Ind ian Journal of Pure & Applied Physics Vol. 4 1, April 2003, pp. 275-279

Acoustic and solvation behaviour of N-iodoacetamide in water + DMSO and water + CH3CN

J Ishwara Bhat & N S Shree Yaraprasad

Department of Chemistry, Mangalore Un ivers ity, Mangalagangothri 574 199

E-mail: bhatij@yahoo.com

Received 16 September 2002; revised I February 2003 ; accepted I 0 February 2003

The ultrasonic velocity and density at different concentrations of N-iodoacetamide in water, DM SO. CH3CN and di fferent comrositions ( V/V) of H20 + DMSO and H20 + CH3CN have been measured at 303 K. The data obtained arc used to evaluate adiabatic compressibi lity, apparent molar compressibi lity, intermolecular free length , spcci lic acoust ic impedance. re lative association and solvati on number. These results was used to calcu late limiting molar compressibility <j>"k· Gucker' s relation has been veri fi ed. Formation of complex at 50% DMSO and 20% CH3CN has been identified. These data are utili zed in the qu alitati ve study or ion-ion and ion-so lvent interactions.

[Keywords: Acoustics, Solvation behaviour, Ult rasonic velocity, N-iodoacetamidc]

1 Introduction

Ion-solvent or solvent-so lvent interaction in volved in an e lec trolyte system can be studied by vari ous methods. The principle of acoustics is one among them 1~ . Studies on acou stic parameters have become an e merging fi e ld in recent years3

.4 . T o understand so luti on chemistry , it is essential to know the so lvati on be hav iour of an ionic system45

.

Acoustic parameters are quite sensitive to changes in ionic concentrations and are useful in e lucidating the so lute-solvent interaction 1

·7

. N-iodoacetamide (C2HJNO, NIA) is a white crystalline compound, solubl e in water and some non-aqueous so lvents . It find s app lication in the field of medicine for the treatment of cancerx. Lite rature does not show any report on the ultrasonic behaviour of lA. Hence, in thi s paper, the study of ultrasonic veloc ity of NIA in water + DMSO and water + CH,CN systems at 303 K has been reported .

2 Experimental Details

Commercially ava ilable AR grade N-iodoacetamide (NIA) (Acros Organics, USA) was used as such, and its stock solutions in water (H20 ), dimethylsulfox ide (OMSO), acetonitrile (CH3CN) and various compositions (V/V) of H20+ DMSO as well as H20+ CH,CN were prepared . Triply di still ed water is used throughout the experiment. Solvents were purified as proposed in lite rature9

.

The ultrasonic ve locity data were obtained from ultrasonic interferometer (M-8 1, Mittal Enterpri ses, Ne w Delhi ) at 2 MHz measuring frequency with a

tolerance ±0.3%. The accuracy of the instrument was checked~ . Experiments were initiated by fillin g the cell with the solutions of known concentratio n of NIA at constant temperature. The density was determined pyknometricall y, at required temperature ±0.0 I oc. The experiments were repeated for consistency and the average value was considered.

3 Results and Discussion

Wide-ranging thermodynamic/acoustic para­

meters such as, adiabatic compress ibility ( ~ ""), apparent mol ar compress ibi I ity ( <j>k), inte rmolecu tar free length (L 1), specific acoustic impedance (Z), relative association (R1J and so lvation number (5,) were investigated for s ix diffe rent concentrations of NIA in H20 , DMSO, CH,CN and the ir mixtures at 303K using the following re lations 111

:

Lr = k-[fi:; ... ( I )

U='AF ... (2)

f3ad . . . (3)

276 INDIAN J PURE & APPL PHYS, VOL 41, APR IL 2003

_d[Vo ]X RA---d0 U

= 1 000 (d f3 - d f3 () )+ f3 .M_ </J k f d 0 nd I , 1 ad d1

t 1 ·o

s = s_[, -[3 (/(, l II !1 /3 ()

2 ""

... (4)

... (5)

... (6)

.. . (7)

... (8)

where A. is the wave length, F the freq uency (2 MHz), d 1 and do are the measured densities of solution and solvent, U and U0 are the experimental ultrasonic velocities, respect ively, of the solution and solvent. M is the molecular weight of the so lute,

~0ad and ~ad are the adiabatic compressibilities of the solvent and soluti on, k is Jacobson constant , C is concentration in mol dm·', n 1 and H 2 a re the number of moles of solvent and so lute respective ly.

