Amines, amino acids and amides

Question 1

What molecules are amines derived from?

Answer 1

Ammonia

Question 2

How does primary, secondary, tertiary and quaternary amines differ?

Answer 2

A primary ammonia is when one hydrogen on ammonia is substituted for an organic group.
A secondary amine is when two hydrogens on ammonia are substituted for 2 organic groups.
A tertiary ammonia is when all hydrogens in ammonia are substituted for 3 organic groups.
A quaternary amine is where ammonia has substituted all 3 hydrogen atoms for 3 organic groups. However, along with this, there is one more organic group bonded to the nitrogen. This is because the lone pair on the nitrogen is able to form a dative covalent bond with the last organic group, however, this results with the nitrogen having a positive charge.

Question 3

What are the different ways to name a primary amine?

Answer 3

If the amine group is on carbon 1 of the (longest) carbon chain, then we can treat it with the suffix being -amine. Next, treat the carbon chain as an alkyl group- if the carbon chain has 5 carbons, it would be called pentyl. Together, it would be called pentylamine.
If the amine group is on a carbon that is not carbon 1 of the chain, treat the prefix as ‘amino’. The suffix is just the carbon chain, being named as an alkane, rather than an alkyl group. Lastly, a number comes prior to the ‘amino’ and this indicates on which carbon the amine group appears. For example, a primary amine where the amine group occurs on carbon 2 of a 7 carbon chain, is called 2-aminoheptane.

Question 4

How to name secondary and tertiary amines that has the same alkyl group attached?

Answer 4

‘-amine’ would be used as the suffix. The prefix would be the alkyl group which occurs on the nitrogen. A ‘di-‘ (secondary amines) or ‘tri-‘ prefix would be used in from of the alkyl group to indicate how many times the alkyl group occurs, and hence that nature of the amine compound.
For example, a secondary amine with 2 methyl groups attached would be called dimethylamine.

Question 5

How to name secondary and tertiary amines with more than one type of organic group attached?

Answer 5

1. First list all organic groups attached to the nitrogen (in terms of alkyl groups).
2. The suffix to the whole molecule name is going to be ‘-amine’.
3. The alkyl groups occur in the molecule name in alphabetical order.
4. The alkyl group occurring last in the alphabet is conjoined with the ‘amine’ at the end.
5. Then list the remaining alkyl groups before this, still in alphabetical order. The compound is named as a N-substituted derivative of the larger group, so before these alkyl groups (except the last occurring alkyl group in the molecule name), an ‘N-‘ is inserted.

Question 6

How to name secondary amine with a methyl and propyl group attached?

Answer 6

N-methylpropylamine

Question 7

How to name tertiary amine with a methyl, ethyl and propyl group attached?

Answer 7

N-ethyl-N-methylpropylamine

Question 8

What are aromatic amines?

Answer 8

Amine compounds containing a benzene group.

Question 9

What are aliphatic amines?

Answer 9

Amines that are non benzene based, and occurs in straight carbon chains (not cyclic).

Question 10

What are alicyclic amines?

Answer 10

Amines that are not benzene based, but has carbon chains that occurs in rings (circles).

Question 11

Why are amines described as ‘bases’?

Answer 11

Firstly, bases can be described as ‘proton acceptors’.
In amines, there is a nitrogen that has 3 bonds (maximum number of bonds N can have), either to a hydrogen or organic group.
Although this is the max number of bonds for N, the nitrogen can form another bond with a hydrogen ion (from acid) by donating its lone pair of electrons, and hence forming a dative covalent bond. As the nitrogen has lost its lone pair to this covalent bond, the nitrogen has gained a positive charge.

Question 12

What determines the strength of amines as bases?

Answer 12

The strength of amines as bases is dependent on the availability of the lone pair on the nitrogen. The availability of the is dependent on the electron density, which is turn dependent on the types of groups attached to the nitrogen. If the nitrogen is more electron dense, it is more likely to attract the positive charge of the hydrogen ion, and after the lone pair on the nitrogen can form a dative covalent bond with the hydrogen ion.

