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A2 Chemistry (Unit 1: F234) > Amines and polymers > Flashcards

Amines and polymers Flashcards

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1
Q

What is a primary amine?

A

An amine in which the nitrogen atom is attached to one carbon chain.

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2
Q

How do we name primary amines?

A
  • Identify name of carbon chain attached to amine group. Name is constructed in the form [Name of carbon chain]amine. E.g. CH3CH2NH2: Ethylamine.
  • Ignore the amine group and pretend it is an H atom. Name the compound with omitted amine group. Identify the number of the carbon atom attached to amine group. Name is constructed in the form [Carbon number attached to amine group]-amino[Name of compound without amine group]. E.g. CH3CH(NH2)CH3: 2-aminopropane.
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3
Q

What is a secondary amine?

A

An amine in which the nitrogen atom is attached to two carbon chains.

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4
Q

How do we name secondary amines?

A
  1. Identify the longest (alkyl) chain attached to the amine group.
  2. Identify the shortest (alkyl) chain attached to the amine group. Add “N-“ as a prefix the the name.
  3. Construct the name in the form N-[Name of shortest carbon chain] [Name of longest carbon chain]amine. E.g. CH3CH2NHCH3: N-methyl ethylamine.
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5
Q

What is a tertiary amine?

A

An amine in which the nitrogen atom is attached to 3 carbon chains.

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6
Q

Why are amines basic?

A
  • Amines are weak bases, just as ammonia.
  • Amines have a lone pair of electrons on the N atom in amine group which are able to accept protons by forming dative covalent bonds with them, making them proton acceptors and thus bases.
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7
Q

What is the general fromula for the reaction of an amine with an acid?

A

Amine +Acid → Amine salt

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8
Q

How do we name amine salts?

A
  1. Take the name of the amine with -amine suffix (e.g. ethylamine). Replace -amine suffix with -ammonium suffix to form name of cation.
  2. Identify the name of the anion.
  3. Construct the name in the form [Name of cation] [Name of anion].
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9
Q

What are aliphatic amines?

A

Amine in which the nitrogen atoms are attached to straight carbon chains only.

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10
Q

What are aromatic amines?

A

Amines in which the nitrogen atoms are attached directly to benzene rings.

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11
Q

How are primary aliphatic amines prepared?

A

Warming a halogenoalkane with the desired alkyl chain with an excess of ammonia in ethanol solvent.

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12
Q

What type of reaction occurs during preparation of aliphatic amines?

A

Nucleophilic substitution.

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13
Q

Why is an an excess of ammonia required for the reaction?

A

To ensure that there are enough ammonia molecules to react with all halogenoalkane molecules in nucleophilic substitution reaction, else the amine groups on the primary amines formed undergo further substitution reactions with to form secondary and eventually tertiary amines.

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14
Q

What is the general formula for the preparation of primary aliphatic amines?

A

Halogenoalkane + Ammonia → Amine + Hydrogen halide

E.g. Chloroethane + Ammonia → Ethyamine + Hydrogen chloride (CH3CH2Cl + NH3 → Ch3CH2NH2 + HCl)

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15
Q

How are aromatic amines prepared?

A

Nitrobenzene and other nitroarenes can be reduced to phenylamines. They are heated with a mixture of tin and concentrated HCl under reflux (both make up reducing agent). The excess HCl in the mixture is then neutralised.

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16
Q

What is the equation for the reduction of nitrobenzene?

A

Nitrobenzene + 6[H] → Phenylamine + 2H2O

(C6H5)NO2 + 6[H] → (C6H5)NH2 + 2H2O

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17
Q

What are amino acids?

A

Basic chemical building blocks to polypeptides and proteins, which make up a majority of chemicals found in the body and have many uses; including structural functions such as collagen, or physiological functions such as haemoglobin. There are 20 naturally occuring amino acids (α-amino acids) which are arranged in specific sequences to form polymers called polypeptides that form proteins, these sequences are determined by the DNA found in or body.

18
Q

What is the structure of an α-amino acid?

A

A central carbon atom is attached to an amine (-NH2) group, a carboxyl (-COOH) group, a hydrogen atom and a residual (-R) group which can be a variety of structures (usually a carbon chain, except for glycine, which is simple an H).

The general formula for an α-amino acid is:

RCH(NH2)COOH

19
Q

What is a zwitterion?

