Some problems in solution microcalorimetry, experimental experiences by the authors, and the enthalpy-entropy compensation in cyclodextrin + alcohol inclusion-complex formation in aqueous solutions

247

Thermochimica Acta, 88 (1985) 241-254 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

SOi,iEPROBLEMS EXPERIENCES

IN SOLUTION

COMPENSATION

IN CYCLOOEXTRIN

FORMATION

IN AQUEOUS

S.TAKAGI,

T.KIMURA,

Department

MICROCALORIMETRY,

BY THE AUTHORS,

EXPERIMENTAL

AND THE ENTHALPY-ENTROPY + ALCOHOL

INCLUSION-COMPLEX

SOLUTIONS

and M.MAEDA

of Chemistry,Faculty

of Science and Technology,Kinki

3-4-l Kowakae,Higashi-osaka,Usaka

University

577 (Japan)

ABSTRACT A short summary of the milestones to the present stage of achievement by the authors,some problems encountered in their course of investigations,and their countermeasures are described. A precise experimental results of the excess znthslp;l for icyclohexnne + n-hexane) at (298.15 ? 0.001) K are given as a reliability test of the microcalorimetry with small amounts of samples. A couple of ent;i;l+i-entropy compensation rules in the formation equilibria of inclusion com+idxes o@tween O- ano s-cyclodextrins and some alcohols in water at 298.15 K are descriaed, which have been found from their calorimetric determination of the >z,ithalgiesand entropies of inclusion after overcoming the problems.

INTKODUCTION Since the senior author changes

on mixing dilute

(S.T.) and Amaya measured

aqueous solutions

of certain

1966 (ref.11, he and the present coauthors measured

small heats of mixing

(AmixH

Amaya

of heat-conduction

(ref.21 and were developed

these measurements formation several

of inclusion

methods, using some kinds of twin-

et al.

problems

(refs.39).

encountered

during the course of

The enthalpy-entropy

complexes

by

between a-

or

compensation

e-cyclodextrin

in the and

in water as solvent is also described, which has been obtained

from the thermodynamic

ing

have

type which had been designed originally

are shortly reported.

equilibria

alcohols

isomersin

) and dilution (AdilH) of liquids and those

by Amaya

In this paper, some experimental

D- and L-optical

and/or his other collaborators

of solution of solids into liquids by batchwise microcalorimeters

about 10 mJ of the heat

functions

determined

by the microcalorimetry

after overcom-

the problems.

OUTLINE OF DEVELOPMENT Sefore describing

the problems, the milestones

to the present

ment is shortly given.

0040-6031/86/$03.30

0 1985 Elsevier Science Publishers B.V.

stage ofachieve-

248 Rocking conduction microcalorimeter of the heat-conduction

A rocking twin-microcalorimeter

type (ref.41 was used.

Mixing vessels used are shown in Fig. 1. In 1966,bmixH

1st stage.

of aqueous solutions

of optical

isomers were mea-

sured (ref.1). The sample size for each run (A) was 2 cm3/2 cm3, and a typical amount of heat (H) was about 10 mJ t less than 20 per cent. The sensitivity temperature

sensor

2nd stage.

(S) was 6.5 mV/K.

The enthalpies

ous cyclodextrin

of transfer of some alcohols from aqueous to aque-

solutions were measured

and the molar enthalpies

of inclusion

AincH) of the alcohols into cavities of the cyclodextrin were determined -141.

(A): 3 g/O.75 g, (H):17.5

a The calculated 3rd stage.

of

Adilfl’S

(refs.10

mJ t 2.2 mJa; -2.6 mJ to.2 mJt (S):6.5 mV/K.

standard deviation

The

(

of the mean.

of aqueous ethanol were measured

loole fraction a(C2H50H)=lO- 2-10-3

over the range of

(ref.l5).(A):3g/0.75g,~rlJ:-10-20mJ

f 0.5mJ,

(S):27 mV/K. B

A

A(B)

Side view

Fig. 1. The mixing vessel used, originally A and B,isolated

designed

sample liquids before mixing;

Side view

sample liquids; C,mercury;

(ref.41

D,manganin

heater.

Front view

Fig. 2. The small mixing vessel used (originally A and B,isolated

by Amya

C,mercury;

designed

by Amaya and Hagiwara).

D,heating manganin

wire.

249 rlixlnc vessels without mercury Jy

USC07 id1 ,kiiaya'S "Twin-Conduction

Microcalorimeter

(ref.5) a;rL ti tnI;i-conduction microcalorimeter benzene solutions of p-terphenyl

AdilH’SOf

methacryist:!) ircf.18) were respectively mercury

having

large capacity"

similar to Kagellloto's (ref.l6),

(ref.171 and

measured

&ly(methyl

fsotii&iC

in the mixin,

v;;sels

without

as sno>v:iin Fig.3.

