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Chemistry revision > Carboxylic Acids and Derivatives > Flashcards

Carboxylic Acids and Derivatives Flashcards

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1
Q

What is a carboxylic acid?

Functional group?

A

-COOH (C=O and C-OH)

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2
Q

How do you name carboxylic acids?

A

-oic acid

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3
Q

Are carboxylic acids soluble in water? Why? What

influences their solubility

A

Yes. Acid group can form hydrogen bonds with water molecules

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4
Q

What are the intermolecular forces in carboxylic acids?

A

Hydrogen bonds in solid state - very strong.

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5
Q

What are esters (what are they formed from)?

Functional group, general formula?

A

Formed from carboxylic acids and alcohols.

RCOOR’ (C=O, C-O-C)

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6
Q

Write an equation for the reaction of ethanoic acid

with propan-1-ol

A

CH3COOH + CH3CH2CH2OH → CH3COOCH2CH2CH3 + H2O

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7
Q

How do you name esters?

A

Start with the group that has replaced the hydrogen, then acid part e.g. propyl (from
alcohol) ethanoate (from carboxylic acid).

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8
Q

What characteristic physical properties do esters have?

A

Volatile, pleasant fruity smells e.g. apple, pear drops

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9
Q

What are some uses of esters?

A

Flavourings, perfumes (both for longer chains), solvents (short chains), plasticisers.

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10
Q

What are some common natural esters?

A

Fats and oils

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11
Q

Write an equation for the equilibrium formed by a

ethanoic acid in solution

A

CH3COOH (aq) ⇌ CH3COO- (aq) + H+ (aq)

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12
Q

What happens to the negative charge on the

ethanoate ion in terms of electrons?

A

Electrons delocalise so the negative charge is shared across the whole of the carboxylate group

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13
Q

How could you distinguish carboxylic acids from other -OH containing compounds?

A

Add NaHCO3, acids will produce sodium salt, water and carbon dioxide.

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14
Q

Write an equation for the reaction of ethanoic acid

with NaOH

A

CH3COOH + NaOH → H2O + CH3COO-Na+

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15
Q

Write an equation for the reaction of ethanoic acid

with Na2CO3.

A

2CH3COOH + Na2CO3 → 2CH3COO-Na+ + H2O + CO2

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16
Q

What catalyst is needed for the formation of esters from alcohols and carboxylic acids?

A

Concentrated strong acid e.g. H2SO4

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17
Q

What catalyst is needed for the hydrolysis of esters?

A

Dilute strong acid e.g. H2SO4

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18
Q

What is an alternative method of hydrolysis?

A

Base hydrolysis

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19
Q

What are the advantages of base hydrolysis?

A

Reaction goes to completion due to neutralisation by base - more product in the mixture than acid catalysed hydrolysis.

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20
Q

Which alcohol forms the esters that make up animal

and vegetable oils?

A

Glycerol / propane-1,2,3-triol

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21
Q

What is the difference between oil and fat?

A
  • Oils are liquid at room temperature, fats are solids

- fats are usually saturated, oils are not

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22
Q

What are the products of hydrolysing fats and oils?

A

Propane-1,2,3-triol and sodium salts of the acids

that make up the ester (hydrolysed with NaOH)

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23
Q

What are the uses of these products (Propane-1,2,3-triol and sodium salts)?

A

Soaps and cleaning products

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24
Q

What does the long hydrocarbon chain of the

carboxylate ion do?

A

Mixes with grease

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25
Q

What does the COO- group do?

A

Mixes with water

26
Q

How does the carboxylate ion with a long carbon chain make a good cleaning agent?

A

Means that grease can be removed from water

27
Q

What is the IUPAC name of glycerol?

A

propane-1,2,3-triol

28
Q

What are some common uses of glycerol?

A
  • Used in pharmaceutical and cosmetic preparations e.g. to
    stop creams drying out
  • Solvent in many medicines, present in toothpaste
  • Solvent in food industry e.g. food colourings
  • Plasticising various materials like sheets and gaskets, cellophane and paper
29
Q

How do you make biodiesel (general equation and

conditions)?

A

NaOH catalyst, 60oC

Lipids (fats/oils - esters) + 3CH3OH → 3 methyl esters + glycerol

30
Q

What does transesterification mean?

A

Converting one type of ester to another

31
Q

What kind of crops is biodiesel made from?

A

Rapeseed oil or soybean oil

32
Q

How is the reaction mixture of biodiesel purified and

separated?

A

Settling tank or centrifuge; remove remainder with water.
Add acid to neutralise excess alkali catalyst.
Solid soap is formed - easy to remove

33
Q

What is a problem with producing biodiesel?

