Dibutyltin dichloride sits in the middle of the butyltin family: one butyl group short of the biocidal tributyltins that were largely banned, one butyl group longer than the monobutyltins used in glass coating. That position explains both what it is used for and why it is regulated – and the regulation, not the chemistry, is usually what decides whether a buyer can use it. This guide covers the properties, the family it belongs to, its legitimate applications and the restrictions that apply. The specification is on the dibutyltin dichloride product page.
Hazard and regulatory notice. Dibutyltin dichloride is toxic and is identified in the EU as a substance of very high concern on reproductive toxicity grounds. Organotin compounds are restricted in articles and consumer products in several markets, and many biocidal uses have been withdrawn. Confirm that your intended end use is lawful in your destination market before ordering – several applications that were routine in the 1990s are no longer permitted.
Identity and properties
| Property | Value | Practical significance |
|---|---|---|
| Formula | C8H18Cl2Sn | A diorganotin dihalide – two butyl groups and two chlorides on the tin centre |
| CAS | 683-18-1 | – |
| Molecular weight | About 304 | Tin is about 39% of the molecule by mass, which is why tin content is the analytical check |
| Appearance | White to slightly yellowish crystalline solid | Yellowing or wetness indicates hydrolysis – the material fumes and degrades in moist air |
| Melting point | About 39 deg C | A solid at room temperature and a liquid when warm: it is handled and dosed as a melt |
| Boiling point | About 135 deg C at 10 mmHg | Purified by vacuum distillation; excessive heat causes decomposition |
| Density | About 1.4 g/mL | Volume-to-mass conversion in charging |
| Refractive index | About 1.4991 | Identity check on the melt |
| Water solubility | About 320 mg/L | Low, but enough that hydrolysis in contact with water is the main stability issue |
| Hydrolysis behaviour | Reacts with water releasing hydrogen chloride | Forms dibutyltin oxide species; this is why the material must be kept dry and why the “main content” figure is always below 100% |
The butyltin family, and why the number of butyl groups matters
| Compound | CAS | Groups on tin | Main use | Regulatory status |
|---|---|---|---|---|
| Monobutyltin trichloride (MBTCl) | 1118-46-3 | One butyl, three chlorides | Glass coating precursor – pyrolytic tin oxide on containers and flat glass | Less restricted than the higher butyltins, since it is largely consumed in a closed process |
| Dibutyltin dichloride (DBTC) | 683-18-1 | Two butyls, two chlorides | Intermediate for PVC stabilisers; also coating and catalytic uses | SVHC in the EU on reproductive toxicity grounds; restricted in articles and consumer products |
| Tributyltin chloride (TBTC) | 1461-22-9 | Three butyls, one chloride | Formerly antifouling biocides | Largely banned internationally as a marine antifoulant; severely restricted elsewhere |
| Tetrabutyltin | 1461-25-2 | Four butyls | Precursor to the other butyltins | Restricted; an intermediate rather than an end product |
The general pattern in organotin chemistry: biocidal activity rises with the number of butyl groups, and so does the regulatory burden. The monobutyltins are mostly consumed in industrial coating processes; the tributyltins were the potent antifoulants that got banned; the dibutyltins sit in the middle, still used as stabiliser intermediates but under increasing restriction.
How it is made
| Route | Chemistry | Why the buyer cares |
|---|---|---|
| Kocheshkov redistribution | Tetrabutyltin reacted with tin tetrachloride to give dibutyltin dichloride in the required ratio | The dominant industrial route; product distribution depends on the exact stoichiometry, which is why “main content” is specified rather than assumed |
| Grignard route | Butylmagnesium chloride reacted with tin tetrachloride | Used where specific organotin ratios are wanted; higher cost and more complex handling |
| Direct synthesis | Tin metal, butyl chloride and a catalyst | Less common; selectivity is the challenge |
Reading the specification
| Parameter | Typical value | What it is controlling |
|---|---|---|
| Main content | 96 – 99% | The organotin content. The balance is largely hydrolysis products and hydrogen chloride from handling, which is why the figure is not 100% |
| Tin content | 38 – 40% | The independent analytical confirmation. Theoretical tin for pure DBTC is about 39%, so a tin figure outside this band means the main-content claim is wrong |
| Appearance | White to slightly yellowish crystal | Wetness or strong yellowing means hydrolysis has already started |
| Melting point | About 39 deg C | Confirms identity and tells you what temperature the drum must reach to be pourable |
| Density and refractive index | About 1.4 and 1.4991 | Identity checks; the refractive index is measured on the melt |
| Water solubility | About 320 mg/L | Sets the hydrolysis risk and the handling of spillage |
The tin content is the parameter worth checking first on arrival. It is a direct, independent measure of how much organotin is actually in the drum, and it catches both under-assay and excessive hydrolysis in one number.
