Molecular association of pentanols in n-heptane II: Viscosities as a function of temperature covering low concentration range

Journal of Molecular Liquids, 38 (1988) 107-133

107

Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

M O L E C U L A R A S S O C I A T I O N OF P E N T A N O L S IN n - H E P T A N E II : V I S C O S I T I E S AS A F U N C T I O N OF T E M P E R A T U R E C O V E R I N G LOW CONCENTRATION RANGE M A N I T R A P P O N 1 and JAMIE

A. K A U K I N E N

D e p a r t m e n t of Chemistry, L a k e h e a d University, Ontario, Canada. P7B 5El

T h u n d e r Bay,

(Received 22 February 1988)

ABSTRACT V i s c o s i t i e s of b i n a r y m i x t u r e s of i s o m e r i c p e n t a n o l s in n - h e p t a n e at various m o l e fractions,

F (F = 0.025 to 0.600)

have been m e a s u r e d in the low t e m p e r a t u r e range

(T = 233 to

293 K) w i t h an a u t o m a t i c v i s c o m e t e r o p e r a t i n g in a c l o s e d system. The t e m p e r a t u r e d e p e n d e n c e of v i s c o s i t y has been found to f o l l o w a simple relation,

t h e r e b y a l l o w i n g for the

c a l c u l a t i o n of E v ,the a c t i v a t i o n e n e r g y for viscous flow. The latter is v e r y s e n s i t i v e to changes in m o l e c u l a r associates,

e s p e c i a l l y at low c o n c e n t r a t i o n s .

The results

show that at low c o n c e n t r a t i o n s

small m u l t i m e r s d o m i n a t e for

both l - p e n t a n o l and 2-pentanol.

At high c o n c e n t r a t i o n s ,

while the former m a y a s s o c i a t e to give large linear multimers

; the latter m a y result in the f o r m a t i o n of large

cyclic m u l t i m e r s w i t h a low d i p o l e moment. and tert-pentanol,

For 3-pentanol

small m u l t i m e r s are likely to d o m i n a t e at

low c o n c e n t r a t i o n s and there is a change in the d o m i n a t i n g multimers

from a linear type to a cyclic one, w i t h

i n c r e a s i n g c o n c e n t r a t i o n in the limit high c o n c e n t r a t i o n s

F<0.100.

However,

at

,dipolar m u l t i m e r s d o m i n a t e for

3-pentanol w h i l e large cyclic m u l t i m e r s of n o n d i p o l a r type

0167-7322/88/$03.50

© 1988 Elsevier Science Publishers B.V.

I08 may be s i g n i f i c a n t for tert-pentanol.

These c o n c l u s i o n s are

c o n s i s t e n t w i t h those results o b t a i n e d from Kerr effect

,

13C NMR r e l a x a t i o n and the K i r k w o o d g - f a c t o r of t h e same or related alcohols.

INTRODUCTION

Perhaps,

one of the most c o m m o n l y used solvents i n

c h e m i c a l reactions is an alcohol. rates

It is k n o w n to affect the

[i], and i n f l u e n c e the s t e r e o c h e m i s t r y of the p r o d u c t s

[2,3] of some c h e m i c a l reactions. roles in m e d i a t i n g the reactions,

Despite its i m p o r t a n t v e r y little i n f o r m a t i o n is

known at m o l e c u l a r

levels as to how an alcohol can m o d i f y a

c h e m i c a l reaction.

In order to gain a better u n d e r s t a n d i n g

on this problem,

it m a y be better to focus our a t t e n t i o n on

the structures of the alcohols themselves. goal,

To achieve this

it is r e q u i r e d that our d e t a i l e d k n o w l e d g e of

H - b o n d i n g be g r e a t l y improved. k n o w l e d g e on alcohols, things,

Apart from e n h a n c i n g our

H- b o n d i n g is also known,

among other

to p l a y important parts in the s t a b i l i z a t i o n of

protein structures

[4,5] and in enzyme k i n e t i c s

Over the years,

[6].

several r e s e a r c h e r s have been a t t r a c t e d

to w o r k on the p r o b l e m of m o l e c u l a r a s s o c i a t i o n of pure alcohols and in their b i n a r y m i x t u r e s w i t h n o n d i p o l a r solvents,

as a p p e a r e d in several reviews

[7-12].

V a r i o u s t e c h n i q u e s have been applied to i n v e s t i g a t e the p r o b l e m of m o l e c u l a r a s s o c i a t i o n in alcohols, [13-16], NMR

e.g.,

[17-22], vapour p r e s s u r e m e a s u r e m e n t s

dielectric relaxation

IR [23],

[24-27], d i e l e c t r i c p o l a r i z a t i o n

[28],

109

pressure dependence of dielectric behaviour [29], nonlinear dielectric effect dipole moments

(NDE)

[30], average square of apparent

[31], magneto-optical rotation [32],

thermodynamic measurements [33] and calorimetry [34].

It is

apparent from these reports that there is no single technique which can be used on its own to elucidate the structures of molecular associates in alcohols. largely to the complex nature of the problem. at a given concentration of an alcohol

This is due For example,

(dissolved in a

nondipolar solvent), several types of associates may be present simultaneously, i.e., monomers, dimers, trimers, etc., polymers and cyclic multimers of various sizes. Because of this complexity, a combination of several techniques is required to study the problem which has thus far remained largely unresolved.

Our objective has been to utilize several selected techniques to investigate the very same system i.e., the binary mixtures of various pentanols in n-heptane. In part I of this series, we have reported the temperature dependence of Kerr effect of pentanols in n-heptane at various concentrations using the low temperature Kerr cell [35]

,

the details of the work have been published [36] and will not be further discussed , only relevant results will be used for later comparisons.

In this communication ( part II ), the temperature dependence of viscosities of various pentanols

(l-pentanol,

2-pentanol, 3-pentanol and t-pentanol) in n-heptane at various concentrations is reported.

