Atropic acid

CAS NO.：492-38-6
Empirical Formula: C9H8O2
Molecular Weight: 148.16
MDL number: MFCD00046531
EINECS: 207-753-6
SAFETY DATA SHEET (SDS)
Update Date: 2026-01-13 11:19:25

What is Atropic acid?

Chemical properties

White to Off-White Solid.

The Uses of Atropic acid

Atropic acid is an Impurity of Ipratropium bromide and Atropine Sulfate. Atropic acid and β,β-dimethylatropic acid are plant growth regulators.

Preparation

The synthesis of atropic acid involves several steps. Firstly, tropic acid is oxidized with hot KMnO4 to form benzoic acid. Secondly, tropic acid reacted with HBr to produce C9H9O2Br. Thirdly, C9H9O2Br is reacted with alcoholic KOH to yield atropic acid, C9H8O2. Finally, atropic acid is catalytically hydrogenated to form hydratropic acid, C9H10O2.

Reactions

Atropic acid is formed by the dehydration of tropic acid. Hence addition of water to atropic acid gives tropic acid.
Atropic acid, on oxidation yields benzoic acid. The formation of benzoic acid reveals that atropic acid and tropic acid contain atleast one benzene nucleus with a side chain containing carboxylic acid in their structure.
atropic acid reaction
As atropic acid is an unsaturated acid it mean atropic acid may be either structure (I) or (II) .
Hence, the structure (II) is atropic acid which is confirmed by oxidation with KMnO4 to form phenylglyoxal.

Properties of Atropic acid

Melting point:	106-107°
Boiling point:	bp ~267° with partial decompn
Density	1.0061 (rough estimate)
refractive index	1.5049 (estimate)
storage temp.	2-8°C
solubility	DMSO (Slightly), Methanol (Slightly)
form	Solid
pka	3.86±0.11(Predicted)
color	White to Off-White
Water Solubility	1.3g/L(20 ºC)
Merck	14,874
Stability:	Light Sensitive
CAS DataBase Reference	492-38-6(CAS DataBase Reference)
NIST Chemistry Reference	Benzeneacetic acid, «alpha»-methylene-(492-38-6)
EPA Substance Registry System	Benzeneacetic acid, .alpha.-methylene- (492-38-6)

Safety information for Atropic acid

Signal word	Warning
Pictogram(s)	Exclamation Mark Irritant GHS07
GHS Hazard Statements	H315:Skin corrosion/irritation H319:Serious eye damage/eye irritation
Precautionary Statement Codes	P264:Wash hands thoroughly after handling. P264:Wash skin thouroughly after handling. P280:Wear protective gloves/protective clothing/eye protection/face protection.