Alcohols Flashcards
Primary, secondary, tertiary alcohol
1° - carbon carrying -OH only attached to one alkyl group
How can alcohols form alkenes
Dehydration reaction- eliminate water
-heated with conc sulfuric acid catalyst
+ allows produce alkene from renewable resource (alcohol from fermentation)
+polymers without oil
How to produce alkene from alcohol
Distillation-
-add conc H2SO4 + H3PO4 to round bottom flask containing cyclohexanol, add carborundum boiling chipe, swirl
-gently heat water bath
-chemicals evaporate, into condenser, turn to liquid
-collect in cooled flask
Separation-
-will contain impurities
-separating funnel, add water to dissolve soluble impurities
-allow mixture settle into layers, drain aqueous lower layer, leave impure cyclohexene
Purification-
-drain into round bottom flask
-add anhydrous CaCl2 add bung, leave to dry
-distil ahain
Hydration to form alcohol conditions
-react ethane with steam to produce ethanol
-300°C
-60atm
H3PO4 catalyst
Hydration properties
- non renewable
- continuous process
- not carbon neutral
- fast
- pure product (100%)
Fermentation conditions
Sugar from plant material (glucose) converted to ethanol and CO2 by fermentation
- 35°C (optimum temp for yeast)
- yeast catalyst
- atmospheric
Fermentation properties
- renewable- sugar
- batch process
- carbon neutral
- slow
- impure product (15%): fractional distillation needed
Biofuel
A fuel made from biological material that’s recently died
How is fermentation carbon neutral?
The CO2 released when the fuel is burnt is equal to the CO2 absorbed by plants
Advantages and drawbacks of biofuels over fossil fuels
+renewable (won’t run out) so more sustainable
+carbon neutral
-petrol car engines must be modified to use fuels with high ethanol conc
-less land to grow food (crops take up space) so harder to feed
Equations to support carbon neutral
Photosynthesis- 6CO2 + 6H2O —> C6H12O6 + 6O2 Fermentation- C6H12O6 —> 2C2H5OH + 2CO2 combustion of ethanol- 2C2H5OH + 6O2 —> 4CO2 + 6H2O
How is it not completely carbon neutral?
Fossil fuels burnt to power machinery used to make fertiliser, harvesting crops, refine + transport bio ethanol
-produces carbon dioxide
Oxidising agent
[o]= acidified potassium dichromate
What are alcohols oxidised to?
Primary alcohol - aldehyde - carboxylic acid (p-a= distillation, p-c= reflux)
Secondary alcohol - ketone (reflux)
Tertiary alcohol- not easily oxidised
How can you tell if it’s been oxidised
Orange dichromate ion reduced to green chromium ion
Primary + secondary- will change from orange solution to green solution
Tertiary- will remain orange solution
What are aldehydes
- H and one alkyl group attached to carbonyl C atom
-al
-C=O
|
H
-C in -CHO group always counted as 1st carbon
What are ketones
- 2 alkyl groups attached to carbonyl C atom
- one
- C=O in middle of carbon chain
What are carboxylic acids
-COOH group at end of carbon chain
-oic acid
-C=O
|
O-H
-C in COOH counted as 1st
How can aldehydes and ketones be distinguished
-Weak oxidising agents can be used to distinguish between an aldehyde and a ketone
The aldehyde will be oxidised to a carboxylic acid, but the ketone will not undergo oxidation
-If an aldehyde is warmed with Fehling’s solution, the aldehyde will be oxidised and a colour change will take place: blue- brick red precipitate
-If gently warmed with Tollens’ reagent, an aldehyde will become oxidised- silver mirror
