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A2 Chemistry > Carboxylic acids & derivates > Flashcards

Carboxylic acids & derivates Flashcards

carboxylic acids, esters and acylation

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1
Q

What is an acyl group?

A 
Carbonyl group (C=O) with an alkyl group attached 
- derived from a carboxylic acid
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2
Q

What is acylation?

A
  • introduction of acyl group to another molecule
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3
Q

Why aren’t carboxylic acids used as acylating agents?

A

COOH contain acyl group but OH bonded to acyl group is a very poor leaving group so COOHs not used as acylating agents
- instead 2 carboxylic acid derivatives used

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4
Q

Acylation reaction is used where?

A
  • pharamaceutical (aspirin)

- textile industries (cellulose acetate or rayon)

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5
Q

Why are acid anhydries preffered to Acyl chlorides?

A
  • cheaper to manufacture
  • less reactive acylating reactions safer and easier to control
  • acyl chlorides produce HCl as product of acylation (this is corrosive), but acid anhydrides produce water
  • doesn’t react with water as readily
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6
Q

how to name carboxylic acids

A
  • the ending is -oic acid

- no numbering needed as it’s always at end of the chain COOH

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7
Q

If there are carboxylic acid groups on both ends of the

chain, how do you name it?

A

it is called a - dioic acid
- Ethanedioic acid
(Note the e in this name)

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8
Q

describe the acidity of carboxylic acids

A
  • weak acids in water and only slightly dissociate, but

they are strong enough to displace carbon dioxide from carbonates

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9
Q

describe the solubility in water of carbonates

A
  • the smaller carboxylic acids (up to C4) dissolve in water in all proportions but after this the solubility
    rapidly reduces
  • they dissolve because they can hydrogen bond to
    the water molecules
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10
Q

what do carboxylic acids partially dissociate into?

A
  • a carboxylate ion and H+ ion
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11
Q

carboxylic acids react with carbonates (contain CO3 2- )to form what?

A
  • salt, carbon dioxide and water

carbon dioxide fizzes out of solution

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12
Q

what happens in esterification?

A
  • carboxylic acids react with alcohols, in the
    presence of a strong acid catalyst, to form
    esters and water
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13
Q

equation to show how esters are formed from alcohols

A

Carboxylic Acid + Alcohol (H+) Ester + water

backwards reaction is a hydrolysis reaction, forwards is condensation or esterficiation

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14
Q

functional group of esters

A
  • COO -
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15
Q

naming esters

A
  • first part of esters name = alcohol (after the C=O)
  • second part of esters name = carboxylic acid (before C=O)

e.g. propanol and ethanoic acid
propyl ethanoate

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16
Q

uses of esters

A 
- Esters are sweet smelling
compounds that can be used in
perfumes and flavourings
- Esters can be used as solvents
for polar organic substances
Ethyl ethanoate is used as a
solvent in glues and printing inks
- Esters can be used as
plasticisers for polymers
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17
Q

importance of plasticisers

A
  • pure polymers have limited flexibility because the polymer chains can’t move over each other
  • incorporating some plasticiser into the polymer allows chains to move more easily and polymer can become more flexible
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18
Q

why do carboxlyic acids have higher boiling points than esters ?

A

Although polar, they do not form H bonds (reason: no hydrogen bonded to a highly electronegative atom)

  • so they have much lower b.p. than the hydrogen-bonded carboxylic acids they came from.
  • also almost insoluble in water
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19
Q

why do carboxylic acids have higher boiling points than esters?

A

Although polar, they do not form H bonds (reason: no hydrogen bonded to a highly electronegative atom)

  • so they have much lower b.p. than the hydrogen-bonded carboxylic acids they came from.
  • also almost insoluble in water
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20
Q

conditions of esters if they’re to be used as perfumes?

A
  • non-toxic, soluble in solvent like ethanol, volatile (turns into gas easily), and not react with water
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21
Q

can carboxylic acids be oxidized?

