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Not to be confused with propanol.
Skeletal structure of propanal Flat structure
Ball-and-stick model
CAS number 123-38-6 YesY
PubChem 527
ChemSpider 512 YesY
UN number 1275
ChEBI CHEBI:17153 YesY
Jmol-3D images Image 1
Molecular formula C3H6O
Molar mass 58.08 g mol−1
Appearance Colorless liquid
Pungent, malty odor
Density 0.81 g cm−3
Melting point −81 °C (−114 °F; 192 K)
Boiling point 46 to 50 °C (115 to 122 °F; 319 to 323 K)
Solubility in water 20 g/100 mL
Viscosity 0.6 cP at 20 °C
Molecular shape C1, O: sp2

C2, C3: sp3

Dipole moment 2.52 D
EU classification Highly flammable (F)
Irritant (Xi)
R-phrases R11, R36/37/38
S-phrases S9, S16, S29
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point −26 °C (−15 °F; 247 K)
Related compounds
Related aldehydes Acetaldehyde
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Propionaldehyde or propanal is the organic compound with the formula CH3CH2CHO. It is a saturated 3-carbon aldehyde and is a structural isomer of acetone. It is a colourless liquid with a slightly irritating, fruity odour.


Propionaldehyde is mainly produced industrially through hydroformylation, by combining synthesis gas (carbon monoxide and hydrogen) with ethylene using a metal (typically rhodium) catalyst:

CO + H2 + C2H4 → CH3CH2CHO

In this way, several hundred thousand tons are produced annually.[1]

Laboratory preparation[edit]

Propionaldehyde may also be prepared by oxidizing propanol with a mixture of sulfuric acid and potassium dichromate. The reflux condenser contains water heated at 60 °C, which condenses unreacted propanol, but allows propionaldehyde to pass. The propionaldehyde vapor is immediately condensed into a suitable receiver. In this arrangement, any propionaldehyde formed is immediately removed from the reactor, thus it does not get over-oxidized to propionic acid.[2]


It is principally used as a precursor to trimethylolethane (CH3C(CH2OH)3) through a condensation reaction with formaldehyde; this triol is an important intermediate in the production of alkyd resins. Other applications include reduction to propanol and oxidation to propionic acid.[1]

Condensation of propionaldehyde with tert-butylamine gives CH3CH2CH=N-t-Bu, a three-carbon building block used in organic synthesis. Deprotonation of this imine with LDA produces CH3CHLiCH=N-t-Bu, which in turn condenses with aldehydes.[3]

Interstellar occurrence[edit]

Astronomers have detected propionaldehyde in the molecular cloud Sagittarius B2 near the center of the Milky Way Galaxy, about 26,000 light years from Earth.[4][5][6] Because molecules emit energy at specific frequencies, researchers were able to identify propionaldehyde and the related compound, acrolein, by measuring radio waves emitted by the cloud.


  1. ^ a b Anthony J. Papa "Propanal" In Ullmann's Encyclopedia of Industrial Chemistry, 2011, WIley-VCH, Weinheim. doi:10.1002/14356007.a22_157.pub2
  2. ^ Charles D. Hurd and R. N. Meinert (1943), "Propionaldehyde", Org. Synth. ; Coll. Vol. 2: 541 
  3. ^ Peralta, M. M. "Propionaldehyde t-Butylimine" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289.
  4. ^ Scientists Discover Two New Interstellar Molecules: Point to Probable Pathways for Chemical Evolution in Space, National Radio Astronomy Observatory, June 21, 2004
  5. ^ Two newly found space molecules. By: Goho, Alexandra, Science News, 00368423, 7/24/2004, Vol. 166, Issue 4
  6. ^ Chemical Precursors to Life Found in Space Scientists say that a universal prebiotic chemistry may be at work