Ac Conductivity of Some Organolithium Complexes in Aromatic Solvents

5 Ac Conductivity of Some Organolithium Complexes in Aromatic Solvents E. O. FORSTER and A. W. LANGER, JR.

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Esso Research and Engineering Co., Linden, N.J. 07036 The nature of the electrical conductance of N-chelated aryl and aralkyl lithium compounds chelated with polyamine -type complexing agents has been studied in aromatic hydro carbons ranging in concentration from 10 to 1 mole/liter between10 and 10 Hz and between —30° and 80°C. The chelating agents included Ν,Ν,Ν',Ν'-tetramethylethylenediamine and N,N,N'N''N"',N'''-hexamethyltriethylenetetraamine; the results obtained with these systems were com pared with those obtained with tetra-n-amylammonium thiocyanate. Ion pairs representing dipoles contribute sig nificantly to the conduction process. The drastic change in conductivity observed at concentrations greater than 10 mole/liter has been attributed to the formation of ion aggre gates. The dielectric constant of one of these complexes has been determined from dilute solutions to be about 16. The behavior of these complexes is similar to that of (n-amyl) NCNS. -5

2

7

-2

4

' T p h e c h e m i s t r y of o r g a n o m e t a l l i c c o m p o u n d s has r e c e i v e d A

a t t e n t i o n recently.

considerable

I n p a r t i c u l a r , a d d u c t s of a l k a l i metals w i t h a l i

p h a t i c a n d a r o m a t i c h y d r o c a r b o n s h a v e b e e n s t u d i e d i n d e t a i l because of t h e i r general usefulness i n o r g a n i c synthesis. U n t i l v e r y r e c e n t l y the role p l a y e d b y the solvent a n d the m e t a l o n the f o r m a t i o n a n d d i s s o c i a t i o n e q u i l i b r i a of these adducts w a s not c l e a r l y u n d e r s t o o d . studies ( I , 2)

Various

i n d i c a t e d t h a t the p o l a r i t y of the C — L i b o n d c o u l d

i n c r e a s e d b y a d d i t i o n of electron-donor c o m p o u n d s

be

as e v i d e n c e d b y a n

increase i n e l e c t r i c a l c o n d u c t i v i t y . T h e significance of the i n c r e a s e d i o n i c c h a r a c t e r of t h e c a r b o n - m e t a l b o n d i n solvents w i t h d i e l e c t r i c constants of less t h a n f o u r w a s not u n d e r s t o o d w e l l . K r a u s ( 3 ) a n d F u o s s (4)

p o s t u l a t e d e a r l i e r that d i s s o l u t i o n

131

In Polyamine-Chelated Alkali Metal Compounds; Langer, A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

132

POLYAMINE-CHELATED

of essentially i o n i c c o m p o u n d s

ALKALI

METAL

COMPOUNDS

s u c h as q u a t e r n a r y a m m o n i u m salts i n

solvents of l o w d i e l e c t r i c constant s h o u l d y i e l d , i n a d d i t i o n to some free ions, i o n p a i r s a n d i o n i c aggregates. subject

are p r e s e n t e d b y

Szwarc

(5)

Comprehensive

r e v i e w s of

this

and Blandamer and Fox

(6).

A c c o r d i n g to these authors three types of i o n pairs c a n b e

encountered

i n solvents of l o w d i e l e c t r i c constant: contact p a i r s t h a t are b a s i c a l l y d i p o l a r molecules, solvent s h a r e d i o n p a i r s i n w h i c h a c a t i o n is l i n k e d e l e c t r o s t a t i c a l l y t h r o u g h a solvent m o l e c u l e to a n a n i o n , a n d

solvent-

separated i o n pairs i n w h i c h b o t h ions are still l i n k e d electrostatically b u t separated b y m o r e t h a n one

solvent m o l e c u l e

(6).

