Indian Journal of Pure & App li cd Physics Vol. 40, Dcccmbcr 2002, pp. ):\SO-SS6

Excess volume, viscosity and compressibility of binary mixtures consisting of o-chlorophenol, o-cresol and m-cresol with n-n-diethyl

acetamide at different temperatures T Satyanarayana Rao, N Vccraiah & C Ramhabu*

Dcpartmcn t of Physics. Nagarj un a Uni vcrsity PG Ccn trc, Nuzv id. Andhra Prades h. 52 1 20 I

*Department of Chemi stry. Naga,juna University PG Ccntre, Nuzvid , Andhra Pradesh, S2 1 20 I

Reccived IX January 2002; accept cd 24 September 2002

The dcnsi tics , viscositi es and ultrason ic velociti es of binary mi xturcs of o-chlorophenol, o-crcso l, m-cresol with N,N ­dieth yl acctamide have hecn determincd at :lOS. IS. 3 13. IS, 3 IS.IS . 323. IS K over the whole composition-range, using dcnsit y hott le, ostwa ld viscomcter, and with single crys tal ultrasoni c pu lse echo-interferomete r respectivel y. These data have heen ut ili zed to cst imatG the excess vo lume (1/\ excess viscosity (11'\ excess compressibility (K,E) , excess intGr­molecula r free-length , and Grunherg and Nissan parameter tf. Values of vE lu I' o-chl orophGnol + N,N-diGt hyl acetamide system and m-creso l + N,N-d iethyl ace tamide system are nega ti ve at all tcmperatures but , for o-cresol + N-N di ethyl acetamidc VE va lucs are positi ve at lower mole fraction of o-cresol and increasc wi th increasc in temperature. ll E va lues arc positi vc for all the systems and the magnitude of 1110 decreases with in creasc of temperature in all cases. K,'" v:llues are negati ve for all the systems over the who le co mpositinn-rangc. Analys is of these suggcsts the absence of any strong speci li c interaction s.

J Introduction

The properties of liquid-liquid mixtures are very important as a part of studi es of the rmodynami c, acoustic and transport aspects. T he compos iti onal dependence of the rmodynamic properties has proved to be a very useful tool in understanding the nature and ext ent of pattern of mo lecul ar aggregati o n resulting fro m inter-mo lecul ar int e ract ion be tween components. T hi s type o f study is a powerful means of c harac te ri zing the var ious aspects of physico-chem ica l behav iour of liquid mixtures and studying the inte rac tion between mo lecul es "'. Mixing vo lume e ffects are also important from both theoretical as well as practica l po in t of view. The above phenomenon is of s ignificance in many practical app li cati ons mainly in paints , varn ishes and printing ink industri es where vo lume effec ts are in vo lvedr.·x. Oswa l e f

0/." ·11 have studied the speed of sound and re lated paramete rs in certa in binary mi xtures involving dimethy l formam ide and dimethyl aceta lide. Am inabha vi et al. ,'~ " -' stud ied ultrasonic ve loc ity, viscos ity, excess vol ume and excess compress ibilities in aqueolls bina ry system of N­methyl ace tamide and N,N-dimethyl acetamide. In both these systems, spec ific inte racti ons between the

mo lecllies of the component liqu ids lead ing to the format ion of complexes through hydrogen bonding are assu med.

A survey of the lite rature reveals no ultrasonic studies for the present mixtures name ly, N,N-di ethyl acetamide + o-cresol, N,N-dicthyl ace tamide + m­cresol, N,N-diethy l acetamide + o-chlorophenol. There fore, in orde r to have a clear unde rstanding of the inte r-molecular interactions be tween the component mol ecules , dens iti es, ultrasonic veloc ities and viscos ities of the mixtu res at four different temperatures over the e ntire composition­range, have been reported here . From the

experimental val lles of densities (p) and ultrasonic velocit ies (u) , isentropic compressibility (KJ, inte r­

mo lecu lar free-length (Lf), excess viscos it ies (r{) , excess isent rop ic compress ibi lities (K,E), excess vo lumes (VI' ) have been calculated. These parameters are found to be se nsiti ve to inte ractions between the component mo lecules, which enab le us to have a better understanding of behaviour of the liquid mi xtures.

