Chemistry

V. O. Mokhnach and N. M. Rusakova

Spectrophotometric Study of Iodine Compounds with One Positive Valence

(Presented by Academician I. I. Chernyaev, 14 X 1961)

In the absorption spectrum of an aqueous iodine solution in the absence of iodide, absorption bands are observed with maxima at (\lambda 288\text{—}290\ \mathrm{m\mu}), (\lambda 340\text{—}360\ \mathrm{m\mu}), and (\lambda 460\ \mathrm{m\mu}). Numerous investigators ((^{1-10})) attribute the first two absorption bands to the complex anion (\mathrm{J}_3^-), and the band at (\lambda 460\ \mathrm{m\mu}) to the solvated molecule (\mathrm{J}_2). In these works we have not found convincing evidence for such an interpretation of the absorption spectra of iodine solutions. Nor is there any information in the foreign literature on the biological properties of iodine with positive valence.

Meanwhile, as we have shown ((^{11-13})), iodine with positive valence is of special interest, since in this form, in contrast to (\mathrm{J}^-), it possesses high biological activity both in pure aqueous solutions and especially in solutions of natural and synthetic high polymers. Iodine–high-polymer complexes are at present acquiring ever greater importance and broad clinical application as nontoxic therapeutic preparations of antiseptic action ((^{14})). Taking this into account, in order to obtain the spectral characteristics and identification of iodine with one positive valence, as well as some of its other forms, we decided to study the absorption spectra of aqueous iodine solutions in the range (220\text{—}800\ \mathrm{m\mu}).

Experimental Part

Iodine solutions were prepared in twice-distilled water from an iodine preparation of “chemically pure” grade that had been subjected to double sublimation. Solutions of iodine chloride were obtained by the method described by Gengrinovich ((^{15})). Starch solutions were prepared from soluble starch of the grade “Reagent OST 27, GOPKh 1866” in twice-distilled water. The acids (\mathrm{H_2SO_4}), (\mathrm{HClO_4}), and (\mathrm{HNO_3}) were of “chemically pure” grade. Dialysis was carried out through a cellophane membrane (40\ \mathrm{m\mu}) thick. All spectrophotometric studies were carried out at room temperature on an SF-4 spectrophotometer in the range (220\text{—}800\ \mathrm{m\mu}).

To obtain the spectral characteristics of compounds containing (\mathrm{J}2^{+1}), we studied the absorption spectra of solutions of (\mathrm{KJO}) and (\mathrm{JCl}), in which the presence of iodine with one positive valence is beyond doubt. A (\mathrm{KJO}) solution was obtained by the action of molecular iodine on a solution of caustic potash cooled to (0\text{—}5^\circ) (with dilution of (0.01\ M\ \mathrm{J}_2) in a 2% (\mathrm{KOH}) solution) according to the equation: (\mathrm{KOH + J_2 \rightarrow KJ + HJO}). As can be seen from Fig. 1, in the absorption spectrum of the solution obtained two absorption bands are distinctly expressed, with (\lambda^-).} 224\text{—}226\ \mathrm{m\mu}) and (\lambda_{\max} 350\ \mathrm{m\mu}). Since the band at (\lambda 224\text{—}226\ \mathrm{m\mu}) belongs, as is known, to (\mathrm{J}^-) ((^{16})), the absorption band at (\lambda 350\ \mathrm{m\mu}) should be attributed to (\mathrm{JO

The iodine chloride solution was obtained by us according to the equation:

[
\mathrm{KJO_3 + 6HCl + 2KJ \rightarrow 3JCl + 3KCl + 3H_2O}
]

As is evident from this equation, the resulting JCl solution contains KCl, which, as is known, promotes the stability of JCl in aqueous solutions and gives no absorption in the range 220–800 mμ. In the absorption spectrum of this solution (Fig. 2) there are two absorption bands, with (\lambda_{\max} 226) mμ and (\lambda_{\max} \lambda 350) mμ. The first, at (\lambda 226) mμ, is explained by the presence of (J^-) (KJ). The second band, at (\lambda 350) mμ, appears as a result of hydrolysis of JCl with formation of (JO^-) according to the equation: (JCl + H_2O \to 2H^{\cdot} + Cl' + JO'). Dilution of (0.1\,N) JCl to (0.005\,N) JCl causes the appearance in the absorption spectrum of a third absorption band at (\lambda 460) mμ (Fig. 2).

