Stephen Aldehyde Synthesis
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Stephen aldehyde synthesis, a
named reaction A name reaction (or named reaction) is a chemical reaction named after its discoverer(s) or developer(s). Among the tens of thousands of organic reactions that are known, hundreds of such reactions are typically identified by the eponym. Well-known ...
in chemistry, was invented by Henry Stephen (
OBE The Most Excellent Order of the British Empire is a British order of chivalry, rewarding valuable service in a wide range of useful activities. It comprises five classes of awards across both civil and military divisions, the most senior two o ...
/ MBE). This reaction involves the preparation of
aldehydes In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...
(R-CHO) from
nitriles In organic chemistry, a nitrile is any organic compound that has a functional group. The name of the compound is composed of a base, which includes the carbon of the , suffixed with "nitrile", so for example is called "propionitrile" (or pro ...
(R-CN) using
tin(II) chloride Tin(II) chloride, also known as stannous chloride, is a white crystalline solid with the formula . It forms a stable dihydrate, but aqueous solutions tend to undergo hydrolysis, particularly if hot. SnCl2 is widely used as a reducing agent (in ac ...
(SnCl2),
hydrochloric acid Hydrochloric acid, also known as muriatic acid or spirits of salt, is an aqueous solution of hydrogen chloride (HCl). It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is ...
(HCl) and quenching the resulting
iminium In organic chemistry, an iminium cation is a polyatomic ion with the general structure . They are common in synthetic chemistry and biology. Structure Iminium cations adopt alkene-like geometries: the central C=N unit is nearly coplanar with a ...
salt ( -CH=NH2sup>+Cl−) with
water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
(H2O). During the synthesis,
ammonium chloride Ammonium chloride is an inorganic chemical compound with the chemical formula , also written as . It is an ammonium salt of hydrogen chloride. It consists of ammonium cations and chloride anions . It is a white crystalline salt (chemistry), sal ...
is also produced. It is a type of nucleophilic addition reaction.


Mechanism

The following scheme shows the reaction mechanism: By addition of
hydrogen chloride The Chemical compound, compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hyd ...
the used
nitrile In organic chemistry, a nitrile is any organic compound that has a functional group. The name of the compound is composed of a base, which includes the carbon of the , suffixed with "nitrile", so for example is called " propionitrile" (or pr ...
(1) reacts to its corresponding salt (2). It is believed that this salt is reduced by a single electron transfer by the
tin(II) chloride Tin(II) chloride, also known as stannous chloride, is a white crystalline solid with the formula . It forms a stable dihydrate, but aqueous solutions tend to undergo hydrolysis, particularly if hot. SnCl2 is widely used as a reducing agent (in ac ...
(3a and 3b). The resulting salt (4) precipitates after some time as aldimine tin chloride (5). Hydrolysis of 5 produces a
hemiaminal In organic chemistry, a hemiaminal (also carbinolamine) is a functional group or type of chemical compound that has a hydroxyl group and an amine attached to the same carbon atom: . R can be hydrogen or an alkyl group. Hemiaminals are intermediat ...
(6) from which an
aldehyde In organic chemistry, an aldehyde () (lat. ''al''cohol ''dehyd''rogenatum, dehydrogenated alcohol) is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred ...
(7) is formed. Substitutes that increase the
electron density Electron density or electronic density is the measure of the probability of an electron being present at an infinitesimal element of space surrounding any given point. It is a scalar quantity depending upon three spatial variables and is typical ...
promote the formation of the aldimine-tin chloride adduct. With electron withdrawing substituents, the formation of an amide chloride is facilitated. In the past, the reaction was carried out by precipitating the aldimine-tin chloride, washing it with ether and then hydrolyzing it. However, it has been found that this step is unnecessary and the aldimine tin chloride can be hydrolysed directly in the solution. This reaction is more efficient when aromatic nitriles are used instead of aliphatic ones. However, even for some aromatic nitriles (e. g. 2-cyanobenzoic acid ethyl ester) the yield can be low.


Sonn-Müller method

In the Sonn-Müller method the intermediate iminium salt is obtained from reaction of an
amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a chemical compound, compound with the general formula , where R, R', and R″ represent any group, typically organyl functional group, groups or hydrogen at ...
PhCONHPh with
phosphorus pentachloride Phosphorus pentachloride is the chemical compound with the formula . It is one of the most important phosphorus chlorides/oxychlorides, others being and . finds use as a chlorinating reagent. It is a colourless, water-sensitive solid, althoug ...
.


See also

*
Amide reduction Amide reduction is a reaction in organic synthesis where an amide is reduced to either an amine or an aldehyde functional group. Catalytic hydrogenation Catalytic hydrogenation can be used to reduce amides to amines; however, the process often re ...
*
Nitrile reduction In nitrile reduction a nitrile is organic reduction, reduced to either an amine or an aldehyde with a suitable chemical reagent. Catalytic hydrogenation The Catalysis, catalytic hydrogenation of nitriles is often the most economical route available ...
*
Pinner reaction The Pinner reaction refers to the acid catalysed reaction of a nitrile with an alcohol to form an imino ester salt (alkyl imidate salt); this is sometimes referred to as a Pinner salt. The reaction is named after Adolf Pinner, who first described ...
– a similar reaction using alcohols or amines as the nucleophile and without the reduction; generated esters,
carboximidate Carboximidates (or more general imidates) are organic compounds, which can be thought of as esters formed between an imidic acid () and an alcohol, with the general formula . They are also known as imino ethers, since they resemble imines () w ...
s or
orthoester In organic chemistry, an ortho ester is a functional group containing three alkoxy groups attached to one carbon atom, i.e. with the general formula . Orthoesters may be considered as products of exhaustive alkylation of unstable orthocarboxylic ...
s.


References

{{DEFAULTSORT:Stephen Aldehyde Synthesis Organic redox reactions Name reactions