Viscometric and spectrophotometric studies of chromium soaps in a benzene—dimethylformamide mixture

Colloids and Surfaces

A: Physicochemical

0927-7757/94/$07.00

0 1994 -

and Engineering

Aspects,

85 (1994)

75-80

75

Elsevier Science B.V. All rights reserved.

Viscometric and spectrophotometric studies of chromium soaps in a benzene-dimethylformamide mixture K.N. Mehrotra”, Department (Received

M. Jain

of Chemistry, 1 September

Institute

of Basic Sciences, Agra University, Khandari,

1993; accepted

23 November

Agra-282002,

India

1993)

Abstract The viscosity results for solutions of chromium formamide (4: 1 v/v) mixture were explained on and Dole. The values of molar volume obtained and increase with increasing chain length of the results show that the soap-soap interactions measurements show that the metal-to-oxygen covalent character. Keq’ words: Chromium

soaps; Ionic character;

soaps (laurate, myristate, palmitate and stearate) in a benzeneedimethylthe basis of equations proposed by Einstein, Vand, Moulik and Jones from Einstein’s and Vand’s plots were found to be in close agreement, fatty acid constituent of the soap molecules. The density and viscosity are almost negligible in dilute solutions. The spectrophotometric bonds in chromium soaps are not purely ionic but possess some

Molar volume; Spectrophotometry;

Viscosity

Introduction

Experimental

Currently, the transition metal soaps are being widely used in many industries but the selection of soap largely depends on economic factors. While major developments have taken place in the study of alkali, alkaline earth and some transition metal

The chemicals used were of AnalaR grade. Chromium soaps (laurate, myristate, palmitate and stearate) were prepared by the reaction of an

soaps, studies on chromium soaps have remained almost untouched with the result that only few references Cl-131 are available in this relatively unexplored field. The present work deals with studies on the viscosity and spectrophotometric measurements of chromium soaps in a benzene-dimethylformamide (DMF) mixture (4:l v/v) with a view to evaluating soap-soap and soap-solvent interactions and various micellar and spectrophotometric parameters.

*Corresponding SSDI

author.

0927-7757(93)02728-W

aqueous solution of chrome alum (KCr(SO,),) with a solution of the corresponding potassium soap. The precipitated soaps were washed with distilled water, methanol and acetone to remove the excess of metal ion, unreacted potassium soap and excess of fatty acid. The soaps were purified by recrystallization from a benzene-methanol mixture and the purity of the soaps was checked by absence of an absorption band at 1715 cm- ’ in the IR spectra and determination of melting points (laurate, 58” C; myristate, 61 ‘C; palmitate, 66 ^ C and stearate, 69 ‘C).

Densit): and viscosity 0.8962

The dilatometer and Ostwald’s type viscometer were used for determining the density and viscosity of solutions. The viscosity q of the soap solutions was calculated

by using the relationship (1)

Volvl= Poroll’r

where qo, 4, cjo, p and to, t are the viscosity, density and time flow for known and unknown solutions respectively. The reproducibility of density results was 1 x 10~“gmlP’.

The spectrophotometric measurements of the solutions of chromium soaps were carried out in the region 350-940 nm with a digital Toshniwal visible spectrophotometer (model CL.Ol.A3) having a wavelength reproducibility of f 5 nm.

Density

The density p of the solutions of chromium soaps in the benzene-DMF mixture (4:l v/v) increases with increasing soap concentration C (Table 1). The plots of p vs. C (Fig. 1) show a gap discontinuity, indicating the sudden aggregation of anions. The plots of density p vs. soap concen-

Sample no.

