BSC SEM : IV Unit : VI (Organic Synthesis Via Enolates)
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Faculty : Science Department : Chemistry Course : BSC SEM : IV Unit : VI (organic synthesis via enolates) Paper : II Teacher : Dr M Karunakar Topic brief description: EAA, ME –synthesis and their chemical properties ORGANIC SYNTHESIS VIA ENOLATES: ACTIVE METHYLENE COMPOUNDS O O- -CH2-EWG -CH C CH C α- hydrogens always in acidic nature α Base can abstract these protane to form a carbanion Active methylene group Enolate (stable) Enolate = anion of enol Active methylene group Enolates are imp compds in org. synthesis for new C-C bond formation EWG EWG Carbonyl β α Ester α -Active methylene carban Ethyl Aceto Acetate (EAA) Acetyl Aceto Ester (AAE) β- keto ester imp β- keto ester Base abstract proton from ketone methyl group carbanion which generated attack upon ester carbonyl carbon H- transferred to O- Cyclo addition Ketene 2 moles EAA H Enol form Important Enol of EAA v Important 2 moles Enol and keto form of EAA Pyrogallol OR Important 1,2,3-trihydroxy benzene Enol of EAA Vii Viii iX α α α R-X Mono alkylation -------> dialkyl In this case act as strong base, alkyl halide undergo elimination Mono Acyl------------ Di acyl substituted Key thing to remember always in conversion important EAA Easy to remember imp H shifted OH H Easy to remember Applications 1. Synthesis of methyl ketones. Example: 2-butanone., 3-methyl-2-pentanone 2. Synthesis of 1, 3 di ketone(β-diketone) example: 2,4-pentanone Ketonic 1,4 diketone (γ -diketone) example: 2,5-hexadione hydrolysis 3.Synthesis carboxylic acid , mono alkyl substituted carboxylic acid, di carboxylic acid [succinic acid, glutaric acid, Adipic acid} , highter carboxylic acid 4. Synthesis of γ-Keto acid Acidic hydrolysis 5. Synthesis of α,β-unsaturated acid eg :crotonic acid hydrolysis Note: in ketonic hydrolysis(dilute Aqueos alkali /acid): prouct formed is methyl ketone derivative in acidic hydrolysis ( Concentrated ethanolic aloholic KOH sol)produce acetic acid and its derivatives Application of EAA R = alkyl gp 1. Synthesis of Methyl Ketone *Mainly depends on R-X Q: how will you synthesize 2- butanone(methyl ethyl ketone) from EAA …………………………………… 2-pentanone( methyl propyl ketone) ………. important 2- 2- butanone or Methyl ethyl ketone or 2,4-pentanone(1, 3 di ketone/ β-diketone) 1 2 3 4 5 1 Carbanion of EAA I-I imp How can be synthesize butyric acid from EAA imp How can be synthesize 2-methyl pentanoic acid from EAA Succnic acid α chloro ester H Di iodo alkane 2moles of EAA with 2 moles of base + di iodo alkane important Di iodo methane Glutaric acid(5C) Adipic acid(6C) Q: How can be syntheise Succinic acid, methyl substituted succinic acid, glutaric acid, adipic acid fromEAA β α γ Synthesis of α,β-unsaturated acid/ crotonic acid Acetaldehyde + EAA Or M E -COOH COOC2H5 α-halogenation α-Alkylation Mono alkyl di alkyl hydrolysis .