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Chemistry A Level CIE > Chapter 15 Nitrogen compounds > Flashcards

Chapter 15 Nitrogen compounds Flashcards

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1
Q

Primary and secondary amines can be prepared from different reactions including:

A
  • The reaction of halogenoalkanes with ammonia
  • The reaction of halogenoalkanes with primary amines
  • The reduction of amides
  • The reduction of nitriles
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2
Q

Primary and secondary amines

A
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3
Q

Reaction of halogenoalkanes with ammonia

A
  • This is a nucleophilic substitution reaction in which the nitrogen lone pair in ammonia acts as a nucleophile and replaces the halogen in the halogenoalkane
  • When a halogenoalkane is reacted with excess, hot ethanolic ammonia under pressure a primary amine is formed
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4
Q

Reaction of halogenoalkanes with primary amine

A
  • This is also a nucleophilic substitution reaction in which the nitrogen in the primary amine acts as a nucleophile and replaces the halogen in the halogenoalkane
  • When a halogenoalkane is reacted with a primary amine in ethanol and heated in a sealed tube, under pressure a secondary amine is formed
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5
Q

Reduction of amides

A
  • Amines can also be formed from the reduction of amides by LiAlH4 in dry ether
  • Whether a primary or secondary amine is formed depends on the nature of the amide
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6
Q

Reduction of nitriles

A
  • Nitriles contain a -CN functional group which can be reduced to an -NH2 group
  • The nitrile vapour and hydrogen gas are passed over a nickel catalyst or LiAlH4 in dry ether can be used to form a primary amine
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7
Q

Production of Amides

A
  • Amides are organic compounds with an -CONR2 functional group
  • They can be prepared from the condensation reaction between an acyl chloride and ammonia or amine
  • In a condensation reaction, two organic molecules join together and in the process eliminate a small molecule
  • In this case, the acyl chlorides and ammonia or amine join together to form an amide and eliminate an HCl molecule
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8
Q

Condensation reaction

A
  • The chlorine atom in acyl chlorides is electronegative and draws electron density from the carbonyl carbon
  • The carbonyl carbon is therefore electron-deficient and can be attacked by nucleophiles
  • The nitrogen atom in ammonia and amines has a lone pair of electrons which can act as a nucleophile and attack the carbonyl carbon
  • As a result, the C-Cl bond is broken and an amide is formed
  • Whether the product is a substituted amide or not, depends on the nature of the nucleophile
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9
Q
  • Whether the product is a substituted amide or not, depends on the nature of the nucleophile (condensation reaction)
A
  • Primary and secondary amines will give a substituted amide
  • The reaction of acyl chlorides with ammonia will produce a non-substituted amide
  • Note that amides can also be formed from the condensation reaction between carboxylic acids and ammonia or amines
  • However, this reaction is slower as carboxylic acids are less reactive than acyl chlorides and the reaction doesn’t go to completion
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10
Q

Acyl chlorides undergo condensation reactions with ammonia and amines to form amides

A
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11
Q

The nitrogen atom in ammonia and amines can donate its lone pair of electrons to form a bond with a proton and therefore act as a base

A
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12
Q

Basicity of Aqueous Solutions of Amines

A
  • The nitrogen atom in ammonia and amine molecules can accept a proton (H+ ion)
  • They can therefore act as bases in aqueous solutions by donating its lone pair of electrons to a proton and form a dative bond
    • For example, ammonia undergoes an acid-base reaction with dilute hydrochloric acid (HCl) to form a salt

NH3 + HCl → NH4+Cl-

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13
Q

Strength of ammonia and amines as bases

A
  • The strength of amines depends on the availability of the lone pair of electrons on the nitrogen atom to form a dative covalent bond with a proton
  • The more readily this lone pair of electrons is available, the stronger the base is
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14
Q

Factors that may affect the basicity of amines include:

A
    • Positive inductive effect - Some groups such as alkyl groups donate electron density to the nitrogen atom causing the lone pair of electrons to become more available and therefore increasing the amine’s basicity
      • Delocalisation - The presence of aromatic rings such as the benzene ring causes the lone pair of electrons on the nitrogen atom to be delocalised into the benzene ring
      • The lone pair becomes less available to form a dative covalent bond with ammonia and hence decreases the amine’s basicity
  • For example, ethylamine (which has an electron-donating ethyl group) is more basic than phenylamine (which has an electron-withdrawing benzene ring)
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15
Q

Phenylamine is an

A

organic compound consisting of a benzene ring and an amine (NH2) functional group

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16
Q

Phenylamine can be produced in a three-step synthesis reaction followed by the separation of phenylamine from the reaction mixture

A
  • Step 1- Benzene undergoes nitration with concentrated nitric acid (HNO3) and concentrated sulfuric acid (H2SO4) at 25 to 60 oC to form nitrobenzene
  • Step 2 - Nitrobenzene is reduced with hot tin (Sn) and concentrated hydrochloric acid (HCl) under reflux to form an acidic mixture that contains the organic product C6H5N+H3
  • Step 3 - Sodium hydroxide (NaOH) is added to the acidic reaction mixture to form phenylamine
  • Step 4 - The phenylamine is separated from the reaction mixture by steam distillation
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17
Q

