Oxalic acid


Oxalic acid

帖子 由 Giraffe 于 周二 七月 28, 2009 7:07 am

Although it can be readily purchased, oxalic acid can be prepared in the laboratory by oxidizing sucrose using nitric acid in the presence of a small amount of vanadium pentoxide as a catalyst. On a large scale, sodium oxalate is manufactured by absorbing carbon monoxide under pressure in hot sodium hydroxide.
Typically oxalic acid is obtained as the dihydrate. This solid can be dehydrated with heat or by azeotropic distillation. Anhydrous oxalic acid exists as two polymorphs; in one the hydrogen-bonding results in a chain-like structure whereas the hydrogen bonding pattern in the other form defines a sheet-like structure.
Oxalic acid can be prepared via oxidation of either Glycolic acid or Ethylene glycol. In one synthetic path, Nitric acid is used to oxidize either of the two in the presence of oxygen.
Oxalic acid is a relatively strong weak acid with pKa1=1.27 and pKa2=4.28. Oxalic acid exhibits many of the reactions characteristic of other carboxylic acids. It forms esters such as dimethyloxalate (m.p. 52.5–53.5 °C).. It forms an acid chloride called oxalyl chloride.
Oxalate, the conjugate base of oxalic acid, is an excellent ligand for metal ions. It usually binds as a bidentate ligand forming a 5-membered MO2C2 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.

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