Question 13

How to produce primary amines?

Answer 13

Haloalkane + excess ammonia > primary amine + ammonium salt.
Excess ammonia is essential because 2 ammonia molecules are required in the mechanism of this reaction. With, just 1, a primary amine would not be able to be produced.

Question 14

What is the problem with producing a primary amine from a haloalkane and ammonia?

Answer 14

There is a problem because multiple substitutions can occur to produce a mixture of products: primary, secondary, tertiary amines and quaternary ammonium salts. This is because after the haloalkane and 2 ammonia molecules undergoes a substitution mechanism to produce a primary amine, this primary amine can then undergo another substitution with another haloalkane molecule. This is because this primary amine has a nitrogen. As well as a nitrogen is present, substitution can occur. This is because the nitrogen has a lone pair that can be donated (to electron deficient carbon in haloalkane) and hence acts as a nucleophile.
For example, excess ammonia can react with bromoethane to form ethylamine. However, due to the lone pair of electrons on the ammonia in ethylamine, this ethylamine can react further with another bromoethane to form diethylamine (as well as another ammonium salt). Like this, even more further substitutions can occur.

Question 15

An impure mixture is produced in the reaction between a haloalkane and excess ammonia to form a primary amine. This is not beneficial to industries. How may this be solved?

Answer 15

Distillation can occur to separate the mixture of products to obtain the wanted products.

Question 16

A student wants to make a tertiary amine using a haloalkane and ammonia. Outline reactions in which this can occur.

Answer 16

Firstly, a primary amine needs to be made, by reacting the haloalkane with excess ammonia, to form the primary amine and the ammonium salt.
Now the primary amine is taken as an intermediate. Two of this primary amine compounds is needed to react with another haloalkane molecule. This in turn produces a secondary amine and ammonium salt.
Now there is another intermediate: the secondary amine. Two of this secondary amine compounds is needed to react with another haloalkane molecule. This produces the tertiary amine the student wanted as well as another ammonium salt.

Question 17

Methylamine reacts with hydrochloric acid. What is produced and why?

Answer 17

Methylammonium chloride is (only) produced because:
The lone pair of electrons on the nitrogen in methylamine forms a dative covalent bond with the hydrogen ions form the HCl acid. As the nitrogen gave its electrons to this dative covalent bond, the nitrogen obtains a positive charge.
The positive charge of the nitrogen attracts the negative charged chlorine (from the acid). The opposing charges allows the methylammonium ion and chloride ion to ionically bond to form methylammonium chloride.

Question 18

Ethylamine reacts with sulfuric acid. What is produced and why?

Answer 18

Ethylammonium sulfate is formed because:
The lone pair of electrons on nitrogen in ethylamine forms a dative covalent bond with hydrogen ions from acid. This bonding gives the nitrogen a positive charge and forms an ethylammonium ion.
The positive charge of the ethylammonium ion attracts the negative charge of the sulfate ion, and through ionic bonding ethylammonium sulfate is formed.

Question 19

How can we prepare aromatic amines such as phenylamine?

Answer 19

Firstly, we need nitrobenzene being reduced (which is heated under reflux with tin and a sulfuric acid catalyst),to produce an ammonium salt, phenylammonium chloride.
The second step is where this phenylammonium chloride reacts with excess sodium hydroxide, to produce the aromatic amine, phenylamine.
So overall, phenylamine (AND WATER IS ALSO A PRODUCT) is produced from nitrobenzene via reduction. The reduction requires tin and sulfuric acid in the first step, and sodium hydroxide in the second step. In the chemical equation, the reducing agent is represented by [H] and 6 of these is needed for this mechanism to occur, so 6[H].

Question 20

What compound are amides derived from?

Answer 20

Carboxylic acids.

Question 21

What is the functional group of amides?

