Sodium acetate, CH3COONa, also abbreviated SodiumOxygenAcetyl,
Applications
Biotechnological
Sodium acetate is used as the carbon source for culturing
Bacterial growth. Sodium acetate can also be useful for increasing yields of
DNA extraction.
Industrial
Sodium acetate is used in the
textile industry to neutralize
sulfuric acid waste streams and also as a
photoresist while using
aniline dyes. It is also a pickling agent in chrome tanning and helps to impede
vulcanization of
chloroprene in
synthetic rubber production. It is also used to reduce static electricity during production of disposable cotton pads.
Concrete longevity
Sodium acetate is used as a
sealant to mitigate water damage to
concrete. It is environmentally benign and cheaper than the commonly used
epoxy alternative for sealing concrete against water
permeation.
Food
Sodium acetate (anhydrous) is widely used as a
preservative and pH control agent.
It is safe to eat at low concentration.
Buffer solution
A solution of sodium acetate (a basic salt of acetic acid) and acetic acid can act as a
buffer solution to keep a relatively constant pH level. This is useful especially in biochemical applications where reactions are pH-dependent in a mildly acidic range (pH 4–6).
Heating pad
Sodium acetate is also used in
,
, and "hot ice". A
supersaturated solution of sodium acetate in water is supplied with a device to initiate crystallization, a process that releases substantial heat.
Sodium acetate trihydrate crystals melt at ,[Ibrahim Dincer and Marc A. Rosen. Thermal Energy Storage: Systems and Applications, page 155.] Unlike some types of heat packs, such as those dependent upon irreversible chemical reactions, a sodium acetate heat pack can be easily reused by immersing the pack in boiling water for a few minutes, until the crystals are completely dissolved, and allowing the pack to slowly cool to room temperature.
Heat stores and batteries
Sodium acetate trihydrate can also be used as a phase-change material to store heat, especially to provide domestic hot water for heat pump applications. The heat store consists of a well-insulated container filled with the salt through which pass a pair of copper coils. One coil is used to melt the material by passing hot water from either solar thermal panels or a
heat pump. Cold mains water passes through the other coil where its temperature is raised to 40 or 50 ˚C to provide water for washing or cleaning. This process can be cycled almost indefinitely.
Preparation
For laboratory use, sodium acetate is inexpensive and usually purchased instead of being synthesized. It is sometimes produced in a laboratory experiment by the reaction of
acetic acid, commonly in the 5–18% solution known as
vinegar, with
sodium carbonate ("washing soda"), sodium bicarbonate ("baking soda"), or
sodium hydroxide ("lye", or "caustic soda"). Any of these reactions produce sodium acetate and water or sodium acetate and carbonic acid. When a sodium and carbonate ion-containing compound is used as the reactant, the carbonate anion (from sodium bicarbonate or carbonate) reacts with the hydrogen from the carboxyl group (-COOH) in acetic acid, forming
carbonic acid. Carbonic acid readily decomposes under normal conditions into gaseous carbon dioxide and water. This is the reaction taking place in the well-known "volcano" that occurs when the household products, baking soda and vinegar, are combined.
- CH3COOH + NaHCO3 → CH3COONa +
- → +
Industrially, sodium acetate trihydrate is prepared by reacting acetic acid with sodium hydroxide using water as the solvent.
- CH3COOH + NaOH → CH3COONa + H2O.
To manufacture anhydrous sodium acetate industrially, the Niacet Process is used. Sodium metal ingots are extruded through a die to form a ribbon of sodium metal, usually under an inert gas atmosphere such as N2, and then immersed in anhydrous acetic acid.
- 2 CH3COOH + 2 Na →2 CH3COONa + H2.
The hydrogen gas is normally a valuable byproduct.
Structure
The crystal structure of
anhydrous sodium acetate has been described as alternating sodium-carboxylate and
methyl group layers.
Sodium acetate
Hydrate's structure consists of distorted octahedral coordination at sodium. Adjacent octahedra share edges to form one-dimensional chains.
Hydrogen bonding in two dimensions between acetate ions and water of hydration links the chains into a three-dimensional network.
| +Comparison of anhydrous and trihydrate crystal structures |
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Reactions
Sodium acetate can be used to form an
ester with an alkyl halide such as
bromoethane:
- CH3COONa + BrCH2CH3 → Ethyl acetate + Sodium bromide
Sodium acetate undergoes decarboxylation to form methane (CH4) under forcing conditions (pyrolysis in the presence of sodium hydroxide):
- CH3COONa + NaOH → CH4 + Na2CO3
Calcium oxide is the typical catalyst used for this reaction.
Caesium salts also catalyze this reaction.
External links
