Compounds Containing the Carbonyl Group

HideShow resource information

Aldehydes and Ketones Intro..

They are both carbonyl compounds as they both contain the functional group C=O. Difference is they have their carbonyl groups in different positions.                                                                       Aldehyde, carbonyl group at end of carbon chain     Ketone, carbonyl group in the middle of chain.

.

.

.

Nomenclature:

Adlehydes end in -al --> e.g. 2-ethylpentanal (Ethyl group on 2 carbon)                   

 Ketones end in -one, have to say which carbon the carbonyl group is on -> e.g. 3-methylbutan-2-one

1 of 17

Testing for Aldehydes and Ketones

Aldehydes can be easily oxidised to a carboxylic acid,  but a ketone can't.

They can be easily oxidised to a carboxylic acid because there is a hydrogen attached to the carbonyl group. 

TOLLENS: -Colourless solution of silver nitrate dissolved in aqueous ammonia. If heated in a test tube with an aldehyde a silver mirror is formed.

Colourless ----> Silver

FEHLINGS: -Blue solution of complexed copper (2) ions dissolved in sodium hydroxide. When heated with an aldehyde copper (2) ions are reduced to a brick-red precipitate.

Blue ---> Brick-Red  /       /   

BENEDICTS: Same as Fehlings but the copper (2) ions are dissolved in sodium carbonate instead.

Blue ---> Brick-Red  /       /

2 of 17

Reducing Aldehydes and Ketones

-Primary alcohols can be oxidised to produce aldehydes and carboxylic acids, Secondary alcohols can be oxidised to make Ketones.  ---> using a reducing agent you can reverse these reactions.   NaBH4 (Sodium tetrahydridoborate (3) or Sodium borohydride) is usually the reducing agent used. -But i equations [H] is often used to idicatea hydrogen from the reducing agent.

Reduction of aldehyde into primary alcohol:

.

.

.

Reduction of ketone to a secondary alcohol:

.

.

.

3 of 17

Nucleophilic Addition Reactions

-This is the reaction mechanism for the reduction of aldehydes and ketones back to alcohols.         -A H- ion from the reducing agent acts as a nucleophile and adds on the + carbon atom of a carbonyl group. 

Nucleophilic Addition:

.

.

.

.

.

.

.

-This reaction mechanism can be applied to any Aldehyde or Ketone.

4 of 17

Hydroxynitriles

Hydroxynitriles are... Molecules that contain a hydroxyl group (OH) and a nitrile group (CN)

.

.

Suffix is -Nitrile  and Prefix Hydroxy- :  e.g. 2-Hydroxy-3-methylbutanenitrile.

Producing Hydroxynitriles                                                                                                              Produced by reacting aldehydes or ketones with hydrogen cyanide (HCN) --> Nucleophilic addition.

.

.

.

RISKS:          HCN is an extremely toxic gas, so to reduce the risk KCN is used instead , it is aso toxic but it can be stored more safely

5 of 17

Carboxylic Acids and Esters Intro...

Carboxylic Acids functional group -COOH. Named using -oic acid e.g. 4-hydroxy-butanoic acid

.

.

Dissociation of carboxylic acids: They are weak acids --> only partially dissociate into a carboxylate ion and a H+ ion. Reversable reaction but equilibrium lies to left as not all molecules dissociate.

.

.

Reaction with carbonates: -React with carbonates (CO3^2-) or hydrogencarbonates (HCO3^-) forming a salt, CO2 and Water.       

E.G. 2CH3COOH (aq) + Na2CO3 (s) ---> 2CH3COONa (aq) + H2O (l) + CO2 (g)

6 of 17

Carboxylic Acids and Esters Intro....

Esterification Reactions                                                                                                                       -If you heat a carboxylic acid with an alcohol in the presence of a strong acid catalyst you get an Ester. ----> this is an esterification reaction.

.

.

Naming Esters                                                                                                                                   -Made up of 2 parts, first from the alcohol and the second from carboxylic acid.

1. Look at alkyl group that came from the alcohol - Thats the first part of esters name.                        2. Look at the part from the carboxylic acid and swap the -oic acid for -oate                                       3. Put two parts together  e.g. Methyl Ethanoate  (Methyl from alcohol & Ethanoate from Carbox)

Same rules if chains are branched or if there is a benzene ring (methyl benzoate)                    -Somtimes might be asked to predict which alcohol and carboxylic acid need to form particular ester.  (e.g. 3 carbon chain from acid ---> Propanoic acid. 1 carbon in the alcohol part ---> Methanol)

7 of 17

Useful properties of esters

Esters have properties that make them very useful.

  • Have a sweet smell  --> Varies from gluey sweet in small esters to fruity smells for the larger ones. This makes them useful in perfumes. Food industry uses them in food and drinks
  • Esters are polar liquids-->  Low boiling points, evaporate easily from mixtures . Makes them good solvents in glues and inks.
  • Used as plasticisers --> Added to plastics during polymerisation making plastics more flexible. After time the plasticiser escape and plastic becomes brittle and stiff.
8 of 17

Hydrolysis of Esters

When a substance is split up by water, often really slow so an acid or alkali used to speed it up. Two types of hydrolysis of esters:

ACID HYDROLYSIS: -Splits an ester into an acid and an alcohol.(reverse of esterification)         -Have to reflux the ester with dilute acid (e.g. Hydrochloric or Sulfuric)

.

