Propionaldehyde or propanal is the

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

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 Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

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 Propionic acid (, from the Greek language, Greek words πρῶτος : ''prōtos'', meaning "first", and πίων : ''píōn'', meaning "fat"; also known as propanoic acid) is a naturally occurring carboxylic acid with chemical formula . It is a ...

Reactions

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 () 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

resin A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Commo ...

s. It is used in the synthesis of several common

aroma compound An aroma compound, also known as an odorant, aroma, fragrance, flavoring or flavor, is a chemical compound that has a smell or odor. For an individual chemical or class of chemical compounds to impart a smell or fragrance, it must be sufficien ...

s ( 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 ''n''propanol to propyl bromide. However, the majority of applications use ''n''propanol proper in

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

s or glycol ethers, or as a gentle alkylant for primary and secondary amines. Oxidants instead give

and propionates, typically used as preservatives.

Laboratory uses

Many laboratory uses exploit its participation in condensation reactions. With ''tert''-butylamine it gives CH₃CH₂CH=N-''t''-Bu, a three-carbon building block used in organic synthesis.

Extraterrestrial occurrence

Propionaldehyde along with acrolein has been detected in the

molecular cloud A molecular cloud—sometimes called a stellar nursery if star formation is occurring within—is a type of interstellar cloud of which the density and size permit absorption nebulae, the formation of molecules (most commonly molecular hydrogen, ...

Sagittarius B2 near the center of the Milky Way Galaxy, about 26,000 light years from Earth.Chemical Precursors to Life Found in Space Scientists say that a universal prebiotic chemistry may be at work
/ref> Measurements by the COSAC and Ptolemy instruments on

comet A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...

67/P surface, revealed sixteen

s, four of which were seen for the first time on a comet, including acetamide,

acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...

, methyl isocyanate and propionaldehyde.

Safety

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.

References

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