Organic: Amines Flashcards
Naming amines?
- Name stem ends in -yl (propylamine) or can be propan-1-amine
- If another priority functional group is present as well as amine group , PREFIX -amino is used. (2-aminopropanoic acid - amino acid)
- If amine is secondary, each chain is named + smaller ALKYL groups attached is preceded by an -N
(N-methylpropylamine or N-methylpropan-1-amine (CH3CH2CH2NHCH3))
If chains are same length dont use -N - If tertiary amine : each alkyl group is given N
- PHENYLAMINE - if benzene ring and NH2 group
- If 2 amines groups - e.g 1,6diaminohexane or hexane-1,6-Diamine
What is an aliphatic and aromatic amine?
Aliphatic - if R group is an alkyl group (methyl,ethyl)
Aromatic - if R group is Aryl group (benzene ring/phenyl)
Primary aliphatic amines reaction with water?
small amines can form H bonds with water + dissolve readily
- as hydrocarbon part becomes longer, solubility decreases (phenylamine only slightly soluble)
BECAUSE : the bigger the amine, greater the LONDON forces between amine molecules + more energy needed to overcome
Larger carbon chain disrupt H bonding in water (cant form H bond with water)
Can also react with water to form ALKALINE SOLUTIONS :
CH3NH2 + H2O ⇌ CH3NH3+ + OH-
Primary aliphatic amines reaction with acids?
React with strong acids - form IONIC AMMONIUM SALTS - SOLID CRYSTALS which are soluble in acid
CH3NH2 (aq) + HCl (aq) → CH3NH3+Cl- (aq)
Methylamine Methyl ammonium chloride
adding NaOH to ammonium salt converts it back to amine
Primary aliphatic amines/phenylamine reaction with ethanoyl chloride?
(Acyl chloride)
Addition - elimination reaction (2 molecules join tgt , a small molecule is eliminated)
Acyl chloride —> SECONDARY AMIDE
Butylamine with ethanoyl chloride:
CH3COCl + CH3(CH2)3NH2 → CH3CONHCH2CH2CH2CH3 + HCl
Forms : N-butylethanamide + HCl
Reaction of Primary aliphatic amines with halogenoalkanes?
Nucleophilic substition reaction - electron deficient C atom on haloalkane and electron rich N atom on amine causes reaction
Butylamine + chloroethane —> SECONDARY AMINE + HYDROGEN HALIDE
CH3CH2CH2CH2NH2 + CH3CH2Cl → CH3CH2CH2CH2NHCH2CH3 + HCl
SECONDARY AMINE can react further with more HALOALKANE as it has electron rich N atom —> form TERTIARY AMINE
- reacts subsequently on to form QUATERNARY AMMONIUM SALT
HALOALKANE + primary aliphatic amine:
Reaction of secondary amine to form tertiary and subsequently quaternary ammonium salt?
Keep reacting with more haloalkane (in this case, (CHLOROETHANE)
FORMING TERTIARY: CH3CH2CH2CH2NHCH2CH3 + CH3CH2Cl → CH3CH2CH2CH2N(CH2CH3)2 + HCl
FORMING AMMONIUM SALT: CH3CH2CH2CH2N(CH2CH3)2 + CH3CH2Cl → CH3CH2CH2CH2N+(CH2CH3)3Cl-
(Doesn’t form HCl here, because requires loss of H from N atom in tertiary amine, but tertiary amine doesn’t have this)
Reaction of primary aliphatic amines with copper(II) ions?
Lone pair on nitrogen allows amines to act as ligands + form dative covalent bond with transition metal ions —> form coloured complex ions
(Similar reaction to when ammonia reacts with Cu)
[Cu(H2O)6]2+ + 2CH3CH2CH2CH2NH2 → [Cu(H2O)4(OH)2] + 2CH3CH2CH2CH2NH3+
Form blue precipitate
excess butylamine: precipitate dissolves to BLUE SOLUTION :
[Cu(H2O)4(OH)2] + 4CH3CH2CH2CH2NH2 → [Cu(CH3CH2CH2CH2NH2)4(H2O)2]2+ + 2H2O +2OH-
How to prepare amines?
- Reaction of HALOALKANE WITH AMMONIA
- REDUCTION OF NITRILES
Preparing primary aliphatic amines:
Reaction of halogenoalkane with ammonia?
