Iodoacetic acid

• Iodethansäure
• Mono-iodoacetic acid

White, pungent -smelling solid

Fixed

80-82 ° C

208 ° C

3.18

Good in water ( 600 g · l-1 at 20 ° C)

Risk

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

Production and representation

The presentation takes place by reaction of chloroacetic acid with potassium iodide ( nucleophilic substitution):

Properties

Iodoacetic acid forms colorless crystals with a pungent odor, melting 80-82 ° C and very easy to dissolve in water, ethanol, diethyl ether and other organic solvents. The aqueous solution is strongly acidic, much stronger acid than acetic acid. The reason for this is to stabilize the anion by means of the right electronegative iodine atom: It acts electron withdrawing and distributed ( delocalized ), the negative charge of the anion throughout the molecule. The anion thus formed more easily than the corresponding anion of acetic acid. In aqueous solution, the iodoacetic acid dissociates to form oxonium and iodoacetate ions.

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

Use

Iodoacetic acid is the starting material for various syntheses, such as pesticides or drugs. Thus, the mucolytic ( a secretion solver for colds ) carbocysteine ​​( " carbocisteine ​​" ), from L- cysteine ​​and iodoacetic acid is produced.

Direct application is iodoacetic acid in biochemistry. Iodoacetic acid irreversibly alkylated SH group of proteins, such as the glyceraldehyde phosphate dehydrogenase. It can be used with -SH at the active site to inactivate enzymes irreversibly. This property of irreversible enzyme blockade also determines the toxicity of iodoacetic acid.

In principle, iodoacetic acid, bromoacetic acid and also useful as preservatives. Because of the relatively high toxicity and instability it is hardly used.

Hazards

Iodoacetic acid and its solutions are highly caustic and toxic.