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Properties of thioacetamide

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  Physical properties

  Extremely soluble in benzene and ether. Its aqueous solution at room temperature or 50 to 60 ℃ is quite stable, but when the presence of hydrogen ions, quickly produce hydrogen sulfide and decomposition. New products sometimes have mercaptan odor, moisture absorption.

  Chemical properties

  (1) in acidic solution, thioacetamide hydrolyzes to form H2S, which can replace H2S to precipitate group II cations. The hydrolysis reaction is as follows:

  CH3CSNH2 + H2O CH3CONH2 + H2S

  After boiling for a long time, CH3CONH2 is further hydrolyzed:

  CH3CONH2 + H2O < = = > CH3COONH4

  (2) in alkaline solution, thioacetamide hydrolyzes to form S2-, which can be used instead of Na2S. The hydrolysis reaction is as follows:

  CH3CSNH2 + 3 oh - < = = > NH3 CH3COO - + + S2 - + H2O

  (3) in ammonia solution, thioacetamide hydrolyzes to form HS-, which can replace (NH4)2S to precipitate group III cations. The hydrolysis reaction is as follows:

  CH3CSNH2 + 2 nh3 < = = > CH3C (NH2) NH + NH + 4 + HS

  The hydrolysis rate of thioacetamide is accelerated with the increase of temperature. The hydrolysis rate is faster in alkaline solution than in acid solution.

  (1) characteristics of thioacetamide as a group reagent:

  (1) it can reduce the emission of toxic H2S gas and reduce the air pollution in the laboratory.

  (2) the precipitation of purer metal sulfide is obtained by means of uniform precipitation, and the co-precipitation is less, which is convenient for separation.

  (3) the reduction of As(V) from thioacetamide to As(III) is fast.

  (4) Sn sulfide precipitation obtained by precipitation Sn(II) with thioacetamide can be dissolved in NaOH or CH3CSNH2+NaOH. The reaction is as follows:

  SNS 2 + 4 oh - < = = > SnO2-2 + SnS22 - + 2 h2o

  (5) Co2+ and Ni2+ react with CH3CSNH2 in NH4+--NH3 solution, and when heated for a long time, it can be precipitated as shop-cos and capital-nis.

  (6) when Cu2+ reacts with thioacetamide in a solution with a pH of less than 1, it is first reduced to Cu+, and then Cu+ and thioacetamide form a complex, which decomposes when heated to form Cu2S precipitation. When the acidity of the solution decreases, Cu2+ and CH3CSNH2 generate a mixture of Cu2S and CuS.

  (7) when Hg2+ reacts with thioacetamide in HCl solution, it often produces a series of intermediate products and precipitates of different colors.

  (2) when using thioacetamide as precipitant, the following points should be noted:

  (1) oxidative substances should be removed in advance to avoid partial oxidation of thioacetamide to SO42- so that the fourth group of cations can precipitate at this time.

  (2) the amount of thioacetamide should be suitably excessive to ensure the complete precipitation of the sulfur substitute.

  (3) precipitation shall be heated in a boiling water bath and heated for an appropriate long time to promote the hydrolysis of thioacetamide so as to ensure the complete precipitation of sulfide.

  (4) after the third group cation precipitation, was left in the solution is quite amount of thioacetamide, in order to avoid premature by oxidation and make the fourth group cation precipitation, should be the fourth group cation analysis immediately.


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