竞赛题库9年第41届ICHO预备试题英文实验部分Word文件下载.docx
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竞赛题库9年第41届ICHO预备试题英文实验部分Word文件下载.docx
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Thepropensityforiodinetocatenateiswellillustratedbythenumerouspolyiodides,whichcrystallisefromsolutionscontainingiodideionsandiodine.Thestoichiometryofthecrystalsandthedetailedgeometryofthepolyhalidedependverysensitivelyontherelativeconcentrationsofthecomponentsandthenatureofthecation.
Inthisexperiment,youwillgenerateandcrystalliseaquaternaryammoniumpolyiodidesaltoftheformMe4N+In–(n=3,5or7)andthentitratetheamountofiodineintheanionusingsodiumthiosulphate.Fromtheresultsofthisanalysis,youcandeterminewhichanionispresentinyoursalt.
Experimental
Twosalts,AandB,ofdifferentcompositionmaybepreparedbyusingdifferentquantitiesofstartingmaterials,asshownbelow.Youcancarryouttheexperimentforeitheroneorboth.
SaltA
SaltB
massofNMe4I/g
1.00
0.50
massofiodine/g
1.26
Preparation
1.Addtheiodinetoa100cm3beakercontaining25cm3ethanolandamagneticbar.Heatandstirthesolutionuntilalltheiodinehasdissolved,thenaddthetetramethylammoniumiodide.Continuetostirwithmoderateheatinguntilnowhitesolidremains.Donotallowthesolutiontoboilatanytime.
2.Allowthesolutiontocoolslowlytoroomtemperatureandfinallyinanicebathoverabout15–20minutes.
3.Collecttheproductundersuction(Hirschfunnel)andwashonthefilterwithcoldethanol(10cm3)followedbyether(10cm3)usingadisposablepipette.
4.Allowtheproducttodryonthefilterforseveralminutes,andthentransferthecrystalsontoafilterpaper.Placeintoadesiccatorandleaveundervacuumtodry.
Analysis
5.Weighapproximately0.5goftheproductontoaweighingboatusingafourdecimalplacebalance.Recordtheweightaccurately.
6.Usingadistilledwaterwash-bottle,carefullytransferalltheweighedproductintoa250cm3bottle.
7.Addapproximately25cm3ofdichloromethane,replacethestopperandshaketoextracttheiodineintotheorganiclayer.
8.Filla50cm3burettewithsodiumthiosulfate(0.100M)usingasmallglassfunnel.
9.Removethefunnelandtitratetheiodinebyrunningsmallquantitiesofthesodiumthiosulfatefromtheburetteandthenreplacingthestopperandshakingthebottle.
10.Theend-pointisverysharpandisgivenbytheremovalofalliodinecolourfromthedichloromethane.
Questions
Fromtheresultsofthetitrations,calculatetheformulaeofthesaltsAandB.Whataretheshapesoftheanions?
Substance
Rphrases
Sphrases
tetramethylammoniumiodide
solid
36/37/38
26-36
iodine
20/21-50
23-25-61
sodiumthiosulfate
0.1Msolution
24/25
dichloromethane
liquid
40
23-24/25-36/37
ProblemP2
TheWilliamsonSynthesisofEthers
Symmetricalaliphaticethersmaybepreparedfromthesimplerprimaryandsecondaryalcoholsbyheatingwithsulphuricacid,butdehydrationtothealkeneisanimportantcompetingreaction.Thesulphuricacidprocessisunsuitedtothepreparationofethersfromtertiaryalcoholsandofunsymmetricalethers.
TheWilliamsonsynthesis,usinganalkylhalideandametalalkoxide,isofbroaderscopeandcanbeusedtoobtainsymmetricalorunsymmetricalethers.Forthelattertype,eitheroftwocombinationsofreactantsispossible.
Theproperchoicedependsmainlyuponthestructureofthealkylhalidesinvolved.Competitionarisesbetweenthesubstitutionreaction(SN2)toanether(1°
>
2°
>
3°
halides)andtheeliminationofHXtoformanalkene(3°
1°
halides).Therefore3°
halidesarenotsuitableforthereaction,butethershavinga3°
alkylgroupcanbepreparedfroma3°
alkoxideanda1°
halide.
TheWilliamsonsynthesisisanexcellentmethodforthepreparationofalkylarylethers–1°
and2°
alkylhalidesreactreadilywithsodiumorpotassiumphenoxides.
Inthisexperimentbenzylchlorideisreactedwith4-chlorophenolunderbasicconditionstoproduceanether.
Theuseofafumecupboardprotectiveclothingincludingglovesisessentialforthisexperiment.
Addabsoluteethanol(50cm3)topotassiumhydroxidepellets(0.87g)ina100
cm3roundbottomedflaskwithaground-glassjoint.
