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CH4 > Topic 11 - Organic Compounds Containing Oxygen. > Flashcards

Topic 11 - Organic Compounds Containing Oxygen. Flashcards

0
Q

What is a primary alcohol?

A

1 carbon attached to the carbon with the OH group.

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1
Q

What are the three groups of alcohols?

A

Primary, secondary and tertiary.

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2
Q

What is a secondary alcohol?

A

2 carbon atoms attached to the carbon with the OH group.

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3
Q

What is a tertiary alcohol?

A

3 carbon atoms attached to the carbon with the OH group.

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4
Q

What are the two methods of preparation of alcohols?

A

Hydrolysis

Reduction.

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5
Q

Outline the production of an alcohol from halogeno-alkanes by hydrolysis.

A

Alcohols can be prepared from halogeno alkanes by hydrolysis using aqueous Sodium Hydroxide or Potassium Hydroxide. The solution is warmed gently:

C₂H₅Cl→ C₂H₅OH + NaCl (NaOH & heat gently)

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6
Q

How can the reduction of a carbonyl compound to produce an alcohol be achieved?

A

By using a reducing agent which is either sodium-tetrahydrido-borateIII (NaBH₄) in water or lithiumaluminateIII in dry ether (LiAlH₄).

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7
Q

What does the reduction of an aldehyde produce?

A

A primary alcohol.

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8
Q

What does the reduction of a keytone produce?

A

A secondary alcohol.

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9
Q

How can you produce a halogeno-Alkane from an alcohol?

A

By heating the alcohol with compounds such as HBr which is made in situe by heating NaBr or KBr with concentrated sulfuric acid.

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10
Q

What do alcohols react with acids to produce, giving an example and commenting on the yield of the reaction.

A

Alcohols react in the presence of sulfuric acid as a catalyst with carboxylic acids to give sweet smelling compounds called esters.

E.g
C₂H₅OH + CH₃COOH ⇄ CH₃COC₂H₅ + H₂O
Ethanol. Ethanoic. Ethylethanoate
Acid
The yield of this reaction is small as it reaches equilibrium. The product is distilled from the reaction mixture.

A better yield is obtained using an acid chloride e.g ethanoile chloride.

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11
Q

How may the dehydration of an alcohol be achieved?

A

Cold Sulfuric acid reacts with an alcohol to give an alkyl hydrogen sulfate. Heating the product (170°) with excess sulfuric acid gives an Alkene. This reaction only happens with primary alcohols. It can also be brought about by alcoholic NaOH or KOH.

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12
Q

How can the oxidation of an alcohol be achieved and what will it produce?

A

Primary and secondary alcohols, not tertiary can be oxidized by using acidified sodium or potassium DichromateVI and heating under reflux. Primary alcohols form aldehydes which on further refluxing will be oxidized to acids. Secondary alcohols will form Keytones which cannot be oxidised further.

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13
Q

Can you oxidise a tertiary alcohol?

A

No.

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14
Q

How can oxidation of an alcohol be used for analysis purposes?

A

It allows you to distinguish between different types of alcohol:-

Primary alcohols can be oxidised twice to form aldehydes and then acids.

Secondary alcohols can only be oxidised once to produce Keytones

Tertiary alcohols cannot be oxidised.

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15
Q

Outline the use of ethanol as a fuel.

A

Ethanol will dissolve in petrol and boils at the same temperature as heptane C₇H₁₆ so will vaporize at a car engine temperature. It burns well producing about 70% as much energy per litre as petrol. A petrol engine can take up to 10% ethanol in the fuel without any adjustment to the carburetor. Ethanol burns to form CO₂ and water and a little ethanal so there is little atmospheric pollution. A mixture of petrol and ethanol is called gasohol.

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16
Q

What is phenol?

A

Phenols are compounds with a a hydroxyl group attached to the benzene ring.

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17
Q

What was phenol used for originally?

A

Originally a mixture of phenols known as carbolic acid was the first substance to be used as an antiseptic. It meant that surgery was much more efficient because spraying wards and operating theaters with phenol mist prevented wounds becoming infected.

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18
Q

What phenols are most effective at killing bacteria?

A

Substituted phenols are better at killing bacteria and less caustic to the skin.

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19
Q

What is 2,4,6-trichlorophenol found in?

A

TCP and Dettol

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20
Q

Describe the physical properties of phenol.

A

Phenol is a solid at room temperature melting point 42°C. It’s melting point is higher than hydrocarbons with a similar Mr due to the presence of hydrogen bonding.

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21
Q

Is phenol acidic and why is it more acidic than alcohols?

A

Phenol will dissociate in water to form a phenoxide ion and H⁺. Phenol is more acidic than alcohols because the phenoxide ion is stabilized as the electrons on the oxygen atom become part of the delocalized ring system. This cannot happen with an alcohol.

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22
Q

Compare the acidity of phenols to that of carboxylic acids.

A

Phenol will colour indicator paper and react with Sodium Hydroxide solution to neutralize it. However phenol is a weaker acid than carboxylic acids and will not react with carbonates and hydrogen carbonates to produce carbon dioxide.

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23
Q

Will phenol form an ester?

A

Phenol forms esters but less readily than alcohols by reacting with acyl
chlorides. It is first converted to sodium phenoxide (by mixing with NaOH) which then reacts with ethanoile chloride to form an ester.

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24
Q

Will phenol react with bromine?

A

Phenol as sodium phenoxide will decolourise bromine water giving a white solid, 2,4,6-tribromophenol. This is an electrophillic substitution reaction.

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25
Q

Is phenol more readily attacked by electrophiles and why?

A

Phenol is more readily attacked by electrophiles than benzene because interaction between lone pairs of electrons on the OH and O⁻(in phenoxide) groups and the ring increase the availability of electrons in the ring.

26
Q

How can you test for a phenol?

A

Phenols give colored products with iron-III-chloride; phenol gives a violet colour which distinguishes it from alcohols which do not give a colour.

27
Q

What phenols give violet colours with iron-III-chloride?

A 
Phenol
1,3-dihydroxybenzene AKA resorcinol
2hydroxymethylbenzene AKA o-cresol
3hydroxymethylbenzene AKA m-cresol
4hydroxymethylbenzene
28
Q

Which phenol gives a rapidly darkening green colour with iron-III-chloride?

A

1,2-dihydroxy-benzene AKA catechol.

29
Q

Which phenol gives a green precipitate with iron-III-chloride?

A

1,4-di-hydroxy-benzene or quinol

30
Q

Which phenol gives a red precipitate with iron-III-chloride?

A

1,2,3-trihydroxy-benzene.

31
Q

How are aldehydes and Keytones formed?

A

Aldehydes are formed by oxidising primary alcohols and Keytones are formed by oxidising secondary alcohols.

32
Q

Describe the physical properties of Keytones.

A

The boiling points are lower than acids and alcohols with similar carbon chains because there is no Hydrogen bonding.

33
Q

How can you test for an aldehyde and how is the test performed?

A

Aldehydes give a silver mirror test in which aqueous silver ions are reduced to
Silver as the aldehyde is oxidised. The aldehyde is treated with ammoniacle silver nitrate (Tollen’s reagent) and warmed in a water bath. The inside of the test tube becomes coated with silver.

34
Q

What is an alternative test for aldehydes?

A

Aldehydes will also reduce Fehling’s Solution (also Benedicts reagent) to Copper-1-oxide giving a brick red colour on heating to boiling point.

35
Q

What is Brady’s reagent?

A

2,4-dinitro-phenyl-hydrazine.

36
Q

Outline the reactions of Brady’s reagent with Aldehydes and Keytones.

A

It reacts with both aldehydes and Keytones in a nucleophillic addition-elimination reaction to produce 2,4-dinitro-phenyl-hydrazones. Which are orange or yellow solids and are easily crystallised and purified and demonstration of the melting point can be used to identify the original aldehyde or keytone.

Reaction details needed

37
Q

Outline the addition of hydrogen cyanide to carbonyl compounds.

A

Carbonyl compounds undergo an addition reaction with Hydrogen-cyanide forming hydroxy nitrile compounds. This addition takes place in two steps. The carbonyl group is polar and the CN⁻ ion joins on to the ᵟ⁺ carbon atom in the rate determining step. The O⁻ is immediately attacked by the H⁺ ion. This is a nucleophillic addition reaction.

38
Q

What is an iodoform reaction?

A

Iodoform (tri-iodo-methane) CHI₃ - a pale yellow solid; is formed when a suitable carbonyl compound is warmed with NaOH and Iodine. In order for the test to be positive the carbonyl group must be next to a methyl group.

39
Q

What substances will give a positive result with an iodoform reaction?

A

All methyl Keytones will test positive. Ethanal will give a positive reaction but no other aldehyde will. Ethanol and secondary alcohols are oxidised to ethanal and methyl Keytones under these conditions so will also give a positive test.

40
Q

Outline the physical properties of aliphatic carboxylic acids.

A

Aliphatic carboxylic acids (C₁ - C₁₀) are liquids at room temperature. Each carboxylic acid molecule forms two hydrogen bonds with another to form dimers. This means they have higher boiling points than corresponding alcohols. They are soluble in water as they can form hydrogen bonds with water.

41
Q

Outline the physical properties of aromatic carboxylic acids.

A

Aromatic acids are solids at room temperatures and are only soluble in hot water.

42
Q

Place the following in order of increasing acidity: Carboxylic acids, alcohols and phenols.

A

Alcohols, phenols, carboxylic acids.

43
Q

Why are carboxylic acids stronger acids than alcohols and phenols?

A

This is due to the relative stabilities of the ions left behind when a proton is lost and also it is easier for a proton to be lost by the Carboxyl group as the oxygen atom of the C=O (carbonyl) group attracts electrons away from the OH group.

