Sodium acetate

Sodium acetate

Names Preferred IUPAC name Systematic IUPAC name Other names Identifiers 3595639 ChEBI ChEMBL ChemSpider DrugBank ECHA InfoCard 100.004.386 EC Number E number E262 (preservatives) 20502 KEGG RTECS number UNII Properties C2H3NaO2 Molar mass 82.034 g·mol−1 Appearance White deliquescent powder or colorless crystals Odor Vinegar (acetic acid) odor when heated to decomposition[1] Density 1.528 g/cm3 (20 °C, anhydrous) 1.45 g/cm3 (20 °C, trihydrate)[2] Melting point 324 °C (615 °F; 597 K) (anhydrous) 58 °C (136 °F; 331 K) (trihydrate) Boiling point 881.4 °C (1,618.5 °F; 1,154.5 K) (anhydrous) 122 °C (252 °F; 395 K) (trihydrate) decomposes Anhydrous: 119 g/100 mL (0 °C) 123.3 g/100 mL (20 °C) 125.5 g/100 mL (30 °C) 137.2 g/100 mL (60 °C) 162.9 g/100 mL (100 °C) Trihydrate: 32.9 g/100 mL (-10 °C) 36.2 g/100 mL (0 °C) 46.4 g/100 mL (20 °C) 82 g/100 mL (50 °C)[3] Solubility Soluble in alcohol, hydrazine, SO2[4] Solubility in methanol 16 g/100 g (15 °C) 16.55 g/100 g (67.7 °C)[4] Solubility in ethanol Trihydrate: 5.3 g/100 mL Solubility in acetone 0.5 g/kg (15 °C)[4] Acidity (pKa) 24 (20 °C)[4] 4.75 (when mixed with CH3COOH as a buffer)[5] Basicity (pKb) 9.25 −37.6·10−6 cm3/mol 1.464 Structure Monoclinic Thermochemistry 100.83 J/(mol·K) (anhydrous)[6] 229 J/(mol·K) (trihydrate)[7] 138.1 J/(mol·K) (anhydrous)[6] 262 J/(mol·K) (trihydrate)[2] −709.32 kJ/mol (anhydrous)[4] −1604 kJ/mol (trihydrate)[2] −607.7 kJ/mol (anhydrous)[4] Pharmacology B05XA08 (WHO) Hazards Occupational safety and health (OHS/OSH): Irritant NFPA 704 (fire diamond) Flash point >250 °C (482 °F; 523 K)[5] 607 °C (1,125 °F; 880 K)[5] Lethal dose or concentration (LD, LC): 3530 mg/kg (oral, rat) >10000 mg/kg (rabbit, dermal) >30 g/m3 (rat, 1 h) Safety data sheet (SDS) Fisher Scientific Related compounds Sodium formate Sodium propionateSodium butyrate Lithium acetatePotassium acetateRubidium acetateCesium acetate Calcium acetate Sodium diacetate

Sodium acetate is a chemical compound with formula CH3COONa, also abbreviated NaOAc.[8] It is the sodium salt of acetic acid. This salt is colorless, deliquescent, and hygroscopic.

Sodium acetate is used as a carbon source for culturing bacteria. Sodium acetate can also be useful for increasing yields of DNA isolation by ethanol precipitation.

Furthermore it acts as pH buffer and antimicrobial preservative in biotechnological applications.[9]

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.

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.[10]

Anhydrous sodium acetate is widely used as a shelf-life extending agent and pH control agent.[11] It is safe to eat at low concentration.[12]

A solution of sodium acetate (a basic salt of acetic acid) and acetic acid can act as a buffer 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).

Sodium acetate is also used in heating pads, hand warmers, 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 58-58.4 °C (136.4-137.1 °F),[13][14] and the liquid sodium acetate dissolves in the released water of crystallization. When heated past the melting point and subsequently allowed to cool, the aqueous solution becomes supersaturated. This solution is capable of cooling to room temperature without forming crystals. By pressing on a metal disc within the heating pad, a nucleation center is formed, causing the solution to crystallize back into solid sodium acetate trihydrate. The process of crystallization is exothermic.[15] The latent heat of fusion is about 264-289 kJ/kg.[13] 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.[16]

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.

Source:[17]

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 with sodium carbonate, sodium bicarbonate, or sodium hydroxide.

Industrially, hydrated sodium acetate is prepared by reacting acetic acid with sodium hydroxide using water as the solvent.[18]

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.

The crystal structure of anhydrous sodium acetate has been described as alternating sodium-carboxylate and methyl group layers.[19] Sodium acetate trihydrate'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.[20][21]

Comparison of anhydrous and trihydrate crystal structures Degree of hydration Anhydrous[19] Trihydrate[20][21] Na coordination Strongly bonded aggregation 2D sheet 1D chain Weakly bonded aggregation sheets stacked withhydrophobic surfaces in contact chains linked by hydrogen bonds(one chain highlighted in light blue)

Sodium acetate can be used to form an ester with an alkyl halide such as bromoethane:

CH3COONa + BrCH2CH3 → CH3COOCH2CH3 + NaBr

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.[citation needed]

• Hot Ice - Instructions, Pictures, and Videos
• How Sodium Acetate heating pads work
• Lavars, Nick (2021-09-15). "Sodium acetate acts as a potential fountain of youth for aging bones". New Atlas. Retrieved 2021-09-16.