Solubility of gallic acid in liquid mixtures of (ethanol + water) from (293.15 to 318.15) K

Solubilityofgallicacidinliquidmixturesof(ethanol+water)from(293.15to318.15)K

AdelNoubigha, ,Chokrijeribia,ArbiMgaidib,ManefAbderrabbaa

ab

LaboratoryofPhysicalChemistryofMaterials,PreparatoryInstituteforScienti candTechnicalStudiesofLaMarsa,CarthageUniversity,Bp51,2070LaMarsa,TunisiaIndustrialInorganicChemistryLaboratory,ChemistryDepartment,FacultyofScienceofTunis,TunisElManarUniversity,1060Tunis,Tunisia

articleinfoabstract

Thesolubilityofgallicacidin(water+ethanol)binarysolventswasdeterminedfrom(293.15to318.15)KatatmosphericpressureusingathermostattedreactorandUV/visspectrophotometeranalysis.Theeffectsofbinarysolventscompositionandtemperatureonthesolubilitywerediscussed.Itwasfoundthatgallicacidsolubilityin(water+ethanol)ingtheexperimentallymeasuredsolubilities,thethermodynamicpropertiesofdissolutionofthegallicacidsuchasGibbsenergy(DsolG°),molarenthalpyofdissolution(DsolH°),andmolarentropyofdissolution(DsolS°)werecalculated.

Ó2012ElsevierLtd.Allrightsreserved.

Articlehistory:

Received3March2012

Receivedinrevisedform5May2012Accepted19June2012

Availableonline29June2012Keywords:GallicacidSolubility

Mixedsolvents

TemperaturedependenceThermodynamicproperties

1.Introduction

Gallicacid(3,4,5-trihydroxybenzoicacid)anditsderivativesarephenoliccompoundscontainedinOliveMillWasteWater(OMWW)[1,2]andpresentinsomeplants,suchasgreenandblackteas[3],andoak[4].Theyareindustriallyimportantchemicalswidelyusedinorganicsynthesis,pharmaceutical,food,andinte-gratedcircuitmanufacturing.Thesephenoliccompoundsareanti-oxidant[5,6],anti-in ammatory[7],phytotoxicandtoxictobacteriaandusedincommonbiologicalwastewatertreatment[8–10].Thesolubilityofsolidcompoundsinpuresolventsandmixedsolventsplaysakeyroleinallcrystallizationprocesses[11].Moreover,solubilitydatainpuresolventsandmixedsolventscanbeconsideredashelpfulintheextractionandpuri cationpro-cessesoforganiccompoundsfromdifferentmatrices.

Insomerecentworks[12,13],solubilitiesofgallicacidinsev-eralpuresolventshavebeenmeasuredasafunctionoftempera-ture.However,inourknowledgenoexperimentalortheoreticalstudyconcerningthesolubilityofgallicacidinbinarysolventshasbeenreportedintheliterature.Asacontinuationofourearlierstudiesconcerningthephenoliccompoundssolubility[14–17],wereporthereontheeffectsofbinarysolventscompositionandtem-peratureonthesolubilityofgallicacid.Thesolubilitiesofgallicacidin(water+ethanol)mixedsolventswithethanolmolefrac-tionsof0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,and1.0,onaCorrespondingauthor.Tel.:+21698934601;fax:+21671746551.

E-mailaddresses:adel.anoubigh@ipest.rnu.tn,anoubigh@yahoo.fr(A.Noubigh).

0021-9614/$-seefrontmatterÓ2012ElsevierLtd.Allrightsreserved./10.1016/j.jct.2012.06.022

solute-freebasisweredeterminedatT=(293.15,298.15,303.15,308.15,313.15,and318.15)K.Obtaineddatawereusedtocalcu-lateappropriatedissolutionthermodynamicproperties.2.Materialsandmethods

Gallicacid(C7H6O5,MW=170.12,>98%pure)andethanolwerepurchasedfromSigma–Aldrich(Germany).Gallicacidwasusedwithoutpriortreatment,butstoredinadessicatorwithP2O5oncethebottlehasbeenopened.AbsoluteEthanolwasofanalyticalgrade(C2H6O,purity=99.8%,MW=46.07,d=0.79g/mL).Distilledwater(conductivityaround1.5lSÁcmÀ1)hasbeenused.

