ALDOL CONDENSATION Traya Traya Levie Grace M. Abstract : The purpose of this laboratory experiment was to synthesize
dibenzaldehyde using aldol condensation rection between benzaldehyde and acet aceton one. e. In this this reac reacti tion on,, the the enol enolate ate ion ion of one one comp compou ound nd unde underg rgoe oes s nucleophilic addition to the carbonyl carbon of a dierent compound. Its products are usually detrimental since there is atendency of reduced yielded product due to the mixture of products. After the ltration we obtained cryst crystals als of dibenz dibenzald aldehy ehyde. de. The obtain obtained ed crysta crystals ls weighe weighed d 0.00 0.00g g and resulted to a !".#$ yield. The lower percentage yield was due to the fact that many crystals were lost during the remo%al of the sol%ent from the reaction reaction mixture mixture during the condensati condensation on of acetone acetone with benzaldeh benzaldehyde. yde. &ome crystals were also lost during the washing of crystals with water. Also, not all of the crystals remained in the lter paper. &ome was ltered right through the paper with the sol%ent and ended up in the bottom of the 'as(. These personal errors contributed to the lower percentage yield obtained. )n loophole, in theory, was that the reaction is a mixture of product thus it was expected to produce a lower yield and therefore contributed to the lower percentage yield.
INTRODUCTION
The aldol condensation relies on the reactivity of a carbonyl ro!" that can b!ild a ne# carbon$carbon bond. This reaction is considered as one of the %ost "ro&cient %ethod that is !sed to for% a carbon$ carbon bond. There are %any ty"es of aldol condensation' and for this e("eri%ent the cross aldol conden condensat sation ion #as e%"loy e%"loyed. ed. This This reaction is bet#een aldehydes and )etone tone that that "rod "rod!c !ce es a %i( %i(ed condensation "rod!cts. The "!r"ose of this e("eri%ent #as to synthesi*e synthesi*e diben*alde diben*aldehyde hyde
via via aldo aldoll cond conden ensa sati tion on react eactio ion n bet#een acetone and ben* ben*al alde dehy hyde de.. This This is by %i(i %i(in n the t#o
react reactant ants s #ith #ith NaO+ NaO+ and ethano ethanoll and and s#ir s#irle led d occa occasi sion onal ally ly for for ,%in! %in!te tes s to all allo# reacti action on.. The The crys crysta tals ls #er #ere then then coll collec ecte ted d by vac!!% <ration #hile #ashin it #ith #ith #ater #ater and chille chilled d ethanol ethanol to enco!rae recrystali*ation. recrystali*ation.
METHODOLOGY
A. *aterials+hemicals+Apparatus
This e("eri%ent !sed the follo#in: a/ -0$%L Erlen%eyer 1as)' b/ bea)er' c/ as"irator' d/ "i"ette' e/ 2!chner f!nnel' f/ <er "a"er' / #ash bottle' h/ 0.3 NaO+ in 4$%L #ater/' i/ 0.5$%L acetone ' 6/ 0.7$%L ben*aldehyde' and )/ 8-9 ethanol. -. rocedure
A sol!tion of 0.3 NaO+ in 4$%L +4O 4$%L 8-9 ethanol #as "re"ared in an Erlen%eyer 1as). The sol!tion #as then cooled. Into the sol!tion' a 0.5 %L acetone and a 0.7 %L ben*aldehyde #as added. The 1as) #as then s#irled fro% ti%e to ti%e for ,- %in!tes to allo# reaction. The "rod!ct #as then <ered !sin a 2!chner f!nnel via vac!!% <ration. The crystals #ere then #ashed #ith +4O and then #ith chilled 8-9 ethanol. The crystals #ere then #eihted and the "ercentae yield #as calc!lated.
