Level 3: Organics Part I

1. Level 3:Organics Part I Aldehydes Ketones Amines

2. Aldehydes - Introduction • Aldehydes are very similar to carboxylic acids in structure (but they are missing the –OH) • Their names have ‘–al’ as a suffix e.g. methanal, ethanal… • The smaller aldehydes are liquids (except for methanal – a gas) because of their polar bonds • The smaller molecules (below hexanal) are soluble in water • Methanal is a gas that is dissolved in water to create a disinfectant, and to preserve biological specimens in jars

3. Aldehydes - Production • As we saw in the extension of level 2 organics section, aldehydes are made if you partially oxidise a primary alcohol: • This means that aldehydes can be oxidised further to create carboxylic acids • Remember: • A thing that can be oxidised is called a reducing agent (because it reduces someone else) • A thing that can be reduced is called an oxidising agent (because it can reduce someone else) • Common oxidising agents (or oxidants) used to create aldehydes are: • Acidified dichromate (Cr2O72-/H+) • Acidified permanganate (MnO4-/H+)

4. Ketones - Introduction • Ketones are very similar to aldehydes except the double bond is not at the end of a carbon chain • Their names have ‘–one’ as a suffix e.g. propanone, butanone… • The smaller ketones are the same as aldehydes. They are liquids because of their polar bonding • The smaller molecules (below hexanone) are soluble in water • Ketones are good solvents and are often used for things like nail polish remover (propanone) or plastic model glue (butanone)

5. Ketones - Production • Ketones can be made by oxidising secondary alcohols: • Note: Tertiary alcohols cannot be oxidised at all. The –OH can’t form double bonds with the carbon that it is attached to because that carbon is already bonded to three other carbons

6. Aldehydes and Ketones – The Tests • Aldehydes can be oxidised a little further while ketones can not. This is the basis for the various tests for difference between these two chemicals: • Acidified permanganate/dichromate – aldehydes will be oxidised and change the colour of these two chemicals. BUT the colour will also change if we have any primary or secondary alcohols present because they can be oxidised also • Benedict’s solution: This blue solution (Cu2+) turns red/orange (Cu2O) when boiled with aldehydes (but not with alcohols) • Tollen’s (silver mirror) test: This colourless (Ag(NH3)2+) solution turns the test tube silver (Ag) when aldehydes are present ® ® ® ®

7. Amines - Introduction Secondary Tertiary Primary • Amines are organic compounds that contain nitrogen in their structure (but no oxygen) • There are three types of amines: primary, secondary and tertiary. Unfortunately we use these words slightly differently than we do with alcohols: Identify the trend… • Amines are bases (like ammonia) and smell like fish. • Most amines liquids but aminomethane and aminoethane boil below 20ºC

8. Amines – Naming and Source • We only look at primary amines this year. This makes life easier when it comes to things like naming and making amines: • The name of the primary amine comes from the length of the alkyl (alkane) chain attached to the –NH2. For example, an amine with a propane chain attached is called aminopropane (CH3CH2CH2NH2) • Primary amines are made using the nucleophilic substitution of haloalkanes (as we saw earlier)

9. Amines - Reactions • Neutralisation • Because amines are bases they will neutralise acids to create salts (just like ammonia) • Ionisation • Amines dissolve in water to create ions (just like ammonia) • Complex ion formation • Amines will form complex ions with Cu2+ (just like ammonia it makes a dark blue solution) CH3CH2NH2 + HCl ® CH3CH2NH3Cl CH3CH2NH2 + H2O ® CH3CH2NH3+ + OH- 4CH3CH2NH3 + Cu2+® Cu(CH3CH2NH3)42+