U ltrasoni c ve lociti es of NIA so luti on in different % composit ions of DMSO or CH,CN with water (V/V) have been determined using Eq. (2) at 303K

±0.0 I °C and are presented in Tab le I . T he variat ion of ultrasonic ve locity in a soluti on depends on the inte rmolecul ar free length L1. Eyring & Kincaid

Table I - Experimental values of density (d). intermolecular free lengt h (Lr), ultrason ic velocity (U) and ad tahatic compressibilit y Cl3ad) at different concentrat ions ofN-iodoacetamide in water+ DMSO and water+ acetonitrile mi xtures at 303 K

Cone Mol/lit ()

0.05 0.1 0.2 0.3 0.4 0.5

0 0.05 0. 1 0.2 0.3 0.4 0.5

0 0.05 0. 1 0. 2 0.3 0.4 0.5

0 0.05 0.1 0.2 0.3 0.4 0.5

0

0.996 1.007 1.0 11 1.022 1.032 1.043 1.051

0.996 1.007 1.0 II 1.022 1.032 1.043 1.05 1

1510 15 10 1509 1505 1505 1503 1501

1510 1510 1509 1505 1505 1503 150 1

d ( 101 Kg m'3) L 1 (A0

)

20 50

1.024 1.066 1.034 1.081 1.040 1.086 1.049 1.095 1.060 1.105 1.072 1.115 1.082 I. 123

0.962 0.904 0.975 0.916 0.98 1 0.9 19 0.993 0.933 1.004 0.945 1.014 0.953 1.017 0.961

1604 1602 1597 1595 15~9

1586 1579

1548 1548 1544 1541 1535 1532 1523

U(ms-1)

1695 1711 1694 1683 1671 1666 1660

1447 1448 1447 1442 1437 1434 1426

80

1.09~

1.106 1.1 12 1.1 20 1.129 1.130 1.148

0.822 0.831 0.~39 0.85 1 0.866 0.875 0.883

1630 1609 1607 1600 1595 159 1 1579

1324 1324 1323 13 1X 13 15 1309 130(1

DMSO 100%

1.093 1. 103 1.107 1.117 1. 127 1.1 33 1.145 CH3CN 0.773 0.779 0.786 0.799 0.8 14 0.826 0.836

DMSO 1475 1473 1471 1467 1464 1462 1477 CH3CN 1262 1258 1257 1252 1249 1243 1 23~

0

0.4 174 0.4150 0.4146 0.4 133 0.4 11 4 0.4098 0.4087

0.4 174 0.4 150 0.4 146 0.4 133 0.4 11 4 0.4098 0.4087

4.403 4.354 4.344 4.3 17 4.278 4.245 4 .221

4.403 4.354 4.344 4.317 4.2n 4.245 4.22 1

20

0.3874 0.3862 0.3863 0.3849 0.3847 0.3831 0.3~29

0.4143 0.4115 0.4114 0.4098 0.4089 0.4078

50

0.3594 0.3536 0.3565 0.3571 0.3580 0.3576 0.3576

0.4573 0.4539 0.4533 0.4516 0.4501 0.4493

0.4094 0.449l) (3,0( 10-111 m"N-1

)

3.794 3.769 3.772 3.746 3.739 3.709 3.705

4.337 4.280 4.277 4.244 4.227 4.203 4.237

3.266 3.229 3.2 18 3.223 3.240 3.232 3.233

5.2X5 5.206 5.195 5.156 5.122 5.103 5. 118

80

0.3709 0.37 17 0.3713 0.3714 0.37 13 0.37 1') 0.371 6

0.5238 0.52 12 0.5191 0.5171 0.5141 0.5137 0.51 26

3.478 3.49l 3.485 3.48(> 3.484 3.497 3.489

6.935 6.865 6.8ll 6.759 6.67lJ 6.671 6.640

I OOC/r

0.407H 0.40(>5 0.4064 0.405l\ 0.4046 0.4042 0 .3979

0.56l\5 0.5667 0.5646 0.5620 0.557l) 0.5566 0.555l)

