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AS Chemistry > WM - Reactions of alcohols > Flashcards

WM - Reactions of alcohols Flashcards

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1
Q

What are the 3 types of alcohols?

A

Primary, secondary and tertiary.

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2
Q

How many types of alcohols are there?

A

3

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3
Q

What is a primary alcohol?

A

An alcohol where the OH is on a carbon with 1 alkyl attached so has 2 hydrogen atoms attached.

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4
Q

What is a secondary alcohol?

A

An alcohol where the OH is on a carbon with 2 alkyl groups attached so only has 1 carbon atom attached.

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5
Q

What is a tertiary alcohol?

A

An alcohol where the OH is on a carbon atom with 3 alkyl groups attached so that there are no hydrogens attached to the same carbon as the OH.

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6
Q

What are the reaction conditions for oxidising an alcohol into a carbonyl compound (aldehydes and ketones) and carboxylic acids?

A

Acidified potassium dichromate(VI) and heat under reflux.

Cr2O7 2- / H+ and h+r.

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7
Q

What are primary alcohols oxidised to?

A

Aldehydes and then to carboxylic acids.

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8
Q

What are secondary alcohols oxidised to?

A

Ketones only.

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9
Q

What are tertiary alcohols oxidised to?

A

They aren’t oxidised.

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10
Q

What types of alcohols are oxidised?

A

Primary and secondary but not tertiary.

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11
Q

When alcohols are oxidised using dichromate(VI) what is the colour change and why?

A

The orange dichromate(VI) ion is reduced to the green chromium(III) ion, Cr3+.

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12
Q

How can the reaction conditions be altered to control how far a primary alcohol is oxidised?

A

Gently heat the alcohol with the dichromate(VI) solution and acid in a flask to produce an aldehyde. To just get the aldehyde, the oxidising solution needs to be removed as soon as the aldehyde is formed. This can be done by using distilling apparatus where the aldehyde (which boils at a lower temp than the alcohol) evaporates and is distilled off immediately.

To produce a carboxylic acid, the alcohol has to be oxidised vigorously - mix with excess oxidising agent and h+r (meaning you increase the temp of the organic reaction to boiling point without losing anything as things that try to escape condense back down in a condenser).

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13
Q

How can secondary alcohols be oxidised into ketones?

A

By refluxing a secondary alcohol with acidified dichromate(VI).

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14
Q

What does [O] mean in the oxidation of alcohols?

A

[O] = Oxidising agent.

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15
Q

What can alcohols be dehydrated to form?

A

Alkenes.

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16
Q

What is the functional group in the alcohol homologous series?

A

The hydroxyl group, -OH.

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17
Q

What does whether an alcohol is primary, secondary or tertiary depend on?

A

Which carbon atom the -OH group is bonded to.

18
Q

What is the simple way to oxidise alcohols?

A

Burn them.

19
Q

Alcohols can be dehydrated to form what?

A

Alkenes.

20
Q

Alkenes can be formed from the dehydration of what?

A

Alcohols.

21
Q

How can you make ethene from ethanol?

A

By eliminating water from ethanol in a dehydration reaction.

22
Q

What is the equation for making ethene from ethanol using a dehydration reaction?

A

C2H5OH –> CH2=CH2 + H2O

23
Q

What happens in an elimination reaction?

A

A small group of atoms break away from a larger molecule. This small group is not replaced by anything else.

24
Q

What are the 2 methods of dehydrating ethanol to form ethene? (Dehydrating alcohols to form alkenes.)

A

1) Ethanol vapour is passed over a hot catalyst of pumice stone or aluminium oxide, Al2O3 - the catalyst provides a large surface area for the reaction.
2) You can reflux ethanol with excess concentrated sulfuric acid at 170oC. The ethene produced is then collected over water.

25
Q

What does the catalyst (pumice stone or aluminium oxide, Al2O3) provide in the dehydration of an alcohol to an alkene?

A

A large surface area for the reaction.

26
Q

Explain what happens in the dehydration of ethanol to ethene using sulfuric acid

A

The concentrated sulfuric acid acts as a dehydrating agent in the elimination reaction.

  • The hydroxyl group will bond to the H+ ion from the strong acid. So the alcohol is protonated, giving the oxygen atom a positive charge.
  • The positively charged oxygen will pull electrons away from the neighbouring carbon, and water will ‘fall off’, creating an unstable carbocation intermediate.
  • The carbocation loses H+ and the alkene is formed (alongside water and a H+ ion).
27
Q

What forms when alcohols react with carboxylic acids?

A

Esters.

28
Q

How do alcohols form esters?

A

When an alcohol reacts with a carboxylic acid, it forms an ester.

29
Q

What has to be present for a carboxylic to react with an alcohol to form an ester?

A

You have to heat a carboxylic acid with an alcohol in the presence of an acid catalyst.

30
Q

What type of reaction is it when a CA and alcohol react to form an ester?

A

An esterification reaction.

31
Q

What is an esterification reaction?

A

When a CA and alcohol react to form an ester.

When an ester is formed by a reaction.

32
Q

What are the acid catalysts used in the esterification reaction between a CA and an alcohol?

A

Concentrated sulfuric or hydrochloric acid.

33
Q

Apart from an esterification reaction, what type of reaction is it when a CA and alcohol react to form an ester? Why?

A

A condensation reaction as it releases water.

34
Q

What can alcohols react with to form esters?

A

Either carboxylic acids or acid anhydrides.

35
Q

What do you get if you react an alcohol with an acid anhydride?

A

An ester and a carboxylic acid.

36
Q

In what types of reaction can alcohols react with compounds containing halide ions (such as HCl)?

A

A substitution reaction.

37
Q

What can alcohols react with in a substitution reaction?

A

Compounds containing halide ions (such as HCl).

38
Q

What happens in the substitution reaction between an alcohol and a compound containing a halide ion?

A

The hydroxyl (-OH) group is replaced by the halide, so the alcohol is transformed into a haloalkane.

39
Q

What is formed in the substitution reaction between an alcohol and a compound containing a halide ion?

A

A haloalkane.

40
Q

How would you make 2-chloro-2-methylpropane from an alcohol and a compound containing a halide ion?

A

Shake 2-methylpropan-2-ol (a tertiary alcohol) with hydrochloric acid.

AS Chemistry (44 decks)

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