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Nature of the complexes of sulphur trioxide with iodine chlorides
J. inorg, nucl. Chem., 1971, Vol. 33, pp. 991 to 995.
NATURE OF TRIOXIDE
Pergamon Press.
Printed in Great Britain
THE COMPLEXES OF SULPHUR WITH IODINE CHLORIDES
RAM C H A N D PAUL, C. L. ARORA and K. C. M A L H O T R A Department of Chemistry, Panjab University, Chandigarh- 14, India (Received 20 January 1970) Abstract-Sulphur trioxide combines with iodine trichloride to form two compounds IC12SO3C1 and 1(SO3C1)3 iodine dichloride monochlorosulphate behaves as a strong electrolyte in chlorosulphuric acid whereas iodine trichlorosulphate behaves as a weak acid. Iodine monochloride combines with sulphur trioxide to form iodine monochlorosulphate which disproportionates into lower and higher oxidation states of iodine when dissolved in highly acidic media.
INTRODUCTION
SULPHUR trioxide is known to combine with ionizable chloride ions to form
chlorosulphates[1-3]. However, it has been demonstrated recently that these metal chlorosulphates are slightly polymerised through chlorosulphate bridging. Iodine mono [4] and trichlorides [5] have been shown to be feebly self ionized by Gutmann et al. It is, therefore, of interest to investigate the nature of the adducts of sulphur trioxide with these chlorides as it may throw some light on their nature. In the present communication we report the isolation of compounds of composition IC13-SO3, IC13.3SO3 and IC1-SO3 and a study of their behaviour in strongly acidic media. EXPERIMENTAL Purification of 1C1 was carried out by fractional crystallisation. IC13 was purified by sublimation. The composition of 100% disulphuric acid was determined from its freezing point and conductance. Chlorosulphuric acid was distilled in an atmosphere of dry nitrogen and the fraction distilling at 151°C was collected directly in the conductivity cells. The design of the conductivity cell and cryoscopic set up was exactly the same as used by Gillespie et al. [6]. The cryoscopic factor v and conductivity factor 3' in disulphuric acid[7] were obtained by the methods already discussed. The u.v. spectrum was observed on a Beckman DB-recording instrument. The path length of the cell used was 1 mm. The i.r. spectra of the compounds were observed in a Perkin-Elmer Model No. 337 Spectrophotometer. Since the compounds reacted with the material of the windows, the i.r. spectrum was observed by retaining a solution of the compound between Teflon sheets. Preparation o f ICI2"SO3CI. Iodine trichloride (10-0g) was suspended in carbon tetrachloride (50 ml) in a 100 ml flask. It was then cooled in ice to 0°. Dry sulphur trioxide (4 g) was then distilled into this mixture. The reactants were allowed to stand for some time. Carbon tetrachloride and excess of sulphur trioxide were removed at 0° in vacuum when a solid orange compound was obtained. I. R. C. Paul, K. K. Paul and K. C. Malhotra, Chem. Ind. 1227 (1968). 2. R. C. Thompson, J. Barr, R. J. Gillespie, J. B. Milne and R. A. Rothenbury, lnorg. Chem. 4, 1641 (1965). 3. R.C. Paul, K. K. Paul and K. C. Malhotra, Austral.J. Chem. 22,847 (1969). 4. V. Gutmann, Z. anorg, allg. Chem. 264, 169 (1951). 5. V. Gutmann, Mh. Chem. 82,473 (1950). 6. R.J. Gillespie and K. C. Malhotra, J. chem. Soc. A, 1994 (1967). 7. R. C. Paul, Darshan Singh and K. C. Malhotra, J. Chem. Soc. A, 1396 (1969). 991
992
R.C. PAUL, C. L. A R O R A and K. C. M A L H O T R A
Preparation o f I(SOzC1)3. Iodine trichloride (8 g) was taken in a 50 ml flask and liquid sulphur trioxide (10.0 g) was distilled into it. The reactants were kept at room temperature for some time. Excess sulphur trioxide was removed in vacuo when an orange liquid remained. Preparation o f I(SO~CI). Iodine monochloride (10.0 g) was taken in a 50 ml flask and cooled in ice. Into this flask sulphur trioxide (6.0 g) was distilled and the mixture allowed to react for some time. Excess of sulphur trioxide was removed in vacuum to leave a partly solid reddish orange residue. RESULTS AND DISCUSSION
When excess of sulphur trioxide is added to cold suspension of iodine trichloride in carbon tetrachloride at 0°C, an orange crystalline compound of composition ICI3SO3(m.p. 8°C)(I) separates. It is an extremely hygroscopic compound and fumes in moist air. Its molar conductance and cryoscopic studies in nitrobenzene indicate it to be a uni-univalent electrolyte. Its i.r. spectrum shows the presence of six absorption bands at 1160, 1030, 840,750,640 and 560 cm -1 which correspond to the chlorosulphate group (C3v) and thus confirm the presence of chlorosulphate ion [8]. This suggests that sulphur trioxide combines with one chlorine atom of iodine trichloride to form a monochlorosulphate ion, indicating that in iodine trichloride one chlorine atom is different from the other two. This also finds support from its dimeric structure where the bridging chlorine atom is different from the other two. Iodine dichloride monochlorosulphate(I) has a high conductance in chlorosulphuric acid. It can behave as an acid (according to equation a) or a base (according to equation b) in this medium. IC12SO3C1 + 2HSO3C1 ~ H2+SO3C1 + IC12(SO3C1)2ICI~SO3CI ~ IC12+ + SO3C1-.
(a) (b)
The strong base, acetic acid [9], when added to the solution would neutralise the acid produced in equilibrium (a) and would cause a decrease in the conductance of the solution whereas it would exhibit its own ionisation if it behaved according to equilibrium (b) (Fig. 1, curve A). Our observations on the conductance support equilibrium (b) and rules out its behaviour as an acid in chlorosulphuric acid. Furthermore, it has been found that it is solvolysed in disulphuric acid, like alkali metal chlorosulphates, and from cryoscopic and conductance studies, its behaviour may be predicted as: ICI~SOaCI+2H2S2OT--~ ICI2++HSO3CI+HSaOi-0+H2SO4. IC12+ cation, being a strong electrophile, is quite stable in a weakly nucleophilic medium. The existence of ICl~+ ion in the solid state has already been indicated by X-ray[10] and i.r. studies[11] of the solid complexes ICla'SbCI~ and ICIa'AICIa. From these observations it may be concluded that in the presence of strong acceptors, iodine trichloride behaves as a chloride ion donor. But when sulphur trioxide is treated with iodine trichloride at room temperature, an orange coloured compound of composition IClz'3SOa is obtained. The 8. 9. 10. 11.
T. C. Waddington, and F. Klanberg, J. chem. Soc. 2339 (1960). E. A. Robinson and J. A. Circuna, J. Am. chem. Soc. 86, 5676 (1964). K.H. Boswijk, and E. H. Wiebenga, Acta. crystallogr. 417 (1954). C. G. Vink and E. H. Wiebenga, Acta. crystallogr. 12,859 (1959).
Complexes of sulphur trioxide with iodine chloride
993
I~'.0
I1'0
I0"0
9"0
/
8.0
7.0
/
/
x
6.0
/
AI
A
/
/
8 5.0 ,4 e') 4.0
30
2"0
1,0
0
o.02
o.04
0.06
O.Oe
0.~
0.12
0"~
0.16
ole
Mololity
Fig. 1. Specific conductances in chlorosulphuric acid (at 25°C). • - acetic acid; ® - 1C!2SO3C1;4~-- ISO3C1; @ - I(SOsCI)a; A - acetic acid in solution of I(SO3C1)3 in chlorosulphuric acid; [] - water in solution of I(SO~CI)3 in chlorosulphuric acid; • - acetic acid in solution o f ICI~(SO3CI) in chlorosulphuric acid.
Infra-red spectrum of the compound shows the presence of the chlorosulphate group. Because of the limited transparency of the window used, the absence of I--CI bond could not be confirmed. Its conductance in chlorosulphuric acid is quite low (Fig. 1) showing it to be a weak electrolyte. To ascertain whether I(SO3C1)a ionizes as an acid or a base, conductivities of the solution obtained by adding successive amounts of acetic acid, which acts as a base in HSOsCI, to I(SO3C1)3 solutions in chlorosulphuric acid were measured. There is no decrease in the conductance of the solution but the slope of the conductivity curve is less than that of acetic acid alone in chlorosulphuric acid indicating that I(SO3C1)3 behaves as a weak acid: I(S03C1)3 + 503C1- ~ I(803C1)4-. The lower values of the conductance may be attributed to the removal of SO3C1ion by I(SOaC1)3, as is shown in the above equation. On addition of water to the solution of I(SO3C1)3 in chlorosulphuric acid, there is no change in the conductance of the solution, indicating no further formation of conducting ions. By analogy
994
R . C . P A U L , C. L. A R O R A and K. C. M A L H O T R A
with the action of water on the solution of iodine trifluorosulphate in fluorosulphuric acid [12], the reaction may be represented as: I(SOzC1)s + H O H ~ IO(SOsCI) + 2HSOsC1. After the addition of sulphur trioxide to iodine monochloride, when the excess of sulphur trioxide is removed under vacuum, a viscous, deep orange red fuming liquid of composition ICI.SOs is left behind. I.R. spectral analysis of the compound shows the presence of chlorosulphate group suggesting that sulphur trioxide has not oxidized iodine monochloride, but has combined with chlorine to form monochlosulphate. On exposure to moisture, it develops green colour, due to the presence of Is + and Is +, etc. [13, 14]. It is a thermally stable ionic compound. Its conductivity in chlorosulphuric acid is quite low, about one-fourth of that of potassium chlorosulphate (Fig. 1). The u.v. spectrum of the solution in HSOaCI shows the presence of the Is + cation[15]. From the value of the molar extinction coefficient and its conductance in chlorosulphuric acid, the mode of dissociation of iodine monochlorosulphate in chlorosulphuric acid may be represented as: 4ISOsCI ~ Is+ + I(SOaCI)s + SOsC1A slightly lower value of y, (SO3C1- is the labile ion in chlorosulphuric acid) than required by the above equation may be due to the feebly acidic behaviour of I(SOsCl)s in HSOsC1 which may remove SOsC1- ions as: I(SOsCl)s + SOsCl- --~ I(SOsCl)4- from the solution. Table 1
x* Adduct
Colour
M.P. or B.P. (°C)
ICI'SOa ICI3SOs ICla3SOa
Reddish orange Orange Orange
20 (m.p.) 8 (m.p.) 96 (b.p.)
Analysis Found CI S
Mol. Wt. Found Calc.
Calc. CI
S
14-71 1 3 . 2 2 1 4 . 6 4 1 3 . 1 9 33.99 10"25 3 3 " 9 7 1 0 . 2 1 22.53 2 0 - 2 3 22.49 20-27
235.5 309.3 462.2
242.5 313"5 473.5
(molar conductance in nitrobenzene) 5-6 22"6 3.5
4" Value for molar c o n d u c t a n c e for 1 : 1 electrolytes in nitrobenzene is 2 0 - 3 0 o h m -1 c m 2.
Iodine monochlorosulphate when dissolved in disulphuric acid forms a greenish blue solution which shows the presence of Is + and Is + cations. As suggested earlier[16], the unit positive oxidation state (I +) is not very stable in disulphuric acid. It disproportionates to form Is+, 13+ and to some extent 13+. Its conductance in disulphuric acid is comparable to that of iodine monochloride in disulphuric acid. The visible spectrum of the solution shows the characteristic 12. 13. 14. 15. 16.
R.J. Gillespie and J. B. Milne, lnorg. Chem. 5, 1236 (1966). J. A r o t s k y , H. C. M i s h r a and M. C. R. S y m o n s , J. chem. Soc. 2582 (1962). J. Barr, R. J. Gillespie and R. C. T h o m p s o n , lnorg. Chem. 3, 1149 (1964). R . J . Gillespie and J. B. Milne, lnorg. Chem. 5, 1577 (1966). R . J . Gillespie and K. C. Malhotra, lnorg. Chem. 8, 1751 (1961).
Complexesof sulphur trioxidewith iodinechloride
995
spectrum of I2+ with a broad band at 640 nm, weaker bands at 510 and 420 nm and a weak characteristic peak due to I3-~ ion at 300 nm. By analogy with the behaviour of iodine monochloride in disulphuric acid [ 16] the behaviour of iodfiae monochlorosulphate in disulphuric acid may be represented: 5ISO3C1 + 6H28207 ~ 212+ + 1(HSO4+)2 + 3HS3010 + 5HSO3C1 + H2SO4. The freezing point and conductance data are in good agreement with the above equation where chlorosulphuric acid behaves as a non-electrolyte[6], and contributes only to the u factor and not to the conductance of the solution. Some of the chlorosulphates are known to be polymeric, polymerisation occuring through chlorosulphate bridging. However, in the present case there has been no indication of any polymerisation which may be because of the absence of accessible vacant d-orbitals in iodine. On the other hand, the chlorosulphates (I.SO3CI, IC12"SO3C1) show ionic character while I(SO3Clh acts as a weak acid in chlorosulphuric acid.