BinarysolventwerepreparedbymassusingaSartoriusCP225Danalyticalbalancewithanaccuracyof±0.01mg.Theuncertaintyinthemolefractionofmixedsolventswasestimatedtobewithin±0.0003.25gofbinarysolventswereintroducedintoadoublejacketedreactorthermostattedat(T±0.1)K(PolystatHuberCC2).Anexcessofthesolidgallicacidwasaddedtotheliquidphaseandthesolutionwascontinuouslystirredwithamagneticstirrer.Tochecktheequilibrium,asampleoftheliquidphasewastakenthrougha0.2lmporesyringe lterandtheconcentra-tionwasmeasuredbyUV/visiblespectrophotometry(BeckmanCoulterUV/visspectrophotometermodelDU-520)at300nm.Thewavelengthof300nmwasdeterminedtobethemostadequateforgallicacidquanti cationbecauseofthemaximumabsorbanceatthiswavelength.Whentheconcentrationofgallicacidintheli-quidphaseremainedconstant,itwasassumedthatthesystemwasatequilibrium.Severalequilibriumtimeshavebeentested(from1

76A.Noubighetal./J.Chem.Thermodynamics55(2012)75–78

to6h),anditappearsthat3hisalwayssuf cienttoreachequilib-rium.Towindependentexperimentswererealisedtodeterminethegallicacidsolubility.Thereproducibilityofthedatawaswithin0.5%.

3.Resultsanddiscussion

Thesolubilityofgallicacidwasmeasuredinpurewater,etha-noland(water+ethanol)mixtures,atdifferenttemperaturesrang-ingfrom(293.15to318.15)K.Thiscomplementarystudypermitsustoextendoursolubilitydatabasisofgallicacid[14–17].

Tovalidatethemethodofsolubilitydetermination,thesolubil-ityofgallicacidinpuresolventswasdeterminedfrom(293.15to318.15)K.Asshownin gure1,paredtopurewater,thesolu-bilityofgallicacidinpureethanolisthehighestandismoredependentontemperature.Thissolubilitytemperaturedepen-dencewas ttedtotheempiricalequationproposedbyHeidmanetal.[18]:

lnx¼AþB

GA

T=K

þClnðT=KÞ;ð1Þ

wherexGAisthemolefractionsolubilityofgallicacidinpuresol-vents,Tistheabsolutetemperature(K),andA,B,andCareempir-icalparameters.

ThevaluesofempiricalparametersA,BandCaregivenintable1togetherwiththecorrespondingroot-mean-squaredeviations(rmsd’s)"calculatedaccording#totheformula:

1=rmsd¼1Xn

À2

nxcalGA

ÀxexpGA

Á2

;ð2Þ

i¼1wherenisthenumberofexperimentalpoints,andxcalexp

GAandxGArepresentthesolubilityofgallicacidcalculatedfromequation(1)andtheexperimentalsolubilityvalue,respectively.Calculatedandexperimentalsolubilitiesinpurewater,shownin gure1,demonstrateaverygoodagreement.

Experimentalsolubilitieswereusedtocalculatethemolefrac-tionsolubilityxGAindifferent(water+ethanol)mixturesbasedonthefollowingequation:

xGA¼0:001ÂmGAÂðxWÂMWþxEÂMEÞ;ð3Þ

wheremGA,xwandxErepresentthemalalityofthegallicacid,

themolefractionofwaterandethanol,respectively,andMGA,MEandMWarethemolecularweightsofthegallicacid,ethanolandwater,respectively.

