Alcohols Flashcards
General formula of alcohols
CnH2n+1OH
Functional group of alcohols
OH
Classifications
Primary, secondary, tertiary
What is primary butanol and its placement
Butan-1-ol, OH group end of chain
What is secondary butanol and its placement
Butan-2-ol, OH group on length of chain
What is tertiary butanol and its placement
2-methylpropan-2-ol, OH group on a branch on chain
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
Hydrogen bonding drawing
- Needs delta + and -
- Lone pair
- Label hydrogen bond
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
What is needed for nucleophilic sub of halogenoalkanes to form alcohols?
Reagent: NaOH or KOH Conditions: aqueous/warm (reflux) OH- ion
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
When does fermentation occur?
When yeast and bacteria convert sugars to alcohols, and acid and various gases such as carbon dioxide and methane
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)
Equation of reaction of glucose to ethanol
C6H12O6 ——> 2C2H5OH + 2CO2 reaction will stop when alcohol level is about 14%
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)
Advantages of fermentation as alcohol production
- Raw material is renewable and sustainable
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)
What is carbon neutral?
Activity in which there is no net annual emissions of CO2 into atmosphere
Example of carbon neutral fuel?
Bioethanol
Production of sugar equation
6CO2 + 6H20 —–> C6H12O6 + 6O2
Complete combustion of ethanol equation
C2H5OH + 3O2 ——> 2H2O + 3CO2
Incomplete combustion of ethanol equation
C2H5OH + 5O2 —–> 6H20 + 5CO
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
- Hydration of ethene using steam to produce ethanol
- Acid catalyst
- High temperature + high pressure
- 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
- Gently heating alcohol with potassium dichromate (VI) and sulfuric acid in test tube = alcohol
- 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)
No
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?
- Mixture of liquids heated to boiling point for prolonged time
- Vapour is formed which escapes from liquid mixture and is changed back into liquid + returned to liquid mixture
- Any alcohol and aldehyde that initally evaporates can be then oxidised
