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5.6Unit 5. Transition Metals and Organic Nitrogen Chemistry

Organic Chemistry: Nitrogen Compounds — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions

25 min read 39 parts Lesson 5 of 43 1 quiz

📚 IAL Edexcel Linear (Chemistry) Hub / Topical Revision
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Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
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Lesson summary

5.6 Organic Chemistry: Nitrogen Compounds — amines, amides, polyamides and amino acids — IAL EDEXCEL LINEAR (CHEMISTRY) notes: Name and classify amines, amides and amino acids, explain basicity, describe preparation and reactions of amines, azo dyes, amides, polyamides, poly(ethe…

  • Condensation polymerisation
  • Zwitterion
  • Isoelectric point
  • Diazonium salt
  • Peptide link
  • Amines are derivatives of ammonia in which hydrogens are replaced by alkyl or aryl groups

Part 1 of 9Amines, amides and amino acids: classification and naming

1
Amines are derivatives of ammonia in which hydrogens are replaced by alkyl or aryl groups.
2
Classified by the number of groups on the nitrogen (R-NH2, R2NH, R3N), unlike alcohols and halogenoalkanes, where it depends on the carbon.
  • An alkyl group gives an aliphatic amine; a benzene ring gives an aromatic amine.
3
Naming amines
  • Common namealkyl or aryl prefix + amine, e.g. ethylamine.
  • Systematic nameamino- + stem, e.g. phenylamine (aminobenzene).
4
Amides contain -CONR2, formed from an acid or acyl chloride with ammonia or an amine.
  • Primary, secondary and tertiary amides depend on the groups on the nitrogen;
    • one is always the carbonyl carbon.
  • Primaryadd -amide, e.g. ethanamide CH3CONH2.
  • Substituents on nitrogen are prefixed N-, in alphabetical order: N-propylethanamide, N-methyl-N-propylethanamide.
5
Amino acids contain a basic -NH2 and an acidic -COOH, so they are amphoteric.
  • 2-aminocarboxylic acids, RCH(NH2)COOH, are the building blocks of proteins; there are 20 natural ones.
  • The R group varies and can be acidic, basic or neutral.

Part 2 of 9Properties and basicity of amines

The first members of the primary aliphatic amines are miscible with water by hydrogen bonding; solubility falls as the hydrocarbon part lengthens,
  • and phenylamine is only slightly soluble.
Amines react slightly with water to give alkaline solutions: CH3NH2 + H2O ⇌ CH3NH3+ + OH−; they smell fishy.
Basicity
  • Basicity the nitrogen lone pair accepts a proton, forming a dative bond.
  • Positive inductive effectalkyl groups push electron density onto N, so the lone pair is more available and the amine is a stronger base.
  • Delocalisationin phenylamine the lone pair delocalises into the ring, so it is less available.
CompoundRelative basicityReason
Secondary amineStronger than primaryMore alkyl groups donate electrons
EthylamineStrongElectron-releasing alkyl group
AmmoniaIntermediateNo alkyl group
PhenylamineWeakerLone pair delocalised into the benzene ring
EthanamideEssentially neutralLone pair delocalised towards C=O

Part 3 of 9Reactions of amines

1
With acids they form ionic ammonium salts: CH3NH2 + HCl → CH3NH3+Cl−.
  • The salts are soluble, so phenylammonium chloride dissolves although phenylamine does not.
  • NaOH converts the salt back to the amine.
2
With acyl chlorides they form N-substituted amides by addition–elimination: CH3COCl + CH3CH2CH2CH2NH2 → CH3CONHCH2CH2CH2CH3 + HCl.
3
With halogenoalkanes, nucleophilic substitution gives secondary, then tertiary amines and finally a quaternary ammonium salt.
  • R'NH2 + R"X → R'NHR" + HX.
  • A tertiary amine reacts with another halogenoalkane to give a quaternary ammonium salt, with no HCl since there is no N-H left.
4
With copper(II) ions, amines act as lone-pair donors like ammonia.
  • A blue precipitate forms, which dissolves in excess amine to give a deep blue solution.
  • [Cu(H2O)6]2+ + 2RNH2 → [Cu(H2O)4(OH)2] + 2RNH3+.

Part 4 of 9Preparation of amines

Preparation of amines
Halogenoalkane with excess ethanolic ammonia
  • Heated under pressure in a sealed tube; a nucleophilic substitution gives the primary amine.
  • Excess ammonia limits further substitution.
Reduction of nitriles to primary amines
  • Pass nitrile vapour and hydrogen over a nickel catalyst, or use LiAlH4 in dry ether.
Phenylamine from nitrobenzene
  • Stage 1: heat nitrobenzene with tin and concentrated HCl under reflux in a boiling water bath;
    • tin is oxidised to Sn2+ and Sn4+ and the product is the phenylammonium ion, C6H5NH3+.
  • Stage 2: add excess NaOH to deprotonate the ion and free phenylamine.
  • Stage 3: steam distil, add NaCl so the phenylamine salts out into ether, separate, distil off the ether and collect the fraction at 180–185 °C.