4.203 4.177 4 . 174 4. 162 4.13~

4.1 29 4.002

l\.170 l\.l 16 g 05X 7.9X4 U:6lJ 7K\I 7.X II

BHAT & SHREE V ARAPRASAD: ACOUSTIC BEHA YHIOUR OF NIA 277

Table 2- Calculated values of acoustic impedance (Z ), rel ative association (RA), apparent molar adiabatic compressibi lity (<Ilk)

and apparent molar volume (cjlv) at different concentrations ofNIA in water+ DMSO and water+ acetonitrile at 303 K

Z I 05 (Kg m2 s' 1) DMSO RA

0 20 50 80 100% 0 20 50 80 100%

0 15 .04 16.43 18.07 17.77 16.1 3 0.05 15.21 16.56 18.49 17.79 16.25 1.0117 1.010 I 1.011 3 1.0086 1.0093 0. 1 15.26 16.60 18.39 17.86 16.28 1.0158 1.0169 1.0188 1.0146 1.0 137 0.2 15.39 16.73 18.44 17.92 16.38 1.0276 1.0259 1.0302 1.0236 1.0241 0.3 15 .53 16.83 18.47 18.00 16.50 1.037 1 1.038 1 1.0415 1.0329 1.0337 0.4 15.68 17.00 18.57 17.97 16.57 1.0494 1.0509 1.0524 1.0343 1.0403 0.5 15.78 17.09 18.63 18. 14 16.91 1.058 1 1.0615 1.0606 1.0541 1.0469

CH3CN 0 15.04 14.89 13.08 10.89 9.76 0.05 15.21 15.09 13.26 10.99 9.79 0. 1 15.26 15. 14 13.30 11 .09 9.88 0.2 15.39 15.29 13.45 11 .22 10.00 0.3 15.53 15.41 13.58 11 .39 10.17 0.4 15.68 15.53 13.67 11 .45 10.27 0.5 15.78 15.49 13.70 11.53 10.34

<!>k(l0' 12 m2 mol' 1)

DMSO 0.05 69.98 6 1.59 40.24 62 .28 64.33 0. 1 66.88 59.35 44.32 59.51 62.35 0.2 58.30 52.84 42.40 56.98 56.91 0.3 49.23 47 .74 41.30 53 .83 50.58 0.4 40.02 39.47 37.27 54.93 47 .22 0.5 33.53 35.47 35.03 48 .19 29.66

proposed the increase in ultrasonic ve locity with the decrease of free length L1 and vice versa4

·10

.

Inte rmolecular free length is a predominant factor, as it determines the sound velocity in a condensed state or in fluid state. Presence of an ion alters the inte rmo lecul ar free length . Therefore, ultrasonic veloci ty of a so luti on wi ll be different fro m that of the so l vent.

3.1 Density (d)

Density increases with increase in concentration due to the presence of ions or particles due to the increased electrostri ction in that solution . This e lectrostriction decreases the volume and hence increases in the dens ity. As the number of particles increases, the e lectrostric tion and density increases. Table I shows the inc rease in dens ity with the increase in concentrati on at a given composition . The density va lues are fo und to increase with the inc rease in % composition of DMSO, whereas they decrease for an increased amount of CH1CN. DMSO is bu lky and brings about more coord inat ion with water, and hence brings about the inc rease in density. But in CH3CN, the density decreased for the increased amount of water due to its lower density ,

1.0117 1.0138 1.0123 1.0 I 02 1.0087 1.0 158 1.0207 1.0165 1.0208 1.0181 1.0276 1.0340 1.0327 1.0371 1.0369 1.037 1 1.0470 1.0472 1.0562 1.0568 1.0494 1.0580 1.0569 1.0679 1.0737 1.0581 1.0630 1.0677 1.0794 1.0881

CH3CN 69.98 69.24 89. 19 125.9 1 184.65 66.88 65.80 85.20 11 8.53 164.9 1 58.30 55.62 70.49 97.23 133.42 49 .23 48 .0 1 58.83 70.21 95 . 17 40.02 40.22 50.08 60.24 73 .49 33 .53 42.80 46.71 47 .35 57.48

bulkiness and less coordination with wate r. It may be proposed that in the presence of DMSO, solvent­solvent and ion-solvent inte ract ions are more compared to CH,CN in water.

