Diglycolic acid
Chemical compound
From Wikipedia, the free encyclopedia
Diglycolic acid is an aliphatic dicarboxylic acid, its acidity is between the one of acetic acid and oxalic acid.[1] It is formed in the oxidation of diethylene glycol in the body and can lead to severe complications with fatal outcome.[2]
| |
 | |
| Names | |
|---|---|
| Preferred IUPAC name
2,2′-Oxydiacetic acid | |
| Identifiers | |
3D model (JSmol) |
|
| ChemSpider | |
| ECHA InfoCard | 100.003.476 |
| EC Number |
|
PubChem CID |
|
| UNII | |
CompTox Dashboard (EPA) |
|
| |
| |
| Properties | |
| C4H6O5 | |
| Molar mass | 134.09 g/mol |
| Melting point | 140-144°C |
| Acidity (pKa) | 2.79, 3.93 (20°C) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Preparation
Oxidation of diethylene glycol with concentrated nitric acid was described by A. Wurtz in 1861[3]
In parallel, W. Heintz reported the synthesis of diglycolic acid from chloroacetic acid by heating with sodium hydroxide solution.[4]
In a version with barium hydroxide solution as an alkaline medium, diglycolic acid is obtained in 68% yield after acidification.[5]
The yields of the described reactions are unsatisfactory for use on a technical scale.
The single-stage nitric acid process gives even in the presence of an oxidation catalyst (vanadium(V)oxide) yields of only 58-60%.[6] In a multi-stage process of nitric acid oxidation at 70 °C and multiple crystallization steps, evaporation of the residues and return of the diethylene glycol-containing mother liquor, product yields of up to 99% (based on diethylene glycol) can be achieved.[7]
The oxidation of diethylene glycol with air, oxygen or ozone avoids the use of expensive nitric acid and prevents the inevitable formation of nitrous gases.[8] In the presence of a platinum catalyst, yields of 90% can be obtained by air oxidation.[9]
On a bismuth platinum contact catalyst, yields of 95% are to be achieved under optimized reaction conditions.[10]
The oxidation of 1,4-dioxan-2-one (p-dioxanone, a lactone which is used as a comonomer in biodegradable polyesters with nitric acid or dinitrogen tetroxide) is also described with yields of up to 75%.[11]
Properties
Diglycolic acid is readily water-soluble and crystallizes from water in monoclinic prisms as a white, odorless solid. At an air humidity of more than 72% and 25 °C, the monohydrate is formed. The commercial product is the anhydrous form as free-flowing flakes.[12]
Application
Diesters of diglycolic acid with (branched) higher alcohols can be used as softeners for polyvinyl chloride (PVC) with comparable properties as di-n-octyl phthalate (DOP).[13]
Basic solutions of diglycolic acid are described for the removal of limescale deposits in gas and oil bores, as well as in systems such as heat exchangers or steam boilers.[14]
Diglycolic acid can be used as a diester component in homo- and copolymeric polyesters (so-called polyalkylene diglycolates) which are biocompatible and biodegradable and can be used alone or in blends with aliphatic polyesters as tissue adhesives, cartilage substitutes or as implant materials:[15]
