Oxalate

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Oxalate
two capital Cs connected to each other by a solid line and each connected to two separate Os by a solid line and a dashed line next to the solid line, the whole thing in brackets with a −2 to the top-right
The structure of the oxalate anion
Names
IUPAC name
Oxalate
Systematic IUPAC name
Ethanedioate[1]
Identifiers
3D model (
JSmol
)
1905970
ChEBI
ChemSpider
2207
KEGG
UNII
  • InChI=1S/C2H2O4/c3-1(4)2(5)6/h(H,3,4)(H,5,6)/p-2
    Key: MUBZPKHOEPUJKR-UHFFFAOYSA-L
  • InChI=1S/C2H2O4/c3-1(4)2(5)6/h(H,3,4)(H,5,6)/p-2
    Key: MUBZPKHOEPUJKR-UHFFFAOYSA-L
  • C(=O)(C(=O)[O-])[O-]
Properties
C2O2−4
Molar mass 88.018 g·mol−1
Conjugate acid
 Hydrogenoxalate[2]
Structure
D2h
Related compounds
Related
isoelectronic
 Dinitrogen tetroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Oxalate (systematic IUPAC name: ethanedioate) is an

conjugate base of oxalic acid. At neutral pH in aqueous solution
, oxalic acid converts completely to oxalate.

Relationship to oxalic acid

The dissociation of

pKa = 1.27). The loss of the second proton, which yields the oxalate ion, has an equilibrium constant of 5.25×10−5 (pKa = 4.28). These values imply, in solutions with neutral pH, no oxalic acid and only trace amounts of hydrogen oxalate exist.[3] The literature is often unclear on the distinction between H2C2O4, HC2O−4, and C2O2−4, and the collection of species is referred to as oxalic acid.[citation needed
]

Structure

The oxalate anion exists in a nonplanar conformation where the O–C–C–O dihedrals approach 90° with approximate D2d symmetry.[4] When chelated to cations, oxalate adopts the planar, D2h conformation.[5][6] However, in the structure of caesium oxalate Cs2C2O4 the O–C–C–O dihedral angle is 81(1)°.[7][8] Therefore, Cs2C2O4 is more closely approximated by a D2d symmetry structure because the two CO2 planes are staggered. Two structural forms of rubidium oxalate Rb2C2O4 have been identified by single-crystal X-ray diffraction: one contains a planar and the other a staggered oxalate.

Nonplanar conformation found in caesium oxalate Cs2C2O4[8][9]
Planar conformation found in potassium oxalate K2C2O4[8][10]

The

electrostatic interactions
as unfavorable O−O repulsion is maximized in the planar form.

Occurrence in nature

Oxalate occurs in many plants, where it is synthesized by the incomplete

saccharides
.

Several plant foods such as the root and/or leaves of

beets, cocoa, chocolate, most nuts, most berries, fishtail palms, New Zealand spinach (Tetragonia tetragonioides), and beans.[citation needed
] Leaves of the tea plant (Camellia sinensis) contain among the greatest measured concentrations of oxalic acid relative to other plants. However, the drink derived by infusion in hot water typically contains only low to moderate amounts of oxalic acid due to the small mass of leaves used for brewing.[citation needed]

Physiological effects

Main article:
Kidney stone
kidney stone showing tetragonal crystals of weddellite
(calcium oxalate dihydrate) emerging from the amorphous central part of the stone; the horizontal length of the picture represents 0.5 mm of the figured original.

Excess consumption of oxalate-rich foods has been linked to

kidney stone formation of metal ions, such as calcium oxalate, a risk factor for kidney stones.[16]

Some fungi of the genus Aspergillus produce oxalic acid.[17]

As a ligand for metal ions

Main article: Transition metal oxalate complex

Oxalate also forms

bidentate ligand. When the oxalate chelates to a single metal center, it always adopts the planar conformation. As a bidentate ligand, it forms a 5-membered MC2O2 ring. An illustrative complex is potassium ferrioxalate, K3[Fe(C2O4)3]. The drug oxaliplatin exhibits improved water solubility relative to older platinum-based drugs, avoiding the dose-limiting side-effect of nephrotoxicity
. Oxalic acid and oxalates can be oxidized by permanganate in an autocatalytic reaction. One of the main applications of oxalic acid is rust-removal, which arises because oxalate forms water-soluble derivatives with the ferric ion.

Excess

An excess oxalate level in the blood is termed hyperoxalemia, and high levels of oxalate in the urine is termed hyperoxaluria.

Acquired

Although unusual, consumption of oxalates (for example, the grazing of animals on oxalate-containing plants such as

gut flora may help alleviate this.[19]

Congenital

Main article: Primary hyperoxaluria

Primary hyperoxaluria is a rare, inherited condition, resulting in increased excretion of oxalate, with oxalate stones being common.

References

  1. ^ "Oxalate".
  2. ^ "oxalate(2−) (CHEBI:30623)". www.ebi.ac.uk. Retrieved 2 January 2019. oxalate(2−) (CHEBI:30623) is conjugate base of oxalate(1−) (CHEBI:46904) … oxalate(1−) (CHEBI:46904) is conjugate acid of oxalate(2−) (CHEBI:30623)
  3. ISBN 3-527-30673-0
    .
  4. ^
    doi:10.1021/ed200202r
    .
  5. doi:10.1107/S0567740881004676
    .
  6. doi:10.1107/S0365110X64002079
    .
  7. ^ In the figure 81(1)°, the (1) indicates that 1° is the standard uncertainty of the measured angle of 81°
  8. ^
    PMID 12611516
    .
  9. doi:10.5517/cc6fzf0
    .
  10. doi:10.5517/cc6fzcy
    .
  11. S2CID 98744097
    .
  12. doi:10.1016/0166-1280(90)85053-P
    .
  13. doi:10.1021/jp002657c
    .
  14. ISBN 9780024180100
    .
  15. ISBN 0-7216-2439-1
    .
  16. PMID 30566003
    .
  17. PMID 16047945
    .
  18. PMID 25830441
    .
  19. PMID 23536130
    .

Further reading

External links

  • Oxalate.org - Oxalate content of 750+ foods from university and government sources
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