T h e relative


c o n t r i b u t i o n of these structures to p h y s i c a l properties of t h e s o l u t i o n c a n b e d e d u c e d f r o m c o n d u c t i v i t y o r k i n e t i c d a t a . O f these t w o

techniques

c o n d u c t i v i t y studies h a v e c o n t r i b u t e d c o n s i d e r a b l y to the u n d e r s t a n d i n g of i o n - p a i r e q u i l i b r i a ( 7 ) . other

fields

T h i s does not m e a n t h a t d e v e l o p m e n t s

s u c h as analysis of k i n e t i c d a t a , e l e c t r o n s p i n

in

resonance

( E S R ) spectra, a n d u l t r a s o n i c r e l a x a t i o n d a t a h a v e h a d no i m p a c t o n this

field.

T h e s e three fields h a v e b e e n v e r y h e l p f u l i n e l u c i d a t i n g the

structure of aqueous electrolytes w h e r e c o n d u c t i v i t y measurements

are

h a r d e r to p e r f o r m . Interest i n N - c h e l a t e d o r g a n o l i t h i u m c o m p o u n d s

stems f r o m t h e i r

r e m a r k a b l e r e a c t i v i t y w h i c h w a s first n o t e d b y L a n g e r (8).

F r o m studies

of v a r i o u s reactions a n d f r o m N M R c h e m i c a l shifts L a n g e r

concluded

that the r e a c t i v i t y of these complexes i n d i l u t e s o l u t i o n is r e l a t e d to the i n c r e a s e d i o n i c character of the L i — C b o n d

(9).

T h e question

arose

w h e t h e r these complexes c o u l d b e c o n s i d e r e d as s o m e sort of s t a b i l i z e d i o n p a i r s . T h u s i t seemed d e s i r a b l e to s t u d y the c o n d u c t i v i t i e s of these systems over a w i d e c o n c e n t r a t i o n range a n d to a n a l y z e the r e s u l t i n g d a t a i n the l i g h t of e x i s t i n g m o d e l s a n d theories.

T h i s p a p e r presents

results of a d e t a i l e d s t u d y of the e l e c t r i c a l c o n d u c t a n c e aralkyllithium compounds

chelated w i t h various polyamine-type

p l e x i n g agents i n a r o m a t i c h y d r o c a r b o n s

the

of a r y l - a n d com-

over a w i d e f r e q u e n c y

and

c o n c e n t r a t i o n range. T h e results are i n t e r p r e t e d i n the l i g h t of c l a s s i c a l theories. Experimental T h e e x p e r i m e n t a l details a n d the c h e m i c a l s u s e d h a v e b e e n d e s c r i b e d elsewhere (10, 11, 12). T h e i n s t r u m e n t a t i o n p e r m i t t e d measurements f r o m 10 to 1 0 H z f r o m - 3 0 ° to 8 0 ° C at concentrations f r o m 10~ to 1.0 m o l e / l i t e r . F o r c o m p a r i s o n , studies w e r e also c a r r i e d out o n t e t r a - n a m y l a m m o n i u m t h i o c y a n a t e i n a r o m a t i c solvents, a system that has b e e n i n v e s t i g a t e d i n c o m p l e t e d e t a i l b y K e n a u s i s et al. (13, 14). 7

5

Results T h e studies p r e s e n t e d here i n v o l v e d several v a r i a b l e s .

First, the

effect of c h e l a t i n g agent w a s s t u d i e d as a f u n c t i o n of b o t h its s t r u c t u r e


5.

FORSTER AND LANGER

133

Conductivity of Organolithium Complexes

a n d c o n c e n t r a t i o n w i t h respect to the a r a l k y l l i t h i u m c o m p o u n d .

The

role of solvent w a s t h e n i n v e s t i g a t e d for a g i v e n c h e l a t e d system.

With

a k n o w l e d g e of the influence of these v a r i a b l e s o n the e l e c t r i c a l c o n d u c t i v i t y , one specific system w a s selected a n d its f r e q u e n c y a n d t e m p e r a t u r e d e p e n d e n c e w e r e s t u d i e d as a f u n c t i o n of c o n c e n t r a t i o n .

