Activity of Water in Aqueous Acetamide Solutions Within the Temperature Range 298.15-358.15 K

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A C T A U N.I V E R S I T A T I S L 0 D Z I E N S I S _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ FOLIA CH IM I C A 8 , 19BB_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

M a r i a n Woldan*

A C T I V I T Y OF WATER IN A Q U E O U S A C E T A M I D E S O L U T I O N S W I TH IN THE TE M P E R A T U R E RANGE 2 9 8 . 1 5 - 3 5 8 . 1 5 K

On the ba sis of our values of the r e l a t i v e pa rt ial molal en t h a l p y of wa ter in aq ue ous a c e t a m i d e solutions' a c t i v i t y , a^, and a c ti vit y co ef fic ie nt , fj, of w a te r and p r e s s u r e of wate r vapour over the aq ue ous a c e t a m i d e s o l u t i o n s and the os mo t i c p r e s s u r e of these s o l u t i o n s have been ca lc ula te d. From the an a l y s i s of ch an g e s of these fu nc t i o n s on the c o n c e n t r a t i o n of a c e t ami de in s o l u t i o n and t e m p e r a t u r e the c o n c l u s i o n that ac e t a m i d e has a small d i s o r d e r i n g effe ct on wa ter s t r u c t u r e has been drawn.

Fr om d e n s i m e t r i c [ l ] , v i s c o s i m e t r i c [2] and t h e r m o c h e m i c a l [3] i n v e s t i g a t i o n s it fo ll ows that the m o l e c u l e s of a c e t a m i d e have litt le d i s o r d e r i n g e f fe ct on wa ter structure. This e f fe ct incre ases wi th the rise of the c o n c e n t r a t i o n of a c e t a m i d e in the s o l u tion and d e c r e a s e s when the t e m p e r a t u r e increases. In the p r e s ent p a pe r we have e x a m i n e d the i n t e r a c t i o n s am ong w a t e r and a c e t a m i de m o l e c u l e s on the ba sis of the d e p e n d e n c e of a c t i v i t y c o e f f i cien t of wate r in aq ue o u s a c e t a m i d e s o l u t i o n s on the c o n c e n t r a tion of s o l u t i o n and te mperature. U t i l i z i n g the values of a c t i vity of wa ter in the aq ue ous a c e t a m i d e s o l u t i o n s the p r e s s u r e of w a te r vapo ur over the i n v e s t i g a t e d s o l u t i o n s and their o s m o tic p r e s s u r e in the c o n c e n t r a t i o n range of AcNHg 0-4 m o l e . k g - ^ of wa ter w i t h i n the t e m p e r a t u r e range 2 9 8 . 1 5 - 3 5 8 . 1 5 K have been c a l c u l a t e d .

#

R e s e a r c h and D e v e l o p m e n t C e nt re for S t a n d a r d R e f e r e n c e M a t e r i als W Z O R MAT - B r an ch in Ł ódź.

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Ex p e r i m e n t a l

The m e t h o d of p u r i f i c a t i o n of a c e t a m i d e and the p r o c e d u r e of the m e a s u r e m e n t s of e n t h a l p y of s o l u t i o n of a c e t a m i d e in w a te r have been d e s c r i b e d p r e v i o u s l y [3] .

It is kn own that the a c t i v i t y of so lv e n t at g i ve n t e m p e r a t u r e one can c a l c u l a t e from e q u a t i o n

a i ^298 15) is the ac ti vit y of s o l v e n t in the s o l u t i o n at 298.15 K; R is the gas constant;

T is the t e m p e r a t u r e in Kelvin;

Lj(y) is the d e p e n d e n c e of the r e l a t i v e p a r t ial mo lal e n t h a l p y of so lv e n t in the s o l u t i o n on the t e m p era tu re ; in case of aq ue o u s a c e t a m i d e s o l u t i o n s the valu es of Lj were taken from l i t e r a t u r e [3] and they have been d e s c r i b e d by equation:

_

2

L i (t ) = Aj + A 2 m + Aj m ( 2)

w h er e m is molal c o n c e n t r a t i o n of a c e t a m i d e in the solution.