1 2 3 4 5 6 7 8

and viscosity

Cont. C x lo3 (mol I-‘)

1.0 2.0 3.0 4.0 5.0 6.0 7.0 X.0

1 (cP) measurements

Laurate

of chromium

/

2.0

4.0 Concentration.

Fig. 1. Density vs. soap concentration: 0, palmitate: A. stearate.

tration tration

Results and discussion

Table 1 Density p (g ml-‘) 40~0.05’C

I

6.0 Cx

8.0

IO3

.J. laurate;

H, myristate;

C are extrapolated to zero soap concenand the extrapolated values are found to

be in agreement with the density of the solvent mixture (0.8929 g ml- ’ ) (Table 2). The density results have been explained in terms of Root’s equation: p = p. + AC ~ BC”2

(2)

where C is concentration of soap (mol 1-l) and p and p. are the densities of soap solution and solvent (g ml-‘) respectively. The constants A and

soap solutions

Myristate

in a mixture

of benzene

Palmitatc

and DMF

(4:

I v:v) at

Stearate

P

‘1

P

‘1

I’

‘1

J’

‘1

0.8930 0.8931 0.X932 0.8933 0.8935 0.8936 0.X938 0.8940

0.47 16 0.473 I 0.473X 0.4747 0.4764 0.4797 0.4842 0.4886

0.8931 0.X933 0.8935 0.8936 0.8940 0.8942 0.X945 0.8948

0.4726 0.4749 0.4770 0.4794 0.4827 0.4861 0.4902 0.4944

0.8932 0.x935 0.8938 0.8942 0.X946 0.8949 (I.8953 0.8956

0.4732 0.4762 0.478X 0.48 14 0.4839 0.4897 0.4924 0.4988

0.8933 0.x937 0.8942 0.x945 0.8950 O.SY55 O.XY60 0.8964

0.4745 0.4779 0.4806 0.4837 0.4x97 0.49 32 0.4990 0.5048

K.N. Mehrotra Table 2 Extrapolated Soap Laurate Myristate Palmitate Stearate

and M. JainjColloids

and experimental Density

Surfaces A: Physicochem.

values of density

pea (g ml-‘)

and viscosity

Viscosity

0.89290 0.89291 0.89288 0.89294

qob (cP)

Eng. Aspects 85 (1994)

II

soap concentration and the extrapolated values are found to be in agreement with the viscosity of the

solvent

(0.4708

cP; Table 2). The

viscosity

results have been interpreted on the basis of equations proposed by Einstein [14], Vand [lS], Moulik [16] and Jones and Dole [17]:

0.4706 0.4708 0.4708 0.4712

Einstein: ‘Experimental bExperimental

75-80

ylsp= 2.5 VC

(3)

density, 0.8929 g ml-‘. viscosity, 0.4708 cP.

Vand: refer to the soap-solvent and soap-soap interactions respectively. The values of (p - pO)/C are almost constant for dilute solutions, indicating that the values of B are equal to zero which shows that there is almost no soap-soap interaction in dilute solutions. The positive values of B for the plots above the discontinuity gap show that there is a significant soap-soap interaction in concentrated solutions. The values of A have been obtained from the intercept of the plots of (p - pO)/C vs. C* (Table 3) and are found to increase with increasing chain length of the fatty acid constituent of the soap molecules.

i=(y)-’

[log(~,~O,]+#~

(4)

B

Moulik:

(q/y1# = A4 + KC2

Jones and Dole:

r&C*

(5)

= A + BC*

(6)

The viscosity y and the specific viscosity qsp of the soap solutions increase with increasing soap concentration (Table 1). The plots of y vs. C are characterized by discontinuity which may be due to the aggregation of fatty acid anions in this range

where v, C, 4, q, y10and ysp are the molar volume of soap (1 mol-‘), concentration (mol l-l), interaction coefficient, viscosity of solution, viscosity of solvent and specific viscosity respectively; M and K are the Moulik’s constants, and the constants A and B of the Jones and Dole equation refer to soap-soap and soap-solvent interactions respectively. The specific viscosity qsp of the solutions of chromium soaps increases with increasing soap concentration. The plots of ysp vs. C (Fig. 2) are characterized by a curved change in a definite range of soap concentration. The plots of v],, vs. C are linear in dilute solutions with intercept equal to zero, indicating that Einstein’s equation is applicable to these soap solutions. The values of molar volume v have been obtained from the slope of

of soap concentration. dilute solutions have

Einstein’s plots and are recorded in Table 4. The values of molar volume v increase with increasing

Viscosity

Table 3 Density and viscosity Soap

Laurate Myristate Palmitate Stearate

The plots of q vs. C for been extrapolated to zero

parameters

of chromium

Root constant A (Soap-solvent interaction)

Moulik

0.10 0.20 0.30 0.40

soaps Interaction

constant

Jones-Dole

constant

M

K

A (Soap-soap interaction)

B (Soap-solvent interaction)

1.004 1.007 1.010 1.013

850 2000 2300 3200

- 0.040 -0.035 -0.030 + 0.025

2.820 5.000 6.208 7.037

109.6 24.8 14.1 7.4

coeff. 4

K.N. Mehrotru

78

and M. Jain/Colloids

Surfaces A: Physicochern.