These

last results w e r e t h e n c o m p a r e d w i t h those o b t a i n e d w i t h the q u a t e r n a r y a m m o n i u m salt system. Effect of Chelating Agent.

B e f o r e the role of the c h e l a t i n g agent

c a n b e p r o p e r l y d e t e r m i n e d , i t is a d v i s a b l e to evaluate the e l e c t r i c a l properties of t h e respective components

alone, u s i n g the a p p r o p r i a t e


solvent ( T a b l e I ) . Table I .

Conductivities of Some Organolithium Compounds (25±:0.1) C,

lKHz

o

Compound — C H Li TMED(CH )2N(CH ) N(CH )2 C4H9L1-TMED C H Li-TMED (C H ) CHLi-TMED (C H ) CHLi-TMED (C H ) CLi-TMED 4

9

3

6

2

5

6

5

2

6

5

2

6

5

3

Cone. mole/liter

Solvent

2

3

n-C H n-C H — n-C H C H C H C H CH C H CH 7

1 6

7

1 6

7

6

1 6

6

6

6

6

5

6

5

3 3

— 0.025 0.02 0.05 0.025 0.025 0.025

Conductivity, (ohm cm)" 1

1.1 1 6 3.8 3.5 3 4

< Χ Χ X Χ Χ X X

1010" 10" 10~ 10~ 10" 10~ 10~ 1 5

11

11

(δ)

because the c o m p l e x r e a c t e d w i t h the solvent w i t h i n

h o u r to p r o d u c e p h e n y l l i t h i u m complexes a r a l k y l complexes soluble.

with T M E D .

u

11

It was not possible to p r e p a r e b u t y l l i t h i u m - T M E D complexes benzene

n

u n

in one

O f the three

tested the d i p h e n y l m e t h y l l i t h i u m p r o v e d

the

most

T h e r e f o r e the d i p h e n y l m e t h y l l i t h i u m c o m p l e x w a s chosen

to

s t u d y f u r t h e r the effect of c h e l a t i n g agent t y p e . T h e results are s h o w n i n Table II. T h e H M T T c o m p l e x at a 1:1 m o l e r a t i o p r o d u c e s n e a r l y as c o n d u c t i v e a s o l u t i o n as T M E D at a 1:2 m o l e r a t i o . T h i s suggests that f o u r n i t r o g e n atoms are p r o b a b l y r e q u i r e d to p r o d u c e the m a x i m u m c o o r d i n a t i o n a r o u n d the l i t h i u m a t o m to o p t i m i z e the i o n i c character of the L i — C b o n d (9,10). H o w e v e r , the efficiency of the c o o r d i n a t i o n is p r o b a b l y h i g h e r w i t h T M E D because its t w o pairs of n i t r o g e n atoms are not as s t e r i c a l l y r e s t r i c t e d i n the a l i g n m e n t as are the f o u r i n H M T T .

The

T M E D a n d H M T T complexes w e r e selected for f u r t h e r studies. Solvent Effects. T h e o v e r a l l effect of solvent o n the c o n d u c t i v i t y of ( C H ) C H L i - ( T M E D ) 2 is s h o w n i n F i g u r e 1. A s the n u m b e r of m e t h y l 6

5

2

groups a r o u n d the benzene r i n g increases, c o n d u c t i v i t y decreases.


The

134

POLYAMINE-CHELATED

Table I I .

ALKALI M E T A L

COMPOUNDS

Effect of Chelating Agents on Conductivity of ( Q H ) C H L i - - C h e l in Toluene 5

2

(0.2M, 2 5 ° C , l K H z )

Chelating TMED* TMED PMDT HMTT

l

1 5 2.6 2

1/1 1/2 1/1 1/1

6

C

Χ ΙΟ" Χ ΙΟ" X 10Χ ΙΟ"

5

5 8 d

5

N,N N ,N'-tetra,methy\ ethylene diamine AT,iV,iV ,iV ',N '-pentamethyl diethylene triamine « N,N,N',N",N" ,N'"-hexamet\iy\ triethylene tetramine Complex does not go completely into solution.

