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OCR A A-Level Organic Chemistry > Chapter 26: Carboxylic Acids and Esters > Flashcards

Chapter 26: Carboxylic Acids and Esters Flashcards

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1
Q

What functional group do carboxylic acids have, and what does this contain?

A
  • Carboxyl groups
  • They contain both a carbonyl and hydroxyl group bonded to the same carbon atom, which is what makes them react differently
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2
Q

Are carboxylic acids soluble? Explain why.

A
  • The C=O and O-H bonds are polar, which allows carboxylic acids to form hydrogen bonds with the water molecules and dissolve in water
  • However, once there are more than 4 carbon atoms in a carboxylic acid molecules, they are no longer soluble, as the non-polar carbon chain has a greater effect
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3
Q

What type of carboxylic acids are more soluble than the others, and why?

A
  • Dicarboxylic acids
  • They have 2 polar carboxyl groups to form hydrogen bonds
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4
Q

What happens when carboxylic acids dissolve in water? What does this mean?

A
  • They partially dissociate
  • They are weak acids
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5
Q

Give the equation for the dissociation of methanoic acid, including state symbols.

A
  • HCOOH (aq) <-> H+ (aq) + HCOO- (aq)
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6
Q

Which reactions do carboxylic acids have in common with other acids?

A
  • Redox reactions with metals
  • Neutralisation reactions with bases (alkalis, metal oxides and carbonates)
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7
Q

What ion do carboxylic acids form in their salt compounds?

A
  • Carboxylate ions
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8
Q

What observations can be made during the reaction of carboxylic acids with metals?

A
  • The metal dissolves
  • Effervescence
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9
Q

What observations can be made during the reaction of carboxylic acids with carbonates?

A
  • The carbonate dissolves if the carboxylic acid is in excess
  • Effervescence
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10
Q

How can carboxylic acids be told apart from other organic compounds? Why does this method work?

A
  • They are reacted with carbonates
  • They are the only common organic compound that is acidic enough to react with carbonates
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11
Q

What are carboxylic acid derivatives?

A
  • Compounds that are formed (derived) from carboxylic acids
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12
Q

List 4 derivatives of carboxylic acids, and the functional group of each.

A
  • Esters, RCOOR (second R cannot be a hydrogen atom)
  • Acyl chlorides, RCOCl
  • Acid anhydrides, RCOOCOR/ (RCO)2O
  • Amides, RCONR2
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13
Q

What causes carboxylic acid derivatives to react in similar ways?

A
  • They all have an acyl group (RC=O) bonded to an electronegative atom
  • It is called an acyl group as it comes from a carboxylic acid (otherwise, it would’ve been called a carbonyl group)
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14
Q

How are esters formed? What is this reaction called?

A
  • Alcohol + carboxylic acid -> ester + water
  • Conditions: heat and sulfuric acid catalyst
  • Esterification
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15
Q

How are ‘simple’ esters named?

A
  • The alcohol’s name changes to end in -yl (e.g. methyl)
  • The name of the carboxylic acid changes to end in -oate (e.g. propanoate)
    (-E.g. methyl propanoate)
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16
Q

How are esters with substituents named?

A
  • The carbon atoms in the ester bond are both numbered 1 in their part of the chain
17
Q

What is hydrolysis?

A
  • A reaction with water (or in the presence of an aqueous solution) that breaks a chemical compound into 2 compounds
18
Q

What can esters be hydrolysed by?

A
  • Aqueous acid
  • Aqueous alkali
19
Q

Give the general equation and conditions for the hydrolysis of esters by aqueous acid.

A
  • Ester + water -> carboxylic acid + alcohol
  • Conditions: reflux, aqueous H2SO4
20
Q

Give the general equation and conditions for the hydrolysis of esters by aqueous alkali.

A
  • Ester + hydroxide ion -> carboxylate ion + alcohol
  • Conditions: reflux, aqueous NaOH
21
Q

What are 3 differences between the hydrolysis of esters by aqueous acid and aqueous alkali?

A
  • The hydrolysis of esters by aqueous acid is reversible, but with aqueous alkali, it’s irreversible
  • The acid is a catalyst, but the alkali is used up
  • In the reversible reaction, some ester will remain in the mixture, but in the irreversible reaction, provided that there is enough NaOH, the ester will be completely converted
22
Q

Other than carboxylic acids, what else can produce esters?

A
  • Acid anhydrides
  • Acyl chlorides
23
Q

What can phenols be esterified by, and why?

A
  • Only acid anhydrides and acyl chlorides
  • Carboxylic acids are not reactive enough to esterify them
24
Q

How are acid anhydrides formed?

A
  • 2 carboxylic acids react, and water is removed (hence the name acid anhydride)
  • This reaction is reversible, as acid anhydrides can be easily rehydrated
25
Q

How are acid anhydrides named?

A
  • If it is formed from 2 of the same carboxylic acid, the word acid is replaced with anhydride
  • For example, 2 ethanoic acid molecules would form ethanoic anhydride
  • If 2 different carboxylic acids are used, put their names in alphabetical order (e.g. butanoic propanoic anhydride)
26
Q

How do acid anhydrides react to form esters? Give a general equation.

A
  • Acid anhydride + alcohol -> ester + carboxylic acid
27
Q

State and explain what is produced in the reaction of propanoic anhydride and ethanol.

A
  • Ethyl propanoate
  • Propanoic acid
  • The acid anhydride splits to form the carboxylic acid, and the part of the ester that would come from the carboxylic acid (this part would have the extra oxygen)
  • The hydroxyl group from the alcohol completes the carboxylic acid, and the alkyl group completes the ester
28
Q

How are acyl chlorides formed?

A
  • The parent carboxylic acid is reacted with SOCl2 (thionyl chloride)
  • This forms an acyl chloride, sulfur dioxide and hydrogen chloride
29
Q

What can acyl chlorides react to form?

A
  • Esters
  • Carboxylic acids
  • Primary amides
  • Secondary amides
30
Q

Which functional group reacts similarly to acyl chlorides?

A
  • Acid anhydrides
31
Q

Why is it useful to use acid anhydrides in some reactions instead of acyl chlorides?

A
  • Acyl chlorides can be too reactive for some reactions
32
Q

How do acyl chlorides react to form esters?

A
  • Acyl chloride + alcohol -> ester + hydrogen chloride
33
Q

Give the general equation for the reaction of acyl chlorides to form carboxylic acids.

A
  • Acyl chloride + water -> carboxylic acid + hydrogen chloride
34
Q

Which mechanism do acyl chlorides undergo to become carboxylic acids? What is the role of water in this reaction? Draw the mechanism.

A
  • Nucleophilic addition-elimination
  • Water acts as a nucleophile
  • Check the mechanism
35
Q

What are primary and secondary amides?

A
  • Primary amides have the functional group CONH2
  • Secondary groups have the functional group CONHR
36
Q

Give the balanced symbol equation of the reaction of methanoyl chloride to form its primary amide.

A
  • HCOCl + 2NH3 -> HCONH2 + NH4Cl
37
Q

Give the general equation of the reaction of acyl chlorides to form secondary amides.

A
  • Acyl chloride + 2 primary amine -> secondary amide + alkyl ammonium chloride
38
Q

Give the balanced symbol equation of the reaction of methanoyl chloride with methyl amine.

A
  • HCOCl + 2CH3NH2 -> HCONHCH3 + CH3NH3+Cl-

OCR A A-Level Organic Chemistry (22 decks)

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