Concentration of

II0 p e n t a n o l s v a r i e d from the mole fraction,

F = 0.600 to F =

0.025 and the t e m p e r a t u r e s were in the low range of 233 to 293 K.

The v i s c o s i t y m e a s u r e m e n t s were m a d e w i t h an

a u t o m a t i c v i s c o m e t e r o p e r a t i n g in a closed system.

P r e v i o u s w o r k related to this system is h e r e b y recapitulated.

Kerr effect of l - p e n t a n o l in c a r b o n

t e t r a c h l o r i d e at room t e m p e r a t u r e has been m e a s u r e d

[37].

B i n a r y m i x t u r e s of l-pentanol in inert solvents have b e e n i n v e s t i g a t e d by n o n l i n e a r d i e l e c t r i c effect polarization

[30], d i e l e c t r i c

[28] and e l e c t r o - d i l a t o m e t r i c effect

[38].

V i s c o s i t i e s of some pure p e n t a n o l s above room t e m p e r a t u r e [39] and their vapour p r e s s u r e s have a p p e a r e d

[40].

THEORY

Several theories on the t e m p e r a t u r e d e p e n d e n c e of v i s c o s i t i e s of liquids have been a d v a n c e d by m a n y i n v e s t i g a t o r s as a p p e a r e d in the reviews

[41,42].

It is not

the p u r p o s e of this c o m m u n i c a t i o n to go over them, however, a few theories r e l e v a n t to the p r e s e n t w o r k is b r i e f l y discussed.

One of the s i m p l e s t r e l a t i o n s on the t e m p e r a t u r e d e p e n d e n c e of v i s c o s i t y is the one o r i g i n a l l y p r o p o s e d by Reynolds

[43] and sometimes r e f e r r e d to as de Guzman

for w h i c h the v i s c o s i t y of a liquid

[44]

(D) at a c o n s t a n t

p r e s s u r e is given as :

D = Ae E/RT

(i)

111

Where

R is the gas c o n s t a n t

assumed kno w n

to be i n d e p e n d e n t

as v i s c o u s

obeyed

heat.

by n o n d i p o l a r

extensively Eyring

of the t e m p e r a t u r e

Eqn.(1)

liquids

has c o n s i d e r e d

V,

[45]

enthalpy liquid

to be

range

is not

theory

flow from the p o i n t and p r o p o s e d

the

:

, the m o l a r

number

/\H$,

of flow does

and /_~S~is taken

m a y be e x p r e s s e d

; h, the P l a n c k ' s

; /_~S and _ _

volume A.

as

[45]

(zl

(Nh/V)e -/AS/R'' • e l I H / R T

%

volume

of a c t i v a t i o n

temperature,

found

if the t e m p e r a t u r e

state

N is the A v o g a d r o ' s

the m o l a r

E is also

is g e n e r a l l y

the v i s c o u s

n =

Where

and

large.

of v i e w of the a c t i v a t e d following

, A and E are c o n s t a n t

constant;

are the e n t r o p y

, respectively.

and

For a g i v e n

not v a r y g r e a t l y w i t h to be constant,

the e q u a t i o n

:

D = A eEv/RT

Where

E

is r e f e r r e d

v

activated

process

(3)

to as a c t i v a t i o n

of v i s c o u s

flow

energy

energy barrier

that m u s t be o v e r c o m e

can occur.

form of eqn.(2) Eqn.(3)

i.e.,

m a y be e x p r e s s e d

l)In =

f l o w ").

as

to later

It r e p r e s e n t s

before

It m a y be seen that

eqn.(3)

for the

(will be r e f e r r e d

as " a c t i v a t i o n

flow p r o c e s s

of v i s c o u s

energy

the

the e l e m e n t a r y the c o n d e n s e d

is the same as eqn.(1).

:

-R

+ in A

(4)

112 EXPERI M E N T A L

Viscosity viscometer.

measurements

It was

were m a d e w i t h

constructed

from an U b b e l o h d e

such that the w h o l e m e a s u r e m e n t s closed

system.

condensation

This

of a t m o s p h e r i c

the e v a p o r a t i o n

from

also p r e v e n t e d particles

facility

For a typical the c a p i l l a r y

served

water

to p r o t e c t

vapour

during

measurement,

light on the transmitted picked

liquid through

level p a s s e d the light

intensity

electrical

was

pulse

liquid

to e n s u r e

level

Specialties).

tube.

liquid

output

digital

of f i n d i n g

The w h o l e

b a t h of a h o m e - m a d e

was

light , was

fed into

a

of the liquid change4in

into an on at the Logical

gating

(and not ascending) a flow time,

could

flow times were

generator

frequency

The time base

The

the c o u n t e r

Accurate

light b u l b

it c r e a t e d

that only d e s c e n d i n g

up

(Masterflex).

sample

and off at the lower one.

by the use of a f u n c t i o n

it

and to focus

then c o n v e r t e d

to trigger

, in the process

a quartz-controlled

10 -6 s.

and the

fibre w h o s e

s t a r t or stop the counter. obtained

source

the t i m i n g mark,

signal

t i m i n g mark,

used

a small

in the glass

w h i c h was

In addition,

sample was d r a w n

As soon as the m e n i s c u s

through

the

and to p r e v e n t

by a p u m p

as light

the glass

up by an optical

phototransistor.

upper

sample

against

of the dust

a liquid

tube of the v i s c o m e t e r

lens was used

in a

the m e a s u r e m e n t s .

