Author: J R Reid Level 3: Organic Reactions Part I Aldehydes Ketones Haloalkanes Amines

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

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 (Cr 2 O 7 2- /H + ) Acidified permanganate (MnO 4 - /H + ) Aldehydes - Production

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)

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 Ketones - Production

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 (Cu 2+ ) turns red/orange (Cu 2 O) when boiled with aldehydes (but not with alcohols) Tollen’s (silver mirror) test: This colourless (Ag(NH 3 ) 2 + ) solution turns the test tube silver (Ag) when aldehydes are present    

Haloalkanes Can be classified as primary, secondary and tertiary just like alcohols.

Haloalkanes Volatile, polar molecules but only slightly soluble in water as no hydrogen bonding can occur (except fluorocarbons) Melting points higher than alkanes Examples: teflon – non stick frying pans, chloroform – CHCl 3 – used as a solvent and in movies as an anaesthetic, CCl 4 – solvent used in dry- cleaning fluid until it was found to cause liver damage

Haloalkane preparation Prepared by : substitution of an alcohol by thionyl chloride Addition of HX to an alkene Substitution of an alkane in UV light with a halogen eg: Br 2

Haloalkane reactions Nucleophilic substitution: A nucleophile is any species that loves nuclei – or is attracted to a positive charge. Nucleophiles are species carrying a lone pair of electrons or a negative charge: eg: H 2 O, OH - or NH 3 The C-X bond is polar is haloalkanes and has a slightly positive charge. The positive carbon is vulnerable to attack by a nucleophile

3 types of nucleophilic substitution reactions 1. OH - (aq) forms an alcohol with a primary or secondary haloalkane 2. H 2 O (l) forms an alcohol with a tertiary haloalkane 3. NH 3(alc) forms an amine with a haloalkane. Note (alc) means dissolved in alcohol. Why not water?

Chloroalkane elimination reactions Haloalkanes can form alkenes by reacting with KOH (alc) or NaOH (alc). Why alcoholic again solvent again? Reverse of Markovnikovs rule applies.

Questions: Write a balanced equation for the reaction of bromoethane with aqueous potassium hydroxide Write a balanced equation for the reaction between 2-iodobutane and alcoholic ammonia Write an equation for the reaction between 2-methyl butan-2-ol and alcoholic potassium hydroxide.

Properties of Esters Have pleasant fruity smells and occur naturally in plants. Used in manufacture of everyday items such as flavouring agents, perfumes. Have the general formula R-COOR’. Polar molecules but no hydrogen bonding Colourless volatile liquids Insoluble in water

Naming: Part that comes from the alcohol is an alkyl group, part from the acid is –anoate on the end. Eg: Ethanol and propanoic acid make ethyl propanoate

Name the ester made from: 1. Propanoic acid and butanol 2. Ethanoic acid and methanol 3. Butanol and methanoic acid 4. Decanol and hexanoic acid 5. This one 

Preparation of an ester Condensation reaction of a carboxylic acid with an alcohol, using concentrated sulfuric acid as a catalyst and dehydrating agent. Reaction carried out by reflux.

Chemical Reactions Hydrolysis (split with water) with dilute acid to form the original acid and alcohol Hydrolysis with a basic solution eg: NaOH to form the salt of the acid and the alcohol. Used in soap manufacture. React with ammonia or amines to form an amide (slow reaction)

Making soap Soaps are the sodium salts of fatty acids (long chain acids). These salts are soluble in water as they are ionised, but they have a carbon chain end that is soluble in fats and oils. This allows them to dissolve and break down dirt. Sodium laurate is the name of the soap molecule made from coconut oil made by boiling it with sodium hydroxide.

See page 97 for an example

Amines - Introduction 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 and haloalkanes Identify the trend… Amines are bases (like ammonia) and smell like fish. Most amines are liquids but aminomethane and aminoethane boil below 20ºC Primary SecondaryTertiary

Amines – Naming and Source The name of the primary amine comes from the length of the alkyl (alkane) chain attached to the –NH 2. For example, an amine with a propane chain attached is called aminopropane (CH 3 CH 2 CH 2 NH 2 ) Primary amines are made using the nucleophilic substitution of haloalkanes (as we saw earlier)

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 Cu 2+ (just like ammonia) CH 3 CH 2 NH 2 + HCl  CH 3 CH 2 NH 3 Cl CH 3 CH 2 NH 2 + H 2 O  CH 3 CH 2 NH OH - 4CH 3 CH 2 NH 2 + Cu 2+  Cu  CH 3 CH 2 NH 3 ) 2+

Nucleophilic Substitution Of halolakanes….the primary amine can act as a nucleophile and displace the halogen atom in a haloalkane. A secondary amine is formed