α

b


Conductivity, (ohm cm)~

Ratio of RLi to Chelating Agent

Agent

f

f

v

/

/

,

d

( Ι Κ Η ζ ) (0.2M) "Τ

J ο >

Ι. 2. 3. 4. 5.

BENZENE TOLUENE m-XYLENE o-XYLENE MESITYLENE

30

20

40

50

60

70

80

90

T E M P E R A T U R E , °C

Figure 1. Effect of temperature on conductivity of (C H ) CHLi/2TMED in various solvents (1 KHz) (0.2M) 6

5

2

significance of the g e n e r a l shape of the t e m p e r a t u r e d e p e n d e n c e c u r v e of these c o n d u c t i v i t i e s is discussed elsewhere i n this p a p e r .

Toluene was

selected as solvent f o r s u b s e q u e n t studies because u n l i k e b e n z e n e i t has a c o n s i d e r a b l y l o w e r f r e e z i n g p o i n t a n d its s o l u t i o n c a n b e s t u d i e d over a b r o a d e r t e m p e r a t u r e range. I n those studies that use solvents other t h a n the h y d r o c a r b o n c o r r e s p o n d i n g to the c a r b a n i o n , a n y m e t a l a t i o n of the solvent w o u l d change the n a t u r e of the c o n d u c t i v e species a n d c o m p l i c a t e d a t a i n t e r p r e t a t i o n . F o r e x a m p l e , the pK 's of toluene ( 3 5 ) a

a n d d i p h e n y l m e t h a n e (ca.

33)

are close e n o u g h so that t o l u e n e m e t a l a t i o n b y d i p h e n y l m e t h y l l i t h i u m c o u l d b e significant at v e r y l o w concentrations of the l i t h i u m

compound

a c c o r d i n g to the e q u i l i b r i u m :


5.

(C H ) CHLi.Chel + C H C H 6

5

No had

2

135


FORSTER AND LANGER

6

5

3

τ± ( C H ) C H 6

5

2

+

2

C H CH Li.Chel 6

6

2

a t t e m p t w a s m a d e to correct for this effect because e a r l y studies

i n d i c a t e d that s i m i l a r systems w e r e

extremely slow i n reaching

e q u i l i b r i u m a n d i n most cases the e q u i l i b r i u m c o n t r i b u t i o n w o u l d not change

the

conclusions.

These

assumptions w i l l

be

examined

more


critically i n future work.

Figure 2. AC conductivity of (C H ) CHLi (TMED) in C H CH at 25°C 6

2

6

5

5

2

·

S

Frequency and Temperature Effects. T h e f r e q u e n c y d e p e n d e n c e (C H ) CHLi-(TMED)2 6

5

2

of

as a f u n c t i o n of c o n c e n t r a t i o n is s h o w n i n

F i g u r e 2. At the highest c o n c e n t r a t i o n s t u d i e d ( 1 M ) , t h e c o n d u c t i v i t y is essentially constant over six decades, c h a n g i n g f r o m 3.9 Χ cm)"

1

at 10 H z to 4.6 Χ

dependence

10"

4

(ohm c m )

- 1

at 1 0

8

10"

4

(ohm

H z . T h e temperature

of the c o n d u c t i v i t y of these solutions is a l l u d e d to i n the

p r e c e d i n g section, a n d i t is s h o w n i n more d e t a i l i n F i g u r e 3 for both the T M E D

and H M T T

complex.

