Functional group composed of a Carbon Atom double-bonded to an Oxygen In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and A ketone (pronounced as key tone) is either the Functional group characterized by a Carbonyl group (O=C linked to two other Carbon atoms or It is named after Rainer Ludwig Claisen, who first published his work on the reaction in 1881 [2] [3] . Rainer Ludwig Claisen ( January 14, 1851 &ndash January 5, 1930) was a famous German Chemist best known for his work with Year 1881 ( MDCCCLXXXI) was a Common year starting on Saturday (link will display the full calendar of the Gregorian calendar (or a Common

Contents

Requirements

At least one of the reagents must be enolizable (have an α-proton and be able to undergo deprotonation to form the enolate anion). The alpha carbon in Organic chemistry refers to the first carbon that attaches to a Functional group (the carbon is attached at the first or alpha position Deprotonation is a Chemistry term that refers to the removal of a Proton ( Hydrogen Cation H+ from a Molecule, forming Enols (also known as alkenols) are Alkenes with a Hydroxyl group affixed to one of the carbon atoms composing the Double bond. There are a number of different combinations of enolizable and nonenolizable carbonyl compounds that form a few different types of Claisen condensations. The Claisen condensation (not to be confused with the Claisen rearrangement) is a Carbon-carbon bond forming reaction that occurs between two Esters

The base used must not interfere with the reaction by undergoing nucleophilic substitution or addition with a carbonyl carbon. In Chemistry, a nucleophile (literally nucleus lover as in nucleus and phile) is a Reagent that forms a Chemical bond to In organic and Inorganic chemistry, nucleophilic substitution is a fundamental class of Substitution reaction in which an "electron rich" In Organic chemistry, a nucleophilic addition reaction is an Addition reaction where in a Chemical compound a π bond is removed by the creation For this reason, the conjugate sodium alkoxide base of the alcohol formed (e. An alkoxide is the Conjugate base of an Alcohol and therefore consists of an organic group bonded to a negatively charged Oxygen atom g. sodium ethoxide if ethanol is formed) is often used, since the alkoxide is regenerated. In mixed Claisen condensations, a non-nucleophilic base such as lithium diisopropylamide, or LDA, may be used, since only one compound is enolizable. As the name suggests a non-nucleophilic base is an organic base that is a very Strong base but at the same time a poor Nucleophile. Lithium diisopropylamide is the Chemical compound with the formula 2NLi 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.

The alkoxy portion of the ester must be a good leaving group. A leaving group is an Atom or group of atoms that detaches from a chemical substance Methyl and ethyl esters, which yield the methoxy and ethoxy leaving groups, respectively, are usually used. In Chemistry, a methyl group is a Hydrophobic Alkyl Functional group named after Methane (4 In Chemistry, an ethyl group is an Alkyl Functional group derived from Ethane ( C 2 H 6

Types


The classic Claisen condensation, where only one enolizable ester is used.


The mixed (or "crossed") Claisen condensation, where an enolizable ester or ketone and a nonenolizable ester are used.


The Dieckmann condensation, where a molecule with two ester groups reacts intramolecularly, forming a cyclic β-keto ester. The Dieckmann condensation is the Intramolecular Chemical reaction of di Esters with base to give β-ketoesters Intramolecular in Chemistry describes a process or characteristic limited within the structure of a single Molecule; a property or phenomenon limited to the extent In Organic chemistry, a cyclic compound is a compound in which a series of carbon atoms are connected to form a loop or ring In this case, the ring formed must not be strained, usually a 5- or 6-membered ring. Ring strain is an Organic chemistry term that describes the destabilization of a cyclic Molecule —such as a Cycloalkane —due to the non-favorable high

Mechanism

In the first step, the ester with the α-proton is deprotonated by the base, resulting in the enolate anion, made relatively stable by the delocalization of electrons. In chemistry delocalized electrons are Electrons in a Molecule that are not associated with a single Atom or to a Covalent bond. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Then, the carbonyl carbon of the other ester undergoes nucleophilic attack by the α-carbon of the enolate. The alkoxy group leaves (resulting in regeneration of the alkoxide), and aqueous acid (e. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are g. sulfuric or phosphoric acid) is added to neutralize the base and any enolate still present. Sulfuric (or sulphuric acid, H 2 S[[oxygen O]]4 is a strong Mineral acid. Phosphoric acid, also known as orthophosphoric acid or phosphoric(V acid, is a mineral (inorganic acid having the Chemical formula The newly-formed β-keto ester or β-diketone is then isolated.

Stobbe condensation

The Stobbe condensation [4] is a modification specific for the diethyl ester of succinic acid requiring less strong bases [5]. Esters are a class of Chemical compounds and Functional groups Esters consist of an inorganic or organic Acid in which at least Succinic acid ( IUPAC Systematic name: butanedioic acid; historically known as spirit of amber) is a Dicarboxylic acid. An example is its reaction with benzophenone [6]:

Stobbe condensation


A reaction mechanism which explains the formation of both an ester group and a carboxylic acid group is centered around a lactone intermediate (5):

Stobbe condensation mechanism

See also

References

  1. ^ Carey, Francis A. Benzophenone is the Organic compound with the formula ( C 6 H 52C O, generally abbreviated Ph 2CO Chemistry, a reaction mechanism is the step by step Sequence of Elementary reactions by which overall Chemical change occurs. Carboxylic acids are Organic acids characterized by the presence of a Carboxyl group, which has the formula -C(=OOH usually written -COOH or -CO2H lactone is a cyclic Ester in Organic chemistry. It is the condensation product of an Alcohol group and a Carboxylic acid An Aldol condensation is an Organic reaction in which an Enolate ion reacts with a Carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone followed (2006). Organic Chemistry, Sixth Edition, New York, NY: McGraw-Hill. ISBN 0-07-111562-5.  
  2. ^ Claisen, L. , and A. Claparede. Ber. Deut. Chem. Ges. , 1887, 14, 2460.
  3. ^ Claisen, L. Ber. Deut. Chem. Ges. , 1887, 20, 655.
  4. ^ Hans Stobbe, Ann. , 308, 89 (1899).
  5. ^ March, Jerry (1985). Advanced Organic Chemistry, Reactions, Mechanisms and Structure, third Edition, John Wiley & Sons. ISBN 0-471-85472-7.  
  6. ^ Organic Syntheses, Coll. Organic Syntheses is a Scientific journal that since 1921 has provided the Chemistry community with annual collections of detailed and checked procedures Vol. 4, p. 132 (1963); Vol. 30, p. 18 (1950). http://www.orgsynth.org/orgsyn/pdfs/CV4P0132.pdf

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