RESULTS
The &nal "rod!ct obtained diben*aldehyde crystals fro% aldol condensation. The crystal "rod!ct #eihed 0.;00. In the calc!lation of the theoretical yield' the li%itin reaent acetone #as !sed as the basis for the theoretical val!e. In
calc!latin the theoretical yield' the follo#in calc!lations #ere %ade: Conversion: %L of A A
→ %oles of A
→ ra%s of
→ %oles of D
→ ra%s of D 0.3− mL A
x
0.731 g
A 1 mol A 1 mol D 244 g D x x x 1− mL A 58.08 g A 1 mol A 1 molD
¿ 0 . 846 g D
#here A denotes acetone and D denoted diben*aldehyde. And in the calc!lation of the "ercentae yield the follo#in calc!lation #as %ade: yield
=
yield
=
experimental value x 100 t h eoretical value 0. 700 g 0.8460 g
x 100
< 74.;39
DISSCUSSION/ INTERPRETATION OF RESULTS
Aldol condensation reactions re"resent an i%"ortant class of reaction for for%in carbon$carbon bonds. In this e("eri%ent the cross aldol condensation #as "erfor%ed. The synthesis bean #ith a stron base' NaO+' #hich #as %i(ed #ith
distilled #ater then #as !sed to react #ith eno!h ethanol. The "artic!lar reaction is an e(other%ic reaction #hich released the heat enery to the s!rro!ndin fro% the reaction. The base f!nctioned as a catalyst in the reaction. The ethanol acts as a solvent #hich allo#s the acetone and ben*aldehyde to dissolve and react #ith each other. After that' acetone and ben*aldehyde #ere %i(ed in the solvent #hich t!rns to yello# color =!ic)ly. Event!ally' the "rod!ct #as for%ed #ith a yello# "reci"itate.
>i!re 4
The acetaldehyde enolate ion attac)s the ben*ylic carbon of ben*aldehyde via n!cleo"hilic addition to for% the inter%ediate as sho#n in belo#:
>i!re 5
>i!re ,. 2efore and after addition of ben*aldehyde
Acetone is considered as a stable and !nreactive co%"o!nd' so it sho!ld be converted into anionic for% to increase its n!cleo"hile "ro"erties to initiate the reaction. The base dissolved in #ater "rod!ces hydro(ide ion and tends to attac) the ?$hydroen in acetone for% #ater %olec!le. The de"rotonation of acetone ca!sed by the enolate ion #as "rod!ced as n!cleo"hile. An enolate ion #as for%ed #hich it e(ists as resonance$stabili*ed str!ct!re that is sho#n in the follo#in &!re:
The o(yen attached to the ben*ylic "osition of carbon tends to attract one "roton fro% #ater %olec!le to for% hydro(ide ro!" in the inter%ediate. This is the for%ation of an aldol since the %olec!le consists of a carbonyl ro!" and an alcohol ro!". In the basic condition' the hydro(ide ion tends to re%ove one "roton fro% the ?$carbon res!ltin the for%ation of C
diben*aldehyde. The %echanis% of diben*aldehyde for%ation #as sho#n in the &!re :
>i!re 3
The ben*alacetone tends to for% ben*alacetone enolate ion after the hydro(ide ro!" fro% the s!rro!ndin attac) the "roton #hich attached to the carbon at ben*ylic "osition.
>i!re -
The )etone !nderone the sa%e enolate condensation reactions #ith the second %ole of ben*aldehyde since this )etone still have the
α $hydroen' #hich is
acidic' and "rod!ced the diben*aldehyde. The ben*alacetone enolate ion acts as a n!cleo"hile #hich attac)s another ben*aldehyde. The "rotonation of the aldol too) "lace follo#ed by the hydro(ide ro!"s bein eli%inated as leavin ro!"s. As a res!lt' the n!cleo"hilic addition and base$cataly*ed dehydration led to the for%ation of the desired "rod!ct #hich is
>i!re
The aldol condensation reaction bet#een acetone and ben*aldehyde yielded diben*aldehyde crystals. The "ercentae yield for the reaction #as 74.;39. The lo#er "ercentae yield #as d!e to the fact that %any crystals #ere lost d!rin the re%oval of the solvent fro% the reaction %i(t!re d!rin the condensation of acetone #ith ben*aldehyde. So%e crystals #ere also lost d!rin the #ashin of crystals #ith #ater. Also' not all of the crystals re%ained in the <er "a"er. So%e #as <ered riht thro!h the "a"er #ith the solvent and ended !" in the botto% of the 1as). These errors contrib!ted to the lo#er "ercentae yield obtained. On loo"hole' in theory' #as that the reaction is a %i(t!re of "rod!ct th!s it #as e("ected to "rod!ce a lo#er yield and therefore contrib!ted to the lo# "ercentae yield.
