Thioacetamide
[CAS# 62-55-5]

Identification

• Classification: Organic raw materials >> Amino compound >> Amide compound
• Name: Thioacetamide
• Synonyms: Ethanethioamide
• Molecular Formula: C₂H₅NS
• Molecular Weight: 75.13
• CAS Registry Number: 62-55-5
• EC Number: 200-541-4
• SMILES: CC(=S)N

Properties

• Density: 1.1±0.1 g/cm³ Calc.^*, 1.37 g/mL (Expl.)
• Melting point: 108 - 112 °C (Expl.)
• Boiling point: 45.3±23.0 °C 760 mmHg (Calc.)^*, 234.1 °C (Expl.)
• Flash point: -18.8±22.6 °C (Calc.)^*
• Solubility: Soluble (water, ethanol) (Expl.)
• Index of refraction: 1.522 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS07;GHS08 Danger
• Risk Statements: H302-H315:-H319:-H350:-H412:
• Safety Statements: P203-P264-P264+P265-P270-P273-P280-P301+P317-P302+P352-P305+P351+P338-P318-P321-P330-P332+P317-P337+P317-P362+P364-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Skin irritation	Skin Irrit.	2	H315
Carcinogenicity	Carc.	1B	H350
Chronic hazardous to the aquatic environment	Aquatic Chronic	3	H412
Eye irritation	Eye Irrit.	2	H319
Eye irritation	Eye Irrit.	2A	H319

Discovery and Applications

Thioacetamide is a small organosulfur compound with the molecular formula C₂H₅NS. It is the sulfur analog of acetamide, in which the carbonyl oxygen atom is replaced by a sulfur atom, forming a thioamide functional group. Structurally, it consists of a methyl group (CH₃–) attached to a thioamide group (–CSNH₂). Thioacetamide appears as a white to gray crystalline solid and has been widely studied due to its chemical reactivity and biological effects.

The compound was first prepared and characterized in the late 19th century during explorations of sulfur analogs of common amides. It can be synthesized via the reaction of acetamide with phosphorus pentasulfide or Lawesson's reagent, which effectively replaces the carbonyl oxygen with a sulfur atom.

Thioacetamide has long been used as a reagent in analytical chemistry. Its principal application is as a source of hydrogen sulfide (H₂S) in qualitative inorganic analysis. Under acidic conditions, thioacetamide hydrolyzes slowly to release H₂S gas, which reacts with metal ions to form metal sulfide precipitates. This controlled release of H₂S makes thioacetamide a convenient alternative to directly bubbling gaseous hydrogen sulfide into solutions, which can be hazardous.

The hydrolysis reaction proceeds as follows:

C₂H₅NS + H₂O → CH₃COOH + H₂S + NH₃

In this process, acetic acid, hydrogen sulfide, and ammonia are formed. The ability of thioacetamide to generate hydrogen sulfide in situ has made it a common reagent in laboratory teaching and classical qualitative inorganic testing schemes.

Beyond its use in analytical chemistry, thioacetamide has been employed in the synthesis of organosulfur compounds and as a sulfur donor in certain metal complex preparations. It can act as a ligand in coordination chemistry and has been investigated in the synthesis of thiazole derivatives.

However, thioacetamide is also known for its hepatotoxic and carcinogenic properties. It has been extensively used as a model compound in toxicological research due to its ability to induce liver injury in laboratory animals. Following metabolic activation in the liver, thioacetamide is converted to reactive metabolites that cause oxidative stress, DNA damage, and liver necrosis. Because of these toxicological effects, it has served as a standard hepatotoxin in studies of liver pathophysiology, fibrosis, and hepatocellular carcinoma in experimental models.

Due to its toxicity, thioacetamide is classified as a possible human carcinogen and should be handled with care. Prolonged or repeated exposure may pose serious health risks, especially by inhalation or ingestion. Appropriate safety measures, such as use of gloves, goggles, lab coats, and working in a fume hood, are essential when handling the compound.

Characterization of thioacetamide includes infrared (IR) spectroscopy, which shows characteristic bands for the thioamide group, including C=S and N–H stretching vibrations. Proton and carbon-13 nuclear magnetic resonance (NMR) spectroscopy are also used to confirm the presence of the methyl group and the thioamide backbone. The melting point is typically around 113 °C.

In summary, thioacetamide is a well-established compound with important applications in analytical chemistry as a controlled hydrogen sulfide source and in experimental toxicology as a model hepatotoxin. Despite its utility, its toxic nature requires careful handling and regulatory compliance in research and laboratory environments.

References

2005. Blockade of intrahepatic adenosine receptors improves urine excretion in cirrhotic rats induced by thioacetamide. Journal of Hepatology, 42(5).
DOI: 10.1016/j.jhep.2004.12.023

2003. Overexpression of Thioredoxin Prevents Acute Hepatitis Caused by Thioacetamide or Lipopolysaccharide in Mice. Hepatology (Baltimore, Md.), 37(5).
DOI: 10.1053/jhep.2003.50203

2003. The effects of early and late administration of inhibitors of inducible nitric oxide synthase in a thioacetamide-induced model of acute hepatic failure in the rat. Journal of Hepatology, 38(5).
DOI: 10.1016/s0168-8278(03)00050-3