2 Experimental Details

The liquids are thoroughl y distill ed to re move di ssolved impurities uSlllg standard chemical

RAO et al.:EXCESS VOLUME, VISCOSITY & COMPRESSIBILITY OF BINARY MIXTURES RS I

1 500 ,----------- -,

14 5 0

g 1400 1:

~ ~ 1 350 5

1 3 00

12 50

on 0 5 10

g ~ u

.~

1'; 5

1500

1450

1400

1350

1300

1250

0 .0

1550

1500

g 1 4 50

~ E 1 400

Sl ~

1350 5

1300

1250 as 10 0 .0 as 10

M o l"" I . actr o n o f o - c h loro p h e r"l ol M o le fr<'l c l lOn 0 1 o ·crcsol M ole fracl lo ll 01 In ·creso l

- + - 308.15 ___ 313.15 - .... - 318 .15 _____ - 323 .15

Fig. I - Variation of ul!rasonic velocity with mole fraction for (a) a-ch loropheno l (b) o-cresol and (c) m-creso l at different temperature~

1 0 ,-------------, a 0 '11;:-----------,.

- 2 .0

~ g - 4 .0

~ -6 .0

ID

.li -8 a

i-a 5

g ro (5 -2 .0 E

ID U X

w -3. 5

IV -0 .5

~ ~ ro ~ - 1 0

., u

W -1 .5

-5 0 L-___ ~~ ___ ----' - 2 .0 '----~------'

Mol e fracllo n o f a - c hia ro ph enol 0 . 0 as 1 0 00 0 . 5 1 0

M o l e fractIOn of a-cresol M o le fract ion of m -creso l

- . - 313.15 - .... - 318 . 15 - e - 323.15

Fig. 2 - Variation of excess molar vo lume with mole fraction for (a) o-chloropheno l (h ) ()-cresol and (c) tn-cresol at dilTerent telllperatures

procedures. By taking two liquids in separate burettes, Job's method of continu ous variation has been used to prepare the mi xtu res of required proporti ons. The mi xed liquid binary sys tems are preserved in well-stoppered coni ca l flasks. After mi xin g the liquids thoroughl y, the flasks are left undisturbed to allow them to attain thermal equilibrium.

The ultrasonic veloc ity measurements are made with the help of a single crystal ultraso ni c pul se echo- interferometer SOUl-Om supp lied by System Dimensions, Banga lore, foll owing the procedure outlined by McSkimin l

(' . umber of pul ses sat isfy ing in phase conditi on are counted and the separat ion between them is est imated in terms of the pulse repetition rate. The accuracy in veloci ty measurements is within ±0.2 %. The densities of all

the mixtures have been determined by using a single pan electrica l balance for the determinati on of mass of a given vo lume of the liquid . The results of the densiti es are accurate to ±O.S!fr.

The coefficient of shear viscos ity '1 has been detcrmined as function of compos ition and the temperature using the os tawa ld viscolllcter. The accuracy in thc measurcments of viscos ity is within ±O.S% . The temperature of the mi xture IS

maintained at the required constant val ue by using consta nt temperature bath , controll ed by thermosta t with an accuracy of 0.1 dc. 3 Theory

The experimental data on densiti es (p), viscosities (11) and sound velocities (If) for binary

H52 INDIAN J PURE & APPL PHYS , VOL 40, DECEMBER 2002

mi xtures o f o-chl orophenol, o-creso l and m-creso l with N ,N-die thy l acetam ide at 308. 15, 3J3. 15, 318. 15 and 323 .15 K were dete rmined . From the measured values o f density , mol ar vo lume ( VIll ) was ca lculated us ing the re lati on:

... (1 )

where X" X2 and M"

MI are the mo le f ract ions and mo lecular weights of components I and 2 respectie ly. Component I is o-c reso l or Ill-c resol or o-c hl oropheno l and cOlllponent 2 is N,N-di ethy l acetamide. The excess vo lume yE for these binary mi xtures were obta ined using the re lati on:

.. . (2)

where P, and P2 are the dens it ies of pure components I and 2, respectively. From densities

and e fflux times (1) the viscos it ies('ll ) were obtained.