A

Crops that could be used to make food are being used to make fuel - are the resources being best used?

34
Q

What are carboxylic acid derivatives?

A

Molecules that have the acyl group as part of their structure, formed from carboxylic acids

35
Q

Name two acid derivatives and give their functional

groups

A

Acyl chlorides: RCOCl

Acid anhydrides: RCOOCR / (RCO)2O

36
Q

Which factors determine how readily the acylation of a nucleophile by an acid derivative occurs? (3)

A
  • Magnitude of the delta + charge on the carbonyl carbon, which depends on the electronegativity of the atom/group being substituted.
  • How easily the atom/group being substituted is lost
  • How readily the nucleophile donates its electrons
37
Q

What effect do the Cl and O atoms in acyl chlorides/acid anhydrides have on the partial charge of the carbonyl carbon?

A

Increase the partial + charge by attracting electrons; this means that they react more readily with nucleophiles

38
Q

Are acyl chlorides or acid anhydrides more reactive?

A

Acyl chlorides

39
Q

What is the name of the mechanism by which acyl

chlorides and acid anhydrides acylate nucleophiles?

A

Addition-elimination

40
Q

If the nucleophile is ammonia for the acylation of acyl chlorides or acid anhydrides, what are the products of the reaction?

A

An amide

41
Q

Write an equation for the reaction of ethanoyl chloride and ammonia

A

CH3COCl + 2NH3 → CH3CONH2 + NH4Cl

42
Q

If the nucleophile is a primary amine, what are the

products of the acylation of acyl chlorides or acid anhydrides?

A

N-substituted amide

43
Q

Write an equation for the reaction of ethanoyl chloride and methylamine

A

CH3COCl + CH3NH2 → CH3CONHCH3 + CH3NH3Cl

44
Q

If the nucleophile is an alcohol, what are the products of the acylation of acyl chlorides or acid
anhydrides?

A

An ester

45
Q

Write an equation for the reaction of ethanoyl chloride and ethanol

A

CH3COCl + CH3CH2OH → CH3COOCH2CH3 + HCl

46
Q

If the nucleophile is water, what are the products of the acylation of acyl chlorides or acid anhydrides?

A

Carboxylic acid (hydrolyses ester linkage)

47
Q

What is the name of this reaction (the acylation of
acyl chlorides/acid anhydrides with water as a
nucleophile)?

A

hydrolysis

48
Q

Write an equation for the reaction of ethanoyl chloride and water.

A

CH3COCl + H2O → CH3COOH + HCl

49
Q

What is a commercially important acylation reaction?

A

The manufacture of aspirin

50
Q

What are the advantages of using ethanoic anhydride as an acylating agent over ethanoyl chloride?

A

It is cheaper, less corrosive and does not react as readily with water.
It is safer, as ethanoic acid is produced, rather than HCl, which is corrosive.

51
Q

What would you observe in a melting point determination if the sample was not pure?

A

Sample melts over a large range (more than 3oC).

Sample’s melting point is below the accepted value due to impurities disrupting structure

52
Q

Why might the melting point appear different to the true value?

A

Temperature of the material in the machine might be different to the temperature shown on the thermometer - apparatus error.

53
Q

When removing flue gases, what are the issues?

A

Disposal of large amounts of CaSO3 and CO2 is produced.

54
Q

What conditions are needed to form methyl esters from an acid anhydride or acyl chloride?

A

React with methanol and heat gently under reflux

55
Q

When purifying by recrystallisation, why is the

minimum volume of hot solvent used?

A

So that a saturated solution is created, so that as many crystals will fall out of solution as possible
when it is cooled

56
Q

Why is the solution filtered hot when purifying by

recrystallisation?

A

To remove insoluble impurities and ensure that

the crystals do not form in the filter paper

57
Q

Why is the solution cooled in an ice bath when

purifying by recrystallisation?

A

To ensure that as many crystals as possible fall out of solution - yield is higher

58
Q

Why are the crystals washed with cold water when purifying by recrystallisation?

A

To remove soluble impurities

59
Q

How would you separate the crystals from the reaction mixture when purifying by recrystallisation?

A

Filter under reduced pressure using a Buchner

funnel

60
Q

Why might percentage yield be below 100% (practical reasons)?

A
  • Product is lost during filtration, drying and weighing - spills, not all transferred from one piece of apparatus to the other
  • Product is left dissolved in the solution - some does not crystallise.
  • Some left on filter paper. Sample still wet

Chemistry revision (46 decks)

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