The values of the c o e f f i c i e n t s A^, A 2 and Aj have been c a l c u l a ted by the least s q u a r e s m e th od u s in g Odra 1305 c o m p u t e r and they are g i ve n in Table 1. U s in g the valu es of c o e f f i c i e n t s Aj, A^ and A^ the valu es of in the c o n c e n t r a t i o n rang e 0. 2- 4 . 0 mo l e of A c N H 2 on kg of wate r for s e l e c t e d c o n c e n t r a t i o n s of a c e t a m i d e we re c a l culated. The valu es of of w a te r in a q u e o u s a c e t a m i d e s o l u t i o n s as a f u n c t i o n of t e m p e r a t u r e we re d e s c r i b e d by e q u a t i o n R e s u lts ln a 1(T ) 298 .15 ( 1) where 2 ₍₃₎

The valu es of the c o e f f i c i e n t s D^, 0 2 and c a l c u l a t e d by the least s q u a r e s m e t h o d u s in g Odra 1305 c o m p u t e r are g i ve n in T a bl e 2.

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S u b s t i t u t i n g e q u a t i o n 3 in e q u a t i o n 1 and u s in g the valu es of a c t i vity of water in aq ue ous a c e t a m i d e s o l u t i o n s at 298. 15 K from l i t e rature data [4] the valu es of a c ti vit y of water, aj, in a q u e ous T a b l e 1

C o e f f i c i e n t s A 1t A 2 and A 3 for e q u a t i o n 2 for aq ue ous a c e t ami de s o l u t i o n s T(K) _{A ,} A 2 A 3 298.15 -0 .0 623 38 0 . 6 8 032 2 0. 37 898 4 313.15 -0 .0 485 07 0 . 5 8 397 2 0. 33 838 4 323.15 -0 .0 492 66 0 . 5 4 874 6 0. 306544 333.15 -0 .031007 0.43 244 1 0. 29 299 0 343.15 -0 .0 287 54 0 . 3 7 864 7 0 .218645 T a b l e 2

9357 T a b l e 4 A c t i v i t y c o e f f i c i e n t of w a te r in a q u e o u s a c e t a m i d e s o l u t i o n w i th in the t e m p e r a t u r e ra nge 2 9 8 . 1 5 - 3 5 8 . 1 5 K m mol .kg"1 X1 298. 15 313.15 323.15 333. 15 343.15 348. 15 358.15 0 .2 0 9964 1 0002 1 .0002 1 0002 1 0002 1 0002 1 0002 1 .0002 0 .4 0 9929 1 0004 1.0004 1 0004 1 0004 1 0004 1 0003 1 .0003 0 .6 0 9893 1 0006 1 .0006 1 0005 1 0005 1 0005 1 0005 1 .0005 0 .8 0 9858 1 0007 1 .0006 1 0006 1 0006 1 0006 1 0006 1 .0005 1 .0 0 9823 1 0007 1 .0006 1 0006 1 0005 1 0005 1 0005 1.0005 1.2 0 9789 1 0009 1 .0008 1 0007 1 0007 1 0007 1 0007 1 .0006 1.4 0 9754 1 0012 1 .0011 1 0010 1 0010 1 0009 1 0009 1 .0009 1 .6 0 9720 1 0014 1 .0013 1 0012 1 0011 1 0010 1 0010 1 .0010 1 .8 0 9686 1 0016 1 .0014 1 0013 1 0012 1 0012 1 0012 1 .0011 2 .0 0 9652 1 0019 1.0017 1 0016 1 0015 1 0013 1 0 013 1 .0012 3 .0 0 9488 1 0032 1 .0027 1 0025 1 0023 1 0022 1 0021 1 .0020 4 .0 0 9328 1 0049 1 .0043 1 0039 1 0035 1 0033 1 0032 1 .0031

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a c e t a m i d e s o l u t i o n s for s e l e c t e d c o n c e n t r a t i o n s of AcNI^ at 298.15, 313.15, 323.15, 333.15, 343.15, 348.15 and 358. 15 K have been c a l culated. The re su lts are given in Table 3. In Ta ble 4 the values of a c ti vit y c o e f f i c i e n t of water, f j , in aq ue o u s a c e t a m i d e s o l u t i o n s c a l c u l a t e d from kn own re la tio n

a i *i -t J

wh ere x^ is the mo le f r a c tio n of w a te r in the s o l u t i o n are p r e sented. The a n a l ysi s of the e x p e r i m e n t a l e r ro rs and the a p p r o xi ma t i o n s us ing in the c a l c u l a t i o n s pe rm i t s to e s t i m a t e the er ror in ac ti vit y (a ct ivi ty c o e f f i c i e n t ) of w a te r as + 0 .001. The p r e s s u r e of w a te r vapo ur over a q u e ous a c e t a m i d e s o l u t i o n s was c a l c u l a t e d from the e q u a t i o n

