2.7 Alcohols and Carboxylic acids Flashcards
Two main methods of producing alcohols
Hydration and fermentation
Hydration of alkenes
- produces alcohols from alkenes in the presence of an acid catalyst
- very high percentage yield - 1 product
- industrial process- high yield
- catalyst - phosphoric acid - increases rate without affecting yield
- 300 degrees celsius- compromise temperature as forward is exothermic so high yield would need a low temperature but would lead to a slow rate of reaction
- high pressure (60-70atm)- less moles of product so high yield favoured by high pressure, increases rate of reaction expensive when too high
Fermentation - sugars are converted to alcohol
• catalysed by enzyme present in yeast
• sugar is dissolved in water
• yeast is added and mixture is left in a warm place
• production of alcoholic drinks
• cheaper than hydration - lower temperature needed
• lower percentage yield than hydration
Eg glucose –> ethanol and carbon dioxide
After fermentation describe and explain how ethanol can be separated from the aqueous mixture left in the fermentation vessel
By fractional distillation as it has a boiling temperature of 80 degrees C
What is a biofuel
Fuel that has been produced using a biological source
Advantages of biofuels
- renewable - grow trees, animal waste material
- greenhouse gases - although they produce CO2 when burned they take some in during photosynthesis- carbon neutral overall
- economic and political security- countries without their own source of fossil fuels are affected bu changes in price + availability
Disadvantages of biofuels
- land-use- deforestation to create land to grow plants for biofuels
- use of resources- need lots of water and fertiliser , short supply of water and water pollution
- carbon neutrailty?- building factories and transport raw material - CO2 production
Alcohol dehydration to form alkenes
- water molecule is eliminated from the molecule and double bond is formed
- need a dehydrating agent/catalyst eg heated Al2O3 or concentrated H2SO4
How can addition polymers be produced from fermentation without the need for crude oil?
Fermentation produces the primary alcohol which can be dehydrated to produce an alkene which is used in the production of addition polymers
Primary alcohol
-OH joined to C that is not joined to more than 1 other C atom
Secondary alcohol
-OH is joined to C that is joined to 2 other C atoms
Tertiary alcohol
-OH joined to C that is joined to 3 other C atoms
Primary
Primary
Secondary
Tertiary
Oxidation of primary alcohol
Primary alcohol –> aldehyde–> carboxylic acid
Oxidation of secondary alcohol
Secondary alcohol–> ketones
Oxidation of tertiary alcohol
No oxidation
Use of acidified potassium dichromate (V)
Behaves as oxidising agent of alcohol
Orange to green
Primary + secondary- positive
Tertiary- negative
Formation of carboxylic acid
Aldehyde produced from primary alcohol will undergo further oxidation to form a carboxylic acid
Secondary won’t
Testing for carboxylic acids
React as acids with sodium hydrogencarbonate
Produce CO2
CO2 collected and tested using limewater- cloudy if it is CO2
Description of carboxylic acids as acids
Weak- slightly dissociate in solution
Form H+ ion and carboxylate ion RCOO-
Carboxylic acids and carbonates reaction
Carboxylate salt, water and carbon dioxide
Carboxylic acids and hydrogen carbonates reaction
Carboxylate salt, water and carbon dioxide
Carboxylic acid and base reaction
Carboxylate salt and water
Carboxylate salt eg Na
CH3COO-Na+
Propene can be formed by a dehydration reaction
Name a suitable reagent for this reaction
Concentrated sulphuric acid
Give an oxidising agent that can be used, in acid solution, to oxidise primary alcohols to carboxylic acids and state what is seen as the reaction proceeds
Potassium dichromate (VI) Colour change from orange to green
State the conditions of temperature and pressure used in the preparation of ethanol from ethene
300 degrees C
60-70 atm
Ethanol can be converted to ethanoic acid in an oxidation reaction.
Give suitable reagents for this reaction
Acidified potassium dichromate (VI)
Ethene can be used as the starting material in the industrial preparation of ethanol
Name the catalyst used in this reaction
Phosphoric acid
