Sulphate exchange

Rates of oxygen exchange in neutral or alkaline solutions of sulphates are very slow. One estimate of the half-life with sodium sulphate is 2.3 x 10 sec. In acidic solutions, oxygen exchange rates appear to depend on the concentration of undissociated H2SO4, at least between 3.6 and 13 The energy of activation 

W2SOA (M) Rate (25 °C) ig.atom l. sec -) Activation energy (Jccal.mole ) 

Rates of sulphur exchange between sulphur dioxide and 97.2 % H2SO4 between room temperature and 211 °C have been examined . The tentative nature of the study may be seen from the author s comment if, as seems probable, the reaction occurs in the liquid phase . On correcting for variation of the solubility of sulphur dioxide an activation energy of 28.8 kcal.mole is found. 

---

In a further study, Brubaker et have reported on the effects of the addition of chloride ion to the sulphate exchange system at virtually constant ionic strength (3.68 M sulphate and hydrogen-ion concentrations. For the concentration ratio [C1 ]/[T1(III)] of 9.2x10" to 9.5 at 24.9 °C results analogous to the effect observed in perchlorate media were obtained. The minimum in the rate corresponded to a ratio of 2.5. Results were also presented for the conditions, constant [CI ] and variable [804 ] and [If"] ( = 3.68 M). Brubaker et al have suggested that the exchange paths most likely to occur in sulphate media are... 

Freshly precipitated lead sulphate exchanged lead ions completely with lead nitrate ( Pb tracer) solution in about 3 minutes. But after the precipitate had stood in its mother liquor 48 hr exchange in the same time was only 35% of the previous value, presumably because of a decrease in available surface (Kolthoff and Rosenblum, VJo4). 

Helfferich, F., and G. Klein. 1970. Multicomponent chromatography. M. Dekker, New York. Helfferich, F.G., D. Petruzzelli, L. Liberti, and R. Passino. 1985a. Anion exchange kinetics in resins of high selectivity. Part II. The case of chloride/sulphate exchange. Isr. J. Chem. 

In rheumatic disease, the main pathological manifestations appear in connective tissue, the chief constituents of which are collagen, elastin and mucopolysaccharides. The last, apart from hyaluronic acid and chondroitin of cornea, are all sulphate esters , the sulphate groups of which are in a dynamic state with a short biological half-life. The sulphate exchange is under enzymic control and can be decreased in vitro and in vivo by corticosteroids " . Bostrom and Mansson examined the effects of a number of salicylates on the incorporation of S into calf costal cartilage slices in vitro. 

The kinetics of sulphate exchange with two iM-sulphato-dichromium(m) coniplexes are reported in the ligand-exchange section of this chapter (p. 247), and the photoaquation of ) -hydroxo-dichromiuni complexes at the appropriate later stage in this section. 

Sulphate exchange with the i -sulphato-dichromium complexes (39) and (40) has been monitored by S labelling. Rates depend on pH ... 

The purified commercial di-n-butyl d-tartrate, m.p. 22°, may be used. It may be prepared by using the procedure described under i o-propyl lactate (Section 111,102). Place a mixture of 75 g. of d-tartaric acid, 10 g. of Zeo-Karb 225/H, 110 g. (136 ml.) of redistilled n-butyl alcohol and 150 ml. of sodium-dried benzene in a 1-litre three-necked flask equipped with a mercury-sealed stirrer, a double surface condenser and an automatic water separator (see Fig. Ill, 126,1). Reflux the mixture with stirring for 10 hours about 21 ml. of water collect in the water separator. FUter off the ion-exchange resin at the pump and wash it with two 30-40 ml. portions of hot benzene. Wash the combined filtrate and washings with two 75 ml. portions of saturated sodium bicarbonate solution, followed by lOu ml. of water, and dry over anhydrous magnesium sulphate. Remove the benzene by distillation under reduced pressure (water pump) and finally distil the residue. Collect the di-n-butyl d-tartrate at 150°/1 5 mm. The yield is 90 g. 

These alloy coatings have advantages over tin in atmospheric exposure where there is heavy pollution by oxides of sulphur. They are cathodic to steel and anodic to copper. In industrial atmospheres, however, formation of a layer of lead sulphate seals pores and produces a generally stable surface and terne-plate has been used extensively as roofing sheet, especially in the USA. It is easily and effectively painted when additional protection is required. Copper heat exchangers in gas-fired water-heaters may be coated by hot dipping in 20% tin alloy . 

In aqueous solution this exchange has been studied, in the absence of oxygen, in chloride and sulphate media. The isotope Sn was used as the indicator and the separation of Sn(IV) and Sn(II) was achieved by the formation of the insoluble salts caesium hexachlorostannate(IV) and stannous oxalate . 

Interaction absorbance data have also been reported by Gordon and Brubaker for mixtures of Sn(IV) and Sn(II) in sulphate media. Exchange via interaction dimers, Sn(IV)-Sn(II), seems likely. 