T h e u n u s u a l shape of the l o g


con-

136

P O L Y A M I N E - C H E L A T E D A L K A L I M E T A L COMPOUNDS

d u c t i v i t y vs. t h e r e c i p r o c a l t e m p e r a t u r e c u r v e d i s a p p e a r s a t c o n c e n t r a tions greater t h a n 0.2M a n d gives w a y to t h e f a m i l i a r l i n e a r d e p e n d e n c e . T h e H M T T c o m p l e x appears to b e m o r e stable e v e n at t h e l o w e r c o n centrations. T h e a c t i v a t i o n energy f o r c o n d u c t i v i t y c a n b e c a l c u l a t e d via the A r r h e n i u s e q u a t i o n to b e a b o u t 1600 c a l / m o l e f o r t h e H M T T w h i l e that f o r t h e T M E D c o m p l e x 1300 c a l / m o l e .

complex

( a t concentrations a b o v e 0 . 4 M ) is

T h e p e c u l i a r shape of t h e c o n d u c t i v i t y vs. t e m p e r a t u r e

c u r v e s h o w n f o r 0 . 2 M solutions of t h e ( C H 5 ) G H L i - ( T M E D ) 2 6

suggests that t h e c o n d u c t i v e

2

complex

species becomes u n s t a b l e at h i g h e r t e m -

peratures w h i c h i n t u r n i m p l i e s that t h e forces h o l d i n g t h e m together are Downloaded by UNIV OF PITTSBURGH on May 3, 2015 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0130.ch005

a b o u t as l a r g e as kT. T h e i m p l i c a t i o n s o f these d e d u c t i o n s a r e d e a l t w i t h i n a later section. A c o n v e n i e n t w a y to s u m m a r i z e t h e c o n c e n t r a t i o n d e p e n d e n c e of this c o m p l e x is s h o w n i n F i g u r e 4, w h e r e t h e l o g a r i t h m of t h e e q u i v a l e n t conductance

of the complex

as d e t e r m i n e d at 1 K H z is p l o t t e d as a

f u n c t i o n of t h e l o g a r i t h m of c o n c e n t r a t i o n .

F o r comparison a similar

10'

• 1 M 0 CHLi«(TMED) ' 1 MHz X

2

2

• 1 M 0 CHLi#(TMED) ' 1 KHz N

2

2

\ l M 0 CHLi«HMTT, 1 MHz 2

• 0.5M

0 CHU«HMMTH

N

2

I

1 KHz

0.4M 0 C H L i « ( T M E D ) , ! KHz 1

0 . 2 M 0^CH|_i»HMTT/ \ 1

2

2

KHz

2.8

3.0

3.2

3.4

3.6

3.8

Figure 3. Temperature dependence of conductivity of (C H ) C H Li complexes in toluene 6

5

2



5.

FORSTER AND LANGER


137

LOG CONCENTRATION

Figure 4. Equivalent conductance of (C H ) CHLi(TMED) in toluene (25° C, 1 KHz) 6

5

2

2

p l o t is s h o w n i n F i g u r e 5 for the w e l l - s t u d i e d q u a t e r n a r y a m m o n i u m salt, t e t r a a m y l a m m o n i u m isocyanate i n p-xylene. Discussion T h e d a t a r e p o r t e d a b o v e i n d i c a t e that the N - c h e l a t e d a r a l k y l l i t h i u m complexes are q u i t e c o n d u c t i v e species, p a r t i c u l a r l y i n c o n c e n t r a t e d s o l u tions. T h i s is e v e n m o r e s u r p r i s i n g since the a r o m a t i c solvent has a l o w d i e l e c t r i c constant a n d t h e absence of a n i n h e r e n t d i p o l e i n the solvent m o l e c u l e seems to h a v e little effect o n the o v e r a l l results. ( T h e d i e l e c t r i c constant of T M E D of 2.8 is c e r t a i n l y not g o i n g to c o n t r i b u t e e i t h e r . ) O b v i o u s l y , the solvent's d i e l e c t r i c constant is n o t the w h o l e story. F r o m the results r e p o r t e d i n the l i t e r a t u r e u s i n g l o w d i e l e c t r i c c o n stant solvents s u c h as d i o x a n e ethane ( 1 6 ) , or b e n z e n e

(15),

(13, 14),

tetrahydrofuran and

dimethoxy-

t h e c h e m i c a l m a k e u p of t h e solvent,

its m o l e c u l a r s t r u c t u r e , or b o t h , m i g h t w e l l influence the final results. W i t h the first three solvents t h e presence of o x y g e n atoms seems to b e



-4

I

I

I

I

I

-6

-5

-4

-3

-2

LOG

Figure 5.

