3.3.5 Alcohols

Hydroxyl group (OH-)

When a hydroxyl group is bonded to a carbon with only one alkyl group bonded to it

When a hydroxyl group is bonded to a carbon with two alkyl groups bonded to it

When a hydroxyl group is bonded to a carbon with three alkyl groups bonded to it

• This reaction allows alkenes to be produced from a renewable source (ethanol from fermentation) • This mean polymers can be produced without oil

Ethanol is heated with a sulfuric acid catalyst C2H5OH -H2SO4-> C2H4 + H2O The product formed is usually a mixture of water acid and ethanol so the alkene must be separated out Phosphoric acid can also be used as a catalyst

• A lone pair of electrons from the oxygen bonds to an H+ from the acid. The alcohol is protonated giving the positve charge • The positively charged oxygen pulls electrons away from the carbon. An H2O molecule leaves, creating an unstable carbocation intermediate • The carboncation loses an H+, the bond from which creates a C=C double bond, and an alkene is formed

If the carbon the hydroxyl group has two carbons attached to it the double bond can form either side of the carbon forming two products

Stage 1 distilation: 1. Add conc. sulfuric acid and phosphoric acid to a round bottomed flask containing cyclohexanol. Mix the solution by swirling the flask and add antibumbing granules 2. The mixture should be gently heated around 83oC using a water bath or electric heater 3. Chemical with boiling points >83oC will evaporate. Warm gas will rise out of the flask and condense 4. The product can be collected in a cooled flask

Step 2 seperation: 1. The product collected after distillation will still contain impurities 2. Transfer the product mixture into a seperating funnel and add water to dissolve water soluble impurites and create an aqueous solution 3. Allow the mixture to settle into layers. Drain the aqueous lower layer, leaving the impure cyclohexene

Step 3 purification: 1. Drain the cyclohexene into a round-bottomed flask 2. Add anyhdrous CaCl2 (a drying agent) and stopper the flask. Let the mixture dry for at least 20 min with occasional swirling 3. The cyclohexene will still have small amount of impurities so distil the mixture one last time

• A pair of electrons from the double bond bonds to an H+ from the acid • A lone pair of electrons from a water molecule bonds to the carbocation • The water loses an H+ • The alcohol is now formed

Ethanol can be produced by the hydration of ethene by steam at a temperature of 300oC and a preasure of 60 atm. It needs a solid phosphoric(V) acid catalyst

When crude oil supplies start running out, petrochemical like ethene will be expensive, so being able to produce ethanol from glucose which can be grown on plants means ethanol can be produced sustainably as its a renewable resource

• Fermentation is an exothermic process, carried about by yeast in anaerobic conditions • The equation is C6H12O6(aq) -30-40oC / yeast-> 2C2H5OHaq + 2CO2(g) • Yeast produces an enzyme which converts sugers, such as glucose, into ethanol and carbon dioxide • The enzyme works at an optimum temperature of 30-40oC. If its too cold, the reaction is slow, if its too hot the enzyme is denatured • Once formed, ethanol is seperated from the rest of the mixture by fractional distillation • Fermentation is low-tech. It uses cheap equipment and renewable resources. Buth the fractional distillation that is neeed to purify the ethanol produced takes extra time an money

A fuel that is made from biological material that’s recently died

• Biofuels are renewable sources of energy, unlike fossil fuels they won’t run out so they are sustainable • Biofuels do produce CO2 when they are burnt, but it’s CO2 that the plants absorbed while growing, so biofuels are normally classed as carbon neutral

• Petrol cars still require modification to be able to use fuels with high ethanol concentrations • Land used to grow crops for fuel cannot be used to grow food, which may cause food shortages

• Plants take in carbon dioxide from the atmoshere to produce glucose by photosynthesis - 6CO2 + 6H2O -> C6H12O6 + and 6O2 - 6 moles of carbon dioxide are removed to produce 1 mole of glucose • In the fermentation process, glucose is converted into ethanol - C6H12O6 -> 2C2H5OH + 2CO2 - 2 moles of carbon dioxide are released into the atmosphere when 1 mole of glucose is converted to 2 moles of ethanol • When ethanol is burned, CO2 and water are produced - 2C2H5OH + 6O2 -> 4CO2 + 6H2O - 4 moles of carbon dioxide are released into the atmosphere when 2 moles of ethanol are burned completely If you combine all three of these equations, you’ll find 6 moles of carbon dioxide are abosrbed and 6 moles are emited, therefore biofuels are theoretically carbon neutral

Fossil fuels still need to be burned to power the machinery used to make fertilisers for the crops, harvest the crops and transport the bioethanol. Burning the fossil fuels to power this machinery produces CO2, therefore its not completely carbon neutral

The oxidising agent acidified potassium dichromate(VI), K2Cr2O7, to mildly oxidise alcohols. The orange dichromate(VI) ion, Cr2O72-, is reduced to the green chromium(III) ion, Cr3+.

Aldehydes then carboxylic acids

Ketones only

Tertiary alcohols cannot be oxidised