A C T A U N I V E R S I T A T I S L O D Z I E N S I S FOLIA CHIMICA 9, 1991
B a rtło m ie j Pałecz*
ENTHALPY OF Nal DISSOLUTION IN AQUEOUS
HYOROPHYLIC UREA DERIVATIVES SOLUTIONS AT 298.15 K**
E n th a lp ie s of d is s o lu tio n of Nal in aqueous so lu tio n s of thiourea and hydroxyurea have been measured at 298.15 K. The e n th a lp ic p a ir in te r a c tio n c o e f f ic ie n t s of urea d e riv a tiv e s molecule - Nal have been determined using standard e n th alp ies of Nal in water and aqueous s o lu tio n s of ureas.
INTRODUCTION
The stu d ies on the physico-chem ical p ro p e rtie s of water s o lu tio n s of urea d e r iv a tiv e s [ l , 2] and aqueous s o lu tio n s of e le c t r o ly te s and urea d e r iv a tiv e s [3, 4] have been c a rr ie d at our la b o ra tory for a long time.
EXPERIMENTAL
Thiourea ( " p u r is s " P.O.Ch. Poland) and hydroxyurea (P o lf a Po lan d ) were c r y s ta liz e d tw ice from ethanol and d rie d under reduced pressure at 333 K (th e m elting temperature were 454 K fo r th iourea and 413 K fo r hydroxyurea, w hile the l i t e r a t u r e data being 454 K fo r th iourea [5] and 413-414 K for hydroxyurea [6 ], Nal (Merck, BRO) was c r y s t a lliz e d from a I : 1 water-acetone m ixture and dried under reduced pressure at 333 K.
Department of P h y s ic a l Chem istry, In s t it u t e of Chemistry U n i v e r s it y of Łódź, Poland.
F in a n c ia l support of th is work from the CPBP 01.15 programme is k in d ly acknowledged.
The measurements were conducted in an is o p e rib o l ca lo rim e te r [7] accurate to 5 x 10~5 K. The ca lo rim e te r was placed in a water thermostat whose temperature s t a b i l i t y was 1 x 10~3 K.
RESULTS
En th a lp ies of Nal d is s o lu tio n in water and aqueous 0 .1 , 0.7, 1.0, 1.5 mol • kg"* H20 s o lu tio n s of thiourea (TU) and hydroxyurea (HU) in the range of e le c t r o ly t e concen tratio n s of 0.002 - 0.05 mol • kg’ 1 at 298.15 K (Tab. 1, 2 ).
T a b l e 1 E n th a lp ie s of s o lu tio n (AH3) of Nal in w ater-thiourea (TU)
mixtures at 298.15 K
(u n it s : m in mol k g "1, AHg in k J m ol"1)
0.1 mol TU/kg h20 0.5 mol TU/kg H20 0.7 mol TU/kg H20
ID ■ - a h 3 m “ AHs m - a h3 0 . 0 0 0 0 7 785 0 . 0 0 0 0 8 410 0 . 0 0 0 0 8 700 0.0034 7 705 0.0029 8 350 0.0026 8 650 0.0071 7 655 0.0085 8 295 0.0091 8 550 0.0149 7 575 0.0121 8 260 0.0351 8 485 0.0289 7 455 0.0225 8 175 0.0249 8 395 0.0349 7 365 0.0251 8 160 0.0389 8 310 0.0481 7 385 0.0485 8 025 0.0499 8 250 0.0501 7 365 0.0501 8 010 0.0558 8 235
1.0 mol TU/kg H20 1.5 mol TU/kg H20
m 1 > X U i m ■- AHs 0 . 0 0 0 0 9 120 0 . 0 0 0 0 9 790 0.0026 9 070 0.0033 9 725 0.0079 8 995 0.0063 9 680 0.0132 8 930 0.0113 9 630 0.0295 8 795 0.0298 9 470 0.0311 8 785 0.0351 9 425 0.0419 8 725 0.0432 9 390 0.0511 8 670 0.0508 9 355
On the b a sis of the s o lu tio n enthalpy values obtained, standard en th alp ies of s o lu tio n of e le c t r o ly t e in aqueous s o lu tio n s of t h io urea and hydroxyurea were determined g ra p h ic a lly (Tab. 1, 2 ). Such a procedure was n ece ssita te d by the u n a v a ila b ilit y of the tempera
ture d e riv a tiv e s of d i e l e c t r i c constant req u ired for e x tra p o la tio n by the C ris s and Cbbble method [8 ].
