University ofHyogo
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35

CationBindingProperties
ofBenzo-type
Crown Ethers.
'EffectofRing Sizeupon ComplexationPhenomena
Mikio OUCHI, Takuya KINASHI,
Department

Hiromutsu UEDA, Masaya KOJIMA,ofMaterials

andRyo MIYOSHI

Scienceand Chemistry

GraduateSchoolofEngineering
Abstract
The cation-binding

different
ring size hasbeenperfbrmedby theK',Rb",
Cs',Ag', and Tl')between water andextraction ofpicrates(Na+,dichlolomethane.
The eflect of ring size and symmetryof the crown ethers upon the cation bindingability isdiscussed.
The results are compared with those of commerciallyavailable crown ethers (diben2o-18-crown-6
and 18-crown-6)and itwas fbund thatthe less-symmetricalbenzo-crown ethers have lowercation binding
ability while unique cation selectivity fbrthallium
hasbeenobserved,(I)solvent

by a s'eries ofbenzo-typemonovalentcrownethers withmetal

1. Introduction
The chemistry of crown ethers has been developed since Pedersen'spioneeringwork in 1967 [1],and anumberof papers and books have been publishedto investigate
thecharacteristics of crown ethers. Recently,
it has shifted from simplemonocyclic
compounds[2]to moTe sophisticated structures involving
supramolecuiarsystems
The synthetie approach fbrthe molecular designof crown ethers has started from[3],of introducing
the substituents.
This study has been done inbenzo-typecrown ethers becauseof the feasibility
many papers,however,the structures ofbenzo-typecrown ethers are mainly symmetricalwith two methylene
chain
betweentheadjacent two oxygen atoms in the crown ether skeletons, 3m-crown-m, The ringsize ofsymmetricalcrownethers increases
with the increaseof the numberof m. The alternative way of increasingof methylene
chaihlengthbetween the adjacent two oxygen
the size of crown ethers isto change the number
ethersof lowatoms in the ring.This crownether has been called less-symmetricalcrownethers or crownsyrnmetrM(13m+nj-crown-m.[4].

alkali
We hhve reviewed complexation
by crown ethers of low symmetry
and demonstratedthe specificcrownethers, crownmetal ion selectivity of lesssymmetricalcrownethers. Compared with symmetricalskeletons
showedlower cation-binding ability ingeneral
ethers of low symmetry
possessing(3m+tij-c[own-mbutexhibit drasticallydifferent
and in some cases, higherselectivities of specfic cations.
ln this context, itis our special interest
to investigate
the cation bindingbehaviorsof benzo-typecrownfrom the standpoint of molecular symmetry and the change of ring size. In the present
ethers of low symmetry
have been evaluated by solvent
thecationbindingability of benzo-crown ethers of low symmetry
paper,
below withextractionof aqueous metal picrates.
Thc compounds
used in this study (1-3and 5-9) are showncommerciallyavailable crown ethers, dibenzo-18-crown-6(4)and 18-crown-6(10).
,

2. ExperimentalDetails
Mass spectra were measured
Infraredspectrophotometer.
spectra were obtained on a JASCO A-1OO gratirig
recordedaJEOL
JNM-EX
270 spectrometer inusipg
Shimazu GCMS-QP5000. IH NMR spectra wereonon
as internalstandard. UV･VIS spectra were recorded
chlorofbrm-d
solution containing 1% tetramethylsilane
from sodium hydride.
a HitachiU-3500 spectrophotometer.
Solventtetfahydrofuran (THF)
was distilled
fUrtherpurification
unlessCommeniallyavailable reagents were used in the fo1!owing
syntheses without
noted otherwise.

