ALCOHOL

general formula

C_nH_2n+1OH

primary

OH group attached to a carbon with 1 AKYL

secondary alcohol

OH group attached to a carbon with 2 AKYL

tertiary alcohol

OH group attached to a carbon with 3 AKYL

dehydrating alcohols equation (ELIMINATION REACTION)

C_nH_2n+1OH → C_nH_2n + H₂O

dehydrating alcohols produces

alkenes from renewable resources

you can produce ethanol by fermenting glucose from plants

so polymers like polyethene can be made without oil

water can be ELIMINATED from alcohols in a dehydration reaction

alcohols are heated with a concentrated sulphuric acid catalyst producing water and alkene

elimination mechanism

• Lone pair from oxygen bonds with H+ from acid

  • this protonates the oxygen, giving it a positive charge

• the positively charged oxygen pulls electrons from its bond between C-O, producing a water molecule + carbocation intermediate

• carbocation loses a H+

• alkene is formed and acid is reformed

dehydration of longer unsymmetrical alcohols produce multiple products

because the double bond can go on either side of the carbon

products of organic reactions

are often impure

in the dehydration of alcohols to form alkenes

the end mixture contains:

• product

• reactant

• acid

• water

• impurities

distillation

use the fact different chemicals have different boiling points to separate them

there are 3 steps to produce cyclohexene on its own from cyclohexanol

• reaction + first distillation

• separation

• purification

Reaction + first distillation

• add conc sulfuric acid and phosphoric acid to a round bottom flask with carborundum boiling chips (so the reaction boils calmly)

• connect flask to distillation apparatus (thermometer, condenser, cooled collection flask)

• gently heat flask around 83℃ using a water bath

• chemicals with a boiling point around 83℃ evaporate, rise out of the flask and into the condenser to be collected

seperation

• products of first distillation will contain impurities that must be removed

• add water to mixture to dissolve soluble impurities then transfer mixture to separating funnel so an organic and aqueous layer forms

• allow the layers to settle then drain off the aqueous layer leaving the impure cyclohexene

purification

• drain off cyclohexene into round bottom flask

• add anhydrous CaCl₂ (a drying agent that will remove water) and stopper the flask

• leave the flask for 20 minutes with regular shakes

• distil the solution 1 last time at 83℃ and collect the pure cyclohexene

hydrating alkenes in the Prescence of an acid catalyst + steam

C_nH_2n + H₂O ⇄ C_nH_2n+1OH

steam hydration of ethene is used industrally to produce ethanol, condition:

• 300℃

• 60 atm

• solid phosphoric acid catalyust

the reaction yeild is low, only 5%, but wiht the recycled unreacted ethene gas the overall yeild is 95%

ethene comes from cracking heavy fractions of crude oil

crude oil is a finite resource

in the future when crude oil supplues start running off making petrochemicals like ethanol very expensive

so producing ethanol by fermentation will be very important

fermentation is an exothermic process carried out by yeast in anaerobic conditions

yeast produces enzymes which convert glucose into ethanol and carbon dioxide

the enzymes work at an optimum temperature of 30-40℃

when the solution reaches around 15% ethanol yeast dies

fractional distillation increases the concentration of ethanol

fermentation is relatively cheap as low cost expirtment and renewable resources

ffractional distilation is needed to purify the ethanol using processes that take extra time and money

biofuel

a fuel made from biological material thats recently died:

example: sugars from sugar canes can be fermented to produce ethanol

ethanol produced this was is a biofuel

advantages of biofuels

• renewable energy source therefroe more sustainable

• produce the same amount of CO2 that plants take in as they grow so its considered carbon neutral

disadvantages of biofuels

• food Vs fuel- the land used to grow crops for fuel cannot be used to grow food therefroe might not be able to feed everyone in the country

• many trees cut down in order to create more land to frow crops for biofuel. deforestation destroys habitats and removes trees that take in CO2. the trees cut down are often burn which releases more CO2

• fertilisers are often added to soils in order to increase biofuel crop production, fetrilisers can pollute waterways and some release nitrous oxides which is a greenhouse gas

• the most current car engines are unable to run on fuels with high ethanol concentrations without being modified

equations to support the theory ethanol is a carbon neutral biofuel

combining the 3 equations youll see exactly 6 moles of CO2 TAKEN IN AND OUT

bioethanol is not completely carbon neutral

• fossil fuels will need to be burned to power machinery used to make fertilisers/crops/harvesters

• refining and transporting the bioethanol also uses energy

reducing agent: acidified potassium dichromate, K2Cr2O7

oxidises primary and secondary alcohols

acidified potassium dichromate colour change:

orange(Cr₂O₇^2-) → green (Cr³⁺)

primary alcohols oxidise to

aldehydes

aldehydes oxidise to

carboxylic acids

secondary alcohols oxidise to

ketones only

tertiary alcohols DO NOT…

OXIDISE

aldehyde + ketone general formula

CnH2nO

aldehyde functional group

ON THE ENDDDDD

aldehyde suffix

-al

ketone functional group

IN THE MIDDLEEE

KETONE SUFFIX

-ONE

gently heating ethanol with potassium dichromate solution and sulfuric acid in a test tube till it produces an “apple” smell AKA ALDEHYDE

HOWEVER ITS TRICKY TO CONTROL THE HEAT and the aldehyde formed can get a vinager smelling ethanoic acid instead if oxidised too much

to get JUST the aldehyde you need to seperate it from the solution as soon as it forms

this is done by gently heating excess alcohol with a controlled amount of oxidising agent in distillation apparatus so when the aldehyde boils (at a lower temeprature than alcohol) its immediately distilled off

vigorous oxidation of primary alcohols produces carboxylic acid

oxidasing agent in excess and heated under reflux

heating under reflux means

you can increase the temeprature of an organic reaction to boiling without losing volatile solvents, reactants or products and any vapourised compunds are colled condensed and drip back into the reaction mixture

aldehydes stay in the reaction mixture

till they’re oxidised to become carboxylic acid

refluxing secodnary alcohols with acidified potassium dichromate produces ketones

the only way to oxidise tertiary alcohols

is to burn them

aldehydes can be easily oxidisedd

ketones cannot be easily oxidised

fehlings solution and benedicts solution are both deep blue Cu2+ complexes (alkaline solutions of copper 2 sulfate)

which reduce to brick red CuO precipitate when warmed with an aldehyde but stay blue with a ketone

tollens reagent is colourless [Ag(NH3)2]+ complex

is reduced to silver by aldehydes but not ketones. this silver will coat the inside of the apparatus to form a silver mirror