Alcohols

What is the general formula of an alcohol

C_nH_2N+1OH

Nomencalture for alcohols (How do you name alcohols)

Alcohols are named using the IUPAC system by identifying the longest carbon chain containing the hydroxyl (-OH) group. The suffix '-ol' is added to the name of the corresponding alkane. Number the carbon chain to assign the lowest possible number to the hydroxyl group. If there are multiple -OH groups, use prefixes like 'di-' or 'tri-' to indicate their quantity.

Alcohols (primary, secondary and tertiary) Image

Positional isomer for alcohols (image)

What are 2 methods for producing ethanol

Fermentation and the hydration of ethene

Fermentation balanced symbol equation

C₆H₁₂O₆ (aq) → 2C₂H₅OH + 2CO₂

Glucose solution → ethanol + carbon dioxide

What are the conditions of fermentation

35^oc - 40^oc (to not denature enyzme) Anaerobic (absence of O₂ to prevent oxidation Aqueous) pressure of 100KPa

Economic and enviromental advantages of of fermentation

Economic: Low equipment and running costs, limited fossil fuels burned

Environmental: Renewable resources, effectively carbon neutral

Economic disadvantages of fermentation ( The environmental disadvantage is the same as the economic)

Slow batch process low purity/yield (15%) takes up a large are of land to grow crops which could be used to grow crops for food → increase in food prices.

How do you industrially produce ethanol

Hydration of ethene (addition of water)

C₂H₄(g) +H₂O → CH₃CH₂OH(g)

What are the conditions for the hydration of ethene to produce ethanol

300^oc 6500KPa pressure, concentrated H₃PO₄ (Phosphoric Acid) or concentrated H₂SO₄ (Sulfuric acid)

Economic and environmental advantages of the Hydration of ethene

Economic: High purity/ yield (99%). Fast and continuous

Land not required to grow large amounts of crops so it can be used for food.

Economic and environmental disadvantages of the hydration of ethene

Environmental: Non-renewable resources large quantities of fossil fuels burned → Global warming

Economic: High equipment and running costs.

When ethanol is produced by fermentation what is it called?

A bio fuel (Similar to vegetable oils which are grown and converted into bio-diesel.)

What is a bio fuel

A biofuel is a renewable energy source derived from organic materials, such as plants and waste.

Advantages of biofuel use

They are considered “Carbon neutral” as the amount of CO₂ taken in during photosynthesis equals the amount of CO₂ released during fermentation and combustion.

They are renewable resources so are sustainable, only release CO₂ and H₂O when combusted and no sulfur impurities.

Disadvantages of biofuel use

Land used to grow crops for fuel and not for food which could lead to food shortage and prices increases.

Need to convert car engines to run on a high concentration of ethanol.

Deforestation to make room to grow crops for fuel. Fertilisers used on crops can polute waterways and release nitrous oxide.

Is ethanol a carbon neutral biofuel?

During photosynthesis: 6H₂O + 6CO₂ → C₆H₁₂O₆ + 6O₂ (6 moles of CO₂ taken in)

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

2C₂H₅OH + 6O₂ → 4CO₂ + 6H₂O (6 moles CO₂ released)

However fossil fuels are burned to power machinery to harvest crops, refine and transport these biofuel. These will release extra CO₂ so it is not completely carbon neutral

How do you differ between different classes of alcohols (Primary etc)

Using acidified potassium dichromate, alcohols undergo oxidation reactions on heating.

What does a primary alcohol oxidise to?

It oxidises to an aldehyde then to a carboxylic acid

What does a secondary alcohol oxidise to

A ketone

What does a tertiary alcohol oxidise to

Do not oxidise → no hydrogen bodned directly to carbon so no oxidation

What does [O] represent?

Oxygen from oxidising agent

Example of making an aldehyde from an alcohol

Function group = COH

Example of how a carboxylic acid is made from an aldehyde and what condition is needed for this to occur

(It needs to be in reflux condition)

What happens when an alcohol reacts with an aldehyde in reflux conditions?

It is converted straight to a carboxylic acid

What colour change happens when an alcohol goes to an aldehyde or when an aldehyde goes to a carboxylic acid?

Orange → green colour chnage

Example of making a ketone from a secondary alcohol

No second oxidation occurs.

Why does the orange to green colour change occur

When a primary or secondary alcohol oxidses Cr₂O₇^2- (orange) → Cr³⁺ (green)

Balanced symbol equation for potassium dichromate → Chromium

Cr₂O₇^2- + 6e^- + 14H⁺ → 2Cr³⁺ +7H₂O

What are the 2 mild oxidising reagent thatr eact with aldehydes?

They are known as fehling solution and tollens reagent.

How is tollens reagent made?

It is made by combinding AgNO₃ with excess aqueous NH₃ . On warming, an aldehyde reduces the Ag⁺ ions to Ag. This Ag precipitates in the form of a silver mirror on the side of tes tube. Ketones, however do not show such a reaction.

What is the observation with tollens reagent

SILVER MIRROR

Reduction reaction for Ag

Ag+ (aq) + e- → Ag(s)

Balanced symbol equation form ethanal for ethanoic acid

CH₃COH + [o] -. CH₃COOH

How is fehling solution made?

Fehlings solution is made up by adding a solution of Cu²⁺ ions to sodium posttassium tartrate dissolved in excess NaOH. This produces a blue solution. An aldehyde reduces the Cu²⁺ ions to a red/brown Cu₂O ppt on warming.

What is made in both tollens reagent reaction and fehlings solution reagent

They both make ethanoic acid from ethanal.

Reduction reaction for fehlings solution

2Cu²⁺ +2H₂O +2e^- → Cu₂O_(s) + 2H⁺

Observation from fehlings solution

Red/brown ppt( precipitate) formed

Test for carboxylic acid

Add sodium carbonate/sodium hydrogen carbonate to unknown solution. Bubbles of gas are positive result. To test gas bubble it through limewater and CO₂ it will turn cloudy

Elimination reaction for alcohols