Hydrogenoxalate or hydrogen oxalate ''(IUPAC name: 2-Hydroxy-2-oxoacetate)'' is an
anion
An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
with
chemical formula
A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as pare ...
or , derived from
oxalic acid
Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula , also written as or or . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name i ...
by the loss of a single
proton
A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...
; or, alternatively, from the
oxalate
Oxalate (systematic IUPAC name: ethanedioate) is an anion with the chemical formula . This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (), and several esters such as ...
anion by addition of a proton. The name is also used for any
salt
In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...
containing this anion. Especially in older literature, hydrogenoxalates may also be referred to as bioxalates, acid oxalates, or monobasic oxalates. Hydrogenoxalate is
amphoteric
In chemistry, an amphoteric compound () is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used.
Etymology and terminology
Amphoteric is d ...
, in that it can react both as an acid or a base.
Well characterized salts include
sodium hydrogenoxalate
Sodium hydrogenoxalate or sodium hydrogen oxalate is a chemical compound with the chemical formula . It is an ionic compound. It is a sodium salt (chemistry), salt of oxalic acid . It is an acid salt, acidic salt, because it consists of sodium ca ...
(),
potassium hydrogenoxalate
Potassium hydrogenoxalate is a salt with formula KHC2O4 or K+·HO2C-CO2−. It is one of the most common salts of the hydrogenoxalate anion, and can be obtained by reacting potassium hydroxide with oxalic acid in 1:1 mole ratio.
The salt is ...
(), ammonium hydrogenoxalate (), rubidium hydrogenoxalate () and dimethylammonium hydrogenoxalate ().
Structure
Most hydrogenoxalate salts are
hydrated
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
. For example, potassium hydrogen oxalate crystallizes as . These materials exhibit extended structures resulting from extensive hydrogen bonding and anion-cation interactions. The hydrates dehydrate upon heating:
: