Indian Journal of Chemistry Vol. 38A, March 1999, pp. 237-243 Excess molar volumes and excess partial molar volumes of diethylene glycol monoethyl ether - n-alcohol mixtures at 298.15 K Arnalendu Pal' & Gurcharan Dass Department of Chemistry, Kurukshetra University, Kurukshetra 136 119, India Received 15 June 1998; revised 7 December 1998 Excess molar volumes V E have been measured for binary mixtures of diethylene glycol monoethyl ether with methanol, ethanol, 1- propanol, I-pentanol and I-hexanol as a function of composition using a continuous-dilution dilatometer at 298.15 K. The excess molar volumes V E are negative over the entire range of composition for the systems diethylene glycol monoethyl ether + methanol, + ethanol , and + and positive for the remaining systems, diethylene glycol monoethyl ether + I-pentanol, and + I-hexanol. The measured V E values increase towards positive direction with increase in chain length of the n-alcohol. The V E results have been used to estimate the excess partial molar volumes V E . of the components and have also been analysed using the Prigogine - Flory - Patterson (PFP) theory. An analysis of each of the three viz. interactional, free volume and internal pressure to V.,E shows that the free volume effect and internal pressure contribution are negative for all the mixtures, whereas the interactional contribution is negative for methanol and positive for remaining systems. The behaviour of V. /' , V.,E ,i ' and XJ 2 (Flory's interaction parameter) with composition and the number of carbon atoms in the alcohol molecule is discussed. In continuation of our program of research on the physico-chemical properties of binary mixtures contain- ing the oxygen (-0-) and hydroxyl (-OH) functional groupsl.4, we report here a new experimental data of ex- cess molar volumes V E of binary solvent mixtures con- m taining diethylene glycol monoethyl ether with metha- nol, ethanol, I-propanol, I-pentanol or I-hexanol over the whole mole fraction range at 298.15 K and at atmos- pheric pressure. The aim of this work is to provide a set of values for the characterization of the molecular inter- action between alkoxyethanol and n-alcohols and also to assess the effect of the chain length of alcohols on excess volumes. The experimental V E results have been m analysed here in the light of Prigogine-Flory-Patterson theory). An attempt is also made to rationalize the re- sults by collecting the data from literatures on alkoxyethanols + n-alcohol mixtures. Materials and Methods Diethylene glycol monoethyl ether (Fluka , purum , GC > 98%) was used without further purification. Metha- nol (SRL, Bombay, GC min. 99.8%), ethanol (Riedel- de Haen, Germany, GC min. 99.8%), I-propanol (SRL, GC min. 99.5%), I-pentanol (Acros, USA, 99%), and 1- hexanol (SRL, Bombay, GC min. 99%) were dried and fractionally distilled as described elsewhereo. All liquids were stored in dark bottles to prevent contamination from air and dried over 4"\ molecular sieves to reduce the water content. Prior to measurements, all liquids were partially degassed under vacuum. The purities of the liquid were checked by measuring and comparing the densities at 298.15 K and atmospheric pressure with their corre- sponding literature The densities were meas- ured with a bicapillary pycnometer that gave an accu- racy of 5 parts in 10 5 • The pycnometer was calibrated at 298.15 K with doubly distilled water. Excess molar volumes, which are accurate to ± 0.003 cm 3 mol· l , were measured using a continuous- dilution dilatometer in similar fashion to that described by Dickinson et al lO • Details of its calibration, experimen- tal set up, and operational procedure have been described previously I. !!. The composition of each mixture was ob- tained with an accuracy of ±.I x 10. 4 from the measured apparent masses of the components. All masses were corrected for buoyancy. The measurements over the full mole fraction range were completed by two runs, i.e: one for the alcohol rich regions starting from pure alco- hol and the other from the alkoxyethanol rich regions starting from diethylene glycol monoethyl ether up to the composition of about 50 wt%. A thermostatically controlled, well-stirred water bath whose temperature was controlled to ± 0.01 K was used for all the measure- ments.
