Unit 4.6 - Amines Flashcards
Where are free amines found?
They do not occur widely in nature but are found in decomposing protein material
Give an example of a free amine found in decomposing protein material
Dimethylamine is found in rotting fish
What can amines be regarded as?
Organic derivatives as ammonia
General primary amines formula
RNH2
Explain the primary amines general formula
RNH2
Hydrogen substituted for an R group
Why is ammonia defined as a weak base?
It’s a Proton acceptor
Is ammonia an acid or a base?
A weak base
Why is ammonia a weak base?
Because the lone pair of electrons on N can form a coordinate bond with a proton
What is a primary amine?
An amine where the nitrogen atom has one alkyl or aromatic group bonded to it. They contain the functional group -NH2
functional group of primary amines
-NH2
What are the 2 ways of naming primary amines?
Add the suffix -amine to the alkyl radicle
Add the prefix amino- to the parent alkane
CH3NH2
Methyl amine
CH3CH2NH2
Ethylamine
CH3CH2CH2CH2NH2
1-propylamine
CH3CH(NH2)CH3
2-propylamine
2-propylamine
CH3CH(NH2)CH3
Hexane-1,6 diamine structural formula and other name
H2N-CH2(CH2)4CH2-NH2
1,6 -diamino hexane
What is hexane - 1,6 diamine used for?
Making nylon
How do we prepare primary aliphatic amines?
Prepared by reacting a halogenoalkane with ammonia
How do we prepare aliphatic amines by reacting a halogenoalkane with ammonia?
The halogenoalkane is heated with a concentrated aqueous solution of ammonia
How do we prevent further reaction in the preparation of primary aliphatic amines by reacting a halogenoalkane with ammonia?
By using equimolar amounts of the two reagents
Equation for the production of a primary amine from bromoethane and ammonia
CH3CH2Br + NH3 —> CH3CH2NH2 + HBr
What does the primary aliphatic amine produced in a reaction go on to do and why?
Reacts with the HBr to form a salt
As he reaction is carried out in a sealed vessel
Why does a primary amine react with the HBr also formed in its production?
Since the reaction is carried out in a sealed vessel
How is the free amine obtained when a primary amine reacts with the side product to form a salt?
By adding sodium hydroxide solution (base)
How do we obtain a pure amine after obtaining a free amine from a salt by adding NaOH solution?
By distillation
Equation for ethylamine forming a salt and then the free amine being regenerated
CH3CH2NH2 ——> CH3CH2NH3+Br- ——> CH3CH2NH2
HBr. NaOH
CH3CH2NH3+Br-
Ethyl ammonium bromide (salt)
Ethyl ammonium bromide
CH3CH2NH3+Br-
Explain how ethyl amine reacts with HBr
The HBr is in the form H+ and Br-. The H+ will bond with the lone pair of electrons in the nitrogen atom, becoming the NH3+ cation which attracts the Br-
How are primary aromatic amines formed?
Prepared by reducing a nitro compound
What is formed by reacting a halogenoalkane with ammonia?
Primary aliphatic amines
What is formed by reducing a nitro compound?
Primary aromatic amines
How is phenylamine made?
By reducing nitrobenzene
What is made by reducing nitrobenzene?
Phenylamine
Reducing agent for reducing a nitro compound to a primary aromatic amine
A mixture of tin metal and concentrated HCl
Conditions when preparing a primary aromatic amine from a nitro compound
Reflux
What is formed when reducing nitrobenzene by refluxing it with a mixture of tin metal and concentrated HCl?
A salt - phenyl ammonium chloride
Why is a salt formed when reducing nitrobenzene with tin metal and concentrated HCl?
As the reaction is occuring in a sealed vessel
How is the free amine obtained from the phenyl ammonium chloride formed from the reduction of nitrobenzene?
By the addition of excess NaOH solution (base)
Equation for the regeneration of the free amine from phenyl ammonium salt
C6H5NH3+ + OH- —> C6H5NH2 + H2O
How is phenylamine obtained when regenerated from the salt using NaOH? Why?
Phenylamine is insoluble in water and is obtained from the mixture by steam distillation
Phenylamine in water
Insoluble
Is phenylammonium chloride soluble in water?