NATURE OF TRIOXIDE
Pergamon Press.
Printed in Great Britain
THE COMPLEXES OF SULPHUR WITH IODINE CHLORIDES
RAM C H A N D PAUL, C. L. ARORA and K. C. M A L H O T R A Department of Chemistry, Panjab University, Chandigarh- 14, India (Received 20 January 1970) Abstract-Sulphur trioxide combines with iodine trichloride to form two compounds IC12SO3C1 and 1(SO3C1)3 iodine dichloride monochlorosulphate behaves as a strong electrolyte in chlorosulphuric acid whereas iodine trichlorosulphate behaves as a weak acid. Iodine monochloride combines with sulphur trioxide to form iodine monochlorosulphate which disproportionates into lower and higher oxidation states of iodine when dissolved in highly acidic media.
INTRODUCTION
SULPHUR trioxide is known to combine with ionizable chloride ions to form
chlorosulphates[1-3]. However, it has been demonstrated recently that these metal chlorosulphates are slightly polymerised through chlorosulphate bridging. Iodine mono [4] and trichlorides [5] have been shown to be feebly self ionized by Gutmann et al. It is, therefore, of interest to investigate the nature of the adducts of sulphur trioxide with these chlorides as it may throw some light on their nature. In the present communication we report the isolation of compounds of composition IC13-SO3, IC13.3SO3 and IC1-SO3 and a study of their behaviour in strongly acidic media. EXPERIMENTAL Purification of 1C1 was carried out by fractional crystallisation. IC13 was purified by sublimation. The composition of 100% disulphuric acid was determined from its freezing point and conductance. Chlorosulphuric acid was distilled in an atmosphere of dry nitrogen and the fraction distilling at 151°C was collected directly in the conductivity cells. The design of the conductivity cell and cryoscopic set up was exactly the same as used by Gillespie et al. [6]. The cryoscopic factor v and conductivity factor 3' in disulphuric acid[7] were obtained by the methods already discussed. The u.v. spectrum was observed on a Beckman DB-recording instrument. The path length of the cell used was 1 mm. The i.r. spectra of the compounds were observed in a Perkin-Elmer Model No. 337 Spectrophotometer. Since the compounds reacted with the material of the windows, the i.r. spectrum was observed by retaining a solution of the compound between Teflon sheets. Preparation o f ICI2"SO3CI. Iodine trichloride (10-0g) was suspended in carbon tetrachloride (50 ml) in a 100 ml flask. It was then cooled in ice to 0°. Dry sulphur trioxide (4 g) was then distilled into this mixture. The reactants were allowed to stand for some time. Carbon tetrachloride and excess of sulphur trioxide were removed at 0° in vacuum when a solid orange compound was obtained. I. R. C. Paul, K. K. Paul and K. C. Malhotra, Chem. Ind. 1227 (1968). 2. R. C. Thompson, J. Barr, R. J. Gillespie, J. B. Milne and R. A. Rothenbury, lnorg. Chem. 4, 1641 (1965). 3. R.C. Paul, K. K. Paul and K. C. Malhotra, Austral.J. Chem. 22,847 (1969). 4. V. Gutmann, Z. anorg, allg. Chem. 264, 169 (1951). 5. V. Gutmann, Mh. Chem. 82,473 (1950). 6. R.J. Gillespie and K. C. Malhotra, J. chem. Soc. A, 1994 (1967). 7. R. C. Paul, Darshan Singh and K. C. Malhotra, J. Chem. Soc. A, 1396 (1969). 991
992
R.C. PAUL, C. L. A R O R A and K. C. M A L H O T R A
Preparation o f I(SOzC1)3. Iodine trichloride (8 g) was taken in a 50 ml flask and liquid sulphur trioxide (10.0 g) was distilled into it. The reactants were kept at room temperature for some time. Excess sulphur trioxide was removed in vacuo when an orange liquid remained. Preparation o f I(SO~CI). Iodine monochloride (10.0 g) was taken in a 50 ml flask and cooled in ice. Into this flask sulphur trioxide (6.0 g) was distilled and the mixture allowed to react for some time. Excess of sulphur trioxide was removed in vacuum to leave a partly solid reddish orange residue. RESULTS AND DISCUSSION
When excess of sulphur trioxide is added to cold suspension of iodine trichloride in carbon tetrachloride at 0°C, an orange crystalline compound of composition ICI3SO3(m.p. 8°C)(I) separates. It is an extremely hygroscopic compound and fumes in moist air. Its molar conductance and cryoscopic studies in nitrobenzene indicate it to be a uni-univalent electrolyte. Its i.r. spectrum shows the presence of six absorption bands at 1160, 1030, 840,750,640 and 560 cm -1 which correspond to the chlorosulphate group (C3v) and thus confirm the presence of chlorosulphate ion [8]. This suggests that sulphur trioxide combines with one chlorine atom of iodine trichloride to form a monochlorosulphate ion, indicating that in iodine trichloride one chlorine atom is different from the other two. This also finds support from its dimeric structure where the bridging chlorine atom is different from the other two. Iodine dichloride monochlorosulphate(I) has a high conductance in chlorosulphuric acid. It can behave as an acid (according to equation a) or a base (according to equation b) in this medium. IC12SO3C1 + 2HSO3C1 ~ H2+SO3C1 + IC12(SO3C1)2ICI~SO3CI ~ IC12+ + SO3C1-.
