310_9 - Organic Lecture Series CH 310 N LECTURE 9 Textbook...

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Organic Lecture Series 1 CH 310 N LECTURE 9 Textbook Assignment: Chapter 17 Carboxylic Acids Homework (for credit): Problem set-none this week Today’s Topics: Nomenclature; structure & properties Notice & Announcements: EXAM 1: Grading in Progress Organic Lecture Series 2 Aldehydes Aldehydes And And Ketones Ketones
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Organic Lecture Series 3 • Catalytic reductions are generally carried out at from 25° to 100°C and 1 to 5 atm H 2 + 25 o C, 2 atm Pt Cyclohexanone Cyclohexanol O OH H 2 1-Butanol trans- 2-Butenal (Crotonaldehyde) 2H 2 Ni H O Note: Both the olefin and the carbonyl are reduced Catalytic Reduction Catalytic Reduction Organic Lecture Series 4 2
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Organic Lecture Series 5 • A carbon-carbon double bond may also be reduced under these conditions: – by careful choice of experimental conditions, it is often possible to selectively reduce a carbon-carbon double in the presence of an aldehyde or ketone 1-Butanol trans- 2-Butenal (Crotonaldehyde) 2H 2 Ni H O OH OO H RCH=CHCR' RCH=CHCHR' 1. NaBH 4 2. H 2 O O H 2 Rh RCH 2 CH 2 CR' O + Catalytic Reduction Catalytic Reduction Organic Lecture Series Clemmensen Clemmensen Reduction Reduction – refluxing an aldehyde or ketone with amalgamated zinc in concentrated HCl converts the carbonyl group to a methylene group – Classic reaction but harsh conditions limit its use Zn(Hg), HCl OH O
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Organic Lecture Series 7 Wolff Wolff -Kishner Kishner Reduction Reduction – in the original procedure, the aldehyde or ketone and hydrazine are refluxed with KOH in a high-boiling solvent – the same reaction can be brought about using hydrazine and potassium tert- butoxide in DMSO (Di- methyl sulfoxide) + diethylene glycol (reflux) KOH N 2 Hydrazine + H 2 NNH 2 + H 2 O O C O H(R) R C H H R Carbonyl Hydrocarbon H(R) N 2 H 4 ;KOH heat; HO O OH Organic Lecture Series 8 Racemization Racemization • Racemization at an α -carbon may be catalyzed by either acid or base • Once stereochemistry is set, this is usually an undesirable side reaction. O Ph OH O An achiral enol ( R )-3-Phenyl-2- butanone ( S
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Organic Lecture Series 9 α -Halogenation Halogenation ¾ α -Halogenation: aldehydes and ketones with at least one α -hydrogen react at an α - carbon with Br 2 and Cl 2 – reaction is catalyzed by both acid and base Caution!! These are lachrymators O Br 2 CH 3 COOH O HBr Acetophenone + + α -Bromo- acetophenone Organic Lecture Series 10 α -Halogenation Halogenation • Acid-catalyzed α -halogenation Step 1: acid-catalyzed enolization- forms the enol enol Step 2: nucleophilic attack of the enol on halogen Step 3: (not shown) proton transfer to solvent completes the reaction H R R' -C- C- R O R' CC H-O R R slow C R R H-O C O R R H Br: - + fast +
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Organic Lecture Series 11 α -Halogenation Halogenation • Base-promoted α -halogenation Step 1: formation of an enolate enolate anion anion Step 2: nucleophilic attack of the enolate anion on halogen •• + - - Resonance-stabilized enolate anion + slow OH R O CC R' O: R'-C-C-R - : H 2 O R R R R + fast OB r R R Br + - R R Organic Lecture Series 12 α -Halogenation Halogenation
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This note was uploaded on 11/21/2011 for the course CH 51455 taught by Professor Colapret during the Spring '11 term at University of Texas at Austin.

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310_9 - Organic Lecture Series CH 310 N LECTURE 9 Textbook...

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