Indian Journal of ChemistryVol. 16A, Au3ust 1978, pp. 691-694

Aq ueous Solubility in Modified Solvent System: Part I - AqueousSolubility in n-Butyl, n-Amyl, n-Hexyl & Benzyl AlcoholsContaining Benzene as Modifier of Solvent Environment

R. PRATAP SINGH & R. SAH

Department of Chemistry, Bh agalpur College of Engineering, Bhagalpur

Received 24 September 1977; revised 24 December 1977; accepted 13 February 1978

Aqueous solubility (Sw) has been determined in various modified solvent systems with twocomponents, obtained by mixing benzene in different concentrations in higher alcohols, viz.n-butyl alcohol, n-amyl alcohol, rr-hexyl alcohol and benzyl alcohol, and the variation of Sw withcomposition discussed. From the smoothed data of Sw and the composition of the modifiedsolvent systems, the values of excess aqueous solubility S! in each case have been determined andthe same fitted in an algebraic equation involving the composition with four adjustable para-meters. Further, the aqueous solubility in a modified solvent system has been treated as anextensive property and the partial aqueous molar solubilities in each case determined and thederived data utilized to calculate the composition for maximum deviation from ideal aqueoussolubility.

MOST of the works on the aqueous solubilityand its correlations based on the physicalparameters and intermolecular forcesl-4 are

confined to pure solvent systems and studiesinvolving modified solvent systems are lacking.With this in view, the aqueous solubilities in alcohols,viz. n-butyl, n-amyl, n-hexyl and benzyl alcohols,have been determined and the effect of benzene asmodifier of the solvent environment studied, Theresults of the study are reported in this paper.

Materials and MethodsBenzene and alcohols, V1Z_ n-butyl, n-amyl,

n-hexyl and benzyl alcohols, were BDHanalar quality. These were purified by standardmethods=> and the purity checked by density andrefractive index measurements. Conductivity waterobtained from an all-glass still was used in this study,

The modified solvent systems were obtained bymixing benzene in different concentrations in alcoholand the solubilitv of water in such media determinedby titration method6_ The titrations were carriedout in well stoppered volumetric flasks in order tocheck the loss due to vapourization, and the shakingafter each addition of water was done in an ultra-sonic shaker [Systronic ultrasonic cleaner (shaker)type 1201] for at least 30 min. The contentswere equilibrated in a thermostat maintained at30° ± 0-05°_ The final end point was determinedwhen a second phase appeared and the volumeof the water added was noted, Each titration wasrepea ted at least three times to check the repro-ducibility of the results.

Results and DiscussionThe aqueous solubility Sw (g of water/mole of

binary solvent) for various alcohol-benzene binariesare included in Table 1.

692

The data in Table 1 reveal that Sw decreasesmore rapidly with the increase of X2 (mole fractionof benzene) in alcohol-rich region and comparativelyless rapidly with the increase of X2 in alcohol-poorregion. In the former region, the benzene in small

TABLE 1 - AQUEOUS SOLUBILITY FORVARIOUS ALCOHOL-BENZENE BINARY MIXTURES AT

30o±0·05°

X 2

n-BUTANOL(I) n-AMYL ALCOHOL(I)+BENZENE(2) +BENZENE(2)

1-000 0-064 1-000 0-0640-902 0-134 0-916 0-1280-804 0-360 0-829 0-2780-706 0-901 0-739 0-4250-607 1-'491 0-645 0-7220-507 2-537 0-548 1-1770-407 3-725 0-447 1-8000-306 5-102 0-342 3-5720-204 7-400 0-233 5-2590-103 10-810 0-119 7-4950-000 19-255 0-000 9-556

n-HExANOL(l) BENZYL ALCOHOL(I)+BENZENE(2) +BENZENE(2)

1-000 0-064 1-000 0-0640-926 0-322 0-912 0-1810-848 0-588 0-822 0-6420-765 0-979 0-730 1-1160-677 1-313 0-634 1-7910-583 1-983 0-536 2-5830-483 2-591 0-435 3-3000-375 3-130 0-331 4-1380-259 3-825 0-224 5-1010-135 5-055 0-114 8-1240-000 7-634 0-000 10-933

SINGH & SAH: AQUEOUS SOLUBILITY IN MODIFIED SOLVENT

quantity forms 'It-bonds with the alcohol in pre-ference to re-bonds with water because the carbonchain in alcohol facilitates this interaction. Inessence, then the rapid decrease in SUIin this regionis a consequence of the reduction of the molefraction of alcohol and the reduction of hydrogenbonding sites along with comparatively decreasedavailability of added benzene for water dissolutiondue to alcohol-benzene 'It-bond formation. On theother hand, in the latter region, the alcohol insmall quantity forms alcohol-water hydrogen bondin preference to alcohol-benzene re-bond. Thuscompara tively less availa bility of alcohol-benzenere-bond with increasing Xi causes SUIto decreaseless rapidly in alcohol-poor region.

