ORGANIC CHEMISTRY II
ORGANIC CHEMISTRY II CH 318N
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This 19 page Class Notes was uploaded by Brady Spinka on Monday September 7, 2015. The Class Notes belongs to CH 318N at University of Texas at Austin taught by Staff in Fall. Since its upload, it has received 9 views. For similar materials see /class/181884/ch-318n-university-of-texas-at-austin in Chemistry at University of Texas at Austin.
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Date Created: 09/07/15
Lecture 22 The Aldol Condensation RCH2C3H CHCH OH R Mil 8 2008 Chemistry 315w Y Classical Claisen Condensation 1NaOCH20H3 ZCHsCOCHZCHs W CHsCCHZCOCHZCHs 393 a Two moles of ethyl acetate condense to give ethyl aceloacelale 0r aceloacelz39c ester Chemistry 318N I lnz ramolecular Claisen Condensation The Dieckmann Reaction Chemistry 318N Y Example CHscHZOCCH20H20H20H2000HZCH3 1 NaOCHZCHs 2 H30 0 0 COCHZCHE Chemistry 318N I via CH30H2000H20H20H20H2000H20H3 NaOCHZCHs CH30HZOCCHchchchCOCHchs Chemistry 318N Y via CH30HZOCCHchchchCOCHchs Chemistry 318N I via 6 CH CH O 3 3 3 2 5 C H20 CHCOCH20H3 Hzc CHz CH30HZOCCHchchchCOCHchs Chemistry 318N Y via 5 CHscHzo 3 3 quot oo o C O H20 CHCOCH20H3 Hzc CHz Chemistry 318N I via D 6 CH CH O z z 3 2quot C H20 CHCOCH20H3 Hzc CHz 5 II 5 C CH30H29 H20 CHCOCHZCHs H20 C39 aemistry 318N Y The Signature of the Claisen Condenstion Bketoesters O O RCH2COCH3 gt R CH2 c IZH c OCH3 R The Dieckmann Reaction works well for 5 6 and 7 membered rings not at all for 4 or 9 and poorly for 8 Chemistry 318N I Acetoacetic Ester synthesis gives symmetrically substituted acetones t it it A CHf c7 OCHZCHj H A7 CHf c7 TE c7 OCHZCHj A Hid Heat ELLEHZ A lt A7 CHf c7 CH2 co2 HOCHZCHJ Acetone A quotit i i Alkylation of Acetoacetic Ester 0 o o o H o HSC Q OCHzCHz a CHgigi iHig OCHZCHg aw 20 CHgigi igiocHZCHg H 2 Pa A 1CH3CHZO39 2 3L quotBco B Bi i HO a lt 1 H3 3 ice iC7COOH B CHgici iciocHzCHg H eat Z Heat Chemistry 318N E Acetoacetic Ester Synthesis an Example 0 R1 CH3C CH R2 Chemistry 318N Y Ketone Synthesis Let s work other examples together 0 0 CH7 CH3 CH3 Chemistry 318N E Note the Signature of these routes 0 Symmetrically substituted acetone 0 Unsymmetrical Substitution of acetone 0 Please carefully consider the stoichiometry of the reactions test questions Chemistry 318N Y Ketone Synthesis Let s work another example together From ethyl acetate only let s make this Chemistry 318N I The Malonic Ester Synthesis Versatile Synthesis of Carboxylic acids 0 I l H C RV OH A substituted acetic acid Chemistry318N Y Malonic Ester C 0 C H H oMalom39c ester is another name for diethyl malonate CH30H20 OCH20H3 oThe quotmalonic ester synthesisquot uses diethyl malonate as a reactant for the preparation of carboxylic acids Chemistry 318N I alkylation O O CH30HZOCCHchCH20H3 1 NaOCHZCHs 2 CHsBr CHscHzocCIDHCOCHZCHs CH3 Chemistry318N Y O 0 CHscHzocCIDHCOCH20H3 CH3 1 NaOCH CH dlalkylatlon 2 3 2 CH3CH2BCHzBr CHscHzocCCOCHchs CH3CH2BCH2 CH3 Chemistry 318N Y 00 CHsCHZOCCCOCHZCHs CH3CH2BCH2 CH3 1 NaOH H20 2 H 3 heat 002 CH3CH2BCH2C3HCOH CH3 Chemistry 318N Y Decarboxylation o Thennal decarboxylation of malonic acids also involves rearrangement of siX electrons in a cyclic sixmembered transition state H H O O Equot t 3 CH 33 3 s I 339 39 2 z c o HO CH o H H H enolofa carboxylic acid Chemistry 318N E Summary Claisen Condensation give B ketoesters Unsymmetrical requires no X hydrogen B ketoesters can be easily alkylated Hydrolysis of Bketoesters