Silicic acid, sodium salt, reaction products with chlorotrimethylsilane and iso-Pr alc.
[CAS 68988-56-7]

Identification

• Classification: Organic raw materials >> Organosilicon compound
• Name: Silicic acid, sodium salt, reaction products with chlorotrimethylsilane and iso-Pr alc.
• CAS Registry Number: 68988-56-7
• EC Number: 273-530-5

Safety Data

• Hazard Symbols: GHS02;GHS07 WarningGHS02
• Risk Statements: H226-H319-H332-H335
• Safety Statements: P210-P233-P240-P241-P242-P243-P261-P264+P265-P271-P280-P303+P361+P353-P304+P340-P305+P351+P338-P317-P319-P337+P317-P370+P378-P403+P233-P403+P235-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335
Flammable liquids	Flam. Liq.	3	H226
Acute toxicity	Acute Tox.	4	H332
Skin irritation	Skin Irrit.	2	H315
Serious eye damage	Eye Dam.	1	H318

Discovery and Applications

Silicic acid, sodium salt, reaction products with chlorotrimethylsilane and iso-propyl alcohol is a modified organosilicon material derived from sodium silicate (the sodium salt of silicic acid) that has been chemically treated with chlorotrimethylsilane (trimethylsilyl chloride, TMCS) and isopropyl alcohol. Rather than representing a single, well-defined molecule, this designation generally refers to a mixture of surface-modified silicate or silica-derived species produced during a silanization process.

The starting material, sodium silicate, consists of polymeric silicate anions built from SiO₄ tetrahedra linked through Si–O–Si bonds. When reacted with chlorotrimethylsilane, hydroxyl groups present on silicic acid or silica surfaces are converted into trimethylsilyl groups:

≡Si–OH + Cl–Si(CH₃)₃ → ≡Si–O–Si(CH₃)₃ + HCl

This reaction replaces hydrophilic silanol groups (Si–OH) with hydrophobic trimethylsilyl functionalities. Isopropyl alcohol commonly serves as a reaction medium, processing aid, or modifier and may participate in partial esterification or alcoholysis reactions during manufacture.

The resulting material contains a siloxane framework with surface-bound trimethylsilyl groups. These groups impart strong hydrophobicity because the exposed methyl substituents reduce the ability of the material to interact with water. Consequently, the product exhibits markedly different surface properties compared with untreated silica or sodium silicate.

Structurally, the material consists of a three-dimensional network of Si–O–Si linkages with varying degrees of trimethylsilyl substitution. Depending on manufacturing conditions, the product may range from partially modified silica to highly surface-treated amorphous silica. The exact composition is often variable and depends on factors such as silicate source, reaction temperature, degree of neutralization, and amount of chlorotrimethylsilane employed.

From a physicochemical standpoint, trimethylsilyl treatment reduces surface energy, decreases moisture adsorption, improves dispersibility in nonpolar media, and increases compatibility with organic polymers. These characteristics make the material useful as a processing additive and filler.

Such modified silicas are widely used in industrial applications including:

* Silicone rubber formulations.
* Sealants and adhesives.
* Paints and coatings.
* Plastics and composites.
* Cosmetic powders and personal-care products.
* Rheology modifiers and anti-caking agents.
* Hydrophobic fillers and reinforcing agents.

Chemically, the siloxane backbone is highly stable, while the Si–O–Si(CH₃)₃ surface groups are resistant to hydrolysis under neutral conditions but may slowly degrade under strongly acidic or strongly alkaline conditions.

The reaction with chlorotrimethylsilane is a classic surface-silylation process. By capping reactive silanol groups, the treatment reduces hydrogen bonding between silica particles, thereby lowering aggregation and improving flow characteristics in powders and dispersions.

Overall, silicic acid, sodium salt, reaction products with chlorotrimethylsilane and iso-propyl alcohol is best described as a hydrophobically modified silicate/silica material containing trimethylsilyl-functionalized siloxane surfaces. It is used primarily as a specialty inorganic-organic hybrid material in coatings, elastomers, adhesives, cosmetics, and polymer formulations where moisture resistance and improved dispersion properties are desired.

References

https://www.epa.gov/tsca-inventory https://www.epa.gov/chemical-data-reporting