Alcohols Final

What are two ways to produce alcohols?

• Hydration of Alkenes

• Fermentation of glucose

What conditions are required for the hydration of alkenes?

steam @

300 C

60atm

What catalyst is required for the hydration of alkenes?

Concentrated H2SO4

What is the equation for the hydration of Alkenes?

Draw out the mechanism for hydration of alkenes (ethene)

How does hydration compare with fermentation?

• continuous

• Faster

• Produces pure ethanol

What conditions are required for the fermentation of glucose?

• yeast

• 25 to 42 C

• absence of air

Why is the fermentation of glucose carried out in the absence of of air?

• Prevent oxidation of alcohol

Why is the fermentation of glucose carried out in low temperatures?

• Higher temperatures will denature enzymes.

What are the 3 features of the fermentation of glucose?

• is a batch process

• slower than hydration

• uses a renewable source (glucose)

What happens to ethanol for industrial use in order for it to be used as a biofuel?

• ethanol is separated by fractional distillation

What is a biofuel?

A fuel obtained from a renewable biological (plant) source.

What does carbon neutral mean?

An activity in which there is no net carbon dioxide emissions to the atmosphere.

Argument FOR ethanol produced by fermentation is a carbon-neutral fuel

• Glucose is made by green plants by photosynthesis

  • Six molecules of carbon dioxide are absorbed

  • Removing carbon dioxide from the atmosphere

• During fermentation, carbon dioxide returned to atmosphere

  • Two molecules of carbon dioxide released

• During the combustion of ethanol

  • four molecules of carbon dioxide are released

  • Overall six molecules of carbon dioxide are absorbed and released

Argument AGAINST ethanol produced by fermentation is a carbon-neutral fuel

• other carbon costs are associated with distribution and production

• energy needed to transport the crops and fuel to power the process

Environmental impacts of fermentation of glucose

• deforestation

• Sacrifice of land that could be used for food, loss of habitats

Photosynthesis equation

Equation for fermentation

Equation for the combustion of ethanol

What is a primary alcohol?

• There are two more hydrogen atoms attached to the carbon atom attached to the OH group.

What is a secondary alcohol?

There is one hydrogen atom attached to the carbon atom attached to the OH group.

What is a tertiary alcohol?

There are no hydrogen atoms attached to the carbon atom attached to the OH group.

What is the oxidising agent used in the oxidation of alcohols?

Acidified potassium dichromate VI

How is acidified potassium dischromate VI acidified?

• using acidified dilute sulphuric acid

What is produced when primary alcohols are oxidised?

Aldehydes

What colour change happens when primary alcohols are oxidised?

Orange to green

How do you prevent further oxidation from taking place during the oxidation of a primary alcohol?

The product is distilled off.

What symbol is used to represent the oxidising agent in the oxidation of alcohols?

[O]

Equation for the oxidation of a primary alcohol

How can you recognise the oxidation of primary alcohols?

• it involves the loss of hydrogen

What is the formula for acidified potassium dichromate VI?

K₂Cr₂O₇

What is the equation for the reduction that takes place as the primary alcohol is oxidised?

Cr2O7(2-) reduced to 2Cr(3+)

How do you produce a Carboxylic acid from an alcohol?

• Reflux with vertical condenser connected to a pear shaped flask

• Water goes in at bottom

• No gaps between flask and condenser

• Excess acidified potassium dichromate (VI)

How does a reflux reaction work?

• reactants are heated for a long period without loss

• Vapour formed which escapes the liquid mixture is changed back into liquid in the condenser and returned to the liquid mixture

• Any alcohol and aldehyde that initially evaporates can then be oxidised.

What colour change happens when a Carboxylic acid is produced from an alcohol?

Orange to green

Equation of the formation of a Carboxylic acid from the reaction mixture of the oxidation of a primary alcohol.

What is produced when secondary alcohols are oxidised?

Ketones

What is an indicator of the secondary alcohols produce when being oxidised?

• it loses a hydrogen in forming a ketone.

What is special about the reaction of acidified potassium dichromate (VI) with a tertiary alcohol?

• The tertiary alcohol is not oxidised.

• The carbon atom bonded to the OH group has no hydrogen atoms available for oxidation.

What mechanism do alcohols undergo?

Elimination

What conditions are required for elimination?

• heating to 180 C

• Concentrated sulphuric acid

What is special about alkenes produced by elimination?

• alkenes produced by this method can be used to produce addition polymers without using monomers obtained from crude oil.

How does elimination take place?

• The OH is protonated by H+ from the concentrated sulphuric acid.

• A molecule of water is lost.

What is the sulphuric acid acting as in elimination reaction?

• a catalyst

Example of an elimination reaction with alcohols

How many products will you get from an elimination reaction with a secondary alcohols produce when with a minimum of four carbon atoms?

• three products

When explaining where the Hydrogens are are lost from, when talking about different products formed, what should you always do?

• number the carbons to show where the hydrogens are lost from.

All the different products when butan-2-ol undergoes elimination:

What is Tollens reagent?

[Ag(NH3)2]+

What is required for a reaction with Tollens’ reagent and an aldehyde?

Heat

What happens when an aldehyde is reacted with Tollens’ reagent?

• silver mirror formed

• Ag+ ions reduced to Ag

• Aldehyde oxidised to a Carboxylic acid

Half Equation for Aldehyde reacting with Tollens’ reagent.

What happens when Tollens’ reagent reacts with a ketone?

• no change

What happens when Fehling’s solution is reacted with an aldehyde?

• blue solution goes to to red precipitate

• Cu2+ reduced to Cu1+

• aldehyde oxidised to Carboxylic acid

What happens when Fehling’s solution reacts with a ketone?

• no change

What is the test for a Carboxylic acid?

• add sodium carbonate

• Bubbles of carbon dioxide are produced

What precaution must you take when handling or reacting with alcohols?

• they are flammable

• Keep away from naked flames

NOTE: EXAM Q on distinguishing between compounds using a minimum number of tests of each compound.