At each t i m i n g m a r k of the v i s c o m e te r , with built-in

in,

samples.

any a c c u m u l a t i o n

in the v i s c o m e t e r

viscometer

c o u l d be c o n d u c t e d

, the liquid

against

an a u t o m a t i c

(Precision)

counter

c o u l d be v a r i e d

viscometer

was

submerged

cryostat

whose

thermal

and

(Global from 1 s to

in the liquid stability

during

113

the m e a s u r e m e n t s than + 0.1 K. viscometer

The d e t a i l e d

were measured 223 K.

will

of ethanol,

at v a r i o u s

n-heptane

concentrations

was c h o s e n

the a v a i l a b i l i t y densities

in the low t e m p e r a t u r e

pentanols

greater

Concordant automatic errors

to be m e a s u r e d

readings

normally

due

caused

All the a l c o h o l s d r i e d by m o l e c u l a r

collected. with

and of

at low

viscometer. obtained

with

to the e l i m i n a t i o n

the

of the

factor.

from Aldrich,

and p u r i f i e d

they w e r e

by fractional

fractions

of w h i c h w e r e

Spectralanalyzed

n-heptane

from F i s h e r was d r i e d

and f i l t e r e d

prior

to use.

AND D I S C U S S I O N

The results various

Concentration

too v i s c o u s

were p u r c h a s e d

)

liquid due to

for v i s c o s i t i e s

range.

by the h u m a n

sieves

to 0.600

to a p p r o x i m a t e l y

by the p r e s e n t

largely

in

o n l y the m i d d l e

s o d i u m wires

RESULTS

down

of the flow times w e r e

viscometer

distillation

( F = 0.025

data

than F = 0.6 was

elsewhere.

and p e n t a n o l s

as a c a l i b r a t i n g

of its e x t e n s i v e

to b e t t e r

of the a u t o m a t i c

be p u b l i s h e d

from r o o m t e m p e r a t u r e

Ethanol

temperatures

and m a i n t a i n e d

construction

and the c r y o s t a t

F l o w times n-heptane

c o u l d be r e g u l a t e d

of v i s c o s i t i e s

pentanols

of pentanols, temperature measurements

F

in n - h e p t a n e

( 0.025

(D) of n - h e p t a n e for d i f f e r e n t

~ F S 0.600

are c o l l e c t e d

in T a b l e s

of n is a p p r o x i m a t e l y

mole

and of fractions

) as a f u n c t i o n 1-5

.

~ 6 %

Error .

of

in the

114 TABLE I. T e m p e r a t u r e d e p e n d e n c e of v i s c o s i t y

(n) of n-heptane.

n ( 1 0 - 4 p a s) 11.46 9.11 7.80 6.31 5.15 4.62

T (K) 223.5 242.0 251.3 267.6 283.0 294.4

T A B L E 2. T e m p e r a t u r e d e p e n d e n c e of v i s c o s i t y fractions

(n) at various m o l e

(F) of l - p e n t a n o l in n-heptane.

F = 0.025 T (K) 223.4 239.2 251.7 268.6 283.2 292.6

D

(10-4pa s) 12.07 9.16 7.55 6.10 5.23 4.83

F = 0.051 T (K) 222.0 234.3 248.0 264.4 276.9 293.9

F = 0.i00 T (K) 221.0 237.4 254.2 266.7 278.2 289.7

n (10-4pa s) 14.23 10.45 8.19 6.79 5.93 5.28

F = 0.202 T (K) 223.1 236.0 252.6 266.0 282.3 291.4

F = 0.300 T (K) 225.6 242.6 251.1 266.2 277.8 293.2

D

(10-4pa s) 23.11 15.19 12.72 9.52 7.80 6.55

F = 0.609 T (K) 222.5 238.4 253.4 268.3 282.7 292.7

D (10-4pa s) 98.15 51.46 31.15 20.23 14.22 11.50

n (10-4pa s) 12.88 10.22 8.31 6.56 5.73 4.91

n (10-4pa s) 17 63 13 16 9 80 7 95 6 43 5 84 F = 0. 500

T (K) 223.4 239.3 254.4 269.4 283.2 293.8

n (10-4pa s) 63 74 35 i0 22 21 15 05 ii 14 9 24

115

T A B L E 3. T e m p e r a t u r e d e p e n d e n c e of v i s c o s i t y fractions

(n) at various m o l e

(F) of 2 - p e n t a n o l in n-heptane.

F = 0.025 T (K) 223.1 237.6 252.5 267.4 283.0 292.0

F = 0.051

n (10-4pa s) 11.92 9.45 7.53 6.15 5.19 4.84

T (K) 223.8 238.0 253.3 268.9 283.3 295.1

F = 0.101 T (K) 223.2 239.5 250.9 268.1 284.3 292.2

D

F = 0.200

(10-4pa s) 13.23 9.89 8.25 6.53 5.47 5.05

T (K) 223.7 239.0 253.7 268.2 283.0 293.0

F = 0.300 T (K) 224.1 237.5 253.2 268.5 281.9 291.9

D

n (10-4pa s) 12.24 9.46 7.50 6.17 5.28 4.77

n (10-4pa s) 15.43 11.28 8.78 7.11 5.96 5.41 F = 0.500

(10-4pa s) 21.43 14.83 10.70 8.24 6.83 6.13

T (K) 223.9 238.3 252.7 268.3 281.8 293.8

n (10-4pa s) 59.27 31.60 19.10 12.48 9.23 7.71

F = 0.600 T (K) 223.5 237.9 253.2 268.3 282.4 292.7

D (10-4pa s) 128.40 61.20 31.27 18.48 12.37 9.88

Each set of v i s c o s i t y values at various t e m p e r a t u r e s for a given mole f r a c t i o n of p e n t a n o l was fitted to eqn.(4) by the use of a linear r e g r e s s i o n program. r e g r e s s i o n analysis,

the slope

From

the

( E v /R ) and the intercept

116

(in A) w e r e of v a l u e s Thus

with

Good

correlation

fits w e r e

are

collected

observed

coefficients

E v and A for e a c h m o l e

results

TABLE

obtained.

fraction,

in T a b l e

for

better were

than

obtained

all

sets

0.99. and

the

6.

4.

