Sodium formate

Sodium formate, HCOONa, is the sodium salt of formic acid, HCOOH. It usually appears as a white deliquescent powder.

Sodium formate

Ball-and-stick model of the formate anion
Names
Systematic IUPAC name Sodium methanoate
Other names formic acid, sodium salt, sodium hydrocarbon dioxide
Identifiers
CAS Number	141-53-7
3D model (JSmol)	Interactive image
ChEMBL	ChEMBL183491
ChemSpider	8517
ECHA InfoCard	100.004.990
EC Number	205-488-0
E number	E237 (preservatives)
PubChem CID	2723810
UNII	387AD98770
CompTox Dashboard (EPA)	DTXSID2027090
InChI InChI=1S/CH2O2.Na/c2-1-3;/h1H,(H,2,3);/q;+1/p-1 Key: HLBBKKJFGFRGMU-UHFFFAOYSA-M InChI=1/CH2O2.Na/c2-1-3;/h1H,(H,2,3);/q;+1/p-1 Key: HLBBKKJFGFRGMU-REWHXWOFAN
SMILES [Na+].[O-]C=O
Properties
Chemical formula	HCOONa
Molar mass	68.007 g/mol
Appearance	white granules deliquescent
Density	1.92 g/cm^3 (20 °C)
Melting point	253 °C (487 °F; 526 K)
Boiling point	decomposes
Solubility in water	43.82 g/100 mL (0 °C) 97.2 g/100 mL (20 °C) 160 g/100 mL (100 °C)
Solubility	insoluble in ether soluble in glycerol, alcohol, formic acid
Thermochemistry
Heat capacity (C)	82.7 J/mol K
Std molar entropy (S^o298)	103.8 J/mol K
Std enthalpy of formation (ΔfH^⦵298)	-666.5 kJ/mol
Gibbs free energy (ΔfG˚)	-599.9 kJ/mol
Hazards
EU classification (DSD) (outdated)	not listed
NFPA 704 (fire diamond)	0 1 0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Preparation

For commercial use, sodium formate is produced by absorbing carbon monoxide under pressure in solid sodium hydroxide at 130 °C and 6-8 bar pressure:[1]

CO + NaOH → HCO₂Na

Because of the low-cost and large-scale availability of formic acid by carbonylation of methanol and hydrolysis of the resulting methyl formate, sodium formate is usually prepared by neutralizing formic acid with sodium hydroxide. Sodium formate is also unavoidably formed as a by-product in the final step of the pentaerythritol synthesis and in the crossed Cannizzaro reaction of formaldehyde with the aldol reaction product trimethylol acetaldehyde [3-hydroxy-2,2-bis(hydroxymethyl)propanal].[2]

In the laboratory, sodium formate can be prepared by neutralizing formic acid with sodium carbonate. It can also be obtained by reacting chloroform with an alcoholic solution of sodium hydroxide.

CHCl₃ + 4 NaOH → HCOONa + 3 NaCl + 2 H₂O

or by reacting sodium hydroxide with chloral hydrate.

C₂HCl₃(OH)₂ + NaOH → CHCl₃ + HCOONa + H₂O

The latter method is, in general, preferred to the former because the low aqueous solubility of CHCl₃ makes it easier to separate out from the sodium formate solution, by fractional crystallization, than the soluble NaCl would be.

Sodium formate may also be created via the haloform reaction between ethanol and sodium hypochlorite in the presence of a base. This procedure is well documented for the preparation of chloroform.

Properties

Physical properties

Sodium formate crystallizes in a monoclinic crystal system with the lattice parameters a = 6,19 Å, b = 6,72 Å, c = 6,49 Å and β = 121,7°.[3]

Chemical properties

On heating, sodium formate decomposes to form sodium oxalate and hydrogen.[4] The resulting sodium oxalate can be converted by further heating to sodium carbonate upon release of carbon monoxide:[5][4]

${\displaystyle {\ce {2HCOONa->[\Delta ]{(COO)2Na2}+H2\!\uparrow }}}$

${\displaystyle {\ce {(COO)2Na2->[{} \atop >\ {\ce {290^{o}C}}]{Na2CO3}+CO\!\uparrow }}}$

As a salt of a weak acid (formic acid) and a strong base (sodium hydroxide) sodium formate reacts in aqueous solutions basic:

${\displaystyle {\ce {HCOO^- + H2O <<=> HCOOH + OH^-}}}$

A solution of formic acid and sodium formate can thus be used as a buffer solution.

