Reaxis®  C188 - Stannous Oxide

REAXIS® C188 (Stannous Oxide), commonly referred to by its formula of SnO and frequently called Tin(II) Oxide, is a high metal content inorganic stannous tin catalyst that is used in a wide range of esterification reactions. REAXIS® C188 is manufactured with low stannic tin content while maximizing active stannous tin. REAXIS® C188 is an ideal alternative for commonly used organotin catalysts such as REAXIS® C248 (Dibutyltin oxide) and monobutyltin oxide.

REAXIS® C188 has a lower toxicity profile when compared to organotins given its inorganic tin composition. REAXIS® C188 is supplied as a free-flowing white solid with a narrow particle size distribution range and low moisture content. Similar inorganic tin products to REAXIS® C188 include, REAXIS® C162 (Stannous Chloride Anhydrous), REAXIS® C129 (Stannous Octoate) and REAXIS® C160 (Stannous Oxalate). REAXIS® C188 is present on most international regulatory lists, making it an ideal choice when developing global formulations. 


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Technical Information

  • Product Category Inorganic Tin

  • Chemical Name Stannous Oxide

  • CAS Number 21651-19-4

Typical Specifications

Parameter Range
Stannous Tin (%) 85.2 Min
Tin (IV) Content (%) 0.7 Max

International Regulatory Listings

  • TSCA (US) Yes

  • DSL (Canada) Yes

  • AICS (Australia) Yes

  • KECI (South Korea) Yes

  • IECSC (China) Yes

  • ENCS (Japan) Yes

  • TCSI (Taiwan) Yes

  • NZloC (New Zealand) Yes

  • PICCS (The Philippines) Yes

  • NDSL (Canada) No

  • REACH (EU) No


REAXIS® C188 is primarily used as a homogeneous catalyst for synthesizing various monomeric and polymeric ester-based products such as nonionic surfactants, polyester polyols, and plasticizers. Typical end-use markets for REAXIS® C188 include plastics, coatings, glass compounds, and personal care. Its inorganic tin nature makes it an ideal catalyst for applications demanding the use of low toxicity raw materials.



Due to its high tin concentration and small ligand, REAXIS® C188, Stannous Oxide is a very active esterification catalyst with comparable reactivity to common organotin catalysts such as dibutyl and monobutyl tin oxides.  Given its inorganic nature, REAXIS® C188 is stable at the high reaction temperatures typical of many esterification reactions. Also, the use of REAXIS® C188 can result in final ester products with low color.  


Package & Storage

  • 55 lb (25 kg) pail

REAXIS® C188 should be stored in the original packaging.  The container should be closed tightly after each use to maximize shelf life. Characteristic of most inorganic tins (Sn(II)), the primary cause of instability would be oxidation.  


Safety and Handling

Before use of Reaxis products please refer to the relevant Safety Data Sheet (SDS) for safety and toxicological data as well as for the information on proper transportation, storage, and use. SDSs are available by request via our web site, contacting your local representative, or emailing direct to

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This information is provided to the best of our knowledge but without obligation. Reaxis is not liable for any incorrect or missing information. This data sheet becomes invalid upon publication of a new version. Please contact us for the latest version.

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