Temperature fractions

dependence (F) of

of v i s c o s i t y

3-pentanol

(O)

n

(10-4pa 11.91 9.01 7.24 6.04 5.04 4.66

F = 0.051 s)

T (K) 222.2 237.5 253.0 268.6 281.3 291.7

~

(10-4pa 12.36 10.04 7.81 6.40 5.41 4.89

s)

T (K) 223.0 239.4 254.0 267.1 283.2 293.4

n

(10-4pa 20 42 13 78 10 15 8 03 6 62 5 90

s)

F = 0.600 T (K) 237.0 253.1 268.8 284.4 292.8

D

(10-4pa 65.29 29.71 16.45 10.92 9.12

(10-4pa 12.79 9.34 7.45 6.04 5.27 4.75

s)

n

(10-4pa 15.70 11.18 8.63 7.11 5.84 5.31

s)

F = 0.500

F = 0.309 T (K) 223.2 238.8 254.0 268.3 281.9 292.4

q

F = 0. 201

F = 0.i01 T (K) 225.1 237.4 253.0 267.6 283.1 294.1

mole

in n - h e p t a n e .

F = 0.026 T (K) 223.9 238.6 253.3 268.6 283.4 294.0

at v a r i o u s

s)

T (K) 223.6 238.4 253.0 268.0 284.9 295.1

q

(10-4pa 71.86 33.22 18.43 12.14 8.55 7.34

s)

117

T A B L E 5. T e m p e r a t u r e d e p e n d e n c e of v i s c o s i t y fractions

(n) at various mole

(F) of t - p e n t a n o l in n-heptane.

F = 0.025 (10-4pa s) 12 41 8 90 7 28 5 99 5 i0 4 70

T {K) 221.9 238.9 252.3 267.5 283.2 293.3

F = 0.050 T (K) 221.2 238.0 253.0 268.0 283.0 295.5

F = 0.i01 T

(K)

D

223.1 239.2 253.5 266.7 281.2 291.8

(10-4pa s) 13.32 9.79 7.82 6.48 5.48 5.06

F = 0.200 T (K) 223.1 237.5 252.5 267.4 281.6 295.1

F = 0.300 T (K) 223.9 237.5 252.9 267.8 283.2 294.2

n (10-4pa s) 20.48 14.68 10.90 8.36 6.71 5.92

D (10-4pa s) 13.77 10.04 7.86 6.12 5.20 4.72

n {10-4pa s) 15.55 11.63 8.90 7.12 5.95 5.03 F = 0.501

T (K) 223.0 238.2 253.2 267.2 281.3 293.4

D (10-4pa s) 41.92 25.42 17.16 12.57 9.54 7.90

F = 0.600 T (K) 236.7 251.8 267.5 282.4 291.2

n (10-4pa s) 38.67 24.00 15.92 11.40 9.62

To f a c i l i t a t e the d i s c u s s i o n of the results, of E v ( kJ/mol pentanols, Fig.l.

the values

) o b t a i n e d from v a r i o u s s o l u t i o n s of

are p l o t t e d against m o l e fractions,

F as shown in

Due to the s i g n i f i c a n c e of the g r a p h at low m o l e

118

fractions

( F < 0.2 ) and because all the curves cannot be

seen c l e a r l y in this region as a p p e a r e d in Fig. graph in this region w i t h e n l a r g e d scales, shown in Fig.

1 ; a second

is p l o t t e d as

2.

TABLE 6. Collections of the p r e - e x p o n e n t i a l a c t i v a t i o n e n e r g i e s of viscous flow

factor

(A) and the

(E v) for p e n t a n o l s in

n - h e p t a n e at various mole fractions of p e n t a n o l s F (mole fraction)

Axl06 (Pa s)

(F). E (kJ Ymol)

0.025 0.051 0.i00 0.202 0.300 0.500 0.609

l-pentanol + n - h e p t a n e 24.4 23.8 21.3 15.6 9.1 1.9 1.2

7.22 7.33 7.71 8.73 10.35 14.99 16.53

0.025 0.051 0.101 0.200 0.300 0.500 0.600

2-pentanol + n - h e p t a n e 24.5 24.0 22.2 17.7 9.5 1.0 0.2

7.21 7.28 7.57 8.27 i0.01 16.04 20.27

0.026 0.051 0.i01 0.201 0.309 0.500 0.600

3-pentanol + n - h e p t a n e 22.6 20.3 22.7 16.3 10.4 0.5 0.I

7.34 7.61 7.47 8.43 9.74 17.39 21.08

0.025 0.050 0.i01 0.200 0.300 0.501 0.600

t-pentanol + n-heptane 22 6 16 7 20 3 15 3 ii 0 39 16

7.34 8.12 7.72 8.56 9.70 12.89 15.33

119

23"0

19"0

• I - - PENTANOL Zh 2 - - P E N T A N O L r7 3 - - P E N T A N O L 0 t -- PENTANOL

/ A Cl / ' L~_ i

• t

13//.

0

71

E

/K 7 "

"-~ 15'0 J¢ LIJ I1"0

7.0 0'00

i

0"10

0"20

0"30

0"40

i

0"50

0"60

i 0"70

F (MOLE FRACTION) Fig.l Plots of E (kJ/mol), the activation energy for viscous flow, against concentration of various pentanols in n-heptane ,in mole fraction (F). Symbol used for each curve represents a given pentanol as specified on the graph.

I0"0 •

A

-6 E

9.0

I-PENTANOL 2-PENTANOL D 3-PENTANOL O t-PENTANOL

,aE v

I,LI

8"0

7"0 0"00

I 0'05

I 0"10

I 0"15

I 0'20

F (MOLE FRACTION) Fig.2 Enlarged curves of E, (kJ/mol), the activation energy for viscous flow , against ~oncentration of various pentanols in n-heptane expressed in mole fraction (F), showing only the low concentration range. Symbols used for various pentanols are given on the graph.

