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Year 13 Chemistry > 6.1.2 - Carbonyls And Carboxylic Acids > Flashcards

6.1.2 - Carbonyls And Carboxylic Acids Flashcards

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1
Q

What is a carbonyl functional group?

Which groups contain a carbonyl group?

A
  • C=O group

- Aldehydes and ketones contain it

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2
Q

What is an aldehyde functional group?

Uses of the simplest aldehyde

A
  • CHO

- Methanal, HCHO, is used to preserve biological specimens

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3
Q

Ketone functional group

Uses of simplest ketone

A
  • CO

- propanone/acetone, CH3COCH, used as an industrial solvent or in nail-varnish removers

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4
Q

Suffix for carbonyl compounds

A

Aldehyde: -al
Ketone: -one

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5
Q

Which is the first carbon in a carbonyl compound?

A

The carbon atom of the carbonyl group is always designated as carbon-1

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6
Q

Common uses and applications of octanal

A
  • CH3(CH2)7CHO
  • Naturally occurring in citrus oils
  • responsible for the smell of oranges
  • used as a component of perfumes
  • flavour production in food industry
  • released in some mating scents for birds (in Alaska) as part of breeding ritual
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7
Q

Oxidation of aldehydes

A 
Oxidised to carboxylic acids
Reagents used:
- Cr2072-/H+ usually acidified potassium dichromate 
- dilute H2SO4
Conditions:
-Heat under reflux
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8
Q

Do ketones undergo oxidation reactions?

A

Ketones do not undergo oxidation reactions

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9
Q

Structure of C=O carbonyl group

A
  • the C=O bond is made up of both sigma and pi bonds
  • pi bond above and below the plane of the carbon and oxygen atoms, formed by the sideways overlap of p-orbitals
  • sigma bond in-between the carbon and oxygen atoms
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10
Q

Difference between carbonyl and alkene group

A
  • C=O is polar, where C=C is not
  • this is because oxygen is more electronegative than carbon
  • so the electron density lies closer to the oxygen atom than the carbon
  • this makes the carbon end of the C=O delta positive, with the Oxygen end being delta negative
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11
Q

What does the polar nature of carbonyl groups allow to happen?

A
  • Aldehydes and ketones can react with some nucleophiles
  • A nucleophile is attracted to and attacks the slightly positive carbon atom, resulting in addition across the C=O double bond
  • Aldehydes and ketones can therefore undergo nucleophilic addition
    (this is different to electrophilic addition in alkene C=C double bonds)
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12
Q

What is sodium tetrahydriborate(III), NaBH4, used for?

A
  • Used as a reducing agent in reactions with aldehydes and ketones to reduce them to alcohols
  • The aldehyde is usually warmed with the NaBH4 reducing agent in aq solution
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13
Q

Reducing an aldehyde mechanisms and info.

A
  • Aldehydes are reduced to primary alcohols by NaBH4

Reagents:
- Heated with NaBH4(aq)

E.g. butanal reduced to butan-1-ol

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14
Q

Reducing a ketone mechanism and info.

A
  • Ketones are reduced to secondary alcohols by NaBH4

Reagents:
- heated with NaBH4(aq)

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15
Q

Hydrogen Cyanide, HCN, info.

A
  • Colourless
  • Extremely poisonous
  • liquid at r.t.
  • boils slightly above room temperature
  • cannot be used safely in an open laboratory
  • in a reaction, sodium cyanide and sulfuric acid are used to provide the hydrogen cyanide
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16
Q

Reaction of HCN with carbonyl compounds

Why is it useful?

A
  • HCN adds across the C=O bond of aldehydes and ketones
  • The reaction will form a hydroxynitrile compound
  • It is a useful reaction as it provides a means of increasing the length of the carbon chain
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17
Q

What groups does a hydroxynitrile compound consist of?

A
  • hydroxyl group, OH
  • Nitrile group, C(triple bond)N
  • these can also be called cyanohydrins
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18
Q

Nucleophilic addition of carbonyl compounds

A
  • The carbon atom in the C=O double bond is electron deficient and attracts nucleophiles
  • Aldehydes and ketones both react by nucleophilic addition to form alcohols
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19
Q

Mechanism for nucleophilic addition to carbonyl compounds, using NaBH4

A
  • In this reaction NaBH4 contains a hydride ion, ..(lone pair)H-, which acts as a nucleophile:
    1. Look in textbook
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20
Q

Mechanism for reaction of carbonyl compounds with NaCN/H+

A
  • In NaCN/H+, A ..(lone pair)CN- acts as the nucleophile in this reaction, which attacks the electron-deficient-carbon atom in the aldehyde of ketone
    1. Look in textbook
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21
Q

Aldehyde def

A

At least one H attached to the carbonyl group

22
Q

Ketone def

A

Two carbons attached to the carbonyl

C=O group is in the middle of at least two carbons

23
Q

Nucleophile def

A

An atom or group of atoms that is attracted to an electron deficient centre.
They are often negative ions (anions) with a lone pair
They often contain an electronegative atom with a lone pair of electrons and a delta negative charge

24
Q

Mechanism of nucleophilic addition with carbonyl compounds

A
  1. Dipole present on carbonyl - hence it is susceptible to nucleophilic attack
  2. Nucleophile donates the pair of electrons to the carbon which is electron deficient
  3. Simultaneously the pi electrons in C=O bond break forming the intermediate
  4. Extra electron pairs are donated to neighbouring H+ ion to form the alcohol which is stable
25
Q

Test for aldehydes with Tollen’s reagent mechanism

A
  • positive test shows a “silver mirror”
  • this happens because the Tollen’s reacts with OH groups and oxidises them
26
Q

Test for aldehydes with potassium dichromate

A
  • positive result goes dark green
27
Q

What is 2,4 NDPH used for?