1 -1

CONCENTRATION ( E Q U I V A L E N T S / L I T E R )

Equivalent conductance of (n-amyl) N CNS- in p-xylene (25°C, 1 KHz) A

+

i m p o r t a n t since t h e y c a n a c t as e l e c t r o n donors o r charge-transfer agents, thus s t a b i l i z i n g t h e charge s e p a r a t i o n w i t h i n t h e c o m p l e x .

I t is h a r d e r

to c o m p r e h e n d t h e s i t u a t i o n w i t h a r o m a t i c solvents s u c h as b e n z e n e or toluene.

A p p a r e n t l y t h e m o l e c u l a r structure is i m p o r t a n t . T h e s e m o l e -

cules h a v e a h i g h degree of s y m m e t r y , a n d s m a l l deformations l e a d to the f o r m a t i o n o f i n d u c e d dipoles (17).

C o n v e r s e l y , i n t h e presence of a

s t r o n g l y p o l a r solute m o l e c u l e t h e nearest-neighbor solvent

molecules

are subject to i n d u c e d p o l a r i z a t i o n . T h u s , m o l e c u l e s s u c h as b e n z e n e and

toluene, w h i c h a r e r e a d i l y p o l a r i z a b l e , w i l l b e v e r y effective i n

" s o l v a t i n g " these solute d i p l o l e s . T h i s process w i l l increase t h e d i e l e c t r i c constant o f t h e s o l u t i o n . S u p e r i m p o s e d o n this effect is t h e t e n d e n c y of t h e solute t o aggregate. T h i s aspect h a s b e e n r e c o g n i z e d b y m a n y w o r k e r s D i e l e c t r i c measurements

(13, 14, 15, 17).

give information concerning the contribution

o f b o t h processes, as s h o w n i n T a b l e I I I , u s i n g t h e O n s a g e r r e l a t i o n s h i p (12). T h e increase i n t h e solute's a p p a r e n t d i e l e c t r i c constant f o l l o w e d b y a subsequent decrease at t h e highest c o n c e n t r a t i o n is s i m i l a r to t h e observ a t i o n r e p o r t e d b y K r a u s (17) o n t h e a b r u p t decrease of t h e association


5.

FORSTER AND LANGER

Table I I I .


139

Dielectric Constant of ( C H ) 2 C H L i - ( T M E D ) 2 Solutions in Toluene 6

5

(10 K H z , 2 5 ° C )


