TRIMETHYLSILANOL

Trimethylsilanol is a colorless, volatile, highly flammable organosilicon liquid with formula (CH₃)₃SiOH, molecular weight 90.20 g/mol, boiling point 84–99°C, and flash point approximately 4°C; it is the simplest silanol and the only possible monohydroxy derivative of trimethylsilane, as the three methyl groups leave exactly one silicon valence position for the hydroxyl group.
Trimethylsilanol is the most important intermediate in the organosilicon industry, used in the production of silicone oils, silicone rubbers, and silicone resins, as a blocking agent for polysiloxane chain ends, as a hydrophobic coating agent for silicate surfaces, and as a silylating reagent in organic synthesis.
Trimethylsilanol is classified under GHS with Signal Word Danger (H225, H332, H412) and arises naturally as the primary volatile degradation product of polydimethylsiloxane (PDMS) silicones in detergents, cosmetics, and industrial silicone materials.

CAS Number: 1066-40-6
EC Number: 213-914-1
Molecular Formula: C₃H₁₀OSi
Molecular Weight: 90.20 g/mol

Synonyms: Hydroxytrimethylsilane, Trimethylsilanol, TMS-OH, TMSOH, Silanol trimethyl-, Silanol 1,1,1-trimethyl-, Hydroxy(trimethyl)silane, Trimethylhydroxysilane, Trimethylsilyl alcohol, n-Propyloxirane, Trimethylsilanole, Trimethylsilanol ≥97.5% GC, Silanole LS 310, Trimethylsilanol tech-95, Medetomidine Impurity 17, CAS 1066-40-6

Trimethylsilanol is the simplest silanol and consists of a silicon atom bonded to three methyl groups and one hydroxyl group.
Trimethylsilanol is a volatile organosilicon liquid with the molecular formula C₃H₁₀OSi and a molecular weight of approximately 90.20 g/mol.

Trimethylsilanol is used to produce hydrophobic coatings on silicate surfaces by reacting with surface silanol groups.
Trimethylsilanol reacts with triethylaluminium to prepare tris(trimethylsiloxy)aluminium, an organoaluminium compound used in chemical synthesis.

Trimethylsilanol behaves as a weak acid and can be converted into sodium trimethylsiloxide through reaction with sodium hydroxide.
Trimethylsilanol undergoes condensation under acidic or alkaline conditions to form siloxane bonds and hexamethyldisiloxane.

Trimethylsilanol can be prepared through the weakly basic hydrolysis of chlorotrimethylsilane, which limits unwanted self-condensation.
Trimethylsilanol occurs in biogas and landfill gas as a volatile product formed through the degradation of silicone materials.

Trimethylsilanol is a colorless and transparent liquid under normal ambient conditions.
Trimethylsilanol has a tetrahedral molecular structure around the central silicon atom.

Trimethylsilanol forms monoclinic crystals when cooled below the melting point.
Trimethylsilanol has a measured boiling point of approximately 97.9°C and a vapor pressure of approximately 19 hPa at 25°C.

Trimethylsilanol has a measured octanol–water partition coefficient of approximately 1.22 at 25°C.
Trimethylsilanol has a measured water solubility of approximately 0.995 g/L at 24°C.

Trimethylsilanol has an enthalpy of vaporization of approximately 45.64 kJ/mol.
Trimethylsilanol displays a characteristic singlet near 0.14 ppm in its proton nuclear magnetic resonance spectrum in CDCl₃.

Trimethylsilanol can be obtained through the basic hydrolysis of hexamethyldisiloxane.
Trimethylsilanol is generated during the hydrolysis of hexamethyldisilazane in humid air together with ammonia.

Trimethylsilanol is produced as a major silicon-containing compound during the steam-assisted thermal degradation of polydimethylsiloxane.
Trimethylsilanol can be monitored as an indicator of hydrolytic degradation in silicone polymers and silicone-based materials.

Trimethylsilanol reacts with atmospheric hydroxyl radicals and is gradually transformed into oxidized organosilicon products.
Trimethylsilanol can be extracted and quantitatively measured at trace and ultratrace levels in water, soil, and sediment samples.

Trimethylsilanol can be measured in occupational indoor air through thermal desorption combined with gas chromatography–mass spectrometry.
Trimethylsilanol is monitored at parts-per-trillion levels in semiconductor cleanrooms because airborne contamination can affect sensitive optical equipment.

