Equivalent conductivities are reported for S-Methyl-, S-n- .
-Butyl, S-n-Amyl- and S-n-Heptylisothiouronium iodides in methanol
(D = 32.63) at 25 °c. The data were analyzed by the Fuoss-Onsager
equation for 1 : 1 associated electrolytes. The characteristic
constants: the equivalent conductance at infinite dilution A0 , the
closest approach distance a0 and the association constant KA are ·
derived

Amina M. Hafez

H. Sadek

N. H. El-Hammamy

English

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CROATICA CHEMICA ACTA CCACAA 49 (4) 713-716 (1977) YU ISSN 0011-1643 CCA-1043 541.137.27 Note Conductance of S-Alkylisothiouronium Iodides in Methanol at 25° C Amina M. Hafez, H. Sadek, and N. H. El-Hammamy Chemistry Department, Faculty of Science, Alexandri a University, Alexandria, A.R.E. Received January 31, 1977 Equivalent conductivities are reported for S-Methyl-, S-n- . -Butyl, S-n-Amyl- and S-n-Heptylisothiouronium iodides in metha-nol (D = 32.63) at 25 °c. The data were analyzed by the Fuoss-On-sager equation for 1 : 1 associated electrolytes. The characteristic constants: the equivalent conductance at infinite dilution A0 , the closest approach distance a0 and the association constant KA are · derived. INTRODUCTION In 1959 Fuoss and Onsager1 suggested the 3-parameter conductance equation for 1 : 1 associated electrolytes A = A0 - S (c y)'/2 + E (c y) log (c y) + J (c y) - KA (c y) A f 2 (1) where A is the equivalent conductance, c is the concentration in equiv./ 1 and y is the degree of dissociation and can be calculated fr~m the following relation y = A/(A0 -S v ~~ ) while, S and E are theoretically predicted constants depending on the dielectric constant D, the viscosity 'YJ and the absolute temperature T, and J is a term which includes the ion-ion and ion-dipole interactions and is given by the equation where, a1 and a2 are functions of the closest approach distance a0 in addition to 'YJ and D. In derivation of equation (1) Fuoss and Onsager took into account both the decrease in mobility due to long-range interionic forces and the decrease in the concentration of free ions as a result of electrostatic attraction ·between op-positely .charged ions due to short-range forces. The model used in their calculat-ions is the sphere-in-continuum. In the present work the conductance measurements are reported for 4 S-Alkylisothiouronium iodides in methanol which is a protic solvent at 25 °c. The possibility of application of the F-0 equation to these electrolytic solutions will be studied by the derivation of the characteristic constants A 0 , a0 and KA. The effect of cationic size on the conductance of the studied salts can be dis-cussed from the variation of both KA and a0• 714 A. M. HAFEZ ET AL. EXPERIMENTAL Preparation of Salts S-Methyl-, S-n-Butyl-, S-n-Amyl- and S-n-Heptylisothiouronium iodides were synthesized and purified as described in previous papers2 •3• Table 1 shows the melting points and analysis of salts. TABLE I Analysis and M. P. of S-Aikylisothiouronium Iodides Salt M. P./°C I/O/o S/O/o Found Calc'd. Found Calc'd. Found Calc'd. Found S-Methyliso-thiouronium iodide (S-MeisI) S-n-Butyliso-thiouronium Iodide (S-n-BuisI) S-n-Amyliso-thiouronium iodide (S-n-AmisI) S-n-Heptyliso-thiouronium iodide (S-n-HeptisI) 109-110 105-106 59-60 60-61 Purification of Solvent 58.21 48.80 46.30 42.01 58.22 12.85 12.88 14.70 14.70 48.76 10.77 10.82 12.33 12.21 46.20 10.22 10.29 11.70 11.60 42.06 9.27 9.34 10.61 10.58 Analar analytical reagent methanol (BDH) was kept in contact with molecular seives 4A (BDH) for about 24 hours with frequent shaking, then distilled and refluxed with analar silver nitrate for 24 hours. After distillation it was refluxed again with analar magnesium turnings for 24 hours and then distilled. The distillate was kept in contact with activated alumina for 24 hours with frequent shaking and then distilled. In all distillations a fractionating column was used and only the middle portion at 65.5 °C/760 mmHg* was collected. Its properties at 25 °c are: density d = 0.78657 g m1-1 and viscosity 17 = 0.54448 cp. Its specific conductance x0 amounts to (4--7 X 10-1 Q -1 cm-1). Conductance Measurements An Erlenmeyer conductivity cell with bright platinum electrodes was used. The cell constant is 0.04056 ± 0.330/o. A Beckman conductivity bridge Model No. 18A was used for measuring the resistance of the solution at 3 Kc/s. All solutions were prepared by weight reduced to vacuo. RESULTS AND DISCUSSION The measured equivalent conductances A (Q-1 equiv.