Diamine
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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.[1]
 General structure of (primary) diamines. The primary amino groups (NH2) are marked blue, R is a divalent organic radical (e.g. a para-phenylene group). |
In terms of quantities produced, 1,6-diaminohexane (a precursor to Nylon 6-6) is most important, followed by ethylenediamine.[2] Vicinal diamines (1,2-diamines) are a structural motif in many biological compounds and are used as ligands in coordination chemistry.[3]
Aliphatic diamines
Summarize
Perspective
Linear
- 2 carbon backbone: ethylenediamine (1,2-diaminoethane). Related derivatives include the N-alkylated compounds, 1,1-dimethylethylenediamine, 1,2-dimethylethylenediamine, ethambutol, tetrakis(dimethylamino)ethylene, TMEDA. Many 1,2-diamine derivatives are of practical interest such as penicillin.[4][5]
- 3 carbon backbone: 1,3-diaminopropane (propane-1,3-diamine)
- 4 carbon backbone: putrescine (butane-1,4-diamine)
- 5 carbon backbone: cadaverine (pentane-1,5-diamine)
- 6 carbon backbone: hexamethylenediamine (hexane-1,6-diamine, HMD). HMD and other long chain diamines can be prepared by hydrocyanation to give dinitrile, which can be hydrogenated.[6]
Branched
Derivatives of ethylenediamine are prominent:
- 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 ((CH2CH2NH)2)
- 1,4-Diazacycloheptane
Xylylenediamines
Xylylenediamines are classified as alkylamines since the amine is not directly attached to an aromatic ring.
- o-xylylenediamine or OXD
- m-xylylenediamine or MXD
- p-xylylenediamine or PXD
Aromatic diamines
Three phenylenediamines are known:[7]
- 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.
Examples with two aromatic rings include derivatives of biphenyl and naphthalene:
Geminal diamines
Geminal diamines (1,1-diamines) are an unusual class of diamines mainly of academic interest. Bis(dimethylamino)methane ([(CH3)2N]2CH2) is a stable 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.[8] Some stable geminal diamines have been isolated.[9] The parent gem-diamine is methylenediamine (diaminomethane), which again is mainly of theoretical interest.
References
External links
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