Description
Tetramethyl orthosilicate is the chemical compound with the formula Si(OCH3)4. This molecule consists of four methoxy groups bonded to a silicon atom.
Two common organic precursors are tetraethyl orthosilicate (TEOS) and tetramethyl orthosilicate (TMOS). The latter is more toxic than the former.
Tetraethyl orthosilicate (TEOS), Si(OC2H5)4, is the first alkoxide of the series, followed by tetramethyl orthosilicate (TMOS), Si(OCH3)4, which is, however, less safe to handle and hydrolyzes faster than TEOS.
The hydrolysis of TMOS is, in fact, around six times faster: in general, a lower hydrolysis rate is associated with an increase of the organic group size in the silicon alkoxide. The properties of the silicon alkoxides change according to the dimension of the alkoxy; larger groups produce an increase in molecular weight, viscosity, and boiling point and a decrease in density of the alkoxides.
As a rule of thumb, a larger size of the alkoxy group is associated with a lower hydrolysis rate due to the steric hindrance. The reactivity follows the sequence, with tetramethyl orthosilicate the most reactive alkoxide:
tetramethyl orthosilicate >tetraethyl orthosilicate>tetra-n-propylorthosilicate>tetrabutyl orthosilicate
Chemical Properties
Tetramethyl orthosilicate (TMOS), the methyl ester of orthosilicic acid, is a colorless, low-viscosity liquid. It is industrially the most important of the tetraalkyl silicates.
Uses
Tetramethyl orthosilicate (TMOS) is popularly used in the sol-gel synthesis of silicates1 and chromium-doped silicates and in the formation of hexagonal mesoporous silica layers.
Uses
Tetramethyl Orthosilicate is a compound used in the research of the multifunctionality of silicified nanoshells and the efficiency at adsorbing cadmium ions at cell interfaces.
Uses
Coating screens of television picture
tubes; mold binders; corrosion-resistant coatings;
catalyst preparation; silicone intermediate
Production Methods
Silica aerogels are usually prepared by base-catalyzed reaction
of tetramethoxysilane or tetraethoxysilane, mostly with
ammonia as the catalyst. A modification of this procedure is
to prehydrolyze Si(OR)4 with a small amount of water under
acidic conditions.
General Description
A clear colorless liquid. Flash point below 125°F. Less dense than water and insoluble in water. Very toxic by ingestion and inhalation and very irritating to skin and eyes. Used to make paints and lacquers.
Air & Water Reactions
Flammable. Insoluble in water.
Reactivity Profile
Tetramethyl orthosilicate is incompatible with the following: Oxidizers; hexafluorides of rhenium, molybdenum & tungsten .
Hazard
Eye damage and upper respiratory tract irri-tant.
Health Hazard
TOXIC; inhalation, ingestion or contact (skin, eyes) with vapors, dusts or substance may cause severe injury, burns or death. Bromoacetates and chloroacetates are extremely irritating/lachrymators. Reaction with water or moist air will release toxic, corrosive or flammable gases. Reaction with water may generate much heat that will increase the concentration of fumes in the air. Fire will produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may be corrosive and/or toxic and cause pollution.
Fire Hazard
HIGHLY FLAMMABLE: Will be easily ignited by heat, sparks or flames. Vapors form explosive mixtures with air: indoors, outdoors and sewers explosion hazards. Most vapors are heavier than air. They will spread along ground and collect in low or confined areas (sewers, basements, tanks). Vapors may travel to source of ignition and flash back. Substance will react with water (some violently) releasing flammable, toxic or corrosive gases and runoff. Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated or if contaminated with water.
Flammability and Explosibility
Flammable
Safety Profile
Poison by
intraperitoneal route. Moderately toxic by
inhalation. Midly toxic by skin contact. A
severe eye irritant. This material can cause extensive necrosis (experimentally),
keratoconus, and opaque cornea. It also
causes severe human eye injuries, as well as
necrosis of corneal cells, which progresses
long after exposure has ceased. It is
destructive and its effects resist treatment.
Permanent blindness is possible from
exposure to it. The kidney seems to be most
subject to injury regardless of the mode of
exposure. Pulmonary edema has also
occurred. This material is more toxic than
either ethyl silicate or silicic acid, although it
has been thought that the injury caused is
largely due to the action of the silicic acid.
Flammable when exposed to heat or flame;
can react vigorously with oxidizing
materials. Potentially violent reaction with
metal hexafluorides (e.g., rhenium,
molybdenum, tungsten). When heated to
decomposition it emits acrid smoke and
irritating fumes.
Potential Exposure
Methyl silicate is used in coating
screens of television picture tubes. It may be used in mold
binders and in corrosion-resistant coatings; as well as in
catalyst preparation and as a silicone intermediate.
First aid
If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek med-ical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, includ-heart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medi-First Aid: If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek med-ical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, includ-ing resuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medi-cal attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit.Medical observation is recommended for 24- 48 h afterbreathing overexposure, as pulmonary edema may bedelayed. As first aid for pulmonary edema, a doctor orauthorized paramedic may consider administering a cortico-steroid spray.
storage
Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. Prior to working with thischemical you should be trained on its proper handling andstorage. Store in tightly closed containers in a cool, wellventilated area away from water and moisture. Sources ofignition, such as smoking and open flames, are prohibitedwhere methyl silicate is used, handled, or stored in a manner that could create a potential fire or explosion hazard.
Shipping
UN2606 Methyl orthosilicate, Hazard class: 6.1;
Labels: 6.1-Poisonous materials, 3-Flammable liquid.
Purification Methods
Purification is as for tetraethoxysilane. It has a vapour pressure of 2.5mm at 0o. [IR: Sternbach & MacDiarmid J Am Chem Soc 81 5109 1959. Beilstein 1 IV 1266.]
Incompatibilities
Vapor may form explosive mixture with
air. Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep
away from alkaline materials, including alkaline earth
metals, metals, strong acids, strong bases; water, moisture,
steam decomposes releasing toxic, flammable gases.
Violent reaction with metal hexafluorides of rhenium,
molybdenum, and tungsten. Contact with metals may
evolve flammable hydrogen gas.
