Dielectric relaxation in propionic acid-tri-n-butylamine system

159

Advances in Molecular Relaxation and Interaction Processes, 22 (1982) 159-165 Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

DIELECTRIC

M.

RELAXATION

Pajdowska

Institute

IN

PROPIONIC

ACID-TRI-N-BUTYLAMINE

SYSTEM

and L. Sobczyk of Chemistry,

University

of Wroclaw,

50-385

Wroclaw,

Poland (Received 7 September 1981) ABSTRACT The range

complex

electric

100 MHz-2GHz

-n-butylamine

permittivity

have been

systems

and viscosity

measured

of varying

composition.

relaxation

time and its distribution

especially

for 1:l species.

over

for the propionic Both,

indicate

the frequency acid-

the value

a remarkable

triof the

aggregation

INTRODUCTION Carboxylic techniques

acid-

both

amine

systems

in solution,

[l-71.

In such

systems

bonds,

leading

to the formation

position, binary The

the most

mixtures

studies

a strong

stable

of a proton

solvation

and

interaction

and

takes

presumably

bonds

self-solvation

and,

place

mixtures

via hydrogen com-

to be present

spectra

revealed

in particular,

equilibrium

In r6,71.

specific

the possible

and furthermore - creation

processes

various

1:l and 2:l adducts.

and infra-red

transfer

using

in binary

of miscellaneous

are also postulated

moments

of O-H.. .N hydrogen

features existence

studied

solvents

of complexes

being

3:l complexes

of dipole

have been

in inert

- due to

of free ions

111-151. The

aim of the present range

frequency

-n-butylamine information processes

related

(TBA)

work

mixtures of varying

on the structure which

processes.

for

could

Searches

is of

to study

composition.

of these

be ascribed

jumping

acid

remained,

over

the dispersion

(PrAH)

We hoped

liquids

and tri-

to gain

new

and on the relaxation

to the kinetics

for the dielectric

to the proton

E*(O)

propionic

response

of proton

which

might

so far, without

0378-4487/82/0000~000/$02.75 0 1982 Elsevier Scientific Publishing Company

transfer be directly

success.

160 EXPERIMENTAL The mixtures object

of carboxylic

for dielectric

and electric

work

the frequency method

range

of 100 MHz

and 5 sun depth

determination -terminal

which

connects

in our experiment

range

at 2 GHz

E’

+5%

for

been measured

of E*(W) have been

RESULTS

and

performed

For all systems

except

distribution

distinct

feature

we applied

cos h

-1

ratio

of

the liquid

line. The

allow

for the

of a two-portresults

the

obtained

+ 2% for E' and f 5% for E" E”

The viscosity

.

viscometer.

of

In addition

while

the liquidswas

the measurements

for PrAH + TBA complexes

in benzene.

whereas

in benzene

of the defined

relation

processes,

in the numerical

reflects

1 the behaviour

1

E’

far binary From

values

2 evaluated

mixtures

the plot

pure

to about

diagram

analysis:

time and

6

: TBA system

as an example

and the Fuoss-Kirkwood for respective

plot.

systems

~~ and 6 are given.

ratio

decrease

increases,

are long

of 17 against value

and

in the mean

Generally

the molar

fraction,

noticing

is, approximately,

relaxation

the relaxation

do not correlate

of n corresponds

3:l. It is worth

components

any

Hence

from monodispersivity.

are compared

show a striking

that the maximum

equal

of relaxation

of the 1:l PrAH

~~ as the acid/amine

it appears

evaluation the deviation

on the Cole-Cole and E"

a sig-

without

(1)

for a graphical which

in Table

of both

solutions

time is observed

=*ln.L!$tZ

The data obtained

cosity.

dilute

E’ ’

is illustrated In Table

the more

of the separation

E" max _

allows

In Fig.

ratio

capacitance

of 4-8 mm diameter

the theory

of the relaxation

the Fuoss-Kirkwood

coefficient,

times

wave

In

out over

AND DISCUSSION

nificant

time

k 7% for

by an Ostwald

the lumped

the end of a coaxial

levels

at 100 MHz

losses

reactivity.

has been carried

capacitor

by using

The confidence

a difficult

C161. In this method

shift and standing

of the impedance

network.

of chemical

glass to

represent

of high permittivity

- 2 GHz using

in our laboratory

of phase

amines

of E*(W)

is put into a cylindrical

measurements

which

because

and because

the measurement

developed

sample

studies

conductivity

the present

acids with

with

vis-

shown in Fig. 2

to the PrAH/TBA

that

the same.

the viscosity

161

A cos h-’

(0)

cmuc

I

E”

1

2-

l-

E” (b)

84-

Fig. 1. Cole-Cole (a) and Fuoss-Kirkwood acid TBA system.

(b) plots for 1:l propionic

In order to compare the relaxation times with the volume of defined species it is necessary to assume some theoretical model. From the literature data it follows that the best agreement between the effective molecular volume and that calculated from the dielectric relaxation time is obtained from the following relation [171:

T

u=

-2 nil

1 73 - 1o12

(2)

162

20 -

10 -

0+

I

Fig. 2. Viscosity PrAH - TBA system.

