Ammonium acetate

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Ammonium acetate

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UN number	3077
Template:Longitem	Template:Chembox Elements/molecular formula
Molar mass	Template:Chem molar mass
Appearance	White solid crystals, deliquescent
Odor	Slightly acetic acid like
Density	1.17 g/cm3 (20 °C) 1.073 g/cm3 (25 °C)
Melting point	Template:Chembox CalcTemperatures
Solubility	Soluble in alcohol, SO2, acetone, liquid ammonia
Solubility in methanol	7.89 g/100 mL (15 °C) 131.24 g/100 g (94.2 °C)
Solubility in dimethylformamide	0.1 g/100 g
Acidity (pKa)	9.9
Basicity (pKb)	33
Template:Longitem	−41.1·10−6 cm3/mol
Viscosity	21
Template:Longitem	Orthorhombic
Template:Longitem	−615 kJ/mol
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Ammonium acetate, also known as spirit of Mindererus in aqueous solution, is a chemical compound with the formula NH₄CH₃CO₂. It is a white, hygroscopic solid and can be derived from the reaction of ammonia and acetic acid. It is available commercially.

History

The synonym Spirit of Mindererus is named after R. Minderer, a physician from Augsburg.

Uses

It is the main precursor to acetamide:

NH₄CH₃CO₂ → CH₃C(O)NH₂ + H₂O

It is also used as a diuretic.

Buffer

As the salt of a weak acid and a weak base, ammonium acetate is often used with acetic acid to create a buffer solution. Ammonium acetate is volatile at low pressures. Because of this, it has been used to replace cell buffers that contain non-volatile salts in preparing samples for mass spectrometry. It is also popular as a buffer for mobile phases for HPLC with ELSD and CAD-based detection for this reason. Other volatile salts that have been used for this include ammonium formate.

When dissolving ammonium acetate in pure water, the resulting solution typically has a pH of 7, because the equal amounts of acetate and ammonium neutralize each other. However, ammonium acetate is a dual component buffer system, which buffers around pH 4.75 ± 1 (acetate) and pH 9.25 ± 1 (ammonium), but it has no significant buffer capacity at pH 7, contrary to common misconception.

Other

• a biodegradable de-icing agent.
• a catalyst in the Knoevenagel condensation and as a source of ammonia in the Borch reaction in organic synthesis.
• a protein precipitating reagent in dialysis to remove contaminants via diffusion.
• a reagent in agricultural chemistry for determination of soil CEC (cation exchange capacity) and determination of available potassium in soil wherein the ammonium ion acts as a replacement cation for potassium.
• part of Calley's method for lead artifact conservation

Food additive

Ammonium acetate is also used as a food additive as an acidity regulator; INS number 264. It is approved for usage in Australia and New Zealand.

Production

Ammonium acetate is produced by the neutralization of acetic acid with ammonium carbonate or by saturating glacial acetic acid with ammonia. Obtaining crystalline ammonium acetate is difficult on account of its hygroscopic nature.