Sodium formate is slightly water-hazardous and inhibits some species of bacteria but is degraded by others.

Uses

Sodium formate is used in several fabric dyeing and printing processes. It is also used as a buffering agent for strong mineral acids to increase their pH, as a food additive (E237), and as a de-icing agent.

In structural biology, sodium formate can be used as a cryoprotectant for X-ray diffraction experiments on protein crystals,[6] which are typically conducted at a temperature of 100 K to reduce the effects of radiation damage.

Sodium formate plays a role in the synthesis of formic acid, it is converted by sulfuric acid via the following reaction equation:

${\displaystyle \mathrm {2\ HCOONa+H_{2}SO_{4}\longrightarrow 2\ HCOOH+Na_{2}SO_{4}} }$

Sodium formate is converted with sulfuric acid to formic acid and sodium sulfate.

The urticating hair of stinging nettles contain sodium formate as well as formic acid.

Solid sodium formate is used as a non-corrosive agent at airports for de-icing of runways in mix with corrosion inhibitors and other additives, which rapidly penetrate solid snow and ice layers, detach them from the asphalt or concrete and melt the ice rapidly. Sodium formate was also used as a road deicer in the city of Ottawa from 1987 to 1988.[7]

The high freezing point depression e.g. in comparison to the still frequently used urea (which is effective but problematic due to eutrophication) effectively prevents the re-icing, even at temperatures below −15 °C. The thawing effect of the solid sodium formate can even be increased by moistening with aqueous potassium formate or potassium acetate solutions. The degradability of sodium formate is particularly advantageous with a chemical oxygen demand (COD) of 211 mg O₂/g compared with the de-icing agents sodium acetate (740 mg O₂/g) and urea with (> 2,000 mg O₂/g).[8]

Saturated sodium formate solutions (as well as mixtures of other alkali metal formates such as potassium and cesium formate) are used as important drilling and stabilizing aids in gas and oil exploration because of their relatively high density. By mixing the corresponding saturated alkali metal formate solutions any densities between 1,0 and 2,3 g/cm³ can be set. The saturated solutions are biocidal and long-term stable against microbial degradation. Diluted, on the other hand, they are fast and completely biodegradable. As alkali metal formates as drilling aids make it unnecessary to add solid fillers to increase the density (such as barytes) and the formate solutions can be recovered and recycled at the drilling site, formates represent an important advance in exploration technology.[9]

See also

• Sodium acetate

References

1. Arnold Willmes, Taschenbuch Chemische Substanzen, Harri Deutsch, Frankfurt (M.), 2007.
2. H.-J. Arpe, Industrielle Organische Chemie, 6., vollst. überarb. Aufl., Wiley-VCH Verlag, 2007, ISBN 978-3-527-31540-6
3. W. H. Zachariasen: "The Crystal Structure of Sodium Formate, NaHCO₂" in J. Am. Chem. Soc., 1940, 62(5), S. 1011–1013. doi:10.1021/ja01862a007
4. T. Meisel, Z. Halmos, K. Seybold, E. Pungor: "The thermal decomposition of alkali metal formates" in Journal of Thermal Analysis and Calorimetry 1975, 7(1). S. 73-80. doi:10.1007/BF01911627
5. T. Yoshimori, Y. Asano, Y. Toriumi, T. Shiota: "Investigation on the drying and decomposition of sodium oxalate" in Talanta 1978, 25(10) S. 603-605. doi:10.1016/0039-9140(78)80158-1
6. Bujacz, G.; Wrzesniewska, B.; Bujacz, A. (2010), "Cryoprotection properties of salts of organic acids: a case study for a tetragonal crystal of HEW lysozyme", Acta Crystallographica Section D: Biological Crystallography, 66 (7), pp. 789–796, doi:10.1107/S0907444910015416, PMID 20606259
7. Frank M. D'Itr (1992). Chemical Deicers and the Environment. Google Books. p. 167. ISBN 9780873717052.
8. Deicer Anti-icing Snow melting Thawing Chemicals Manufacturers
9. William Benton and Jim Turner, Cabot Specialty Fluids: Cesium formate fluid succeeds in North Sea HPHT field trials (PDF; 88 kB); In: Drilling Contractor, Mai/Juni 2000.