Brubaker and Sincius have reported the exchange reaction as not occurring in sulphate media ([H ], 3 to 12 M) unless chloride ions are present. McKay plots deviating from linearity were observed for added chloride ion 0.4 to 6.0 M, and complicated dependencies on the ions H , and Sb(V) were also found. For mixtures of Sb(lll) and Sb(V), the principle of additivity of absorbance was obeyed in sulphate media. 

The early studies on the exchange system, carried out by Muxart et al., Menker and Garner, and Burgus and Kennedy, showed the exchange to be slow in sulphate , perchlorate, nitrate, and hydroxide media -. The isotopic method ( Cr) was used with separation of the Cr(III) and Cr(VI) being achieved by the precipitation of chromic oxide and lead chromate. Some evidence was obtained for the retardation of the exchange by hydrogen ions. 

Polissar has observed 100 % exchange between Mn(III), as the oxalato ion Mn(Ox)J, and manganous sulphate. Adamson, using manganic chloride as the source of Mn(III), has observed the exchange to be incomplete in a time 15 sec with reactant concentrations 10 M. Both workers used a separation technique based on the precipitation of Mn(IV), present via the equilibrium... 

Four recent kinetic studies have been made of the exchange in the presence of the sulphate ion in perchlorate media, some measure of agreement being observed between the results of the various workers. 

Reynolds and Fukushima have made an extensive study of this system and have interpreted their results, obtained with varying sulphate and hydrogen-ion concentrations, in terms of the exchange paths... 

Eichler and Wahl have attempted an isotopic study ( Os and Os) of the exchange reaction between Os(dipy)3 and Os(dipy)3 using a direct injection technique so that reaction times 7 x 10 sec were possible. With total osmium 10" M in aqueous sulphate media at 0 °C complete exchange was observed. The separation methods used were, (a) perchlorate precipitation (in presence of iron(II) carrier) and (6) extraction with p-toluenesulphonic acid in nitromethane, of the osmium(II) complex. A lower limit of 1 x 10 l.mole. sec was placed on the rate coefficient (0 °C, 3.0 M H2SO4). Dietrich and Wahl using the line broadening effect produced by Os(dipy)3 on the nmr spectrum of Os(dipy)3 have been able to propose a value of > 5x 10" l.mole . sec at 6 °C in D2O (0.14 M [Cr] and 5x10 M [D- ]). 

The earliest investigation of the exchange reaction between the aquated ions of Co(III) and Co(II) was carried out by Hoshowsky et al., using the isotopic method ( Co). When sulphate salts ( 10 M) were employed, complete exchange was observed between the two oxidation states of cobalt, in a time of less than two min. Two separation methods were employed (a) adsorption on an alumina column, and (b) precipitation of the Co(III) as the cobaltinitrite. 

The effect of the addition of sulphate and fluoride ions were found by these workers to increase the rate of exchange addition of acetate and trifluoroacetate ions produced relatively minor changes. For the addition of sulphate ions, a rate law... 

Shankar and De Souza have also recently investigated the effect of the additions of various anions to this system in both water and heavy water solvent. Fluoride was found to have very little influence on the exchange rate while acetate, nitrate and sulphate ions produced an increase. For the addition of sulphate ions an estimate of the rate coefficient kj of 20 l.mole . sec (at 14 °C and = 2.0 M) was made. For the addition of nitrate and acetate, values of the coefficients k and kj (where k = k K and kj = k K ), viz. 

The exchange reaction between U(VI) and U(IV) in aqueous sulphate chloride and perchlorate media and in various mixed aqueous-organic solvents... 

Betts obtained evidence for the exchange in sulphate media being catalysed by light of wavelengths 340 m/t, the region of absorption of U(VI). In the presence of light a rate law, approximately... 

Kinetic data exist for all these oxidants and some are given in Table 12. The important features are (i) Ce(IV) perchlorate forms 1 1 complexes with ketones with spectroscopically determined formation constants in good agreement with kinetic values (ii) only Co(III) fails to give an appreciable primary kinetic isotope effect (Ir(IV) has yet to be examined in this respect) (/ ) the acidity dependence for Co(III) oxidation is characteristic of the oxidant and iv) in some cases [Co(III) Ce(IV) perchlorate , Mn(III) sulphate ] the rate of disappearance of ketone considerably exceeds the corresponding rate of enolisation however, with Mn(ril) pyrophosphate and Ir(IV) the rates of the two processes are identical and with Ce(IV) sulphate and V(V) the rate of enolisation of ketone exceeds its rate of oxidation. (The opposite has been stated for Ce(IV) sulphate , but this was based on an erroneous value for k(enolisation) for cyclohexanone The oxidation of acetophenone by Mn(III) acetate in acetic acid is a crucial step in the Mn(II)-catalysed autoxidation of this substrate. The rate of autoxidation equals that of enolisation, determined by isotopic exchange , under these conditions, and evidently Mn(III) attacks the enolic form. 

---