Preparation of Thioacetamide - Organosulfur Compounds - Lu Le Laboratory

Thioacetamide (TA) is an organosulfur compound. This white crystalline solid is soluble in water and serves as a source of sulfide ions in the synthesis of organic and inorganic compounds. It is a prototypical thioamide.

Thioacetamide was widely used in classical qualitative inorganic analysis as an in situ source for sulfide ions. Thus, treatment of aqueous solutions of many metal cations to a solution of thioacetamide affords the corresponding metal sulfide:

M²⁺ + CH₃C(S)NH₂ + H₂O → MS_(s) + CH₃C(O)NH₂ + 2 H⁺

(M = Ni, Pb, Cd, Hg)

Related precipitations occur for sources of soft trivalent cations (As³⁺, Sb³⁺, Bi³⁺) and monovalent cations (Ag⁺, Cu⁺). (Wikipedia)

See Also: The Systematic Analysis of Cation Group 2

Reaction Equation:

Chemicals

1.     Acetamide(Link to Preparation): 0.1500 g

2.     Phosphorus Pentasulfide(Link to Preparation): 0.1250 g

3.     Ammonium bicarbonate: saturated solution

4.     95% Ethanol

Procedure

1.     Add 0.1500g dried acetamide and 0.1250g crashed phosphorus pentasulfide in a test tube and bland the powder thoroughly.

 

2.     Heat the mixture to 60℃ and then the mixture will melt and react spontaneously. When the temperature raise to 80~90℃, the reaction will become violent and release a lot of hydrogen sulfide[1].

 

 

3.     Keep the temperature at 85~100℃ for 3~4 hr.

4.     Leave the mixture to cool down .

5.     Neutralize the solid to pH 3~4 with saturated ammonium bicarbonate [2].

 

6.     Filter the yellowish solid.

7.     Recrystallize the solid with 95% ethanol.

 

Notes

[1] Some of hydrogen sulfide may release in the procedure. It should be handled in a fume hood.

[2] Do not add too much ammonia bicarbonate solution, because thioacetamide is very soluble in aqueous phase.

Experimental Record

Weight of Acetamide	0.1498g
Weight of Phosphorus Pentasulfide	0.1267g
Theoretical Weight of Thioacetamide	0.1904g
Weight of Thioacetamide (recrystalized)	0.0806g
Yield	42.33%