Proxan-sodium

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the substance is readily biodegradable

other:

Reference 2

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Justification for type of information:

Report prepared for the Norwegian Government regarding degradation of xanthates in seawater
Peer reviewed publication.
Confirms degradation pathways and attempts to quantify formation of CS2

Qualifier:

no guideline followed

Principles of method if other than guideline:

Experiments were performed to evaluate the kinetics of degradation of Sodium Isopropyl Xanthate (SIPX) in marine water.
Both, the decay of the target compound SIPX and the production of carbon disulphide (CS2) have been tracked in time-course experiments during 28 days.
In order to distinguish between two anticipated degradation pathways, hydrolysis and biological degradation, the decay of SIPX in marine water has been tracked through experiments in sterile and non-sterile water. Apart from CS2 other potential transformation products were investigated

GLP compliance:

not specified

Radiolabelling:

no

Analytical monitoring:

yes

Buffers:

Performed with sea water under natural pH 7.5

Details on test conditions:

28 days duration at 9.5 C

Duration:

28 d

pH:

7.5

Temp.:

9.5 °C

Initial conc. measured:

ca. 10 mg/L

Number of replicates:

Not specified

Positive controls:

no

Negative controls:

yes

Remarks:

Pure water. No test material

Transformation products:

yes

No.:

#1

No.:

#2

% Recovery:

0

pH:

7.5

Temp.:

95

Duration:

28 d

pH:

7.5

Temp.:

9.5

DT50:

ca. 7 d

Type:

not specified

Details on results:

Degradation of SIPX was observed at investigated conditions.
The concentrations of CS2 found are below the theatrical concentration (around 1.8 mg/L) expected for the degradation observed in the solution with initial concentration of 10 mg/L of SIPX.
The evolution observed in the concentration of SIPX and the CS2 during the 28 days period might be explained as intermediates generated would be unnoticed since the analysis was only focusing in the CS2 measurements.
After several days of SIPX exposure, the microbial community naturally present in marine water might adapt to the media and lead to reducing conditions in the sample with biodegradation of the carbon disulphide to sulphates and CO2

Conclusions:

Degradation of SIPX was observed at investigated conditions.

Executive summary:

The concentrations of CS2 found are below the theatrical concentration (around 1.8 mg/L) expected for the degradation observed in the solution with initial concentration of 10 mg/L of SIPX.
The evolution observed in the concentration of SIPX and the CS2 during the 28 days period might be explained as intermediates generated would be unnoticed since the analysis was only focusing in the CS2 measurements.
After several days of SIPX exposure, the microbial community naturally present in marine water might adapt to the media and lead to reducing conditions in the sample with biodegradation of the carbon disulphide to sulphates and CO2. This is in with other studies, including the microbial biodegradation of the Zahn Wellens showing 98% evolution of carbon as CO2.

Reference 3

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

no guideline followed

Principles of method if other than guideline:

A review of available publications on (hydrolytical) degradation of xanthates. The impact of pH and temperature on degradation half-lives in pure solutions have been recalculated based on data from Granville et al. 1972, and compared to measured data of Walterson (1984) in tailings water. Results of laboratory degradation tests reported from literature are compared to the real conditions (monthly temperatures) in tailing ponds in central Sweden. Abiotic and/or biotic reaction processes and in tailings pond are additionally simulated based on the key parameters obtained from literature.

GLP compliance:

no

Radiolabelling:

no

Analytical monitoring:

not specified

Estimation method (if used):

Re-calculated results from Granville et at. (1972

Details on test conditions:

Conditions of laboratory degradation tests are compared to the real conditions (monthly temperatures) in tailing ponds in central Sweden.
The comparison is presented in Table 1

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

No.:

#5

Details on hydrolysis and appearance of transformation product(s):

First reaction is the hydrolytical decomposition to xanthic acid
(1), which decomposes to alcohol (ROH)
(2) and carbon disulphide (CS2)
(3):H+ + ROCS- < == > ROCS2H --> ROH + CS2.