Eng. Aspects 85 ( 1994) 75-80

/

200

Fig. 3. Vand’s I. stearate.

the 2.0

Fig. 2. Einstein A. stearate.

Table 4 Molar volume

4.0 Concentration,

plots:

v(l

6.0 Cx lo3

3, laurate;

0,

8.0

myristate:

A, palmitate;

mol-‘)

SOLIp

Einstein

Laurate Myristate Palmitate Stearate

0.90 1.52 2.13 2.15

equation

Vand equation 0.83 1.56 2.13 2.72

chain length of the fatty acid constituent of the soap molecule (0.6 1 mol-’ with each -(CH,),-). The plots of l/C vs. l/log(yI/q,) (Fig. 3) are linear, indicating that the Vand’s equation is applicable to these soap solutions. The values of interaction coefficient 4 and molar volume I/ have been obtained from the intercept and slope of plots of l/C vs. l/log(q/g,) and are recorded in Tables 3 and 4. It is observed that the molar volume obtained from Vand’s equation is in close agreement with

values

plots:

2,

obtained

400 1 / log h /lo)

laurate:

0.

from

myristate:

Einstein’s

600

A, palmitate;

equation

(Table 4). The values of Moulik’s constants M and K have been obtained from the intercept and slope of the linear plots of (11/17~)~vs. C2 in dilute solutions. The values of M and K increase with increasing chain length of the soap molecules (Table 3). The viscosity results have also been explained in terms of the Jones-Dole equation. The values of constants A and B, determined from the intercept and slope of plots in dilute solutions, are recorded in Table 3. The values of constant B (soap-solvent interaction) are higher than those of A (soap-soap interaction) in dilute solutions which confirms that the molecules of soaps do not aggregate in dilute solutions but there is a marked change in aggregation of molecules in concentrated solutions. Spectrophotonzetq

The solutions of chromium soaps (laurate, myristate, palmitate and stearate) in benzeneDMF (4:l v/v) mixture exhibit well-defined maxima at 575-585 nm (17391~17094cm~‘) and 420-440 nm (23 809922 727 cm-‘) (Table 5). The absorption studies were also carried out in aqueous

K.N. Mehrotru

and M. JainlColloids

solutions

of chrome

observed

at

alum

590 nm

(23 256 cm-‘).

Surfaces A: Physicochem.

and

maxima

(16949 cm-‘)

This shows

that

and

Eng. Aspects 85 (1994)

were

tage covalency

of

figuration following

and

possesses

the d3 electronic

chromium(II1)

three electronic

4T~,(F)-4A~,(F)

vi

4T,,(W4Az,(F)

~2

soaps

transitions

con-

permit

the

[ 181:

ratio j? [ 201, percenparameter

b” [21]

(Table 5) by using

the rela-

6 and bonding

have been evaluated tionships

chromium soaps in benzeneeDMF (4:l v/v) mixture is quite similar to that of aqueous solutions of chrome alum. Chromium(II1)

79

B and C [ 191, nephelauxetic

420 nm

the behaviour

75-80

vr = 1ODq

(7)

Dq/B = 2.45

(8)

CIB=3.7

(9)

B = BIB,

(10)

l-b (~ 1

6:

(11)

x100

P

4T&‘)+4A2,(F)

~3

b+=

The electronic bands observed between 17 391 and 17094 cm-’ are assigned to the first transition (v,), and the second electronic band (v2) lies between 23 809 and 22 727 cm-‘. The third transition (v3) usually occurs at about 37 000 cm-’ and is beyond the range of our instrument. The crystal field splitting energy parameter Dq [IS], Racah interelectronic repulsion parameters Table 5 Electronic

spectral

Soap

bands

and various

parameters

Transition (cm-‘)

of chromium Racah (cm-‘)

