Propionaldehyde

Not to be confused with propanol.

Propionaldehyde or propanal is the organic compound with the formula CH₃CH₂CHO. It is the 3-carbon aldehyde. It is a colourless, flammable liquid with a pungent and fruity odour. It is produced on a large scale industrially.

Propionaldehyde

Skeletal formula of propionaldehyde (propanal) Flat structure
Names
IUPAC name Propionaldehyde
Preferred IUPAC name Propanal
Other names Methylacetaldehyde Propionic aldehyde Propaldehyde Propan-1-one
Identifiers
CAS Number	123-38-6 Y
3D model (JSmol)	Interactive image
3DMet	B01258
ChEBI	CHEBI:17153 Y
ChEMBL	ChEMBL275626 Y
ChemSpider	512 Y
ECHA InfoCard	100.004.204
EC Number	204-623-0
KEGG	C00479
PubChem CID	527
RTECS number	UE0350000
UNII	AMJ2B4M67V Y
UN number	1275
CompTox Dashboard (EPA)	DTXSID2021658
InChI InChI=1S/C3H6O/c1-2-3-4/h3H,2H2,1H3 Y Key: NBBJYMSMWIIQGU-UHFFFAOYSA-N Y
SMILES CCC=O
Properties
Chemical formula	C3H6O
Molar mass	58.080 g·mol−1
Appearance	Colourless liquid
Odor	Pungent and fruity
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
Magnetic susceptibility (χ)	-34.32·10−6 cm3/mol
Viscosity	0.6 cP at 20 °C
Structure
Molecular shape	C1, O: sp2 C2, C3: sp3
Dipole moment	2.52 D
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H225, H302, H315, H318, H332, H335[1]
Precautionary statements	P210, P261, P280, P304+P340+P312, P305+P351+P338, P310, P403+P235[1]
NFPA 704 (fire diamond)	2 3 2
Flash point	−26 °C (−15 °F; 247 K)
Autoignition temperature	175 °C (347 °F; 448 K)
Related compounds
Related aldehydes	Acetaldehyde Butyraldehyde
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Production

Propionaldehyde is mainly produced industrially by hydroformylation of ethylene:

CO + H₂ + C₂H₄ → CH₃CH₂CHO

In this way, several hundred thousand tons are produced annually.^[2]

Laboratory preparation

Propionaldehyde may also be prepared by oxidizing 1-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.^[3]

Reactions

Main article: aldehyde

Propionaldehyde exhibits the reactions characteristic of alkyl aldehydes, e.g. hydrogenation, aldol condensations, oxidations, etc. It is the simplest aldehyde with a prochiral methylene such that α-functionalized derivatives (CH₃CH(X)CHO) are chiral. If water is available, propionaldehyde exists in equilibrium with 1,1-propanediol, a geminal diol.

Uses

Both industrially and in the laboratory, propionaldehyde has primary application as a chemical building block.^{[2]: 4 [4]}

It is predominantly 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. It is used in the synthesis of several common aroma compounds (cyclamen aldehyde, helional, lilial).^[2]

Reduction of propionaldehyde gives n‑propanol, and reductive amination gives propanamine. Rising demand for non-chlorocarbon solvents has caused some manufacturers to substitutively brominate n‑propanol to propyl bromide. However, the majority of applications use n‑propanol proper in esters or glycol ethers, or as a gentle alkylant for primary and secondary amines.^[2]: 5

Oxidants instead give propionic acid and propionates, typically used as preservatives.^[2]: 5

Laboratory uses

Many laboratory uses exploit its participation in condensation reactions.^{[5][better source needed]} With tert-butylamine it gives CH₃CH₂CH=N-t-Bu, a three-carbon building block used in organic synthesis.^[6]

Extraterrestrial occurrence

Propionaldehyde along with acrolein has been detected in the molecular cloud Sagittarius B2 near the center of the Milky Way Galaxy, about 26,000 light years from Earth.^[7][8][9]

Measurements by the COSAC and Ptolemy instruments on comet 67/P's surface, revealed sixteen organic compounds, four of which were seen for the first time on a comet, including acetamide, acetone, methyl isocyanate and propionaldehyde.^[10][11][12]

Safety

With an LD50 of 1690 mg/kg (oral),^[2] propionaldehyde exhibits low acute toxicity, but is a lung and eye irritant and is a combustible liquid.

References

1. Record of Propanal in the GESTIS Substance Database of the Institute for Occupational Safety and Health, accessed on 22 March 2020.
2. Hensel, A. (2018). "Propanal". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a22_157.pub3. ISBN 978-3527306732.
3. Hurd, Charles D.; Meinert, R. N. (1932). "Propionaldehyde". Organic Syntheses. 12: 64. doi:10.15227/orgsyn.012.0064.
4. Wehrli, Pius A.; Chu, Vera (1978). "Y-Ketoesters from Aldehydes Via Diethyl Acylsuccinates: Ethyl 4-Oxohexanoate". Organic Syntheses. 58: 79. doi:10.15227/orgsyn.058.0079.
5. See, e.g., Sessler, Jonathan L.; Mozaffari, Azadeh; Johnson, Martin R. (1992). "3,4-Diethylpyrrole and 2,3,7,8,12,13,17,18-Octaethylporphyrin". Organic Syntheses. 70: 68. doi:10.15227/orgsyn.070.0068.
6. Peralta, M. M. "Propionaldehyde t-Butylimine" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289X.rp271.
7. Scientists Discover Two New Interstellar Molecules: Point to Probable Pathways for Chemical Evolution in Space, National Radio Astronomy Observatory, June 21, 2004
8. Two newly found space molecules. By: Goho, Alexandra, Science News, 00368423, 7/24/2004, Vol. 166, Issue 4
9. Chemical Precursors to Life Found in Space Scientists say that a universal prebiotic chemistry may be at work
10. Jordans, Frank (30 July 2015). "Philae probe finds evidence that comets can be cosmic labs". The Washington Post. Associated Press. Archived from the original on 23 December 2018. Retrieved 30 July 2015.
11. "Science on the Surface of a Comet". European Space Agency. 30 July 2015. Retrieved 30 July 2015.
12. Bibring, J.-P.; Taylor, M.G.G.T.; Alexander, C.; Auster, U.; Biele, J.; Finzi, A. Ercoli; Goesmann, F.; Klingehoefer, G.; Kofman, W.; Mottola, S.; Seidenstiker, K.J.; Spohn, T.; Wright, I. (31 July 2015). "Philae's First Days on the Comet - Introduction to Special Issue" (PDF). Science. 349 (6247): 493. Bibcode:2015Sci...349..493B. doi:10.1126/science.aac5116. PMID 26228139.