Alcohols Flashcards
What is the alcohol functional group?
⦾ -OH group
What is the general formula for alcohols?
⦾ CnH2n+1
What does whether an alcohol is primary, secondary or tertairy depend on?
⦾ Which C -OH bonded to
Which C is the -OH bonded to in primary alcohols?
⦾ C with 1 alkyl group
Which C is the -OH bonded to in secondary alcohols?
⦾ C with 2 alkyl groups
Which C is the -OH bonded to in tertiary alcohols?
⦾ C with 3 alkyl groups
Draw out the general structure (with R groups) for primary, secondary and tertiary alcohols?
⦾ pg. 226
What are the 2 main methods for producing alcohols?
⦾ Hydration of alkenes
⦾ Fermentation
What are the reaction conditions for the hydration of alkenes to produce alcohol?
⦾ Steam ⦾ Acid catalyst - solid phosphoric (V) acid ⦾ Aqueous cond. ⦾ 300C ⦾ High pressures (60atm)
What is the equation (+ conditions) for the industrial hydration of ethene to produce alcohol?
⦾ CH2=CH2(g) + H2O(g) + H3PO4 + 300C + 6atm → CH3CH2OH(g)
What is the reaction yield?
⦾ Low - 5%
⦾ BUT - recycle unreacted ethene - ~95%
Draw out the reaction mechanism for the reaction of steam with ethene?
1 ⦾ Pair of e- from C=C bonds with H+ from acid
2 ⦾ Lone e- pair from water bonds to carbocation
3 ⦾ Water loses a H+
4 ⦾ Alcohol formed
Explain fermentation?
⦾ Yeast
⦾ Enzymes break down starch from crops into sugars
⦾ Sugars fermented to form alcohol
Is fermentation exothermic or endothermic?
⦾ Exothermic
What are the reaction conditions for the fermentation of yeast?
⦾ Anaerobic conditions
⦾ Optimum temp - 30C - 40C
What is the equation for the reaction of glucose to ethanol?
C6H12O6(aq) → 2C2H5OH(aq) + 2CO2(aq)
When the solution reaches about 15% ethanol, the yeast…
⦾ …dies,
Which method/equipment can be used to increase the concentration of ethanol?
⦾ Fractional distillation - purify ethanol
Compare the advantages and disadvantages of the 2 main ethanol production methods?
Hydration of Ethene:
⦾ ROR - V. fast
⦾ Quality of product - Pure
⦾ Raw material - Ethene from oil - finite resource
⦾ Process/Costs - Continous - expensive equipment needed - low labor costs
Fermentation:
⦾ ROR - V. slow
⦾ Quality of product - V. impure - needs more processing
⦾ Raw material - Sugars - renewable
⦾ Processes/Costs - Batch process - cheap equipment needed - high labor costs
Define biofuel?
⦾ Fuel made from recently dead biological material
What are the advantages of biofuel?
1 ⦾ More sustainable than crude oil - renewable
2 ⦾ Carbon neutral - Burnt crop releases same amount taken in when growing.
What are the disadvantages of biofuel?
1 ⦾ Ethical “Food vs Fuel” - land of crops burnt not fed
2 ⦾ Environmental Deforestation - land clearing removes trees that take in CO2 and are burnt
3 ⦾ Fertilisers added to soils may pollute waterways or releas NO2 (GHG)
4 ⦾ Switching from FFs to biofuel - most cars unable to run.
Write and explain the equations for whether is a carbon neutral fuel?
1 ⦾ Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2 2 ⦾ Fermentation: C6H12O6 → 2C2H5OH + 2CO2 Ethanol burned 3 ⦾ 2C2H5OH + 6CO2 → 4CO2 + 6H2O
Do these equation support that carbon is a neutral fuel?
⦾ All species in equations cancel each other out
⦾ CO2 neither take in/out of environment
Explain why bioethanol isn’t a completely carbon neutral fuel?
⦾ FFs need to be burnt to power machinery to make fertilisers
⦾ Refinining + transport uses FFs
Which of the following: primary, seconday and tertiary alcohols can be oxidised to produce products?
⦾ Primary
⦾ Secondary
Explain the full oxidation of primary alcohols?
Include equations
⦾ Heat in presence of acidified potassium dichromate
⦾ Distill to produce aldehydes
ethanol + [O] + K2Cr2O7 → Ethanal + H2O
⦾ Heat further under reflux
⦾ Produce carboxylic acids
Ethanal + [O] → Ethanoic acid + H2O
Explain the full oxidation of secondary alcohols?
Include equations
⦾ Heat in presence of acidified potassium dichromate
⦾ Produce ketones
What is the oxidising agent used in the oxidation of alcohols?
⦾ K2Cr2O7 - Potassium dichromate
What is the colour change when an alcohol is oxidised?
⦾ Orange to Green
What ion is reduced the reaction? (include colours)
⦾ Orange dichromate (VI) ion Cr2O7 2-
⦾ Reduced to green Chromium ion, Cr3+
What are the conditions for the initial oxidation of primary alcohols?
What is its hard to control?
What are the methods to prevent it reacting further into ________ ____?
⦾ Gently heat ethanol with potassium dichromate (VI) solution + sulfuric acid in test tube
⦾ “apple” smelling ethanal produced
⦾ Hard to control heat amount
⦾ Aldehyde oxidised more to “vinegar” ethanoic acid
⦾ Get aldehyde out of [O] solution as soon as formed - gently heat excess alcohol with controlled amount of [O] in distillation apparatus
⦾ Aldehyde has lower bp. than alcohol distills off quick
What are the reaction conditions for the second part of oxidising alcohols?
⦾ Vigorously [O} alcohol ⦾ Mix with excess [O] ⦾ Heat under reflux ⦾ Vaporised compounds cooled, condense back into reaction mixture ⦾ Aldehyde stays in reaction mixture ⦾ Further [O] to carboxylic acid
What are the reaction conditions for the oxidation of secondary alcohols?
⦾ Reflux with acidified dichromate(VI) to produce ketone
⦾ Ketones not easily oxidised so prolonged refluxing won’t produce anything more.
Which 2 solutions can be used to test for aldehydes and ketones?
⦾ Fehling’s/Benedicts solution
⦾ Tollen’s reagent
What is Fehling’s/Benedicts solution?
⦾ Deep blue Cu+ complex
⦾ Alkaline solutions of Cu(II)sulfate
What is Tollen’s reagent?
⦾ Colourless
⦾ [Ag(NH3)2]+ complex
Which is easily oxidised from ketones and aldehydes?
⦾ Aldehydes
How can Fehling’s solution be used to distinguish between Aldehydes and Ketones?
⦾ Warm with aldehyde
⦾ Reduce to brick-red Cu2O prec.
⦾ Stays blue with ketone
How can Tollen’s reagent be used to distinguish between Aldehydes and Ketones?
⦾ Warm with aldehyde
⦾ Reduced to silver - silver mirror
⦾ Remains colourless with ketone