Fig. 1. Absorption spectra of solutions: 1 — KJO ((0.01\,M\,J_2 + 2\%) KOH solution); 2 — (0.01\,M) (KJO_3); 3 — (0.004\,M) (KJO_4) (layer thickness 0.0063–5.00 cm)

Fig. 2. Absorption spectra of aqueous JCl solutions: (a) — (0.01\,N) JCl; (b) — (0.1\,N) JCl (layer thickness 0.0015–0.5 cm)

The absence in the spectra presented of a band at (\lambda 288)—290 mμ indicates the possibility of the separate existence of absorption bands at (\lambda 288)—290 mμ and (\lambda 350) mμ. We showed this further in the following way. An aqueous iodine solution containing 0.0083 g (J_2) in 100 ml of water was subjected to dialysis through a cellophane membrane 40 μ thick. As can be seen from Fig. 3, in the absorption spectrum of the solution being dialyzed, 6 hr 40 min after the start of dialysis, two absorption maxima were observed at (\lambda 226) mμ and (\lambda 280)—282 mμ. The absorption maximum at (\lambda 350) mμ was entirely absent. In the spectrum of the dialysate, 5 hr after the start of dialysis, maxima were found at (\lambda 224)—226 mμ and 282—284 mμ, as well as at (\lambda 440)—455 mμ.

Fig. 3. Absorption spectra: (a) — aqueous (J_2) solution subjected to dialysis; (b) — dialysate

The absorption band at (\lambda 350)—360 mμ without the band at (\lambda 288)—290 mμ was also obtained by us in the absorption spectrum of an aqueous iodine solution in the presence of starch taken in excess, which is in agreement with our data on the absorption spectrum of iodamylose solutions ((^{17})).

An absorption band with (\lambda_{\max} 350) mμ in the absence of a band at (\lambda 288)—290 mμ was also observed by Gillam and Morton ((^{18})) in the absorption spectra of JCl solutions in acetic acid, chloroform, ethyl acetate, and HCl.

It follows from the above that absorption bands at (\lambda 288)—290 mμ and (\lambda 350) mμ in the absorption spectra of iodine solutions and its compounds can exist separately. As our studies show in comparison with the literature data, (\lambda_{\max} 288)—290 mμ belongs to the complex anion (J_3^-). The absorption band with (\lambda_{\max} 350) mμ, as shown above, is present in the spectra of solutions containing the complex anion (JO^-), compris-

forming (J^{+1}). The absorption band with (\lambda_{\max} 450\text{–}460\ \mathrm{m}\mu) in the absorption spectra of iodine solutions belongs, according to some assumptions ((^{7}) and others), to the solvated iodine molecule; moreover, along with this band others are always present, which greatly complicates the interpretation of absorption at (\lambda\ 450\text{–}460\ \mathrm{m}\mu). In view of this, we decided to isolate in the absorption spectrum of an iodine solution the absorption band with (\lambda_{\max} 460\ \mathrm{m}\mu). Taking into account that the reaction of interaction of halogens, in particular iodine, with water is reversible: (\mathrm{H_2O + J_2 \rightleftarrows HJ + HJO}), and that in an acidic medium there is a shift to the left with suppression of the formation of (\mathrm{KJO_3}), (\mathrm{HJ}), (\mathrm{JO^-}), etc., which create additional difficulties in deciphering the spectra, we investigated aqueous iodine solutions acidified with (\mathrm{H_2SO_4}), (\mathrm{HNO_3}), and (\mathrm{HClO_4}).