Concentration, mole/liter 0 0.001 0.005 0.01 0.05 0.1 1.0

Dielectric

constant

Solution

Solute

2.37 2.40 2.41 2.42 2.70 3.02 6.10

16 16 17 19 21 16.5

n u m b e r of t e t r a a m y l a m m o n i u m t h i o c y a n a t e . T h i s d r o p m i g h t b e i n t e r p r e t e d as suggesting that the r a t i o of solute to solvent of r o u g h l y 1 to 3 at t h e 1 M l e v e l favors c o m p l e t e s o l v a t i o n of the solute, thus l e a v i n g f e w if a n y solute molecules associated. T h e q u e s t i o n c a n t h e n b e r a i s e d as to the n a t u r e of the c o n d u c t i v e species. T h e s o l u t i o n w i t h a n a p p a r e n t d i e l e c t r i c constant of 6.1 is n o l o n g e r u n f a v o r a b l e t o w a r d d i s s o c i a t i o n of solute molecules, a n d it is l o g i c a l to v i s u a l i z e the existence of s o l v a t e d ions i n e q u i l i b r i u m w i t h solvent-separated i o n p a i r s . T h e p i c t u r e is less definite o n the other side of the c o n c e n t r a t i o n s p e c t r u m . It is not easy to g a i n a d e t a i l e d u n d e r s t a n d i n g of the c o n d u c t i v e species i n v e r y d i l u t e solution. F r o m the d a t a i n F i g u r e 2 there appears to be some i n d i c a t i o n of a f r e q u e n c y - i n d e p e n d e n t , o h m i c - c o n d u c t i o n r e g i o n d o w n to c o n c e n trations of a b o u t 0 . 0 0 5 M , w h i c h w o u l d be a t t r i b u t a b l e to ions. F o r l o w e r concentrations the c o n d u c t i v i t y vs. f r e q u e n c y p l o t becomes q u i t e n o n l i n e a r d o w n to b e l o w 100 H z , r e n d e r i n g t h e existence of a f r e q u e n c y i n d e p e n d e n t c o n d u c t i o n m e c h a n i s m q u e s t i o n a b l e (18). I n a d d i t i o n to these considerations i t is a p p r o p r i a t e to examine the f r e q u e n c y d e p e n d ence of the d i e l e c t r i c constant i n these v e r y d i l u t e solutions, as s h o w n in Table IV. E l e c t r o d e p o l a r i z a t i o n effects p r o d u c e d b y the m i g r a t i o n of ions to the electrode surface s h o u l d be e v i d e n t i n the presence of ions (19). S u c h a n i o n l a y e r c a n h a v e c o n s i d e r a b l e influence o n the a p p a r e n t c a p a c i tance, p a r t i c u l a r l y for c o n d u c t i v i t y levels greater t h a n 10" ( o h m c m ) " . A t the l o w levels of c o n d u c t i v i t y p r e v a i l i n g i n d i l u t e solutions c o n t a i n i n g less t h a n 10" m o l e / l i t e r s u c h p o l a r i z a t i o n effects are n o t expected a l t h o u g h the d r o p i n d i e l e c t r i c constant for the 0 . 0 5 M s o l u t i o n c a n b e a t t r i b u t e d to this effect. A l l this suggests that there are f e w i f a n y ions present i n these d i l u t e systems. A t the i n t e r m e d i a t e c o n c e n t r a t i o n levels, there m i g h t exist m u l t i p l e ions w h i l e at the highest concentrations ( a b o v e 8

3


1

140

POLYAMINE-CHELATED

ALKALI

METAL

COMPOUNDS

Table I V . Frequency Dependence of the Dielectric Constant of ( C H ) C H L i - ( T M E D ) Solutions i n Toluene ( 2 5 ° C ) 6

5

2

2

Dielectric Cone,

mole/liter 0.05 0.001 0.0005

constant (Hz)

100

200

500

1000

5000

10000

18 2.42 2.38

10 2.45 2.38

4.6 2.40 2.38

4.1 2.40 2.38

3.1 2.40 2.38

2.7 2.40 2.38

1 m o l e / l i t e r ) h i g h l y polarized, solvated i o n pairs f o r m the b u l k of the Downloaded by UNIV OF PITTSBURGH on May 3, 2015 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0130.ch005

s o l u t i o n (see T a b l e I I I ) . R e f e r e n c e has b e e n m a d e t o results o b t a i n e d w i t h s u c h i o n i c s u b stances as q u a t e r n a r y a m m o n i u m salts ( 1 3 , 14). T h e v a l i d i t y o f these c o m p a r i s o n s is s u p p o r t e d b y a c o m p a r i s o n of F i g u r e 4 w i t h 5. T h o s e t w o figures s h o w plots o f t h e e q u i v a l e n t c o n d u c t a n c e of ( C H 5 ) C H L i 6

(TMED)

i n toluene ( F i g u r e 4 ) a n d o f ( n - a m y l )

2

4

2

N C N S i n p-xylene

( F i g u r e 5 ) as a f u n c t i o n o f c o n c e n t r a t i o n . T h e s i m i l a r i t y o f b o t h curves is s t r i k i n g . T h e slight c h a n g e i n slope at h i g h concentrations i n F i g u r e 4 is p r o b a b l y c a u s e d b y v i s c o s i t y effects (13). B o t h systems s h o w a d r a s t i c c h a n g e i n slope near 10" m o l e / l i t e r , yet one is a n i o n i c substance i n the 2

s o l i d state w h i l e the o t h e r is a t best o n l y p a r t i a l l y i o n i c i n c h a r a c t e r . I t seems a p p r o p r i a t e , therefore, t o q u e s t i o n t h e e x p l a n a t i o n offered b y K e n a u s i s et al. (13, 14) that o n l y ions a r e r e s p o n s i b l e for t h e c o n d u c t i o n i n dilute solution.