120 E v has been concentration various

found

to be v e r y s e n s i t i v e

of pentanols.

concentration

information

when viewed

as follows

Detailed

discussion

i.

over

E

the entire

obtained

from other is g i v e n

large E v values the d o m i n a t i o n large n u m b e r

in the s o l u t i o n

or r e l a t e d

obtained

systems

change

v

at

associates The

m a y be a t t r i b u t e d

per each multimers,

thereby

for v i s c o u s

techniques,

flow.

There

of the same

and these are

hereunder.

Kerr effect concentration

investigation

range

0.299

of the same

S F S 0.601

range,

the details

of w h i c h have been p u b l i s h e d

features The

has been c o n d u c t e d

relevant results

formed at F = 0.299 small d i p o l e moment. that small m u l t i m e r s

and 0.399 This

in this

to the p r e s e n t

showed

system

laboratory,

[36] and o n l y discussion

that d o m i n a n t are of d i p o l a r

is in a g r e e m e n t

are formed

for the

and for the same

temperature

to

possessing

from the i n v e s t i g a t i o n s

by other

in E

per multimers.

by the species

energy

as shown

and r a p i d l y

the d o m i n a t i n g

at h i g h c o n c e n t r a t i o n s

large a c t i v a t i o n

are some data

The g r a d u a l

that

range

for F < 0.3,

of few m o n o m e r s

of m o n o m e r s

increases

concentration

.

suggesting

are small c o n s i s t i n g

mentioned.

especially

for each p e n t a n o l

gradually

0.3 < F < 0.6

low c o n c e n t r a t i o n

salient

in terms of

association,

for this a l c o h o l

v

It i n c r e a s e s

in the range

discussed

useful

:

monotonically

requiring

in

of E v from

are more

values,

on m o l e c u l a r

(i) l-Pentanol.

in Fig.

viscosity

in the light of results

techniques.

values

of the same pentanol,

than their c o r r e s p o n d i n g providing

The r e l a t i v e

to changes

are

multimers type w i t h a

w i t h the view

at low c o n c e n t r a t i o n s

as

121

s u g g e s t e d by the low E v values. F = 0.600,

At h i g h c o n c e n t r a t i o n up to

the t e m p e r a t u r e d e p e n d e n c e of Kerr c o n s t a n t

(B)

is c h a r a c t e r i s t i c of m o l e c u l e s w i t h a large dipole m o m e n t [36,46].

In addition,

B changes r a p i d l y w i t h i n c r e a s i n g

c o n c e n t r a t i o n and its m a g n i t u d e is large c o m p a r a b l e to that of p o l y

( n-butyl i s o c y a n a t e

) having Mn

= 1.3 x 105

[47].

T h e s e results support the v i e w that large linear m u l t i m e r s are d o m i n a t i n g at high c o n c e n t r a t i o n s

as i m p l i c a t e d by the

h i g h E v values.

Electro-dilatometric

effect

(R),

R = (V - Vo)/ VoE2

,

a new t e c h n i q u e d e v e l o p e d in this l a b o r a t o r y w h i c h m e a s u r e s the r e l a t i v e change in volume w i t h applied e l e c t r i c field

(V) and w i t h o u t

(E), has b e e n o b t a i n e d for F = 0.399

at 298 K to be 6.25 x 10 -17 m 2 V -2 [38].

It m a y be i n f e r r e d

from the p o s i t i v e i n c r e m e n t in v o l u m e that a p p l i e d field,

(V o) the

, under the

r e o r i e n t a t i o n of alcohol molecules,

created a

net r e d u c t i o n in the number of H-bonds.

The excess m o l a r volume of this b i n a r y m i x t u r e at 298.15 K has also b e e n r e p o r t e d to be p o s i t i v e up to F = 0.7 [48].

It was c o n c l u d e d that the h e p t a n e m o l e c u l e s cannot

fit in p r o p e r l y b e t w e e n the i n t e r s t i t i a l

spaces c r e a t e d by

the m o l e c u l e s of l-pentanol.

The K i r k w o o d g - f a c t o r for a r e l a t e d system of 1-butanol in c y c l o h e x a n e

[49] is s l i g h t l y < 1 at F = 0.1, i m p l y i n g

that species w i t h lower d i p o l e m o m e n t than m o n o m e r i c alcohol m a y be present.

At higher c o n c e n t r a t i o n s ,

0.2 < F < 0.6 ,

g i n c r e a s e s r a p i d l y a t t a i n i n g the value g = 3.

Such a large

value of g i n d i c a t e s that m u l t i m e r s w i t h a large d i p o l e

122 moment

are dominating,

suggested

earlier

therefore

by viscosity

, supporting

results

the v i e w

of the p r e s e n t

experiments.

(ii) is small

2-Pentanol. in the range

case of l-pentanol. (0.300

< F < 0.600

concentration at low mole consisting

The c h a n g e F < 0.300,

and is v e r y

However

at high c o n c e n t r a t i o n s

,

) , Ev increases

as shown

fractions

in Fig.

i.

similar

rapidly with The g r a d u a l

is p r o b a b l y

of few m o n o m e r s

concentrations,

in E v w i t h c o n c e n t r a t i o n to the

increasing

change

in E v

c a u s e d b y small m u l t i m e r s

per associate.

m a y be a t t r i b u t e d

Large

Ev

to the f o r m a t i o n

,at high of large

multimers.