In tailings pond many other factors contribute to degradation reactions: seasonal variation in water volumes, the presence of metal ions, sulphide minerals, xanthates, precipitation with metal ions (especially lead) and other intermediates formed and consumed in the reactions. The simulation results has been presented under section 5.2.4. It must be noted that the author has not specified hydrolysis separately of possible biodegradation, which may take place in parallell in the tailings water.

In the presence of metal ions at high pH, or in the presence of sulphide minerals, xanthates are oxidized to form dixanthogen (4).

In tailings pond, dixanthogen can be present both as liquid and dissolved form. Hydrolytical decomposition of dixanthogen is dependent on the concentration of OH- ions - reaction rate is higher at higher pH (DT100 in a few minutes at pH >12; DT100 = 20 h at pH 9.2; DT25 = 16h at pH 2.4; temperature not mentioned). The decomposition products are mainly xanthate ions (1) and monothiocarbonate (5). Suspended dixanthogens decompose in a similar way as dissolved dixanthogens, but more slowly. The water solubility of dixanthogens decrease with increasing hydrocarbon chain length.

Monothiocarbonates (5) formed as intermediates decompose to alcohol (1) and carbonyl sulphide (6). Their decomposition is also pH dependent. It is rapid at low pH. At pH > 7, the t 1/2 is approximately 10 h - the author concludes that it is about 50 times higher than that of xanthates.

Xanthates also form precipitates with metal ions, especially lead, which sedimentate to the bottom of the pond. The rates increase in most cases at dfecreasing temperatures.

pH:

7.5

Temp.:

17 °C

DT50:

47 d

Type:

other: arious reactions and mechanisms

Remarks on result:

other: Calculated as function of temperature

pH:

7.5

Temp.:

15 °C

DT50:

60 d

Type:

other: various reactions and mechanisms

Remarks on result:

other: Calculated as function of temperature

pH:

7.5

Temp.:

14 °C

DT50:

68 d

Type:

other: various reactions and mechanisms

Remarks on result:

other: Calculated as function of temperature

pH:

7.5

Temp.:

10 °C

DT50:

112 d

Type:

other: various reactions and mechanisms

Remarks on result:

other: Calculated as function of temperature

pH:

7.5

Temp.:

5 °C

DT50:

211 d

Type:

other: various reactions and mechanisms

Remarks on result:

other: Calculated as function of temperature

pH:

7.5

Temp.:

3 °C

DT50:

274 d

Type:

other: various reactions and mechanisms

Remarks on result:

other: Calculated as function of temperature

Other kinetic parameters:

Half-lives have not been calculated for temperatures < 3 oC due to uncertainties in the calculation when approaching 0 oC.
Degradation of xanthates is strongly dependent also on pH. Above pH 8 the half-life for xanthates is constant, 24 days. Below pH 7 the rate is proportional to H+ concentration. At pH 6.5 and 7.5 the degradation rate in tailings water was of the same order of magnitude as in the pure solution. At pH 5.5 the rate was lower than in pure solution. In tailings water other reactions apart from a first grade degradation are likely to occur. In this studty the pH value 7.5 was used in the simulation.
The stability of the xanthate also increases with the length of the carbon chain and with increasing concentration.

Details on results:

In the model simulations both a (conservative) constant degradation half-life of 47 days (B), and a calculated temperature-dependant half-life (C) was used for xanthates. They were compared to a conservative non-degradable substance (A) with t1/2 of 100000 days.

Validity criteria fulfilled:

not specified

Conclusions:

Temperature, pH and the concentration of the xanthate are among the key factors determining the degradation of xanthates in tailing ponds.

In pure solutions at pH 0.5 - 12, xanthates dissociate to xanthate ions and then mainly hydrolyse to xanthic acid, which decomposes. Main degradation products of xanthates are identified to be (1) alkyl alcohol and (2) carbon disulphide. Additional intermediate reaction products (3) include dixanthogen, thiocarbonates (especially monothiocarbonate) and carbonyl sulphide (COS). They all are found to be degradable under the conditions of the tailings pond. The dependence of (hydrolytical) degradation rate of xanthates on temperature and pH is studied first in pure solutions.