-1 cm2) and the cor-responding concentrations c in equiv.fl of solution are shown in Table II. Values of A 0 were estimated from the Fuoss-Kraus-Shedlovsky equation4 • (2) * mmHg = 133 322 Pa S-ALKYLISOTHIOURONIUM IODIDES 715 TABLE II Conductance of S-Alkylisothiouronium Iodides in Methanol at 25 °c (1) S-MeisI (2) S-n-BuisI 104c A 104c A 27.555 96.97 16.618 94.32 22.436 98.26 13.219 95.38 16.157 100.08 10.285 96.34 13.205 101.11 8.1064 97.26 11.484 101.72 6.7135 97.84 9.9196 102.31 5.4893 98.44 8.5392 102.96 4.4538 98.98 6.5190 103.89 3.5428 99.52 (3) S-n-Amisl (4) S-n-Heptisl lO'c A 1o•c A 18.476 92.99 17.234 90.61 15.136 93.96 13.584 91.73 11.651 95.07 10.645 92.73 9.0631 96.00 8.0423 93.74 7.5598 96.61 6.8093 94.36 6.1633 97.27 5.6846 94.85 4.9267 97.88 4.7338 95.35 4.1576 98.30 3.9125 95.79 (The deduced A0 values from (FKS) equation for these salts are: (1) 110.62, (2) 104.38, (3) 103.62 and (4) 100.91). where, Kn is the dissociation constant and Scz> is the Shedlovsky's function which was tabulated by Dagett5 for various values of Z. A compact represent-ation of the data is shown by Figure 1. 1.0 1.0 0. 9 EXPERIMENTAL DATA ONSAGER'S SLOPE o 5-Meis I o 5-n-Buis I • 5-n-Amis I 0 5-n- Heptis I a.a o._ __ _._ ___ 2.__ ___ 3._. __ .__ __ _.5.__-,0""'2"""1r_c_, FIG. I : REDUCED CONDUCTANCES OF S -ALKYL/SOTHIDURONIUM /OOIDES I N ME THNAOL AT 25 C 716 A . M. HAFEZ ET ' AL. A computer program on an IBM 1620 machine was used to determine true values of A 0 , a0 and KA. The accuracies required in these computations are ± 0.02 for Ao, ± 10 for J < 1000 and ± 20 for J > 1000. It can be readily seen .from Table III that, the standard deviation, <JA, is small indicating that our computations are correct. Table III also shows that, there is a sudden decrease in KA value from 18.18 (S-MeisI) to 6.87 .(S-n-Buisl) and it remains almost constant for other normal salts having large cations; while a0 decreases as the cationic size increases. This behaviour can be interpreted in the light of the interaction energy U term which is &iven by the relation6 : ln KA = ln (4 n Na0 3/3000) + e2/a0 D kT) + U (3) where . U = !'J.S/k-E5 /kT in which S/k is an entropy term responsible for the rearrangement of solvent molecules around free ions and around pairs and E5/kT, a term which allows for ion-dipole interaction7• TABLE III Constants Derived from Conductance Data Using Equation (3) Salt Ao J ao K A <JA u S-MeisI 111.03 2408 6.45 18.18 0.069 0.629 S-n-BuisI 104.34 2009 5.48 6.87 0.049 -0.326 s~n~ArriisI i03.50 1993 5.48 7.24 0.045 -0.374 S-n-HeptisI 100.83 1810 4.98 6.68 0.052 -0.381 From the last column of Table III, the U term for S-MeisI is higher than for the other salts. This indicates that, the term responsible for the orientation of solvent molecules near the ion is higher than the ion-dipole interaction term for this salt. REFERENCES 1. R. M. Fuoss and L. Onsager, J. Phys. Chem. 61 (1957) 668; R. M. Fuoss, J . Amer. Chem. Soc. 81 (1959) 2659. 2. H. Sade k and Amin a M. Ha fez, Proc. Pakistan Acad. Sci. 11 (1974) 1. 3. H. Sade k and Amin a M. Ha fez, Electrochim. Acta 21 (1976) 767. 4. R. M. Fu o s s, and C. A. Kraus, J. Amer. Chem. Soc. 55 (1933) 476; R. M. Fu o s s, ibid. 57 (1935) 488; R. M. Fu o s s and T. Shed 1 o vs k y, ibid. 71 (1949) 1496. 5. H. M. Dage t t, ibid., 73 (1951) 4977. 6. F. Ac ca sci n a, A. D' Apr an o, and R. Trio 1 o, J. Phys. Chem. 71 (1967) 3469. 7. W. R. G i 1 k er son, J. Chem. Phys. 25 (1956) 1199. SAZETAK Vodljivost S-alkilisotiouronijevih jodida u metanolu pri 25 oc Amina M. Hafez, H. Sadek i N. H. EL-Hammamy Odredene su molarne vodljivosti S-metil-, S-n-butil-, S-n-amil- i S-n-heptili-zotiouronij jodida u metanolu. Karakteristicne konstante izracunane su s pomocu Fuoss-Onsagerove jednadzbe za 1 : 1 elektrolite. CHEMISTRY DEPARTMENT FACULTY OF SCIENCE, ALEXANDRIA UNIVERSITY ALEXANDRIA, A .R.E . Prlspje!o 31. sijecnja 1977. 

Conductance of S-Alkylisothiouronium Iodides in Methanol at 25° C

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