TABLE

System

- values v(MH2)

6:l

binary mixture

against

molar

fraction

of PrAH

1.0

for the

at 298 K E'

E"

162 250 520 1000 2000

7.44 6.47 5.33 4.47 4.42 3.78

4.0 4.16 3.08 1.92 1.51 0.91

100 162 250 520 1000 2000

9.10 8.22 6.33 5.82 3.92 4.15

6.33 6.20 4.06 3.35 2.70 1.11

100

162 250 520 1000 2000

9.45 8.76 6.94 6.59 4.38 4.50

5.37 5.84 4-69 3.95 2.99 1.29

100 162 250 520 1000 2000

10.59 9.79 7.15 6.73 4.35 4.32

4.37 6,03 7.23 S-25 3.68 1.63

100

111 binary mixture

3:l binary mixture

plotted

XA

1.

E’ and E"

2:l binary mixture

08

a2

System

1.6M PrAH in TBA

2.2M PrAH in TBA

1.6M complex in benzene

l.OM complex in benaene

v(MH.2)

E'

E"

100 165 250 600 1000 1600

3.79 3.52 3.32 3.00 3.12 2.90

0.85 0.69 0.93 0.53 0.44 0.49

100 165 250 600 1000 1600

4.52 3.98 3.69 3.25 3.29 3.40

1.58 1.38 1.28 0.65 0.54 0.71

100 165 250 730 1000 2000

6.75 5.86 5..87 4.29 4.03 3.64

1.11 1.46 1,88 1.85 1.54 1.36

100 165 250 730 1000 1666

5.00 4.74 4.48 3.91 3.64 3.33

0.66 0.68 0.94 1.33 l-05 1.01

163

TABLE

2.

Mean macroscopic relaxation time ~~ and the % Fuoss-Kirkwood parameter for PrAHsTBA systems. T=298

K

System

To'Ps

1:l 2:l 3:l 6:l 1.6M l.OM 2.2M 1.6M

binary mixture binary mixture binary mixture binary mixture complex in benzene complex in benzene PrAH in TBA PrAH in TBA

TABLE

3.

3150 1991 1600 760 398 282 2500 700

% 0.64 0.79 0.76 0.89 0.72 0.86 0.65 1.0

Molecular volumes of PrAH.TBA complexes VM compared with those calculated from dielectric relaxation times VD

cz31

System 1:l 2:l 3:l 6:l

binary binary binary binary

mixture mixture mixture mixture

528 659 790

?493 1712 994 1186

where Tu (from Powles) equals

2EO+ E, F--, ~~ being the macroscopic

relaxation time, while nU =O,l

n (from Debye)

0

where n is the macro-

scopic viscosity. Moreover, analysis of the literature data shows a distinctly positive deviation from equation (2) for polar associated liquids. In Table 3 the effective molecular volumes are compared with those calculated from dielectric relaxation time for various composition of liquids. Therefore, the liquids of 1:l ratio are, in terms of molecular volumes,. the most associated. The lowest % parameter occurs in conjunction with the highest relaxation time, thereby confirming the largest distribution of molecular volumes of reorientating species. In benzene solutions the PrAHtTBA system behaves normally but at a higher concentrations ho increases and % parameter decreases providing evidence of the aggregation process. The aggregation process is also observed in solutions .with excess TBA, where only 1:l complexes are formed., Considering the possible mechanisms of dielectric relaxation in our systems, the structural relaxation cannot be omitted L19, 20 1.

164

The

fact that, with

could

indioate

the ordered

excess PrAH, the

such a mechanism

structure

of

relaxation

since an

time decreases

excess

the liquid. However,

should disturb

at excess

of

amine which can be treated as a neutral solvent the observed relaxation time is again very long. Thus, one can suggest that there are relatively large molecular clusters with a life-time considerably exceeding the dielectric relaxation time. The distribution of relaxation times as a consequence of a statistical distribution of molecular masses seems to be in agreement with such an argument. The appearance of an expected additional relaxation process connected with proton motion is still not clear. Dielectric losses at the highest frequencies used in this work disappea.r but the ~~ value is considerably higher than ni which could indicate some faster process to be expected beyond the GHz frequency range. Table 4 contains collected data on e--n:

for the investigated

systems. TABLE 4. Molar ratio PrAH/TBA

EC0

1:l 2:l 3:l 6:l

4. 4.4 4.2 3.9

2 "D 2.0497 2.0598 2.0535 2.0135

2 ccc-n D 1.95 2.34 2.15 1.89

It is difficult to judge whether such remarkable increments can be entirely assigned to fairly well known effects like Poley absorption C201 and intramolecular motions giving rise to a change of dipole moment. The observed increment is close to those found for hydrogen bonded strongly associated liquids L21-231. Presumably, the main reason for the large E, - ni values in all systems of this type is the anomalous polarizability related to various protonic vibrations which are distinguished by .a high intensity in the absorption spectra.

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