Synthesis. Dibenzo-16-Crown-4 (1), Dibenzo-22-Crown-6 (2), Dibenzo-28-CrQwn-6 (3),orBenzo-20-Crown-6 (8)were synthesizedfrom 1,2-bis(bromomethyl)benzene
Dibenzo-24;Crown-6(5),1,3-bis(bromomethyl)benzene
in THF in the presenceof NaHfLiOH and KCI acoording to the previous'NII-Electronic Library Service

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36

No.57 (2oo4)

method22-Crown-6 (9)methodwas preparedaccording to the reported[6,7,8,9],[1Oi.
Benze-14-Crown-4 (6).
Sodiurnhydride(1O.6g,O.44mol)and THF (300mL)
were introducedintoa 1-L threeneckedflaskequippedwith a magneticstirreg
refiuxcondenser,droppingfunnel,and nitrogeninlettube. To
thestirred suspension at 66 ℃ was added triethyleneglycol(g.9g,O.06mol)in THF (100mL),
and stirring
wascontinued
for 1 h with continuous
bubblingof nitrogen, Then potassiumchloride (4.8g,O.06mol)wasadded. 1,2-Bis(bromomethyl)
benzene (16.0g,O,06mol) in THF(100mL) was then added dropwise to thestirred mixtureover 2 h,and thestirring was continued
for3 daysat 66 ℃ under a nitrogen
atmosphere.
Theexcess amountofNaH
waseliminatedmethanol.
Thewasresidue
bysolventevaporated
and thewas extractedwith dichloromethane.
The dichloromethaneextract was driedover magnesium
sulfate and the solvent wasevaporated. Afterwork-up, itwas purifriedby column chromatography
5% ethyl acetate in hexane)(alumina,iH
and Kugel rohr distillation
to give 3.lg (21%)of the product 6: bp 142℃ tO.2 [Ibrr.; NMR6 3.64-3.76
4.76 (s.4H),
7.22-7.37(m4H);IR(neat)
2860, 1460, 1130,1100,750 cm'i ; MS (EI),
mle 252 (M');(m.12H),
Anal.Calcd forCi4H2e04]C,66.65;H, 7.99;Found: C, 66.84,H. 7.97.
Benzo-17-Crewn-5 (7)waspreparedin 11% (2,8g)
yieldby the reaction of 1,2-bis(bromomethyl)benzene
O.09mol)
withtetraetlrylene
O.09mol)in THF in the presence
O.36mol)ofKOH(17.5g,glycoi (23.8g,(20.2g,iH
accordingto the procedure describedabovei
bp 158-160℃ 10.2Tbrr.; NMR63.64-3.73 (m.16H),
4.71(s.4H),
7.25-7.28(m2H),7.38-7.42(m.2H);
IR(neat)2850, 1450,1105,750 cm']; MS (EI),mle296 (M);AnaL CalcdforCi6H240s:C,64.84; H, 8.16; Found: C,64.54;H, 8.22.
SolyentExtraction.The generalextraction proceduresemployed
are similar to those previously
presented
Distilled
dichloromethaneanddemineralizedwater
wereused.
Thesolvents
weresaturatedwith
each[5].
otherinbeforeuse order to preventvolume changes ofthe phase duringextraction. Equal yolumes(1OmL) ofdichloromethanesolution of the respective crown ,ether (3.0mM)and of an aqueous
solution of
thecorresponding
metal picratemM)
wereMIOOL incubator.
shaken fbr 10 minutes
at 25 ℃ in a Tleiiyo(3,OThe mixture was thenal16wdto stand forat least
2 hoursat thattemperature in order to complete phaseseparation. The organic phase was separated
by fi1tration(Tbyofilter
paper No.2s). Sincethe picratesdoes
not dissolve
in dichloromethane,themo!ar extinction coefficients in 1:1 mixture of dichloromethane
andacetonitrile
weredeterminod.The concentration of alkali and heavy metal metal picrate in the organic phase
was deterrninedfrom absorbance at 375nm ina mixture ofdichloromethane
and acetonitrile,
reported

ccggD
AL.Y

q g gD q gzglZD
AoWL/W

2gc(z gD c[g gg)q1'-X

wwoAn.

ww

1/-x

1-X

1-N/-N.

wwrAoAoq VoJ )ooosoow)

Aoo --x,o---->

oLvO

s5

1oforr-Xo

zczwg..g)(gg:)
IN-KnAAvv

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Universityof Hyogo.esmu.-LM.,lhte .:'ff)(pt: CationBindingPropertiesof Bentotype
Crownemhers
Effectof Ring
Size
upen Complexation
Phenemena37