7
Embed
Excess molar volumes and excess partial molar …nopr.niscair.res.in/bitstream/123456789/15650/1/IJCA 38A(3) 237-243... · Excess molar volumes and excess partial molar volumes of
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Indian Journal of Chemistry Vol. 38A, March 1999, pp. 237-243
Excess molar volumes and excess partial molar volumes of diethylene glycol monoethyl ether - n-alcohol mixtures at 298.15 K
Arnalendu Pal' & Gurcharan Dass Department of Chemistry, Kurukshetra University,
Kurukshetra 136 119, India
Received 15 June 1998; revised 7 December 1998
Excess molar volumes V E have been measured for binary mixtures of diethylene glycol monoethyl ether with methanol, ethanol, 1-propanol, I-pentanol and I-hexanol as a function of composition using a continuous-dilution dilatometer at 298.15 K. The excess molar volumes V E are negative over the entire range of composition for the systems diethylene glycol monoethyl ether + methanol, + ethanol , and + I-p;~panol and positive for the remaining systems, diethylene glycol monoethyl ether + I-pentanol, and + I-hexanol. The measured V E values increase towards positive direction with increase in chain length of the n-alcohol. The V E results have been used to estimate the excess partial molar volumes V E . of the components and have also been analysed using the Prigogine - Flory - Patterson (PFP) theory. An analysis of each of the three ·~o'ntributions viz. interactional, free volume and internal pressure to V.,E shows that the free volume effect and internal pressure contribution are negative for all the mixtures, whereas the interactional contribution is negative
for methanol and positive for remaining systems. The behaviour of V./' , V.,E ,i ' and XJ2 (Flory's interaction parameter) with composition and the number of carbon atoms in the alcohol molecule is discussed.
In continuation of our program of research on the physico-chemical properties of binary mixtures containing the oxygen (-0-) and hydroxyl (-OH) functional groupsl .4, we report here a new experimental data of excess molar volumes V E of binary solvent mixtures con-
m
taining diethylene glycol monoethyl ether with metha-nol, ethanol, I-propanol, I-pentanol or I-hexanol over the whole mole fraction range at 298.15 K and at atmospheric pressure. The aim of this work is to provide a set of values for the characterization of the molecular interaction between alkoxyethanol and n-alcohols and also to assess the effect of the chain length of alcohols on excess volumes . The experimental V E results have been
m
analysed here in the light of Prigogine-Flory-Patterson theory). An attempt is also made to rationalize the results by collecting the data from literatures on alkoxyethanols + n-alcohol mixtures.
Materials and Methods
Diethylene glycol monoethyl ether (Fluka , purum , GC > 98%) was used without further purification. Methanol (SRL, Bombay, GC min. 99.8%), ethanol (Riedelde Haen, Germany, GC min. 99.8%), I-propanol (SRL, GC min. 99.5%), I-pentanol (Acros, USA, 99%), and 1-hexanol (SRL, Bombay, GC min. 99%) were dried and fractionally distilled as described elsewhereo. All liquids
were stored in dark bottles to prevent contamination from air and dried over 4"\ molecular sieves to reduce the water content. Prior to measurements, all liquids were partially degassed under vacuum. The purities of the liquid were checked by measuring and comparing the densities at 298.15 K and atmospheric pressure with their corresponding literature values6.~. The densities were measured with a bicapillary pycnometer that gave an accuracy of 5 parts in 105
• The pycnometer was calibrated at 298.15 K with doubly distilled water.
Excess molar volumes, which are accurate to ± 0.003 cm3 mol·l, were measured using a continuous- dilution dilatometer in similar fashion to that described by Dickinson et al lO
• Details of its calibration, experimental set up, and operational procedure have been described previously I . !!. The composition of each mixture was obtained with an accuracy of ±.I x 10.4 from the measured apparent masses of the components. All masses were corrected for buoyancy. The measurements over the full mole fraction range were completed by two runs, i.e: one for the alcohol rich regions starting from pure alcohol and the other from the alkoxyethanol rich regions starting from diethylene glycol monoethyl ether up to the composition of about 50 wt%. A thermostatically controlled, well-stirred water bath whose temperature was controlled to ± 0.01 K was used for all the measurements.