Part 5 of 9Diazonium salts and azo dyes

  • Azo compounds contain R1-N=N-R2 and are used as dyes.
1
Make nitrous acid in situ from sodium nitrite and hydrochloric acid, because it is unstable.
2
Diazotisation: react phenylamine with HNO2 in dilute HCl below 10 °C to form the benzenediazonium ion; C6H5NH2 + HNO2 + H+ → C6H5N2+ + 2H2O.
3
Keep it in ice, because above 10 °C the diazonium ion decomposes to phenol and N2.
4
Coupling: add the diazonium solution to phenol dissolved in NaOH; the diazonium ion is an electrophile that substitutes at the 4-position of phenol.
5
A coloured azo dye (yellow or orange precipitate) forms.
  • The -N=N- group links the two rings, extending the delocalised system, which gives colour and stability.

Part 6 of 9Amides

Amides
Amides form by condensation of an acyl chloride with ammonia or an amine, with loss of HCl.
The acyl chlorine draws electron density from the carbonyl carbon, which the nitrogen lone pair attacks as a nucleophile.
  • Ammonia gives an unsubstituted amide; primary and secondary amines give substituted amides.
  • The HCl is neutralised by excess base: CH3CH2COCl + 2NH3 → CH3CH2CONH2 + NH4Cl.
Amides are almost neutral because the nitrogen lone pair is delocalised towards the electronegative C=O group.

Part 7 of 9Condensation polymers and polyamides

1Condensation polymerisation
  • Condensation polymerisation monomers with two functional groups join by repeated condensation reactions, losing a small molecule (H2O or HCl) at each link.
2
Condensation polymers have ester or amide links and can be hydrolysed at the links, unlike addition polymers; they can be made from diacids and diols, diacids and diamines,
  • or amino acids.
3Polyamide
  • Polyamide repeat units joined by amide (peptide) links, -CONH-.
  • A diamine reacts with a dicarboxylic acid, or with a more reactive but costlier dioyl dichloride.
  • Nylon 6,6 is made from hexane-1,6-diamine and hexanedioic acid;
    • the 6,6 refers to six carbons in each monomer.
  • Kevlar is made from benzene-1,4-diamine and benzene-1,4-dicarboxylic acid (or benzene-1,4-dioyl chloride).
4
Properties
  • Kevlar chains are rigid, neatly arranged and strongly hydrogen bonded, so it is strong, flexible and fire resistant, used in bullet-proof vests.
  • Polyamides are tough with good thermal and chemical resistance and make strong fibres; they absorb moisture,
    • which raises flexibility but lowers stiffness.
  • Polyamide film is used in food packaging and boil-in-the-bag foods.
5
Proteins are polymers of amino acids; polyamides are hydrolysed by hot acid or alkali.
6
To deduce monomers from a condensation polymer, break the ester or amide links and add back H and OH (or Cl).

Part 8 of 9Poly(ethenol)

1
Poly(ethenol) (poly(vinyl alcohol)) is an addition polymer with repeat unit -[CH2-CH(OH)]-.
2
It is made in two stages, not directly.
  • Polymerise ethenyl ethanoate.
  • Poly(ethenyl ethanoate) reacts with methanol in ester exchange to give poly(ethenol) and methyl ethanoate;
    • the temperature controls the amount of exchange.
3
Its many OH groups hydrogen bond with water,
  • so it is water soluble;
    • solubility depends on how many ester groups are replaced and ranges from insoluble through soluble in hot water to soluble in cold.
4
Uses: dissolving hospital laundry bags and liquid-detergent capsules.

Part 9 of 9Amino acids: zwitterions and isoelectric point

Amino acids react like amines and carboxylic acids, but can interact within themselves to form a zwitterion with -NH3+ and -COO−.
Zwitterion
  • Zwitterion an ion with both a positive and a negative charge but no overall charge.
  • Strong ionic attractions give high melting points and make amino acids soluble crystalline solids.
  • They dissolve in water but not in non-polar solvents.
In water they act as buffers.
  • Adding acid-COO− accepts H+, giving a cation.
  • Adding base-NH3+ donates H+, giving an anion.
Isoelectric point
  • Isoelectric point the pH at which the amino acid exists as the neutral zwitterion.

Key terms

TermMeaning
AmineAn organic compound derived from ammonia in which hydrogens are replaced by alkyl or aryl groups.
AmideA compound containing the -CONH2 or substituted -CONR2 group.
Amino acidA molecule containing both an amine and a carboxylic acid group.
ZwitterionAn ion carrying both a positive and a negative charge with zero overall charge.
Isoelectric pointThe pH at which an amino acid exists as the neutral zwitterion.
Condensation polymerisationJoining monomers with the loss of a small molecule at each link.
Diazonium saltAn ion containing -N2+, formed from phenylamine and nitrous acid below 10 °C.
Peptide linkThe amide link -CONH- between amino acids.

Avoid these mistakes

1
Classifying amines by the carbon, as for alcohols — amines are classified by the number of groups on nitrogen.
2
Saying phenylamine is a stronger base than ammonia — its lone pair is delocalised into the ring.
3
Using one mole of ammonia with an acyl chloride — a second mole neutralises the HCl.
4
Letting the diazonium solution warm above 10 °C — it decomposes to phenol and nitrogen.
5
Saying amino acids are neutral molecules in solid form — they exist as zwitterions.

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