Amines are organic compounds that contain a lone pair of nitrogen atoms. They are derived from ammonia (NH3) by replacing one or more hydrogen atoms with an alkyl or aryl group, and thus are known as alkylamines and arylamines, respectively. Nitrogen is trivalent with a lone pair because it has 5 valence electrons. According to VSEPR theory, nitrogen in amines is sp3 hybridised, and because of the presence of a lone a pair, it has a pyramidal shape rather than the tetrahedral shape that most sp3 hybridised molecules have. Depending on the Amines configuration, the three sp3 hybridised orbitals of nitrogen overlap with orbitals of hydrogen or carbon. Due to the presence of a lone pair, the C-N-H angle in amines is less than 109 degrees which is a characteristic angle of tetrahedral geometry. The angle of amines is near about 107 degrees. Types of Amines-
Methylamine CH3NH2, Aniline C6H5NH2 are two examples.
Dimethylamine (CH3)2NH, Diphenylamine (C6H5)2NH are two examples.
Trimethylamine N(CH3)3, ethylenediaminetetraacetic acid, for example (EDTA)
Preparation of Amines- The procedure will take place in a sealed tube. Haloalkanes will be heated with a concentrated ammonia solution in ethanol. The mixture cannot be heated under reflux because ammonia would escape as a gas from a container. When it comes to preparing primary amine from halogenoalkane, the reaction occurs in two stages. The first stage will result in the formation of salt. The salt in this case is ethyl ammonium bromide. It is similar to ammonium bromide except that an ethyl group replaces one of the hydrogens in the ammonium atom. Ammonia and salt can react in the opposite direction. It is demonstrated in the preceding reaction. Basicity of Amines- Primary and secondary amines, like ammonia, have protic hydrogens and thus exhibit some acidity. Tertiary amines, on the other hand, lack protic hydrogen and thus lack acidity. The pKa value of primary and secondary amines is around 38, indicating that they are extremely weak acids. The pKb, on the other hand, is around 4. As a result, the amines become much more basic than acidic. As a result, an amine aqueous solution is strongly alkaline.
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