Pl - p 0 .3l (5)

w h er e p Q is the p r e s s u r e of water vapo ur over pure water. In the c a l c u l a t i o n s f o l l o w i n g values of p Q w e re used: 31.672, 73.759, 123.337, 199.157, 311.574, 385.435 and 57 8. 086 hPa at 298.15, 313.15, 323.15, 333.15, 343.15, 348.15 and 358.15 K [5] r e s p e c t iv el y. For the pu rp o s e to ob se r v e the d e v i a t i o n of w a t e r - a c e t a m i d e s y s t e m from R a o u l t ’s law the valu es A p = Pj - P 0 -Xi were also ca lc ula te d. The resu lts of the c a l c u l a t i o n s of p^ and A p for aq ue o u s a c e t a m i d e s o l u t i o n s are p r e s e n t e d in Table 5. The valu es of os mo t i c p r e s s u r e of aque ous a c e t a m i d e s o l u t i o n s were c a l c u l a t e d from r e l a tio n

IT = - In a^ (6)

w h er e is the pa rt ial mola l volu me of water. With r e ga rd for the small d e p e n d e n c e of the pa rt ial molal v o lu me of. w a te r in a q u e ous a c e t a m i d e s o l u t i o n s on c o n c e n t r a t i o n in the c a l c u l a t i o n s the valu es Vj equal to mo lal volu me of w a te r at g i ve n t e m p e r a ture were taken. The o b t a i n e d valu es of o s m o t i c p r e s s u r e of aq ue ous a c e t a m i d e s o l u t i o n s are g i ve n in Ta ble 6 .

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T a b l e 5 The p r e s s u r e of wa ter vapo ur ov er the a q u e o u s a c e t a m i d e s o l u t i o n s

w i t h i n the t e m p e r a t u r e range 2 5 8 . 1 5 - 3 5 8 . 1 5 K [hPa]

m 298. 15 313.15 323 . 15 333. 15 m o l .k g '1 _Pi A p Pi A p Pi Ap Pi A p 0 .2 31 .56 0 o o 73 .51 0 .02 122.92 0 .03 19B .48 0 04 0 .4 31 .46 0 .01 73 .26 0 .02 122.51 0 .05 197. 81 0 07 0 .6 31 .35 0 02 73 .01 0 .04 122.08 0 .06 197. 13 0 10 0 .8 31 .24 0 02 72 .76 0 .05 121.66 0 .07 196 .45 0 12 1 .0 31 .13 0 02 72 .50 0 .05 121.23 0 .08 195. 74 0 11 1.2 31 .03 0 03 72 .26 0 06 120.83 0 .10 195. 09 0 14 1 .4 30 .93 0 04 72 .02 0 08 120 .43 0 .13 194 .45 0 19 1 .6 30 00 rr\ 0 04 71 .79 0 .10 120.03 0 .15 193. 80 0 22 1.8 30 .73 0 05 71 .55 0 11 119. 63 0 .17 193. 15 0 25 2 .0 30 .63 0 06 71 .31 0 12 119. 23 0 .19 192. 50 0 27 3 .0 30 .15 0 10 70 .18 0 20 117. 32 0 .30 189. 40 0 44 4 .0 29 .69 0 15 69 .10 0 30 115. 50 0 .45 186. 44 0 67 mol kg-1 343.15 A P 348.15 Pi A p 358.15 Pi A p 0.2 0.4 0.6 0 . 8 1 . 0 1.2 1.4 1 . 6 1 . 8 2 . 0 3.0 4.0 310.51 309.47 308.40 307.33 306.22 305.21 304.19 303.18 302.16 301.14 296.26 291.60 0.06 0.11 0.16 0.18 0 . 16 0.21 0.28 0.33 0.37 0.41 0.64 0.96 384.12 382.83 381.51 380.18 378.81 377.55 376.30 375.04 373.78 372.51 366.47 360.69 0.07 0.13 0 . 2 0 0.22 0 . 2 0 0.25 0.35 0.40 0.45 0.49 0.77 1.16 576.11 574.18 572.19 570.19 568.15 566.25 564.36 562.47 560.58 558.68 549.59 540.89 0.11 0 . 2 0 0.29 0.31 0.30 0.36 0.49 0.57 0.65 0.71 1 . 1 0 1.65

