alcohols Flashcards
what is the general formula for the alcohol
the alcohol homologous series has a general formula of CnH2n+1OH
when is an alcohol primary, secondary or tertiary
an alcohol is primary depending on which carbon atom the hydroxyl group -OH is bonded to
Primary alchols- the -OH it attached to a carbon with one alkyl group attached
Secondary alcohol - the -OH group is attached to a carbon with two alkyl groups attached
tertiary alcohol - the -OH group is attached to a carbon with three alkyl groups attached
how do we make alkenes from an alcohol
you can make alkenes by eliminating water from alcohols in a dehydration reaction (i..e. elimination of water)
what does a dehydration reaction allow you to produce
this reaction allows you to produce alkenes from renewable resources
you can produce ethanol from the fermentation of glucose, which you can get from plants
we can the dehydrate this ethanol to make ethene which can be used to make polymers e.g. poly(ethene)
this whole process does not require oil
outline the mechanism for the elimination of water from an alcohol
The OH acts as a base
a lone pair of electrons from the oxygen bonds to an H+ from the acid
- The alcohol is protonated giving the oxygen a positive charge
- the positively charged oxygen pulls electrons away from the carbon. An H2O molecule leaves, creating an unstable carbonation intermediate
- the carbonation loses an H+ and the alkene is formed
what are the conditions for acid catalysed elimination
REAGENT: concentrated sulfuric or phosphoric acid
CONDITIONS: warm (under reflux)
ROLE OF REAGENT: dehydrating agent/ catalyst
what happens when you dehydrate longer unsymmetrical alcohols
the result is more than one product
this is because the double bond can go either side of the carbon that had the OH group on it
why must we purify the products of an organic reaction
the products are often impure so you need to get rid of any unwanted by-products or leftover reactants from the reaction mixture
for example, in the dehydration of alcohols to form alkenes, the mixture at the end contains:
- the reactant
- acid
- water
- other impurities
distillation is a technique which used the fact that different chemicals have different boiling points to separate them
example
how do you produce cyclohexane from cyclohexanol and separate and purify the product
reaction and first distillation
1) add concentrated H2SO4 and H3PO4 to a round bottom flask containing cyclohexanone
Mix the solution by swirling the flask and add 2-3carborundum boiling chips (these make the mixture boil more calmly)
2) connect the flask to the rest of the distillation apparatus, including a thermometer, condenser and a cooled collection flask
3) Gently heat the mixture to around 83C ( the boiling point of cyclohexane) using a water bath or electric heater
4) chemicals with boiling points up to 83C will evaporate. The war, gas will rise out of the flask and into the condenser
5) the condenser has cold water running through the outside. The cooler temps turn the gas back into a liquid
6) the liquid can the be collected in a cooled flask
stage 2 in separating and purifying a product: separation
1) the product collected after the first distillation will still contain some impurities which need to be removed
2) transfer the product mixture to a separating funnel and add water to dissolve water-soluble impurities and create an aqueous solution
3) allow the mixture to settle in LAYERS. Drain off the aqueous layer at the bottom leaving behind the impure cyclohexene
the impure cyclohexane is at the top of this layer and the aqueous layer containing water-soluble impurities is at the bottom
what is likely to be the water-soluble impurities
most of the unreacted cyclohexanol
stage three: purification
1) drain the impure cyclohexene into a round bottomed flask
2) add anhydrous CaCl2 (a drying agent- it removes any traces of water) and stopper the flask. Let the mixture dry for at least 20 minutes with occasional swirling
3) the cyclohexene may still have small amounts of impurities so distil the mixture one last time. This time, only collet the product that is released when the product is around 83C - this will be the pure cyclohexane
what are the two methods to make methanol/ ana alcohol
- hydrating alkenes
- fermentation of glucose
what is the standard industrial method for producing alcohol
the standard industrial method for producing alcohols is to hydrate an alkene using steam in the presence of an acid catalyst:
CnH2n + H2O ⮀ CnH2n+1OH
Steam hydration of then is used industrially to produce ethanol
Ethene can be hydrated by steam at 300C and pressure of 60atm. It needs a solid phosphoric acid catalyst
the reaction is reversible and the reaction yield is low -only 5%
however, you can recycle the unreacted ethene gas so the overall yield is a more profitable 95%
what is the mechanism for the hydration of ethene
what are the conditions:
high temps of 300C
high pressures of 60atm-70atm
strong acid catalyst of H3PO4
what are the advantages of using hydration to form an alkene
- faster reaction
- purer product
- continuous process (which means cheaper manpower)
why is making ethanol carbon neutral
if you combine these three equations, you will see that exactly 6 moles of CO2 are taken in and exactly 6 moles of CO2 were given out
equation 1:
photosythesis
- fermentation
3, burning ethanol
write an equation for the partial oxidation of a primary alcohol to an aldehyde
write an equation for the full oxidation of a primary alcohol
draw a diagram for distillation
draw a diagram for reflux
write the equation for the oxidation of a secondary alcohol to a ketone
how do we distinguish between an aldehyde and a ketone
ab aldehyde can be further oxidised while a ketone can not. This is the chemical basis for tests that distinguish the two apart:
