What Is Tetramethylammonium Hydroxide?
Tetramethylammonium hydroxide is a quaternary ammonium salt with the chemical formula (CH3)4NOH, often abbreviated as TMAH. It is known for its strong basicity and potential neurotoxicity upon skin contact, necessitating careful handling.
Uses of Tetramethylammonium Hydroxide
As a versatile chemical, TMAH is used in various industries. In the semiconductor sector, it serves as a developer in the photolithography process. It also finds application as a phase-transfer catalyst in organic synthesis, a reagent in polymerization and condensation reactions, and a component in the manufacture of organic nitrogen compounds.
In addition to these, TMAH is utilized in gas chromatography, zeolite synthesis, and as a cleaning agent for integrated circuits. Its role extends to the textile industry for surface treatment and in rechargeable batteries as an alkaline electrolyte.
Properties of Tetramethylammonium Hydroxide
Typically found as a stable solid pentahydrate (CH3)4NOH-5H2O or as a trihydrate (CH3)4NOH-3H2O, TMAH is also available in 2% and 25% aqueous and methanol solutions. It forms colorless solids or solutions, and its solutions exhibit strong basicity. The pentahydrate variant has a melting point of 67°C and decomposes at around 135-140°C.
Structure of Tetramethylammonium Hydroxide
With a molar mass of 91.15 g/mol, TMAH is composed of a tetramethylammonium ion ((CH3)4N+) and a hydroxide ion (OH-). It’s also referred to as TMAOH, TMNOH, and N,N,N,-trimethylmethanaminium hydroxide.
Other Information on Tetramethylammonium Hydroxide
1. Synthesis of Tetramethylammonium Hydroxide
Traditional synthesis involves reacting tetramethylammonium chloride with potassium hydroxide in anhydrous methanol. However, this method may introduce impurities like chlorine and potassium ions. An electrolysis approach using a cation exchange membrane yields higher purity TMAH with minimal metal and chlorine ions.
Alternate methods include the conversion of tetramethylammonium chloride to sulfate with sulfuric acid, followed by treatment with barium hydroxide.
2. Reaction of Tetramethylammonium Hydroxide
TMAH undergoes acid-base reactions with strong or weak acids to form various tetramethylammonium salts. For instance, a reaction with ammonium thiocyanate produces tetramethylammonium thiocyanate. Concentrating its aqueous solution under reduced pressure yields crystals of the pentahydrate, and further dehydration can lead to its monohydrate form.