Further, treating SUIas a mixture property andremembering that it differs from the weightedalgebraic sum of the aqueous solubilities in thepure components of a nonideal binary system, wecan write:

S; = Sw-[Xl(S~)l+X2(S~)2J ... (1)

where Xl and X2 are the mole fractions of thecomponents 1 and 2 forming the binary, (S~)l and{S~)2 are the aqueous solubilities in pure components1 and 2 respectively and S; is the excess aqueoussolubility. From experimentally determined valuesof (S~)l' {S~)2 and Sw for different compositionsof each binary studied, the corresponding S; valueswere calculated utilizing Eq. (1). The variation ofS; with X I was found to be unsymmetrical with aminimum in S; occurring at X2<0'5 in each case.The smoothed S; composition data were fitted inEq. (2)7

S; = XlX2[A+B(Xl-X2)+C(Xl-X2)2+D(X1-X2)s+ .... J .•• (2)

and the values of the constants A, B, C and Dwere determined by least square method. Thesevalues with the corresponding standard deviationswere listed in Table 2. The form of Eq. (2) is a

general one for computing an excess property ofbinary liquid mixtures and its applications toaqueous solubility data for the systems studied hereis amply tested as is evident from the values ofstandard deviations in Table 2.

Since Sw is directly proportional to the quantityof the material contained in the system, it isobviously an extensive property. As such, writingSw in terms of partial molar solubilities (Sw)l and(SW)2 in Eq. (1), differentiating it with respect toXI and applying the conditions of Gibbs-Duhemequation we have:

OS~/OX2 = [(Swh-(S~)2]-[(SW)l-(S~)lJ ... (3)For maxima in S~ vs X2 plot, oS~/oXs = 0, andtherefore, for this condition Eq. (3) gives

(Sw)2-(S~h = (S")l-(S~)l ... (4)

As Eq. (4) is satisfied at the point of intersectionof the [(Swh-(S~)2] vs X2 and [(SW)l-(S~)Jvs X2 curves, it is clear that the maxima ofS~ vs X2 curve will also occur at this point.In order to verify this conclusion, the requiredvalues of (SW)l and (Sw)s for the [(SW)l-(S~)lJ vsX2 and [(Sw)I-(S~)2] vs XI curves respectivelywere calculated from the plot of SUI VS X2 byRoozenboom's constructions method and those ofS~ for the curve S~ vs Xz were obtained fromEq. (1). When the relevant data were plottedon the same scale, it became obvious graphicallythat the values of X2 for the point of intersectionof the curves give the values of (Xz)ma.: corres-ponding to the maximum value of S! in each case.A typical plot showing the point of commonintersection is shown in Fig. 1.

It may be pointed out that the values of(X2)max can also be calculated by determining thevalues of O(SW)l/OXZ and o(Sw)z/oXz from the slopes

- 0 - 0of the curves [(SW)l-(SW)lJvs XI and [(Sw)z-(Sw)Jvs X2 respectively at the point where these curvesintersect and by substituting the same in the

TABLE 2- VALUES OF CONSTANTS A, B, C AND D WITH CORRESPONDING STANDARD DEVIATIONS AT 30o±0·05°

n-Butanol(I) n-Amyl alcohol(I) n-Hexanol(I) Benzyl alcohol(l)+ •. + + +

benzene(2) benzene(2) benzene(2) benzene (2)

A -28'290 -12·910 -6·010 -11'274±8A 0·101 0·014 0·040 0·039B -16'684 -2-671 -3·229 -6·408±3B 0'295 0·041 0·116 0·114C -18·971 +6'078 -4·989 -6'453±3C 0'828 0·115 0'325 0·321D -16·760 +4-892 -5·851 -2·058±3D 2'451 0·341 0'962 0·950

±3S~ 0·057 0·008 0·022 0·022

693

e--1,0

~It -2·0<lzCD - 3·0u.0 -4·0III5 -5,0~

'-.....-8·0It~ -7·0<l

~ -8·0IL0 -90()

<ri~ -10,0<lItC!> -11·0

-12·0

INDIAN J. CHEM., VOL. 16A, AUGUST 1978

X&0·6 ()os 1·0

-13,0-14,0 L- ~

Fig. 1- Plots of (Sw-S~) and S~ against composition forn-amyl alcohol (1)+benzene(2)

rearranged Gibbs-Duhem equation for this casein the following form:O[(Sw)l- (S~h]_ X [Of(Swh - (S~h}_ of (Swh- (S~b}]

3X2 - 2 3X2 3X2•.. (5)

The values of (X2)ma:r calculated from Eq. (5)and obtained graphically from S~ vs X2 curvefor each system studied are given in Table 3.

The calculated and graphical values of (X2)maxare in good agreement. Incidentally this provides

694

TABLE 3 - COMPARISONOF (X,)mu VALUES AT 30° ±O'Oso

System (X.)ma:r

Calc. FromS~ vs XI

curve

n-Butanol(l) +benzene(2)n-Amyl alcohol(l) +benzene(2)n-Hexanol(l) +benzene(2)Benzyl alcohol (1)+benzene(2)

0·2650'4510·2580·305

0·2700·4500·2600·310

a convenient technique to determine the value of(X2)ma" for which S~ is maximum and overcomesthe difficulty in locating the same from the plotof S~ vs X2 alone specially when the maxima isnot sharp.Acknowledgement

The authors are thankful to Principal S. N.Sinha for laboratory facilities. One of them (R.S.)is thankful to the UGC, New Delhi, for financialassistance.

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