“1

y2

Laurate Myristate Palmitate Stearate

17391 17241 17241 17094

22127 22727 23256 23809

Table 6 Optical density

of chromium

1739.1 1724.1 1724.1 1709.4

1-P (H 2

+

(12)

where vi is the wavenumber of the electronic band due to the first transition (4T2g(F)t4A2g(F)) and B, is the value of the interelectronic repulsion parameter for free Cr(II1) ion, equal to 1030 cm-‘. The values of fi for chromium soaps (Table 5) are less than unity which suggests that the metal-

soaps parameters

B

C

710 704 704 698

2627 2605 2605 2583

Nephelauxetic ratio /I

Percentage covalency S

Bonding parameter

0.6893 0.6835 0.6835 0.6776

45.0% 46.3% 46.3% 47.6%

0.1553 0.1582 0.1582 0.1612

soap solutions

Sample no.

Cont. C x lo3 (mol I-‘)

Laurate

Myristate

Palmitate

Stearate

1 2 3 4 5 6 I 8

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

0.140 0.265 0.360 0.475 0.565 0.690 0.830 0.930

0.130 0.240 0.310 0.410 0.470 0.570 0.665 0.745

0.125 0.200 0.305 0.375 0.455 0.560 0.640 0.735

0.120 0.185 0.240 0.330 0.420 0.480 0.540 0.625

hi

K.N. Mehrotra

80

to-oxygen

bonds in chromium

and M. JainlColloids

soaps are not purely

ionic but have some covalent character. The values of percentage covalency (6) and bonding parameter (b”) also indicate that these soaps are partially covalent

in character.

The plots of optical density vs. soap concentration are linear, with the intercept almost equal which proves the validity of the to zero, Beer-Lambert

law for these solutions

(Table 6). It

is evident that the spectrophotometric method can be used to estimate chromium content at i,,, in dilute solutions of these soaps. References J.H. Balthis and J.G. Bailar, Inorg. Synth., I (1939) 123. M.R. Hatfield, Inorg. Synth., 3 (1950) 148. A. Suszer, Rev. Chim. (Bucharest), 9 (1959) 262. G. Doyle, J. Organomet. Chem., 84 (1975) 323. A.K. Rai and G.K. Parashar, Thermochim. Acta, 29 (1979) 175.

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Surfaces A: Physicochem.

Eng. Aspects 85 (1994) 75-80

A. Suszer, A. Bader, J. Pliz and E. Maurer, Chem. Tech. (Berlin), 12 (1960) 412. A.K. Rai and R.C. Mehrotra, J. Indian Chem. Sot., 40 (1963) 359. H.A. Lehmann, G. Kessler, P. Denecke and G. Nickl, 2. Anorg. Allg. Chem., 340 (1965) 16. L. Dubicki and P. Day, Inorg. Chem., 11 (1972) 1868. W.U. Malik and S.I. Ahmad, J. Am. Oil Chem. Sot., 42 (1965) 42. W.U. Malik and S.I. Ahmad, Kolloid Z. Z. Polym., 234 (1969) 1045. E.H. Abbott and J.M. Mayer, J. Coord. Chem., 6 (1977) 135. G. von Holste and H. Schaefer, Z. Anorg. Allg. Chem., 391 (1972) 263. A. Einstein, Ann. Phys., 19 (1906) 289; 34 (1911) 581. V. Vand, J. Phys. Colloid Chem., 52 ( 1948) 277. S.P. Moulik, J. Phys. Chem., 72 (1968) 4682. G. Jones and M. Dole, J. Am. Chem. Sot., 51 (1929) 2960. B.N. Figgis, Introduction to Ligand Field, Wiley Eastern Limited, New Delhi, 1964, p.222. Griffith, Theory of Transition Metal Ion, Cambridge University Press, London, 1961. S. Olavi and B.G. Harry, Inorg. Chem., 13 (1974) 1185. D.E. Hanrie and G.R. Choppin, J. Chem. Phys., 49 (1968) 477.