A

A dipolar ionic form of an amino acid that is formed by the donation of a hydrogen ion from the carboxyl group to the amino group. Because both charges are present, there is no overall charge.

20
Q

How are zwitterion formed?

A

Effectively, because the amine group is basic (proton acceptor) and the carboxyl group is acidic (proton donor) on an amino acid, a proton is transferred from the carboxyl group of an amino acid onto its amine group (if allowed, i.e. in aqueous form). This results in a +ve charge being formed on the amine group and a -ve charge being formed on the carboxyl group that cancel out to give a neutral charge.

21
Q

What is the isoelectric point?

A

The pH value at which the amino acid exists as a zwitterion.

22
Q

What is the significance of the isoelectric point?

A

There is no net electrical charge at the isoelectric point, this means that zwitterions of an amino acid exist at this pH. Each amino acid has a different isoelectric point due to the influence of different -R groups.

23
Q

Why are amino acids described as amphoteric?

A

They can take part in both acid and base reactions.

24
Q

How can amino acids act as acids?

A

When put into an environment with pH greater than that of its isoelectric point, an amino acid acts as an acid. The +ve amine (-NH3+) group on the zwitterion donates protons to the base in solution and reacts to form a negatively charged ion.

E.g. RCH(NH3+)COO- + OH- → RCH(NH2)COO- + H2O

25
Q

How can amino acids act as bases?

A

When put into an environment with pH lesser than that of its isoelectric point, an amino acid acts as a base. the -ve carboxyl (-COO-) group on the zwitterion accepts protons from the acid in solution and reacts to form a positively charged ion.

RCH(NH3+)COO- + H+ → RCh(NH3+)COOH

26
Q

What is a condensation reaction?

A

A reaaction in which two small molecules react together to form a larger molecule with the elimination of a small molecule such as water.

27
Q

How are polypeptides formed?

A

When the amine group on one amino acid reacts with the carboxyl group on another in a condensation reaction (omitting a molecule of water), a peptide (amide) bond is formed which joins together the two amino acids to form a dipeptide. This process may repeat as more amino acids are added onto the ends of the growing peptide by condensation reactions, omitting a water molecule per new amino acid joined. This growing chain of amino acids is called a polypeptide and will form the basis of proteins.

28
Q

What is the formula for the formation of a peptide bond?

A

H2N-CH(R)-COOH + H2N-CH(R’)-COOH →

H2N-CH(R)-CO-NH-CH(R’)-COOH + H2O

Note how the -NH2 on R amino acid could react with -COOH on R’ amino acid to produce a structural isomer.

29
Q

What is hydrolysis?

A

The breaking of bond by reaction with water. Hydrolysis can be catalysed by acid or alkali.

30
Q

What is the process of acid hydrolysis of a polypeptide?

A

Conditions: Heat under reflux in a solution of concentrated aqueous HCl.

Reactants: Polypeptide, H2O, H+

Products: The amine salt form of the amino acid.

Equation (Dipeptide equation shown, applies to polypeptides):

H2N-CH(R)-CO-NH-CH(R’)-COOH + H2O + 2H+ →

H3N+-CH(R)-COOH + H3N+-CH(R’)-COOH

31
Q

What is the process of alkaline hydrolysis of polypeptides?

A

Conditions: Heat under reflux in a solution of aqueous NaOH.

Reactants: Polypeptide, OH-.

Products: Carboxyl salt form of the amino acid.

Equation (Dipeptide equation shown, applies to polypeptides):

H2N-CH(R)-CO-NH-CH(R’)-COOH + 2OH- →

H2N-CH(R)-COO- + H2N-CH(R’)-COO- + H2O

32
Q

What other types of condensation polymers are there (besides polypeptides)?

A
  • Polyesters.
  • Polyamides.
33
Q

What is required for the formation of a condensation polymer?

A
  • One type of monomer with two different types of functional groups that are able to react and bond to each other.
  • Two types of monomers with different functional groups, but with two identical functional groups in each molecule; that are able to react to and bond to each other.
34
Q

How are polyesters formed?

A

Reactants: One type of monomer if monomer is a hydroxycarboxylic acid. Two types of monomers; one being a dicarboxylic acid, the other a dialcohol.

Products: Polyester, H2O.