Applications
| Application | Role of DBTC | Status to confirm |
|---|---|---|
| PVC heat stabiliser intermediate | Converted into dibutyltin maleate, laurate or mercaptide, which are the actual stabilisers used in PVC processing | Organotin stabilisers are restricted or withdrawn in many consumer, food-contact and potable-water applications. Industrial pipe, profile and film uses differ by market – confirm yours |
| Glass coating precursor | Pyrolytic precursor in tin oxide coatings on glass containers, providing hot-end lubricity and strength | Industrial closed-process use; the main legitimate volume application in many regions |
| Catalyst | Organotin catalysis in esterification and transesterification, and in some urethane systems | Some catalyst uses are restricted; confirm per market and application |
| Biocide and preservative | Antifungal and antibacterial action in industrial preservation | The most tightly controlled area – biocidal uses require authorisation and many have been withdrawn |
| Analytical reagent | Derivatising agent and reference in tin analysis | Laboratory scale; disposal and waste rules apply |
Regulatory position in more detail
| Framework | What applies | Practical consequence |
|---|---|---|
| EU REACH – candidate list | Listed as a substance of very high concern on reproductive toxicity grounds | Supply triggers communication obligations; use may require authorisation depending on the application |
| EU REACH – Annex XVII | Organotin compounds restricted in articles and consumer products above defined thresholds | The limit applies to your finished article, not only to the raw material you buy |
| Biocidal Products Regulation | Biocidal products require authorisation for each product type | Determine whether your application is a biocidal use at all – a stabiliser intermediate usually is not, but the classification must be established rather than assumed |
| China and other Asian markets | Listed as a hazardous chemical with transport and storage requirements | Confirm the classification and any use restriction in the destination |
| Marine antifouling | Tributyltin antifoulants are banned under international convention | DBTC is not a substitute route to that use – it would be an unlawful application |
| Transport | Toxic organotin; classification and packing group per the applicable regulations | A material that melts near 39 deg C also needs temperature-aware shipping in hot climates |
Handling
| Point | Requirement |
|---|---|
| Moisture | Keep sealed and dry. On contact with water or moist air it hydrolyses, releasing hydrogen chloride and forming oxide species |
| Drum warming | Heat gently and evenly to melt before use – it is solid below about 39 deg C. Local overheating degrades the product and accelerates corrosion of the drum |
| Materials | Stainless steel or lined equipment for melts; avoid moist air above open vessels |
| PPE | Chemical-resistant gloves, face shield and closed handling. Organotins are absorbed and are reproductive toxicants – treat skin contact as a serious exposure |
| Spillage | Absorb, do not wash into drains; the material has finite water solubility and is toxic to aquatic life |
| Packaging | 25 kg plastic drums. The closure and liner must suit a material that can melt in transit in warm climates |
For the family comparison see butyltin compounds compared, and for the monobutyltin used in glass coating see monobutyltin trichloride.
Frequently asked questions
Is dibutyltin dichloride the same as a PVC stabiliser?
No – it is the intermediate from which stabilisers are made. DBTC is reacted with a carboxylic acid or a mercaptan to produce dibutyltin maleate, laurate or mercaptide, and those are what go into the PVC formulation.
Why is the main content only 96-99% and not higher?
Because the material hydrolyses readily and the specification allows for the hydrolysis products and residual hydrogen chloride that come with handling. The tin content provides the independent check on how much organotin is really present.
Can it still be used as a biocide?
Only where the specific use is authorised in that market. Many biocidal uses of dibutyltin compounds have been withdrawn or restricted, and assuming the old approvals still apply is a compliance risk.
What should I check before buying?
That your end use is lawful in your destination, that your downstream article meets the organotin restriction thresholds, and that your storage and drum-warming arrangements do not cause hydrolysis. Then check the tin content on arrival.