(a) (b)
The strong base, acetic acid [9], when added to the solution would neutralise the acid produced in equilibrium (a) and would cause a decrease in the conductance of the solution whereas it would exhibit its own ionisation if it behaved according to equilibrium (b) (Fig. 1, curve A). Our observations on the conductance support equilibrium (b) and rules out its behaviour as an acid in chlorosulphuric acid. Furthermore, it has been found that it is solvolysed in disulphuric acid, like alkali metal chlorosulphates, and from cryoscopic and conductance studies, its behaviour may be predicted as: ICI~SOaCI+2H2S2OT--~ ICI2++HSO3CI+HSaOi-0+H2SO4. IC12+ cation, being a strong electrophile, is quite stable in a weakly nucleophilic medium. The existence of ICl~+ ion in the solid state has already been indicated by X-ray[10] and i.r. studies[11] of the solid complexes ICla'SbCI~ and ICIa'AICIa. From these observations it may be concluded that in the presence of strong acceptors, iodine trichloride behaves as a chloride ion donor. But when sulphur trioxide is treated with iodine trichloride at room temperature, an orange coloured compound of composition IClz'3SOa is obtained. The 8. 9. 10. 11.
T. C. Waddington, and F. Klanberg, J. chem. Soc. 2339 (1960). E. A. Robinson and J. A. Circuna, J. Am. chem. Soc. 86, 5676 (1964). K.H. Boswijk, and E. H. Wiebenga, Acta. crystallogr. 417 (1954). C. G. Vink and E. H. Wiebenga, Acta. crystallogr. 12,859 (1959).
Complexes of sulphur trioxide with iodine chloride
993
I~'.0
I1'0
I0"0
9"0
/
8.0
7.0
/
/
x
6.0
/
AI
A
/
/
8 5.0 ,4 e') 4.0
30
2"0
1,0
0
o.02
o.04
0.06
O.Oe
0.~
0.12
0"~
0.16
ole
Mololity
Fig. 1. Specific conductances in chlorosulphuric acid (at 25°C). • - acetic acid; ® - 1C!2SO3C1;4~-- ISO3C1; @ - I(SOsCI)a; A - acetic acid in solution of I(SO3C1)3 in chlorosulphuric acid; [] - water in solution of I(SO~CI)3 in chlorosulphuric acid; • - acetic acid in solution o f ICI~(SO3CI) in chlorosulphuric acid.
Infra-red spectrum of the compound shows the presence of the chlorosulphate group. Because of the limited transparency of the window used, the absence of I--CI bond could not be confirmed. Its conductance in chlorosulphuric acid is quite low (Fig. 1) showing it to be a weak electrolyte. To ascertain whether I(SO3C1)a ionizes as an acid or a base, conductivities of the solution obtained by adding successive amounts of acetic acid, which acts as a base in HSOsCI, to I(SO3C1)3 solutions in chlorosulphuric acid were measured. There is no decrease in the conductance of the solution but the slope of the conductivity curve is less than that of acetic acid alone in chlorosulphuric acid indicating that I(SO3C1)3 behaves as a weak acid: I(S03C1)3 + 503C1- ~ I(803C1)4-. The lower values of the conductance may be attributed to the removal of SO3C1ion by I(SOaC1)3, as is shown in the above equation. On addition of water to the solution of I(SO3C1)3 in chlorosulphuric acid, there is no change in the conductance of the solution, indicating no further formation of conducting ions. By analogy
994
R . C . P A U L , C. L. A R O R A and K. C. M A L H O T R A
with the action of water on the solution of iodine trifluorosulphate in fluorosulphuric acid [12], the reaction may be represented as: I(SOzC1)s + H O H ~ IO(SOsCI) + 2HSOsC1. After the addition of sulphur trioxide to iodine monochloride, when the excess of sulphur trioxide is removed under vacuum, a viscous, deep orange red fuming liquid of composition ICI.SOs is left behind. I.R. spectral analysis of the compound shows the presence of chlorosulphate group suggesting that sulphur trioxide has not oxidized iodine monochloride, but has combined with chlorine to form monochlosulphate. On exposure to moisture, it develops green colour, due to the presence of Is + and Is +, etc. [13, 14]. It is a thermally stable ionic compound. Its conductivity in chlorosulphuric acid is quite low, about one-fourth of that of potassium chlorosulphate (Fig. 1). The u.v. spectrum of the solution in HSOaCI shows the presence of the Is + cation[15]. From the value of the molar extinction coefficient and its conductance in chlorosulphuric acid, the mode of dissociation of iodine monochlorosulphate in chlorosulphuric acid may be represented as: 4ISOsCI ~ Is+ + I(SOaCI)s + SOsC1A slightly lower value of y, (SO3C1- is the labile ion in chlorosulphuric acid) than required by the above equation may be due to the feebly acidic behaviour of I(SOsCl)s in HSOsC1 which may remove SOsC1- ions as: I(SOsCl)s + SOsCl- --~ I(SOsCl)4- from the solution. Table 1
x* Adduct
Colour
M.P. or B.P. (°C)
ICI'SOa ICI3SOs ICla3SOa
Reddish orange Orange Orange
20 (m.p.) 8 (m.p.) 96 (b.p.)
Analysis Found CI S
Mol. Wt. Found Calc.
Calc. CI
S
14-71 1 3 . 2 2 1 4 . 6 4 1 3 . 1 9 33.99 10"25 3 3 " 9 7 1 0 . 2 1 22.53 2 0 - 2 3 22.49 20-27
235.5 309.3 462.2
242.5 313"5 473.5
(molar conductance in nitrobenzene) 5-6 22"6 3.5
4" Value for molar c o n d u c t a n c e for 1 : 1 electrolytes in nitrobenzene is 2 0 - 3 0 o h m -1 c m 2.
Iodine monochlorosulphate when dissolved in disulphuric acid forms a greenish blue solution which shows the presence of Is + and Is + cations. As suggested earlier[16], the unit positive oxidation state (I +) is not very stable in disulphuric acid. It disproportionates to form Is+, 13+ and to some extent 13+. Its conductance in disulphuric acid is comparable to that of iodine monochloride in disulphuric acid. The visible spectrum of the solution shows the characteristic 12. 13. 14. 15. 16.
R.J. Gillespie and J. B. Milne, lnorg. Chem. 5, 1236 (1966). J. A r o t s k y , H. C. M i s h r a and M. C. R. S y m o n s , J. chem. Soc. 2582 (1962). J. Barr, R. J. Gillespie and R. C. T h o m p s o n , lnorg. Chem. 3, 1149 (1964). R . J . Gillespie and J. B. Milne, lnorg. Chem. 5, 1577 (1966). R . J . Gillespie and K. C. Malhotra, lnorg. Chem. 8, 1751 (1961).
Complexesof sulphur trioxidewith iodinechloride
995
spectrum of I2+ with a broad band at 640 nm, weaker bands at 510 and 420 nm and a weak characteristic peak due to I3-~ ion at 300 nm. By analogy with the behaviour of iodine monochloride in disulphuric acid [ 16] the behaviour of iodfiae monochlorosulphate in disulphuric acid may be represented: 5ISO3C1 + 6H28207 ~ 212+ + 1(HSO4+)2 + 3HS3010 + 5HSO3C1 + H2SO4. The freezing point and conductance data are in good agreement with the above equation where chlorosulphuric acid behaves as a non-electrolyte[6], and contributes only to the u factor and not to the conductance of the solution. Some of the chlorosulphates are known to be polymeric, polymerisation occuring through chlorosulphate bridging. However, in the present case there has been no indication of any polymerisation which may be because of the absence of accessible vacant d-orbitals in iodine. On the other hand, the chlorosulphates (I.SO3CI, IC12"SO3C1) show ionic character while I(SO3Clh acts as a weak acid in chlorosulphuric acid.