.

Reversable, need lots of waterto push equilibrium to the right to get lots of product.

BASE HYDROLYSIS: -Reflux ester with a dilute alkali (e.g. NAOH)   -OH- ions from base react with ester ---> Carboxylate ion and an alcohol

.

.

9 of 17

Fats and Oils Intro...

Fats and Oils are esters of glycerol and fatty acids. -Fatty acids are long chain carboxylic acids. They combine with glycerol to make fats and oils.  -Fatty acid can be saturates (no =) or saturated (C=C). Most of a fat or oil is made from fatty acid chains --> giving them their properties.

.

.

.

.

Fats have mainly saturated hydrocarbon chains -- fit neatly together, increasing Van der Waals forces between them. Means they need higher temps to melt them + solid at room temp

Oils have unsaturated hydrocarbon chains -- Chains bent + don't pack together, easier to melt and liquid at room temp as they have weaker Van der Waals

10 of 17

Hydrolysis of Fats and Oils

Hydrolyse Fats and Oils by heating with Sodium hydroxide ---> Base Hydrolysis. 

OH- Ions from NaOH react with fat/oil to form a carboxylate ion and an alcohol. Alcohol formed is glycerol (propane-1,2,3-triol)

Carboxylate ions react with Na+ ions from NaOH to form a sodium salt ---> SOAP

.

.

.

.

Can convert sodium salt back into a long chain carboxylic acid by adding an acid (e.g. HCl). H+ ions from acid displace the Na+ ions in the salt to form a carboxylic acid :

CH3(CH2)16COO-Na+  H+ ----> CH3(CH2)16COOH  +  Na+                                                        Sodium Salt (Soap)                              Fatty Acid

11 of 17

Biodiesel

Vegetable oils make good vehicle fuels, can't burn them directly in an engine. Oil must be converted into BIODIESEL.                                                                                                                          Involves reacting them with methanol, using a strong alkali (e.g. KOH or NaOH) as a catalyst.

You get a mixture of methyl esters of fatty fatty acids (mix of methyl esters of long chain carboxylic acids)

.

.

.

.

.

Can be thought of a carbon neutral, as crops grow they absorb same amount of CO2 as they release when burnt. Energy needed to grow them which needs fossil fuels so not so carbon neutral.

12 of 17

Acylation

Acyl Chlorides functional group COCL.  General formula = C(n)H(2n-1)OCL.                              Name ends in -oyl chloride  e.g. 2,3dimethylpentanoyl chloride.

REACTION WITH WATER: Vigorously with cold water -----> Carboxylic Acid

.

REACTION WITH ALCOHOLS: Vigorous ----> produce an ester

.

REACTION WITH AMMONIA: vigorous ---> produce an amide.

.

REACTION WITH AMINES: Vigorous ---> produce N-substituted amide.

.

13 of 17

Nucleophilic addition-elemination

All the reactions with acyl chlorides are nucleophilic addition-elimination. They have two step:         1. The Nucleophile adds onto the acyl chloride displacing a Cl- ion.                                                    2. The Cl- ion steals a hydrogen ion from the nucleophile and HCl is eliminated.

STEP 1: Both Cl and O atom draw in electrons towards themselves, so C has slight + charge --> easily attacked by nucleophiles

.

.

STEP 2:

.

.

Change in nucleophile for each reaction: water (H20:), alcohol (e.g.CH3O:H), ammonia (N:H3) or an amine (e.g. CH3N:H2)

14 of 17

Acid Anhydrides

Acid Anhydride is made from 2 identical carboxylic acid molecules. Joined together via oxygen with carbonyl groups on either. Oxygen come from OH group of one of the carboxylic acids, other OH and spare H released as water:

.

.

.

.

Naming: take away acid from carboxilic acid and add -anhydride. methanoic acid --> methanoic anhydride

.

.

15 of 17

Reactions with anhydrides

Need to know reactions with water, alcohol, ammonia and amines.  they are almost the same as the acyl chloride ones - reactions are just less vigorous and carboxylic acid is formed instead of HCl

E.G.

WATER: ---> Carboxylic acid

.

ALCOHOL: ---> Ester

.

AMMONIA: ---> Amide

.

AMINES: ---> N-Substituted amide

.

16 of 17

Manufacture of Aspirin

Aspirin is an ester.   Made by reacting salicylic acid with either ethanoic anhyride or ethanoyl chloride.

ETHANOIC ANHYDRIDE: used in industry as it is cheaper than ethanoyl chloride. It is also safer to use than ethanoyl chloride, reacts slower and doesn't produce dangerous hydrogen chloride fumes.

.

.

.

17 of 17

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Carbonyl Compounds resources »