DOTL

Overview

DOTL — dibutyltin diacetate, CAS 1067-33-0 — is the long-pot-life counterpart to DBTDL in the organotin condensation-cure catalyst family. Same tetravalent Sn(IV) chemistry, but with two acetate ligands instead of laurate, the resulting catalyst is approximately 30–50% slower than DBTDL at equivalent loading. Molecular formula C₁₂H₂₄O₄Sn, molecular weight 351.0 g/mol, supplied as a clear pale-yellow to amber liquid at ≥98% active content with tin assay 33.0–34.0% — substantially higher than DBTDL's 18% on a mass basis because acetate is far lighter than laurate.

The acetate ligand is what differentiates DOTL operationally. Acetate is a smaller, more electron-donating carboxylate than laurate, paradoxically reducing the Lewis acidity of the tin centre. The benefit is process latitude: formulators get a longer pot-life and tack-free window without dropping tin content low enough to risk under-cure in deep sections. The drawback is acetate byproduct release on cure (mild vinegar odour, possible copper or marble staining if applied to those substrates).

DOTL operates by the same Lewis-acid catalysis mechanism as DBTDL — coordination to silanol oxygen, activation for nucleophilic attack by alkoxysilane crosslinker, alcohol byproduct release. The rate constant is approximately 0.5–0.7× that of DBTDL at equivalent molar concentration, giving tack-free times of 60–120 minutes at 23°C and 50% RH at 0.20% loading in alkoxy-cure RTV-1 (versus 30–60 minutes for DBTDL at the same loading). This is the catalyst of choice when a formulation requires extended hand-tooling time — large bead architectural sealants, cast-in-place RTV-2 mould rubber, production lines where slow tack-free is acceptable but skin-over within the catalyst-to-skin window must be predictable.

Like DBTDL, DOTL poisons platinum addition-cure systems at ppm levels — segregate handling and metering. REACH compliance: DOTL (CAS 1067-33-0) is REACH-registered for industrial catalyst use; the 2010 Annex XVII restrictions target skin-contact and food-contact articles, not industrial silicone catalysts. Avoid DOTL for sealants on copper, brass, marble, or carbonate stone — the acetate byproduct corrodes these substrates; specify TBT or TET titanate dealcoholisation cure for those applications.

Technical Specifications

Applications

RTV-2 Cast-in-Place Mould Rubber

The largest application — prototype tooling, decorative resin casting moulds, candle moulds, food-contact silicone moulds. DOTL at 0.20–0.40% paired with TEOS or ethyl-silicate-40 gives a 45–90 minute pot-life and 24-hour cure, allowing the moulder to mix, degas, pour, and register the master without rushing.

Hand-Tooled Architectural Sealants

Large building joints, expansion seal cast in place, vertical-bond overhead applications. DOTL at 0.10–0.20% paired with methyltrimethoxysilane gives a 60–90 minute working time before skin formation begins.

Alkyd Resin Transesterification

200–230°C process uses DOTL at 0.05–0.15% on resin solids — the higher reaction temperature compensates for the lower intrinsic catalyst activity, giving an acceptable rate while reducing residual catalyst activity in the finished resin.

Polyurethane-Modified Alkyds

DOTL at 0.02–0.08% for the urethane formation step before alkyd transesterification, leveraging its lower activity to suppress side reactions.

Selection Guide vs Other Catalysts

Choose DOTL over DBTDL when: extended pot-life or hand-tooling window matters more than peak cure speed; cast-in-place RTV mould-making (45–90 min open time before skin); large architectural sealant beads (60+ min before tooling resistance climbs); slow-cure dental and prosthetic silicones. Choose DBTDL when: fastest possible skin formation is needed (vertical applications, production-line robotic dispensing, thin-section bonding).

Equivalent Grades

• TIB Chemicals TIB Kat 233 — German specialty supplier
• Evonik TIB Kat 233 — European equivalent
• Galata Catalyst T-1 — North American equivalent
• Generic DOTL — Chinese commodity grade ≥98%