T a b l e 2 E n th a lp ies of s o lu tio n ( AHS > of Nal in water-hydroxyurea (HU)
m ixtures at 298.15 K
(u n it s : m in mol • kg l , AHS in k J • mol *)
0.1 mol HU/kg H2U 0.5 mol HU/kg H20 0.7 mol HU/kg H20
m - *HS m
. :
A h3 m - AHS 0.0000 7 760 0.0000 8 325 0.0000 8 580 0.0029 7 700 0.0031 8 270 0.0028 8 520 0.0069 7 635 0.0062 8 245 0.0072 8 450 0.0098 7 590 0.0092 8 200 0.0101 8 415 0.0189 7 510 0.0154 8 140 0.0195 8 320 0.0251 7 460 0.0321 8 025 0.0298 8 225 0.0401 7 370 0.0451 7 960 0.0352 8 190 0.049B 7 330 0.0539 7 935 0.0509 8 1001.0 mol HU/kg H20 1.5 mol HU/kg H20
m - AHs m - AHS 0.0000 8 975 0.0000 9 580 0.0037 8 910 0.0033 9 530 0.0070 8 870 0.0062 9 490 0.0100 8 845 0.0098 9 455 0,0175 8 775 0.0164 9 405 0.0299 8 680 0.0312 9 300 0.0432 8 620 0.0422 9 245 0.0510 8 580 0.0521 9 205 DISCUSSION
The p lo ts of enthalpy of d is s o lu tio n of Nal in the aqueous s o lu tio n s of ureas e x h ib it the in crease of exotherm ic e f f e c t of d is s o lu tio n along w ith the content of the organic component [ i ] . More evid en t increase of the exothermic e f f e c t of Nal d is s o lu tio n
in due to the in crease of the th io urea and hydroxyurea co n cen tra tio n (Tab. 1, 2 ).
Using the standard e n th a lp ie s of s o lu tio n s AH®(NaI) d eterm i ned in th is work the e n th a lp ic p a ir in te r a c tio n c o e ffic e n ts none le c t r o ly t e - e le c t r o ly t e (h N l) were c a lc u la te d [3] (Tab. 3 ). The hNE values fo r the s o lu tio n of urea and h y d ro p h ilic urea d e r i v a t i ves is n egative u n lik e those for a lk y lu re a s [a] .
T a b l e 3 E n th a lp ic p a ir in te r a c tio n c o e ff ic ie n t s fo r urea d e riv a tiv e s - averaged ion (Na+I " ) in water
so lu tio n s at 298.15 K N o n e le c tro lit ( N a V ) " hNE , 3 • kg • mol” U - Nal* 310 - 20 HU - Nal 370 - 20 TU - Nal 420 - 20 * Ref. [4 ].
As has alreddy been mentioned, in the case of the threecompo- nent systems with h y d ro p h ilic urea d e r iv a tiv e s , th iourea s o lu tio n s e x h ib it la rg e r negative values of the e n th a lp ic rio n e le c tro ly te - averaged ion in te ra c tio n c o e f f ic ie n t s than hydroxyurea so lu tio n s (Tab. 3 ). The sm aller n egative h^g values fo r aqueous hydroxyurea so lu tio n s with e le c tr o ly t e s are most probably due to the weakening of the hydroxyurea molecule - ion in te ra c tio n s re la te d to the com p e t it iv e process in which hydroxyurea molecules enter in to strong in te ra c tio n s with water.
REFERENCES [1] S. T a n i e w s k a-0 s i r i s k a , B. P a t e c z , Thermodynamics, 1_2, 775 (1980). [2] S. T a n i e w s k a-0 s i r i s k a , B. P a t e c z , Thermodynamics, JU , 11 (1982). [3] B. P a t e c z , S. T a n i e w s k a-0 s i rt s k a, chim ica Acta, 116. 349 (1987).
[4] B. P a t e c z, S. T a n i e w s k a-0 s i rt s k a, chim ica Acta, (1989) in press.
[5] K. B. 3 a c i m i r s k i , W. P. W a s i 1 i e w, l i t y Constants of Complex Compounds, Oxford 1960.
[6] I . K. L a r s e n , B. 3 e r s 1 e v, Acta Chem. Sca n d ., 2Q,
983 (1966). 3. Chem. 3. Chem. Thermo- Thermo- In s ta b
i-[7] 8. P a ł e c z, S. T a n i e w s k a-0 s i rt s k a, Thermo- chimica Acta, 79.» 299 (1984).
[8] C. M. C r i s s, J . W. C o b b l e , J . Am. Chem. S o c ., 82, 3223 (1961).
B a rtło m ie j Pałecz
ENTALPIE ROZPUSZCZANIA Nal W WOONYCH ROZTWORACH HYDROFIŁOWYCH POCHODNYCH MOCZNIKA W TEMPERATURZE 298,15 K
Zmierzono ca łk o w itą e n ta lp ię rozpuszczania Nal w z ak re sie s t ę żeń 0,002-0,05 m ol(N aI)kg (ro z p u sz cz a ln ik a) w wodzie 1 wodnych
roztworach zaw ierających 0,1, 0,7, 1,0 i 1,5 mol TU lub HU/kg H20. Wyznaczono entaipowe w spółczynniki oddziaływ ania cząsteczka pochod nej mocznika - uśredniony jon Nal w roztworze wodnym i porównano z analogicznymi wartościam i odnoszącymi s ię do mocznika i jego hydro fobowych pochodnych.