TABLE1

Parametersofequation(2)correlatedfromexperimentalmolarfractionofsolubilityofgallicacidinpuresolvents.SolventA

B/KC105rmsdWaterÀ93.9147À2.645315.32710.0125Ethanol

À16.0367

À0.6321

2.3083

0.0010

TABLE2

Experimental(xexpGA)solubilityofgallicacidindifferent(ethanol+water)mixedsolventsatvarioustemperaturesandatmosphericpressure.T/K

103.xexpGAxE=0.100

xE=0.200xE=0.300xE=0.400293.15

2.486±0.0105.893±0.01512.977±0.02122.477±0.027298.153.177±0.0097.276±0.01416.018±0.02625.581±0.029303.154.180±0.0129.487±0.01618.804±0.02430.622±0.045308.155.479±0.01612.002±0.01922.193±0.02635.142±0.048313.157.079±0.01414.719±0.02326.186±0.02940.060±0.029318.15

8.995±0.01319.294±0.02531.712±0.03146.515±0.058

xE=0.500

xE=0.600xE=0.700xE=0.800293.1530.433±0.05230.836±0.03629.001±0.03428.006±0.033298.1535.418±0.04336.750±0.04333.788±0.04432.158±0.041303.1539.815±0.03840.733±0.02937.321±0.04836.371±0.058308.1545.917±0.04247.990±0.05145.258±0.04641.938±0.033313.1552.140±0.05455.602±0.06151.986±0.05648.854±0.053318.1559.261±0.05763.033±0.06259.282±0.065

55.324±0.061

xE=0.900

xE=0.950293.1531.750±0.04137.972±0.031298.1536.855±0.02943.797±0.034303.1544.006±0.04555.489±0.075308.1550.470±0.06163.203±0.071313.1558.611±0.05774.612±0.064318.1567.394±0.074

87.011±0.077

Gallicacidsolubilitiesinabinary(water+ethanol)mixturearelistedintable2andalsoshownin gure2.We ndmaximaandminimainrangesofethanolmolefractionsrespectively.

A fth-orderpolynomialequationwasproposedtocorrelatethesolubilitydataofgallicacidinthebinarymixedsolventsasafunc-tionofxEasfollows:

lnxGA¼B0þB1xEþB2x2345

EþB3xEþB4xEþB5xE;

ð4

Þ

A.Noubighetal./J.Chem.Thermodynamics55(2012)75–78

TABLE3

Parametersofequation(4)correlatedfromexperimentalmolarfractionofsolubilityofgallicacidindifferent(ethanol+water)mixedsolvents.77

T/KB0

B1B2

293.15À6.62323.607835.3446298.15À6.40324.393128.5852303.15À6.17015.476020.5549308.15À5.87665.884913.1289313.15À5.62716.35507.3615318.15

À5.4229

7.4505

À0.3023

TABLE4

Parametersofequation(5).Parametere

fR2B0À21.0820.04930.9980B1À39.0240.14580.9800B2452.92À1.42480.9985B3À1162.33.63430.9979B41200.4À3.80470.9961B5

À445.59

1.4403

0.9944

wherexGAisthemolefractionsolubilityofgallicacidinbinarysolvents,xEistheethanolmolefractioninbinarysolvents,andB0,B1,B2,B3,B4,andB5aretheempiricalparameters.Calculatedsolu-bilityvaluesofgallicacidfromequation(4)arealsogivenin gure2.

ThevaluesofthesixparametersB0,B1,B2,B3,B4,andB5togetherwiththeroot-mean-squaredeviation(rmsd)arelistedinthetable3.Furthermore,thevaluesB0,B1,B2,B3,B4,andB5werecorrelatedasafunctionoftemperaturewiththefollowinglinearequation:

y¼eþfT;ð5Þ

whereyreferstothevaluesofB0,B1,B2,B3,B4,andB5;Tistheabsolutetemperature,andeandfaretheparameters.Theresultsarepresentedintable4withR2.Finally,aglobalexpressionforthesolubilityofgallicacidinthe(ethanol+water)mixturewasobtainedasfollows:

lnxGA¼À21:082À39:024xEþ

452:92x2EÀ

1162:3x3Eþ1200:4x4E

À

445:59x5E

þ0:0493Tþ0:1458TxEÀ

1:4248Tx2E

þ

3:6343Tx3E

À

3:8047Tx4E

þ

1:4403Tx5E:

ð6Þ

Calculatedsolubilitiesofgallicacidin(water+ethanol)mixed

solventsshowgoodagreementwithexperimentalvalues.After-wards,theseexperimentalsolubilityvaluesandthecorrelationequationcanbeusedasessentialdataandmodelsinpracticalpuri cationprocessofgallicacid.