Yes
How is phenylamine separated from its water during steam distillation?
Using a separating funnel
How is pure phenylamine recovered during its steam distillation?
By re-distilling
What is steam distillation useful for?
With liquids which have high boiling points high do not decompose in water
Why are amines able to form hydrogen bonds?
Due to the presence of the N-H bond
Why are lower aliphatic amines readily soluble in water?
Since they form hydrogen bonds with water molecules
Why do lower aliphatic amines have higher boiling points compared to alkanes of similar molar mass?
Since they can form hydrogen bonds with themselves
Describe phenylamine at room temperature
Liquid
Describe phenylamine with water
Does not mix readily with water (is immiscible with water)
Odour of amines
Distinct, somewhat like rotting fish
Chemical properties of amines to remember
Basic properties
Reaction with ethanoyl chloride
Reaction with nitrous acid (nitric III acid)
What type of substances are amines - basic or acidic?
Basic
How do we know that amines are basic substances?
Since they react with acids to form salts
Where is the lone pair of electrons in primary amines?
On the nitrogen atom
Why are primary amines able to accept protons?
Due to the lone pair of electrons on the nitrogen atom
Explain why primary amines are basic substances
Primary amines, like ammonia, have a lone pair of electrons on the nitrogen atom which is available for bonding. Thus, they are able to accept a proton and can act as weak bases.
Are amines hydrolysed by water?
Only partially
Equation for the hydrolysis of methylamine in water
CH3NH2 + H2O —> CH3NH3+ + OH-
How do primary amines react with dilute acids and why?
Produce a salt
They are basic substances
Methylamine and HCl equation + name the product
CH3NH2 + HCl —> CH3NH3+Cl-
Methyl ammonium chloride
Phenylamine and HCl equation + name the product
C6H5NH2 + HCl ——> C6H5NH3+Cl-
Phenylammonium chloride
Methylamine and H2SO4 equation + name the product
CH3NH2 + H2SO4 —> (CH3NH3)2SO4^2-
Methyl ammonium sulphate
How can the salts formed from amines and dilute acids by isolated?
As white crystalline solids with fairly high melting temperatures
How do we regenerate the amine from the salt formed from reacting an amine with a dilute acid?
By the addition of sodium hydroxide solution
Equation for the addition of NaOH to the methyl ammonium chloride salt
CH3NH3+Cl- + NaOH —> CH3NH2 + H2O + HCl
What can be seen when phenylammonium chloride is reacted with NaOH? Why?
Two layers are formed
Phenylamine is immiscible in water
Phenylamine in water
Immiscible
List the following in terms of basicity
Ammonia
phenylamine
Primary aliphaphatic amine
Most basic = primary aliphatic amine
Ammonia
Phenylamine
What is R in R-NH2?
CH3, CH3CH2…etc
Explain exactly why primary aliphatic amine are stronger bases than ammonia
As the alkyl groups bonded to the nitrogen atoms are electron releasing. As a result, electrons are released towards the nitrogen atom. This makes the nitrogen atom more electronegative and increases the electron density around it. This makes the lone pairs of electrons on the nitrogen more available for bonding and is more able to accept a proton than the nitrogen in ammonia.
Explain exactly why phenylamine is a weaker base than ammonia
Th lone pair of electrons on the nitrogen atom is partially delocalised into the ring which means that is it less available for bonding. This is because it’s less electron rich and so less likely to accept a proton than NH3.
What is more stable - phenyl ammonium salt or ammonium salt?
Ammonium salts
What is it that makes amines all basic?
The lone pair of electrons on the nitrogen atom that can accept a proton
What can primary aliphatic amines react as?
Nucleophiles
Why can primary aliphatic amines react as nucleophiles?
Because of the presence of the lone pair of electrons on the nitrogen atom
Give 2 things that primary aliphatic amines can react with due to them being able to react as nucleophiles
React with transition metals to form a complex
React with acid chlorides to form amides
What do amines react with to form amides?
Acid chlorides
What forms when primary aliphatic amines react with acid chlorides?
Amides
What is the reaction between a primary aliphatic amine and an acid chloride ac example of?