Our Kerr effect m e a s u r e m e n t s indicated

the f o l l o w i n g

(B) is v i r t u a l l y The t e m p e r a t u r e characteristic at F = 0.590 dipolar

type.

unchanged dependence

of m u l t i m e r s

to 0.800

with

a low d i p o l e

( to account

in the range

with

high r e s i s t a n c e

large E v .

at m o l e

.

is and

are of

linear

and

fraction

of the cyclic m u l t i m e r s

in the range

0.400

< F < 0.800

in B for these c o n c e n t r a t i o n s

The type of the cyclic m u l t i m e r s possess

< F < 0.800

multimers

that both

formation

for no c h a n g e

0.400

a small d i p o l e moment;

m a y be s i g n i f i c a n t

moment

[36]

The Kerr c o n s t a n t

of B at F = 0.399

, the d o m i n a t i n g

and i n c r e a s i n g

alcohol

features.

It m a y be i n f e r r e d

cyclic multimers F=0.399;

salient

of this

should be such that

to viscous

flow

they

, as implied b y

).

123

(iii)

3-Pentanol.

with concentration. concentrations

increase

); however,

value

from F = 0.025

increasing

explanations increasing

a minimum

formation

the d i m e r s

of 3 - p e n t a n o l

increase

in E v observed.

linear m u l t i m e r s favourable

cannot

from F = 0.050 domination

to 0.100

by m u l t i m e r s

the dimers.

it c o u l d

Among

is, perhaps,

possess

low Ev,

cyclohexane

with

less

the m o s t

closely

At h i g h e r

of h i g h e r

of the alkyl

of some of the

c y c l i c multimers, to form.

In order

similar

to that of the

occupying

concentrations,

b y large multimers.

than

w o u l d be the

formed

with

increases

hindered

trimers

of E v m a y be a s s o c i a t e d

less

to the i n c r e a s i n g

at the e x p e n s e s

likely

to 0.050.

, however,

sterically

the p o s s i b l e

a dimers)

for the

hindrance

choices

the

sterically

as the c o n c e n t r a t i o n

v

w i t h O and H atoms

on the ring.

it is

, m a y be a s c r i b e d

the c y c l i c

conformation

(possibly

account

be r u l e d out;

of c y c l i c m u l t i m e r s

trimers

be to assume

the f o r m a t i o n

One of the p l a u s i b l e

linear m u l t i m e r s .

it

For F > 0.100,

s h o u l d be m o r e

While

in E

reveals

, and then

from F = 0.025

to form due to the steric

The i n c r e a s e

domination

would

is i n c r e a s e d

than the monomers,

2),

look at

One of the p l a u s i b l e

of linear m u l t i m e r s

hindered

A closer

at F = 0.100

again.

a

at F = 0.600

( Fig.

to 0.050

to this o b s e r v a t i o n

as the c o n c e n t r a t i o n

values

).

of E v at low c o n c e n t r a t i o n s

it starts

chair

at h i g h e r

the h i g h e s t

investigated

in E v

at low

reaching

to r e a c h

formation

little

), it e x p e r i e n c e s

decreases

groups.

very

change

< F < 0.600

that E v i n c r e a s e s

Sin c e

the o v e r a l l

( 0.300

(among all the p e n t a n o l s the trends

shows

E v changes

( F < 0.300

concentrations rapid

Fig.l

should

assume

the a l t e r n a t e F > 0.300,

the i n c r e a s i n g

a to the

sites

the large

124

Our Kerr e f f e c t multimers

studies

of n o n d i p o l a r

are dominant. multimers

type

At h i g h e r

(233 K);

233 to 293 K multimers

conjecture

) is a c c o m p a n i e d

at F < 0.300

3-pentanol,

(iv)

v

at high

moment.

the change

in E v with

3-pentanol

( Fig.2

and attains decreases

reaching

E v starts

increasing

pentanols

measured

It is l i k e l y

of v i s c o s i t y

( F > 0.500

increases

( 0.300 ,in this

( Fig. that the

studied.

that of

E

steadily ).

concentration lies

)

v

For F > 0.100

< F < 0.600

,

in the

It is also range,

the lowest

the

among

the

1 ). linear m u l t i m e r s

for the o b s e r v e d

be ruled o u t , a r e

) for

from F = 0.025

for the c o n c e n t r a t i o n

concentration.

that the

, beyond which

It i n c r e a s e s

results.

( F < 0.300

resembles

at F = 0.100

concentration

and a c c o u n t

increasing cannot

again.

are d o m i n a t i n g

to 0.050

v

at F = 0.050

that

of E v a g a i n s t

E

by

the

the p e n t a n o l s

concentration

range

to note

to test

At low c o n c e n t r a t i o n s

a trough

high c o n c e n t r a t i o n interesting

among

(from

domination

for later c o m p a r i s o n s

) , i.e.,

a maximum

at low

More Kerr e f f e c t

are r e q u i r e d

are the h i g h e s t

),

in t e m p e r a t u r e

by i n c r e a s i n g

concentrations

t-Pentanol.

( F = 0.600

dominate

made by the i n t e r p r e t a t i o n

of E

that at F = 0.399,

some cyclic multimers)

and an i n c r e a s e

It should be m e n t i o n e d

dimers

(e.g.,

concentration

w i t h a low d i p o l e

measurements

curve

showed

w i t h a high d i p o l e m o m e n t

temperature

values

[36]

Longer

,possibly

range F = 0.025

increase

in E

linear multimers,

less s i g n i f i c a n t

the

due,

with

v

while

firstly

to the

125

steric h i n d r a n c e of t - p e n t y l groups,

and s e c o n d l y to the

v e r y low c o n c e n t r a t i o n s of t-pentanol. range 0.050 < F < 0.100, m u l t i m e r s are formed. linear m u l t i m e r s

The d r o p in E v in the

suggests that a new kind of

Such m u l t i m e r s m a y be

formed from the

-in order to account for the o b s e r v e d

d e c r e a s e in E v w i t h i n c r e a s i n g c o n c e n t r a t i o n .

One p l a u s i b l e

e x p l a n a t i o n w o u l d be, to assume that cyclic m u l t i m e r s are the d o m i n a t i n g species. m a y be important,

It is p r o b a b l e that cyclic trimers

and in order to have the o b s e r v e d low Ev,

it should exist in the chair form similar to that of the cyclohexane,

h a v i n g O and H atoms o c c u p y i n g the a l t e r n a t e

p o s i t i o n s of the ring.

