## AMINES THEORY

Rule 1. Amines can be named as derivatives of alkylamines or alkanoamines. Let's see some examples.

Amines have lower melting and boiling points than alcohols. Thus, ethylamine boils at 17ºC, while the boiling point of ethanol is 78ºC.

CH 3 CH 2 OH P.b. = 78ºC
CH 3 CH 2 NH 2 P. eb. = 17ºC

The lower electronegativity of nitrogen, compared to that of oxygen, makes the hydrogen bonds formed by amines weaker than those formed by alcohols.

Amines have acidic hydrogens on the amino group. These hydrogens can be subtracted using strong bases (organometallic, metal hydrides) forming amides (amine bases).

Methylamine [1] reacts with methyllithium, transforming into its conjugate base, lithium methylamide [2] . For its part, methyllithium is transformed into its conjugate acid, methane.

Amines are nitrogenous compounds with a pyramidal structure, similar to ammonia. Nitrogen forms three single bonds through sp 3 . The lone pair occupies the fourth orbital with sp 3 and is responsible for the basic and nucleophilic behavior of amines.

Amines can be prepared by nucleophilic substitution reactions between haloalkanes and ammonia.

The first equivalent of ammonia acts as a nucleophile, substituting for bromine. The second equivalent acts as the base by deprotonating the amine.

Nitriles can be prepared by reacting haloalkanes with sodium cyanide. The reduction of nitriles with LiAlH 4 produces amines.

The reaction of primary and secondary haloalkanes with sodium azide produces alkylazides, which by reduction with LiAlH 4 give rise to amides.

Amides are reduced with LiAlH 4 to form amines. The carbon number of the final amine is equal to that of the starting amide.

Amides are converted to amines, with one less carbon, by treatment with bromine in a basic medium. This reaction is known as the Hofmann rearrangement.

The Gabriel synthesis allows primary amines to be obtained from haloalkanes, without the formation of mixtures of secondary and tertiary amines.

Reductive amination consists of forming an imine, from aldehydes or ketones and amines, which is reduced to an amine in a subsequent stage. This reduction can be carried out with $H_2$ catalyzed by Nickel or with $NaBH_3CN$.

Epoxides (oxacyclopropanes) open by nucleophile attack, due to the significant ring strain. If the nucleophile used is ammonia, a β-aminoalcohol is obtained. This type of product can also be obtained by opening the epoxide with sodium azide, and reducing the azide in a second stage.

The Hofmann elimination allows the conversion of amines to alkenes. It is a regioselective reaction that follows Hofmann's rule, forming the least substituted alkene.

The Cope elimination makes it possible to obtain alkenes from tertiary amines. The reaction consists of oxidizing the tertiary amine, forming an amine N-oxide, which is eliminated intramolecularly by heating, giving rise to the alkene.

Mannich prepares 3-aminocarbonyls from primary or secondary amines, methane, and an enolizable carbonyl. Let's see an example: