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

•

•

•

•

•

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)

•

•

•

•

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)

•

•

•

READSAFETYNOTE

useofdustmaskisESSENTIALto

avoidunintendedinhaltionof

finelypowderedsodiumtert-pentoxide;otherPPEasusual

(gloves,labcoat,goggles)

importantthatglasswareisdried

inoven,assembledquickly,and

flushedwithnitrogen

BEFOREfinishingonWed.,leave

glasswareinmetalbowlreadyto

beovendriedbeforeFriday’slab