Chemistry:Acetamidine

Acetamidine is an organic compound with the chemical formula CH
3C(NH)NH
2. Its structural formula is H
3C–C(=NH)–NH
2. It is a colorless crystalline solid. It is a nitrogen analog of acetic acid H
3C–C(=O)–OH, where the carbonyl oxygen =O is replaced by imino group =NH, and the hydroxyl group –OH is replaced by amino group –NH
2.

Acetamidine also refers to the group of compounds called acetamidines, whose formula is H
3C–C(=NR)–NR'R", where R, R' and R" are typically hydrogen, halogen or organyl.

Acetamidine is usually available as its hydrochloride salt [CH
3C(NH
2)
2]+
Cl−
(acetamidinium chloride).

Structure

In the molecule of acetamidine, nonhydrogen atoms and hydrogen atoms attached to the nitrogen atoms are coplanar, thus, the molecule is trigonal planar at the nonmethyl carbon atom. The rotational barrier of the methyl group is very small. Crystals of acetamidine are tetragonal, with these parameters: a = 10.964 Å, c = 5.701 Å, Z = 8 and V = 685.3 ų, with P4₂/n space group. The molecules are connected by a hydrogen bond by =NH and –NH
2 groups.

Uses

Acetamidine (and other acetamidines) is used for the synthesis of heterocycles, e.g. quinazoline, pyrrole, imidazole, purine, pyrimidine, triazine, and their derivatives, which play an important role in biochemistry and medicinal chemistry.

Reactions

The free base of acetamidine is hygroscopic. It decomposes into ammonia and acetonitrile at high temperatures, and produces acetamidinium carbonate [CH
3C(NH
2)
2]
2CO
3 during one day at room temperature when stored in air. Because of that, it is unsuitable as a starting material for synthesis and the use of an acetamidinium salt is necessary. Acetamidinium cation forms salts with various counterions, such as sulfate, hydrogensulfate, formate, acetate, oxalate, chloride, perchlorate, nitrate, and dinitromethanide.

Structure of the acetamidinium cation