Unit 5- Topic 19 Flashcards
What is an amine
Nitrogen containing compounds where the nitrogen is has 3 bonds to one or more alkyl groups.
There are primary, secondary and tertiary amine. CH3NH2 (1), CH3NHCH3 (2), CH3N(CH3)CH3 (3)
Two main ways of making primary aliphatic amines
From nucleophilic substitution of halogenoalkanes or reduction by hydrogenation of nitriles
Preparation of primary aliphatic amines from halogenoalkanes
Heating a halogenoalkane with ammonia, (under pressure and in a sealed container since ammonia is a gas) or with concentrated aqueous ammonia. It creates a primary amine and hydrogen chloride. This reaction is done by the nucleophilic attack of the lone pair of electrons to the C of halogeno… Amine creates also has lone pair which exults in the reaction going further (previous halogeno + product) to produce a secondary amine and HCl.
Why is excess ammonia used in the preparation of aliphatic primary amines from halogenoalkanes
Excess used to prevent unwanted side-reaction (a further reaction between halogeno and primary amine). In excess so that it out-numbers the molecules of the primary amine formed. However the excess ammonia may react with the acidic hydrogen chloride formed so:
CH3Cl + 2NH3 -> CH3NH2 + NH4Cl.
the products can be separated from the reactants by fractional distillation which will also prevent unwanted reactions.
Preparation of primary aliphatic amines from nitriles
Nitriles (RCN) (are reduced) + LiAlH4 in dry ether -> primary aliphatic amines
Eg: CH3CN + 4[H+] -> CH3CH2NH2
Preparation of Aromatic amines
C6H5NO2+ 6[H+] -> C6H5NH2 +. H2O
Nitrobenzene (is reduced)
Reagent: Tin mixed with concentrated hydrochloric acid
Conditions: heated under reflux
Why may you add an alkali after the preparation of an aromatic amine
the phenylamine produced will react with the acid needed for the preparation to occur to form phenylammonium: that by adding sodium hydroxide is easily converted into a phenylamine
uses for phenylamine
Manufacture of polymers and pharmaceuticals.
reaction of aliphatic amine with water
aliphatic amines + water -> produces a hydroxide ion and a aliphatic amine with a positive charge.
the hydroxide ions makes the solution alkaline.
difference in solubility of phenylamines and aliphatic amines
aliphatic amines are completely miscible. As size of molecule increases, solubility decreases. they dissolve in water due to hydrogen bonding with water molecules.
phenylamine is only slightly soluble therefore only slighlty alkaline when reacting with water
order from most basic compound to least: ammonia, water, phenylamine and methylamine
methylamine
ammonia
water
phenylamine
why is methylamine a stronger base than ammonia
because the methyl group is electron-releasing, and so has an increased electron density on nitrogen compared with ammonia.
why is phenylamine not very basic
because the lone-pair of electrons on nitrogen is incorporated into the delocalised electrons in the benzene ring, making nitrogen less electron-rich therefore the lone pair of electrons less available for donating to the hydrogen of a water molecule.
reaction of amines with acids
all react with strong acids to form ionic salts
C6H5NH2 + HCl -> C6H5NH3+Cl-
phenylamine+ HCl -> phenylammonium chloride
reaction of amines with acyl chlorides
mechanism: addition- elimination
products: amide (RCONH2) or N-substituted amide (RCONHR’) and hydrogen chloride
normally, phenylamine: amide. butylamine: N- substituted amide
why do reaction between amines and halogenoalkanes occur?
halogenoalkanes contain an electron-deficient carbon atom and amines contain an electron-rich nitrogen atom. it is a substitution reaction. however since the product also conatins a electron-rich nitrogen, it can further react to form a tertiary and quaternary ammonium salt.
RNH2 + R’X -> RNHR’ + HX -> product a secondary amine.
