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Chemistry > Carboxylic Acids and Derivatives > Flashcards

Carboxylic Acids and Derivatives Flashcards

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

In what way is the carboxylic acid group polarised? (Diagram)

A

check

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12
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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13
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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14
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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15
Q

Write an equation for the reaction of ethanoic acid with NaOH

A

CH3COOH + NaOH → H2O + CH3COO-Na+

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16
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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17
Q

What is an alternative method of hydrolysis?

A

Base hydrolysis

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18
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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19
Q

Which alcohol forms the esters that make up animal and vegetable oils?

A

Glycerol / propane-1,2,3-triol

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20
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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21
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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22
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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23
Q

What does the long hydrocarbon chain of the carboxylate ion do?

A

Mixes with grease

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24
Q

What does the COO- group do?

A

Mixes with water

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25
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

26
Q

What is the systematic name of glycerol?

A

propane-1,2,3-triol

27
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

28
Q

How do you make biodiesel (general equation and conditions)?

A

NaOH catalyst, 60oC
Lipids (fats/oils - esters) + 3CH3OH → 3 methyl esters + glycerol

29
Q

What does transesterification mean?

A

Converting one type of ester to another

30
Q

What kind of crops is biodiesel made from?

A

Rapeseed oil or soybean oil

31
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

32
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?

33
Q

What are carboxylic acid derivatives?

A

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

34
Q

Name two acid derivatives and give their functional groups

A

Acyl chlorides: RCOCl
Acid anhydrides: RCOOCR / (RCO)2O

35
Q

Draw the mechanism for the acylation of a nucleophile by an acid derivative.

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 good the nucleophile is (how readily it will donate 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?

41
Q

Write an equation for the reaction of ethanoyl chloride and ammonia

A

CH3COCl + 2NH3 → CH3CONH2 + NH4Cl

42
Q

Draw the mechanism for the reaction of ethanoyl chloride and ammonia

43
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

44
Q

Write an equation for the reaction of ethanoyl chloride and methylamine

A

CH3COCl + CH3NH2 → CH3CONHCH3 + CH3NH3Cl

45
Q

Draw the mechanism for the reaction of ethanoyl chloride and methylamine.

46
Q

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

47
Q

Write an equation for the reaction of ethanoyl chloride and ethanol

A

CH3COCl + CH3CH2OH → CH3COOCH2CH3 + HCl

48
Q

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

A

hydrolysis

49
Q

Draw the mechanism for the reaction of ethanoyl chloride and ethanol

50
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)

51
Q

What is a commercially important acylation reaction?

A

The manufacture of aspirin

51
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.

52
Q

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

A

CH3COCl + H2O → CH3COOH + HCl

52
Q

Draw the mechanism for the reaction of ethanoyl chloride and water.

53
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

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

54
Q

When removing flue gases, what are the issues?

A

Disposal of large amounts of CaSO3 and CO2 is produced.

55
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

56
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

57
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

58
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

59
Q

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

A

To remove soluble impurities

60
Q

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

A

Filter under reduced pressure using a Buchner funnel

61
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 (30 decks)

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