The author compared concentrations of xanthates determined in pure solutions to calculated residual concentrations in tailings water, and concluded that the concentrations decreased more in tailings water (at pH 6.5 and 7.5), suggesting that also other reactions occur. In must be noted that the author did not specify hydrolytical and possible biodegradation products.

For the experimental part, the author selected a constant t1/2 of 45 days (at pH 7.5 at 17 oC), a temperature-dependent t1/2 ( 47 < t1/2 < 274 days or more at pH 7.5) and a conservative reference substance ( t1/2 100000 d) and simulated the impact of seasonally varying water volumes to alternative water treatment techniques.

Executive summary:

This report reviews available degradation data on xanthates focusing on the seasonal variation in Swedish tailing ponds in subarctic climate.

Temperature, pH and the concentration of the xanthate are among the key factors determining the degradation of xanthates in tailing ponds. In pure solutions at pH 0.5 - 12, xanthates dissociate to xanthate ions and then mainly hydrolyse to xanthic acid, which decomposes. Main degradation products of xanthates are identified to be (1) alkyl alcohol and (2) carbon disulphide. Additional intermediate reaction products (3) include dixanthogen, thiocarbonates (especially monothiocarbonate) and carbonyl sulphide (COS). They all are found to be degradable under the conditions of the tailings pond.

The dependence of (hydrolytical) degradation rate of xanthates on temperature and pH is studied first in pure solutions. The author compared concentrations of xanthates determined in pure solutions to calculated residual concentrations in tailings water, and concluded that the concentrations decreased more in tailings water (at pH 6.5 and 7.5 at temperature > 5 ^oC), suggesting that also other reactions occur. In must be noted that the author did not specify hydrolytical and possible biodegradation products.

For the experimental part, the author selected a constant t_1/2 of 45 days (at pH 7.5 at 17 oC), a temperature-dependent t_1/2 ( 47 < t_1/2 < 274 days or more at pH 7.5) and a conservative reference substance ( t_1/2 100000 d) and simulated the impact of seasonally varying water volumes to alternative water treatment techniques.

The results summarise available scientific infromation applying it to realistic conditions in tailing ponds in subarctic climate and are therefore rated as scientifically acceptable.

Reference 4

Endpoint:

hydrolysis

Type of information:

other: published data

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Justification for type of information:

The Sodium Isopropyl Xanthate (SIPX) (CAS No. 140-93-2), the subject of this dossier) is expected to exhibit very similar toxicity to Potassium amyl xanthate (CAS No.2720-73-2 ), which is also xanthate compound. Comparable metabolism would occur.

Qualifier:

no guideline required

Qualifier:

according to guideline

Guideline:

other: Acetone method

Principles of method if other than guideline:

The average loss of active xanthate from 10 % and 25 % water solutions is determined by the Acetone method.
The amount of carbon sulphide released has been estimated via use of mole rations of a proposed equation.

GLP compliance:

no

Radiolabelling:

no

Analytical monitoring:

yes

Buffers:

HCl - 0.1 N standard
NaOH - 0.1 N standard

Estimation method (if used):

The CS2 emissions were estimated via use of mole rations of a proposed equation (see below).

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

Details on hydrolysis and appearance of transformation product(s):

The following mechanism for hydrolytic decomposition is proposed:
6 R-OCS2-X (xanthate) + 3 H2O (water) --> 6 ROH (alcohol) + X2CO3 (carbonate) + 3 CS2 (carbon disulphide) + 2 X2CS3 (trithiocarbonate),
where X = sodium or potassium.
The decomposition products are alcohols, canbonate and trithiocarbonate salts and carbon disulphide.

The amount of carbon disulphide released by decomposition has not been measured, but estimated with the preceding reaction equation (based on the amount of xanthate decomposed):
For PAX, m (CS2) = 3 x M(CS2)/[6 x M(PAX)] = 3 x 76 / (6 * 202) = 228 / 1212 = 0.19.
E.g. for 1 kg of 10 % PAX solution at 20 oC, the amount of CS2 would be 0.19 x m[PAX used] = 0.19 x 1.04 kg/kg x 0.10 X 0.8 % = 0.016 %
For 1 kg of 25 % PAX solution at 20 oC, the amount of CS2 emitted would be 0.19 x 1.09 x 0.25 x 0.7 % = 0.036 %.