Indeed, from the frequency

d e p e n d e n c e of these

d i l u t e systems i t seems reasonable t o c o n c l u d e t h a t i o n p a i r s r e p r e s e n t i n g d i p o l e s m i g h t c o n t r i b u t e t o t h e o v e r a l l c o n d u c t i o n process b y c a u s i n g a n increase i n a c c o n d u c t i v i t y w i t h f r e q u e n c y .

O n t h e other h a n d , t h e

assignment of i o n aggregates as the c o n d u c t i v e species at concentrations a b o v e 10" high

2

m o l e / l i t e r seems q u i t e satisfactory i n b o t h cases.

concentrations

(around

1 mole/liter a n d above)

A t very

deaggregation

a p p a r e n t l y takes p l a c e , l e a d i n g t o a n e q u i l i b r i u m b e t w e e n

individual

s o l v a t e d ions a n d solvent-separated i o n pairs.

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9.

Shatonshtein, A. I., Petrov, E. S., Usp. Khim. (1967) 36, 269. Bagdasar'yarr, A. Kh. et al., Dokl. Akad.Hauk.SSR (1965) 162, 1293. Kraus, C. Α., J. Phys. Chem. (1956) 60, 129. Fuoss, R. M., Aecascina, F., "Electrolytic Conductance," Chap. 16, Interscience, New York, 1959. Szwarc, M., Makromol. Chem. (1965) 89, 44. Blandamer, M. J., Fox, M. F., Chem. Rev. (1970) 70, 1. Barthel, J., Angew. Chem., Intern. Ed. Engl. (1968) 7, 260. Langer, A. W., Trans. Ν. Y. Acad. Sci. (1965) 27, 741. Langer, A. W., Amer. Chem. Soc., Div. Polym. Chem., Preprint, 7(1), 132 (Phoenix, Jan., 1966).



5. FORSTER AND LANGER Conductivity of Organolithium Complexes 141

10. Forster, E. O., Langer, A. W. in "Phenomenes de Conduction dans les liquids isolants," p. 236, Colloques Intern. No. 179, Grenoble, Sept. 1968, CNRS Ed., Paris, 1970. 11. Forster, E. O., Langer, A. W., in "1969 Annual Report, Conference on Electrical Insulation and Dielectric Phenomena," Nat. Acad. Sci. Publ. 1764, 87 (1970). 12. Forster, E. O., Langer, A. W., Amer. Chem. Soc., Div. Polym. Chem., Preprint, 13 (2), 656 (New York, August, 1972). 13. Kenausis, L. C., et al.,Proc.Natl. Acad. Sci. (1962) 48, 121. 14. Kenausis, L. C., et al.,Proc.Natl. Acad. Sci. (1963) 49, 141. 15. Kraus, C. Α., J. Phys. Chem. (1956) 60, 129. 16. Ellingsen, T., Smid, J., J. Phys. Chem. (1969) 73, 2712. 17. Kraus, C. Α., J. Phys. Chem. (1954) 58, 673. 18. Forster, E. O., in "4th Intern. Symposium on Conduction and Breakdown Phenomena in Liquid Dielectrics," Dublin, 1972. 19. Hill, Ε. N., et al., "Dielectric Properties and Molecular Behavior," p. 285, Van Nostrand-Reinhold, New York, 1969. RECEIVED March 26, 1973.


Ac Conductivity of Some Organolithium Complexes in Aromatic Solvents

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