A
  • cannot be oxidized by oxidizing agents

- but methanoic acid can be (because its structure is effectively an aldehyde group)

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22
Q

describe the oxidation of methanoic acid

A
  • can be oxidized because its structure is effectively an aldehyde group
  • forms carbonic acid (H2CO3) which can decompose to give CO2
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23
Q

hydrolysis of esters

A
  • esters can be hydrolyzed and split up by either heating with acid or with sodium hydroxide
  • reaction is the reverse reaction of esterification, when an ester is hydrolyzed a carboxylic acid and an alcohol are formed
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24
Q

product and conditions of acid hydrolysis of esters

A
  • (carboxylic) acid and alcohol
  • reflux with dilute acid (hydrochloric or sulfuric)
    (equilibrium reaction)
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25
Q

product and conditions of base hydrolysis of esters

A
  • carboxylate ion and (COO-) and an alcohol

- reflux with dilute alkali (i.e. NaOH)

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26
Q

why is the base hydrolysis of esters, not a reversible reaction?

A
  • carboxylic acid salt product is anion of the carboxylic acid
  • anion is resistant to attack by weak nucleophiles like alcohols, so reaction not reversible.
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27
Q

fatty acids are long chains of what?

A

carboxylic acids

- they combine with glycerol to make esters

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28
Q

fat and oils relation to esters?

A
  • fats and oils are ESTERS of glycerol and

long-chain carboxylic acids (fatty acids)

29
Q

vegetable oils and animal fats can be hydrolyzed to give what?

A
  • soap, glycerol and long-chain carboxylic (fatty) acids
30
Q

fatty acids can be what?

A
  • saturated (no double bonds) OR

- unsaturated (C=C)

31
Q

IUPAC name of glycerol

A

propane-1,2,3-triol

32
Q

properties of animal fats

A
  • mainly saturated hydrocarbons chains
  • fit neatly together, increasing van der waals forces between them so need higher temps to melt them
  • so solid at room temp
33
Q

properties of vegetable oils

A
  • unsaturated hydrocarbon chains
  • double bonds mean chains are bent and don’t pack together well, decreasing van der Waals forces
  • so easier to melt and liquid at room temp
34
Q

what is soap and how is it made?

A
  • salt of a long-chain carboxylic acid

- hydrolyzes vegetable oils/animal fats by heating them with sodium hydroxide (NaOH)

35
Q

what is biodiesel?

A
  • mixture of methyl esters of fatty acids
36
Q

the equation for formation of methyl esters?

A

triester + methanol —-> (KOH) glycerol + methyl ester

37
Q

catalyst for methyl ester (biodiesel) formation?

A

KOH

potassium hydroxide

38
Q

acyl chloride functional group

A
  • COCl
39
Q

naming acyl chlorides

A
  • no numbering because carbon numbering starts at end with -COCl
  • suffix is: -oyl chloride
40
Q

acyl chlorides react with water to form?

vigorous reaction with cold water

A
  • carboxylic acid + HCl
41
Q

acyl chlorides react with alcohols to form?

vigorous reaction at room temp

A
  • ester and HCl
    reaction is irreversible
    (easier, faster way to produce an ester than esterification)
42
Q

acyl chlorides react with ammonia to form?

violent reaction at room temp

A
  • amide and ammonium chloride

amide (-CONH2)

43
Q

why isn’t HCl really formed in the reaction of an acyl chloride and ammonia?

A

because any hydrogen chloride formed would immediately react with excess ammonia to give ammonium chloride.
NH3 + HCl —> NH4Cl

44
Q

what is given off in reactions of acyl chloride with:

  • water
  • alcohols
  • ammonia (not in excess)
  • primary amines
A

misty fumes of hydrogen chloride

45
Q

products of the reaction of acyl chloride and ammonia (not in excess)

A

amine and HCl

46
Q

products of reaction of acyl chloride with primary amines

A
  • N-substituted amide and HCl (misty fumes)
47
Q

how are acid anhydrides formed and named?

A

2 identical carboxylic acid molecules

  • take away ‘acid’ and replace with ‘anhydride’
    e. g. 2 ethanoic acids would be ethanoic anhydride
48
Q

state products of reactions of water, alcohol, ammonia and primary amines with acid anhydrides

A

(same as acyl chlorides but -COOH instead of HCl)
water: carboxylic acid + carboxylic acid
alcohol: ester + carboxylic acid
ammonia (not in excess) : amide + carboxylic acid
primary amines: N-substituted amide and COOH

49
Q

describe products formed in the reaction between acid anhydride and excess ammonia

A
  • amide (-CONH2) and carboxylic acid (COOH)
  • COOH produced reacts with excess ammonia to give a salt (e.g. ammonium ethanoate formed if acid produced was ethanoic acid)
50
Q

write and draw out ammonium ethanoate

A

CH3COO-NH4+

51
Q

name of mechanism in acyl chloride reactions with water, alcohol, ammonia and primary amines

