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Solid sodium ethyl xanthate(CAS# 140-90-9)is hygroscopic, absorbing moisture decomposes, releasing very toxic and extremely flammable carbon disulfide. Decomposition rate increases with increase in temperature and decrease pH.

In acidic media, pH <1.5, decomposition of xanthates runs very fast ( logk0= 7.5), illustrated by the reaction equation:

ROC(S)SNa + HA  = ROH + CS2 + NaA

Rate constant for acid-catalyzed decomposition of potassium ethyl xanthate(CAS# 140-89-6)

k1= 194 /mol min in the presence of H3O+at 250C.

In aqueous solution, in neutral and alkaline media, xanthates decompose by the hydrolytic way:

6ROC(S)SNa  +  H2O   =   6ROH  +  Na2CO3  +  3CS2  +  2CS3Na2

Further hydrolysis of sodium trithiocarbonate to sodium carbonate and hydrogen sulfide and carbon disulfide to carbon dioxide and hydrogen sulfide may occur.

 

Decomposition of xanthates depends on temperature and NaOH concentration:

-dx/dt = k1x + k2x [NaOH]2

At 650C for: sodium ethyl xanthate(CAS# 140-90-9): k1 = 9.7 10-4min-1and k2 = 3.3 10-4

                sodium isopropyl xanthate(CAS# 140-93-2): k1 = 2.0 10-4min-1and k2 = 6.1 10-5

                sodium n-butyl xanthate(CAS# 141-33-3): k1 = 6.4 10-4min-1and k2 = 2.4 10-5

At 750C for: sodium ethyl xanthate(CAS# 140-90-9): k1 = 2.1 10-3min-1and k2 = 6.3 10-4

              sodium isopropyl xanthate(CAS# 140-93-2): k1 = 4.2 10-4min-1and k2 = 1.2 10-4

              sodium n-butyl xanthate(CAS# 141-33-3): k1 = 1.4 10-3min-1and k2 = 4.6 10-4

It was found that the minimum of xanthates decomposition rate is at pH range from 7 to 9.

 Investigation of potassium ethyl xanthate(CAS# 140-89-6)water solution at pH 6-10 shoved coexistence of xanthate ions, EtX-, dixanthogen , (EtX)2and carbon disulfide(CAS# 75-15-0).

Simultaneous reactions leading to decomposition of xanthate/or dixanthate species to alcohol and carbon disulfide were detected.

Decomposition of sodium ethyl xanthate as 40% solution at 200C would give rise to an increase in CS2concentration of approximately 0.1% per day.

Reactivity:

Xantates react with oxidizing agents, acids and alkaline solutions. With strog acids the substance decomposes quantitatively producing carbon disulfide and an alcohol. In strong alkali solutions, at pH >13, react forming carbon disulfide, hydrogen, an alcohol, trithiocarbonate and sodium carbonate. Salts of copper, iron, lead or zinc accelerate decomposition of xanthates.

Reaction with strong oxidizing agents as peroxides, nitrates and perchlorates causing risk of fire and explosion.

Solid xanthates decompose exposed to moisture in air, releasing carbon disulfide. Hydrolysis is a significant factor in determination the environmental fate of xanthates. In neutral or mildly alkaline water solution, sodium ethyl xanthate decomposes to ethyl alcohol, carbon disulfide, sodium carbonate and sodium trihiocarbonate. (Full Public Report Sodium Ethyl Xanthate Priority Existing Chemical No. 5 May 1995Australian Government Publishing Service Canberra)

Water solutions are also relatively stable at temperature <180C and the pH within the range 10 - 11.(NICNAS. Sodium Ethyl Xanthate. Priority Existing Chemical, Secondary Assessment , Report No. 5S. February 2000)