Answer 21

-CONH2
The carbon of a carbonyl group is directly bonded to nitrogen of NH2 (or just NH for secondary amides). Other than the bonds to the nitrogen and oxygen, the carbon (in the carbonyl group) can also be bonded to an organic group.

Question 22

How do primary, secondary and tertiary amides differ?

Answer 22

A primary amide has -CONH2. The carbon of the carbonyl is directly bonded to the nitrogen of NH2.
A secondary amide has -CONH. It is the same as a primary amide, except one hydrogens on the -NH2 is substituted for an organic group.
A tertiary amide has all hydrogens on the nitrogen substituted for organic groups.

Question 23

How do you name a primary amide?

Answer 23

For any amide, the suffix will be -‘amide’. The prefix is dependent on the longest carbon chain, including the carbon in the carbonyl group. This is put prior to the -‘amide’.
For example, a primary amide, with a carbon chain of 3 (including the carbon in the carbonyl group) is called propanamide.

Question 24

How do you name a secondary amide?

Answer 24

There are now two parts of the compound in a secondary amine, in terms of nomenclature. There is the carbon chain starting from the carbon in the carbonyl group, then there is the organic group attached to the nitrogen. The suffix is based on the carbon chain with the carbonyl group, followed by -‘amide’. The prefix if then the alkyl group (organic group) attached to the nitrogen atom.
For example, a secondary amide that has a carbon chain of 3 on the carbonyl side (including the carbonyl) and a carbon chain of 2 on the nitrogen side is called N-ethylpropanamide.

Question 25

Describe the general structure of an amino acid.

Answer 25

An amino acid has a carbon at its centre. On one side of the carbon, there is an amine group (-NH2), and on the other side there is a carboxylic acid group (-COOH). The carbon at the centre is also bonded to a hydrogen and an R group. This R group is an organic chain that varies between amino acids, and is hence what makes each amino acid different.

Question 26

Why are amino acids described as amphoteric?

Answer 26

Amino acids are amphoteric as they have acidic (carboxylic acid group) and basic (amine group) properties.

Question 27

What is the criteria for molecules to demonstrate chirality?

Answer 27

For a molecule to be chiral, it should have 4 different groups around a central carbon atom.

Question 28

Glycine is an amino acid. Why is it the only amino acid to not demonstrate chirality?

Answer 28

The R group of glycine is just a hydrogen. Hence, on the central carbon atom there are two hydrogens bonded, as well as the amine and carboxyl group- there are not 4 different groups. Hence, glycine does not demonstrate chirality.

Question 29

Alkalis can react with amino acids to form a salt and water. How does this occur and why?

Answer 29

Alkalis reacts with acids in a neutralisation reaction to form a salt. When an alkali reacts with an amino acid, the carboxylic acid group acts as the acid. Focus on the carboxylic acid group and carry out a normal neutralisation reaction. Other than the carboxylic acid group, no other part of the molecule should change. Water is also produced.

Question 30

Acids can react with amino acids to form a salt. How does this occur and why?

Answer 30

If this is a reaction with an acid, like HCl, there will be hydrogen ions in solution. The nitrogen on the amine group of the amino acid forms a dative covalent bond with the hydrogen ion, hence, the nitrogen gains a positive charge. This positive charge attracts the negative chloride ion from the acid and an ionic bond is formed between the two, to produce a salt.

Question 31

Esters can be formed by reacting an amino acid with an alcohol. How does this occur and why?

Answer 31

In the carboxylic acid topic, we found reacting a carboxylic acid and an alcohol forms an ester through a condensation reaction (and in turn an oxygen atom bonds the carboxylic acid and alcohol together). An amino acid should also react in the same way as it also contains a carboxylic acid group. The -OH of the carboxylic group, and hydrogen from the -OH in the alcohol is lost to produce water. An oxygen atom should now bond the two molecules together. Again, as this is a reaction involving the carboxylic acid group, the amine group and R group of the amino acid should not change. This reaction requires a strong acid catalyst, like sulfuric acid.