Trimethylsilanol can accumulate on optical surfaces and contribute to contamination of scanner lenses used in semiconductor manufacturing.
Trimethylsilanol serves as a reference analyte in analytical methods developed for volatile methylsilicon compounds.

Trimethylsilanol has been investigated as a representative compound for studying the environmental behavior of methylsilanols.
Trimethylsilanol has been evaluated in adsorption and removal systems designed to control volatile silicon compounds in process gases.

Trimethylsilanol has demonstrated antimicrobial activity against Escherichia coli in aqueous laboratory testing.
Trimethylsilanol has also been evaluated for antimicrobial activity against Staphylococcus aureus.

Trimethylsilanol exhibited a reduction of more than eight logarithmic units in viable Escherichia coli under the reported experimental conditions.
Trimethylsilanol showed stronger antimicrobial activity than structurally analogous tert-butanol in comparative laboratory experiments.

Trimethylsilanol provides a model structure for investigating how silicon-bound hydroxyl groups influence biological activity.
Trimethylsilanol can participate in hydrogen-bonding interactions through the hydroxyl group attached to silicon.

Trimethylsilanol can be deprotonated to produce trimethylsiloxide salts that function as organosilicon reagents.
Trimethylsilanol can react with carboxylic acids to generate trimethylsilyl ester derivatives.

Trimethylsilanol is useful in equilibrium studies involving esterification, deprotonation, and silanol reactions in aqueous alcohol solutions.
Trimethylsilanol can be detected by Fourier-transform infrared spectroscopy during studies of gas-phase organosilicon reactions.

Uses of Trimethylsilanol:
Trimethylsilanol is the most critical intermediate in the organosilicon industry, serving as the primary building block for silicone oils, silicone rubbers, and silicone resins through its participation in Si-O-Si bond formation via condensation reactions with other silanols.
Trimethylsilanol acts as a blocking agent (chain stopper) for straight-chain polydimethylsiloxane polymers, introducing trimethylsilyl end-groups that control molecular weight, regulate viscosity, and impart surface hydrophobicity to the final silicone material.
Trimethylsilanol is used to prepare tris(trimethylsiloxy)aluminium(I) by reaction with triethylaluminium, a Lewis acid catalyst used in Meerwein–Ponndorf–Verley reductions and related organoaluminium-mediated transformations.
Trimethylsilanol is applied as a hydrophobic surface-treatment agent for silica, glass, mineral fillers, and silicate surfaces, where the Si-OH group condenses with surface silanol groups to create a durable, water-repellent trimethylsilyl monolayer.
Trimethylsilanol is used as an antimicrobial agent in certain formulations and has been evaluated for its activity against bacteria and fungi; it serves as a reference compound and analytical standard in environmental monitoring of volatile methylsiloxanes (VMS) in air, water, and biological matrices.
Trimethylsilanol is a silylating reagent in synthetic organic chemistry, used to introduce the trimethylsilyl (TMS) protective group onto hydroxyl, carboxyl, and amine functionalities, and to prepare a wide range of trimethylsilyl ethers and esters as protected intermediates or analytical derivatives.
Trimethylsilanol is formed as the principal volatile by-product of PDMS hydrolysis — (CH₃)₃SiO[Si(CH₃)₂O]ₙR + H₂O → (CH₃)₃SiOH + HO[Si(CH₃)₂O]ₙR — and its monitoring serves as a quality indicator for silicone material degradation in industrial, environmental, and aerospace applications.

Benefits and Advantages of Trimethylsilanol:
The Si-OH group of trimethylsilanol is significantly more acidic (pKa ≈ 11) than that of structurally analogous carbon alcohols such as tert-butanol, making trimethylsilanol a more reactive partner in condensation, esterification, and siloxide formation reactions under mild conditions.
Trimethylsilanol condenses efficiently with surface silanol groups on glass, silica, and mineral substrates to form stable Si-O-Si bonds, delivering a durable, covalently anchored hydrophobic coating that outperforms physisorbed surfactant treatments in thermal and chemical stability.
As a chain-end blocking agent for polysiloxanes, trimethylsilanol provides precise molecular weight control and reproducible end-group functionality, enabling formulation of silicone fluids with tightly specified viscosities across a wide range from low-viscosity oils to high-molecular-weight gums.
Trimethylsilanol is the most concise trimethylsilyl source available — three methyl groups plus one hydroxyl on a single silicon atom — offering the highest atom efficiency and lowest molecular weight overhead among commonly used TMS transfer reagents in protecting-group chemistry.

Features of Trimethylsilanol:
Trimethylsilanol is a colorless, transparent, volatile liquid at room temperature with a boiling point of 84–99°C (sources vary; 90°C at 760 Torr is widely cited), melting point −4.5°C, density approximately 0.950 g/cm³, refractive index 1.3889, and vapor pressure 19–55 hPa at 25°C.
The flash point is approximately 4°C (39°F), classifying trimethylsilanol as a highly flammable liquid (GHS Flammable Liquid Category 2, H225); vapors are heavier than air and may accumulate in low-lying areas near ignition sources.
Trimethylsilanol is soluble in water (approximately 1 mg/mL) and miscible with common organic solvents including ethanol, diethyl ether, acetone, and chlorinated solvents; the Si-OH bond is susceptible to condensation with other silanols to form hexamethyldisiloxane (HMDSO) and water, particularly under acidic or basic conditions.
The initial risk screening level (IRSL) established for trimethylsilanol is 65 μg/m³ (annual average); it is classified as Aquatic Chronic 3 (H412), reflecting potential long-term effects on aquatic organisms at elevated environmental concentrations.

Chemical Properties of Trimethylsilanol:
Trimethylsilanol has IUPAC name trimethylsilanol, molecular formula C₃H₁₀OSi (or (CH₃)₃SiOH), SMILES C[Si](C)(C)O, InChI=1S/C3H10OSi/c1-5(2,3)4/h4H,1-3H3, InChIKey AAPLIUHOKVUFCC-UHFFFAOYSA-N; PubChem CID 66110, ChemSpider 59498, ECHA InfoCard 100.012.650, CompTox DTXSID7061433, UNII Z4BIN3300P, Beilstein/REAXYS 1361356, MDL MFCD02751657.
The Si-OH bond of trimethylsilanol shows acidity (pKa ≈ 11) substantially greater than that of analogous carbon alcohols, enabling reaction with strong bases such as NaOH or LiAlH₄ to form sodium trimethylsiloxide or reduction to trimethylsilane respectively; the Si-OH bond undergoes condensation with other silanol groups to form Si-O-Si (siloxane) linkages — the backbone of all polysiloxanes.
Under acid catalysis, trimethylsilanol readily forms hexamethyldisiloxane (HMDSO, (CH₃)₃Si-O-Si(CH₃)₃) by self-condensation; under base catalysis it forms sodium trimethylsiloxide (NaOSi(CH₃)₃), which is itself a useful alkoxide reagent; trimethylsilanol also undergoes esterification with carboxylic acids to form trimethylsilyl esters, useful as volatile GC derivatives of acids.
Trimethylsilanol is relatively stable under neutral conditions but condenses under acidic or basic conditions; incompatible with strong oxidising agents, strong acids, strong bases (which promote rapid condensation or siloxide formation), and moisture-sensitive reagents.

Production of Trimethylsilanol:
Trimethylsilanol is produced industrially by the controlled weakly basic hydrolysis of chlorotrimethylsilane (trimethylchlorosilane, TMSCl): (CH₃)₃SiCl + H₂O → (CH₃)₃SiOH + HCl; weakly basic conditions are preferred over neutral or acidic hydrolysis to suppress the competing formation of hexamethyldisiloxane (HMDSO), which is the thermodynamically favored product under acidic conditions where the HCl by-product promotes self-condensation.
Trimethylsilanol is also formed as the natural hydrolytic end-group degradation product of trimethylsilyl-terminated PDMS polymers and is recovered as a by-product from silicone manufacturing processes; laboratory synthesis from benzyloxytrimethylsilane and related trimethylsilyl ethers by hydrogenolysis or methanolysis represents an alternative route.
Trimethylsilanol is commercially available at ≥97.5% or ≥98.0% purity (GC) as a colorless liquid; storage at 2–8°C in tightly closed containers under inert atmosphere is recommended to prevent condensation to HMDSO.