Acetylation in which a CH3CO group is added to the amine
Acetylation
CH3CO group is added
Additional of a CH3CO group
Acetylation
Conditions for the addition of ethanoyl chloride to primary aliphatic amines
Room temperature
Dry
Equation for the reaction between methyl amine and ethanoyl chloride
CH3COCl + CH3NH2 —> CH3CONHCH3 + HCl
HCl appearance in the reaction between ethanoyl chloride and a primary aliphatic amine
White misty fumes
N-methylethanamide
CH3CONHCH3
CH3CONHCH3
N-methylethanamide
What does “N” mean in, for example, N-methylethanamide?
That the methyl group is bonded to the nitrogen atom because of the lone pair of electrons and is known as an n substituted derivative of ethanamide
Nitrous acid other name
Nitric III acid
Nitric III acid
Nitrous acid
Describe the nitric acids we normally use
Stable, H is in the +5 oxidation state
Formula of nitrous acid
HNO2
HNO2
Nitrous acid
Describe nitrous acid
An unstable compound that is prepared in situ during the course of the reaction
What is nitrous acid formed from?
Sodium nitrite NaNO2, conc. HCl
Do primary aliphatic amines and primary aromatic amines react in eh same way with nitrous acid?
No
1-butylamine other name
1-aminobutane
In what condition should the nitrous acid be when reacting it with aliphatic or aromatic amines?
Cold (less than 10 degrees Celsius)
What happens when 1-aminobutane is reacted with cold nitrous acid?
There is effervescence as nitrogen gas is released. A mixture of products is formed in the reaction including butan-1-ol.
Equation for the reaction between 1-butylamine and nitrous acid
CH3Ch2CH2CH2NH2 + HNO2 ——> CH3CH2CH2CH2OH + N2 + H2O
What is formed when phenylamine is reacted with cold nitrous acid?
A diazonium salt is formed
When is a diazonium salt formed?
When phenylamine is reacted with cold nitrous acid
Does the diazonium salt form with aliphatic amines?
No
What type of amine does the diazonium salt form with the reaction with nitrous acid?
Aromatic amines
Why doesn’t the diazonium salt form when aliphatic amines react with nitrous acid?
As the aliphatic diazonium ion is too unstable to be isolated
Diazonium ion
C6H5N2+
C6H5N2+
Diazonium ion
Why is the reaction between an aliphatic and an aromatic amine with nitrous acid completely different?
Because the diazonium salt only forms with aromatic amines
Equation for the reaction between phenylamine and nitrous acid
C6H5NH2 + HNO2 + HCl ——> C6H5N2+Cl- + 2H2O
Under which condition is the benzene diazonium ion stable?
When it’s cold (under 10 degrees Celsius)
Under which condition can benzene diazonium salts be isolated?
At low temperatures
What can be done to benzene diazonium ions at low temperatures?
Can be isolated
Why do benzene diazonium ions have to be stored at ow temperatures?
They’re unstable above 10 degrees Celsius
Above which temperature are benzene diazonium ions unstable?
10 degrees Celsius
What are benzene diazonium salts important for?
They’re an important groups of reagents in organic synthesis - especially in the formation of azo dyes
Which salts are important in the formation of azo dyes?
Benzene diazonium salts
What happens to benzene diazonium ions above 10 degrees Celsius?
It decomposes
What happens as the benzene diazonium ion decomposes above 10 degrees Celsius?
Phenol is formed and nitrogen gas is liberated
Equation for the reaction between benzene diazonium chloride and water
C6H5N2+Cl- + 2H2O —> C6H5OH + N2 + HCl
How are azo dyes formed?
When benzonium ions are kept below 10 degrees Celsius and phenol is added
What forms when benzonium ions are kept below 10 degrees Celsius and phenol is added?
Synthetic dyes - azo dyes
What are azo dyes?
Synthetic dyes
What type of reactions are azo dyes made in?
Diazo-coupling reactions (diazotization reaction)
What happens during a diazo-coupling reaction?
A benzene diazonium ion is reacted with a phenol
What are retained during the reaction between a benzene diazonium ion and a phenol?
The nitrogen atoms
What type of reaction does it involve to retain the nitrogen atoms during the reaction between the benzene diazonium ion and a phenol?
A coupling reaction
What are the compounds formed during the reaction between diazonium ions and phenol known as and why?
