Identify unknown Week 5 Lecture Synthesis of 2,3 ...
Transcript of Identify unknown Week 5 Lecture Synthesis of 2,3 ...
sodium salt of unknown aromatic carboxylic acid + soluble impurities + insoluble impurities total mass: ? g
dissolve in water, filter
insoluble impurities mass: ? g
aq. sol’n of unk. sodium salt + sol. impurities
decolorize, filter
colored dye(s) mass: ~ 20 mg
aq. sol’n of unk. sodium salt + sol. impurities
conc. HCl; filter
crude unk. carboxylic acid mass: ? g
water-soluble imp. recrystallize “pure” unk.
carboxylic acid mass: ? g
melting point (“mp”)
mp, MW, pKa, derivative mp
Identify unknown carboxylic acid
account for all masses; calculate %recovery
CH361/361HWeek5LectureSynthesisof
2,3-DimethylbuteneIsomers
ExperimentIIOverview:Preparation&EquilibrationofIsomeric2,3-Dimethylbutenes
synthesisof“2-ene”(major)/“1-ene”mixturebyGrignard reactionfollowedbyacidmediateddehydration (E1elimination)
synthesisof“1-ene”byWittigolefination
purificationandisomerseparationbydistillation /fractional distillation
equilibrationofalkeneisomersandanalysisofalkeneisomerdistributionsbygaschromatography(GC)
determinationofthermodynamicproperties(DG°,DH°,DS°)byanalyzingtemperaturedependenceofequilibriumconstant(Keq)
last name starts with A-Le
last name starts with Li-Z
majoractivitiesinexperimentII
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REPO
RT2
REPO
RT3
2,3-dimethyl-2-butene“2-ene”
2,3-dimethyl-1-butene“1-ene”
Keq = ?ΔG° = ?ΔH° = ?ΔS° = ?
1
2
3
4
1
2
3
4
H+ cat.
SyntheticStrategy:HowtoMakeAlkenesfrom3-Methylbutanone
O+
3-methylbutanone
?
"2-ene" "1-ene"
O
δ+
δ–
OH3C
C-centerednucleophile
C-centeredelectrophile
OH3C
GrignardReaction/Dehydration:1.FormationofGrignard/AdditiontoKetone
H3C I
Mgmagnesium
metal
diethyl ether(Et2O)
Oiodomethane(methyl iodide)
H3C MgI
methylmagnesiumiodide
δ+ δ– δ+δ–
H3C
(a synthetic equivalent of methyl carbanion)
“ “O
O MgIaq. HClOH
magnesiumalkoxide
2,3-dimethylbutan-2-ol• purified by
simple distillation
SO3H
p-toluenesulfonicacid
+
“2-ene”major product
“1-ene”minor product
δ+
δ–
F.A.VictorGrignard
•winnerof1912NobelPrize
GrignardReaction/Dehydration:2.DehydrationReaction(E1Elimination)
H3C I
Mgmagnesium
metal
diethyl ether(Et2O)
Oiodomethane(methyl iodide)
H3C MgI
methylmagnesiumiodide
δ+ δ– δ+δ–
H3C
(a synthetic equivalent of methyl carbanion)
“ “O
O MgIaq. HClOH
magnesiumalkoxide
2,3-dimethylbutan-2-ol• purified by
simple distillation
SO3H
p-toluenesulfonicacid
+
“2-ene”major product
“1-ene”minor product
δ+
δ–
GrignardReaction/Dehydration:2.DehydrationReaction(E1Elimination)
OH
2,3-dimethylbutan-2-ol
SO3H
p-toluenesulfonicacid
+
“2-ene”major product
bp. 72 °C
“1-ene”minor product
bp. 56 °C
O HH
H
H
H– H2Otertiary (3°)
carbocation
• separated by fractional distillation
• purified bysimple distillation
–H–H
ExperimentalSet-UpforGrignardReaction(INFUMEHOOD)
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READSAFETYNOTE
iodomethaneisacancersuspect
agent;ALLWORKINHOOD!
(wearproperPPE);PRBwill
depenseiodomethaneintopress.
equal.funnelsforyou
diethyletherishighlyflammable;
Grignardreagentsarepotentially
pyrophoric
importantthatglasswareisdried
inoven,assembledquickly,and
flushedwithnitrogen
BEFOREfinishingonWed.,leave
glasswareinmetalbowlreadyto
beovendriedbeforeFriday’slab
C P
H
H
HBr
methyltriphenylphosphonium bromide
NaOCMe2Etsodium
tert-pentoxide
bmim+ BF–
an ionic liquid
C PH
HC P
H
H
methylenetriphenylphosphoranea phosphorus ‘ylide’
MeN NBu BF4
ONa
O
H2C PPh3
O
the betaine (a zwitterion)the oxaphosphetane
OPPh3CH2 PPh3
O+
“1-ene”triphenylphosphine
oxide
GeorgWittig
•winnerof1979NobelPrize
WittigOlefinationtoGenerate“1-ene”Directly
C P
H
H
HBr
methyltriphenylphosphonium bromide
NaOCMe2Etsodium
tert-pentoxide
bmim+ BF–
an ionic liquid
C PH
HC P
H
H
methylenetriphenylphosphoranea phosphorus ‘ylide’
MeN NBu BF4
ONa
O
H2C PPh3
O
the betaine (a zwitterion)the oxaphosphetane
OPPh3CH2 PPh3
O+
“1-ene”triphenylphosphine
oxide
WittigOlefinationtoGenerate“1-ene”Directly
ExperimentalSet-UpforWittigOlefination(onbench)
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READSAFETYNOTE
useofdustmaskisESSENTIALto
avoidunintendedinhaltionof
finelypowderedsodiumtert-pentoxide;otherPPEasusual
(gloves,labcoat,goggles)
importantthatglasswareisdried
inoven,assembledquickly,and
flushedwithnitrogen
BEFOREfinishingonWed.,leave
glasswareinmetalbowlreadyto
beovendriedbeforeFriday’slab