Nucleophilic substitution
Ammonia is nucleophile + replaces halogen
Conditions: excess, hot ethanolic ammonia under pressure
PRIMARY AMINE FORMED
(NOT AS EFFICIENT for preparing HIGH YEILD OF primary amine, because further substitution reactions could occur)
Preparing primary aliphatic amines:
Reduction of nitriles?
-CN can be REDUCED TO -NH2 group
- Convert haloalkane to nitrile , USE KCN in aqueous ethanol (under reflux)
-
Nitrile vapour + H2 GAS passed over nickel catalyst
OR
LiAlH4 in dry ether used
E.g CH3CN + 4[H] —> CH3CH2NH2
Ethanitrile —> ethyl amine
FORM PRIMARY AMINE
(2 step reaction so may have LOW YIELD + KCN is toxic)
Why can ammonia and amines act as Bronsted-Lowry BASES?
N atom can accept a proton (H+ ION)
- act as Bronsted Lowry bases in aqueous solutions by DONATING its lone pair to PROTON - FORM DATIVE BOND
What is strength of a base dependent on?
Ability of lone pair on N ATOM to accept proton+ form dative bond
The more readily a proton is attracted, stronger the base is
Factors that affect the basicity of amines?
Positive inductive effect: some groups (like alkyl groups) donate electron density to N atom, causing lone pair of electrons to become more available —> INCREASE BASICITY
Delocalisation : presence of aromatic ring (benzene ring) cause lone pair of electrons on N atom to become delocalised in benzene ring
- lone pair less available to form dative bond with H+ —> DECREASE BASICITY
ORDER from strongest base to weakest base?
Secondary amines > Aliphatic amines > ammonia > aromatic amines
Secondary amines > primary - have more alkyl groups around N atom, in place of H atoms
More electron density pushed onto N ATOM (as inductive effect of alkyl groups > that of H atoms)
Primary aliphatic amine > ammonia - alkyl groups are electron releasing, pushing electrons towards N ATOM
Aromatic amines are weakest (DONT FORM BASIC SOLUTIONS) because: Nitrogen’s lone pair become delocalised in benzene ring - they’re less available to form dative bond with H+
How are aromatic amines formed from NITROARENES?
NITROBENZENE (C6H5NO2)—> PHENYLAMINE (C6H5NH2)
Stage 1 : reduction of nitrobenzene
Nitrobenzene reacted with TIN (Sn) and conc HCl + heat under reflux - form C6H5NH3+Cl-
Tin and HCl are reducing agents
Phenylammonium ions (C6H5NH3+) are pronated due to acidic conditions
STAGE 2: formation of phenylamine
Phenylammonium ions, (C6H5NH3+) deprotonated by adding EXCESS NaOH
Forming phenylamine - must be separated form reaction mixture by STEAM DISTILLATION
How are amides formed?
Have CONR2 functional group - derivative of CARBOXYLIC ACIDS
CONDENSATION REACTION between acyl chloride + ammonia or amine
2 molecules join tgt and small molecule is eliminated (in this case HCl eliminated)
Explain the condensation reaction to form AMIDES?
Cl- from acyl chloride is electronegative + draws electron density from Carbonyl carbon in acyl chloride
Carbonyl carbon is therefore electron deficient - can be attacked by nucleophile (N atm on ammonia/amine)
As a result:
C-Cl bond broken and amide formed
If primary/secondary amine used —> N-SUBSTITUTED AMIDE
If ammonia used —> NON SUBSTITUTED AMIDE PRODUCED (primary amide)
If ammonia used in condensation reaction to form amide , what extra reaction occurs?
NH3 + HCl —> NH4Cl
Overall example reaction :
Propyl chloride + ammonia
CH3CH2COCl + 2NH3 → CH3CH2CONH2 + NH4Cl
Formation of polyamides?
Diamine (NH2 groups) + dicarboxylic acid (2 COOH)—-> polyamide
Condensation polymerisation
OH group from dicarboxylic acid and H from Diamine —> form water (expelled) and AMIDE BOND FORMED
How is Nylon made?
POLYAMIDE formed in CONDENSATION REACTION:
Dicarboxylic acid + Diamine reaction:
Hexanedioic acid + hexane-1,6-Diamine
How is Kevlar made? Properties?
Condensation polymerisation Between DIAMINE AND DICARBOXYLIC ACID
1,4-diaminobenzene + benzene-1,4-dicarboxylic acid
Polymer chains have H bonds between them —> strong/flexible + fire resistant
- used for bullet proof vests
How are condensation polymers identified?
Monomers linked by ESTER or AMIDE bonds
Different ways condensation polymers can be formed?
Dicarboxylic acid + diol -> polyester
Dicarboxylic acid or DIOYL DICHLORIDES (acyl chloride) + Diamines —> polyamides
Dioyl dichloride - has 2 -COCl groups (Cl removed)
Amino acids - have NH2 and COOH Group so can 2 amino acids can react together to form DIPEPTIDES or POLYPEPTIDES (amide bond)
Why do polyamides have higher melting points that polyesters?
Polyamides (and proteins) have H bonding between lone pairs on OXYGEN in C=O bond and HYDROGEN in N-H bond on different chains
Have permanent dipole-dipole forces : polar C=O and polar C-N bond
London forces - many electrons in molecule
What are acidic and basic amino acids?
Acidic : have extra carboxylic acid group on R group
Basic : have extra amine group on R group
What is a ZWITTERION? What does this cause?
Ion with both a POSITIVE (NH3+) and NEGATIVE(COO-) charge
Bc of this:
Strong intermolecular forces of attraction between amino acids —> amino acids are SOLUBLE CRYSTALLINE SOLIDS
How do zwitterions act as buffer solutions?
Resist any chnages to pH when small amounts of acids/alkali are added
ACID ADDED(low pH): -COO- part of ZWITTERION accepts H+ to reform -COOH group
Contains NH3+
ZWITTERION becomes + charged ion
ALKALI ADDED(high pH): -NH3+ part donated H+ to reform NH2 group (form water)
Contains COO-
ZWITTERION becomes - charged ion
What is the isoelectronic point?
The pH at which the amino acid exists as a NEUTRAL ZWITTERION (has both NH3+ AND COO- group)
- neither the negatively charged (COO-) or the positively charged (NH3+) ions dominate
What reactions do amino acids undergo?
Most reactions of amines/carboxylic acids INCLUDING
Amines with acids
Carboxylic acids with bases
Amino acid + acid?
AMINE GROUP - basic
Reacts with acid to form SALTS
H2NCHRCOOH + HCl ⇌ H3N+CHRCOOH + Cl-
Amino acid + aqueous alkalis (KOH or NaOH)?
Form SALT AND WATER
H2NCHRCOOH + NaOH ⇌ H2NCHRCOO- Na+ + H2O
Amino acids esterification with alcohols ?
Heat with ALCOHOL in presence of conc. H2SO4
COOH group is esterified , whilst basic AMINE GROUP is porotonated due to acidic conditions
H2NCHRCOOH + C2H5OH + H+ ⇌ H3N+CHRCOOC2H5 + H2O
Which amino acids are optically active?
All amino acids , EXCEPT GLYCINE (has 2 H groups), are CHIRAL bc there are 4 different groups around the C
- aqueous solutions of the enantiomers ROTATE PLANE OF POLARISED LIGHT
If amino acids made in lab, RACEMIC MIXTURE MADE
How to hydrolyse proteins ?
Polypeptides chains in protein broken down into their individual amino acids by:
Prolonged HEATING with CONC HCl
Due to acids environment, amino acids formed will have protonated NH2 group (NH3+ groups)
Chromatography of amino acids?
After hydrolysing polypeptide/protein into amino acids:
1. Use chromatography paper and draw pencil line 1.5 cm from bottom
2. With a capillary tube , put small drop of amin acid on pencil line
3. Lower paper into beaker with appropriate solvent - wait for solvent to travel up paper
4. Dry chromatography paper + spray with NINHYDRIN solution
5.Analyse
What are amines derivative of and what are primary,secondary, tertiary, quaternary ammonium ion?
Amines - derivative of AMMONIA
Primary amine - 1 alkyl group attached to N atom
Secondary amine - 2 alkyl group attached to N atom
Tertiary Amine - 3 alkyl group attached to N atom
Quaternary - N bonded to 4 alkyl groups - positive QUATERNARY AMMONIUM ION
How are amides named and what are N-substituted amides?
Stem of CARBON CHAIN + suffix -amide
N-SUBSTITUTED AMIDES: have prefix, N-alkyl-, for alkyl group attached to N atom
N substituted amides are when a H atom on the CONH2 group is substituted by alkyl/aryl group
Why would yield of crystals be different from expected?
Reaction incomplete
Crystals not dry/still damp when weighed
Transfer loss when filtering
May not have all crystallised
Impurities
Why is phenylamine a weaker base than butylamine?
Lone pair of electrons on N atom
Interacts with the pi electrons of the ring
Electrons less readily available therefore less able to accept a proton
