What is an Amine? What types do you get and what is it used for?
Stupid question. I know....
woelen - 2-4-2012 at 22:09
Too lazy to read yourself?
Google, wikipedia and many books, the answer is everywhere.The_Wurx - 2-4-2012 at 22:37
Ok. Let me rephrase.
What amines do one get.
Dyes - methyl orange, direct brown 138, sunset yellow FCF, ponceau
They are used in drugs as well according to wikipedia. But those I have no need for.
What else are they used for is actually what I wanted to know. Where do you get them which ones are illegal? Can they be bought OTC?AndersHoveland - 3-4-2012 at 00:01
Urea can be bought as fertilizer, and is also somewhat like an amine, although its chemistry is more related to amides.
Aromatic compounds can be partially nitrated, then reduced. For example, toluene to nitrotoluene (using mixed HNO3/conc. H2SO4), then reduce with zinc
and hydrochloric acid to form 2-amino-toluene.
[Edited on 3-4-2012 by AndersHoveland]Hexavalent - 3-4-2012 at 01:32
What are amines?
The easiest way to think of amines is as near relatives of ammonia, NH3.
In amines, the hydrogen atoms in the ammonia have been replaced one at a time by hydrocarbon groups. On this page, we are only looking at cases where
the hydrocarbon groups are simple alkyl groups.
The different kinds of amines
Amines fall into different classes depending on how many of the hydrogen atoms are replaced.
Primary amines
In primary amines, only one of the hydrogen atoms in the ammonia molecule has been replaced. That means that the formula of the primary amine will be
RNH2 where "R" is an alkyl group.
Examples include:
Naming amines can be quite confusing because there are so many variations on the names. For example, the simplest amine, CH3NH2, can be called
methylamine, methanamine or aminomethane.
The commonest name at this level is methylamine and, similarly, the second compound drawn above is usually called ethylamine.
Where there might be confusion about where the -NH2 group is attached to a chain, the simplest way of naming the compound is to use the "amino" form,
for example;
Secondary amines
In a secondary amine, two of the hydrogens in an ammonia molecule have been replaced by hydrocarbon groups. At this level, you are only likely to come
across simple ones where both of the hydrocarbon groups are alkyl groups and both are the same.
For example:
There are other variants on the names, but this is the commonest and simplest way of naming these small secondary amines.
Tertiary amines
In a tertiary amine, all of the hydrogens in an ammonia molecule have been replaced by hydrocarbon groups. Again, you are only likely to come across
simple ones where all three of the hydrocarbon groups are alkyl groups and all three are the same.
The naming is similar to secondary amines. For example:
Physical properties of amines
Boiling points
The following shows the boiling points of some simple amines.
(apologies if my table comes out strangely)
type formula boiling point (°C)
primary CH3NH2 -6.3
primary CH3CH2NH2 16.6
primary CH3CH2CH2NH2 48.6
secondary (CH3)2NH 7.4
tertiary (CH3)3N 3.5
We will need to look at this with some care to sort out the patterns and reasons. Concentrate first on the primary amines.
Primary amines
It is useful to compare the boiling point of methylamine, CH3NH2, with that of ethane, CH3CH3.
Both molecules contain the same number of electrons and have, as near as makes no difference, the same shape. However, the boiling point of
methylamine is -6.3°C, whereas ethane's boiling point is much lower at -88.6°C.
The reason for the higher boiling points of the primary amines is that they can form hydrogen bonds with each other as well as van der Waals
dispersion forces and dipole-dipole interactions.
Hydrogen bonds can form between the lone pair on the very electronegative nitrogen atom and the slightly positive hydrogen atom in another molecule.
The hydrogen bonding isn't as efficient as it is in, say, water, because there is a shortage of lone pairs. Some slightly positive hydrogen atoms
won't be able to find a lone pair to hydrogen bond with. There are twice as many suitable hydrogens are there are lone pairs.
The boiling points of the primary amines increase as you increase chain length because of the greater amount of van der Waals dispersion forces
between the bigger molecules.
Secondary amines
For a fair comparison you would have to compare the boiling point of dimethylamine with that of ethylamine. They are isomers of each other - each
contains exactly the same number of the same atoms.
The boiling point of the secondary amine is a little lower than the corresponding primary amine with the same number of carbon atoms.
Secondary amines still form hydrogen bonds, but having the nitrogen atom in the middle of the chain rather than at the end makes the permanent dipole
on the molecule slightly less.
The lower boiling point is due to the lower dipole-dipole attractions in the dimethylamine compared with ethylamine.
Tertiary amines
This time to make a fair comparison you would have to compare trimethylamine with its isomer 1-aminopropane.
If you look back at the table further up the page, you will see that the trimethylamine has a much lower boiling point (3.5°C) than 1-aminopropane
(48.6°C).
In a tertiary amine there aren't any hydrogen atoms attached directly to the nitrogen. That means that hydrogen bonding between tertiary amine
molecules is impossible. That's why the boiling point is much lower.
Solubility in water
The small amines of all types are very soluble in water. In fact, the ones that would normally be found as gases at room temperature are normally sold
as solutions in water - in much the same way that ammonia is usually supplied as ammonia solution.
All of the amines can form hydrogen bonds with water - even the tertiary ones.
Although the tertiary amines don't have a hydrogen atom attached to the nitrogen and so can't form hydrogen bonds with themselves, they can form
hydrogen bonds with water molecules just using the lone pair on the nitrogen.
Solubility falls off as the hydrocarbon chains get longer - noticeably so after about 6 carbons. The hydrocarbon chains have to force their way
between water molecules, breaking hydrogen bonds between water molecules.
However, they don't replace them by anything as strong, and so the process of forming a solution becomes less and less energetically feasible as chain
length grows.
Smell
The very small amines like methylamine and ethylamine smell very similar to ammonia - although if you compared them side by side, the amine smells are
slightly more complex.
As the amines get bigger, they tend to smell more "fishy", or they smell of decay.
If you are familiar with the smell of hawthorn blossom (and similarly smelling things like cotoneaster blossom), this is the smell of trimethylamine -
a sweet and rather sickly smell like the early stages of decaying flesh.
I completely understand all of the chemistry contained within, and felt yet that there was no need to reinvent the wheel by writing it out again.
Merely trying to help was I