R= alkyl in amine and R’= alkyl group in halogenoalkane
what is special about the reaction of a tertiary amine and halogenoalkane
HCl is not formed since tertiary amines do not have a hydrogen bonded to the nitrogen atom. therefore there is only one product which causes the nitrogen to become positive and chloride negative eg: CH3CH2CH2CH2N+(CH2CH3)3Cl-
reaction of aliphatic amines with copper (ii) ions
copper ions react with water to form a copper aqua ion: [Cu(H2O)6]2+
the amine then accepts protons to give a pale blue precipitate and ammonium salt.
so: [Cu(H2O)6]2+ +2CH3CH2CH2CH2NH2 -> [Cu(H2O)4(OH)2] + 2CH3CH2CH2CH2NH3+
it can further react to give a deep blue solution
so: [Cu(H2O)4(OH)2] + 4CH3CH2CH2CH2NH2 -> [Cu(CH3CH2CH2CH2NH2)4(H2O)2]2+ +2H2O + 2OH-
reaction of aromatic amines with copper (ii) ions
overall reaction of phenylamine with copper solution:
[Cu(H2O)6]2+ + 4C6H5NH2 -> [Cu(C6H5NH2)4(H2O)2]2+ + 4H2O
why is nitrous acid prepared in situ
because it is a very unstable compound. it exists only in a very aqueous solution and decomposes at room temperature.
how to prepare nitrous acid in situ
due to the acid decomposing at room temperature, any reactions involving nitrous acid have to be carried out in under very carefully controlled conditions. Can be prepared by: mixing ice-cold solutions of sodium nitrite and dilute hydrochloric acid.
NaNO2(aq) + HCl(aq) -> NaCl(aq) + HNO2(aq)
how to form a diazonium ion
by adding an aromatic amine (phenylamine) to the reaction mixture to create nitrous acid in situ giving this chemical formula:
(phenylamine) + HNO2(aq) + HCl (aq) -> (benzenediazonium ion) + Cl- + 2H2O (l)
conditions: reaction vessel must be ice-cold or 5ºC or below since if the temperature rises phenol is formed. (forming with it N2 gas and water)
reaction of diazonium ions (benzenediazonium ions) with phenols
diazonium ions act as strong electrophiles. they react with alikaline solutions of phenol to produce (after acidificaton with dilute HCl), a (4-hydroxyphenyl)azobenzene.
Reaction: coupling
Formed: coumpound formed creates a energetically stable, yellow azo dye
System of product: conjugated system
why are azo dyes energetically stable
the stability comes from extensive delocalisation of electrons ia the nitrogen-to-nitrogen double bond.
What is the molecular formula for amides
RCONH2
Why do amide have a basic character
Because the carbonyl group alters th chemical character of the NH2
Solubility of amides
Aliphatic amides are soluble in water because it can form hydrogen bonds with water since the carbon is very electron deficient because it is bonded to oxygen and nitrogen
How to prepare amides
Acyl chloride + conc. aqueous ammonia -> amide + HCl (misty fumes)
However ammonia reacts with HCl due to the basic nature of ammonia and the acidity of HCl.
So overall reaction: CH3CH2COCl + 2NH3 -> CH3CH2CONH2 + NH4Cl
How to form a polyamide nylon
Dicarboxylic acid + aliphatic diamide -> polyamide nylon + water
By condensation polymerisation
How to form polyamide Kevlar
Aromatic diamide + phenyl dioyl chloride -> polyamide Kevlar + hydrogen chloride
Properties of polyamides
Gas particles cannot pass through the material easily.
Tend to be semi-crystalline
Very tough due to strong bonding
Good thermal and chemical resistance (they can be attacked by strong alkalis and acids due to the peptide link being hydrolysed by the acids/alkalis)
As moisture absorbance increases, resistance and flexibility increases while strength and stiffness decrease
High temperature resistance
What is poly(ethenol)
An addition polymer. Formed in two stages, polymerisation of ethenyl ethanoate followed by a reaction with methanol (ester exchange)
Formed by additions polymerisation.
Properties of poly(ethenol)
Multiple -OH so it can hydrogen bond to water. Soluble.
Solubility depends on the percentage of ester groups that have been replaced by OH groups.
What is an amino acid
A compound that contained and amine group and a carboxylic acid group separated by a carbon atom. This allows both group to maintain their typical properties
Uses for poly(ethenol)
Make disposable laundry bags for use in hospitals. Since the laundry bag is soluble, they can put the whole laundry bag inside the washing machine to prevent doctors from being in contact with the microorganisms of the patient
Make liquid-detergent capsules since the bags will dissolve in the water
What occurs in addition polymerisation
This is when many monomers with double bonds join together to form a long-chain molecule (polymer). One of the bonds in the double bon is broken and the monomers are linked together by single bonds.
