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Identification, Synonyms & Grade Specification
Name (IUPAC / Common):
Thiourea dioxide (also spelled “thiourea dioxide” or “thiourea S,S-dioxide”)
Formamidine sulfinic acid (common synonym)
Amino(imino)methanesulfinic acid
Aminoiminomethanesulfinic acid
Other synonyms listed: Thiourea S,S-dioxide; Thiurea dioxide; “Tiourea dioxide” (less common)
CAS Registry Number(s):
CAS: 1758-73-2 is the primary accepted CAS for thiourea dioxide.
Some supplier sources list 4189-44-0 as an alternate or older number.
Thus one should verify the grade and CAS on supplier certificates.
Chemical Formula & Molecular Weight:
Formula: CH₄N₂O₂S
Molecular weight: approximately 108.12 g mol⁻¹
Grade / Purity Spec: “90 %” grade:
Industrial suppliers list a 90 % grade of thiourea dioxide (often referenced in textile/pulp applications) with key claims of “better thermal stability and stronger reducing properties”.
For example: a specification sheet from a supplier describes “Thiourea Dioxide, Formamidine Sulfinic Acid 80 %, 90 %, 99 %” and for 90 % grade the appearance is white crystals/powder, purity ≥ 90% and moisture/impurity limits accordingly.
Note: When using 90 % grade, the balance (≈ 10 %) may consist of moisture, by-products, inert matter or stabilisers, so for highly critical applications (fine chemicals) higher purity (95–99%) may be used instead.
Physical & Chemical Properties
Appearance & basic physical data:
Solid: white to light-yellow crystalline powder, odorless.
Melting point (decomposition) ~124-127 °C (many sources say ~126 °C)
Density: one source gives 1.703 g cm⁻³ at 20 °C.
Solubility: ~26.7–30 g L⁻¹ in water at ~20 °C.
pH of aqueous (~10 g L⁻¹) ~3.5-5.5 (some sources ~4) at 20 °C.
Partition coefficient (log P) ~ –2.12 in one source.
Other: estimated pKa for the sulfinic acid form ~2.4 ± 0.1.
Chemical stability & reactivity:
The compound is described as a “reducing agent and a derivative of sulfinic acid (a weak inorganic acid)”.
According to one source: “very stable even in 20-30 ° C aqueous solution; under heating or alkaline conditions it decomposes gradually”.
Decomposes exothermically above ~126 °C with emission of noxious gases (sulfur oxides, ammonia, CO, nitrogen oxides, H₂S) according to one chemical summary.
Incompatibilities: strong oxidising agents, strong bases; may decompose on moist air or water.
Structural / mechanistic remarks:
Crystal structure: for “thiourea dioxide”, the following structural features are reported—S-C ~186 pm, C–N ~130 pm, S–O ~149 pm (in gas/crystal); the sulfur centre is pyramidal; the bonding is described via a dipolar resonance structure with contributions of multiple bonding between C and N.
It tautomerises in water or DMSO to the sulfinic acid form: (H₂N)HN=CS(O)(OH) (“formamidine sulfinic acid”).
Production / Synthesis Methods
Industrial synthesis:
The main industrial route: oxidation of Thiourea ((NH₂)₂CS) with hydrogen peroxide (H₂O₂). For example: (NH₂)₂CS + 2 H₂O₂ → (NH)(NH₂)CSO₂H + 2 H₂O.
Control of pH (~3-5) and low temperature (<10 °C) is beneficial to prevent side-reactions (e.g., disulfide formation).
Alternative oxidants: chlorine dioxide is mentioned as a route.
One Chinese supplier description: “Distilled water and thiourea added, H₂O₂ added dropwise at ~8-10 °C, pH 2-3, after reaction product cooled to ~5 °C, centrifuged, dried.”
Quality control / specification considerations:
Purity: Analytical titration methods are used. One source gives ≥99.0 % for fine-chemical (not specifically 90 % grade) with residual thiourea ≤0.10 %.
Moisture content, iron/metal impurities, residual sulphate levels etc are typically specified in full specs.
For the 90 % grade, the impurity profile (10 %) may include moisture, minor inorganic salts, un-reacted starting material, etc, so user should define specification (e.g., “≥90.0% min assay”, “Moisture ≤ …%”, “Residue on ignition ≤ …%”, etc).
Mechanism of Action / Reducing Behaviour
Reductive bleaching / reducing agent behaviour:
Thiourea dioxide acts as a reducing agent rather than as an oxidiser.
It is used to decolourise or bleach substrates by chemical reduction of chromophores (often in textile or pulp contexts) rather than via oxidation.
Although some sources describe the compound as “neither oxidation nor reduction in the solid state” (see below), its reducing potential becomes manifest under certain conditions (e.g., heating, alkaline medium).
For example: “In fact … its solubility in 1 L water is 26.7 g and under the action of alkali can be decomposed into urea and sodium sulfite” thus showing its latent reducing power.
One supplier description: “Has high reduction potential” and “better thermal stability and stronger reducing properties compared with sodium hydrosulfite” (Na₂S₂O₄) when used in textile bleaching.
Mechanistic notes (academic):
The tautomeric sulfinic acid form (formamidine sulfinic acid) is implicated in reduction: H₂N–HN= C–S(O)OH.