3. ResultsandDiscussion
Synthesis.Benzo-l4-Crown-4 (6)was synthesized from 1,2-bis(bromomethyl)benzene
and triethylene
inTHF
intheofNaH
and
KCI
in
21%
Benzo-17-Crown-5
synthesized
fromglyeolpresenceyield,(7).was
1,2-bis(bromomethyl)benzene
andtetraethyleneglycol in THF in the presence of KOH in 11% yield.
SelventExtraction.A yariety of measurement techniques forrecording the cation bindingability of crownethers
have beenreported. Notable among them are ion-selectivemethods,andelectrode techniques, NMR
solvent extraation techniques. In thispaper,dataobtained by solvent extraction ofmetal
are presented
picrates

forgeneral discussi6n.
The solyent

extractionof metal

has been employed
picrates

as a convenient

forevaluating

methodcationbindingability of macrocyclic 'compounds, in the presentstudM aqueous alkali
and heavymetal picrates
K',Tl')
25
were extracted at℃ dichloromethane
solution ofthe crown ethers (1-10).
(Na', Rb', Cs',Ag' andThe extractabilities obtained
are shownin Table 1. In order to discussthe cation selectivity from a moreofviewl
theextraction
studieshave been done under a variety of conditions to determine
thequantitative
point
extraction equilibrium constants (Kex).
TheKex values fbr 1:1 crown ether metal complex (1-8,,and10) are
shown in [letble2.

Table 1.SolventExtraction.
of Metal Picratesa)%Extractabilityb)
LigandNa'

12345678910a)'femperature25

K'

Rb'

Cs'

Ag'

Tl'

o,oO.lO.6o.gD.1O,11.2O.8O.56.3
o.oO.74.023.6O,2O.1O.95.7O.669,O
o.o1.14.315.1O.2O.1O.6S.51.057.6
o.o2.16.97.9O.5O,2O.74.21.831.3
1,93.33,34,3O.7O.5IL56.28.131.3
S.118,718.730.82.31.41℃ ;aqueous(10rn1)/[Picrate];3rnM.OrganicphasofCHiC12.10ml)i[Ligand]=3mM,b) Definedas percent
extracted
picrateintoorganic Iihase.

Table2.Extraction
Equilibriurn
Constants(Kex)a)Log Kexb)

LigandNa'K"

Rb'

Cs+SelectivityC}
Ag'

Tl'

Tl'/K'Tl'LAgel.862.823.674.842.382.553.013.866.20d)2.963.734.432.382.402.883.835.17d)3.223.974.082.632.372.903.675.17
3.443.293,583.742.912.944.313.975.09
3.7S4,414.585.023.393.224295.036.71
77.638,9g.11.510.27.819.114.83.2
2.0]6,6lo.e19.13.01.9l.
1234567810 d)2.042.842.812.102.333.IS2,923,89a) CH2Cli-H20 systemat 25℃b) Xlalues
for 1:1crownc) Relativecation

etheFcatipn

selectivity

complexes,deterrninedby Kex.

d) Not rneasured.

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No.57 (2oo4)

As seen from Thble 1. Iess-symmetricalimg-enlaigeddibenzo-crownethers (1,2,3,and S) which
possess
methylenechain
adjacent
to the benzene ring showed,
in general, lower extractabilities comparedwiththoseof symmetrical Benzo-18-Crown-6 (4)and 18-Crown-6 (10).
Dibenzo-16-Crown-4 (1)showed noextractabilities
foralkali metal picrateswhile itshowed
low extractability
fbrAg' and Tl'.Ilshould be notedthat1 showed highTl' selectivities among meta1 cations used inthis study. A more quantitative
discussion
wasmadefrom the Kex values shown from Table2. The degreeof decreasein Kex values forTl' were lesssensitive to the methylene
chain lengththan thoseof the alkali metal ions.Thus, fbrthe firsttime,higherTl'
extra

to alkali metal cations has been observed
fbr ring-enlarged
compounds
Dibenzo-18-Crown-6 (4) showed
the selectivity for K'. Ring-enlarged Dibenzo-22-Crown-6
selectivity

with reference

1.