CONCLUSION RECCOMENDATION
AND
The "!r"ose of this e("eri%ent #as to synthesi*e diben*aldehyde thro!h aldol condensation of acetone and ben*aldehyde. The e("eri%ent yielded crystals #hich #as an indication of a s!ccessf!l e("eri%ent. Tho!h there #ere errors that res!lted to lo#er "ercentae yield it can be avoided by considerin the la"ses %entioned earlier. One thin to avoid s!ch errors is by caref!lly selectin the startin %aterials #here only one reactant has an enoli*ed
α $hydroen
and can
%ini%i*e the for%ation of %i(t!res. The other one is the "roverbial of %ost reco%%endations B handlin and "erfor%in the e("eri%ents %ore viilantly.
ANSWERS TO QUESTIONS
,. Calc!late the "ercentae yield of the reaction. yield
yield
=
=
experimental value x 100 t h eoretical value 0.700 g 0.8460 g
x 100
< 74.;39
4. Give the %echanis% involved in the reaction. Acetone has ?$hydroens on both sides/ and th!s can be de"rotonated to ive a n!cleo"hilic enolate anion. The aldehyde carbonyl is %!ch %ore electro"hilic than that of a )etone' and therefore reacts ra"idly #ith the enolate. The al)o(ide "rod!ced is "rotonated by solvent' ivin a @$ hydro(y)etone' #hich !nderoes base$cataly*ed dehydration. The eli%ination "rocess is "artic!larly fast in this case beca!se the al)ene is stabili*ed by con6!ation to not only the carbonyl b!t also the ben*ene.
5. hat "rod!ct sho!ld be for%ed by %i(ed aldol condensation of ben*aldehyde #oth "roionaldehyde ith acetone e(cess/ The "rod!cts for%ed by the %i(ed aldol condensation of ben*aldehyde #ith "roionaldehyde and acetone e(cess/ are 5$ hydro(y$,$"henyl$4$b!tanone and diben*aldehyde' res"ectively. 3. Mi(ed aldol condensation !sin )etones havin %ethyl ro!"s often led to a "ossibility of for%in %ono or dis!bstit!ted "rod!cts. hat "rod!ct is for%ed if ben*aldehyde and acetone in e(cess a%o!nt/ are allo#ed to
Chan' Hey%ond. Che%istry. ,0th ed. McGra#$+ill. 40,0
react Give the reaction e=!ation and describe the %echanis%. The reaction bet#een ben*aldehyde and acetone in e(cess via aldol condensation "rod!ces dis!bstit!ted "rod!ct #hich is the diben*aldehyde. This %i(t!re of addition "rod!cts that are for%ed #hen 4 dierent enoli*able carbonyl co%"o!nds are s!b6ected to aldol conditions. Since the carbonyl carbon of aldehyde is %ore electro"hilic than that of )etone' the reaction bet#een an aldehyde an a )etone is synthetically viable. The ?$carbon of )etone !s!ally adds to the carbonyl carbon of aldehyde' leadin to only one %a6or "rod!ct.
REFERENCE
ade' L. G. Oranic Che%istry th ed./. J""er Saddle Hiver' NK: Frentice +all. 400-
/ournals
Mahr#ald' H. 4003/. Modern Aldol Heactions' ol!%es , and 4. einhei%' Ger%any: iley$C+ erla G%b+ Co. GaA. "". ,4,7B45. IS2N 5$-4;$50;,3$,. Nielsen' A. T. +o!lihan.' . K. ,87/. The Aldol Condensation. Oranic Heactions ,: ,B357. doi:,0.,004P03;,43,70.or0,.0,. eb
Aldol Condensation. SynArchive:The Oranic Synthesis Archive. Hetrived on ,, A"ril 40,-' fro% htt":PP###.synarchive.co%Pna%ed$ reactionsPAldolQCondensation
-oo(s
2r!ice' Fa!la . Oranic Che%istry. 3th ed. Fearson Frentice +all. 4003 2oyd' H. N. Morrison' H.T. Oranic Che%istry. th Ed. Frentice +all. ,884 Carey' >rancis A. Oranic th Che%istry. 3 ed. McGra#$+ill. 4000
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Aldol Heaction. Che%i)i. retrived on ,, A"ril 40,-' fro%
htt":PPche%#i)i.!cdavis.ed!POrani cQChe%istryPHeactivityQofQAl"haQ+ ydroensPAldolQHeaction
