Benzaldehyde (C
6H
5CHO) is an
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
consisting of a
benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
ring with a
formyl substituent. It is the simplest
aromatic
In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
aldehyde
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl gro ...
and one of the most industrially useful.
It is a colorless liquid with a characteristic
almond
The almond (''Prunus amygdalus'', syn. ''Prunus dulcis'') is a species of tree native to Iran and surrounding countries, including the Levant. The almond is also the name of the edible and widely cultivated seed of this tree. Within the genu ...
-like
odor
An odor (American English) or odour (Commonwealth English; see spelling differences) is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and animals can perceive via their sense ...
. The primary component of
bitter almond oil, benzaldehyde can be extracted from a number of other natural sources. Synthetic benzaldehyde is the flavoring agent in imitation almond extract, which is used to flavor cakes and other baked goods.
History
Benzaldehyde was first extracted in 1803 by the French pharmacist Martrès. His experiments focused on elucidating the nature of
amygdalin, the poisonous material found in
bitter almonds
The almond (''Prunus amygdalus'', syn. ''Prunus dulcis'') is a species of tree native to Iran and surrounding countries, including the Levant. The almond is also the name of the edible and widely cultivated seed of this tree. Within the genu ...
, the fruit of ''
Prunus dulcis''. Further work on the oil by
Pierre Robiquet
Pierre Jean Robiquet (13 January 1780 – 29 April 1840) was a French chemist. He laid founding work in identifying amino acids, the fundamental building blocks of proteins. He did this through recognizing the first of them, asparagine, in 180 ...
and Antoine Boutron-Charlard, two French chemists, produced benzaldehyde. In 1832,
Friedrich Wöhler
Friedrich Wöhler () FRS(For) Hon FRSE (31 July 180023 September 1882) was a German chemist known for his work in inorganic chemistry, being the first to isolate the chemical elements beryllium and yttrium in pure metallic form. He was the fi ...
and
Justus von Liebig
Justus Freiherr von Liebig (12 May 1803 – 20 April 1873) was a German scientist who made major contributions to agricultural and biological chemistry, and is considered one of the principal founders of organic chemistry. As a professor at th ...
first synthesized benzaldehyde.
Production
As of 1999, 7000
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s of synthetic and 100 tonnes of natural benzaldehyde were produced annually.
Liquid phase
chlorination and
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
of
toluene
Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) ...
are the main routes. Numerous other methods have been developed, such as the partial oxidation of
benzyl alcohol,
alkali hydrolysis of
benzal chloride, and the
carbonylation
Carbonylation refers to reactions that introduce carbon monoxide into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry. The term carbon ...
of benzene.
[Brühne, Friedrich and Wright, Elaine (2002) “Benzaldehyde” in ''Ullmann's Encyclopedia of Industrial Chemistry''. Wiley-VCH, Weinheim. ]
A significant quantity of natural benzaldehyde is produced from
cinnamaldehyde
Cinnamaldehyde is an organic compound with the formula(C9H8O) C6H5CH=CHCHO. Occurring naturally as predominantly the ''trans'' (''E'') isomer, it gives cinnamon its flavor and odor. It is a phenylpropanoid that is naturally synthesized by the shi ...
obtained from
cassia oil by the retro-
aldol reaction
The aldol reaction is a means of forming carbon–carbon bonds in organic chemistry.
Discovered independently by the Russian chemist Alexander Borodin in 1869 and by the French chemist Charles-Adolphe Wurtz in 1872, the reaction combines two ...
:
the cinnamaldehyde is heated in an
aqueous/
alcoholic solution between 90 °C and 150 °C with a
base (most commonly
sodium carbonate or
bicarbonate
In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula .
Bicarbonate serves a crucial biochemi ...
) for 5 to 80 hours, followed by distillation of the formed benzaldehyde. This reaction also yields
acetaldehyde
Acetaldehyde (IUPAC systematic name ethanal) is an organic chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is a colorless liquid or gas, boiling near room temperature. It is one of the ...
. The
natural status of benzaldehyde obtained in this way is controversial.
"Site-specific
nuclear magnetic resonance spectroscopy", which evaluates
1H/
2H isotope ratios, has been used to differentiate between naturally occurring and synthetic benzaldehyde.
Occurrence
Benzaldehyde and similar chemicals occur naturally in many foods. Most of the benzaldehyde that people eat is from natural plant foods, such as
almonds.
Almonds,
apricot
An apricot (, ) is a fruit, or the tree that bears the fruit, of several species in the genus '' Prunus''.
Usually, an apricot is from the species '' P. armeniaca'', but the fruits of the other species in ''Prunus'' sect. ''Armeniaca'' are al ...
s,
apple
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ancest ...
s, and
cherry kernels contain significant amounts of
amygdalin. This
glycoside
In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. ...
breaks up under enzyme catalysis into benzaldehyde,
hydrogen cyanide
Hydrogen cyanide, sometimes called prussic acid, is a chemical compound with the formula HCN and structure . It is a colorless, extremely poisonous, and flammable liquid that boils slightly above room temperature, at . HCN is produced on a ...
and two equivalents of
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
.