(2),

Dibenzo-28-Crown-8 (3),and Dibenzo-24-Crown-6 (5)showedthe selectivity fbr Cs' among alkalimetal
cations whichis explained
ring-enlarged
22-Crown-6 (9)by the size-fit concept. Unsubstimted
also showed
thesarne results.
Ring-enlargedBenzo-14-Crown-4 (6),Benzo-l7-Crown-5 (7),andBenzo-20-Crown-6 (8)lowershowedextractabilities and no drasticchange of cation selectivity seen from 1fable
1 and 2. Thiswould be beeauseof
the small ringsize of 6 and the effect of extra methylene
chain in the crownether ring. Itcan be concluded
tliatdibenzo-crown-6derivatives
are superior to monobenzo-crownethers (6-8)
in view of cation(1-5)

bindingand cation selectivity.

As seen from fable 2, discussionon higherTl' selectivity over K' and Ag' can be made from the dataof
Kex values. Although .thecation diametersof K' and Tl' are similar, higher Tl'IK' selectivities weredeterminedforring-enlarged
benzo-typecrown ethers 1, 2, 3,5, 6, 7, 8 compared withthose of commerciallyavailable 4, and 10.However, there
was no drasticchange of Tl'IAg'selectivity comparedwith
4 andpositivele, The presentresult also suggests the effbct of benzeneringtoward cation binding.
Thiscan be also
explained by the high Tl',and Ag' selectivity
over alkali metal cations seen in Calixarene
compounds[11,12].
The molecular designof Tl' selective host molecules might be desiredby the presentdiscussion.
Further
investigationsin progress toward elucidating theselectivities of ring-enlarged
are nowdibenzo-typecrownethers used inTl' sensing by the method
ofsolvent extraction artd ESI Mass spectra methods[13].
References
Z Am. Chem. Sbc.,89,7017 (1967).
[1]C.J.Pcclersen,[2]C.J.Pedersen,Angeui(]hem.,100, 1053(1988).
WJ. Steed.
and J.L.Atwood (Eds.),
Sletpr`miolecularC7iemistty
Jolm WileM London, 2000.
[3]inYlInoueand GWI Gokel(Eds.),
CationBindingbyMacrocysles,[4]M. Ouchi,T. Hakushi,and Ylinoue,
Marcel Dekker,New Ybrk, 1990,Chapter14.
T. Hakushi,and E. Webe4 l Org.Chem,,52, 2420 (1987).
[5]M. Ouchi,Y Inoue,K.Wada,S.Iketani,
K.Yakabe,Y Shono,H. Shintani,
A. Ybneda,T.Hakushi,and E.Weber,Bioorg.
[6]M. Ouchi,Yl Shibutani,
Mled C7,em.,7, 1123 (1999).
M. Ouchi,T. Hakushi,and Yl Inoue,BulL enem. Sbc..ipn.,
63,3670 (1990).
[7]E. Weber, K. Skobridis,
D.N.
Reinhoubt
7letrahedlon
andRT.
Gray;
Lett,32,1161[8](1975).
[9]D.N. Reinhoubtand R.T.CiraMfetrahedlonLett.,25,2105 (1975).
M. Ouchi,Y Inoue,T. Kanzaki,and T. Hakushi,X Org.(:hem., 49,1408(1984).
[1O]
D. Couton,
M. Mocerino,C.RapleM C. Kitamura,A. Ydneda,and M. Ouchi,Aorst.
I Chem., 52,227,[11](1999).
M. Ouchi,T.Mizuno,T,Maeda, N. Ebashi,C.Kitarnura,
A. Ybneda,and M. Mocerino,Deu Chem.Ehg,[12]
Mineral Process.,
11,529 (2003).
keliminary
results of the work havebeenpresented:
M. Ouchi,T. Maeda, N. Orino,
Y Otoshi,[13]
H. Sakamoto,and K. Kimura,Abstractsof the53rdAnnual Meeting of the JapanSociety
forAnalytical
Chemistyp.340,Chiba,2004.

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