Propionaldehyde

 ( Alkanals ) 

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.

---

Production Propionaldehyde is mainly produced industrially by hydroformylation of ethylene:

CO + H₂ + C₂H₄ → CH₃CH₂CHO

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

---

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.

---

Reactions Propionaldehyde exhibits the reactions characteristic of alkyl , 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 () arises by aldol condensation of propionaldehyde followed by dehydration and hydrogenation.

---

Uses Both industrially and in the laboratory, propionaldehyde has primary application as a chemical building block.

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 . It is used in the synthesis of several common (cyclamen aldehyde, helional, lilial).

Reduction of propionaldehyde gives n-propanol, and reductive amination gives propanamine. Rising demand for non-chlorocarbon solvents has caused some manufacturers to substitutively brominate npropanol to propyl bromide. However, the majority of applications use npropanol proper in or , or as a gentle alkylant for primary and secondary .

Oxidants instead give propionic acid and propionates, typically used as preservatives.

---

Laboratory uses

Many laboratory uses exploit its participation in condensation reactions.See, e.g., 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. .

---

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. 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 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 surface, revealed sixteen , four of which were seen for the first time on a comet, including acetamide, acetone, methyl isocyanate and propionaldehyde.

---

Safety

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

Categories: Alkanals

Post Comment