|Jmol-3D images||Image 1|
|Molar mass||58.08 g mol−1|
Pungent, malty odor
|Density||0.81 g cm−3|
−81 °C, 192 K, -114 °F
46-50 °C, 319-323 K, 115-122 °F
|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)
|S-phrases||S9, S16, S29|
|Flash point||−26 °C|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
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.
- CO + H2 + C2H4 → CH3CH2CHO
In this way, several hundred thousand tons are produced annually.
Laboratory preparation 
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.
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.
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.
Interstellar occurrence 
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. Because molecules emit energy at specific frequencies, researchers were able to identify propionaldehyde and the related compound, propenal, by measuring radio waves emitted by the cloud.
- Anthony J. Papa "Propanal" In Ullmann's Encyclopedia of Industrial Chemistry, 2011, WIley-VCH, Weinheim. doi:10.1002/14356007.a22_157.pub2
- Charles D. Hurd and R. N. Meinert (1943), "Propionaldehyde", Org. Synth.; Coll. Vol. 2: 541
- 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.
- Scientists Discover Two New Interstellar Molecules: Point to Probable Pathways for Chemical Evolution in Space, National Radio Astronomy Observatory, June 21, 2004
- Two newly found space molecules. By: Goho, Alexandra, Science News, 00368423, 7/24/2004, Vol. 166, Issue 4
- Chemical Precursors to Life Found in Space Scientists say that a universal prebiotic chemistry may be at work