- what is a positive result?

A

Used to test for ketones or aldehydes - test for carbonyl compounds with the C=O double bond.

  • orange/brown precipitate will form
28
Q

Testing for different carbonyl compounds using melting point

A

D,,Dodd,d,d,e

29
Q

How to make Tollen’s reagent

A
  1. React AgNO3 and NaOH (aq)
30
Q

Why does Tollen’s cause aldehydes to form a solver mirror/layer?

A

Silver ions in Tollen’s reagent are reduced
The silver ions then form solid silver (no oxidation number)
The aldehyde is then oxidised
Hence the silver layer forms

31
Q

Why does 2,4 NDPH not react with other carbony-containing functional groups such as carboxylic acids, ester, or amides?

A
  • With a -COOH or a die the compound acts as a base
  • this leaves the carboxylate ion negatively charged
  • so the ion is unable to be attacked by a nucleophile
  • In aldehydes and ketones the carbocation is positively charged
  • so the carbocation can be attacked by a nucleophile
32
Q

Uses of esters

A
  • Flavourings - e.g. fruit flavourings, etc.
  • Scents - e.g. soap
  • nail varnish remover
33
Q

Functional group of Carboxylic acids

A

-COOH

34
Q

pH strength of carboxylic acids

A
  • Classified as weak acids

- this is because when dissolved in water, they partially dissociate

35
Q

Reactions of carboxylic acids

A
  • Redox with metals

- neutralisation with bases - alkalis, metal oxides, carbonates etc.

36
Q

Esterification of carboxylic acid mechanism

A

Reagents:
- alcohol + carboxylic acids

Conditions

  • reflux
  • conc. H2S04

H2SO4 is a dehydrating agent - removes water - causes equilibrium to move to the right
- this increases yield of the ester

37
Q

Esterification of acid anhydrides mechanism

A

Reagents:
- alcohol + acid anhydride

Conditions:

  • reflux
  • dry conditions

Equation:

Ethanoic anhydride + methanol —> methyl ethanoate + ethanoic acid

  • Reaction is not reversible
  • Acid anhydrides are less toxic than acts chlorides
38
Q

What is hydrolysis

- what is it in context of esterification?

A
  • A reaction in which water or OH ions break a compound in two
  • hydrolysis is the opposite of esterification and occurs under reflux
39
Q

What conditions does hydrolysis occur in?

A
  • Reflux conditions
40
Q

Example of acidic hydrolysis reaction of ester

A

Methyl ethanoate + water —> Ethanoic acid + methanol

41
Q

Alkaline hydrolysis reaction of esters example

A

Methyl ethanoate + Sodium hydroxide —> sodium ethanoate - methanol

42
Q

Use of sulphur dichloride oxide and info

A
  • SOCl2 replaces the -OH group in carboxylic acids to produce an acyl chloride, sulphur dioxide and thionyl chloride
43
Q

Symbol equation for reaction between ethanoic acid and thionyl chloride

A

CH3COOH(l) + SOCl2(l) —> CH3COCl(l) + SO2(g) + HCL(g)

44
Q

Different reagents and product that acrylic chlorides can be used in

A

Amides:
- Reagents: concentrated ammonia, NH3

Alcohols:
- Reagents: H2O
Conditions:

To make ester:
reagents:
- alcohols with a methyl group
Conditions:
- heat
- catalyst

To make methylamines(?):
- Reagents: primary amines

45
Q

Equations and products of reactions with acyl chlorides

A

Ddijej

46
Q

Test for carboxylic acids

A
  • React with a metal carbonate - Sodium Carbonate

- Effervescence should occur

47
Q

Butanal and butanone both react with 2,4-DNPH (Brady’s reagent) to produce orange precipitates.
Outline how the mixtures containing these orange precipitates can be used to distinguish between butanal and butanone.
(3 Marks)

A
  • Recrystallise/purify the precipitate
  • Measure melting points of each precipitate
  • Compare with known values
48
Q

How to prepare acyl chlorides and why it should be carries out in a fume hood

A
  • React carboxylic acid with Thionyl chloride (SOCl2) to produce the acyl chloride
  • Replace the OH on the carb acid with a Cl atom
  • Produces SO2 and HCl gas
  • both of these products are toxic
  • needs to be done in a fume hood to prevent inhalation of toxic gases
49
Q

Acid Anhydride formation

A
  • React two carboxylic acids together
  • produce acid anhydride and a molecule of water - condensation reaction
  • e.g. two ethanoic acid molecules react together to form ethanoic anhydride
50
Q

Butanal and butanone both react with 2,4-dinitrophenylhydrazine to produce mixtures containing orange precipitates.
Outline how the mixtures containing these orange precipitates can be used to distinguish between butanal and butanone.
(3 Marks)

A

Purify/recrystallise the precipitate
Measure the melting points of both
Compare the melting points with known values (online, etc.)

Year 13 Chemistry (20 decks)

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