Larger cyclic m u l t i m e r s are also

possible.

At h i g h e r c o n c e n t r a t i o n s

( 0.300 < F < 0.600

), E v

values w h i l e i n c r e a s e w i t h i n c r e a s i n g c o n c e n t r a t i o n ,

are

among the lowest of all the p e n t a n o l s at the same concentrations.

Such results i m p l y that large m u l t i m e r s are

formed h a v i n g the t - p e n t y l groups a r r a n g e d in such a w a y as to offer the least r e s i s t a n c e to flow w h e n c o m p a r e d to other m e m b e r s of the p e n t a n o l s at the same concentrations.

The

p o s s s i b l e s t r u c t u r e for the large m u l t i m e r s will be p r o p o s e d later f o l l o w i n g the e v i d e n c e s o b t a i n e d from other techniques.

The i m p o r t a n c e of the cyclic m u l t i m e r s at F = 0.i00 m a y be p a r t i a l l y s u b s t a n t i a t e d by n o t i n g that, s y s t e m of t - b u t a n o l in cyclohexane,

for a r e l a t e d

the K i r k w o o d g - f a c t o r

attains the m i n i m u m value w i t h g < 1 at F = 0.i [49]. It m a y thus be i n f e r r e d that the m u l t i m e r s

formed p o s s e s s e s a lower

d i p o l e m o m e n t than m o n o m e r i c alcohol.

126 General

agreement

is o b t a i n e d

of t-butanol

in h e x a n e

in w h i c h

been

suggested

multimers

Kerr e f f e c t [36]

nondipolar

type d o m i n a t e

indicated

increases

higher

of m o n o m e r s

concentration

implicated (F=0.399)

( e.g.,

results

), are

than those important.

we m a y assume

the trimers

) whic

concentration

even at h i g h e r

concentrations

3-pentanol

( Fig.

for both

1 ).

As d i s c u s s e d

3-pentanol

(e.g.,

trimers

significant

increasingly

) are p r o b a b l y At h i g h e r

larger

of a s s o c i a t i o n

between

that

, the

suggested

at high

in sections

concentrations

between

E

v

multimers

at low ( F > 0.3

their E v values

),

becomes

increases

is a good r e f l e c t i o n the two p e n t a n o l s

(iii)

that thier

cyclic

as the c o n c e n t r a t i o n

Such a large d i f f e r e n c e

from

further

and t - p e n t a n o l and the

the d i f f e r e n c e

Thus,

concentration

and t - p e n t a n o l

follow the same trends

however,

at

in the curve of E v a g a i n s t

values

concentrations.

formed

studies.

The d i f f e r e n c e

for

are

with

, are also

is one final p o i n t w h i c h m e r i t s i.e.,

of

, cyclic m u l t i m e r s

to form at F = 0.i00

by Kerr e f f e c t

discussion,

(iv),

( F = 0.399

from this

Also as the

per m u l t i m e r s

to be i m p o r t a n t

There

and

to F = 0.600

have

[20].

alcohol

.

trimers

and h i g h e r

that cyclic m u l t i m e r s

at low c o n c e n t r a t i o n ,

cyclic m u l t i m e r s by v i s c o s i t y

of this

at F = 0.399

concentration

these results

the cyclic

at F = 0.4 to 0.5

investigation

laboratory

lower

case

to form at low c o n c e n t r a t i o n ,

are s i g n i f i c a n t

number

from 13C N M R r e l a x a t i o n

(Fig.l).

that the m o d e s

cannot

be the same.

127

The r e l a t i v e l y low values of Ev, in c o n j u n c t i o n w i t h the e v i d e n c e s o b t a i n e d from Kerr effect studies of t - p e n t a n o l as d i s c u s s e d previously, the cyclic m u l t i m e r s

have led us to assume that , p e r h a p s ( e.g.,

trimers

) m a y a s s o c i a t e among

t h e m s e l v e s to form larger m u l t i m e r s as furhter e l a b o r a t e d below.

For example,

if it is assumed that the cyclic m u l t i m e r s

is the cyclic trimers e x i s t i n g in the chair conformation; each trimers m a y a s s o c i a t e w i t h two n e i g h b o u r i n g ones, one above and one b e l o w the plane of the ring. a s s o c i a t i o n c o u l d a c c o u n t for the

small changes in the Kerr

c o n s t a n t o b s e r v e d at high c o n c e n t r a t i o n s 0.800

) [36].

Such an

( F = 0.500 to

This ring s t a c k i n g a s s o c i a t i o n m o d a l i t y of

t - p e n t a n o l can be b e t t e r u n d e r s t o o d w i t h the aid of a model. F r o m the model,

each t - p e n t y l g r o u p is in a s t a g g e r e d

c o n f o r m a t i o n w i t h r e s p e c t to its n e a r e s t n e i g h b o u r s other t - p e n t y l groups H-bonding between

).

( of

To a l l o w for this, b i f u r c a t e d

-OH groups is a s s u m e d

, i.e., each of O

and H atoms of the -OH p a r t i c i p a t i n g in the f o r m a t i o n of a cyclic trimers, m a y form up to 2 H-bonds.

Such an

a r r a n g e m e n t allows for the free r o t a t i o n of all the alkyl groups

[2(-CH 3) and -C2H 5 ] w i t h o u t i n h i b i t i n g the f o r m a t i o n

of H-bonds b e t w e e n the rings.

However,

in the case of

3-pentanol,

this ring s t a c k i n g m o d e of a s s o c i a t i o n is

inhibitive,

due to the i n t e r m o l e c u l a r steric i n t e r a c t i o n s

among the ethyl groups

( two -C2H 5 per m o l e c u l e

to m i n i m i z e the steric interactions,

).

