Diamine

General structure of the diamines (primary). Primary amino groups (NH2) are marked in blue, A is a divalent organic radical (e.g. for- phenylene group).

The diamine is an organic substance in whose molecule there are two -NH2 groups attached to one or two carbons of hydrocarbon radicals. The simplest and most well-known is ethylenediamine with the composition H₂N - CH₂ - CH₂ - NH₂, being a liquid with an odor similar to ammonia whose boiling point is 116 °C.

Diamines are used as monomers to prepare polyamides and polyureas. The term diamine mainly refers to the primary diamines, as they are the most reactive.

Regarding the quantities produced, 1,6-hexanediamine (a precursor of Nylon 6-6) is the most important, followed by ethylenediamine. The vicinal diamines (1,2 -diamines) are a structural motif in many biological compounds and are used as ligands in the chemistry of coordination compounds.

Aliphatic diamines

Linears

• 1 carbon: methandiamine (diaminomethane)
• 2 carbons: ethylenediamine (1.2-diaminoethane). Related derivatives include N-alkylated compounds, 1,1-dimetilendiamine, 1,2-dimethylenediamine, etambutol and TMEDA.

• 

  Ethylenediamine

• 3 carbons: 1.3-diaminopropane (propano-1,3-diamine)
• 4 carbons: putrescina (butano-1,4-diamine)
• 5 carbons: perverine (pentano-1,5-diamine)

• 

  Cadaverina

• 6 carbons: hexametilenediamine (hexano-1,6-diamine), trimetilhexametilenediamine

Branches

Derivatives of ethylenediamine are prominent:

• 1,2-diaminopropane, which is a chiral.

• dienilethyndiamine, which is C2.-simetric
• trans-1,2-diaminocyclohexane, which is C2-simetric.

Cyclic

• 1,4-diazacicloheptano

• 

  1,4-diazacicloheptano

Xylylenediamines

Xylylenediamines are classified as alkylamines since the amine is not directly attached to an aromatic ring.

o-xylenediamine or OXD

m-xylylenediamine or MXD

p-xylylenediamine or PXD

Aromatic diamines

Three phenylenediamines are known:

o-phenylenediamine or OPD

m-phenylenediamine or MPD

p-phenylenediamine or PPD. 2,5-diaminotoluene is related to PPD but contains a ring methyl group.

• 

  p-fenylenediamine

Several N-methylated derivatives of phenylenediamines are known:

• dimetil-4-fenilendiamine, a reactive.
• N,N'-di-2-butil-1,4-fenilendiamine, an antioxidant.

Examples with two aromatic rings include biphenyl and naphthalene derivatives:

• 4,4'-diaminobiphenyl
• 1.8-diaminonaphthalene