In aqueous solution the equilibrium shifts, and the compound can release sulfoxylic species that reduce azo, nitro, and other chromophoric groups.
In textile bleaching, the mechanism is not always fully elucidated, but the compound reduces disulfide or oxidised dye intermediates, enabling decolourisation.
Some research indicates that it can reduce nitro-aldehydes and nitroketones to nitro-alcohols.
Thermal/alkaline decomposition pathway (leading to reductive species):
Under heating and/or alkaline conditions, thiourea dioxide decomposes, releasing urea and sulfoxylic acid, which act as reducing intermediates.
The decomposition/side-products may include sulphur dioxide, hydrogen sulphide, ammonia, etc when improperly handled (see safety section).
Applications & Uses
Textile Industry:
One of the major uses for the 90 % grade is in reductive bleaching of textiles (cotton, wool, silk) and in sulphur dye reduction operations.
Supplier commentary: “used to replace sodium hydrosulfite as a replacement; has better thermal stability and stronger reducing properties.”
It is used for stripping of dyes, machine-cleaning agents in textile mills, bleaching of cotton, man-made fibres, wood fibre, artificial silk, artificial wool.
Paper / Pulp Industry:
Used as a de-inking agent for waste paper and for reductive bleaching of pulp.
Leather / Photographic / Precious Metal Recovery & Organic Synthesis:
Leather processing: reducing agent for cleaning, stripping dyes.
Photographic industry: for decolourisation or bleaching of photographic materials.
Precious metal recovery/separation: Some mention that thiourea dioxide is used for reduction in metal recovery contexts.
Organic synthesis: used in the reduction of certain aromatic nitroaldehydes/nitroketones to nitro-alcohols.
Advantages in industrial use:
Compared to sodium hydrosulfite, it is claimed to have better thermal stability (less premature decomposition) and easier operation.
In aqueous solution at moderate temperature, it is reasonably stable, facilitating handling and storage.
SAFETY INFORMATION ABOUT THIOUREA DIOXIDE 90%
First aid measures:
Description of first aid measures:
General advice:
Consult a physician.
Show this safety data sheet to the doctor in attendance.
Move out of dangerous area:
If inhaled:
If breathed in, move person into fresh air.
If not breathing, give artificial respiration.
Consult a physician.
In case of skin contact:
Take off contaminated clothing and shoes immediately.
Wash off with soap and plenty of water.
Consult a physician.
In case of eye contact:
Rinse thoroughly with plenty of water for at least 15 minutes and consult a physician.
Continue rinsing eyes during transport to hospital.
If swallowed:
Do NOT induce vomiting.
Never give anything by mouth to an unconscious person.
Rinse mouth with water.
Consult a physician.
Firefighting measures:
Extinguishing media:
Suitable extinguishing media:
Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide.
Special hazards arising from the substance or mixture
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas
Advice for firefighters:
Wear self-contained breathing apparatus for firefighting if necessary.
Accidental release measures:
Personal precautions, protective equipment and emergency procedures
Use personal protective equipment.
Avoid breathing vapours, mist or gas.
Evacuate personnel to safe areas.
Environmental precautions:
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
Methods and materials for containment and cleaning up:
Soak up with inert absorbent material and dispose of as hazardous waste.
Keep in suitable, closed containers for disposal.
Handling and storage:
Precautions for safe handling:
Avoid inhalation of vapour or mist.
Conditions for safe storage, including any incompatibilities:
Keep container tightly closed in a dry and well-ventilated place.
Containers which are opened must be carefully resealed and kept upright to prevent leakage.
Storage class (TRGS 510): 8A: Combustible, corrosive hazardous materials
Exposure controls/personal protection:
Control parameters:
Components with workplace control parameters
Contains no substances with occupational exposure limit values.
Exposure controls:
Appropriate engineering controls:
Handle in accordance with good industrial hygiene and safety practice.
Wash hands before breaks and at the end of workday.
Personal protective equipment:
Eye/face protection:
Tightly fitting safety goggles.
Faceshield (8-inch minimum).
Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).
Skin protection:
Handle with gloves.
Gloves must be inspected prior to use.
Use proper glove
removal technique (without touching glove's outer surface) to avoid skin contact with this product.
Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices.
Wash and dry hands.
Full contact:
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
Splash contact
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
It should not be construed as offering an approval for any specific use scenario.
Body Protection:
Complete suit protecting against chemicals, The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.
Respiratory protection:
Where risk assessment shows air-purifying respirators are appropriate use a fullface respirator with multi-purpose combination (US) or type ABEK (EN 14387) respirator cartridges as a backup to engineering controls.
If the respirator is the sole means of protection, use a full-face supplied air respirator.
Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).
Control of environmental exposure
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
Stability and reactivity:
Chemical stability:
Stable under recommended storage conditions.
Incompatible materials:
Strong oxidizing agents:
Hazardous decomposition products:
Hazardous decomposition products formed under fire conditions.
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas.
Disposal considerations:
Waste treatment methods:
Product:
Offer surplus and non-recyclable solutions to a licensed disposal company.
Contact a licensed professional waste disposal service to dispose of this material.
Contaminated packaging:
Dispose of as unused product