gives B ketoacids B ketoacids undergo facile decarboxylation to give ketones Resulting ketones are acetones that can have 3 substituents Malonic ester can be readily alkylated Hydrolysis and decarboxylation of malonates gives acetates oooqchIAwN Watch for disguised acetones and disguised acetic acids Chemistry 318N Y Examples of Malonic Ester Synthesis 0 Work backwards Chemistry 318N I How far can you expand this web 0 7 o II 0 new GR New 0 I LiAIH4 c 0 0 r lt R H3 0 0 II II oreco gt Chemistry 318N Y Interconversions 0 Problem show reagents and experimental conditions to bring about each reaction 0 PhCH2llCI 6 t1 ii PhCH NH PhCH2 OHQ 9 2 2 PhCszOCH3 L PhCH2 H2NH2 o V 63 PhCH2 CH2 0H 4 PhCH2 EH Chemistry 318N The Aldol Reaction 0 An important reaction of enolate anions is nucleophilic addition to the carbonyl group of another molecule of the same or different compound Claisen Condensation is but one example The Aldol is another 0 Actually the Aldol reaction may be catalyzed by either acid or base but base catalysis is more common Chemistry 318N Y The Aldol Reaction 0 The product of an aldol reaction is a Bhydroxyaldehyde nucleophilic acyl substitution is not possibe here why H 0 OH 0 I M NaOH Bl a H CH3 CH CH2 CH CH3 CHCH 2 CH Ethanal Ethanal 3Hydr0xybutanal Acetaldehyde Acetaldehyde a 3hydr0xya1dehyde Aldol Aldehyde Alcohol Chemistry 318N Y The Aldol Reaction or a Bhydroxyketone I H O OH 39 OH O cHs CH 3 kHz 3m 3 Vg cH E H 23m 3 CH3 Chemistry 318N Y Base Catalyzed Aldol Reaction 0 The mechanism of the basecatalyzed aldol reaction can be divided into three steps Step 1 formation of a resonancestabilized enolate anion 0 2 HO39G HFCHzdlH 4 39 dH lt gt CH2cH 2 Enolate anion Chemistry 318N Y The Aldol Reaction base Step 2 addition of the enolate anion to the carbonyl group of another carbonylcontaining molecule to form a Tetrahedral intermediate sp3 hybridized carbon CH3 4 o 0 6 I U39CHZ H CH3 CHCH 2 0 ll CH A tetrahedal intermediate Chemistry 318N Y The Aldol Reaction base Step 3 with Reaction of the tetrahedral intermediate a proton donor gives the aldol product b o I II I ll CH3CHCH 2cH HOH f2 CHa39CH39CH 2quotH OH 0 6H Chemistry 318N E Loss of water Aldol products are very easily dehydrated so the major product is an LBunsaturated aldehyde or ketone 39OH OH H O H o I l gt CH C d C CH C C C 3 3 K H I H H H H H 39OH H OH An 13 aldehyde Chemistry 318N Y A Note about Aldol Reactions aldol reactions are reversible and particularly for ketones there is often little aldol present at equilibrium Keq for dehydration is generally large and if reaction conditions bring about dehydration good yields of product can be obtained It takes special efforts to isolate an Aldol the product is generally the LB unsaturated aldehyde or ketone Chemistry 318N E Aldol condensation O JKH M O H H 0 m v H0 91139 H HO H lt H h H Ph OHO o A H o AlgtkgtQ1H h A H H gtPh 0 Chemistry 318N Y From what Chemistry 318N I Aldol reactions of ketones 0 2 I ZCHsCCHs CHsCCHzCCHs 98 CH3 0 the equilibrium constant for aldol addition reactions of ketones is usually unfavorable but can be driven by dehydration OH O HO OH I II CH3C30H200H3 CH3C3C CCH3 CH3 CH3 Chemistry318N Y Aldol Reactions 0 Intramolecular aldol reactions when the enolate anion and the carbonyl acceptor are in the same molecule are most successful for formation of five and sixmembered rings 0 O 0 x3 051 rs ze e 6 CH3 HO CH3 CH3 27 Octanedione Chemistry 318N I
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