3.2 Intermolecular free length (L r)

Increase in concentrat ion leads to decrease in gap between two spec ies and whic h is referred by intermo lecul ar free length (L1), i.e. w ith the increase in concentration, inte rmolecular free length (L1) has to decrease. Thi s ideal trend is c learly observed in both the cases under study . It may be stated that , density and intermolecular free length are in versely re lated . As concentrati on decreases , the density decreases, whereas L1 increases . This is c lear from Table I . L1 decreased with inc rease in % composi ti on of DMSO till 50% of it and inc reased in the case of CH3CN.

3.3 Ultrasonic velocity ( U)

Ultrasonic ve loc ity U ts re lated to intermolecular free length . As the free length decreases due to the increase in concentrat ion, the ultrasonic velocity has to increase and vice ve rsa . The experimental result s of the au thors support the

27S INDIAN J PURE & APPL PHYS , VOL 4 1, APRIL 2003

above statement in both the cases. At a g iven compos iti on, the ultrasonic ve loc ity decreases with inc rease in concentrati on. For a g iven concentrati on U va lue inc reases up to 50% DMSO and 20% CH:,CN and decreases the reafte r. Thi s is true for a ll the concentrati ons. The bulkiness of DMSO mo lecules and increased ion-solvent in teracti on hinders the free fl ow of sound waves in DMSO rich region. In the case of CH ,CN, probab ly the decrease in ve loc ity is due to the inc reased L, and ion-so lvent in terac ti on . The max imum in ve loc ity indi cates the formati on of a complex at that compos ition .

Tnhlc 3-Computed va lues of limiting apparent molar comprcssihil ity (1)>11~: m~ mol-1

) and its slopes~ for NIA in water + DMSO and water+ C H,CN

water + DMSO water+ CH3C

o/r $11k X I 0- 1 ~ - s~ x Hr 12

1)>0.x l0-12 -s. x Hr 12

0 93 85.19 93 85. 19 20 80 64.29 88 75.00 50 54 26.43 112 97.67 xo 69 30.00 178 184.50 100 ~n 43.64 230 265.96

3.4 Adiabatic compressibility (~ "")

When an ion is added to a so lvent it a ttracts certa in solvent mo lecules towards itse lf by wrenching the mo lecule from bul k of the so lvent due to the fo rces of e lectros tri cti on. Because o f thi s, the ava i I able solvent mo lecule fo r the nex t incoming ion gets dec reased . Thi s process is ca lled the compress ion. Every so lvent is hav ing a li mit for compress ion ca ll ed the limiting compress ib ility va lue . The compress ibility of a so lvent is higher than that of a so luti on and it decreases with inc rease in concent rati on. It is an ideal trend . In the present case, the compress ibility decreases with inc rease in concentrati on at a given compos ition of DMSOI CH ,CN. The adiabati c compress ibility decreased from 0 to 50% DMSO and 0 to 20% CH,CN and late r it inc reased till 100% of co-so lvent. That means, ion-so lvent inte raction inc reases till 50% DMSO and 20% C H,CN and , late r decreases for a given concentration. Adiabati c compress ibility is

calculated using the ex press ion I I U 2d 1 • The

produc t o f U2d1 inc reased t ill 50% and decreased

la te r. T herefore, I I U 2 d 1 decreases ti II 50% and

increases afterwards . So, at 50%, one can observe

minimu m ~ ad· But, in the case o f CH,CN, the

product of Vld 1 decreased continuous ly from 0-100% CH1CN. Since the ultrasoni c 've locity is high

at 20%, one can observe minimu m ~ ad at 20% CH3CN.