Fromtables1and2and gures1and2,itcanbenoticedthatequations(1)and(5)canbeusedtocorrelatetheexperimentalre-sultsofthesolubilityofgallicacidinpurewater,ethanolandbin-ary(water+ethanol)mixturesatdifferenttemperatures.Basedonobtainedresults,wecanreachthefollowingconclusions:(1)thesolubilityofgallicacidin(water+ethanol)mixturesincreasesslightlywithtemperatureincreasing;(2)atthesametemperature,thesolubilityofgallicacidinpureethanolismuchlargerthaninanyother(water+ethanol)mixedsolvents;(3)theexperimentaldataindicatethatthesolubilitiesincreasefromx=0.0to0.5andslowlydecreaseuntilx=0.8.Fromx=0.8to1.0,thesolubilitycurveofgallicacidrisessharply.TheMaximainthesolubilitycurvescanbeexplainedbythecompetitiveeffectsofhydrophobicandhydrophilichydrationofethanolmolecules.The rsteffectprevailsintherangeofbinarysolventscompositionsuptothepointcorrespondingtothemaximuminthesolubility.Minimaaredueprobablytothemaximumstabilizationofthewaterstruc-turebythenonelectrolyte.

B3

B4

B5

105rmsdÀ96.862785.0099À23.47770.0030À79.723967.0460À16.73530.0083À61.409448.4309À9.39140.0030À39.353723.69730.15370.0068À24.55788.80215.47430.0089À7.1739

À8.2604

11.6963

0.0233

TABLE5

Thermodynamicpropertiesofthedissolutionofgallicacidindifferent(etha-nol+Water)mixedsolventsatvarioustemperatures:DsolG°(kJ.molÀ1).DsolH°(kJ.molÀ1).andDsolS°(J.molÀ1KÀ1).+T/K

xE=0.100

xE=0.200

DsolH°

DsolG°

DsolS°

DsolH°

DsolG°

DsolS°

293.1537.82314.61979.15232.11412.49566.924298.1539.12514.21383.55433.21912.15170.661303.1540.44713.78487.95534.34211.78974.398308.1541.79313.33392.35635.48511.40778.135313.1543.16012.86096.75736.64611.00781.872318.1544.54912.366101.15937.82510.58985.609

xE=0.300

xE=0.400

DsolH°

DsolG°DsolS°DsolH°DsolG°DsolS°

293.1525.46510.55450.86521.1609.19040.832298.1526.34110.29253.82821.8888.98043.294303.1527.23210.01556.79222.6288.75745.757308.1528.1379.72459.75523.3818.52248.219313.1529.0589.41862.71824.1468.27550.681318.1529.9939.09765.68124.9238.01653.144

xE=0.500

xE=0.600

DsolH°

DsolG°DsolS°DsolH°DsolG°DsolS°

293.1519.6648.50838.05519.8548.38639.120298.1520.3418.31240.34320.5388.18541.431303.1521.0298.10542.63121.2327.97243.741308.1521.7287.88644.92021.9387.74846.052313.1522.4397.65647.20822.6567.51248.362318.15

23.1617.41449.49623.3857.26450.672

xE=0.700

xE=0.800

DsolH°

DsolG°DsolS°DsolH°DsolG°DsolS°

293.15

20.2598.38640.50120.2928.62639.797298.1520.9568.18542.83520.9918.42142.158303.1521.6657.97245.16921.7018.20444.520308.1522.3867.74847.50322.4227.97646.881313.1523.1187.51249.83723.1567.73649.242318.15