Results and Discussion The experimental values of excess molar volumes V E
11/
where Ai is the polynomial coefficients, k is the polynomial degree and x is the mole fraction of alkoxyethanol , respect ively. The values of the coefficients A were evalu-for the systems of diethylene glycol monoethy l ether with
five alcohols are presented as a function of mole fraction in Table I and are graphica ll y represented in Fig. I . The va lues of V E for all systems were fitted to an em-
11/
pirical equation of the form:
n
V /: =x( l -x) L A ( 1-2x)i //I 1=0 J
.. . ( I )
J ated by the method of leas t squares with all points weighted equally and are listed in Tab le 2 along with standard deviations s (V E):
11/
... (2)
where N is the number of experimental data. For all mixtures s(V 1:: ) < 0.003, in accord with the good accuracy
111 -
attainable with the d il atometer used here .
240 INDIAN J CHEM, SEC. A, MARCH 1999
XXXX JC X X x 0.2
x · x 000000000<>0000 0 x o x
0 ·' x 0 0 00 x 00 0
• 00 • . .0'0 '00 .
0 o • lP, o 0 .. D
0 D
06 ODD D D D D
DaooDctO o D .. 0 .. -0·' o ..
E .. .. M~
. 0 <- .. 0
-0.2 .. .. .. ..... o · .. .. WE .... .. .. > 0 A t.66 .. 0
V;'2 = (Vm.2- V:.2)from VmE whereV~. 1 andV~.2 represent the molar volume of the components. The par
tial molar volumes Vm.1 and Vm.2 are given in
Table I, while Fig. 2 shows the excess partial molar vol
umes, Vm.1 and V!.2 plotted against x . The partial mo
lar volumes V m.1 and Vm.2 in these mixtures were
evaluated ' 2. 13 over the whole composition range by us
ing Eqs (3) and (4) :
Vm.1 = v./' +V~.I-(I-X)(OV}/o (I-X») P. T ... (3)
Vm.2 = V .. E V* + m,2 ... (4)
The derivatives in Eqs (3) and (4) were obtained by differentiation of Eq. (l).
Excess volume against composition plots in Fig. I show that VmE are negative over the entire range of composition for methanol, ethanol, and I-propanol and positive in the case of I-butanol (reported by Cobos et al. '4 from density values obtained using vibrating-tube densitometer are also plotted in Fig. 1) , I-pentanol and I-hexanol at 298.15 K. For the same value of x, the excess V E increases with increase in the chain length of
m
alcohol. The location of the V E minimum shifts from x m
= 0.37 for methanol to x = 0.35 for I-propanol whereas the V E maximum shifts from x = 0.64 for I-butanol to x
m
= 0.55 for I-hexanol. It is well-known that alkoxyethanols exist as associ
ated structures like the alcohols '5. '7 in the liquid state; the association may be due to the intramolecular hydrogen bond formation between the ether oxygen atom and the -OH group, as in the case of alcohols, this association may be through the H-bonding of their -OH groups . The magnitude of V £ is the result of contributions from
m
different effects which can be divided into physical, chemical and structural contributions. The physical interactions involve mainly disruption of liquid order on mixing; unfavourable interactions between the same unlike molecules produce positive V E values. The chemi-
m
calor specific interactions result in a volume decrease and these include possible depolymerisation of self-associated alkoxyethanols by the alcohols and self associated alcohols by the alkoxyethanols and/or formation of new hydrogen bonds between alkoxyalkanols and
Table 2- Parameters Aj and standard deviations O'(V} ) for least-squares representations by equation(l ) of V f: for studied mixtures at 298.15 K
PAL el al. : EXCESS MOLAR VOLUMES OF ETHER -Il-ALCOHOL MIXTURES 24 1
Table 3- Calcul ated values of the three contribution to the excess volume from the Prigoginc-Flory-Patterson theory fo r diethylene glycol monoethyl ether + alcohols at 298. 15 K
Table 4 - Parameters of pure components at 298. 15 K
Component k/TPa-') V V(cm>mol-') V'(cm>mol-') T '(K) p. (J em-I)
Diethylene glycol
monoethyl ether 627.56 1.2 153 136.37
Methanol 1265.77 1.2875 40.75
Ethanol. 11 58.22 1.2663 58.65
I-Propanol 10 18.58 1.2483 75 .1 8
I-Butanol 940. 15 1.2336 9 1.96
I-Pentanol 883 .79 1.2253 108 .68
I-Hexnanol. 842.39 1.2204 125 .32