Commercial

A:naya-Hagiwara twin-microcalorimeter

Applied

Electric

the present

Laboratory,Ltd.

authors

(ref.lg,ZO)

in Fig.2, whose capacity The

1st stage. were measured

AmixH

(ref.20).

model TCC-204Dl

was used. The mixing vessels

2nd stage.

used ,t-e illustrated

is about 2.7 cm3. of (DMSO + methyl methylthiomethyl (A):1 cm3/1 cm3-1.2

6.5 mV/K. Total amount of each component The excess enthalpies

were measured

which had been ailodifiedby

as described

below.

cm3/U.Z

sulfoxide)

cm3, (HI:12 mJt0.5

required was about 15

of (cyclohexane

(A): e.g.,l.U

cm3,

mJ, (S):

cd.

+ n-hexane)

cm3/0.2

(S):27 mV/K. Total amount of each pure component

et ~2.

at 298.15 I<

(i-l):200 J+

0.4 J,

needed was about 10 cm3.

PROSLEMS AND COUNTERMEASURES Rocking conduction

microcalorimeter

At the first stage, deviations the thermal

e.m.f.'s

thermopi les

n semiconductor statted.

Then, the purified

with purified

of experimental

and thermal conductivities were balanced mercury

water. After separated

values were large, even when of the reference

and the circulating

to be used in the mixing it from the water,

and measuring

vessels was shaken

it was passed through pin

-

Bottomc-

1

Top

1

0

14cm

Fig. 3. A mixing A,Pyrex

P-

water was thermo-

vessel

(Pyrex) without mercury

sliding Gartition;

wire; F,Pyrex 1,opening

lid.

6,PTFE-Stopper;

(ref.17).

C,spring;

stopper; ti,mercury; H,electrical

D,tungsten

heating

wire; E,metal

resistance

(manganin wire);

250 holes on a filter paper.

It was transferred

into the mixing

sample liquids were loaded. By this procedure, of the optical

isomers were reproducible

peated runs. Recently orimeter

sured precisely: ref.131

and dry surfaces

0.2 mJ of calculated

shows the attainment

standard

into cyclodextrin

of reasonable

will be discussed

fractions)

of p-terphenyl

stage, relative were obtained.

To avoid the problems

of dilute benzene

and heat of friction

solutions

(less than 0.004 in mole at the first

trere large and no reproducible

j&;s

of successive

stirrings.

were designed

values

behind

The reason

mixing

as shown in Fig.3. By use of

values of AdilH of dilute benzene

these vessels required

relatively

solutions

were

large amounts of samples

was large.

Amaya-Hagiwara

twin-microcalorimeter

The same kinds of problems Reliable

as described

above were overcome

by the same coun-

results were obtained with small amounts of samples. An ex-

ample will be described

under next sub-heading.

(HE) OF (CYCLO~~EXANE t YZ-HEXANE)

To test the reliability ,+ of (cyclohexane

The cyclohexane

of the results obtained

+ n-hexanel

idaterials and experimental

toxide. Analysis

AincH

was determined, which

from heats of we-tting and any others,new

contact with mercury

(ref.l7),but

EXCESS ENTHALPY

experi-

is now unGissolve4. produced

this kind of vessels,accurate

termeasures.

in aqueous solutions

every peak of the first stirring which followed

for the latter phenomenon

Commercial

Consequently,

Under these conditions, the

on the rocking co;lduction microcalorimeter

mixing was smaller than reproducible

determined

the

of the mean determinedt

reproducibility.

amounts of heats of wetting Moreover

vessels without

Then, by use of dry mercury

mercury

measurements

AdilH

in the cal-

later.

Mixinq vessels without

In the

cavities

solutions

of the Pyrex vessels can be meadeviation

mental values of small heats may be corrected. of alcohol

and the

of the mixing vessels

to t 10-6 K or better.

of the mercury

vessels

of aqueous

Ami#‘S

to about less than 220 per cent on re-

the temperature-stability

has been enhanced

heat of wetting

the

was determined

overcoming

was fractionally

distilled

(ref.211 showed no impurity

was obtained

by d.s.c. on Daini-Seikosha

(Phillips

Co.,Research

Grade),whose

cent,was

used without

further

termined

by coulometric

purification.

pen-

SSC/560.

