D-Galacturonic acid is a sugar acid, an oxidized form of Dgalactose. It is the main component of pectin, in which it exists as the polymer polygalacturonic acid. It has an aldehyde group at C1 and a carboxylic acid group at C6. Other oxidized forms of D-galactose are D-galactonic acid (carboxylic group at C1) and meso-galactaric acid (mucic acid) (carboxylic groups at C1 and C6). It is also a uronic acid or hexuronic acid. Naturally occurring uronic acids are D-glucuronic acid, D-galacturonic acid, L-iduronic acid and D-mannuronic acid.
Crystallisation of the acid from 95% EtOH and drying it in a vacuum desiccator (12mm) over P2O5 gives the monohydrate mixture of and anomers (mostly -) as white micro needles, which sinter at ~100-111o and melt at 159-160o, [] D 20 +107o (initial, c 4 in H2O mutarotating to +51o). [Link & Sell Biochemical Preparations 3 74, 78 1953, Beilstein 3 IV 2000.] The -anomer is obtained by warming the -anomer in EtOH, AcOH or EtOAc and has m 1 6 0o (165o, sinters at 1 4 0o), [] D 20 +27o (initial, c 2 in H2O mutarotating to +55.3o in 24hours). The sodium salt [14984-39-5] M 216.1 has [] D 20 +27o (c 10 in H2O after 5hours). The phenylhydrazone has m 141o(from MeOH). [Ehrlich & Schubert Chem Ber 62 1974, 2014 1929, Anderson & King J Chem Soc 5333 1961, Beilstein 3 IV 2001.]
