3.3.5 Alcohols Flashcards
How do you produce an alkene from an alcohol, what are the conditions?
- via dehydration (eliminate water from alcohol)
- require sulfuric acid or phosphoric acid catalyst
(e.g ethanol —> ethene + water)
How can alkenes be made from alcohols more sustainably?
By using alcohol that is made from fermentation of plants
What mechanism is undergone when you dehydrate alcohol? and what are the products
elimination mechanism
products : alkene , h2o, H+ (catalyst reformed)
Draw out the mechanism for the dehydration of ethanol
Why can dehydration of a non-primary alcohol lead to 2 different alkenes?
Cuz the double bond can be formed on either side of the carbon that the OH is attached to
What equipment + reagents is required for purifying the product of dehydrating alcohols and why
distillation- to separate the useful alkene from impurities (separates chemical by bpt)
separation funnel- despite distillation separating alkenes from impurities, further separation and purification may be needed (separates aqueous layers and organic layers)
drying agent- used to get rid of excess water that could remain
what are the steps to making cyclohexene
STEP 1 :
- DISTILLATION, add CONCENTRATED sulfuric or phosphoric acid and cyclohexanol into round bottomed flask. Add several anti-bumping granules to allow smooth boiling process (distributes heat evenly)
- use heating mantle to warm reactants up to 83 degrees (bpt of cyclohexanol) (NO Bunsen burner AS ITS FLAMMABLE)
- chemicals with bpt less than 83 degrees will evaporate, enter condenser and turn back into liquid
- product collected in flask (cyclohexane) may have small impurities such as unreacted cyclohexanol and water
STEP 2 :
- SEPARATION, add products from step 1 into a SEPERATING FUNNEL . Add water to dissolve soluble impurities creating aqueous solution
- after allowing the solution to settle, 2 LAYERS form (top layer = impure cyclohexene) (bottom layer = aqueous layer with water soluble impurities) Drain the aqueous layer off (ensure to remove stopper)
STEP 3:
- take the impure cyclohexene from step 2 and add to a round bottom flask
- add ANHYDROUS CaCl2. this dehydrating agent will remove aqueous substances still remaining. (keep adding until no more clumps for (clumps due to cacl2 absorbing water))
- INVERT flask and leave for 20-30mins
How are alcohols formed from Alkenes and what are the conditions
hydration of alkenes
requires steam and acid catalyst
300 degrees and pressure of 60atm
Why would fermentation be better than hydration to form an alcohol ?
Hydration uses an alkene formed from crude oil which is a non-renewable source (not sustainable)
Fermentation directly produces the alcohol from fermentation of glucose from plants.
What are 2 cons of fermentation?
Less yield of ethanol and slow process.
fractional distillation of ethanol at the end is also costly (still cheaper than other forms) and takes time
How does fermentation work?
it uses yeast in ANAEROBIC conditions (exothermic reaction) , the ethanol made then needs to undergo FRACTIONAL DISTILLATION to obtain pure ethanol
glucose –> ethanol + carbon dioxide
What are the conditions for fermentation and why?
temp at 30-40 degrees (yeast is an enzyme and this is the optimum temperature for the enzyme to work)
(at high temps the enzyme denatures and the reaction is too slow at lower temps)
Define biofuel
- renewable energy source made from living materials
- made from dead biological matter
Why are countries who plant lots of sugar cane bigger users of biofuels?
Sugar cane contains glucose which can be fermented by yeast to produce ethanol.
Bioethanol is added to petrol
What are 2 main advantages of biofuels
- they are renewable so they are more sustainable than crude oil
- they are carbon neutral (co2 released to make but co2 absorbed when growing sugar cane)
