- Feedstock for chemical processes - Solvents - Alcoholic drinks - Fuels

3.5 Alcohols Flashcards by Jessica Taylor

General formula of alkanes

C₂ₙH₂ₙ₌₂

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Functional group of alcohols

R-O-H

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How can alcohols be classified?

Primary, secondary or tertiary (based on the number of carbon atoms attached directly to the C bonded to oxygen)

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Why do alcohols have relatively high melting and boiling points?

They form hydrogen bonds

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Why are alcohols with a low Mr soluble in water?

They form hydrogen bonds with the water molecules

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Reagent for the hydration of alcohols

Steam

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Conditions for the hydration of alcohols

300°C
60atm
Phosphoric acid catalyst (H₃PO₄)

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Uses of alcohols

Feedstock for chemical processes
Solvents
Alcoholic drinks
Fuels

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Methods for industrial preparation of ethanol

Fermentation and hydration of alkenes

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Process for fermentation

Carbohydrates from crops are broken down into sugar
Sugars converted to ethanol by anaerobic respiration
Ethanol is separated from the mixture with fractional distillation

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Reagents for fermentation

Glucose
Yeast (catalyst)

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Conditions for fermentation

30-40°C
Aqueous
Anaerobic

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Products of fermentation

Ethanol + Carbon dioxide

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Why is fermentation carried out under anaerobic conditions?

This prevents oxidation of ethanol to form ethanoic acid

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Why is a temperature around 35°C used for fermentation

This is a compromise between maximising rate of reaction and avoiding denaturing enzymes

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When does the fermentation reaction stop?

Around 15% ethanol (higher concentrations of ethanol damage the yeast enzymes)

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Quality of ethanol produced through hydration of alkenes

Pure

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Quality of ethanol produced from fermentation

Inpure

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Rate of reaction of hydration of alkenes

Very fast

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Rate of reaction of fermentation

Very slow

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What type of process is hydration of alkenes?

Continuous

What type of process is fermentation?

Batch

Raw materials for the hydration of alkenes

Crude oil

Biofuel

A fuel derived or produced from renewable biological sources

Why is the statement that bioethanol is carbon neutral not valid?

- Fossil fuels are burnt in farming equipment, transportation, and refining the bioethanol - This fuel releases carbon dioxide when burnt

Disadvantages of using crops for the production of fuels

- Less land available for food production - Fertilisers are used to increase crop production - Deforestation

Reagent for the elimination reaction of an alcohol

Concentrated sulfuric acid catalyst

Conditions for elimination reaction of an alcohol

Heat

Which small molecule is produced in the elimination reaction of an alcohol

Water (this is a dehydration reaction)

What can be used to oxidise alcohols?

Acidified potassium dichromate(VI)

K₂Cr₂O₇ + H₂SO₄ Abbreviated to: H⁺/Cr₂O₇²⁻

Symbol for a generic oxidising agent

[O]

Oxidation (organic chemistry)

An increase in carbon-oxygen bonds

How can tertiary alcohols be distinguished from other alcohols?

They are not oxidised when mixed with acidified potassium dichromate(VI), so there will be no colour change.

Possible oxidation products of primary alcohols

Aldehydes and carboxylic acids

Oxidation products for secondary alcohols

Ketones

Reagent/conditions for oxidation of an alcohol to an aldehyde

Acidified potassium dichromate

Apparatus for oxidation of an alcohol to an aldehyde

Immediate distillation

Why is immediate distillation used to produce aldehyde from alcohols?

It prevents further oxidation of the aldehyde to a carboxylic acid

Why do aldehydes have lower boiling points than carboxylic acids?

Aldehyde have permanent dipole dipole force between molecules and carboxylic acids have hydrogen bonds

Reagents/conditions for oxidation of alcohols to form carboxylic acids

- Acidified potassium dichromate - Reflux

Apparatus for producing carboxylic acids from alcohols

Reflux

Why is reflux used to produce carboxylic acids from alcohols?

Any aldehyde produced is returned to the reaction and further oxidised to carboxylic acids

Tests for aldehyde functional group

Tollen's reagent or Fehling's solution (mild oxidising agents)

Method for testing for aldehydes (Tollen's reagent)

- Add 1 drop of sodium hydroxide to ~ 2cm³ of silver nitrate (brown precipitate forms) - Dissolve precipitate in ammonia - Warm resulting solution with the test substance **Silver mirror forms if positive**

Method for testing for aldehydes (Fehling's solution)

Add ~ 2cm³ of Fehling solution to the test solution and warm **Brick red precipitate forms (Cu₂O)**

What is Fehling's solution?

Blue solution containing Cu²⁺ ions

What is the organic product of testing for aldehyde groups (Fehling's solution or Tollen's reagent)

Aldehyde is oxidised to **carboxylic acid**

Why do ketones not react with Fehling's solution or Tollen's reagent?

They cannot be further oxidised

Test for carboxylic acids

Sodium carbonate or Sodium hydrogencarbonate **Effervescence if positive (CO₂ produced)**

Organic product of carboxylic acid + sodium carbonate

Sodium carboxylate salt (RCOONa)