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Chemistry A2 UNIT 4 > Carbonyl Compounds > Flashcards

Carbonyl Compounds Flashcards

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1
Q

What are aldehydes and ketone?

A

Carbonyl compounds that contain the functional group C=O

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2
Q

What is the difference between aldehydes and ketones?

A

Aldehydes have their C=O at the end of the chain and ketones have their C=O within the chain.

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3
Q

Why are aldehydes easily oxidised and ketones aren’t?

A

Aldehydes have a hydrogen atom attached to the carbonyl group. the only way to oxidise a ketone would be to break a carbon- carbon bond so not easily oxidised.

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4
Q

What are two ways to distinguish between an aldehyde and a ketone?

A
  • Tollens

- Fehlings

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5
Q

Describe Tollens and the reaction of an aldehyde and a ketone with Tollen’s.

A

Tollen’s reagent is a colourless solution of silver nitrate dissolved in aqueous ammonia.
ALDEHYDE: If it is heated in a test tube with an aldehyde, a silver mirror forms after a few minutes.
As the aldehyde is oxidised the diaminesilver ions in the Tollen’s reagent are reduced, producing silver and ammonia.

Ag(NH3)2+(aq) +e- = Ag(s) + 2NH3(aq)
KETONE: No reaction.

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6
Q

Why must aldehydes an ketones be heated in a water bath rather than over a flame?

A

They are flammable.

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7
Q

Describe Fehling’s solution and the reaction of an aldehyde an a ketone with Fehling’s.

A

BLUE SOLUTION of complexed copper (II) ions in sodium hydroxide.
ALDEHYDE: if heated with an aldehyde the copper(II) ions are reduced to a brick red precipitate of copper(II) oxide.
Cu2+(aq) + e- = Cu+(s)

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8
Q

What compound can be used to reduce aldehydes and ketones to alcohols?

A

NaBH4, in equations usually just written as [H]

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9
Q

How does nucleophilic addition work? (aldehyde/ketone to alcohol)

A

1: The C=O bond is polar so the Cδ+ attracts the -vely charged lone pair of electrons on H- ion/
2: The H- ion attacks the slightly +ve carbon atom and donates its lone pair of electrons forming a bond with carbon.
3: As carbon can only have 4 bonds, the addition of the H+ ion causes one of the carbon-oxygen bonds to break. This forces a lone pair of electrons from the C=O bond onto the oxygen.
4: The oxygen donates its lone pair of electrons to a H+ ion (usually from water but sometimes a weak acid)
5: primary (from aldehyde) alcohol produced/ secondary (from ketone) alcohol produced.

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10
Q

What are hydroxynitriles?

A

Hydroxynitriles are molecules which contain a hydroxyl group (OH) and a nitrile group (CN).

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11
Q

How do you name hydroynitriles?

A

Nitrile group is the most important so the suffix is -nitrile and the carbon that’s attached to the nitrogen is always carbon-1. Hydroxy- prefix because OH group.

e.g. CH3CH(CH3)CH(OH)CN
2-hydroxy-3-methylbutanenitrile

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12
Q

How do you make hydroxynitriles?

A

Reacting aldehydes or ketones with hydrogen cyanide (HCN). NUCLEOPHILIC ADDITION.

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13
Q

Describe how you make hydroxynitriles from aldehydes/ketones by nucleophilic addition.

A

1: Hydrogen cyanide is a weak acid- partially dissociates in water to form H+ ions and CN- ions: HCN H+ +CN-
2: The CN- ion from the HCN attacks the partially positive carbon atom and donates a pair of electrons forming a bond with the carbon.
3: A pair of electrons from the C=O double bond is pushed onto the oxygen.
4: The oxygen bonds to a H+ ion (from either HCN or water) to form the hydroxyl group.

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14
Q

Why is HCN a risk? How is it avoided?

A

EXTREMELY TOXIC GAS.
So to reduce risk KCN is used.
KCN also toxic but stored more easily.

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15
Q

What are carboxylic acids?

A

Contain functional group -COOH.

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16
Q

Why do carboxylic acids partially dissociate in water?What into?

A

Weak acid
RCOOH RCOO- + H+
Equilibrium lies to left because most doesn’t dissociate.

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17
Q

What do carboxylic acids form when they react with carbonates (CO3^2-) or hydrogencarbonates (HCO3-)?

A

Salt, CO2 and water
e.g.2CH3COOH + Na2CO3 = 2CH3COONa +H2O + CO2
HCOOH + NaHCO3 = HCOONa + H2O +CO2

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18
Q

What do you get when you react a carboxylic acid with an alcohol in the presence of a strong acid catalyst?

A

Ester (esterification)

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19
Q

What catalyst is usually used in esterification reaction?

A 
conc. H2SO4 
or
HCl
or
H3PO4
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20
Q

How do you name an ester?

A
  1. Look at the alkyl group that came from the alcohol. first part of name.
  2. Look at part that came from the carboxylic acid. Swap -oic to -oate.

e.g. ethanoic acid + methanol = CH3COOCH3
methyl ethanoate

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21
Q

What are useful properties of esters?

