Tetramethylammonium hydroxide

Preparation

There are many methods for preparing tetramethylammonium hydroxide, the most common being the silver oxide method, which involves the reaction of tetramethylammonium chloride with silver oxide. However, this method is complex, uses expensive silver oxide as a raw material, and produces a product with high levels of impurity ions, such as halide ions and alkali metal ions. When used in the catalytic polymerization of organosilicon monomers, this severely affects the properties of the organosilicon products and fails to meet the cleaning and corrosion requirements of the electronics industry.
Since the 1970s, foreign countries have adopted a new electrolytic process for preparing tetramethylammonium hydroxide, gradually replacing the silver oxide method. The electrolytic method produces a product of better quality and lower cost, meeting the needs of organosilicon production and entering the electronics industry.

Description

Tetramethylammonium hydroxide is a solid in the hydrated form or a colorless liquid with a strong ammonia-like odor. It is soluble in water, and corrosive to metals and tissue.

Chemical Properties

colourless to yellow liquid

Uses

Uses

Tetramethylammonium hydroxide is used to produce tetramethyl-ammonium azide. It is used as an anisotropic etchant of silicon, basic solvent in the development of acidic photoresist in photolithography process, as surfactant in the synthesis of ferrofluid and as a polarographic reagent. It finds application in the production of organic silicon, where it is used for computer silicon wafer surface brightener and cleaning agent. It is also involved in the purification of some metallic elements.
Tetramethylammonium hydroxide solution (25 wt.% solution in water) may be used as a base for pH adjustment to obtain hexagonal mesoporous aluminophosphate (TAP).

General Description

Tetramethylammonium hydroxide is a quaternary ammonium salt generally used as an anisotropic etchant for silicon due to its high silicon etching rate.

Reactivity Profile

Tetramethylammonium hydroxide acts like a base. Bases are chemically similar to sodium hydroxide (NaOH) or sodium oxide (Na2O). They neutralize acids exothermically to form salts plus water. When soluble in water they give solutions having a pH greater than 7.0. Mixing these materials with water can generate troublesome amounts of heat as the base is dissolved or diluted. Bases react with certain metals (such as aluminum and zinc) to form oxides or hydroxides of the metal and generate gaseous hydrogen. Bases may initiate polymerization reactions in polymerizable organic compounds, especially epoxides). They may generate flammable and/or toxic gases with ammonium salts, nitrides, halogenated organics, various metals, peroxides, and hydroperoxides. Materials of this group often serve as catalysts.

Health Hazard

TOXIC; inhalation, ingestion or skin contact with material may cause severe injury or death. Contact with molten substance may cause severe burns to skin and eyes. Avoid any skin contact. Effects of contact or inhalation may be delayed. Fire may 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

Combustible material: may burn but does not ignite readily. When heated, vapors may form explosive mixtures with air: indoors, outdoors and sewers explosion hazards. Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated. Runoff may pollute waterways. Substance may be transported in a molten form.

reaction suitability

reaction type: Acid-base reactions
reaction type: Redox Reactions

Safety Profile

Poison by subcutaneous route. A powerful caustic. A corrosive irritant to skin, eyes, and mucous membranes. When heated to decomposition it emits toxic fumes of NOx and NH3.

Purification Methods

It is freed from chloride ions by passage through an ion-exchange column (e.g. Amberlite IRA-400, prepared in its OH-form by passing 2M NaOH until the effluent is free from chloride ions, then washed with distilled H2O until neutral). A modification, to obtain carbonate-free hydroxide, uses the method of Davies and Nancollas [Nature 165 237 1950]. [Beilstein 4 IV 145.]

References

1.https://en.wikipedia.org/wiki/Tetramethylammonium_hydroxide#Uses
2.http://sacheminc.com/other-chemicals/tetramethylammonium-hydroxide-tmah/
3.https://www.fs.usda.gov/treesearch/pubs/15506
4.https://www.concordia.ca/content/dam/concordia/services/safety/docs/EHS-DOC-020_TMAHGuidelines.pdf
5.https://www.chemicalbook.com/ChemicalProductProperty_EN_CB2854236.htm