3.3.5 Alcohols Flashcards
What is the suffix and prefix used when naming alcohol?
-ol, hydroxyl-
What are the two different methods for producing ethanol?
Fermentation, direct hydration.
How does fermentation produce ethanol, under what conditions?
Produced by using living yeast to convert glucose sugars into ethanol and CO2. Atmospheric pressure, 35-37C, anaerobic.
Why does fermentation need to happen under anaerobic conditions?
Prevents oxidation of ethanol to ethanoic acid.
What is the equation for fermentation?
C6H12O6 —–(yeast)—-> 2C2H5OH + 2CO2
How does direct hydration produce ethanol, under what conditions?
Ethene reacts with steam, at 300C, at pressure of 6.5 x 10^3 KPa and with phosphoric acid as a catalyst.
What is the equation for direct hydration?
CH2=CH2 + H2O(g) —-phosphoric acid catalyst—> C2H5OH
What happens in the mechanism for the reaction from direct hydration?
The = breaks to give the e- to the H+ ion (from the acid), this forms C2H5 with a carbocation and the O from the H2O donates an e- to the carbocation, the C2H5 then bonds to the H2O making O a + ion as it has too many bonds. One of the Hs from the H2O donates an electron to the O forming C2H5OH and a H+ (proton).
Explain why the phosphoric acid catalyst isn’t used up in direct hydration.
Because the H+ ions are used up at the start of the reaction and then given back out at the end.
What are the speeds of the methods to form ethanol?
Hydration is fast, fermentation is slow.
What are the purities of the methods to form ethanol?
Hydration is pure (around 100%), fermentation is impure (max. 20%).
What are the raw materials used in the methods to form ethanol, which are renewable?
Hydration uses ethene from crude oil (non-renewable), fermentation uses sugars/biomass (renewable).
What are the types of processes used in the methods to form ethanol?
Hydration is continuous, fermentation is batch.
What are the costs for the methods to form ethanol?
Hydration is cheap on manpower, expensive on equipment. Fermentation is expensive on manpower, cheap on equipment.
What are alcohols classified as?
Primary, secondary or tertiary.
What is the oxidising agent used to oxidise alcohols? What is it usually represented as?
Acidified potassium dichromate (VI) solution/ acidified K2Cr2O7.
Usually represented as [O].
What can primary alcohols be oxidised to? What are the conditions?
Aldehydes. Room temp, ethanal must be removed by distillation to prevent further oxidation.
What is the equation for oxidising an alcohol to an aldehyde?
. H H H
| | [O] |
H - C - C - OH ——> H - C - C = O + H2O
| | | |
H H H H
CH3CH2OH(l) + [O] -> CH3CHO(l) + H2O(l)
What can primary alcohols be oxidised further into? What are the conditions?
Carboxylic acids. Higher temperature, must be refluxed.
What is the equation for the oxidation of a primary alcohol into a carboxylic acid?
. H H H
| | 2[O] |
H - C - C - OH ——> H - C - C = O + H2O
| | | |
H H H OH
CH3CH2OH(l) + 2[O] -> CH3COOH(l) + H2O(l)
What are secondary alcohols oxidised to?
Ketones.
What is the equation for oxidising a secondary alcohol into a ketone?
. H H H H H H
| | | [O] | | |
H - C - C - C - H ——> H - C - C - C - H + H2O
| | | | || |
H OH H H O H
CH3CH(OH)CH3(l) + [O] -> CH3COCH3(l) + H2O(l)
What do we oxidise tertiary alcohols into?
Nope. Can’t oxidise because oxidation means a C-C bond has to be broken, needs lots of energy, no H atoms available for oxidation.
What are the 3 chemical tests used to distinguish between aldehydes and ketones?
Acidified potassium dichromate (VI), Tollen’s reagent, Fehling’s solution.
What are the results for the potassium dichromate test?
Aldehyde colour change = orange to green solution
Ketone = no change.
What are the results for the Tollen’s reagent?
Only reacts with aldehydes, silver atoms coat the test tube to make a silver mirror.
What are the results for the Fehling’s solution test?
Only reacts with aldehydes, produces a brick red precipitate on warming.
What do elimination reactions involve?
The loss of water from a molecule.
What is an elimination reaction often called?
Dehydration.
What are the conditions for acid catalysed elimination?
Heated (180C) with H2SO4 or H3PO4. OR vapours heated (600K) over aluminum oxide catalyst.
What is produced from acid catalysed elimination? How is it collected?
Ethene product is collected over water.
Why is ethene useful?
It’s the starting point for plastic manufacturing (making polymers).
What is the mechanism for an elimination reaction?
Curly arrow starts from lone pair on the O of the alcohol and goes to a proton (H+). Next step, arrow starts from C-H bond and goes to C-C bond, other arrow goes from C-O bond to the O+. Last step, alkene formed along with H2O and H+.
What could acid catalysed elimination be used to replace?
Replace making polymers from crude oil, ethanol from plants could be used to make the alkane monomers.
