Amine

Is referred to as amine organic derivatives (derivatives) of the ammonia (NH3), in which one or more hydrogen atoms are replaced by alkyl or aryl groups.

Nomenclature of Amines

Dividing the amines, depending upon the number of hydrogen atoms of ammonia have been replaced by organic molecular groups, into the following groups:

The alkyl groups of secondary or tertiary amines can be closed to form a ring. There are then cyclic secondary or tertiary amines, before, such as piperidine.

Properties

Chemical Properties

As ammonia react amines basic by a proton is attached to the free electron pair of the nitrogen ( the simplest method for the separation of amines is the extraction with aqueous hydrochloric acid. )

The degree of substitution of amines affected their basicity. Alkyl groups concentrate electron density at the nitrogen atom, so that the free electron pair can be more easily shared with an acid. For pure ( anhydrous ) amines, therefore, the basicity with increasing degree of substitution to:

In the presence of water, the amine is hydrated, heat is released. This hydration is lowest at primary amines greatest and tertiary. With increasing degree of substitution but also an increasing steric hindrance during the hydration takes place. Both together leads to an altered order of basicity in aqueous solutions:

The basicity of aliphatic amines is due to the I effect greater than that of ammonia, the aromatic amines is much lower, since the - I effect of the aromatic rings comes into play. In aqueous solution show alkylamines following order of basicity: tertiary < primary < secondary

The decrease in the basicity of tertiary amines is due to poorer solvation of ammonium ions through the water; in the gas phase, they are more basic than amines.

Electron withdrawing groups on the organic radical at the nitrogen atom or reduce the basicity on.

Physical Properties

Monomethylamine, dimethylamine and trimethylamine and ethylamine are gaseous at room temperature, the following elements are liquid, or higher homologues thereof fixed. Amines have, if they are sufficiently volatile, often an ammonia - or fish- like odor, which is less pungent than that of ammonia.

Because of their polarity amines are much more soluble in water than comparable hydrocarbons; with increasing length of the alkyl chain decreases the aqueous solubility. Primary and secondary amines are associated by hydrogen bonds; This leads - as with alcohols - in higher boiling points as compared to analogous hydrocarbons.

Production

In biological processes, among other amines are formed by decarboxylation of amino acids or by transamination of aldehydes.

Preparative are amines by alkylation of ammonia, for example with alkyl halides, accessible, whereby in this case mixtures of all alkylation stages receives as the primary amines are initially formed also alkylated as well as the secondary and so

For the presentation of primary amines the Gabriel synthesis is often used. In this first phthalimide is reacted with the appropriate alkyl halide and then worked up basic with sodium hydroxide ( as a gentle alternative to the workup has prevailed with hydrazine ) in order to release the primary amine. Primary amines can also be prepared by the carboxylic acid degradation by Hofmann, while the carbon chain is shortened by one carbon atom.

A further possibility for the synthesis of primary amines is the Curtius reaction, in which on the elimination of an acyl hydrazide, the amine is prepared.

The secondary amines can be prepared in several ways. First, it is possible to alkylate aniline twice and then to nitrate the aromatic ring at the para position. A basic work leads to the desired amine. Alternatively, secondary amines from imines (R- CH = N- R ') synthesized by hydrogenation of the double bond. Especially for tertiary amines suitable the Leuckart -Wallach reaction.

Industrial processes useful for the preparation of amines, the reaction of ammonia with alcohols (for example, alkylamines such as methylamine and ethylamine ) and aldehydes or ketones (for example, isopropylamines ), the reduction of nitriles (for example, fatty amines ) and the reaction with chlorine alkanes (especially fine chemicals and quaternary ammonium salts). On an industrial scale, the reaction of epoxides with amines or ammonia is performed ( ethanolamines, isopropanolamines etc.). Aromatic amines can be prepared by nitration and subsequent reduction (for example, aniline, toluidine, etc.). The nitration of alkanes and alkyl amine and subsequent reduction to the hydroamination of olefins has technically only minor importance. However, they are both also operated on an industrial scale.

Occurrence

The in plants, animals and humans naturally occurring, biogenic amines have great importance as tissue hormones, transmethylation partner or transmitter substances. Also amine derivatives can be found as bases in the DNA. Amino acids, the building blocks of peptides are amines. The peptide-bound amino acids in the protein of fish are removed after the death of the animals biochemically to amines and carbon dioxide. The resulting amines are responsible for the characteristic smell of the fish, which is sometimes perceived as unpleasant. That's why fish is often served with a piece of lemon. Citric acid protonated (like all other acids also ) amines, thus reducing the intense amine odor.

Chemical reactions

Amines react with nitrous acid, depending on the amine used for different products. Primary amines react to form diazonium compounds. Alkyldiazonium ions are relatively stable even at temperatures of 0 ° C. They split from nitrogen and respond to a carbocation. They then react further to give an alkene. Secondary amines react to form nitrosamines and tertiary amines can also react to form nitrosamines slowly with elimination of an alkyl group; aromatic tertiary amines at a reaction on the aromatic ring will take place and there is an aromatic nitroso compound. Particularly important is the reaction of primary aromatic amines.

Amines are used as reactants in many nucleophilic substitutions in the formation of, for example, carboxylic acid amides / imides or lactones and imines, amines and therefore can be used as protective groups of carbonyls or as chiral auxiliaries. With elimination bulky secondary or tertiary amines are used as proton acceptors which, although basic, but not nucleophilic. Furthermore find amines, usually diamines or triamines application as ligands in coordination chemistry.

Use

Amines are used for the preparation of azo compounds, for example in the production of dyes. In addition, amines blocks for agricultural and pharmaceutical chemicals, and for surfactants, coatings and lubricants. In the field of foundry technology amines find application as a catalyst to accelerate the curing of the binder in the molding sand in the core production by the cold box process. As catalysts, amines are also used for the production of polyurethanes. Their buffering action is used, if they are used in aqueous systems as corrosion inhibitors. Another important application is the gas scrubbing in refineries and power plants.

Detection of amines

Amines are often ( like ammonia to fishy ), by their characteristic pungent odor recognizable. But this is not sufficient for detection.

For the detection of nitrogen, a sodium digestion of the test substance can be performed. In the neutralized digestion solution nitrogen can be demonstrated with the cyanide Lassaigne sample as Berlin blue, or, if at the same time, the substance containing sulfur as thiocyanate iron (III ) chloride. However, these documents are not specific for amines, but only to show that the analysis of nitrogen containing substance.

Then, the degree of substitution of the amine can be detected, that is, whether a primary / secondary / tertiary amine is present. Hinsberg to the separation is carried out. Here, the amine is reacted with p - toluenesulfonamide:

• Tertiary amines and quaternary ammonium salts do not form sulfonamides,
• Secondary amines are sulfonamides, which are not soluble in alkali,
• Primary amines are sulfonamides, which are soluble in alkali

The unique identification of an unknown amine is carried out either by spectrophotometry or a suitable derivative:

• Primary & Secondary amines: As a derivative of the sulfonamide already recovered from the Hinsberg separation is ( see above).
• Tertiary amines: Here the precipitation of Pikrates is recommended.