Diamine
General structure of diamines. The primary amino groups are marked blue, R is a divalent organic radical. |
A diamine is an amine with two amino groups. Diamines are used as monomers to prepare polyamides, polyimides, and polyureas. The term diamine refers mostly to primary diamines, as those are the most reactive.
Practical considerations
In terms of quantities produced, 1,6-diaminohexane is most important, followed by ethylenediamine. Vicinal diamines are a structural motif in many biological compounds and are used as ligands in coordination chemistry. Many diamines are used as hardeners in the curing of epoxide resins. Putrescine and cadaverine are simple diamines that occur widely in nature.Aliphatic diamines
Linear
- 2 carbon backbone: ethylenediamine. Related derivatives include the N-alkylated compounds, 1,1-dimethylethylenediamine, 1,2-dimethylethylenediamine, ethambutol, tetrakisethylene, TMEDA. Many 1,2-diamine derivatives are of practical interest such as penicillin.
- 3 carbon backbone: 1,3-diaminopropane
- 4 carbon backbone: putrescine
- 5 carbon backbone: cadaverine
- 6 carbon backbone: hexamethylenediamine. HMD and other long chain diamines can be prepared by hydrocyanation to give dinitrile, which can be hydrogenated.
Branched
- 1,2-diaminopropane, which is chiral.
- 2,3-Butanediamine, two diastereomers, one of which is C2-symmetric.
- Diphenylethylenediamine, two diastereomers, one of which is C2-symmetric.
- trimethylhexamethylenediamine, several isomers
- 1,2-Diaminocyclohexane, two diastereomers, one of which is C2-symmetric.
Cyclic
- piperazine
- 1,4-Diazacycloheptane
Xylylenediamines
- o-xylylenediamine or OXD
- m-xylylenediamine or MXD
- p-xylylenediamine or PXD
Aromatic diamines
- o-phenylenediamine or OPD
- m-phenylenediamine or MPD
- p-phenylenediamine or PPD. 2,5-diaminotoluene is related to PPD but contains a methyl group on the ring.
Various N-methylated derivatives of the phenylenediamines are known:
- dimethyl-4-phenylenediamine, a reagent.
- N,N'-di-2-butyl-1,4-phenylenediamine, an antioxidant.
File:Wurster's cation.svg|thumb|100px|Structure of Wurster's cation, illustrating the ability of amino substituents to stabilize arene radical cations.
Geminal diamines
diamines are an uncommon class of diamines mainly of academic interest. Of the few that exist, most are di-tertiary amines. Bismethane is an isolable example.Geminal diamines with N-H bonds are particularly rare. They are invoked as intermediates in transimination reactions and the reduction of amidines. In aqueous conditions they preferentially eliminate the less basic amine to leave an iminium ion. Some stable geminal diamines have been isolated. The parent gem-diamine is methylenediamine, which again is mainly of theoretical interest.