Organic Nitrogen compounds

What is the general formula of a primary amine?

RNH2

Describe how to form an amide from a halogenoalkane

Heat with halogenoalkane in a sealed tube with a concentrated ammonia and an ethanol solvent

Why can’t reflux be used to form an amide from a halogenoalkane?

Ammonia is too volatile so it would escape from the reaction vessel

Why is excess ammonia used when forming a primary amine from a halogenoalkane?

So further substitution doesn’t occur.

If ammonia is not in excess then a secondary, tertiary or quaternary amine may form

Describe how to form a primary amine from an amide

Reduction using LiAlH4

Write an equation for the formation of ethylamine from ethanamide

CH3CONH2 + 4[H] ——> CH3CH2NH2 + H2O

Describe how to from a primary amine from a nitrile

Either reduction using LiAlH4 or reduction using Ni catalyst and H2 gas

Write equations for the formation of ethylamine from ethanenitrile

LiAlH4: CH3CN + 4[H] ——> CH3CH2NH2

Ni/H2: CH3CN + 2H2 ——> CH3CH2NH2

Describe how to form phenylamine

Reduction of nitrobenzene with Sn and concentrated HCl. Reflux for 30 minutes

When synthesising phenylamine from nitrobenzene, why is NaOH added after the mixture has been refluxed?

To remove a proton from the -NH3+ group

What is the overall equation for the synthesis of phenylamine?

C6H5NO2 + 6[H] ——> C6H5NH2 + 2H2O

Why are amines basic?

The lone pair on the nitrogen in the amine group can accept a proton/hydrogen ion

What affects the strength of a base?

How easily the lone pair can accept a hydrogen ion

The stability of the ions formed

What is the order of relative basicity between ammonia, ethylamine and phenylamine? (most reactive to least)

Ethylamine, Ammonia, Phenylamine

Why is ethylamine a stronger base than ammonia?

Alkyl groups tend to push away from themselves creating a positive inductive effect

This increases the negative charge of the nitrogen in ethylamine, making the lone pair more attracted to hydrogen ions

The electron pushing effect also spreads the charge more so the ethylammonium ion is more stable than the ammonium ion

Why is phenylamine a weaker base than ammonia?

Phenylamine has one of the p-orbital on the nitrogen overlaps with the pi-bonding system in the ring

This causes the lone pair on nitrogen to be delocalised into the ring, making the lone pair less available to form dative bonds with H+

Why is phenylamine more reactive than benzene?

The -NH2 group in phenylamine activated the benzene ring when the lone pair on the nitrogen is delocalised into the pi system making phenylamine more reactive because of the electron density in the pi system so more electrophiles are attracted

Describe the conditions for the reaction between phenylamine and aqueous bromie

Room temperature

No catalyst

Describe what would be observed when phenylamine reacts with aqueous bromine

Bromine water is decolourised

2,4,6-tribromophenylamine is formed with a white precipitate forms

What is formed in the reaction between phenylamine and nitrous acid when the mixture is warmed?

Phenol, H2O and N2

When reacting phenylamine with nitrous acid, why is the nitrous acid typically made in situ and how?

Because it decomposes rapidly

It is made by reacting HCl with sodium or potassium nitrate so phenylamine is added to HCl and NaNO3 at the same time

What is formed from the reaction between phenylamine and nitrous acid when the reaction vessel is below 10 degrees?

A Benezenediazonium ion is formed with water

What group does a diazonium ion contain?

N2+ group

Describe the formation of dyes from benzenediazonium chloride and phenol

Phenol is reacted with NaOH to from sodium phenoxide

Sodium phenoxide is cooled in ice ana a cool solution of benzenediazonium chloride is added

A yellow orange precipitate forms and this is the azo compound

What is an azo compound?

A compound containing two benzene rings joined by a nitrogen bridge

What is they type of reaction that occurs when reacting sodium phenoxide and benzenediazonium chloride? List the reagent and conditions

Diazotisation

Reagents: Nitrous acid and HCl

Conditions: Keep below 10 degrees

During the formation azo-compounds, at which position does coupling typically take place?

At the 4-position

If the 4-position is occupied, coupling will take place at the 2-position

What functional group do amides contain?

-CONH2

Are amides acidic, neutral or basic?

Neutral

Describe how an amide can be formed from ammonia

React with an acyl chloride and HCl gas is also produced

Write an equation for the reaction between ammonia and propanoyl chloride

If excess ammonia is used, the overall equation is:

CH3CH2COCl + 2NH3 ——> CH3CH2CONH2 + NH4Cl

Describe the acid hydrolysis of amide

Upon heating with acid, an amide will be broken down into a carboxylic acid and either ammonium ions or RNH3+ ions

Describe the alkaline hydrolysis of amides

Upon heating with NaOH, an amide will be broken down into a carboxylate salt and either ammonia or an amine

Describe the reduction of amides

LiAlH4 is used with a dilute acid

An amine and water is formed

Write an equation for the reduction of propanamide

CH3CH2CONH2 + 4[H] ——> CH3CH2CH2NH2 + H2O

What functional groups do all amino acids contain?

COOH

NH2

Why can amino acids act as both acids and bases?

The -COOH group can donate a proton

The -NH2 group can accept a proton

What is a zwitterion? How do amino acids from zwitterions?

A zwitterion is an ion containing a positive and negative charge. It has no overall charge

Amino acids form zwitterions when carboxylic acids group donates a proton to the amine group

What happens when an alkali is added to an amino acid zwitterion?

The NH3+ group donates a hydrogen ion to the OH- ions of the alkali to form water. The organic compound isn’t a zwitterion anymore because it only contains a negative charge

What happens when an acid is added to an amino acid zwitterion?

The COO- group accepts a hydrogen ion from the acid. The organic compound isn’t a zwitterion anymore because it only has positive charge

How does a peptide bond form?

During a condensation reaction between amino acids

What is a buffer solution?

A substance that resists changes in pH when small amounts of acids or bases are added

What is electrophoresis?

The separation of ions placed in an electric field between a positive and negative electrode

What must the pH for a specific amino acid to form its zwitterion?

The pH must be the isoelectric point of the amino acid

When the pH is the isoelectric point of the amino acid, why doesn’t this amino acid movie during electrophoresis?

The amino acids forms its zwitterion making it no overall charge, so it is not attracted to the anode or cathode

When do amino acids moves towards the cathode during electrophoresis?

When they are positively charged and may occur when an amino acid has an extra hydrogen in the amine group

When do amino acids moves towards the cathode during electrophoresis?

When they are negatively charged and may occur when an amino acid has lost a hydrogen from the carboxylic acid

What are the factors that affect the rate at which ions move towards electrodes during electrophoresis?

• Size of the ion

• Charge on the ions

• Voltage applied

• Temperature

  Mass and voltage affect the speed

  Charge on the ion and pH affect direction

How is the size of ions related to the speed at which they travel during electrophoresis?

Smaller ions travel faster because there’s less resistance to their movement through the paper fibres

How does using buffer with a LOW pH affect the results when using electrophoresis to separate amino acids?

-COOH groups remain as -COOH

-NH2 groups accept a proton to become -NH3+

All amino acids will be positively charged so they move to the cathode

How does using buffer with a HIGH pH affect the results when using electrophoresis to separate amino acids?

-COOH groups donate a proton to become -COO-

-NH2 groups remain as -NH2

All amino acids will be negatively charged so they move to the anode

What must be done before peptides can undergo electrophoresis? Describe how the molecules are changes

Treat the peptides with SDS and denature them by heating

The secondary and tertiary structures are lost and the molecules become amino acid chains surrounded by negative charges