Excess viscos ities (ll E) were obta in ed as fo ll ows:

... (3)

where 'll l and 'll 2 are the viscositi es of pure

components I and 2, respective ly and 11 is the vi scosity of the mi xture.

The parameter d , regarded as a measure of the strength of the inte raction between components o f the binary mi xtures, has been estimated using re lationship proposed by Grunberg & Ni ssan2 as

C>­o

12

;;8

00 L-_ ___ L-_ __ _

00 0 .5 1.0 0 .0 0 .5 1.0 0 .0 0.5 10 Mole fr~ ct ion of o-chloro phenol M ole fraction o f a -c resol Mole fraction of m-cresol

4

.~ 3 o u OF> '5 :!l 2 ~ W

-+- 308.15 ____ 313.15 -A- 318.15 -x- 323.15

Fi£!. 1- Vari ati on of shear viscos ity with mole fraction for (a) o-chloropheno l (b) a-cresol and ~ tc) m-cresol at different temperatures

>-""5i 3 o ~ .;;

:!l 2 <l> U X

W

o ~~----'-------0 .0 0 .5 1.0 00 as

Mole fra ction of a-chiaro phenol Mole fraction of a-cresol Mole fra ction of m-cresol

-+- 308.15 ____ 313.15 -A- 318.15 --e- 323.15

Fi £!. 4 - Vari ati on of excess viscosit y wi th mole fracti on for (a) a-chlorophenol (b) o-rresol and - (e) m-creso l at different temperatures

1 0

~

.e ~

~ E 0 0 ~

'" u x w

RAO et al.:EXCESS VOLUME, VISCOSITY & COMPRESSIBILITY OF BINARY MIXTURES

M ole fracllon 01 a -chiaro phenol

00 0 2 04 06 08 10 0.0

Mole fra ction of a-cresol

05 10

~--------------------~ O __ ~------------------~

-~

~

-~ W

~ ~ '" '" ~ a. E a U

'" '" Q) U x

w

-2

-4

-6

Mole fraction of m ·cresol

05 1.0

. 9 L-____________________ ~ -8 L-_________ ---'

-+- 308.15 ___ 313.15 -.6.- 318_15 -*- 323.15

Fig. 5 - Variation of excess adiabatic compressibility with mole fraction for (a) o-chlorophenol (b) o-cresol and (c) m-cresol at dirrerenttemperatures

0 .54 ,------------------, 0 .5 4 .----------------, 0 .54 ,-----------.-- --,

= rn c ~ 0.47

c ro

'" :2

.co

'" co ~ 0.47 Q)

~ c '" Q)

:2

0.40 L _______ ~~~~~::J DAD L. ________ ~ _ ___ ~

0 .0 0 .5 1.0 0 .0 05 1.0 00 05

M o lp- fraction of o -c hlora phenol Mole fraction of a- c resol Mole fraction of m -crcsol

--+- 308_15 ___ 313.15 -~- 318.15 ____ 323_15

Fi g. 6 - Variation of mean free-length with mole fraction for (a) o-chlorophenol (h) o-cresol and (c) Ill-cresol at difrcrcnttcmperatures

1 .0

853

follows : where K, is the compressibility of the mixture K" and K,2 are the compressibilities of pure components I and 2, respectively.

. . . (4)

The ex pression of Jacobson is used to compute inter-molecular free- length given by:

I - K * A 1 /2 ..11' - J-l ad ... (5)

The values of densities (p) and ultrasonic velocities (u) were used to calcu late compressibilities (KJ by using the relation :

K,= I/u"p ... (6)

Excess compressibi lities (K,E) were obtained using re lation :

... (7)

4 Results and Discussion

In N,N-diethyl acetamide + o-chlorophenol system ultrasonic velocities are plotted with respect to composition in Fig. I for different temperatures of measurements . The curves of velocity are in general convex upward, all I)f them reaching maxima at certain intermediate composition of 0.38 mole fraction of o-chloro-phenol. Increasing the temperature seems to produce little or no shift in the composItIon corresponding to the maximum ve locity. However, the curves at high temperatures can be observed to have shifted downwards indicating that, there is a decrease in velocity at any

854 INDIAN J PUR E & APPL PHYS, VOL 40, DECEMBER 2002

specified concentrati on of the mixture with an inc rease in temperature.