Reactions of Phenylamine

A
  • Both the benzene ring as well as the -NH2 group in phenylamine can take part in chemical reactions
  • These reactions include
    • The bromination of phenylamine
    • Formation of a diazonium salt
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18
Q

Bromination of phenylamine

A
  • Phenylamines react in electrophilic substitution reactions in a similar way as phenols
  • The lone pair of electrons on the nitrogen atom in phenylamines donate electron density into the benzene ring
    • In phenols, the oxygen atom donates its lone pair of electrons instead
  • The delocalisation of the electrons causes an increased electron density in the benzene ring
  • The benzene ring, therefore, becomes activated and becomes more readily attacked by electrophiles
  • The incoming electrophiles are directed to the 2,4 and 6 positions
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19
Q

Phenylamines, therefore, react under what conditions

A

milder conditions with aqueous bromine at room temperature to form 2,4,6-tribromophenylamine

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20
Q

Formation of diazonium salt

A
  • Diazonium compounds are very reactive compounds containing an -N2+ group
  • The amine (-NH2) group of phenylamines will react with nitric(III) acid (HNO3) at a temperature below 10 °C to form diazonium salts
    • Since nitric(III) acid is unstable, it has to be made in the test-tube by reacting sodium nitrate (NaNO2) and dilute acid (such as HCl)
  • These diazonium salts are so unstable that they will upon further warming with water to form a phenol
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21
Q

Ammonia and amines act as bases

A
  • as they can donate their lone pair of electrons to form a dative covalent bond with a proton
  • The basicity of the amines depends on how readily available their lone pair of electrons is
  • Electron-donating groups (such as alkyl groups) increase the electron density on the nitrogen atom and cause the lone pair of electrons to become more available for dative covalent bonding
    • The amine becomes more basic
  • Delocalisation of the lone pair of electrons into an aromatic ring (such as a benzene ring) causes the lone pair of electrons to become less available for dative covalent bonding
    • The amine becomes less basic
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22
Q

Trends in the basicity of ammonia, ethylamine, and phenylamine

A
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23
Q

Azo (or diazonium) compounds are

A
  • organic compounds that have an R1-N=N-R2 group
  • They are often used as dyes and are formed in a coupling reaction between the diazonium ion and an alkaline solution of phenol
24
Q

Coupling of benzenediazonium chloride with phenol in NaOH

A
  • Azo compounds can be formed from the coupling reaction of a benzenediazonium chloride salt with alkaline phenol
  • Making an azo dye is a multi-step process
25
Q

Formation of azo compounds table

A
26
Q

Reaction mechanism of the formation of azo compounds

A
27
Q

As a result of the delocalisation of electrons throughout the compound, azo compounds are

A

very stable

  • The delocalised electrons in the π bonding systems of the two benzene rings are extended through the -N=N- which acts as a bridge between the two rings
28
Q

Making other azo dyes

A
  • Other dyes can be formed via a similar route as described above
  • For example, the yellow dye can be formed from the coupling reaction between benzenediazonium chloride and C6H5N(CH3)2 instead of phenol (C6H5OH)
29
Q

Amides are formed from the

A
  • condensation reaction of carboxylic acids or acyl chlorides with ammonia or amines
  • The amide group (CONR2) in these compounds can undergo reactions including
    • Hydrolysis with aqueous alkali or aqueous acid
    • Reduction with LiAlH4
30
Q

Hydrolysis of amides

A
  • The -CON- group in substituted amides links two hydrocarbon sections of their molecules together
  • This amide link can be broken down by hydrolysis by refluxing it with an acid or alkali
  • The products of a non-substituted amide are:
    • Carboxylic acid
    • Ammonia
  • The products of a substituted amide are:
    • Carboxylic acid
    • Primary amine
  • Ammonia will react in excess acid to form an ammonium salt
  • Carboxylic acid will get deprotonated in excess base to form a carboxylate ion
31
Q

Hydrolysis of substituted and non-substituted amides (diagram)

A
32
Q

Amides are hydrolysed to carboxylic acids and ammonia or primary amine when refluxed with acid or alkali

A
33
Q

Reduction of amides

A
  • The C=O group in amides can be reduced by the strong reducing agent LiAlH4 to form an amine
  • The products of a non-substituted amide are:
    • A primary amine and water
  • The products of a substituted amide are:
    • A secondary amine and water
34
Q

A base is a species that can

A

donate its lone pair of electrons to form a dative covalent bond with another species

35
Q

Amines are acidic or basic

A

basic as the nitrogen atom has a lone pair of electrons which can form a dative covalent bond with an

electron-deficient species (such as an H+ ion)