alcohols and other complex-forming interactions. Structural effec ts ari sing from interstiti al accommodation due to differences in the molar vo lumes and free volumes 'x
between liquid components contribute to negati ve V}
values . The V E values increase in the sequence methanol <
11/
eth anol < I-propanol < I-butanol < I-pentanol < 1-hexanol. The interactions between die thylene g lyco l monoethyl ether and methanol are relati vely strong. Increasing the chain length of the alcohol tends to dilute
the interaction between die thylene g lycol diethyl ether and alcohol; V E decreases and becomes pos itive for the
"' larger alcohols. It is observed that the molar vo lumes of the alcohols increase with chain length and the free volumes fo ll ow in verse trend (Table 3). Therefore, the structural contributi ons ari sing from insterstiti al accommodati on due to difference in molar vo lume and free vo lume between the components does not play any s igni ficant role in the magnitude of V E. In fact, we observe
11/
s imilar characteri stics for V E as in mi xtures of diethyl-11/
ene g lyco l monomethy l ether2. , ~ or e th yle ne g lyco l monoethyl ether20 with alcohols: a marked decrease in the algebra ic value of V E here . It is suggested 1 ~ . 21 that
11/
increas in g the number of OC2H4
groups or repl ac ing methyl by e thyl groups leads to more negati ve excess
molar vo lumes .
11 2.2 1 5758 593.63
3 1.65 4752 468.74
46.32 4989 450.75
60.23 5223 457.49
74.55 5442 449.78
88.70 5579 452.30
102.69 5664 458.6 1
The excess partial molar vo lumes increase systematically with increasing chain length of the alcoho l. T he sharp increase in V,}.I values at small x (Fig . 2) prov ides evidence for the breaking of the self-assoc iated structure of diethylene g lycol monoethyl ether. The increase in V E 7 values at higher x suggests the breaking of the
III ._
alcohol structure in thi s concentration range. Thi s ob-servation leads us to suggest that there is relatively strong hydrogen bonds formati on between die thylene g lyco l monoethyl ether and methanol molecules rathe r than structure breaking effect.
Prigog ine-Flory -Patterson Theory The Prigogine-F lory-Patterson (PFP) theory5.22.26 has
been commonly employed to estimate theoreticall y and analyse the excess the rmodynamic fun ctions. In thi s theory, V E is divided into an interactional contributi on,
11/
a free volume contributi on and internal pressure contri -bution. The e xpress ion for V E which separates the th ree
Fig. 2- Pa rti a l molar exccss vo lum cs VEw . 1 and VI""" for
[xClI5{O(CH,), lPH(I) + ( I-x) CnH1n•1 OH (2)]: A, methanol; B, ethanol; C, I-propanol; D, I-pentanol; E, I-hexanol.
2 ( \'1':-'2 ) [( 14/9) v - I ] \jf\jf ____ --,-,-__ ....:.1--=.2 ( V curvature
[(4/3 )v- 1/3 _1]\i
... (5)
where lfI represents the contact energy fraction and is
g iven by
... (6)
The va lues of the parameters for the pure liquid components and the mixture are obtained us ing the Flory theory2l24 . The parameters for the pure liquid components derived by using Flory 's ex press ion are given in
Table 4. The contact interacti on parameter X12 required for the
calcul at ion of V E using the Flory-Patterson theory was adjusted by fittil~'~ the experimental V",E data at equimolar compositi on for each system investigated here . The ca lcul ated equimolar va lues of the three contribut ions together with the X
I2 parameter fo r each liquid mixture are
li sted in Table 3.
)0
20
c;'~ 10
" "-~ a ci
-~ - 10
-20
-)0 0 5 6
Fig. 3- Plot of interacti on energy parameter (XJ against number of carbon atoms in alcohols (n= 1-6).
Study of the data in Table 3 reveals th at both the p' contribution and free volume effects are negative for a ll the mixtures whereas the interactional contribution is positive for all mixtures except methanol which has a highly negative interactional term .
The interactional contribution, which is proportional
to Xll
' when negat ive for methanol system, suggests re lative ly strong intermolecular hydrogen bonding interaction with diethylene glycol monoethyl ether.
