Benzoin

• 2-hydroxy -1 ,2- diphenylethanone
• α -hydroxy- α -phenylacetophenone

White or yellowish solid with an aromatic odor

Fixed

1.3 g · cm -3

344 ° C

1.3 hPa ( 136 ° C)

• Very poor in water ( 0.3 g · l-1 at 25 ° C)
• Soluble in acetone and warm ethanol

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Benzoin is the simplest aromatic hydroxy ketone. It naturally occurs in some plants, such as in the oil of bitter almonds. Benzoin is a chiral substance which is commercially available in both racemic as well as in the two pure enantiomeric forms.

History

Benzoin was first synthesized in 1832 by Justus von Liebig and Friedrich Wöhler in their investigation of oil of bitter almonds, which consists of benzaldehyde with traces of cyanide. The catalytic synthesis in the form of the benzoin condensation was improved by Nikolai Zinin in his time with Liebig.

Production

Benzoin can be produced from benzaldehyde by cyanide - catalyzed addition ( benzoin addition).

The cleaning can be effected by sublimation. This reaction takes place for many aromatic aldehydes and glyoxals. The resulting α - hydroxy carbonyl compounds are referred to as benzoin.

Properties

Benzoin is a white in pure form, otherwise white to pale yellow solid with an aromatic odor. Its optical rotation is (R): -115 ° (c = 1.5 in acetone) or (S ): 115 ° (c = 1.5 in acetone).

Benzoin has a reducing effect than α - hydroxyketone. In the dehydrogenation occurs benzil.

Use

Benzoin is in the powder coating area as degassing and leveling agent application and is used as starting material for the synthesis of benzil.

Benzoin is also suitable for an interesting chemical experiment. To small amounts of benzoin are dissolved together with benzil at room temperature in a closed vessel in ethanol and then added to sodium hydroxide. If the vessel shaken so does the solution immediately a clear yellow color, which turns to rest after a few seconds after purple. Reason as often repeatable reaction is the formation of a radical anion, which reacts with the oxygen when shaken.