propionaldehyde

Propionaldehyde is mainly produced industrially by hydroformylation of ethylene:

:CO + H₂ + C₂H₄ → CH₃CH₂CHO

In this way, several hundred thousand tons are produced annually.{{Ullmann|doi= 10.1002/14356007.a22_157.pub3|title=Propanal|year=2018|last1=Hensel|first1=A.|isbn=978-3527306732}}

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.{{cite journal | doi= 10.15227/orgsyn.012.0064| volume = 12 | page = 64 | year = 1932 | title = Propionaldehyde | first1= Charles D.|last1=Hurd|first2=R. N.|last2=Meinert| journal = Organic Syntheses }}

{{main|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.

2-Methylpentanal ({{chem2|CH3CH2CH2CH(CH3)CHO}}) arises by aldol condensation of propionaldehyde followed by dehydration and hydrogenation.

Both industrially and in the laboratory, propionaldehyde has primary application as a chemical building block.{{Rp|4}}{{cite journal |first1=Pius A.|last1=Wehrli|first2=Vera|last2=Chu|doi=10.15227/orgsyn.058.0079|title=Y-Ketoesters from Aldehydes Via Diethyl Acylsuccinates: Ethyl 4-Oxohexanoate|journal=Organic Syntheses|year=1978|volume=58|page=79}}

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).

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

Oxidants instead give propionic acid and propionates, typically used as preservatives.{{rp|5}}

Many laboratory uses exploit its participation in condensation reactions.See, e.g., {{OrgSynth|title=3,4-Diethylpyrrole and 2,3,7,8,12,13,17,18-Octaethylporphyrin|first1=Jonathan L.|last1=Sessler|first2=Azadeh|last2=Mozaffari|first3=Martin R.|last3=Johnson|prep=CV9P0242|year=1992|volume=70|page=68|doi=10.15227/orgsyn.070.0068}}{{better source needed|date=October 2021}} With tert-butylamine it gives CH₃CH₂CH=N-t-Bu, a three-carbon building block used in organic synthesis.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}}.

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.[http://www.nrao.edu/pr/2004/GBTMolecules/ Scientists Discover Two New Interstellar Molecules: Point to Probable Pathways for Chemical Evolution in Space], National Radio Astronomy Observatory, June 21, 2004Two newly found space molecules. By: Goho, Alexandra, Science News, 00368423, 7/24/2004, Vol. 166, Issue 4[http://news.softpedia.com/news/Chemical-Precursors-to-Life-Found-in-Space-32259.shtml Chemical Precursors to Life Found in Space Scientists say that a universal prebiotic chemistry may be at work]

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.{{cite news |url=https://www.washingtonpost.com/world/philae-probe-finds-evidence-that-comets-can-be-cosmic-labs/2015/07/30/63a2fc0e-36e5-11e5-ab7b-6416d97c73c2_story.html |archive-url=https://web.archive.org/web/20181223235109/https://www.washingtonpost.com/world/philae-probe-finds-evidence-that-comets-can-be-cosmic-labs/2015/07/30/63a2fc0e-36e5-11e5-ab7b-6416d97c73c2_story.html |url-status=dead |archive-date=23 December 2018 |title=Philae probe finds evidence that comets can be cosmic labs |work=The Washington Post |agency=Associated Press |first=Frank |last=Jordans |date=30 July 2015 |access-date=30 July 2015}}{{cite web |url=http://www.esa.int/Our_Activities/Space_Science/Rosetta/Science_on_the_surface_of_a_comet |title=Science on the Surface of a Comet |publisher=European Space Agency |date=30 July 2015 |access-date=30 July 2015}}{{cite journal |last1=Bibring |first1=J.-P. |last2=Taylor |first2=M.G.G.T. |last3=Alexander |first3=C. |last4=Auster |first4=U. |last5=Biele |first5=J. |last6=Finzi |first6=A. Ercoli |last7=Goesmann |first7=F. |last8=Klingehoefer |first8=G. |last9=Kofman |first9=W. |last10=Mottola |first10=S. |last11=Seidenstiker |first11=K.J. |last12=Spohn |first12=T. |last13=Wright |first13=I. |title=Philae's First Days on the Comet - Introduction to Special Issue |date=31 July 2015 |journal=Science |volume=349 |issue=6247 |page=493 |doi=10.1126/science.aac5116 |bibcode=2015Sci...349..493B |pmid=26228139|doi-access=free |url=https://elib.dlr.de/97953/1/Science-2015-Bibring-493.pdf }}

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

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Category:Alkanals