Alcohols Flashcards by Jonny Billinton

General formula of alcohols

CnH2n+1OH

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Functional group of alcohols

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Classifications

Primary, secondary, tertiary

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What is primary butanol and its placement

Butan-1-ol, OH group end of chain

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What is secondary butanol and its placement

Butan-2-ol, OH group on length of chain

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What is tertiary butanol and its placement

2-methylpropan-2-ol, OH group on a branch on chain

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What are alcohols boiling point compared to alkanes of similar relative molecular mass?

Higher due to hydrogen bonding between molecules (as well as van der waal) Alkanes only have van der waal Hydrogen bonding stronger

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Hydrogen bonding drawing

Needs delta + and -
Lone pair
Label hydrogen bond

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What are the various ways of forming alcohols?

Nucleophilic substitution of halogenoalkane
Hydration of alkenes (elimination)
Electrophillic addition of alkene with sulfuric acid followed by reaction with water
Fermentation

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What is needed for nucleophilic sub of halogenoalkanes to form alcohols?

Reagent: NaOH or KOH Conditions: aqueous/warm (reflux) OH- ion

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What are the conditions of a hydration of alkenes (industrial method) and equation

C2H4 + H20 —–> C2H5OH - Needs conc phosphoric acid absorbed on solid silica surface as catalyst - 60 atm pressure - 600K temp - excess ethane to give high yield

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When does fermentation occur?

When yeast and bacteria convert sugars to alcohols, and acid and various gases such as carbon dioxide and methane

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Conditions of fermentation to produce ethanol?

Yeast provides enzymes - Anaerobic respiration process/remove air - Temp 35 degrees - Aqueous solution (neutral) - Batch process/ uses renewable resources/ slow (days)

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Equation of reaction of glucose to ethanol

C6H12O6 ——> 2C2H5OH + 2CO2 reaction will stop when alcohol level is about 14%

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Uses of fermented alcohol

Wine/ beer (if alcoholic drinks need higher conc of alcohol, fractional distillation used) - Biofuels (made from living organisms or their waste)

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Advantages of fermentation as alcohol production

Raw material is renewable and sustainable

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Disadvantages of fermentation

Food supply is depleted as land is used to grow crops for fuel - Production of crops is subject to weather and climate - It takes time to grow crops and further processing is needed (like fractional distillation to seperate water and alcohol)

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What is carbon neutral?

Activity in which there is no net annual emissions of CO2 into atmosphere

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Example of carbon neutral fuel?

Bioethanol

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Production of sugar equation

6CO2 + 6H20 —–> C6H12O6 + 6O2

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Complete combustion of ethanol equation

C2H5OH + 3O2 ——> 2H2O + 3CO2

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Incomplete combustion of ethanol equation

C2H5OH + 5O2 —–> 6H20 + 5CO

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How does an alcohol form an alkene and what are the conditions needed?

Elimination (dehydration reaction) Conditions: Concentrated H2SO4 / 170 degrees or Al2O3 / 600 degrees

OH group alcohols can

hydrogen bond to water molecules

...cannot bond to water molecules

non-polar hydrocarbon chain

Why are alcohols with short hydrocarbon chains soluble in water?

because hydrogen bonding predominates

Why are alcohols with longer hydrocarbon chains insoluble in water?

Non-polar hydrocarbon chain dominates

What is the benefit of making alcohols from a dehydration reaction?

Allows you to make alkenes from renewable resources i.e. without crude oil

Elimination reaction Name the condition and product when an alcohol is used as a reactant

Product: alkene Al203 catalyst 450 K Concentrated hot H2SO4

Ethanol + H2SO4 = Name mechanism

elimination

Ethanol + H2SO4 Mechanism

elimination

How does distillation work?

Uses the fact that chemicals have different boiling points and seperates them out to get a single purified substance

Name two ways ethanol can be produced

Describe hydration

1. Hydration of ethene using steam to produce ethanol 2. Acid catalyst 3. High temperature + high pressure 4. H20 added across double bond

Hydration Name 3 conditions for producing ethanol

Describe fermentation

(exothermic reaction) is carried out by yeast in anaearobic respiration Yeast produces sugars into ethanol and cabron dioxide Ethanol formed is seperated by fractional distillation

What is an advantage of using fermentation to make alcohol

Low tech process (uses cheap equipment and renewable resources)

State the equation for hydration of ethene (including state symbols)

Name 2 ways an alcohol can be oxidised

Define oxidation

Loss of eectrons Gain of oxygen (Loss of hydrogen)

Define reduction

Gain of electrons. Loss of oxygen (Gain of hydrogen)

Define oxidising agent

Gain electrons

What are primary alcohols oxidised to?

Aldehydes

Describe how you would oxidise and alcohol to just get an aldehyde

1. Gently heating alcohol with potassium dichromate (VI) and sulfuric acid in test tube = alcohol 2. To just get alcohol distill it off immediately

Describe how you would oxidise an alcohol to just get a carboxylic acid

Alcohol has to be vigorously oxidised: alcohol mixed with excess oxidising agent and heated under reflux

Explain how heating under reflux ensures the complete oxidation of an alcohol to a carboxylic acid

Any escaped vapour is condensed back into liquid So any unreacted aldehyde can be oxidised/reduced further

What are secondary alcohols oxidised into?

ketones

Describe how you would oxidise a secondary alcohol into a ketone

Reflux a secondary alcohol with acidifed potassium dichromate (VI)

State what colour changes occur when potassium dichromate (VI) is added to a primary, secondary and tertiary alcohol

Primary and secondary alcohol: Orange ----\> green Tertiary alcohol: No colour change - remains orange

Explain why potassium dichromate (VI) turns from orange to green

Orange dichromate(VI) ion, Cr2O7(2-) is reduced to green chromium(III) ion, Cr3+

Can tertairy alcohols be oxidised when reacting them with potassium dichromate (VI)

Why can't tertiary alcohols be oxidised by reacting them with potassium dichromate (VI)?

Because of a lack of hydrogen atoms on carbon atom which the hydroxyl group is attached to

Explain why butanal has a lower boiling point than both butan-1-ol and butanoic acid

Dipole-dipole forces between butanal molecules where as there are hydrogen bonds in both other molecules Dipole-dipole forces are weaker than hydrogen bonds as they require less energy to break

Ethanol can be oxidised into ethanal, describe this reaction

Oxidising agent, 2 hydrogen atoms removed, forming water

Describe what happens when an alcohol is heated uner reflux?

1. Mixture of liquids heated to boiling point for prolonged time 2. Vapour is formed which escapes from liquid mixture and is changed back into liquid + returned to liquid mixture 3. Any alcohol and aldehyde that initally evaporates can be then oxidised