In order

the ring s e p a r a t i o n

will be too far apart to a l l o w for any e f f e c t i v e H - b o n d f o r m a t i o n b e t w e e n the rings.

Thus, o t h e r m o d e of

~association w i l l have to be a d v a n c e d in order to account for

128

the fact that d i p o l a r a s s o c i a t e s d o m i n a t e at high concentration

( F = 0.600

) as s u g g e s t e d by our t e m p e r a t u r e

d e p e n d e n c e Kerr effect i n v e s t i g a t i o n of 3 - p e n t a n o l

It is of i n t e r e s t to note that,

[36].

from the v i s c o s i t y and

vapour p r e s s u r e m e a s u r e m e n t s of a number of pure alcohols above room temperature,

a c o n c l u s i o n was d r a w n that

b r a n c h i n g of the alkyl group leads to an i n c r e a s e in association

[39].

This is in general a g r e e m e n t w i t h our

p r o p o s e d f o r m a t i o n of and d o m i n a t i o n by large m u l t i m e r s for t-pentanol at high c o n c e n t r a t i o n s .

CONCLUSIONS

V i s c o s i t i e s of b i n a r y m i x t u r e s of various p e n t a n o l s in n - h e p t a n e as a f u n c t i o n of t e m p e r a t u r e have been m e a s u r e d w i t h an a u t o m a t i c v i s c o m e t e r o p e r a t i n g in a c l o s e d system. T e m p e r a t u r e d e p e n d e n c e of v i s c o s i t y has b e e n found to follow a simple r e l a t i o n w i t h i n the t e m p e r a t u r e and c o n c e n t r a t i o n ranges specified, w h i c h allows for the e x t r a c t i o n of E vThe latter has been shown to be v e r y s e n s i t i v e to changes in m o l e c u l a r associates,

e s p e c i a l l y at very low c o n c e n t r a t i o n s .

A n a l y s e s of the results have led to the e n s u i n g conclusions.

For l-pentanol,

the m u l t i m e r s formed at low

c o n c e n t r a t i o n s c o n s i s t of few m o n o m e r s per multimers.

As

the c o n c e n t r a t i o n increases, m u l t i m e r s w i t h larger number of m o n o m e r s dominate.

The linear m u l t i m e r s are p r o b a b l y m o r e

s i g n i f i c a n t than the cyclic ones. 2-pentanol,

In the case of

small m u l t i m e r s d o m i n a t e at low c o n c e n t r a t i o n s .

At higher c o n c e n t r a t i o n s ,

there are e v i d e n c e s s u g g e s t i n g

129

that large c y c l i c m u l t i m e r s w i t h a low d i p o l e m o m e n t m a y be dominant.

A s s o c i a t i o n in the case of 3 - p e n t a n o l at low

concentrations,

is d i f f e r e n t from the p r e v i o u s two a l c o h o l s

as d i s c u s s e d above.

T h e r e is a c h a n g e in the d o m i n a t i n g

a s s o c i a t e s from a linear type

( plausibly,

( plausibly,

trimers

dimers

) to a cyclic

) at the c o n c e n t r a t i o n s F< 0.i00.

The cyclic m u l t i m e r s d o m i n a t e at least up to F = 0.399. M u l t i m e r s w i t h a low d i p o l e m o m e n t are s i g n i f i c a n t at high concentrations

( F < 0.600

).

Perhaps,

results are o b t a i n e d from t-pentanol. low c o n c e n t r a t i o n s

( F < 0.100

the m o s t i n t e r e s t i n g W h i l e the results at

) are v e r y similar to that of

3 - p e n t a n o l in that there is a shift in the d o m i n a t i n g multimers

from the linear type to the cyclic one;

results at h i g h c o n c e n t r a t i o n s

the

are quite different,

i.e., E v

values for t - p e n t a n o l at high c o n c e n t r a t i o n s are among the lowest of all the p e n t a n o l s

studied.

It has been s u g g e s t e d

that cyclic m u l t i m e r s of n o n d i p o l a r type, d o m i n a t e at high c o n c e n t r a t i o n s up to F = 0.600

.

The o b s e r v e d e x p e r i m e n t a l

results have led to the a s s u m p t i o n that,

a s s o c i a t i o n among

the cyclic m u l t i m e r s m a y be significant.

It m a y be seen that our i n t e g r a t e d a p p r o a c h of u t i l i z i n g various t e c h n i q u e s to i n v e s t i g a t e of b i n a r y mixtures,

the same s y s t e m

has b e g u n to reveal some of the c o m p l e x

f e a t u r e s of m o l e c u l a r a s s o c i a t i o n in pentanols. w i l l have to be done by u s i n g other t e c h n i q u e s

More w o r k to further

test some aspects of the c o n j e c t u r e p r o p o s e d thus far. A c t i v i t i e s a l o n g this line are c u r r e n t l y b e i n g p u r s u e d in our laboratory.

130 ACKNOWLEDGEMENTS

This p r o j e c t was funded in part by the N a t u r a l S c i e n c e s and E n g i n e e r i n g R e s e a r c h Council of Canada

( NSERC

Senate R e s e a r c h C o m m i t t e e of L a k e h e a d University. of an a s s i s t a n t s h i p to one of us

( J.A.K.

The a w a r d

) by the

G o v e r n m e n t of Canada through the C h a l l e n g e g r a t e f u l l y acknowledged.

) and the

'86 Program,

is

P r o f e s s o r S. Krause of the

Rensselaer Polytechnic Institute

, is t h a n k e d for the

h o s p i t a l i t y and for p r o v i d i n g the facilities to the author ( M.R.

) w h i l e he was on leave at RPI.

1 Address requests for reprints to this author (formerly, M. R u j i m e t h a b h a s ) at the above address. On leave at the R e n s s e l a e r P o l y t e c h n i c Institute, Troy, N.Y.

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