The rrhexane

stated purity was 99.95 mole per

The water content

Karl Fischer titration

over phosphorus

peak. Its purity was 99.99

mole per cent,which Petroleum

;the problems,

procedures

(MerCk,Uvasol)

by g.1.c.

after

at (298.15 * 0.001) K.

on Mitsubishi

of the samples deMoisture

Meter Model

251 CA-05 was 0.001 and 0.0064 mole per cent,respectively,for hexane. The mercury was purified The modified ing vessels

commercial

from a weighed

previously(ref.21).

calorimeter

syringe fitted with a suitably

of the calorimeter

Results

and n-

(ref.22) and the small mix-

(Fig. 2) were used. Each sample liquid was loaded into the vessel

mic needle. Circulating

described

as described

Amaya-Hagiwara

the cyclohexane

bent Hamilton

water was thermostatted

temperature

Model KF 730 hypoder-

within -I low3 K and fluctuation

was less than + 10-6 K. The procedures

has been

(refs.21,22).

and discussions

The Hi results are given in Table 1. The coefficients

Ai's of the smoothing

equation:

(1)

= s(l-z);zI~(l-2r)i-'

.$/J.mol-'

and the calculated

standard deviation

least squares are

A1 = 864.12, A2 = ?5ii.Y3, A3 = 101.41, A4 = 29.534, and sf =

0.14 J*mol-'

of i;he fits sf obtained

by the method of

, where x denotes the ;,ioldfract.ion of n-hexane and choice of the

TABLE 1 Molar excess enthalpies

Hi for {(I-z)C6Hl2

+ xC6Hl41

at 298.15 K.

3:

H$/J.mol-1

2

Hk/J.mol-1

3c

Hk/J.mol-1

D.03905 0.06684 0.16499 0.19925 0.29541

45.18 73.14 149.70 169.00 205.27

0.34306 0.43798 0.46957 0.58339 0.64692,

214.99 220.72 218.82 200.70 182.38

0.73582 0.78928 0.80147 0.86665 0.95325

148.68 124.32 118.38 83.45 31.00

appropriate

number of the coefficients

sf:Oeviations

of the experimental

was based on the variation

of the value of

values of H: from the calculated

ones are

within f 0.2 per cent of the latter, except a most dilute run, as shown in Fig.4. Fig. 4 shows also the overall the most reliable termined

measurements

by different

methods:

J*mol-'; Marsh and Stokes, and Benson,

isothermal

D'arcy,and Benson,

dilution

of the present results with those of

by different

this work, twin-batch

isothermal

displacement

calorimeter,sf

LK8 flow microcalorimeter,sf

ations of all three comparison The present

agreement

reported

microcalorimeter,sf

calorimeter

= 0.14

(ref.23); Murakami

= 0.21 Jamol-'

(ref.24); Tanaka,

= 0.29 J*molW1

(ref.25). The devi-

sets fall almost within the ? 0.2 per cent range.

results for cyclohexane

with those of Marsh and Stokes

authors which have been de-

+ n-hexane

(ref.23).

mixture ?re in excellent

agreement

252

I

I

B E _, . " 0

. . . . . .. . . . . . . . . . .

I

. . . . .

0.3

0.0

z WE :

-0.3 WE 4 -

. . . . . .. . . . . .. . .. .**. 0.2

0.0

0.4

0.6

0.6

1.0

1 -x

Fig. 4. Difference

plot for molar excess enthalpies

at 298.15 K wherezis calculated results.

the mole fraction

from Eq.(l) with the coefficients Curves:

Tanaka,D'arcy,and

of (cyclohexane

of n-hexane

given in the text.

l,Marsh and Stokes(ref.23);

2,Murakami

0,Experinental

and Benson (ref.24);

Dotted curves represent

Benson (ref.25).

+ n-hexane)

and ,$ (talc) is the value

20.2

3,

per cent devi-

ation.

Other reliability

tests of the lllicrocalorimeter system were carried

lier by use of an endothermic nificantly

different

densities

,rrixture(chlorobenzene

ENTHALPY-ENTROPY

(benzene + carbon tetrachloride)

and overall perforl,lanceof the calorimeter

COMPENSATION

IIN CYCLODEXTRIN

+ ALCOHOL

values of

Ar,ljxH

and

the enthalpies

aqueous cyclodextrin

of transfer

INCLUSION-COMPLEX

FORMA-

solutions were obtained

of those as a function

calorimetrically

of the mole fraction,

at various mole fractions

the limiting

and the (molar ratio of the alcohol included

equilibrium

constants,the

and the entropies

of inclusion

proposed

of inclusion,the

were determined

The results elucidate

the importance

"driving force" of the molecular

at infinite dilution,the

Gibbs energies

(refs.

by using merely

of inclusion,

the direct r,licro-

10~14).

of the enhancement

inclusion

values of the enthalpy

on the basis of the theoretical

by the authors (refs.l0,12)

data at only one temperature

of the

range. By using the knowledge

of transfer

enthalpies

of

by the

of some alcohols frola aqueous to

alcohols at 298.15 K in very dilute concentration

procedures

system.