3.5 Acoustic impedance (Z)

Thi s is found to be almos t rec iprocal of ~ ad · The calcul ated va lues of Z are shown in Tabl e 2 . As can

be seen from Tables I and 2, ~ atl dec reases w ith the inc rease in concentrati on, wher as, acousti c impedance inc reases for a g iven concentrati on. Fo r a

g iven concentrati on, ~ ad dec reases till 50% DMSO and Z inc reases. So, the 50% compos iti on is the compos iti on spec ific , where the acous ti c parameter becomes e ither max imum or minimum. Probabl y thi s is the stage where complex formati on is tak ing place in the syste m due to the preferen tial so lvat ion of the spec ies by DMSO and hence inc reased ion­solvent interacti on. ln the case of C H,CN, fo r a g iven concentrati on a decreas ing trend in the va lue of acousti c impedance is obtained . The increase in Z with the concentrati on can be ex pl a ined on the bas is of lyophobic inte racti on between so lute and so lvent molecules3

·4

, which increases the intermo lecul ar di stance, making re lati ve ly w ider ga between the molecules.

3.6 Relative association (R")

The re lati ve assoc iati on R", is influenced e ithe r by breaking up of the so lvent mo lecul es on additi on of e lect ro lyte or by the so lvati on of ions that are simultaneous ly present . The former results in decrease and latter in inc rease o f R". The cal cul ated R" va lues for NlA so luti on in H20 , DMSO, C H,C and diffe rent compos iti ons (V/V) of H20 + DMSOI CH3C N are shown in Tabl e 2.

T he RA inc reases with inc rease in concent ratio n due to decrease in L, and increase i>l e lectros tati c attracti on, whic h is c lear from the va lues of R" in Table 2. R" slowly inc reased till 50% DMSO with a late r decrease. Whereas in the case o f H~O + CH,CN, it has decreased continuously for a g iven concentrati on.

3.7 Apparent molar compressibility (<j>k)

The apparent mola r compress ibil ity <j>k> was calcul ated fro m ultrasonic ve loc ity and dens ity, using Eq . (6). Te rms on the ri ght hand side of Eq .

(6) are constants except ~ad and d. T hese te rms

depend on concentrati on. Hence, <!>. is re lated to

BHAT & SHREE VARAPRASAD: ACOUSTIC BEHAVHIOUR OF NIA 279

concentration . As concentration increases, <j>, has to decrease. Therefore, at zero concentration of the

solute, <j>, is supposed to reach its limiting value <j>11,.

Hence, Gucker' s re lati on, viz, ¢ k = ¢ :' + S k .JC is

applicable34 .+ Using thi s, the limiting apparent molar compress ibility <j>11

, and the experimental slope

S, are determined from the plot of <j>, versus fC . The values of <j>11

, and S, are presented in Table 3. S, represents the measure of ion-ion and solute-solvent interac tion 11

•12

•

3.8 Solvation number (S .. )

The solvation numberS," is calculated using Eq . (7) (Ref. 3) and the values obtained in H20 , DMSO and CH,CN. Solvation number is found to decrease with increase in concentration in all the three cases of solvents. It clearly indicates the increase in ma<rnitude of ion-ion interact ion with concentrati on. b

Solvation number is around one or nearing one (values not shown). It means that, there is a solvent molecule in between two ions. So, it is the case of solvent-shared ion-pair or comp lex. It is a lso observed that, S, is s li ghtly higher in water than in other solvents . Pos itive so lvation number values indicate the structure promoter nature of the solvent.

3.9 Apparent molar volume (<j>.)

The apparent molar vo lume <l>v is the practically available molar volume of the solute, i.e., molar vo lume of the so lute densi ty per unit concentration . Thi s was calculated using the Eq. (8). All terms are constant for a given system except concentration and Jensity . Concentrat ion and dens ity are inter­related. That has made Masson to propose a new

equation, viz, </J,, = </J,~ + S,. fC (Refs 5,6). By

plotting <l>v versus fC the limiting apparent molar

vo lume <J>11

v and the experimental s lope S,, can be calculated . But, in the present case, the plot is found to be non-linear and hence, the authors cou ld not get

the values of <j>11v and S, ..

Acknowledgement

The authors are thankful to Uni versity Grants Commission, New De lhi , for the financial assistance in the form of major research projec t to carry out thi s work.

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