Temp.:

20 °C

DT50:

63 d

Remarks on result:

other: 10 % solution, calculated from % loss of xanthate/day

Temp.:

30 °C

DT50:

24 d

Remarks on result:

other: 10 % solution, calculated

Temp.:

40 °C

DT50:

12 d

Remarks on result:

other: 10 % solution, calculated

Temp.:

20 °C

DT50:

71 d

Remarks on result:

other: 25 % solution, calculated

Temp.:

30 °C

DT50:

25 d

Remarks on result:

other: 25 % solution, calculated

Temp.:

30 °C

DT50:

10 d

Remarks on result:

other: 25 % solution, calculated

Other kinetic parameters:

No pH of the solutions were reported.

Details on results:

The half-life was calculated by a simple ratio from the measured % loss value presented in Table 1: t1/2 = 50/(% loss) day.

Table 1. Measured stability of xanthate solutions (during two weeks storage).

PAX	Average loss of real xanthate  (%/day)	Calculated t 1/2 (d)
10 % solution at 20 C	0.8	63
10 % solution at 30 C	2.1	24
10 % solution at 40 C	4.2	12
25 % solution at 20 C	0.7	71
25 % solution at 20 C	2.0	25
25 % solution at 20 C	4.8	10

 

Calculated via formula: t1/2 = 50/(% loss) day

Table II. Estimated CS2 formation per day of 10% and 25 % solutions.

PAX Pounds/ gallon Kilograms/liter % 10 % solution at 20 C 0.00 0.00016 0.02 10 % solution at 30 C 0.003417 0.000409 0.04 10 % solution at 40 C 0.006917* 0.000829* 0.08* 25 % solution at 20 C 0.003 0.000359 0.04 25 % solution at 30 C 0.008583 0.001029 0.10 25 % solution at 40 C 0.020583* 0.002466* 0.25** Indicates formation of a separate layer of carbon disulphide in the solutions during two weeks storage.

With PAX, the separate layer rises to the top of water phase.

 

Validity criteria fulfilled:

no

Conclusions:

(Hydrolytical) decomposition curves for PAX at 20, 30 and 40 oC temperature were obtained. Half-lives calculated using a simple ratio indicate them to vary in the range of 12 - 63 d for 10 % solution and 10 - 71 d in 25 % solution. The study determined stability of 10 % and 25 % (pure) xanthate solutions during two weeks storage. The estimated amount of CS2 released varied 0.2 - 0.8 g/L (for 10 % solution at 20...40 oC) and 0.4 - 2.5 g/L (25 % solution at 20...40 oC temperature).

pH was not among the monitored parameters.

The following decomposition products are proposed: (1) alcohol, (2) carbon disulphide, (3) (dipotassium)carbonate and (4) dipotassium trithiocarbonate salts. The amount of carbon disulphide released by decomposition has not been measured, but was estimated with an equation proposed. The amount of carbon disulphide released by decomposition has not been measured, but estimated with the preceding reaction equation (based on the amount of xanthate decomposed): For PAX, m (CS2) = 3 x M(CS2)/[6 x M(PAX)] x m(PAX) = 3 x 76 / (6 * 202) x m(PAX) = 228 / 1212x m(PAX) = 0.19 x m(PAX).The estimated release rates for CS2 varied 0.02 - 0.08 % (for 10 % solution at 20...40 oC) and 0.04 - 0.25 % (25 % solution at 20...40 oC temperature). The authors noted that for the both concentrations at the highest 40 oC temperature a formation of a separate layer of CS2, which rised in the top (of the aqueous phase) of PAX.

Executive summary:

The study determined stability of 10 % and 25 % (pure) xanthate solutions during two weeks storage, and estimated amount of CS₂ released.