The ex istence of a broad maxima or convex ity upward in these curves suggests that, the sound prefers to trave l faster in the mixture than e ithe r of the pure solvents N,N-diethyl acetamide or 0-

chloro-phenol. It would appear that, a definite s truc tura l re-adjustment of mo lecul ar packing is taking pl ace in the solution. The inc rease in sound veloc ity is a consequence of the enhanced bulk modulus of the liquid mixture over and above its va lue for idea l-mi xing conditi on. Similar trends in ve loc ity curves of binary aqueous mi xtures of non­e lectrolytes were reported by many investi gators carlicr1x and a few non-aqueous mi xtures conta ining strong hydrogen bonds arc also known to behave in thi s manner.

The va ri at ion of excess mo lar vo lume with compos iti on of o-chloro-phenol is shown in Fig. 2. The excess vo lumes in the mi xture are most ly nega ti ve and also are tempen.lture-dependent (Fig. 2). T he excess vo lumes remaining negative over the entire compos ition range sugges ts that , the mixture pre fe rs to have a compact structure in solution .

The compos iti on dependence of shear viscos ity is shown in Fig. :\ for thi s mi xture. These curves appear to reach peak va lues at about 0.58 mol e fracl ion of o-d !orophenol. Temperature dependence is s ignificant. The maxima shift towards lower magnitudes at hi ghe r te mperatures o f study. 1\ is ev ident fro m the curves o f Fig. 4 , whe re a max imum in excess viscosity can be noti ced at 0.59 mo le fract io n o f o-ch lo rophenol and above 0 .59 mole fracti on for o-c reso l and m-c resol. From these curves it is ev ident that, the disruptive fo rces which cause the breaking of weakly-assoc iated stru ctures of o-c reso l w hen it is added in sma ll quantiti es to dieth yl ace tamide. However, as the concentra tion of o-c reso l, o-c hl oropheno l and m-c reso l inc reases there Illay be st rong inter-molecular inte raction through hyd rogen nond formation between unlike

mo lec ule s_

The absence of such di spe rs ive inte rac ti on at low concentrati on o f o-chl o ropheno l in diethyl ace tanlide + o-chl orophenol mi xture mi ght be due to the fact that o-chl orophenol readil y forms complexes wi th diethyl acetamide as it contains highly active chloride atoms. The complex formation of a-chlorophenol through inter-

molecular hydrogen bonds has been established by several investigato rs 1').2 1.

Variation of excess adiabatic compressibility pl otted against the composition of o-chlorophenol in the binary system for diffe rent temperatures of study is shown in F ig. 5 . It can be seen that, the excess compressibility is negative over the entire composition-range, reaching broad negative maxima at about 0.:\ 8 mo le fraction of o-chloro-phenol. Further, the max ima found to shift towards lowe r va lues. These observations support the viewpoint that , the mix ture has a tendency for close r packing and hence is in a decreased compressibility phase in the inte rmediate composition-range. The effect of temperature on the compressibility curves is in agreement with the idea that , inte rac tion between unlike molecules predominantl y rupture the hydrogen bonded struc tures, which is the main cause of excess compress ibility.

The structural changes arc a lso found to affect the variation of inte r-mo lecul ar free- length (Lr). In fact , when the liquid mi xtures assu me a less compress ible phase of decreased flow capability as evidenced by excess adi abat ic compress ibility versus compOSItion and viscos ity versus compositi on curves, the free- length in the system might also be affected by the same structural changes. Variation of mean free-length is plotted with the compos ition o f o-chl o ro-pheno l in the mixture as shown in Fig. 6. The free- length curves show an initi a l decrea.-e with the inc rease in the compos iti on of o-chl oro-pheno l in the mixture and a minimum in free- length occurs at abou t 0.78 . The ex istence of minimum free-l e ngth is an indi cati on that , the structura l readjustment in the liquid mi xture is in the direction o f less compress ible phase or c loser pack ing of mo lecu les.

