Iodoacetic acid

Structural formula
General
Surname	Iodoacetic acid
other names	Iodoethanoic acid Monoiodoacetic acid
Molecular formula	C 2 H 3 IO 2
Brief description	light yellow, hygroscopic solid
External identifiers / databases
CAS number 64-69-7 EC number 200-590-1 ECHA InfoCard 100,000,537 PubChem 5240 ChemSpider 5050 Wikidata Q416375
properties
Molar mass	185.96 g mol −1
Physical state	firmly
density	4.6 g cm −3
Melting point	82-83 ° C
boiling point	208 ° C
pK s value	3.18
solubility	good in water (600 g l −1 at 20 ° C)
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 301-314 P: 280-260-301 + 310 + 330-331-303 + 361 + 353-305 + 351 + 338-310
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Iodoacetic acid (also: monoiodoacetic acid ) is a derivative of acetic acid in which one hydrogen atom of the methyl group is replaced by an iodine atom . Their salts are known as (mono-) iodine acetates .

Extraction and presentation

It is represented by the reaction of chloroacetic acid with potassium iodide ( nucleophilic substitution ):

${\displaystyle {\ce {Cl-CH2-COOH + KI <=> I-CH2-COOH + KCl}}}$

properties

Iodoacetic acid forms colorless crystals with a pungent odor, which melt at 82–83 ° C and dissolve very easily in water , ethanol , diethyl ether and other organic solvents . The aqueous solution reacts strongly acidic, significantly more acidic than acetic acid. The reason for this is the stabilization of the anion by the rather electronegative iodine atom: It has an electron-withdrawing effect and distributes ( delocalizes ) the negative charge of the anion over the entire molecule . The anion is therefore formed more easily than the corresponding anion of acetic acid. The iodoacetic acid dissociates in aqueous solution to form oxonium and iodoacetate ions.

Like many other alkyl iodides, iodoacetic acid is unstable to sunlight and decomposes quite easily. Iodoacetic acid should therefore be stored in brown bottles at temperatures below 15 ° C.

use

Iodoacetic acid is the starting material for various syntheses, for example for pesticides or pharmaceuticals . The mucolytic (a secretion remover for colds) carbocysteine ​​can be produced from L - cysteine and iodoacetic acid.

Iodoacetic acid is used directly in biochemistry . Iodoacetic acid alkylation irreversibly SH group of proteins , such as the glyceraldehyde phosphate - dehydrogenase . It can be used to irreversibly deactivate enzymes with -SH at the active site. This property of irreversible enzyme blockage also causes the toxicity of iodoacetic acid.

In principle, iodoacetic acid, like bromoacetic acid , is suitable as a preservative . However, due to its relatively high toxicity and instability, it is rarely used.

hazards

Iodoacetic acid and its solutions are highly corrosive and toxic.

Individual evidence

1. ↑ ^{a b c d e f} Entry on iodoacetic acid in the GESTIS substance database of the IFA , accessed on January 8, 2020(JavaScript required) .
2. ↑ Data sheet iodoacetic acid from Sigma-Aldrich , accessed on January 4, 2016 ( PDF ).
3. ↑ Zvi Rappoport (Ed.): CRC Handbook of Tables for Organic Compound Identification . 3 ^rd Edition, CRC Press / Taylor and Francis, Boca Raton, FL, 1967, ISBN 0-8493-0303-6 , Acid Dissociation Constants of Organic Acids in Aqueous Solution, S. 430th
4. ↑ Entry on Iodoacetic acid in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
5. ↑ Entry on iodoacetic acid. In: Römpp Online . Georg Thieme Verlag, accessed on May 1, 2014.