CHAPTER 11 • Hydrolysis Processes of Organotin(lV} Compounds in Sea Water
219
creasing in the dilute solution. Analogous behaviour was found by Tobias and co-workers (1962,1964,1965,1966) and more recently by De Stefano et al. (1996,1999) in studying the interactions of (CH3hSn 2 + and (CH 3 )Sn 3 + in chloride solutions. Investigations
into the hydrolysis products of ethyl-, butyl- and octyltin trichlorides carried out by
Luijten (1966) report their properties and solid-state preparation. Some potentiometric studies of hydrolysis and sulfide complex formation of ethyl-trichlorotin(IV) in
mixed water/methanol solution have been carried out by Devaud (1969,1970,1971,1972)
and by Langlois and Devaud (1974), in an organometallic compound concentration
range of 6-60 mmol dm- 3 • The results obtained by these authors are not altogether
consistent with findings for monomethyltin trichloride (Van den Berghe and Van der
Kelen 1965), probably owing to the different solvent and concentration ranges used.
The results of IH_ and 119Sn-NMR and 119Sn-Mossbauer spectroscopic studies on the
hydrolysis of methyl- and butyltin trichloride (0.5 mol dm- 3 ) have been reported by
Blunden et al. (1982) and Blunden and Hill (1990). From analysis of published data it
can be affirmed that there are, in general, great discrepancies among the results of
investigations into the hydrolysis of mono-organotin(IV) derivatives, probably owing
to the difficulty of investigating a very reactive species such as RSn 3 +, which presents
a hardness in a Lewis acid scale, which is higher than that of mono- and di-charged
cations. Moreover, the majority of studies have been carried out by using a very high
concentration of monoalkyltrichloride, and, therefore, the formation of mixed hydroxochloride complexes cannot be avoided. Consequently, the picture of the chemical speciation of this system is not clear. It has been suggested that methyltin trichloride exists in aqueous solution only as a hydroxide species according to the following pH
dependent equilibrium
CH3Sn(OH)CI2· 2 (H20) ~ CH3Sn(OHhCl· H20 ~ CH3Sn(OHh ~ CH3Sn(OH)4
Species 1
Species 2
Species 3
Species 4
pH increasing ----~
Blunden et al. (1982) report the formation of the Species 1 at pH 1.4. It might be expected that, at environmental pH, Species 3 will predominate. Potentiometric investigations by De Stefano et al. (1999a) on the CH 3 Sn 3 + system (NaN0 3 , NaCI and Na2S04
ionic media) show the formation of the following simple hydrolytic species:
[CH3Sn(OHhl+' [CH3Sn(OHhlo, [(CH3Snh(OHhl+ and [CH 3 Sn(OH)4r (log f3 in
Table 11.3), whose formation percentages, in the pH range 2-12, are reported in Fig. 11.3.
As can be seen, the species [«CH3)Snh(OH>st and [CH3Sn(OHhlo predominate
in the pH range of natural fluids (6.5-9.5), both reaching about 50% formation at seawater pH value.
11.3
Salt Effect on the Hydrolysis Process
In order to establish the effects of seawater salt on the hydrolysis process of mono- diand trimethyltin(IV) cations, we carried out investigations into these systems both in
chloride (0 ::;; 153 mol dm -3) and sulfate media (0 ::;; 151 mol dm -3), and in synthetic
sea water (5-45%0 salinity range, see Section 11.6). The formation constants of chlo-
219
creasing in the dilute solution. Analogous behaviour was found by Tobias and co-workers (1962,1964,1965,1966) and more recently by De Stefano et al. (1996,1999) in studying the interactions of (CH3hSn 2 + and (CH 3 )Sn 3 + in chloride solutions. Investigations
into the hydrolysis products of ethyl-, butyl- and octyltin trichlorides carried out by
Luijten (1966) report their properties and solid-state preparation. Some potentiometric studies of hydrolysis and sulfide complex formation of ethyl-trichlorotin(IV) in
mixed water/methanol solution have been carried out by Devaud (1969,1970,1971,1972)
and by Langlois and Devaud (1974), in an organometallic compound concentration
range of 6-60 mmol dm- 3 • The results obtained by these authors are not altogether
consistent with findings for monomethyltin trichloride (Van den Berghe and Van der
Kelen 1965), probably owing to the different solvent and concentration ranges used.
The results of IH_ and 119Sn-NMR and 119Sn-Mossbauer spectroscopic studies on the
hydrolysis of methyl- and butyltin trichloride (0.5 mol dm- 3 ) have been reported by
Blunden et al. (1982) and Blunden and Hill (1990). From analysis of published data it
can be affirmed that there are, in general, great discrepancies among the results of
investigations into the hydrolysis of mono-organotin(IV) derivatives, probably owing
to the difficulty of investigating a very reactive species such as RSn 3 +, which presents
a hardness in a Lewis acid scale, which is higher than that of mono- and di-charged
cations. Moreover, the majority of studies have been carried out by using a very high
concentration of monoalkyltrichloride, and, therefore, the formation of mixed hydroxochloride complexes cannot be avoided. Consequently, the picture of the chemical speciation of this system is not clear. It has been suggested that methyltin trichloride exists in aqueous solution only as a hydroxide species according to the following pH
dependent equilibrium
CH3Sn(OH)CI2· 2 (H20) ~ CH3Sn(OHhCl· H20 ~ CH3Sn(OHh ~ CH3Sn(OH)4
Species 1
Species 2
Species 3
Species 4
pH increasing ----~
Blunden et al. (1982) report the formation of the Species 1 at pH 1.4. It might be expected that, at environmental pH, Species 3 will predominate. Potentiometric investigations by De Stefano et al. (1999a) on the CH 3 Sn 3 + system (NaN0 3 , NaCI and Na2S04
ionic media) show the formation of the following simple hydrolytic species:
[CH3Sn(OHhl+' [CH3Sn(OHhlo, [(CH3Snh(OHhl+ and [CH 3 Sn(OH)4r (log f3 in
Table 11.3), whose formation percentages, in the pH range 2-12, are reported in Fig. 11.3.
As can be seen, the species [«CH3)Snh(OH>st and [CH3Sn(OHhlo predominate
in the pH range of natural fluids (6.5-9.5), both reaching about 50% formation at seawater pH value.
11.3
Salt Effect on the Hydrolysis Process
In order to establish the effects of seawater salt on the hydrolysis process of mono- diand trimethyltin(IV) cations, we carried out investigations into these systems both in
chloride (0 ::;; 153 mol dm -3) and sulfate media (0 ::;; 151 mol dm -3), and in synthetic
sea water (5-45%0 salinity range, see Section 11.6). The formation constants of chlo-