Thiourea dioxide
[CAS# 1758-73-2]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Oxides and peroxides >> Non-metal oxides and peroxides
• Name: Thiourea dioxide
• Synonyms: Thiourea S,S-dioxide; Aminoiminomethanesulfinic acid; Formamidinesulfinic acid; Formamidine sulfinate
• Molecular Formula: CH₄N₂O₂S
• Molecular Weight: 108.11
• CAS Registry Number: 1758-73-2 (4189-44-0)
• EC Number: 217-157-8
• SMILES: C(=N)(N)S(=O)O

Properties

• Density: 2.3±0.1 g/cm³, Calc.^*, 1.68 g/mL (Expl.)
• Melting point: 124-127 °C (decomp.) (Expl.)
• Index of Refraction: 1.805, Calc.^*
• Boiling Point: 355.3±25.0 °C (760 mmHg), Calc.^*
• Flash Point: 168.7±23.2 °C, Calc.^*
• Water solubility: 30 g/L (20 °C)

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

Safety Data

• Hazard Symbols: GHS02;GHS05;GHS07;GHS08 Danger
• Risk Statements: H251-H252-H302+H332-H302-H315-H318-H319-H332-H335-H373
• Safety Statements: P235-P260-P261-P264-P264+P265-P270-P271-P280-P301+P317-P302+P352-P304+P340-P305+P351+P338-P305+P354+P338-P317-P319-P321-P330-P332+P317-P337+P317-P362+P364-P403+P233-P405-P407-P410-P413-P420-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335
Self-heating substances or mixtures	Self-heat.	1	H251
Self-heating substances or mixtures	Self-heat.	2	H252
Acute toxicity	Acute Tox.	2	H330
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Serious eye damage	Eye Dam.	1	H318
Acute toxicity	Acute Tox.	4	H332

• Transport Information: UN 3341

Discovery and Applications

Thiourea dioxide (TUD), with the chemical formula CH4N2O2S, is a white crystalline compound that has a wide range of applications in both industrial and laboratory settings. It is primarily used as a reducing agent, but its versatility extends to applications in dyeing, textile processing, and as a stabilizer in some chemical reactions. Thiourea dioxide is notable for its ability to selectively reduce certain chemicals without causing significant side reactions, making it highly valuable in various chemical syntheses and industrial processes.

Thiourea dioxide was first synthesized in the early 20th century when chemists were exploring potential alternatives to conventional reducing agents, such as sodium borohydride and hydrosulfite. The compound was initially recognized for its potential to reduce carbonyl groups and azo compounds, leading to its use in textile dyeing processes. Over time, researchers discovered that thiourea dioxide could also serve as a more environmentally friendly alternative to other, more toxic reducing agents, which contributed to its widespread adoption.

One of the key applications of thiourea dioxide is in the textile industry, where it is used as a reducing agent in the process of dyeing and printing fabrics. In this context, it is particularly useful for the reduction of dyes, helping to brighten colors and increase the intensity of prints. Thiourea dioxide is favored over other chemical reducers, such as sodium hydrosulfite, due to its more selective action, which reduces the likelihood of unwanted side reactions during the dyeing process. Additionally, thiourea dioxide is less hazardous than other conventional reducing agents, making it safer for workers and more environmentally friendly.

Beyond its use in textiles, thiourea dioxide is widely employed in organic synthesis, particularly in reactions that require selective reduction. It is used in the reduction of nitro compounds to amines, aldehydes to alcohols, and in the synthesis of certain pharmaceutical compounds. Its ability to selectively reduce carbonyl groups while avoiding over-reduction makes it highly valuable in producing chemicals with specific functional groups intact. Thiourea dioxide is also employed as a stabilizer in certain chemical processes, where it helps maintain the stability of sensitive compounds and prevent unwanted degradation.

Another area where thiourea dioxide is applied is in the production of photographic chemicals. It has been used in the development and processing of photographic films and prints, where it acts as a stabilizer and reducing agent, helping to enhance image quality and prevent fading. Thiourea dioxide's role in the preservation of photographic images is particularly important in the creation of archival-quality materials, where long-term stability is crucial.

In recent years, there has been growing interest in the environmental applications of thiourea dioxide. Due to its ability to reduce pollutants and break down harmful chemicals, it is being studied for use in environmental remediation. Thiourea dioxide's ability to treat wastewater and reduce contaminants, such as heavy metals and organic pollutants, positions it as a potential agent for improving water quality in industrial and municipal settings.

In summary, thiourea dioxide is a highly versatile chemical with applications spanning various industries, from textiles and photography to organic synthesis and environmental remediation. Its selective reducing properties, safety profile, and environmental benefits make it a valuable tool in modern industrial and laboratory processes.

References

1959. Aromatische Nitroverbindungen lassen sieh in Urin. Fresenius' Zeitschrift für analytische Chemie, 166(5).
DOI: 10.1007/bf00460480

2023. Radical approaches to C-S bonds. Nature Reviews Chemistry, 7(7).
DOI: 10.1038/s41570-023-00505-x

2024. Preparation of recycled dissolving pulp from waste dark-color dyed cotton-polyester denim fabrics with sulphur dyes. Cellulose, 31(12).
DOI: 10.1007/s10570-024-06122-1