44
Q

Why are carboxylic acid groups not attacked by nucleophiles?

A

The flow of electrons from the OH group towards the C of the carbonyl group reduces the Δ⁺ charge on it (C on the carbonyl) and it is not attacked by nucleophiles. This cannot happen with the OH group of an alcohol.

45
Q

Why is the carboxylate ion stable?

A

Once a carboxylate ion has been formed (COO⁻) the negative charge is shared equally between the two oxygen atoms. This delocalisation makes the carboxylate ion less ready to accept a proton back.

46
Q

Will carboxylic acids liberate CO₂ from carbonate and hydrogen carbonate and how is this useful?

A

Carboxylic acid is stronger than carbonic acid (H₂CO₃) and will liberate carbon dioxide from carbonate and hydrogen carbonate. This can be used to distinguish them from phenols.

47
Q

Which is strongest, aliphatic or aromatic carboxylic acids?

A

Benzoic acid is stronger than ethanoic acid as the negative charge on the carboxylate ion can be distributed into the π electron system of the benzene ring. (The ion formed when it dissociated is more stable).

48
Q

How can carboxylic acids be formed from primary alcohols and aldehydes?

A

Alcohols and aldehydes can be oxidised to carboxylic acids using acidified(H₂SO₄) Potassium-dichromateVI as an oxidising agent.
Sulphuric acid is used and the required product can be distiller from the mixture after heating under reflux.

49
Q

How may aromatic carboxylic acids be formed?

A

Aromatic carboxylic acids can be made in the same means as aliphatic carboxylic acid but they can also be obtained by oxidation of methyl side chains using alkaline Potassium-Manganate-VII. The Potassium salt of the acid is first obtained and then is acidified to give the free acid.

50
Q

How can an ester be made from a carboxylic acid?

A

These can be prepared from acids by heating with alcohols in the presence of conc Sulphuric acid. The Sulfuric acid is a catalyst and also a dehydrating agent, removing water and pushing the equilibrium to the right.

C₂H₅OH + CH₃COOH ⇄ CH₃COOC₂H₅ + H₂O

51
Q

How are acid chlorides formed from carboxylic acid?

A

Acid chlorides can be formed by treating acids with phosphorous-V-chloride.

CH₃COOH + PCl₅ → CH₃COCl + POCl₃ + HCl.

52
Q

How can you get a primary alcohol from a carboxylic acid?

A

Primary alcohols can be prepared by heating with Lithium-tetrahydro-AluminateIII in dry ether.

CH₃COOH → CH₃CH₂OH (with LiAlH₄ in dry ether)

53
Q

How may you achieve the decarboxylation of a carboxylic acid?

A

This occurs when acids are heated with soda-lime. A hydrocarbon is formed which has one less Carbon atom than the acid.

CH₃COOH + NaOH → CH₄ + NaCO₃ + H₂O
This reaction is widely used in structure determination since the hydrocarbon is easily identified once the Carboxyl group has been removed.

54
Q

How is the hydrolysis of an ester acheived?

A

Th Hydrolysis of an ester is catalysed by acids and alkalis. If a base is used the first product is the salt of this base e.g with sodium Hydroxide The two products (salt and alcohol) can be easily separated since the salt is non volatile and insoluble in organic solvents whereas the alcohol is volatile and soluble in organic solvents. To obtain the acid from the salt it is treated with a mineral acid e.g Sulfuric acid.

55
Q

Outline the hydrolysis of acid chlorides.

A

Acid chlorides are very easily hydrolysed, the water in moist air brings about hydrolysis.

56
Q

How can Amides be produced?

A

Amides can be prepared by the action of ammonia on a.) acid chlorides and b.) Esters.

57
Q

How may nitrile compounds be formed from halogeno Alkanes?

A

When a halogeno alkane was heated with potassium cyanide dissolved in either ether or propanone nitriles are formed. This is a way of increasing the number of carbon atoms in a chain.

58
Q

How may a nitrile be reduced?

A

LiAlH₄ will reduce a nitrile to an amine.

59
Q

How may the hydrolysis of nitriles and amides be acheived?

A

Nitriles can be hydrolysed to amides and then to acids using acid or alkali as catalysts.

60
Q

How is ethanoic anhydride produced?

A

By heating Sodium ethanoate with ethanoile chloride.

61
Q

What is one use of ethanoic anhydride?

A

It is used in the manufacture of aspirin.

62
Q

How is aspirin produced?

A

First phenol is heated with CO₂ in the presence of NaOH under pressure. The mixture is acidified to produce 2-hydroxybenzoic acid. Reaction of this with ethanoic anhydride gives 2-ethanoyl-oxybenzoic acid also known as aspirin.

63
Q

How are polyesters formed?

A

Polyesters are formed When an esterification takes place with an acid with 2 Carboxyl groups and an alcohol with 2 hydroxyl groups. E.g 1,4-dicarboxylic acid and Ethan-1,2-diol. This is a condensation polymerisation reaction.

CH4 (5 decks)

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