of dilute aqueous solutions

AdilH

and some alcohols which were determined

present authors,

calorimetric

and an exothermic

SOLUTIONS

Froln the reliable cyclodextrins

out dir-

of a pair of liquids havin;J s.lg-

+ toluene) (ref.221,. All results verify the high reliabil-

ity of this microcalorimeter

TION IN AQUEOUS

r,lixturecomposed

of entropy

of the alcohol molecules

as a main

in these

253 .: aqueous 531~...)ns. :n this case two different were o!>Ci~~:~cu 2s Mu. .: in Fig. 5.

enthalpy-entropy

One (a) corresponds

compensation

to the formation

rules

equilfb-

rium of stron:;cr !$.,~lr : ..iable) complexes to that of weazf temperatures

(AincGm< -22 kJ.mol-'1 and the other (bl -1 1. The isoequilibriul: i;s;s stable) oties (AincGm > -20 kJ*mol

(rci'z.;L,i7j are respectively,

(a) 339 K and

b) 292 I(.

1. C6Hl10H + a-CyD (-24.9) 2. C5HllOH + a-CyD (-24.4) 3. C6HllOH + a-CyD

(-23.8)

4. C5H110H + 8-CyD (-22.6) 5. i-C3h701-l+ a-CyD (-19.7) 6. i-C3H7UH

+ a-CyD

(-19.2)

7. n-C3H70H

+ a-CyD

(-17.8)

8. n-C3H70ti + a-CyD (-17.5)

30

T AincSm/ k J-mol’ Fig. 5. Compensation formation

rules between the enthal?y

of 1:l inclusion

complexes

in aqueous solutions

in parentheses

are the values of AincCm/kJ*mOl-l

were tabulated

in ref. 14.

All of these results reveal the significant in the molecular

inclusion

In concluding,the follows.

phenomena

authors predict

values and entropy values of the at 298.15 K. Figures

:valUeS for AincH,, and AincS,,

role of the hydrophobic

in aqueous I,iedia.

some future probler#lsin Inicrocalorimetry as

If one will proceed with the effort for better accuracy

the batchwise

methods,he

tion of heat of oxidation

might encounter

any problems

about,e.g.,

of mercury with oxygen dissolved

iation of the heat of wetting with liquid concentration,or The present work was partially search frokt the Ministry

hydration

supported

of Education,Science

and precision by the superposi-

in salllpleliquids,varpreferential

by a Grant-in-Aid

wetting.

for Scientific

and Culture of Japan.

Re-

254 REFERENCES

5 6 7 8

19 20 21 22 23 24 25 26 27

S.Takagi,R.Fujishiro,and K.Amaya, Chem.Cormun., 1968,480. K.iiiiaya,Kogyo Kagaku Zasshi, 69 (1966),1978. K.Amaya and S.Hagiwara, Abstr. 1st Japanese Calorimetry Conf.,Osaka,iiov.l965. K.Amaya, S.Hagiwara,and S.Takagi, Abstr. 2nd Jpn.Calorim.Conf.,Tokyo, Nov. 1966,1-8. K.Amaya and S.Hagiwara, Abstr. 2nd Jpn.Calorim.Conf.,Tokyo,Nov.1966,1-Y,l-11; Abstr. 3rd Jpn.Calorim.Conf.,Osaka,Nov.lJ67,8109. K.Amaya,S.Hagiwara,and M.Uetake, Abstr.3rd Jqn.Calorim.Conf.,Osaka,Nov.1967, 8210. K.Amaya,S.Hagiwara,and M.SUZUki, Abstr.4th Jpn.Calorim.Conf.,Tokyo,Nov.1968, 9.53; Abstr. 5th Jpn.Calorirn.Conf.,Osaka,Nov.l979,p.50. M.Suzuki,S.Hagiwara,and K.Amaya, Abstr. 6th Jpn.Calorim.Conf.,Yokohama,Nov. 1970, p.34. H.Suzuki and K.Amaya, Abstr. 7th Jpn.Calorim.Conf.,Nagoya,Nov.lY71,+.76. M.Maeda and S.Takagi, Nippon Kagaku Kaishi,1%3,188. (with English sua#ialarj') lrl.Maedaand S.Takagi, Netsu Sokutei,lO (1%;3),43. M.Maeda and S.Takagi, Netsu Sokuiel,ib \irs31,103. iin English) M.Maeda and S.Takagi, submitted to j.ti;idilF in press. S.Takagi,T.Kimura,M.Maeda,and M.I:~r,_,a,;i, ~I!Ibe published in B~ll.Che,~l.Soc.J$n. A.Kagemoto,S.Murakani,and ~~.Fuj:s:r;,-v,LIuIl.Chem.Soc.Jpn.,39 (1966),15. S.Takagi and R.Fujishiro, J.Fac.,;;. Te