Add4-Chlorophenol(2g)followedbybenzylchloride(1.8cm3)andlithiumiodide(approx.20mg-theendofamicro-spatula).
Addaboilingstick,fittheflaskwithacondenserandheatundergentlerefluxfor1hour(anisomantleisrecommendedbutkeepcarefulcontroloftheheatingtomaintaingentlerefluxotherwisevigorousbumpingcanoccur).
Allowthereactionmixturetocoolandpourontoice/water(150cm3)withswirling.Isolatethecrudeproductbysuctionfiltrationandwashwithice-coldwater(3x10cm3).Pressdryonthefilter.
Thecrudeproductshouldberecrystallisedfromaqueousethanol.Thisentailsdissolvingyourcompoundintheminimumvolumeofboilingethanolandthenaddingwaterdropwiseuntilthefirstcrystalsappear.Thensetthehotsolutionasidetocoolintheusualmanner.
Recordtheyieldofyourproductandrunathinlayerchromatogramonasilicaplateusingether/petroleumether2:
8astheeluent.RecordtheRfvalue.Measureandrecordthem.p.
1.Whatistheroleofthelithiumiodideaddedtothereactionmixture?
2.SubstantialincreasesintherateofreactionareoftenobservedifSN2reactionsarecarriedoutinsolventssuchasdimethylformamide(DMF)ordimethylsulphoxide(DMSO).Suggestwhythisisso.
benzylchloride†
45-22-23-37/38-48/22-41
53-45
4-chlorophenol
20/21/22-51/53
28-61
potassiumhydroxide
22-34-35
26-36/37/39-45
lithiumiodide
36/37/38-61
22-26-45-36/37/39-53
diethylether
12-19-66-67
9-16-29-33
petroleumether†
45-22
†ThiscompoundwillnotbeusedattheOlympiad
ProblemP3SelectiveReductionofaHighlyUnsaturatedImine
Sodiumborohydrideisaselectivereducingagent.Inthisexperimentyouwillcondense3-nitroanilinewithcinnamaldehydetoproducethehighlyunsaturatedintermediateA(animine).ThisisthenselectivelyreducedwithsodiumborohydridetoproduceB.ThestructureofBcanbededucedfromthe1HNMRspectrum.
Theexperimentillustratestheclassicmethodofimineformation(azeotropicremovalofwater).
Place3-Nitroaniline(2.76g)andabsoluteethanol(20cm3)ina100cm3roundbottomedflask,togetherwithafewanti-bumpinggranules.Setuptheflaskfordistillationasshownaboveusinganisomantleorsteambathastheheatsource.Useagraduatedmeasuringcylindertocollectthedistillate.
Adddropwiseasolutionofcinnamaldehyde(2.9g)inabsoluteethanol(5cm3)throughthethermometerinlet.Turnontheheatsourceanddistiloffapprox.22cm3ofsolventoveraperiodofabout30minutes.Duringthedistillationdissolvewithstirringsodiumborohydride(0.76g)in95%ethanol(20cm3).
Afterthe22cm3ofsolventhasdistilledoff,disconnecttheapparatus.SetasideasmallsampleoftheresidueAwhichremainsintheflaskforthinlayerchromatography.Thenadd95%ethanol(20cm3)totheflasktodissolvetheremainingresidue.TothissolutionofAaddVERYCAREFULLYthesodiumborohydridesolution.Thismustbeaddedslowlyandwithconstantswirlingofthereactionflask(vigorouseffervescenceoccurs).Aftertheaddition,heatthemixtureunderrefluxfor15minutes,thencooltheflaskandpourthecontentsintowater(50cm3).TheproductB,shouldcrystalliseoutslowlyonstandinginanicebath.Recrystalliseyourproductfrom95%ethanol.
Recordtheyieldofyourproduct.RunathinlayerchromatogramofyourproductBandthesampleofAonasilicaplateusinghexane/ethylacetate1:
1astheeluent.RecordtheRfvalueofeach.Measureandrecordthem.p.ofB.PredictthestructureofBusingthe1HNMRspectrumgivenbelow.
InthepreparationofAwhyisabsoluteethanolandnot95%used?
Whyisthesolventremovedduringthereaction?
3-nitroaniline
33-23/24/25-52/53
28-45-36/37-61
cinnamaldehyde
41
26-39
sodiumborohydride
25-34-43
26-27-28-45-36/37/39
hexane
11-38-48/20-51/53-62-65-67
9-16-29-33-36/37-61-62
ethylacetate
11-36-66-67
16-26-33
ProblemP4ASimpleAldolCodensation
TheClaisen-Schmidtreactioninvolvesthesynthesisofanα,β-unsaturatedketonebythecondensationofanaromaticaldehydewithaketone.Thearomaticaldehydepossessesnohydrogensα-tothecarbonylgroup,itcannotthereforeundergoselfcondensationbutreactsrapidly
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