Fig. 4. Absorption curves of systems: 1 — (\mathrm{J_2—H_2O—H_2SO_4}) (20%); 2 — (\mathrm{J_2—H_2O—HNO_3}) (15%); 3 — (\mathrm{J_2—H_2O—HClO_4}) (16%); 4 — (\mathrm{J_2—H_2O—HClO_4}) (8%), (C_{\mathrm{J_2}} — 0.015\%) (layer thickness (0.0015\text{–}5.0\ \mathrm{cm}))

As can be seen from Fig. 4, the absorption spectrum of the system (\mathrm{J_2—H_2O—H_2SO_4}) showed, as was to be expected, one absorption band with (\lambda_{\max} 465\ \mathrm{m}\mu). In the spectrophotometric study of the system (\mathrm{J_2—H_2O—HNO_3}), two absorption bands were obtained with (\lambda_{\max} 300\ \mathrm{m}\mu) and (\lambda_{\max} 465\ \mathrm{m}\mu). Since (\lambda_{\max} 300\ \mathrm{m}\mu) belongs, as is known ((^{19,20})), to the complex anion (\mathrm{NO_3^-}), this spectrum also gives an unambiguous solution to the problem. In the absorption spectrum of the third system, (\mathrm{J_2—H_2O—HClO_4}), at 8% acid content, two absorption bands were obtained with (\lambda_{\max} 348\ \mathrm{m}\mu) and (\lambda_{\max} 465\ \mathrm{m}\mu). Since the absorption band at (\lambda 348\ \mathrm{m}\mu), according to our data, belongs to the complex anion (\mathrm{JO^-}), we explained its presence in the spectrum by the insufficient concentration of (\mathrm{HClO_4}). Indeed, when the concentration of (\mathrm{HClO_4}) was doubled, then, as can be seen in Fig. 4, (\lambda_{\max} 348\ \mathrm{m}\mu) disappeared completely, and in the spectrum there remained a single absorption band with (\lambda_{\max} 460\ \mathrm{m}\mu).

The obtaining in the absorption spectrum of an isolated absorption band at (\lambda 465\ \mathrm{m}\mu) is in complete agreement with the chemical reaction cited above and clearly establishes that the absorption band with (\lambda 460\ \mathrm{m}\mu) belongs to the (\mathrm{J_2}) molecule. Thus, the assumptions available in the literature ((^{7}) and others) concerning the attribution of this absorption band to the solvated (\mathrm{J_2}) molecule receive experimental confirmation. In describing the absorption spectra of iodine solutions in all the works known to us on this question, the authors confine themselves to the formal attribution of the absorption band with (\lambda_{\max} 460\ \mathrm{m}\mu) to the solvated (\mathrm{J_2}) molecule, supposedly possessing a symmetrical electronic structure. It seems to us that, for understanding the absorption spectra of iodine solutions, especially those that are colored, it is necessary to take into account the results of special studies of the polarization of the (\mathrm{J_2}) molecule in different solvents.

Dissociation of the iodine molecule has been assumed in a number of studies to explain experimental results ((^21) and others). Of particular interest are data concerning iodine solutions in nonpolar solvents. Williams (^22, ^23) obtained (\mu = 1.2) for iodine in benzene and carbon disulfide. Fairbrother (^24), on the basis of determinations of (\mu) for (J_2) in various solvents, gives values of (\mu) from 0.6 to 1.5 and concludes that the fact of polarization of (J_2) in red and brown iodine solutions is beyond doubt. This is also confirmed by Kleinberg and Davidson (^25).

In view of the fact that the absorption band at (\lambda 460\ \mathrm{m}\mu), isolated by us in the absorption spectrum of an iodine solution, can belong, as shown above, only to the (J_2) molecule, and since only this single band accounts for the red-brown color of the solution, it may be concluded that the (J_2) molecule in a 0.015% aqueous solution must be polarized. Since the biologically inactive (^11) complex ions (JO_3^{-}) and (JO_4^{-}), containing (J^{+5}) and (J^{+7}), respectively, do not absorb in the visible region of the spectrum (^13), just as the colorless compounds of trivalent iodine do not, it must be assumed that the (J_2) molecule associated with the absorption band at (\lambda 460\ \mathrm{m}\mu) must contain (J^{+1}). In that case the (J_2) molecule in aqueous solutions should be represented in the form (n \cdot H_2O[J^{+1}\ldots J^{-1}]). The absorption spectra of highly dilute aqueous solutions of JCl and JBr contain an absorption band at (\lambda 460\ \mathrm{m}\mu), which also, apparently, is explained by the presence in the solution of polarized iodine molecules formed as a result of dissociation of dihalogen molecules.

