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The Delépine reaction is the
Depending on the hydrolysis conditions and structure, the nitrogen might instead be lost from the carbon where it had bonded in the first step to give a benzylic
organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
of primary amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...
s (4) by reaction of benzyl or alkyl
In organic chemistry, an alkyl group is an alkane missing one hydrogen.
The term ''alkyl'' is intentionally unspecific to include many possible substitutions.
An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloalk ...
halide
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluor ...
s (1) with hexamethylenetetramine (2) followed by acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
of the quaternary ammonium salt (3). It is named after the French chemist Stéphane Marcel Delépine (1871–1965).
Advantages of this reaction are selective access to the primary amine without side reactions from easily accessible reactants with short reaction times and relatively mild reaction conditions. Downsides include that the reaction is often performed using chloroform
Chloroform, or trichloromethane, is an organic compound with chemical formula, formula Carbon, CHydrogen, HChlorine, Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to ...
as solvent, which is toxic, and poor atom economy
Atom economy (atom efficiency/percentage) is the conversion efficiency of a chemical process in terms of all atoms involved and the desired products produced. The simplest definition was introduced by Barry Trost in 1991 and is equal to the ratio ...
, including the formation of several equivalents of formaldehyde
Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...
(a known carcinogen) during quaternary ammonium salt formation.
An example is the synthesis of 2-bromoallylamine from 2,3-dibromopropene.
Reaction mechanism
The benzyl halide or alkyl halide 1 reacts with hexamethylenetetramine to a quaternary ammonium salt 3, each time just alkylating one nitrogen atom. By refluxing in concentrated ethanolichydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid
Acid strength is the tendency of an acid, symbol ...
solution this salt is converted to the primary amine together with formaldehyde
Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...
(as the acetal with ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
) and ammonium chloride.
:
Depending on the hydrolysis conditions and structure, the nitrogen might instead be lost from the carbon where it had bonded in the first step to give a benzylic 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 grou ...
(the Sommelet reaction
The Sommelet reaction is an organic reaction in which a benzyl halide is converted to an aldehyde by action of hexamine and water.
:
One example, thiophene-2-carboxaldehyde is prepared by the reaction of hexamine with 2-chloromethylthiophene. T ...
).
See also
*Gabriel synthesis
The Gabriel synthesis is a chemical reaction that transforms primary alkyl halides into primary amines. Traditionally, the reaction uses potassium phthalimide. The reaction is named after the German chemist Siegmund Gabriel.
The Gabriel reaction ...
References