Why does amine acts as a base

Since the amide ion is such a terrible leaving group, it would still have to be converted to the ammonium form, so that the leaving group could be a neutral amine.

This can only be done if all of the acidic protons of the ammonium ion are removed and replace by alkyl groups, specifically methyl groups.

At this point, there are no more acidic protons, so base can be employed in an E2 reaction. At this point we have a good base and a reasonable leaving group. Heating this ionic compound up to arount eighty degrees usually succeeds in effecting elimination of trimethylamine.

Transition State for the Hoffmann Elimination Reaction. Fortunately, it is the alkene character which is dominant in the eliminations of alkyl halides.

The importance of including the more complete treatment which reveals the carbanion character in the present instance eliminations where the leaving group is an amine is that it is now the carbanion character which is dominant over alkene character, resulting in a sharp change in the regiochemical selectivity. We called that Saytzeff regiochemistry. This kind of regiochemistry is called Hoffmann regiochemistry. The order of carbanion stability is: methyl more stable than primary than secondary than tertiary.

Note that of the three canonical structures for the TS, the one which gives rise to alkene character is the last one in our drawing above. The structure will be of lower energy and contribute more when the leaving group is of lower energy in this structure the leaving group has left. That is, the better the leaving group the more alkene character there is in the TS. Since chloride or bromide or iodide ions are better leaving groups than trimethylamine, the alkyl halide eliminations have much more alkene character than do the alkylammonium ion eliminations.

All primary amines are readily converted by nitrous acid to diazonium salts. In the case of aliphatic R groups, the diazonium ions are extremely unstable, rapidly decomposing to give carbocations which undergo reaction with whatever nucleophiles may be present such as water. The reason this especially high level of reactivity is that dinitrogen, being thermodynamically highly stable, is an outstanding leaving group. Positive charge on nitrogen is inherently not very favorable electronegative atom , but resonance stabilization makes this ion stable enough to form.

Even when these diazonium ions are formed at ice bath temperatures, they lose nitrogen extremely quickly, forming a carbocation, which then reacts with available nucleophiles e. This permits the use of the aryldiazonium ions in reactions with substances supplied after the diazonium ion is generated.

In other words, the pi system of the N-N pi bond overlaps with the pi system of the benzene ring, providing delocalization of the positive charge onto the ortho and para positions of the benzene ring. Azo Compounds. However, they are relatively mild not highly reactive, but very selective electrophiles, because of their resonance stabilization.

As very mild and selective electrophiles, they do not react with benzene or toluene or even anisole methoxybenzene—normally considered a highly reactive aromatic. They do, however, reactive with aromatics which have the powerfully electron donating amine function. In particular, N,N-dimethylaniline reacts readily with aryl diazonium ions as shown below:. Another common use for aryldiazonium ions is in the transformation of the amino group of aniline or a derivative of aniline to other functionality such as a halide or a nitrile function.

This involves the addition of an appropriate salt containing the desired nucleophile to the cold, aqueous solution containing the diazonium ion and the allowing the temperature to ascend to room temperature. In this way, the diazonium ion decomposes to the aryl carbocation, which then reacts with the appropriate nucleophile.

However, when the potent leaving group is dinitrogen, even aryl systems can undergo an S N 1 substitution reaction. Consider the acid dissociation, in dilute aqueous solution, of ammonia and a representative primary, secondary, and tertiary amine: q Note that the strongest acid least positive pK a is ammonia. See the indicated overlap in the orbital picture shown below: q This conjugation is only possible when the orbital external to the ring is in the benzylic-type position that is, on an atom directly attached to the ring.

The Hoffmann Elimination Reaction. Recall that alkyl halides except fluorides and alcohols in the presence of acid can undergo elimination reactions to give alkenes. In both of these systems, good leaving groups are present, thus permitting an E2 elimination or in some cases an E1 elimination.

In the case of halides, the chloride, bromide, and iodide ions are good leaving groups. Many heterocyclic compounds are important in medicine and biochemistry.

Some compose part of the structure of the nucleic acids, which in turn compose the genetic material of cells and direct protein synthesis. For more information about nucleic acids, see Chapter 19 "Nucleic Acids". Many heterocyclic amines occur naturally in plants. Like other amines, these compounds are basic.

Such a compound is an alkaloid A nitrogen-containing organic compound obtained from plants that has physiological properties. Caffeine is a stimulant found in coffee, tea, and some soft drinks. Its mechanism of action is not well understood, but it is thought to block the activity of adenosine, a heterocyclic base that acts as a neurotransmitter, a substance that carries messages across a tiny gap synapse from one nerve cell neuron to another cell.

The effective dose of caffeine is about mg, corresponding to about two cups of strong coffee or tea. Nicotine acts as a stimulant by a different mechanism; it probably mimics the action of the neurotransmitter acetylcholine. People ingest this drug by smoking or chewing tobacco. Its stimulant effect seems transient, as this initial response is followed by depression. Nicotine is highly toxic to animals. It is especially deadly when injected; the lethal dose for a human is estimated to be about 50 mg.

Nicotine has also been used in agriculture as a contact insecticide. Cocaine acts as a stimulant by preventing nerve cells from taking up dopamine, another neurotransmitter, from the synapse. High levels of dopamine are therefore available to stimulate the pleasure centers of the brain. After the binge, dopamine is depleted in less than an hour.

This leaves the user in a pleasureless state and often craving more cocaine. Cocaine is used as the salt cocaine hydrochloride and in the form of broken lumps of the free unneutralized base, which is called crack cocaine.

Because it is soluble in water, cocaine hydrochloride is readily absorbed through the watery mucous membranes of the nose when it is snorted.

Such things don't exist on their own in solution in water. If the reaction is happening in the gas state, the ammonia accepts a proton directly from the hydrogen chloride:. The nitrogen lone pair behaves exactly the same. The fact that one or more of the hydrogens in the ammonia has been replaced by a hydrocarbon group makes no difference.

If the reaction is done in solution, the amine takes a hydrogen ion from a hydroxonium ion and forms an ethylammonium ion. The solution would contain ethylammonium chloride or sulfate or whatever. Alternatively, the amine will react with hydrogen chloride in the gas state to produce the same sort of white smoke as ammonia did - but this time of ethylammonium chloride.

These examples have involved a primary amine, but it makes no real difference if a secondary or tertiary amine were used. The product ions from diethylamine and triethylamine would be diethylammonium ions and triethylammonium ions respectively.

Again, it is easiest to use the Bronsted-Lowry theory and, again, it is useful to do a straight comparison with ammonia. Ammonia is a weak base and takes a hydrogen ion from a water molecule to produce ammonium ions and hydroxide ions.

However, the ammonia is only a weak base, and doesn't hang on to the hydrogen ion very successfully. The reaction is reversible, with the great majority of the ammonia at any one time present as free ammonia rather than ammonium ions. The presence of the hydroxide ions from this reaction makes the solution alkaline. The amine still contains the nitrogen lone pair, and does exactly the same thing. For example, with ethylamine, you get ethylammonium ions and hydroxide ions produced.

There is, however, a difference in the position of equilibrium. Amines are usually stronger bases than ammonia there are exceptions to this, though - particularly if the amine group is attached directly to a benzene ring. Just like ammonia, amines react with copper II ions in two separate stages.