Trimethylsilanol Material Safety Data Sheet (MSDS):

Handling of Trimethylsilanol:
Trimethylsilanol must be handled with strict precautions due to its high flammability (flash point approximately 4°C); all ignition sources including open flames, sparks, and hot surfaces must be eliminated in handling areas, and adequate exhaust ventilation must be provided at all points where vapors may form.
Work must be carried out in a well-ventilated area or fume hood; avoid breathing vapors or mist, avoid contact with skin and eyes, and do not eat, drink, or smoke during use; containers must be kept tightly closed when not in use to prevent both vapor release and moisture-promoted condensation to HMDSO.

Trimethylsilanol SDS:

Stability and Reactivity of Trimethylsilanol:

Chemical stability:
Trimethylsilanol is stable under recommended storage conditions in tightly closed containers at 2–8°C under inert atmosphere.
Trimethylsilanol undergoes self-condensation to hexamethyldisiloxane (HMDSO) on exposure to acid, base, or prolonged moisture contact.

Reactivity:
The Si-OH group condenses with other silanol groups, surface silanols, and carboxylic acids under acidic or basic conditions.
Contact with strong bases produces sodium trimethylsiloxide; contact with LiAlH₄ reduces the Si-OH to Si-H; reaction with strong acids promotes rapid HMDSO formation.

Conditions to avoid:
Ignition sources — open flames, sparks, hot surfaces (flash point ≈ 4°C).
Moisture and humidity (promotes self-condensation to HMDSO).
Strong acids and strong bases (promote rapid condensation or siloxide formation).
Static discharge during transfer.

Incompatible materials:
Strong oxidising agents.
Strong acids and strong bases.
Moisture-sensitive reagents.
LiAlH₄ and other strong hydride reducing agents.

Hazardous decomposition products:
Carbon monoxide (CO) and carbon dioxide (CO₂).
Silicon dioxide (SiO₂) and methylsiloxane fragments upon combustion.
Hexamethyldisiloxane (HMDSO) upon self-condensation.

Handling and Storage of Trimethylsilanol:

Handling:
Handle only in well-ventilated areas or under local exhaust ventilation.
Eliminate all ignition sources; use explosion-proof electrical equipment.
Avoid contact with skin, eyes, and clothing; avoid breathing vapours.
Use appropriate personal protective equipment at all times.
Do not eat, drink, or smoke in work areas.
Wash hands thoroughly after handling.

Storage:
Store at 2–8°C in tightly closed containers under inert atmosphere (nitrogen or argon) to prevent HMDSO formation.
Keep away from heat, sparks, open flames, oxidising agents, and moisture sources.
UN number: UN 1993 (flammable liquid, n.o.s.); Hazard Class 3; Packing Group II.

First Aid Measures for Trimethylsilanol:

Inhalation:
Move the affected person to fresh air immediately and keep comfortable for breathing.
If symptoms develop or persist, consult a physician.

Skin contact:
Remove contaminated clothing immediately and wash the affected skin with soap and plenty of water.
Consult a physician if irritation develops or persists.

Eye contact:
Rinse thoroughly with plenty of water for at least 15 minutes, occasionally lifting eyelids.
Consult a physician immediately.

Ingestion:
Never give anything by mouth to an unconscious person; rinse the mouth with water.
Consult a physician immediately.

Firefighting Measures for Trimethylsilanol:

Suitable extinguishing media:
Water spray, alcohol-resistant foam, dry chemical powder, or carbon dioxide.

Specific hazards:
Trimethylsilanol is a highly flammable liquid with a flash point of approximately 4°C; vapors form explosive mixtures with air and may travel to ignition sources and flash back.
Combustion produces carbon monoxide, carbon dioxide, silicon dioxide, and irritating organic silicon-containing fumes.

Protective equipment for firefighters:
Self-contained breathing apparatus (SCBA) and full chemical-protective clothing must be used.

Firefighting procedures:
Evacuate non-essential personnel; fight the fire from an upwind position using appropriate extinguishing media.
Cool containers exposed to fire with water spray to prevent pressure build-up and rupture.

Accidental Release Measures for Trimethylsilanol:

Personal precautions:
Eliminate all ignition sources immediately; ensure adequate ventilation.
Avoid breathing vapors and prevent contact with skin and eyes; wear full PPE.