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T a b l e 6

The os mo t i c p r e s s u r e of aq ue o u s a c e t a m i d e s o l u t i o n w i th in the t e m p e r a t u r e range 2 9 8 . 1 5 - 3 5 0 . 1 5 K [kPa]

m mol k g -1 298.15 313.15 323.15 333.15 343.15 348.15 358.15 0.2 467 489 504 517 530 537 549 0.4 922 967 995 1 022 1 048 1 062 1 086 0.6 1 392 1 461 1 504 1 545 1 585 1 606 1 643 0.8 1 863 1 957 2 014 2 071 2 124 2 152 2 202 1.0 2 351 2 469 2 543 2 612 2 681 2 718 2 780 1.2 2 798 2 940 3 029 3 111 3 194 3 237 3 313 1.4 3 246 3 413 3 516 3 614 3 709 3 760 3 848 1.6 3 696 3 887 4 006 4 121 4 227 4 286 4 386 1.8 4 148 4 364 4 498 4 627 4 748 4 814 4 927 2.0 4 601 4 842 4 992 5 137 5 272 5 345 5 471 3.0 6 273 7 142 7 371 7 591 7 796 7 907 8 097 4.0 8 863 9 364 9 676 9 973 10 250 10 399 10 653 D i s c u s s j U m

As it is seen from Ta ble 3 the v a lu es of a c t i v i t y of water, a ^ in a q u e o u s a c e t a m i d e so lu t i o n s d e c r e a s e wi th the i n c r eas e of the c o n c e n t r a t i o n of a c e t a m i d e in so lu tion. The a c t i v i t y of wa te r in s o l u t i o n s c o n t a i n i n g less than 1 m o l e of a c e t a m i d e in 1 kg of wa ter does not d e pe nd on the t e m p e r a t u r e and it d e c r e a s e s a small as the t e m p e r a t u r e i n c r eas es for mo r e c o n c e n trat ed so lu tio ns . Mo re over, the a c t i v i t y of w a te r di ff e r s a litt le fr om the m o la r f r ac tio n of w a te r in the solution. These c h a n g e s are mo r e vi si b l e in case of the a c t i v i t y c o e f f i c i e n t of water, fj. For all i n v e s t i g a t e d s o l u t i o n s the v a lu es of a c t i vity c o e f f i c i e n t of wa ter are larg er than unity. From this it fo ll o w s that the m o l e c u l e s of w a te r in aq ue ous a c e t a m i d e s o l u tions are more free than they are in pure water. Hence, one co n c l u d e that a c e t a m i d e w e ak ly d i s o r d e r s w a te r structure. This d i s o r d e r i n g effe ct of a c e t a m i d e on the s t r u c t u r e of w a te r

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de-c r e a s e s a litt le w i th the i n c r e a s e of t e m p e ra tu re . It is k n ow n that the a c t i v i t y c o e f f i c i e n t can s e rv e as a m e a s u r e of d e v i a t i on of a g i ve n s o l u t i o n f r om the b e h a v i o u r of ideal so lu tion. As it is seen fr o m T a bl e 4 the aq ue o u s a c e t a m i d e s o l u t i o n s sh ow s m all p o s i t i v e d e v i a t i o n from ideal s o l u t i o n w h ic h d e c r e a s e s wi t h the i n cr eas e of t e m p e ra tu re . S i m i l a r c o n c l u s i o n it fo ll o w s from the a n a l y s i s of re su l t s in T a bl e 5. All i n v e s t i g a t e d a q u e ous a c e t a m i d e s o l u t i o n s sh ow p o s i t i v e d e v i a t i o n from the R a u o l t ’s law. It c o n f i r m s that a c e t a m i d e -has sm all d i s o r d e r i n g e f fe ct on w a te r s t r u c t u r e w h i c h d e c r e a s e s a l i tt le w i t h the i n c r e a s e of te m p e r a t u r e . Finally, it is i n t e r e s t i n g to c o m p a r e the a c t i v i t y c o e f f i c i e n t of w a te r in the s o l u t i o n s c o n t a i n i n g o t he r n o n e l e c t r o l y t e s w i th s i m i l a r n a tu re and d i m e n s i o n of m o l e c u l e s as ac et ami de . The n o n e l e c t r o l y t e c h os en for this p u r p o s e is urea. The v a lu es of a c t i v i t y c o e f f i c i e n t of w a t e r in a q u e o u s urea s o l u t i o n s w e re c a l c u l a t e d fr om L o g v i n i e n k o ’s t h e r m o c h e m i c a l data [6] and the o s m o t i c c o e f f i c i e n t s from l i t e r a t u r e data