Benzaldehyde contributes to the scent of
oyster mushrooms (''Pleurotus ostreatus'').
Reactions
Benzaldehyde can be oxidized to
benzoic acid
Benzoic acid is a white (or colorless) solid organic compound with the formula , whose structure consists of a benzene ring () with a carboxyl () substituent. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin ...
; in fact "
nzaldehyde readily undergoes autoxidation to form benzoic acid on exposure to air at room temperature" causing a common impurity in laboratory samples. Since the boiling point of benzoic acid is much higher than that of benzaldehyde, it may be purified by
distillation
Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the he ...
.
Benzyl alcohol can be formed from benzaldehyde by means of
hydrogenation
Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic ...
. Reaction of benzaldehyde with anhydrous
sodium acetate and
acetic anhydride yields
cinnamic acid, while alcoholic
potassium cyanide can be used to
catalyze the condensation of benzaldehyde to
benzoin. Benzaldehyde undergoes
disproportionation
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can ...
upon treatment with concentrated alkali (
Cannizzaro reaction): one molecule of the aldehyde is reduced to the
benzyl alcohol and another molecule is simultaneously oxidized to
benzoic acid
Benzoic acid is a white (or colorless) solid organic compound with the formula , whose structure consists of a benzene ring () with a carboxyl () substituent. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin ...
.
:
With diols, including many sugars, benzaldehyde condenses to form
benzylidene acetals.
Uses
Benzaldehyde is commonly employed to confer
almond
The almond (''Prunus amygdalus'', syn. ''Prunus dulcis'') is a species of tree native to Iran and surrounding countries, including the Levant. The almond is also the name of the edible and widely cultivated seed of this tree. Within the genu ...
flavor to foods and scented products, including e-cigarette liquids. It is sometimes used in cosmetics products.
In industrial settings, benzaldehyde is used chiefly as a precursor to other organic compounds, ranging from pharmaceuticals to plastic additives. The
aniline dye malachite green is prepared from benzaldehyde and
dimethylaniline. Benzaldehyde is also a precursor to certain
acridine dyes. Via
aldol condensations, benzaldehyde is converted into derivatives of
cinnamaldehyde
Cinnamaldehyde is an organic compound with the formula(C9H8O) C6H5CH=CHCHO. Occurring naturally as predominantly the ''trans'' (''E'') isomer, it gives cinnamon its flavor and odor. It is a phenylpropanoid that is naturally synthesized by the shi ...
and
styrene. The synthesis of
mandelic acid starts with the addition of
hydrocyanic acid to benzaldehyde:
:
The resulting
cyanohydrin
In organic chemistry, a cyanohydrin or hydroxynitrile is a functional group found in organic compounds in which a cyano and a hydroxy group are attached to the same carbon atom. The general formula is , where R is H, alkyl, or aryl. Cyanohyd ...
is
hydrolysed to
mandelic acid. (The scheme above depicts only one of the two formed
enantiomers).
Niche uses
Benzaldehyde is used as a
bee repellent. A small amount of benzaldehyde solution is placed on
Fume Boardnear the honeycombs. The bees then move away from the honey combs to avoid the fumes. The
beekeeper
A beekeeper is a person who keeps honey bees.
Beekeepers are also called honey farmers, apiarists, or less commonly, apiculturists (both from the Latin '' apis'', bee; cf. apiary). The term beekeeper refers to a person who keeps honey bees i ...
can then remove the
honey frame
A hive frame or honey frame is a structural element in a beehive that holds the honeycomb or brood comb within the hive enclosure or box. The hive frame is a key part of the modern movable-comb hive. It can be removed in order to inspect the bees ...
s from the bee hive with less risk to both bees and beekeeper. It is also sometimes used as an
electronic cigarette flavorant.
Safety
As used in food, cosmetics, pharmaceuticals, and soap, benzaldehyde is "generally regarded as safe" (
GRAS) by the
US FDA and
FEMA
The Federal Emergency Management Agency (FEMA) is an agency of the United States Department of Homeland Security (DHS), initially created under President Jimmy Carter by Presidential Reorganization Plan No. 3 of 1978 and implemented by two Ex ...
.
This status was reaffirmed after a review in 2005.
It is accepted in the European Union as a flavoring agent.
Toxicology studies indicate that it is safe and non-carcinogenic in the concentrations used for foods and cosmetics,
and may even have
anti-carcinogenic (anti-cancer) properties.
For a 70 kg human, the lethal dose is estimated at 50 mL.
An
acceptable daily intake of 15 mg/day has been identified for benzaldehyde by the
United States Environmental Protection Agency
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it ...
.
Benzaldehyde does not accumulate in human tissues.
It is metabolized and then excreted in urine.
References
External links
*
Archived
{{Use dmy dates, date=March 2018
Flavors
Solvents
Phenyl compounds