Topic 7b: Organic Compounds

What are alkenes

• Alkenes are unsaturated hydrocarbons with a double carbon-carbon bond.

(alkene molecules are unsaturated because they contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms)

What is the smallest alkene

Ethene, because it’s the lowest number with 2 carbons

Why are alkenes more reactive than alkanes

• They have a double bond which can open up to become a single bond, allowing the two carbon atoms to bond with other atoms

• But not as good at combustion

Combustion of alkenes

Alkenes react with oxygen in combustion reactions in the same way as other hydrocarbons to produce water and carbon dioxide, but they burn in air with smoky flames because of incomplete combustion. Carbon dioxide and water are still produced, but you can also get carbon and the poisonous gas carbon monoxide

Testing for alkenes

• When orange bromine water is added to an alkane, no reaction will happen and it’ll stay bright orange

• If its’s added to an alkene, a reaction occurs and the bromine water turns colourless

Alkene reactions

In addition reactions the C=C double bond will open up to leave a C-C single bond and a new atom is added to each carbon

Hydrogenation:

• The reaction takes place between the alkene and hydrogen when in the presence of a catalyst

For example, the reaction of ethene and hydrogen forms ethane:

Ethene + Hydrogen → Ethane

• So - propene forms propane, butene forms butane, and pentene forms pentane

Hydration (+ water):

• When alkenes react with steam in the presence of a catalyst, water is added across the double bond, and an alcohol is formed. For example:

Ethene + Steam → Ethanol

Butene + Steam→ Butanol

Propene + Steam → Propanal

Halogens:

• When alkenes react with halogens such as bromine, chlorine, and iodine. For example:

Ethene + Bromine → Dibromoethane

Butene + Bromine → Dibromobutane

What are alcohols

• They are organic bases (PH above 7)

• Functional group of OH

• Named by adding the suffix - OL

How are alcohols made

via hydration of alkenes

Uses of alcohols

• Disinfectant

• Cleaning

• Drinking (ethanol only)

• Fuel

Ethanol production (Hydration)

Positives -

• 100% ethanol concentration

• 95% yield

• Continous process

• Quick

Negatives -

• Getting more expensive

• Requires high temp and catalyst

• Specialist equipment needed

Ethanol production (Fermentation)

Positives -

• Yeast as a catalyst

• Renewable

• 20% yield max (yeast denatures)

• 35-40 degrees

• No specialist equipment needed

Negatives -

• Batch process

• Slow

• Requires further processing to increase ethanol concentration → distillation

Combustion of alcohols

Alcohols undergo combustion to form carbon dioxide and water

What happens when alcohol react with sodium and with an oxidising agent

Reaction with sodium:

• Alcohols react with sodium metal to produce hydrogen gas and a metal salt

Oxidation of alcohols:

• Alcohols undergo oxidation to produce carboxylic acids, an organic acid

What are carboxylic acids

• Organic weak acids

• Named by adding - oic acid