(Hydrolytical) decomposition curves for PAX at 20, 30 and 40 ^oC temperature were obtained. Half-lives calculated using a simple equation indicate them to vary in the range of 12 - 63 d for 10 % solution and 10 - 71 d in 25 % solution. pH was not among the monitored parameters.

The following decomposition products are proposed: (1) alcohol, (2) carbon disulphide, (3) (dipotassium)carbonate and (4) dipotassium trithiocarbonate salts. The amount of carbon disulphide released by decomposition has not been measured, but was estimated with an equation proposed:

6 R-OCS₂-X (xanthate) + 3 H₂O (water) --> 6 ROH (alcohol) + X₂CO₃ (carbonate) + 3 CS₂ (carbon disulphide) + 2 X₂CS₃ (trithiocarbonate), where X = sodium or potassium. The amount of carbon disulphide released by decomposition was estimated from the preceding reaction equation (based on the amount of xanthate decomposed): m (CS2) = 3 x M(CS2)/[6 x M(PAX)] x m(PAX) = 3 x 76 / (6 * 202) x m(PAX) = 228 / 1212 x m(PAX) = 0.19 x m(PAX). The estimated release rates for CS₂ varied 0.2 - 0.8 g/L (for 10 % solution at 20...40^oC) and 0.4 - 2.5 g/L (25 % solution at 20...40 ^oC temperature). The authors noted that for the both concentrations at the highest 40 ^oC temperature a formation of a separate layer of CS₂, which rises in the top (of the aqueous phase) of PAX.

This handbook presents a review of company data for real xanthate solutions according to other than accepted guidelines, and not in compliance with GLP. Furthermore, a key parameter pH was not monitored. The results are therefore rated as reliable with restrictions, but can be used as weight of evidence for assessment of hydrolysis and environmental stability.

Reference 5

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Principles of method if other than guideline:

The decomposition half-lives of aqueous xanthate solution were monitored at different temperatures and pH values in contact with nitrogen, oxygen and air (obtained from Finkenstein 1967). The aqueous concentrations were monitored with spectrophotometry.

GLP compliance:

no

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

At intervals samples of the solutions were analyzed by reading of the absorbance at wavelengths 2065 (characteristic to CS2 aq.), 2260 and 3010 Å (characteristic to aqeous xanthate radical).

Preliminary study:

The handbook reviews decomposition reactions of xanthates in aqueous solution. On dissolutions, xanthates dissociate to alkali metal cations and xanthate anions. Three main reaction routes depending on the pH of the solution and the presence of dissolved oxygen are identified:
(1) slow hydrolysis to xanthic acid, which further decomposes into alcohol and carbon disulphide - especially at low pH and presence of carbon dioxide
(2) oxidation of xanthate to dixanthogen - equilibrium is reached after 5 - 10 % of the xanthate is oxidised in a neutral medium, above pH 9 the reaction is virtually suppressed
In neutral and alkaline media, decomposition occurs via (3) decomposition to alcohol and carbon disulphide, which will be neutralised with the hydroxyl ions formed in hydrolysis forming carbonate and thiocarbonate ions.
In strong alkaline solution, full neutralisation of carbon disulfide can take place resulting in (4) alcohol, carbonate and sulphide anions and water (without formation of free carbon disulphide).

Test performance:

Data for experimental verification of reactions (2) to (4) is referred from publications of Rao and Patel (1960a, 1960b, 1961), including the experimental details.

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

pH:

6

Temp.:

25 °C

Hydrolysis rate constant:

1.85 d-1

DT50:

37.5 d

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0.265 h-1

DT50:

260 h

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.122 h-1

DT50:

570 h

pH:

11

Temp.:

25 °C

Hydrolysis rate constant:

0.124 h-1

DT50:

560 h

Other kinetic parameters:

All three main modes of decomposition (1), (2), and (3) were examined. It was shown that the decomposition is very significant during the first hour, and that it decays following first-order law. The oxidation of xanthate by oxygen to dixanthogen according to reaction (2) is much less significant than hydrolytic decomposition accorning to eq. (3) in the absence of carbon dioxide. In the presence of carbon dioxide, however, oxidation to dixanthogen is significant, as is the acid decomposition of xanthic acid according to reaction (1). Some of the results obtained with different xanthates are shown in Fig. 3 -5.
Decomposition of xanthates in aqueous solution is greatly influenced by the presence of metal salts such as those of copper, iron, lead and zinc, which are also commonly present in the flotation pulps of sulphide minerals.

Details on results:

Hydrolysis will be a significant factor in determining the environmental fate of Sodium Isopropyl Xanthate (SIPX). In neutral or mildly alkaline solutions, Sodium Isopropyl Xanthate (SIPX) decomposes to the alcohol, carbon disulphide, sodium carbonate and sodium trithiocarbonate, the two salts arising from neutralisation of carbon disulphide with the sodium hydroxide liberated. In more strongly alkaline media, hydrogen sulphide is liberated. However, strongly alkaline conditions are unlikely to be encountered under the conditions of use in the mining industry. The half-life at pH 7 at 25°C is reportedly about 260 hours, increasing to over 500 hours in the pH range 8 to 11
Under almost all the experimental conditions, the decomposition of of xanthate solutions as indicated by the decrease in absorption at 3010 Å shows good first-order kinetics. The half-lives and reaction rate constants at various pHs and temperatures are shown below in table 3-2. The rates of decomposition of xanthate in solutions containing dissolved oxygen and their comparison with the corresponding rates in the absence of oxygen are recorded in Table 3-3. The differences between the half-lives of decomposition of solutionbs in equilibrium with nitrogen and oxygen, t1/2 (N2) - t1/2(O2), and with nitrogen and air, t1/2 (N2) - t1/2(air) are also shown.

Table 3 -2. Half-lives and reaction constants for the decomposition of xanthate solutions of different pH

values in contact with nitrogen (after N.P.Finkelstein 1967).

pH	Temp (oC)	t ½ (h)	Reaction rate constant (1/h)
6	25	37.5	1.85
6	35	13.5	5.14
6	45	5.5	12.1
7	25	261	0.265
7	35	93.5	0.742
7	45	32	2.16
8	25	520	0.132
8	35	187	0.371
8	45	69	1.00
9	25	570	0.122
9	35	196	0.352
9	45	63	1.11
10	25	671	0.121
10	35	202	0.345
10	45	67.5	1.03
11	25	560	0.124
11	35	198	0.35
11	45	73	0.95

Table 3 -3. Effect of the concentration of dissolved oxygen on xanthate decomposition half-lives

at different temperatures and pH values (after N.P.Finkelstein 1967).

pH	Temp (oC)	t1/2(with N2)	t1/2(N2) - t1/2(Z)
			Z = oxygen		Z = air
			(h)	(%)	(h)	(%)
6	25	37.5	0	0	0	0
6	35	13.6	-0.5	-3.7	-0.5	-3.7
6	45	6.5	0.2	3.5	0.4	7.0
7	25	261	4	1.5	-2.0	-0.8
7	35	93.5	2.5	2.7	2.5	2.7
7	45	32.0	0.7	2.2	2.5	7.9
8	25	520	0	0	0	0
8	35	187	0	0	0	0
8	45	69	1.9	2.7	9.0	13
9	25	571	38	6.6	-	-
9	35	196	8	4.1	-	-
9	45	63	0.5	0.8	-	-
10	25	671	44	7.5	-	-
10	35	202	12	6.0	-	-
10	45	67.5	-0.5	-0.5	-	-
11	25	560	-8.0	-0.15	-	-
11	35	193	11	5.5	-	-
11	45	73	1	1.4	-	-

 

Validity criteria fulfilled:

yes

Conclusions:

The half-life at pH 7 at 25°C is reportedly about 260 hours, increasing to over 500 hours in the pH range 8 to 11

Executive summary:

Hydrolysis will be a significant factor in determining the environmental fate of Sodium Isopropyl Xanthate (SIPX). In neutral or mildly alkaline solutions, Sodium Isopropyl Xanthate (SIPX) decomposes to the alcohol, carbon disulphide, sodium carbonate and sodium trithiocarbonate, the two salts arising from neutralisation of carbon disulphide with the sodium hydroxide liberated. In more strongly alkaline media, hydrogen sulphide is liberated. However, strongly alkaline conditions are unlikelyto be encountered under the conditions of use in the mining industry. The half-life atpH 7 at 25°C is reportedly about 260 hours, increasing to over 500 hours in the pH range 8 to 11. Sodium Isopropyl Xanthate (SIPX) is hydrolytically unstable when exposed to acidic conditions, reverting rapidly to Isopropyl alcohol, carbon disulphide and sodium hydroxide, and therefore will not persist in the acidic environment of tailings dams. If dischargedto waterways, the chemical would be likely to persist for at least some days,hydrolysing only slowly in this more neutral environment. However, it is notexpected to bioaccumulate in view of its ionic character.

Reference 6

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Justification for type of information:

Special study performed to confirm rapid hydrolysis of potassium and sodium xanthates in simulated gastric fluid with identification of key metabolites.
This study is used to justify the use of surrogate data in animal testing on the basis that if ingested, the substance will rapidly degrade.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Study of the decomposition of eight samples of xanthates in simulated gastric fluid; sodium isoamyl xanthate, sodium isobutyl xanthate, sodium ethyl xanthateр potassium isoamyl xanthate, potassium ethyl xanthate (PEX). sodium isopropyl xanthate (SIPX), Potassium amyl xanthate and potassium isobutyl xanthate
The chemical reaction for this decomposition is:

Xanthate Salt + Hydrochloric acid Alcohol + Sodium Chloride + Carbon Disulphide

The reaction between simulated gastric fluid and the xanthate salts was carried out at 0oC for reasons of safety, as the reaction was expected to occur very quickly. The reaction mixture was then allowed to warm to room temperature over 1 hour, the final temperature being 25oC. A high degree of degradation at this temperature would lead to the inference that degradation would be at least as complete, if not more so, in actual gastric conditions.
Following the reaction solvent was added to produce a biphasic mixture, and the resulting organic
phases were analysed by GC-MS to confirm the presence of the corresponding alcohols. These
alcohols were quantified by comparison to known standards in order to confirm the completeness of the reaction, and to show that these salts behave in the same way under these reaction conditions.

Radiolabelling:

no

Analytical monitoring:

yes

Buffers:

Performed at pH 1.5 in synthetic gastric fluid

Details on test conditions:

Performed at 5 g/l to simulate possible concentration following ingestion
Performed at low temperatures for safety reasons due to exothermic nature of reaction

Duration:

1 h

pH:

1.5

Temp.:

0 °C

Initial conc. measured:

ca. 5 000 mg/L

Remarks:

Performed at initial temperature of 0 C, but in view of exothermic reaction, temperature will have risen by the end of the reaction.

Number of replicates:

One replicate per substance
A number of xanthates were evaluated as part of this study; all showed the same outcome

Positive controls:

no

Negative controls:

no

Statistical methods:

Not required

Preliminary study:

No

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

Details on hydrolysis and appearance of transformation product(s):

Exothermic reaction. No direct measurement of carbon disulphide possible, but elemental sulphur noted (estimated to be as dissolved sulphur dioxide or sulphates

% Recovery:

0

pH:

1.5

Temp.:

0 °C

Duration:

1 h

Remarks on result:

other: No parent material detected

Remarks on result:

not determinable because of methodological limitations

Remarks:

Too rapid to determine a rate constant

Details on results:

Rapid exothermic reaction in simulated gastric fluid at a loading of 5g/l

Sodium isoamyl xanthate, sodium isobutyl xanthate, sodium ethyl xanthateр  potassium isoamyl xanthate, potassium ethyl xanthate (PEX), sodium isopropyl xanthate (SIPX), Potassium amyl xanthate and potassium isobutyl xanthate were added to separate solutions of simulated gastric fluid at 0 C over 1 hour. The low starting temperature was to prevent reaction occurring too quickly, for reasons of safety.

Following the reaction, a liquid-liquid extraction was performed with ethyl acetate and the organic solvent analysed using GCMS. The extracts were compared to a standard curve of ethanol, isoamyl alcohol and isobutyl alcohol were quantified.