23.8627.26452.17123.9017.48451.604

xE=0.900

xE=0.95

DsolH°

DsolG°DsolS°DsolH°DsolG°DsolS°

293.1521.4898.23945.19923.8888.23953.382298.1522.2298.00747.70024.7108.00756.022303.1522.9807.76250.20125.5467.76258.662308.1523.7457.50552.70126.3957.50561.303313.1524.5227.23555.20227.2597.23563.943318.1525.3116.95357.70228.1366.95366.583

Fromanenergeticaspect,thedissolutionofagallicacidintoaliquidisrelatedtosomethermodynamicchanges,speci callytheGibbsenergy(DsolG°),molarenthalpy(DsolHo)andmolarentropy(DsolS°)ofdissolution.Thesethermodynamic’sparameterscanbecalculatedusingtheexperimentalsolubilitydata ttedtoequation(4).Theseparametersre ectthemodi cationofthesolutionprop-ertiesduetothepresenceofthesoluteatitsin nitedilutionstateatagiventemperature[19–21].Assumingthattheactivitycoef -cientofwaterinaqueousphaseisequalto1therefore,withthehelpoftheGibbs–Helmholtzequation,thefollowingequationcanbeobtained[22]:

78A.Noubighetal./J.Chem.Thermodynamics55(2012)75–78

Do

2

dlnx

solH¼RTdT;

ð7Þ

P

wherethemolarenthalpyofdissolutionDsolHoisthedifferencebe-tweenthepartialmolarenthalpyofgallicacidinsolution,HÃ;liquid

GA

andthemolarenthalpyofgallicacidinthesolidstate,Ho;solid

GA,attemperatureT:

D¼Ho;solidsolHo;liquid

GAÀHÃGA

:ð8Þ

Theremainingparameters,DsolG°andDsolS°,canbecalculatedasfollows[20,23,24]:

DosolG¼ÀRTlnðxÞP;

ð9ÞDo

dðlnxÞ

solS¼RdðlnTÞ:

ð10Þ

P

Thevaluesofthethermodynamicfunctions,DsolH°,DsolG°,andDsolS°,ofthegallicaciddissolutionindifferentconcentrationsofethanol–watersolutionswerecalculatedusingequations(6),(8),and(9),respectively,andarereportedintable5.

Theenthalpyofdissolutionversustemperature,derivedfromexperimentalsolubilitydataforeachsolution,isdepictedin gure3.Estimatedenthalpiesofdissolutionfromsolubilitymeasure-mentsofgallicacidineachmixedsolventatdifferenttempera-turesarecomparable,withthemajordeviationcorrespondingtothelessconcentratedethanolsolution.Forallthestudiedsolu-tions,itwasfoundthattheenthalpyofdissolutionisalinearfunc-tionoftemperature,thusgivingaconstantheatcapacityofsolution.Whenthesolubilityisatamaximum,theenthalpyofdis-solutionspentfortheformationofsolventstructurecavitiesisaminimum.

Thermodynamic’sparametersvaluesprovethatthewholepro-cessisendergonic(DsolG°>0),thereforenon-spontaneous.Even

thoughDsolS°ispositive,theDsolH°issuf cientlypositivetopro-videpositiveDsolG°values.Subsequently,thedissolutionofgallicacidisespeciallyofenthalpicorigin.

4.Conclusions

Inthisworknewdatawereprovidedforthesolubilityofgallicacidin(water+ethanol)mixedsolventsattemperaturerangefrom(293.15to318.15)K).Thevaluesofthesolubilityofgallicacidinbinarymixedsolventsincreasewithrisingtemperatures.Twoequationswereusedtocorrelatetheexperimentalvaluesforthegallicacidsolubility.Oneisanonlinearequationforthepuresolventswhiletheotherisa fthpolynomialequationforthemixedsolvents.Calculatedsolubilityvaluesshowgoodagree-mentwithexperimentalvalues.Datapresentedinthisworkareessentialfortheindustrialdevelopmentofgallicacidextractionandpuri cationprocesses.

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JCT

12-114

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