Environmental precautions:
Do not allow trimethylsilanol to enter drains, surface water, or groundwater; classified H412 (harmful to aquatic life with long-lasting effects).

Clean-up methods:
Absorb the spill with inert absorbent material such as sand or vermiculite; collect in sealed, labelled containers.
Ventilate the area thoroughly after clean-up and dispose of waste in accordance with applicable regulations.

Exposure Controls / Personal Protective Equipment for Trimethylsilanol:

Engineering controls:
Use local exhaust ventilation or work in a fume hood to control vapor concentrations.
Initial Risk Screening Level (IRSL): 65 μg/m³ (annual average).

Eye protection:
Face shield and safety glasses; use equipment tested and approved under NIOSH (US) or EN 166 (EU).

Hand protection:
Chemically resistant gloves; inspect gloves before use and replace contaminated gloves immediately.

Skin and body protection:
Complete chemical-protective suit; the type of protective equipment must be selected according to concentration and amount at the specific workplace.

Respiratory protection:
For nuisance exposures use type P95 (US) or type P1 (EU EN 143) particle respirator.
For higher level protection use type OV/AG/P99 (US) or type ABEK-P2 (EU EN 143) respirator cartridges.

Hygiene measures:
Wash hands before breaks and at the end of the workday; do not eat, drink, or smoke in work areas; remove contaminated clothing before leaving the work area.

Trimethylsilanol Identifiers:
CAS Number: 1066-40-6
EC Number: 213-914-1
MDL Number: MFCD02751657
PubChem CID: 66110
ChemSpider: 59498
ECHA InfoCard: 100.012.650
CompTox (EPA): DTXSID7061433
UNII: Z4BIN3300P
Beilstein/REAXYS: 1361356
IUPAC Name: Trimethylsilanol
Molecular Formula: C₃H₁₀OSi
Molecular Weight: 90.20 g/mol
SMILES: C[Si](C)(C)O
InChI: InChI=1S/C3H10OSi/c1-5(2,3)4/h4H,1-3H3
InChIKey: AAPLIUHOKVUFCC-UHFFFAOYSA-N
GHS Signal Word: Danger
GHS Hazard Statements: H225, H332, H412
GHS Precautionary Statements: P210, P233, P240, P241, P273, P304+P340+P312
Hazard Class: 3 (Flammable liquids)
Packing Group: II
UN Number: UN 1993
IRSL: 65 μg/m³ (annual average)
NACRES: NA.22
UNSPSC: 12352103

Properties of Trimethylsilanol:
Physical state: Liquid
Appearance: Colorless transparent liquid
Odour: Characteristic mild organosilicon odour
Molecular formula: C₃H₁₀OSi
Molecular weight: 90.20 g/mol
Melting point: −4.5°C
Boiling point: 84–99°C (90°C at 760 Torr widely cited)
Flash point: ≈ 4°C (39°F) — highly flammable
Density: ≈ 0.950 g/cm³
Refractive index: 1.3889
Vapor pressure: 19–55 hPa (25°C); 21 mbar (20°C)
Water solubility: ≈ 1 mg/mL
pKa (Si-OH): ≈ 11
GHS Classification: Danger — H225, H332, H412
Storage temperature: 2–8°C (tightly closed, inert atmosphere)

Trimethylsilanol Properties — Specifications:
Product name: Trimethylsilanol (Hydroxytrimethylsilane)
CAS Number: 1066-40-6
EC Number: 213-914-1
Molecular Formula: C₃H₁₀OSi
Molecular Weight: 90.20 g/mol
Purity (GC): ≥97.5% or ≥98.0%
Appearance: Colorless transparent liquid
Boiling point: 84–99°C
Density: ≈ 0.950 g/cm³
Refractive index: 1.3889
Storage: 2–8°C; tightly closed; inert atmosphere; away from ignition sources and moisture
Format: Liquid
Documents: CoA (Certificate of Analysis), MSDS/SDS available

Names of Trimethylsilanol:
Trimethylsilanol
Hydroxytrimethylsilane
TMS-OH
TMSOH
Silanol, trimethyl-
Silanol, 1,1,1-trimethyl-
Hydroxy(trimethyl)silane
Trimethylhydroxysilane
Trimethylsilyl alcohol
Trimethylsilanole
Silanole LS 310
Medetomidine Impurity 17
CAS 1066-40-6