Azo compounds
They contain the azo group, -N=N-
Azo group
-N=N-
-N=N- group
Azo group
Typical phenol used for the production of azo dyes
Napthalene-2-ol
How come napthalene-2-ol is still a phenol?
Since the OH group is directly bonded to the benzene ring
Conditions for the reaction between benzene diazonium chloride and napthalene-2-ol
Below 10 degrees Celsius
In aqueous NaOH
Product of the reaction between napthalene-2-ol in aqueous NaOH and benzene diazonium chloride
Red solid
The reaction between benzene diazonium chloride and which phenol forms a red solid?
Napthalene-2-ol
Describe azo compounds + their use
Highly coloured
Used widely in fabric dyes and food colouring e.g - E104
What are the different colours in different azo dyes due to?
The different substituents
Why does methyl red have a red colour?
Because it absorbs light at the blue end of the spectrum, leaving the red light to be transmitted
Thus, it is red because it allows red light to pass through it while absorbing all other light
What happens to the electrons in a substance when light is absorbed by it?
The outer electrons are promoted form their normal energy level to a higher (excited) energy level
Why do many organic molecules absorb visible light?
Because of the presence of a particular functional group
What does the presence of a particular functional group cause many organic molecules to do?
Absorb visible light
Chromophores
The functional group responsible or the absorption of visible light and the colour changes in an organic compound
The functional group responsible or the absorption of visible light and the colour changes in an organic compound
Chromophores
Chromophore in azo dyes
-N=N-
What does the -N=N- group act as in azo dyes?
A chromophore
What do the wavelengths of light absorbed by different molecules depend on?
The other groups present in the molecule
What does the intensity of the colour observed in solution depend on?
The concentration of the compound present and is the basis of colorimetry
How can we easily identify the colour absorbed and the coloured transmitted (not absorbed) by a compound when light is shone through it?
Using a colour hexagon
Give an example of how we would use a colour hexagon
If magenta was absorbed, it would appear green (colour on the opposite side of the hexagon)
What would happen if we mixed all of the colours in the colour hexagon?
It would appear white
Energy equations when talking about light
E=hf
H = hc/lambda
What would we input into E=hc/lambda with a graph?
The maximum wavelength (highest peak wavelength)
Give a detailed explanation of the colour in organic molecules
Pi electrons belonging to the two nitrogen atoms interact with the delocalised pi electrons in the benzene rings
As they interact, there is a change in the energy gap, which corresponds to the frequencies in the visible part of the spectrum, between the energy levels of the nitrogen electrons
Visible light causes electrons to transfer between these levels and the compound is coloured because of the light frequencies which are transmitted
Which light frequencies are the ones that actually cause the colour of an organic molecule?
The ones which are transmitted
Which electrons interact with the delocalised pi electrons in benzene rings?
The pi electrons belonging to the two nitrogen atoms
What happens when the pi electrons belonging to the two nitrogen atoms interact with the delocalised pi electrons in benzene rings?
There is a change in the energy gap, which corresponds to the frequencies in the visible part of the spectrum, between the energy levels of the nitrogen electrons
What causes electrons to transfer between energy levels?
Visible light
What type of bonding is the lone pair of electrons on the nitrogen atom of amines available for?
Covalent bonds
How is a covalent bond formed form the lone pair of electrons on the nitrogen atom of amines?
The lone pair of electrons are donated
Equation for the reaction between ethyl ammonium chloride and sodium hydroxide
CH2CH2NH3+Cl- + NaOH —> CH3CH2NH2 + H2O + NaCl
Which part of NH2 always bonds to the phenol?
The N
Describe and explain what used be seen in a test tube containing phenylamine and water
Top layer = water
Bottom layer = phenylamine
Type of HCl used to as a reducing metal with tin metal to prepare aromatic amines
Concentrated
% yield equation
Actual/theoretical x 100
What do we need to remember to do when naming amines?
Specify the type e.g - primary or secondary
What do we need to do with phenylamine after it’s formed and why?
Since it’s an immiscible aromatic amine, it needs to be separated, dried and redistilled to produce the pure amine
What is there as a side product when NaOH is added to form a free amine from the salt? What do we do therefore?
Complex mixture of tin compounds
Steam distillation needed
