Unit 4 The carbonyl group

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How can compounds containing the carbonyl group be formed?
from the oxidisation of alcohols
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What is a carbonyl group?
a C=O
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What oxidising agent does the formation of the carbonyl group require?
acidified Potassium permanganate or acidified potassium dichromate
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How are primary alcohols oxidised?
heated in a condenser and distilled off, then boiled in an excess of the oxidising agent under reflux
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Can secondary alcohols be oxidised?
Yes, to ketones
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Can primary alcohols be oxidised?
yes, to aldehydes and further to carboxylic acids
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Can tertiary alcohols be oxidised?
no
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Why do alcohols have higher boiling points than aldehydes and ketones?
the hydrogen bonding in the OH bond is stronger than any other intermolecular forces
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Why do carboxylic acids have an even higher boiling point than alcohols?
the C=O group withdraws more electons from the OH oxygen incresing the polarity of the bond and the strength of the hydrogen bonding
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What can you use to distinguish between aldehydes and ketones?
Tollens reagent, which will create a silver mirror on aldehydes, but there will be no visable change on ketones
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How are aldehydes and ketones reduced?
by ydride ions attacking the C in the presence of H2/Ni catalyst
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How does hydrogen cyanide react with an aldehyde or ketone?
using a nucleophillic addition mechanism to produce a racemic mixture of hydroxyalkannitrile
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Why is pottassium cyanide typically used instead of hydrogen cyanide?
Hydrogen cyanide is highly toxic and pottassium cyanide will produce the same product
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What reactions can nitriles undergo?
hydrolysed to a carboxilic acid in the presence of water and an acid catalyst, and reduced to a primary amine by catalytic hydrogenation with H2 and Ni
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Why do carboxylic acids only partially dissociate in soluton?
they are weak acids, so this produces a low concentration of H3O+ ions
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How are esters formed?
in the reaction between ccarboxylic acids and alcohols in the presence of a strong acid catalyst. This is called esterification
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What is the structure of an ester?
a carboxylic acid with the hydrogen replaced by the alkyl group from the alcohol
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Why can't esters hydrogen bond?
they have no free OH group
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What properties do esters have?
the are immiscible with water, volatile and have a lower melting/boiling point than carboxylic acids
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What are esters used for?
solvents eg. nail varnish, Plasticisers and food flavourings
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How are esters hydrolysed and what to?
to an alcohol and a carboxylate salt using excess aqueous NaOH and heating, naturally occuring esters (oils and fats) can be hydrolysed to soaps and glycerol
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What are soaps?
long chain fatty acids formed from saponification which is the hydrolysis of fats and oils
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How can acid cholrides be synthesised?
from carboxylic acids using PCL3: R-COOH+PCL5 -> R-COCl + PCl2O +HCl
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Do acid chlorides and acid anhydrides undergo acylation reactions?
yes, with a nucleophilic addition-elimination mechanism
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What are the main acylation reactions of acid chlorides?
water->carboxic, alcohol->ester, ammonia->amide, Primary amine->N-substituted amide
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What is produced in an acid anhydride reaction?
a carboxylic acid rather than HCl and alkanoate salt rather than a chloride salt
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How is the acylation reaction used in the formation of aspirin?
in the conversion of salicylic acid into aspirin. The hydroxyl group is acylated with ethanoate anhydride
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How can salicylic acid be formed?
the reaction of phenol with CO2
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Why are acid anhydrides used rather than acid chlorides in industry?
they are cheaper, COOH is formed rather HCl which is hard and expensive to deal with and they react more slowly so the reaction is easier to control
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Other cards in this set

Card 2

Front

What is a carbonyl group?

Back

a C=O

Card 3

Front

What oxidising agent does the formation of the carbonyl group require?

Back

Preview of the front of card 3

Card 4

Front

How are primary alcohols oxidised?

Back

Preview of the front of card 4

Card 5

Front

Can secondary alcohols be oxidised?

Back

Preview of the front of card 5
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