Equation (hydroxycarboxylic acid):

n HO-R-COOH → -[-O-R-CO-]-n + n H2O

Equation (dialcohol + dicarboxylic acid):

n HO-R-OH + n HOOC-R’-COOH →

-[-O-R-O-OC-R’-CO-]-n + 2n H2O

Ester bonds form between the hydroxyl (-OH) and carboxyl (-COOH) groups on the monomers, joining them together to form a polymer.

35
Q

What are examples and uses of polyesters?

A
  • Terylene is a polyester formed by the condensation polymerisation of ethane-1,2-diol and benzene-1,4-dicarboxylic acid. It is often blended with cotton and used to make clothing and bedding.
  • Poly(lactic acid) is a polyester formed by the condensation polymerisation of lactic acid (2-hydroxypropanoic acid). It is used to make biodegradable plastics in bags and disposable cutlery.
36
Q

How are polyamides formed?

A

Reactants: One type of monomer if monomer is an amino acid. Two types of monomers; one being a dicarboxylic acid, the other a diamine.

Products: Polyamide, H2O.

Equation (diamine + dicarboxylic acid):

n H2N-R-NH2 + n HOOC-R’-COOH →

-[-HN-R-NH-OC-R’-CO-]-n + 2n H2O

Amide bonds form between the amine (-NH2) and carboxyl (-COOH) groups on the monomers, joining them together to form a polymer.

37
Q

What are examples and uses of polyamides?

A
  • Nylon-6,6 is a polyamide formed from the condensation polymerisation of 1,6-diaminohexane and hexane-1,4-dioic acid. It is commonly used in clothing as well as for rope making due to its great strength and lightness.
  • Kevlar is a polyamide formed from the condensation polymerisation of benzene-1,4-diamine and benzene-1,4-dioic acid. It is used mostly for protective clothing and bulletproof vests due to its lightness and strength.
38
Q

What is the process of acid hydrolysis of polyesters?

A

Conditions: Heated under reflux in aqueous HCl (catalyst).

Reactants: Polyester, H2O.

Products: Hydroxycarboxylic acid/ dialcohol + dicarboxylic acid.

Equations:

  • [-O-R-CO-]-n + n H2O → n HO-R-COOH
  • [-O-R-O-OC-R’-CO-]-n + 2n H2O →

n HO-R-OH + n HOOC-R’-COOH

39
Q

What is the process of alkaline hydrolysis of polyesters?

A

Conditions: Heated under reflux in aqueous NaOH.

Reactants: Polyester, OH-.

Products: Hydroxycarbonyl salt/ dialcohol + dicarboxylate salt.

Equations:

  • [-O-R-CO-]-n + n OH- → n HO-R-COO-
  • [-O-R-O-OC-R’-CO-]-n + 2n OH- →

n HO-R-OH + n -OOC-R’-COO-

40
Q

What is the process of acid hydrolysis of polyamides?

A

Conditions: Heated under reflux with aqueous HCl.

Reactants: Polyamide/polypeptide, H+, H2O.

Products: Amine salt form of amino acid/ diammonium salt + dicarboxylic acid.

Equation:

-[-HN-R-NH-OC-R’-CO-]-n + 2n H2O + 2n H+ →

n H3N+-R-NH3+ + n HOOC-R’-COOH

41
Q

What is the process of alkaline hydrolysis of polyamides?

A

Conditions: Heated under reflux with aqueous NaOH.

Reactants: Polyamide/polypeptide, OH-.

Products: Carboxylate salt form of amino acid/ diamine + dicarboxylate salt.

Equation:

-[-HN-R-NH-OC-R’-CO-]-n + 2n OH- →

n H2N-R-NH2 + n -OOC-R’-COO-

42
Q

What are the differences between addition polymers and condensation polymers?

A

Functional groups involved

Addition polymerisation: Alkene (C=C).

Condensation polymerisation: Amine (-NH2) and carboxyl (-COOH)/ alcohol (-OH) and carboxyl (-COOH).

Type of reaction

Addition polymerisation: Addition reactions.

Condensation polymerisation: Condensation reactions.

Number of monomers involved

Addition polymerisation: 1

Condensation polymerisation: 1 or 2

Products formed

Addition polymerisation: Poly(alkene).

Condensation polymerisation: (Polyester or polyamide) + H2O.

Type of backbone:

Addition polymerisation: C-C backbone.

Condensation polymerisation: C-C backbone with amide (CO-NH) groups or ester (CO-O) groups at regular intervals between the once monomers.

A2 Chemistry (Unit 1: F234) (5 decks)

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