IUPAC Name: propanoic acid 
Empirical Formula: C₃H₆O₂
Molecular Weight: 74.0785g/mol
EINECS: 201-176-3 
Structure of Propionic adid (CAS NO.79-09-4):

Index of Refraction: 1.397
Molar Refractivity: 17.51 cm³
Molar Volume: 72.6 cm³
Polarizability: 6.94×10^-24cm³
Surface Tension: 32.3 dyne/cm
Density: 1.019 g/cm³
Flash Point: 57.7 °C
Enthalpy of Vaporization: 40.08 kJ/mol 
Melting Point: −24-−23 °C(lit.)
Boiling Point: 141.7 °C at 760 mmHg
Vapour Pressure: 4.23 mmHg at 25°C 
storage temp: 0-6°C
Water Solubility: 37 g/100 mL 
Stability: Stable. Incompatible with strong oxidizing agents. Flammable. 
Product Categories: Alkylcarboxylic Acids;Monofunctional & alpha,omega-Bifunctional Alkanes;Monofunctional Alkanes 
Canonical SMILES: CCC(=O)O
InChI: InChI=1S/C3H6O2/c1-2-3(4)5/h2H2,1H3,(H,4,5)
InChIKey: XBDQKXXYIPTUBI-UHFFFAOYSA-N

Propionic acid was first described in 1844 by Johann Gottlieb. Over the next few years, other chemists produced propionic acid in various other ways, none of them realizing they were producing the same substance. In 1847, the French chemist Jean-Baptiste Dumas established that all the acids were the same compound, which he called propionic acid,it was the smallest H(CH₂)nCOOH acid that exhibited the properties of the other fatty acids, such as producing an oily layer when salted out of water and having a soapy potassium salt.

 Propionic acid can prepare the propionate ester for the use of spices,and it also can be used as solvents for cellulose nitrate and plasticizers, etc.

In industry, propionic acid is mainly produced by the hydrocarboxylation of ethylene using nickel carbonyl as the catalyst:
H₂C=CH₂ + H₂O + CO → CH₃CH₂CO₂H 
It is also produced by the aerobic oxidation of propionaldehyde. In the presence of cobalt or manganese ns, this reaction proceeds rapidly at temperatures as mild as 40–50 °C:
CH₃CH₂CHO + 1/2O₂ → CH₃CH₂COOH.

Reported in EPA TSCA Inventory.

Hazard Codes:  C
Risk Statements:  36/37/38-34
R36/37/38:Irritating to eyes, respiratory system and skin. 
R34:Causes burns.
Safety Statements:  26-36-45-23
S26: In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. 
S36:Wear suitable protective clothing. 
S45:In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.) 
S23:Do not breathe vapour.
RIDADR:  UN 3463 8/PG 2
WGK Germany:  1
HazardClass:  8
PackingGroup:  II
Propionic acid is poisonous by intraperitoneal route,and it is moderately toxic by ingestion, skin contact, and intravenous routes. It is corrosive irritant to eyes, skin, and mucous membranes.Propionic acid is flammable liquid and highly flammable when exposed to heat, flame, or oxidizers. To fight fire, use alcohol foam. When heated to decomposition it emits acrid smoke and irritating fumes.

OSHA PEL: TWA 10 ppm
ACGIH TLV: TWA 10 ppm
DFG MAK: 10 ppm (31 mg/m³)
DOT Classification:  8; Label: Corrosive

  Propionic adid , its cas register number is 79-09-4. It also can be called 4-02-00-00695 (Beilstein Handbook Reference) ;
 AI3-04167 ; Acide propionique ; C3 acid ; CCRIS 6096 ; Carboxyethane ; Caswell No. 707 ; EPA Pesticide Chemical Code 077702 ; Ethanecarboxylic acid ; Ethylformic acid ; FEMA No. 2924 ; FEMA Number 2924 ; HSDB 1192 ; Kyselina propionova ; Luprosil ; Metacetonic acid ; Monoprop ; Propanoic acid ; Propionic acid grain preserver ; Propionoic acid ; Prozoin ; Pseudoacetic acid ; Sentry grain preserver ; Tenox P grain preservative ; UNII-JHU490RVYR . Propionic adid (CAS NO.11135-81-2) is a Clear, colorless liquid.