[7, 8]. The r e s u l t s are g i ve n in Table 7. As it is s e en from Ta ble 7 the v a lu es of a c t i v i t y c o e f f i c i e n t of w a t e r in a q u e o u s a c e t a m i d e and ur e a s o l u t i o n s w i t h i n the e x p e r i m e n t a l erro r are identical. Thus, it can c o n c l u d e that the i n t e r a c t i o n s w a te r - a c e t a m i d e and w a t e r - urea are similar.

T a b l e 7 A c t i v i t y c o e f f i c i e n t s of w a te r in aq ue o u s n o n e l e c t r o l y t e s s o l u t i o n s at 298. 15 K m mo le k g - * Ac e t a m i d e Urea 0.5 1.0005 1.0000 1.0 1.0007 1.0007 1.5 1.0013 1.0013 2.0 1.0019 1.00 18 2.5 1.0025 1.0022 3.0 1.0032 1.0034 4.0 1.00 49 1.0045

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R e fe re n c e s

[1] W o l d a n M. , T a n i e w s k a-0 s i rt s k a S. , Acta Univ. L o d z ., F o l i a Chim ., J,, 85(1 902).

[2] T a n i e w s k a-0 s i r t s k a S., W o l d a n M., Acta Univ.

L o d z ., F o l i a C h i m . , _ L 103(1902), [3] W o l d a n M . , T a n i e w s k a-0 s i ń s k a S . , Acta U n iv . L o d z ., F o l i a Chim ., JL, 3 (1 98 2 ). [4] K a n g r o W . , G r o e n e v e l d A . , Z. Phys. Chem. N. F., 2 2 , 110 (1 96 2 ). [5] M i s h c h e n k o K. P . , R a v d e 1 A. A . , K r a t k i j spra- vochnik f i z ik o - k h im ic h e s k ik h v e l i c h i n , ed. " K h i m i y a " , Le n in g rad (1 97 2 ). [6] L o g v i n e n k o R . , D o c t o r a l T h e s is , U n iv . Lodz. (1 9 7 2 ). [7] S t 0 k e s R. H., Aust. J . Chem., 20, 2087 (1 9 6 7 ). [ 8 ] E l l e r t o n D . A . , D u n l o p P . J . , 3. Phys. Chem., 70 ( 6 ) , 1831 (1 96 6 ). M a r i a n W o ld an A K T Y W N O Ś Ć WODY W W O D N Y C H R O Z T W O R A C H A C E T A M I D U W Z A KR ESI E T E M P E R A T U R Y 298.15-358.15 K Na p o d s t a w i e w ł a s n y c h w a rt ośc i w z g l ę d n e j c z ą s t k o w e j m o l o w e j e n talpii wo dy w w o d n y c h r o z t w o r a c h a c e t a m i d u o b l i c z o n o a k t y w n o ś ć a, i w s p ó ł c z y n n i k ak t y w n o ś c i f Ł wody, p r ę ż n o ś ć pary w o dn ej nad wo dn ymi r o z t wor am i a c e t ami du oraz ich c i ś n i e n i e os mo tyc zn e. Z a n a l i z y z a l e ż ności tych funkcji od s t ęż eni a a c e t a m i d u i t e m p e r a t u r y w y s n u t o wnio sek, o n i e w i e l k i m n i s z c z ą c y m w p ł y w i e a c e t a m i d u na s t r u k t u r ę wody.