However, it shows pos iti ve for other systems, suggesting that the absence of hydrogen bonding or other specific interactions. Also, Fig.3 shows the variation of X
l l w ith the number of carbon atoms in a lcohols.
Th e free vo lume e ffec t whi c h is pro porti ona l to
2 - (VI - \12)' is a measure of geometrical o r interstiti al
accommodation . It becomes less negati ve as the differ
ence between the reduced volume v of two compone nts
in the mixture decreases, as shown in Table 3. It suggests that , as the chain length of the alcoho l increases, interstitial accommodation becomes less significant, resulting V,,/' decreases. T he p' effect, which is propor-
2 tional to - (~ - \12) (PI * - p/ ), is negati ve for all sys-
tems. It appears that the dominant role is played by the difference in internal pressures and reduced vo lumes of the respective components. Thi s is the main parameter for deciding the sign and magnitude of excess vo lumes as the ir may be pos itive o r negative on the relative cohes ive energy of the ex panded and less ex panded component.
Acknowledgement Thi s work was financed by a DST(No. SP/SIIH-16/
94) and CSIR grant (No. 01 ( I 428)/96-EMR-II).
PAL el 01.: EXCESS MOLAR VOLUMES OF ETHER -II -ALCOHOL MIXTURES 243
References
Pal A & Singh Y P, J chem Th erll1odYII , 26 ( 1994) 1063 .
2 Pal A & Ku mar A, Acouslic Lellers,20 ( 1997) 203.
3 Pal A & Kum ar A, J solll Chelll , ( 1998) in press.
4 Pal A & Sharma S, Fluid phase Equilibria, 145( 1 998) 15 1.
6 Riddi ck 1 A & Bunger W B, Orgall ic solvelll.\', Techlliques of chemis/J)', edited by A Weissberger, Vol. II (Wiley Interscience, New York), 1970.
7 Douheret G, Salgado C, Davis M 1& Loya 1, Th e/'lllOchilll ACla, 207 ( 1992) 3 13.
8 Ki yohara 0 & Benson G C, J .1'0111 Chelll , 11 ( 1979) 86 1.
9 Arce A, Martinez-Ageitos 1, Mendoza T & Soto A, J chon ellg Dora, 4 1 ( 1996) 724.
10 Dick inson E, Hunt D C & McLu re I A, J chelll Therlllodyn, 7( 1975) 73 1.
II Pal A & Si ngh Y P, .I chem eng Dala, 40 ( 1995) 8 18.
12 Acree W E. 1r .. Th erlllodynalllic properries of 1I01l-eleclrolyte .I'oluriolls, (Academic Press, New York), ( 1984).
13 Dav is M I, Chelll Soc Rev, 22( 1993) 127. 14 Cobos 1 C, Garcia I & Casanova C, Therlllochilll Acra, 131
( 1988) 73. 15 Frank F & I ves D 1 G Quarl sRel', 20( 1966) I. 16 Miura T & Nakamura M, 8ul/ chelll Soc .Iapall , 50 ( 1977)
2528. 17 Caminati W & Wilson E B, J 11101 Speclrosc, 8 1 ( 1980)356. 18 Prolongo M G, Masegosa R M, Fuentes H I & Horta A, J Ilhys
Chelll , 88( 1984)2 163. 19 Pal A & Singh W, J chem Th erlllodl'll , 28 ( 1996) 1369. 20 Ramana Reddy K Y, Rambabu K, Dcvaraj ulu T & Krishnaiah
A, Ph),s chelll . Liq, 3 1 ( 1996) 9. 2 1 Davis M I & Chacon M, Therlllochilll Acra , 190 ( 1991 ) 259. 22 Prigogine I, The 1II0Iecular/heor,)' of SO llll ioll S, (North Holl and ,
Amsterdam), (1957). 23 Flory P 1, J Alii chem Soc, 87( 1965) 1833 . 24 Abe A & Flory P 1, J Alii chelll Soc, 86( 1964) 3563. 25 Costas M & Patterson D , J solll Chelll , II ( 1982) 807. 26 Patterson D & Rastogi A K, J ph)'.\' Chelll , 74 ( 1970) 1067.