36
Q

The basicity of the amine depends on the availability of this lone pair of electrons

A
  • The more readily available the lone pair of electrons is for dative covalent bonding, the stronger the base
  • The less readily available the lone pair of electrons is, the weaker the base
  • Electron-donating groups such as alkyl groups increase the electron density on the nitrogen atom causing the lone pair to become more available
  • Electron-withdrawing groups such as aromatic benzene rings, cause delocalisation of the lone pair of electrons which become less readily available
37
Q

Basicity of amides

A
  • Amides also contain a nitrogen atom with a lone pair of electrons
  • Again, the basicity of the amide depends on the availability of this lone pair for dative covalent bonding
  • Due to the presence of the electron-withdrawing oxygen atom in the amide group, electron density is removed from the nitrogen atom
  • The lone pair on the nitrogen atom, therefore, becomes less readily available and is not available to donate to an electron-deficient species
  • Since this electron-withdrawing oxygen is characteristic of amides and is not present in amines, amides are much weaker bases than amines
38
Q

Amino acids are

A

are organic compounds that contain two functional groups:

  • A basic amino (-NH2) group
  • An acidic carboxylic acid (-COOH) group
39
Q

Due to the presence of both a basic and acidic group in amino acids

A

they are said to be amphoteric

  • They can act as both acids and bases
40
Q

Naturally occurring amino acids

A
  • 2-aminocarboxylic acids are a type of amino acids in which the amine (-NH2) group is bonded to the carbon atom next to the -COOH group
  • These type of amino acids form the ‘building blocks’ that make up proteins
  • There are 20 naturally occurring amino acids with the general structural formula of RCH(NH2)COOH
41
Q

General structural formula of amino acids

A
42
Q

The R group varies in different amino acids and can be:

A
  • Acidic
  • Basic
  • Neutral
43
Q

Acid / base properties of amino acids

A
  • Amino acids will undergo most reactions of amines and carboxylic acids including acid-base reactions of:
    • Amines with acids
    • Carboxylic acids with bases
  • However, they can also interact intramolecularly (within themselves) to form a zwitterion
44
Q

A zwitterion is an ion

A
  • with both a positive (-NH3+) and a negative (-COO-) charge
  • Because of these charges in a zwitterion, there are strong intermolecular forces of attraction between amino acids
    • Amino acids are therefore soluble crystalline solids
45
Q

Isoelectric point

A
  • A solution of amino acids in water will exist as zwitterions with both acidic and basic properties
  • They act as buffer solutions as they resist any changes in pH when small amounts of acids or alkali are added
46
Q

Isoelectric point, If an acid is added (and thus the pH is lowered):

A
  • The -COO- part of the zwitterion will accept an H+ ion to reform the -COOH group
  • This causes the zwitterion to become a positively charged ion
47
Q

Isoelectric point, If a base is added (and thus the pH is raised):

A
  • The -NH3+ part of the zwitterion will donate an H+ ion to reform the -NH2 group
  • This causes the zwitterion to become a negatively charged ion
48
Q

A solution of amino acids can act as a buffer solution by resisting any small changes in pH

A
49
Q

the isoelectric point of the amino acid

A

The pH can be slightly adjusted to reach a point at which neither the negatively charged or positively charged ions dominate and the amino acid exists as a neutral zwitterion

50
Q

Formation of Peptide Bonds

A
  • Each amino acid contains an amine (-NH2) and carboxylic acid (-COOH) group
  • The -NH2 group of one amino acid can react with the -COOH group of another amino acid in a condensation reaction to form a dipeptide
    • The new amide bond between two amino acids is also called a peptide link or peptide bond
51
Q

Formation of Peptide Bonds happens with what reaction

A
  • is a condensation reaction, a small molecule (in this case H2O) is eliminated
  • The dipeptide still contains an -NH2 and -COOH group at each end of the molecule which can again participate in a condensation reaction to form a tripeptide
52
Q

A polypeptide is formed when

A

many amino acids join together to form a long chain of molecules

53
Q

Electrophoresis is an

A

analytical technique which separates ions by placing them in an electrical field

  • This method is often used in biochemical analysis to identify and purify proteins
54
Q

Electrophoresis of A sample of amino acids

A
  • they placed between two oppositely charged electrodes
    • The positively charged ions will move towards the negative electrode
    • The negatively charged ions will move towards the positive electrode
55
Q

The rate (how fast) at which the ions move towards the electrodes depends on:

A
  • The size of the ions: larger ions move more slowly
  • The charge of the ions: highly charged ions move more quickly
56
Q

An electropherogram is the series of

A

bands which are observed on the paper or gel after electrophoresis has occurred

  • Each band in the electropherogram corresponds to a particular species
57
Q

Separating mixtures of amino acids by varying the pH

A
  • The charge on the amino acid ions depends on the pH of the solution
  • The movement of the ions to the electrodes during electrophoresis will therefore be affected by the pH

Chemistry A Level CIE (18 decks)

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