Let us summarize the above: 1) in the spectra of solutions of iodine compounds, absorption bands with (\lambda_{\max} 288\text{—}290\ \mathrm{m}\mu) and (\lambda_{\max} 340\text{—}360\ \mathrm{m}\mu) may exist separately; 2) these absorption bands belong, respectively, to the complex anions (J_3^{-}) and (JO^{-}); 3) the absorption band with (\lambda_{\max} 460\ \mathrm{m}\mu) belongs to the polarized molecule (n \cdot H_2O[J^{+1}\ldots J^{-1}]); 4) solutions containing iodine compounds with valence (-1, +5, +7) are colorless and devoid of biological activity; 5) the biological activity and coloration of iodine compounds are associated with the presence of iodine with one positive valence, (J^{+1}).

Botanical Institute
named after V. L. Komarov
Academy of Sciences of the USSR

Received
12 X 1961

REFERENCES

^1 Chr. Winther, Zs. phys. Chem., Abt. A, 108, 236 (1924). ^2 P. Job, Ann. Chim., 9, 113 (1928). ^3 T. M. Lowry, R. R. Goldstein, F. Gilbert, J. Chem. Soc., 1928, 307. ^4 H. Fromherz, Kun Hou Lih, Zs. phys. Chem., Abt. A, 153, 321 (1931). ^5 F. Gilbert, R. R. Goldstein, T. M. Lowry, J. Chem. Soc., 1931, 1092. ^6 A. D. Awtrey, R. S. Connick, J. Am. Chem. Soc., 73, 1842 (1951). ^7 L. J. Katzin, J. Chem. Phys., 21, No. 3, 409 (1953). ^8 H. N. Hersch, Phys. Rev., 105, No. 4, 1410 (1957). ^9 J. A. Thoma, D. French, J. Am. Chem. Soc., 80, 6142 (1958). ^10 J. A. Thoma, D. French, J. Am. Chem. Soc., 82, 4144 (1960). ^11 V. O. Mokhnach et al., Microbiology, 29, issue 3, 451 (1960). ^12 V. S. Mokhnach et al., Microbiology, 29, issue 4, 600 (1960). ^13 V. O. Mokhnach, I. P. Zueva, DAN, 136, No. 4, 832 (1961). ^14 V. O. Mokhnach, Collection of Scientific Works of the LSGMI, 46, 146 (1959). ^15 A. I. Gengrinovich, Farmatsiya, No. 6, 5 (1946). ^16 H. Fromherz, W. Menschik, Zs. phys. Chem., Abt. B, 7, 439 (1930). ^17 V. O. Mokhnach, N. M. Rusakova, DAN, 135, No. 5, 1143 (1960). ^18 A. E. Gillam, R. A. Morton, Proc. Roy. Soc., 132A, 152 (1931). ^19 G. Scheibe, R. Römer, G. Rössler, Ber., 59, 1321, 2616 (1926). ^20 H. Halban, J. Eisenbrand, Zs. phys. Chem., Abt. A, 132, 401, 433 (1928). ^21 Chr. Winther, Zs. phys. Chem., Abt. B, 3, 299 (1929). ^22 J. Williams, Phys. Zs., 29, 174 (1928). ^23 J. Williams, E. F. Ogg, J. Am. Chem. Soc., 94 (1928). ^24 F. Fairbrother, J. Chem. Soc., 1948, 1051. ^25 J. Kleinberg, A. W. Davidson, Chem. Rev., 42, 3, 601 (1948).