The butyltins are a family where the number of butyl groups on the tin atom predicts almost everything: what the compound is used for, how toxic it is, and how tightly it is regulated. Monobutyltins coat glass. Dibutyltins stabilise PVC. Tributyltins were the marine antifoulants that got banned worldwide. Buying one in place of another is therefore not a grade substitution – it is a different substance with a different legal position.
The three you will meet commercially
| Compound |
CAS |
Tin centre |
Tin content |
Physical form |
Main use |
| Monobutyltin trichloride (MBTCl) |
1118-46-3 |
One butyl, three chlorides |
About 38% |
Colourless to pale liquid |
Hot-end coating precursor for glass containers and flat glass |
| Dibutyltin dichloride (DBTC) |
683-18-1 |
Two butyls, two chlorides |
About 39% |
White crystalline solid, melts about 39 deg C |
Intermediate for PVC heat stabilisers; coating and catalytic uses |
| Tributyltin chloride (TBTC) |
1461-22-9 |
Three butyls, one chloride |
About 37% |
Liquid to low-melting solid |
Formerly antifouling biocides – now largely banned |
| Tetrabutyltin |
1461-25-2 |
Four butyls |
About 34% |
Liquid |
Precursor for making the other butyltins |
Biocidal potency and regulatory burden rise together
| Family member |
Biocidal activity |
Regulatory position |
What that means commercially |
| Monobutyltin |
Low |
Least restricted of the family |
Largely consumed inside a closed industrial process as a coating precursor, so exposure and end-use concerns are limited |
| Dibutyltin |
Moderate |
SVHC in the EU on reproductive toxicity grounds; restricted in articles and consumer products |
Still used as an intermediate, but the downstream article has to meet organotin limits – and some end uses have been withdrawn |
| Tributyltin |
High – this is why it worked |
Banned as a marine antifoulant under international convention; severely restricted elsewhere |
Not available for its historic use; any remaining uses are narrow and authorised |
| Tetrabutyltin |
Low as supplied, but a precursor |
Restricted |
An intermediate for producing the others rather than an end product |
The pattern is not accidental. Increasing butyl substitution increases lipophilicity and biological activity – which is precisely what makes a molecule a good biocide, and precisely what makes it a regulatory problem. The family’s history is the standard example of a useful class being withdrawn compound by compound as the hazard became clear.
Choosing between them requires knowing the application
| If the job is… |
The family member |
Why not the others |
| Tin oxide coating on a glass container |
Monobutyltin trichloride |
DBTC would put two butyl groups into a process designed around one, changing the film chemistry and adding regulatory burden |
| Making a PVC heat stabiliser |
Dibutyltin dichloride |
MBTCl does not give the same stabiliser structure; TBTC is banned for biocidal and restricted for other uses |
| Marine antifouling |
None of them |
The tributyltin route is banned; the answer is a copper or silicone foul-release system, not an organotin |
| Industrial preservation |
Usually not an organotin any more |
Biocidal approvals have been withdrawn for many uses; alternatives such as isothiazolinones or DBNPA are the mainstream |
How they are made, in one paragraph each
| Product |
Route |
Note |
| MBTCl |
Butyltin trichloride from tin tetrachloride and a butyl source, or by redistribution |
Supplied as a liquid; the dominant application is glass coating, where it is vapourised and pyrolysed |
| DBTC |
Kocheshkov redistribution of tetrabutyltin with tin tetrachloride |
The ratio of the two feeds sets the product distribution, which is why “main content” is specified at 96-99% rather than assumed |
| TBTC |
Redistribution or Grignard routes |
Production continues for the remaining authorised uses, but the historic antifouling market is gone |
What to check before switching family members
| Check |
Why |
| That the end use is lawful for the specific compound |
Approvals and restrictions are per substance and per use, not per family |
| The organotin limit on the finished article |
Restrictions in several markets apply to the article, not the raw material |
| Physical handling differences |
MBTCl is a liquid; DBTC melts near 39 deg C and hydrolyses readily. The plant equipment is not interchangeable |
| Tin content as the analytical check |
All three sit around 34-39% tin, so a tin figure confirms which compound was actually supplied |
| Hydrolysis behaviour |
All the chlorides fume and degrade in moist air; DBTC is the most obviously affected because it is a solid that can be seen to wet and yellow |
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