A
  • SWEET SMELL- perfumes, food flavourings
  • POLAR LIQUIDS- Lots of polar organic molecules will dissolve in them.
  • LOW BOILING POINTS- evaporate easily from mixtures, good solvents in glues and printing inks.
  • PLASTICISERS- Added to plastics during polymerisation to make plastics more flexible. Over time plasticiser molecule escapes and molecule becomes brittle and stiff.
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22
Q

What is hydrolysis?

A

When a substance is split up by water.

23
Q

What is added to speed up hydrolysis?

A

An acid or an alkali

24
Q

What is acid hydrolysis and how does it work?

A

Splits ester into an acid and an alcohol.
You have to reflux the ester with a dilute acid, such as HCl or H2SO4. The ester will then split back into its acid and alcohol that it was originally made from.

25
Q

What do you need to make acid hydrolysis work and why?

A

Reversible so need lots of water to push equilibrium to the right.

26
Q

What is base hydrolysis and how does it work?

A

Reflux ester with a dilute alkali, such as NaOH.

OH- ions from the base react with the ester and you get a carboxylate ion and an alcohol/

27
Q

What are fats and oils?

A

Esters of glycerol (propane-1,2,3-triol) and fatty acids.

28
Q

What are fatty acids?

A

Long chain carboxylic acids.

29
Q

Why do most of the properties of fats and oils mainly come from fatty acid?

A

Makes up mostly from fatty acid chains.

30
Q

Describe the structure of fats.

A

Mainly saturated hydrocarbon chains- fit neatly together, increasing the van der Waals forces between them.

31
Q

What are the properties of fats?

A

High melting point and solid at room temp.

32
Q

Describe the structure of oils.

A

Unsaturated hydrocarbon chains- double bonds mean the chains are bent and don’t pack together well. Weaker vdw forces.

33
Q

What are the properties of oils?

A

Easier to melt and liquids at room temp.

34
Q

How do you hydrolyse fats and oils?

A

Like any ester- heating with sodium hydroxide.
OH- mions from NaOH react with fat/oil to form a carboxylate ion and an alcohol.
lcohol formed is glycerol and carboxylate ions combine with Na+ ions from sodium hydroxide to form a sodium salt (SOAP).

35
Q

How do you turn sodium salt back into a long chain carboxylic acid?

A

Heating with an acid such as HCl. H+ ions form the acid displace the Na+ ions in the salt to form a carboxylic acid.
Releases Na+ ion.

36
Q

How do you make biodiesel from vegetable oil.

A

React with methanol, using a strong alkali (e.g. KOH, NaOH) as a catalyst. Get a mixture of methyl esters of fatty acids (biodiesel).

37
Q

What is biodiesel?

A

A mixture of methyl esters of fatty acids which can be used as a carbon neutral fuel.

38
Q

What are acyl chlorides?

A

Have functional groups -COCl- general formula

CnH2n-1OCl

39
Q

How do you name acyl chlorides?

A

like carboxylic acid except end in -oyl chloride.

40
Q

How do acyl chlorides react with water?

A

React vigorously with cold water, producing a carboxylic acid and HCl.

41
Q

How do acyl chlorides react with alcohols?

A

React vigorously with alcohols at room temperature producing an ester and HCl.
Much easier, faster way to produce an ester.

42
Q

How do acyl chlorides react with ammonia?

A

React vigorously with ammonia at room temperature to produce an amide and HCl.

43
Q

How do acyl chlorides react with amines?

A

React vigorously with amines at RT producing an N-substituted amine.

44
Q

What are the two steps of nucleophilic addition- elimination with acyl chlorides?

A
  1. Nucleophile adds onto acyl chloride displacing a Cl- ion.

2. The Cl- ion steals a hydrogen ion from the nucleophile and HCl is eliminated.

45
Q

Describe the nucleophilic add. elim.

A

STEP 1:
In acyl chloride both Cl and O draw electrons towards themselves so carbon has a slight +ve charge- easily attacked by nucleophiles.
1: Nuc. attacks the delta + carbon.
2: Pair of electrons transferred from C=O bond onto O.
3: Pair of electrons on oxygen reform the double bond and Cl kicked off.
4: Leaves +vely charged Cl ion.

STEP 2:

5: The Cl- ion bonds with hydrogen on nucleophile.
6: A pair of electrons is transferred onto the nucleophile from the bond.
7: This leaves an acyl chloride derivative.

46
Q

What are acid anhydrides?

A

Made from two identical carboxylic acid molecules joined together via an oxygen with carbonyl groups on either side.
The oxygen has come from one of OH groups on carboxylic acid.
Other OH and H released as water.

47
Q

How do you name acid anhydride?

A

Name carboxylic acid and swap acid with anhydride.

48
Q

How does acid anhydride react with water?

A

carboxylic acid produced

49
Q

How does acid anhydride react with alcohols?

A

ester produced

50
Q

How does acid anhydride react with ammonia?

A

Produces amide

51
Q

What is always produced in reactions with acid anhydride?

A

Carboxylic acid.

52
Q

How does acid anhydride react with amine?

A

N- substituted amide produced.

53
Q

How is aspirin (ester) made?

A

reacting salicylic acid (has alcohol group) with either ethanoic anhydride or ethanoyl chloride.

54
Q

Why is ethanoic anhydride used in industry?

A

Cheaper

Safer- less corrosive, reacts more slowly with water and doesn’t produce dangerous HCl.

Chemistry A2 UNIT 4 (5 decks)

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