S imilar trends were observed w ith system N,N­d iethy l acetam ide w ith o-cresol and N,N-d ie thyl acetamide with m-creso l. The corresponding graphs were shown in Figs I to 6 , respect ivel y . These observa t ions are in agreement w ith the reported behav iour of respecti ve parameters in li qui d bi nary system, whi ch are known for the ab ility of comp lexati on between unli ke mol ecules through hyd rogen bonding~~·~' .

Variolls types of interacti ons whic h are possible and which can operate in the present binary systems containi ng N,N-d iethyl acetamide are charge

RAO el al.: EXCESS VOLUME, VISCOSITY & COMPRESS IBILITY OF BINARY MIXTUR ES 855

transfe r, hydrogen bonded complex formation, dipole-dipole and dipo le induced dipol e. These can produce negative dev iations in excess volumes, excess free- lengths and excess compressibility. A second type, ca lled di spersion forces, a lso ex ist which contribute to pos itive deviations in the above paramete rs . h appears by several ev idences that , 0-H hydrogen bonded complex formati on is the ma in cause ror the observed excess va lues of the paramete rs studied.

The excess volumes for a ll the binary mixtures in the present study are typi ca ll y negative, reachin g maximum negative values at certa in inte rmed iate compositions. Since the carbonyl group of N,N­diethyl acetamide has a cons iderabl e proton accepting ability appropriate negati ve contributi ons may be anticipated to ori ginate in O- H-O=C bonds between the amide and aromatic alcoho ls studied2

•' .

In addition, geometrica l or struc tural e ffec ts allowing accommodation of one type o f mol ecules into the other type causing, thereby, a dense liquid structure at intermediate compos iti on are quite poss ible in these systems25

.

A systematic stud y of excess compress ibi I ity o f mixing for an aromatic a lcoho l + a co-so lvent like N,N-die thy l ace tamide is important. The presence o f aromatic rings for the hydrogen atom o f a lky l a lcohol (a lkano l), changes the hyd rogen bonding ability of the alcoho l and would , the re fore, be ex pec ted to affec t, considerab ly, the excess thermodynamic para meters like excess compressibi I ity.

Lisa Pikkana inen2(' po inted out fro m studies o f

the mixtures o f (a liphatic alcohol + methy l e th yl ke tone) and aromatic alcohols + methy l ethy l ketone syste m that, a greate r tendency for the formation of O-H---O=C hydrogen bonded compl exes In aromatic than a liphatic alkanol mi xtures.

Further, the s ignificance of suc h compl exes be tween sol vent mo lecules is more ev ident where binary mixture contained aromatic alcoho l and N,N­die thyl acetamide. The diethy l ace tamide is a good proton acceptor and even a better proton acceptor than simple ethyl acetamide, because, the carboxy l bond of die thy l acetamide is known to be a bette r proton acceptor than carboxy l bond o f ethyl acetamide.

Oswal & Pate F7 studi ed the e ffects o f hydrogen bonding between dimethyl formamide and alkane

IlItntes. The syste m, N,N-dimethy l acetamide + water was studied by Aminabhavi & Gopal

Krishna2X• Excess viscosity 1l E> was positi ve and ~ ,,/'

was negati ve over entire composition reg ion, reaching max imum nega ti ve values at middle

concentrati ons. ~ "d"' of this sys te m varies simil a r to

V"' . Hence, ~ "d can be taken as a measure of

hardness and ~,,/' as a measure o f free vo lume change. The s ize and shapes o f constituent mo lecules affect the ex tent of deviation from idea l­miXing. Similar conc lusi ons were drawn by Shiohama et aFI; Janquera et af. 10; Pandharinath el a/. 1 1

; 8 anipal & Amrit Pal Toor '! ; Anwar Ali & Anil Kumar Nain" .

5 Conclusion

All these observati ons point out c learly , the emergence of a new, c lose-packed structure in the inte rmed iate composition-ranges o f the binary sys tems . The hydrogen bonded inte r-mo lecular complexes mi ght be formed between N,N-dimethyl acetamide and the solute mo lecules hav in g de fini te sto ichiometric proportions fo r eac h syste m. The temperature dependence of the diffe rent parameters suggests that , the degree o f dev iat ion from idea li ty is strongly te mperature-sensiti ve and is influenced by the weakening of hydrogen bonds.

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