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Acetoacetic Ester Synthesis

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Acetoacetic Ester Synthesis Programme: B.Sc. B.ed. (Integrated) Course: ORGANIC CHEMISTRY- III Semester: VI Code: CHE-352 Topic: ETHYLACETOACETATEE Date- 07/04/2020 y Only PPe Dr. Angad Kumar Singh ForF Department of Chemistry, Central University of South Bihar, Gaya (Bihar) Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Ethylacetoacetate The Claisen Condensation between esters containing - hdhydrogens, promotdted byabase such as sodium ethoxy ide, toproduce a !- ketoester. One equiv serves as the nucleophilele (enolate)(eno and the other is OnlyO the electrophile which undergoes additiontion andae elimination. The use of stronger bases, e.g. sodium amide or sodiumsodUse hydride instead of sodium ethoxide, often increases the yield.d. al onal Ethylacetoacetate Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Mechanism of the Claisen Condensation The reaction is driven to product by the final deprotonation step. Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Mixed Claisen Condensation Like mixed aldol reactions, mixed Claisen condensations are useful if differences in reactivity exist betweenn they two esters as for example when one of the esters has no -hydrogenydrogOnlyO . Examples of such esters are: e Use ers excess Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Diethyl malonate Diethyl malonate may be prepared by reacting the sodium salt of chloroacetic acid with sodium cyanide, followedowedy by base hydrolysis of the resultant nitrile to give the sodiummOnlyO saltsal malonicacid. Fischer esterification gives diethyl malonate . e Use l nal Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Acidity of alpha-Hydrogens Alklkyl hdhydrogen atoms bddbonded toacarbon atom in a (lh)(alpha) position relative to a carbonyl group display unusual acidity.The pKa values for alkyl C-H bonds is typically ony thet order of 40-50, pK values for these ()alpha hydrogens is the ordero of 19-20. This can a OnlyO most easily be explained by resonancenancee stabilizations of the product carbanion, as illustrated in the diagramagramUse below. al Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. In the presence of a proton source, the product can either revert back into the starting ketone or aldehyde or can form a new product, the enol. The equilibrium reaction betweenbetww the ketone or aldehyde and the enol form is commonly referredreferr to as "keto-enol OnlyO tautomerism". The ketone or alde hy de issgen generae lly strongly fdfavored in this reaction. Use Because carbonyl groupsups arearal sp2 hybridized the carbon and oxygen both have unhybridizedized p orbitals which can overlap to form the C=O 4 bond. Personal Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. The presence of these overlapping p orbitals gives hydrogens (Hydrogens on carbons adjacent to carbonyls) special ppproperties. In pp,articular, hyygdrogens are weaklea y acidic because the conjugate base, called an enolate, is stabilizedbilizedy thoughth conjugation with the 4 orbitals of the carbonyl. The effectffeectOnlyOof the carbonyl is seen when comparing the pK for the hydrogenshydrog of aldehydes (~16-18), a Use ketones (~19-21), and esters (~23-25) tot the pK of an alkane (~50). al a Of the two resonanceceonal strstructures of the enolate ion the one whic h pllaces thenegative cPersoPehargea on the oxygen is themost stbltable. This is because the negativegative cchange will be better stabilized by the greater electronegativity of thethForF oxygen. Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Programme: B.Sc. B.ed. (Integrated) Course: ORGANIC CHEMISTRY- III Semester: VI Code: CHE-352 Topic: KETO-ENOLTAUTOMERISMO Date- 09/04/2020 y Only PPe Dr. Angad Kumar Singh ForF Department of Chemistry, Central University of South Bihar, Gaya (Bihar) Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Keto-enol TiTautomerism The acidity of hydrogens carbonyls undergo keto-enol tautomerism. Tautomers are rapidly interconvertedonvery constitutional isomers, usually distinguished by a differententOnlyO bobonding location for a labile hydrogen atom and a differentlyentlye locatedl double bond. The equilibrium between tautomers is notUse only rapid under normal conditions, but it often stronglyy favorsfaval one of the isomers (acetone, for example, is 99.999%keto tautomer). Even in such one-sided equilibria, evidence foror thehePersonalPe presence of the minor tautomer comes from the chemical behaviorehavioForF of the compound. Tautomeric equilibria are catalyzed by traces of acids or bases that are generally present in most chemical samples. Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Mechanism for Enol Formation Acid conditions OnO e 1) Protonation of the Carbonyl Use l 2) Enol formation Pe r Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. How Enols React U al Alkylation of diethyl malonateate is knownk as Malonic Ester Synthesis Malonic ester issarea a reagent sppfecificall yused in a reaction which converts alkyl halidesdes toPersonalPe carboxylic acids called the Malonic Ester Synthesis. Malonicic esteresForF synthesis is a synthetic procedure used to convert a compound into a carboxylic acid Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Sodium Malonic Ester Due to the fact that Malonicnic ester’sesteUsUse hydrogens are adjacent to al two carbonyls, they can be deprotonatedprotonnal by sodium ethoxide (NaOEt) to form Sodium Malonic Ester.r. Person Sodium Malonic Ester is an enolate, it can then be alkylated with alkyl halides. Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. After alkylation the product can be converted to a dicarboxylic acid through saponification and subsequently one of the carboxylic acids can be removed through a decarboxylation step y Only al Mechanism PersonalPe Step-1 Saponificationion For Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Step-2 Decarboxylation OnO Step-3 TtTautomeri itization e Use Alkylation of ethyl acetoacetateacetatPersPe is known as Acetoacetic Ester Synthesis The acetoaceticacetic eester synthesis allows for the conversion of ethyl acetoacetate into a methylForFt ketone with one or two alkyl groups on the alpha carbon Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Mechanism OnlyO Step-1 Deprotonation with ethoxide e Use Step-2 Alkylation via andnd SNPerPe2 Reaction For Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Step-3 Hydrolysis and decarboxylation Addition of a second alky group After the first step and additional alkylalkylk OnlyOgroup can be added prior to the decarboxylation step. Overall this allowsllowsUse for the addition of two different alkyl groups. al Note: These materials are only for classroom teaching purpose at Central University of South Bihar. All the data taken from several books, research articles including Wikipedia. Programme: B.Sc. B.ed. (Integrated) Course: ORGANIC CHEMISTRY- III Semester: VI Code: CHE-352 Topic: ALKYLATION Date- 11/04/2020 y Only PPe Dr. Angad Kumar Singh ForF Department of Chemistry, Central University of South Bihar, Gaya (Bihar) Note: These materials
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