What is poly(propenamide) and how is it formed
It is an addition monomer
Formed by polymerising 2-propenamide.
The polymer chains can be easily cross linked with other chains which produces a thick gel with a larger capacity to absorb water therefore used for making soft contact lenses.
What is poly(propenamide) used for
Used as thickener and as filler in facial surgery. Can be used in water treatment and paper making.
In the preparation of poly(ethenol), how can the amount of ester exchange be controlled
By altering the temperature
Common name this amino acid: H2N - CH - COOH
I
CH3
Alanine
Common name this amino acid: H2N - CH - COOH
I
CH2 - SH
Cysteine
Common name this amino acid: H2N - CH - COOH
I
CH2 - CH2 - COOH
Glutamic acid
Common name this amino acid: H2N - CH2 - COOH
Glycine
Common name this amino acid: H2N - CH - COOH
I
CH2 - CH2 - CH2 - CH2 - NH2
Lysine
Behaviour of amino acids with water
Soluble in water. They can behave as bases and form an alkaline solution:
H2N -CHR -COOH + H2O <——> H3N+ - CHR - COOH + OH-
They can behave as acids ad form an acidic solution
H2N -CHR -COOH + H2O <——> H2N - CHR - COO- + H3O+
Third alternative
What is the third alternative for the behaviour of amino acids + water
An H+ ion could transfer from the COOH group to the NH2 group:
H2N -CHR -COOH + H2O <——> H3N+ - CHR - COO-
The product is electrically neutral as it has a positive an negative charge which balance each other. They are known as zwitterions.
What is the isoelectric point of an amino acid
The pH at which the zwitterion exists in aqueous solution. A low isoelectric point means the molecule is predominantly acidic. A high isoelectric point means the molecule is predominantly basic. This numbers are directly related to the number of NH2 and COOH groups in each molecule.
Optical activity of 2-amino acids
Expect glycine, they all contain a chiral centre therefore they are optically active. Aqueous solutions of the enantiomers rotate the plane of polarisation of plane-polarised light. If an amino acid is synthesised in the laboratory, then a race mixture is formed.
What occurs when two amino acids react together
It is an acid-base reaction and condensation polymerisation. Due to COOH losing OH and NH2 losing H, the amino acids are joined by an amide group therefore the bond is called peptide bond. And a dipeptide is formed
How are polypeptides and proteins formed
By condensation polymerisation of many amino acids
Difference between polypeptides and proteins
Proteins have further levels to their structures due to the polypeptide chains interacting in three dimensions to form secondary, tertiary and quaternary structures
How can polypeptide chains be broken down into individual amino acids
By hydrolysing through prolonged heating with concentrated HCl acid. The amino acids formed will have the NH2 group protonated (+NH3) due to the strongly acidic conditions.
(Dipeptide) + H2O + 2H+ -> (amino acid with extra H+ in NH2) + (amino acid with extra H+ in NH2)
How can you separate amino acids produced after the hydrolysis of protein
Using chromatography paper. Using a suitable solvent the individual amino acids will rise to different heights. A developing agent is needed to identify the positions of the amino acids since they are colourless. Their Rf values are calculated so individual amino acid identified.
What does separating amino acids with chromatography depend on
The relative solubilities of the amino acids in the mobile and stationary phases.
Give the systematic name of: H2NCH2COOH
2-aminoethanoic acid
Give the systematic name of: CH3CH(NH2)COOH
2-aminopropanoic acid
Give the systematic name of: H2NCH2CH2COOH
3-aminopropanoic acid
Give the systematic name of: CH3CH(NH2)CH2COOH
3 - aminobutanoic
Give the systematic name of: C6H5CH(NH2)COOH
2 - aminophenylethanoic acid
Give the systematic name of: HCONH2
Methanamide
Give the systematic name of: CH3CONH2
Ethanamide
Give the systematic name of: CH3CH2CONH2
Propanamide
Give the systematic name of: CH3CH2CH2CONH2
Butanamide
Give the systematic name of: CH3NH2
Methylamine
Give the systematic name of: CH3CH2NH2
Ethylamine
Give the systematic name of: CH3CH2CH2NH2
Propylamine
Give the systematic name of: CH3CH2CH2CH2NH2
Butylamine
Give the systematic name of: C6H5NH2
Phenylamine