A

nucleophilic addition-elimination

52
Q

describe the nucleophilic addition-elimination mechanism of an acyl chloride (ethanoyl chloride) and methanol (alcohol)

A

ADDITION:
- methanol is nucleophile
- attacks partially positive carbon (because C=O is polar), and pair of electrons from C=O bond transferred to oxygen (so double bond breaks)
ELIMINATION:
- pair of electrons on oxygen reform double bond and Cl leaves
- Cl bonds with hydrogen in hydroxyl group
- Oxygen in hydroxyl group has positive charge and stabilized by Hydrogen (arrow from bond between oxygen and hydrogen to positive oxygen)
- HCl eliminated

53
Q

what is aspirin and how is it made?

A

aspirin is an ester

- reacting salicylic acid with ethanoic anhydride (or ethanoyl acid)

54
Q

why is separation necessary in purifying an organic compound?

A
  • product is insoluble, separation allows you to remove any impurities that do dissolve in water
55
Q

describe how to separate product

A

once product formed:

  • pour mixture into separating funnel and add water
  • shake funnel and allow to settle, organic layer and aqueous layer(contains water-soluble impurities) are immiscible so separate out into 2 distinct layers
  • open tap and run each layer off into separate container
56
Q

describe how water can be removed from a purified product

A

(if separation used to purify product, there’ll still be traces of water - needs to be dried)
- add anhydrous salt (CaCl2 or MgSO4). salt is a drying agent - binds to any water present to become hydrated
- keep adding drying agent until it disperses evenly when you swirl the flask
- filter out mixture to remove solid drying agent
(filter paper in funnel that feeds into flask and pour)

57
Q

how can impurities be further removed if product still contaminated by leftover reagents or unwanted side products?

A
  • washing the product (adding another liquid and shaking)
  • e.g. aqueous sodium hydrogencarbonate added to an impure product in solution to remove acid
  • acid reacts with sodium hydrogencarbonate to give CO2 gas and product removed using separating funnel
58
Q

how can volatile liquids be separated?

A
  • distillation
  • connect condenser to round bottomed flask containing impure product in solution
  • place thermometer in neck of the flask so bulb sits next to entrance of condenser, temp on thermometer will show boiling point of substance evaporating at any given time
  • heat impure product (electric heater because organic chemicals are flammable)
  • when product boils (thermometer showing ts boiling point), place flask at open end of condenser to collect pure product
59
Q

purpose of anti-bumping granules

A

prevent the formation of larger bubble

60
Q

how can organic solids be purified?

A

recrystallisation

61
Q

describe how to purify an organic solid (recrystallisation)?

A
  • dissolve solid in hot solvent to make saturated solution (max possible ammount of solid dissolved in solvent), let it cool
  • as solution cools, solubility of product falls
  • when it reaches the point where it can’t stay in solution, it forms pure crystals
62
Q

describe briefely how to purify an organic solid (recrystallisation)?

A
  • dissolve solid in hot solvent to make saturated solution (max possible ammount of solid dissolved in solvent), let it cool
  • as solution cools, solubility of product falls and crystals begin to form
  • when it reaches the point where it can’t stay in solution, it forms pure crystals
63
Q

describe how melting and boiling points are good indicators of purity?

A
  • pure subtances have specific M.P and B.P
  • if impure, M.P. lowered and B.P raised
  • if very impure, melting and boiling will occur across wide range of temps
64
Q

describe experimentally how melting point apparatus can determine melting point of an organic solid

A
  • pack small sample of solid in glass capillary tube and place inside heating element
  • increase temp until sample turns from solid to liquid
  • measure melting range, which is range of temps from where solid begins to melt and where its melted completely
    (use MP of substance from data book to compare)
    -
65
Q

what will impurities in sample do to melting range?

A
  • lower MP

- broaden Melting range

66
Q

what is the carbonyl functional group?

A

C=O

67
Q

describe how aldehydes and ketones differ, in terms of position of carbonyl group and naming

A
  • aldehydes have carbonyl group at end of c chain
    names end in -al
  • ketones have carbonyl group in middle of C chain, names end in -one
    (numbering required to show which carbon the carbonyl group is on)
68
Q

aldehydes and ketones can be oxidised into what?

A
  • aldehydes to carboxylic acids (e.g. propanal to propanoic acid)
  • ketones can’t be oxidised

A2 Chemistry (9 decks)

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