Based on analysis of the alcohols. degradation of sodium isopropyl xanthate (SIPX), was found to be  100% under the experimental conditions and degradation of potassium amyl xanthate was found to give 93% under the experimental conditions , potassium isobutyl xanthate was found to give 94%, sodium isobutyl xanthate was found to give 96% under the experimental conditions .  However, no xanthates could be found at the end of the exposure period.

To confirm that potassium salts will behave in a similar manner, potassium xanthates was added to simulated gastric fluid under the same conditions as the sodium salts above. A liquid-liquid extraction was performed with ethyl acetate and the organic solvent analysed using GCMS. Isoamyl alcohol was observed in the resulting gas chromatogram, as expected.

NMR spectroscopy did not provide any further evidence of the presence of xanthate post addition to gastric fluid. 

To confirm that the sodium or potassium remains in solution as the chloride salt, ICP-OES analysis was carried out on the aqueous phase of the reaction mixture, as well as on the simulated gastric fluid with the difference between the two measurements being an indication of how much sodium or potassium has been added as a result of the xanthate degradation. The analysis showed increased levels of potassium and sodium in the gastric fluid phase upon addition of potassium and sodium xanthates respectively. This provides further evidence that the potassium salts behave in a similar manner to the sodium salts under the experimental conditions.

The increase in sodium could not be quantified owing to the high levels of Na observed, and the addition of Na from processing.

For Potassium Xanthates, a significant increase in potassium was observed and the potassium and sodium salts can be considered as behaving in identical manner.

Carbon disulphide was not detected and due to limitations of the methods detection of carbon dioxide or sulphur dioxide was not possible.  There was no reported odour of carbon dislulphide.

Executive summary:

Based on analysis of the alcohols. degradation of sodium isopropyl xanthate (SIPX), was found to be  100% under the experimental conditions and degradation of potassium amyl xanthate was found to give 93% under the experimental conditions , potassium isobutyl xanthate was found to give 94%, sodium isobutyl xanthate was found to give 96% under the experimental conditions .  However, no xanthates could be found at the end of the exposure period.

 

To confirm that potassium salts will behave in a similar manner, potassium xanthates was added to simulated gastric fluid under the same conditions as the sodium salts above. A liquid-liquid extraction was performed with ethyl acetate and the organic solvent analysed using GCMS. The corresponding alcohol was observed in the resulting gas chromatogram, as expected.

NMR spectroscopy did not provide any further evidence of the presence of xanthate post addition to gastric fluid. 

To confirm that the sodium or potassium remains in solution as the chloride salt, ICP-OES analysis was carried out on the aqueous phase of the reaction mixture, as well as on the simulated gastric fluid with the difference between the two measurements being an indication of how much sodium or potassium has been added as a result of the xanthate degradation. The analysis showed increased levels of potassium and sodium in the gastric fluid phase upon addition of potassium and sodium xanthates respectively. This provides further evidence that the potassium salts behave in a similar manner to the sodium salts under the experimental conditions.

The increase in sodium could not be quantified owing to the high levels of Na observed, and the addition of Na from processing.

For Potassium Xanthates, a significant increase in potassium was observed and the potassium and sodium salts can be considered as behaving in identical manner.

Carbon disulphide was not detected and due to limitations of the methods detection of carbon dioxide or sulphur dioxide was not possible.  There was no reported odour of carbon dislulphide.

 

Description of key information

This endpoint is waived in accordance with Column 2 of Annex VII of the REACH Regulation as the substance is readily biodegradable. Data waiving.

Key value for chemical safety assessment

Half-life for hydrolysis:

260 h

at the temperature of:

25 °C

Additional information

The hydrolysis of xanthate in aqueous solution at room temperature is characterized by the following reaction:

6ROC(S)SNa + 3H₂O = 6ROH + 2NaSC(S)SNa + Na₂CO₃+ 3CS₂

Further hydrolysis of the CS₂gives H₂S and CO₂and the trithiocarbonate hydrolysis produces H₂S and sodium carbonate