Alcohols

How are alcohols are produced?

• Produced industrially by hydration of alkenes in the presence of an acid catalyst

How is ethanol produced and what’s the formula?

• By the fermentation of glucose

• Glucose→Ethanol+Carbon dioxide

• C6H12O6 → C2H5OH+CO2

How can ethanol produced by fermentation be seperated?

• Fraction distillation

When the ethanol is separated what can it be used as?

• Biofuel

Define biofuel

• A fuel derived from organic matter like plants

• Can be considered a renewable source of energy

What are the conditions needed for fermentation?

• Temperatures around 30-40 degrees

• Yeast (which produces an enzyme)

• No air (presence of oxygen would lead to aerobic respiration instead of fermentation)

Explain why the optimum temperature for fermentation is 38 degrees

• At lower temperatures the reaction is too slow

• At high temperatures the enzymes will denature

Why is fermentation done in the absence of air

• Oxygen can oxidise the ethanol

• producing ethanoic acid (Vinegar) instead

Advantages of fermentation

• Sugar (glucose) is a renewable source

• Production uses cheap equipment

Disadvantages of fermentation

• Uses up land that could be used for food

• Batch process is slow and raises production costs

• Ethanol made is not pure and needs purifying by fractional distillation

Why is a batch process used in fermentation?

• Allows for a high ethanol yield

• Fermentation stops when ethanol concentration becomes toxic to yeast

• Batch process ensures fermentation occurs for an optimal time before the yeast becomes inactive

Define the term carbon neutral

• An activity that has no net carbon emissions to the atmosphere

Why is the production of ethanol considered carbon neutral

• Its a biofuel formed from fermentation

• Any carbon dioxide given off when the biofuel is burned would have been extracted from the air via photosynthesis by the plants grown

• Meaning there is no net carbon emission

Equations showing that the production of ethanol is carbon neutral

Removal of CO2 by photosynthesis

• 6CO2 + 6H2O → C6H12O6 + 6o2

Production of CO2 by fermentation and combustion

• C6H1206 → C2H5OH + 2CO2 (fermentation)

• C2H5OH + 6O2 → 4CO2 + 6H2O (Combustion)

For every 6 molecules of carbon dioxide absorbed, 6 molecules of carbon dioxide are emitted

Why may the production of ethanol not be considered carbon neutral?

• The equations that show it being a carbon neutral process do not take into consideration

  • Energy required to fractionally distil the ethanol

  • Energy required to irrigate( water) the plants.- Water pumps are powered by fossil fuels

What does dehydrating an alcohol do?

• Removes a water molecule to form an alkene and water

Conditions for dehydration

• Alcohol is heated under reflux (heating a reaction without losing the volatile substances)

• Heated in the presence of concentrated sulfuric acid or phosphoric (v) acid

• Acid act as a catalyst

Dehydration of alcohols is an example of an…

• Elimination reaction

Products of dehydration of alcohols

• Alkene

• H2o

First stage of dehydration of alcohols

• Lone pair of electrons on oxygen atom will be attracted to the positive hydrogen ion from the acid catalyst

• Lone pair forms a covalent bond with the hydrogen ion

• Forming an intermediate molecule with a positive oxygen atom

Second stage of dehydration of alcohols

• Pair of electrons in the covalent bond between the C-O move onto the oxygen

• This releases the molecule of water to be released

• At the same time the pair of electrons between a C-H bond move between 2 carbon atoms

• Hydrogen is now released as H⁺ (regenerating the acid catalyst

What can alkenes produced from dehydration of alcohols be used for ?

• used to produce addition polymers (without using monomers derived from crude oil)

Describe a primary alcohol

• Carbon atom bonded to the hydroxyl group (OH) is bonded to one more carbon atom