Dichloromethylsilane

Description

Methyl dichlorosilane, is a colorless liquid with a sharp irritating odor. It is a dangerous fire risk, corrosive, and water reactive. The flammable range is wide, from 6% on the lower end to 55% on the upper end. Boiling point is 107°F (41°C), flash point is 15°F (9°C), and ignition temperature is more than 600°F (315°C). Specific gravity is 1.11, which is heavier than water. Vapors are heavier than air and will travel to ignition sources. It is immiscible in water and decomposes on contact to release hydrogen chloride gas. Methyl dichlorosilane is toxic by inhalation and skin absorption; it is irritating to the skin, eyes, and respiratory system. Contact with the material may cause burns to the eyes and skin. The four-digit UN identification number is 1242. The NFPA 704 designation is health 3, flammability 3, and reactivity 2. The white space at the bottom of the diamond has a W with a slash through it, indicating water reactivity. The primary use is in the manufacture of siloxanes, which are straight-chained compounds similar to paraffin hydrocarbons.

Chemical Properties

Methyl dichlorosilane is a clear, straw-colored liquid.

Uses

Dichloromethylsilane is a monomer ('building block') in the production of silicone polymers. An intermediate (starting material) in the production of other organic and inorganic chemicals. In the electronics industry for the production of ultra-pure polysilicon and in the manufacture of semiconductors and photovoltaics.

Application

Provides better diastereoselective reductive aldol reactionbetween an aldehyde and an acrylate ester than othersilanes. Forms high-boiling polymeric by-products uponaqueous work-up.

General Description

A colorless fuming liquid with a pungent odor. Flash point: -26°F; Boiling point: 41°C (106°F) . Vapors heavier than air. Vapor and liquid may cause burns. Denser than water and decomposed by water to form hydrochloric acid, a corrosive material.

Reactivity Profile

Chlorosilanes, such as Dichloromethylsilane, are compounds in which silicon is bonded to from one to four chlorine atoms with other bonds to hydrogen and/or alkyl groups. Chlorosilanes react with water, moist air, or steam to produce heat and toxic, corrosive fumes of hydrogen chloride. They may also produce flammable gaseous H2. They can serve as chlorination agents. Chlorosilanes react vigorously with both organic and inorganic acids and with bases to generate toxic or flammable gases. Impact of dichlorosilane causes mixtures to burst into flame. This is the case, when the dichlorosilane and most likely related substances are mixed with oxidants such as potassium permanganate, lead oxide, copper oxide, or silver oxide, even under inert gas atmosphere [Bretherick, 1995, pg. 193]. With Dichloromethylsilane, toxic hydrogen chloride and phosgene gases may be formed when burned.

Hazard

Flammable, dangerous fire risk. Very toxic.

Health Hazard

Inhalation causes irritation of respiratory tract; heavy exposure can cause pulmonary edema. Contact of liquid with skin or eyes causes severe burns. Ingestion causes burns of mouth and stomach.

Chemical Reactivity

Reactivity with Water Reacts violently to form hydrogen chloride (hydrochloric acid); Reactivity with Common Materials: Reacts with surface moisture to evolve hydrogen chloride, which is corrosive to common metals; Stability During Transport: Stable; Neutralizing Agents for Acids and Caustics: Flood with water, rinse with sodium bicarbonate or lime solution; Polymerization: Not pertinent; Inhibitor of Polymerization: Not pertinent.

Safety Profile

Moderately toxic by inhalation. Corrosive. A severe irritant to skin, eyes, and mucous membranes. Ignites spontaneously in air. A very dangerous fire hazard when exposed to heat or flame. Forms impact-sensitive explosive mixtures with potassium permanganate, lead(Ⅱ) oxide, lead(Ⅳ) oxide, copper oxide, silver oxide. To fight fire, use water, foam, CO2, mist. When heated to decomposition it emits toxic fumes of Cl-. See also CHLOROSILANE.

Potential Exposure

This material is used to make siloxanes and other silicone polymer (polysiloxane) materials. Incompatibilities: May form explosive mixture with air. Reacts violently with water producing heat, corrosive hydrochloric acid and flammable hydrogen. Methyl dichlorosilane may spontaneously ignite on contact with air (even under inert gas) and on contact with potassium permanganate, lead(II) oxide; copper oxide; silver oxide. Violent reaction with oxidizers. Decomposes on contact with hot surfaces or flames producing toxic and corrosive fumes including silicon oxides, hydrogen chloride, and phosgene. Decomposes on contact with alkaline compounds producing highly flammable hydrogen gas. Corrodes many metals in presence of water. Attacks some plastics, rubber and coatings.

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifing upper and lower lids. Seek med-facility. 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 pulmonaryedema may bedelayed. As first aid for pulmonary edema, a doctor orauthorized paramedic may consider administering a cortico-steroid spray.

storage

(1) Color Code—Red: Flammability Hazard: Storein a flammable liquid storage area or approved cabinet awayfrom ignition sources and corrosive and reactive materials.(2) Color Code—Blue: Health Hazard/Poison: Store in asecure poison location. (3) Color Code—White: Corrosive orContact Hazard; Store separately in a corrosion-resistantlocation. Prior to working with this chemical you should betrained on its proper handling and storage. Before enteringconfined space where this chemical may be present, check tomake sure that an explosive concentration does not exist.Methyl dichlorosilane must be stored to avoid contact withwater, since violent reactions occur once hydrogen chlorideis produced. Store in tightly closed containers in a cool, wellventilated area away from heat. Sources of ignition, such assmoking and open flames, are prohibited where methyldichlorosilane is handled, used, or stored. Metal containersinvolving the transfer of 5 gallons or more of methyl dichlorosilane should be grounded and bonded. Drums must beequipped with self-closing valves, pressure vacuum bungs,and flame arresters. Use only nonsparking tools and equipment, especially when opening and closing containers ofmethyl dichlorosilane. Wherever methyl dichlorosilane isused, handled, manufactured, or stored, use explosion-proofelectrical equipment and fittings.

Shipping

UN1242 Methyldichlorosilane Hazard Class: 4.3; Labels: 4.3-Dangerous when wet material; 8-Corrosive material, 3-Flammable liquid.

Purification Methods

Impurities are generally other chloromethyl silanes. Distil it through a conventional Stedman column (p 11) of 20 theoretical plates or more. It should be protected from H2O by storing over P2O5. [Stck & Somieski Chem Ber 52 695 1919, Sauer J Am Chem Soc 68 962 1946, Beilstein 4 IV 4096.]

Incompatibilities

Forms explosive mixture with air. Reactsviolently with water producing corrosive hydrochloric acid.Methyl dichlorosilane may spontaneously ignite on contactwith air (even under inert gas) and on contact with potassium permanganate, lead(II) oxide, copper oxide, silveroxide. Violent reaction with oxidizers. Decomposes on contact with hot surfaces or flames producing toxic and corrosive fumes including silicon oxides, hydrogen chloride, andphosgene. Decomposes on contact with alkaline compoundsproducing highly flammable hydrogen gas. Corrodes manymetals in presence of water. Attacks some plastics, rubber,and coatings.

Toxics Screening Level

The ITSL for Dichloromethylsilane is 4 μg/m3, with annual averaging time.

Waste Disposal

See “Spill Handling.”