2.7 alcohols and carboxylic acids Flashcards
what is the functional group of alcohols?
-OH
how can you work out wether an alcohol is primary, secondary or tertiary?
- look at the carbon directly bonded to the -OH group
- count how many carbons this carbon is bonded to
name:
. H H H
I I I
H - C - C - C - H
I I I
OH OH OH
propane-1,2,3-triol
e - bc more than 1 alcohol group
decide whether this alcohol is primary, secondary or tertiary?
. H H H H
I I I I
H - C - C - C - C - H
I I I I
H OH H H
secondary
what are the 3 ways of making alcohols?
- fermentation
- from alkenes
- from halogenoalkanes
how does making alcohols from fermentation work?
- glucose from the sugar cane plant is converted to ethanol and CO2
- reaction is carried out between 30-35.C
- enzyme (zymase) in yeast convert the glucose to the products
- reaction is carries out in the absence of oxygen (anaerobic conditions) otherwise ethanol is oxidised to vinegar
- the ethanol is separated from the mixture by filtering and then by distillation to give 96% pure ethanol
- ethanol produced this way is sometimes referred to as a biofuel (a fuel produced by a biological process)
what is the formula for the reaction of making alcohols from fermentation?
C6H12O6 —> 2C2H5OH + 2CO2
what are the conditions for the reaction of making alcohols from fermentation?
- between 30-35°C
- enzyme (zymase) in yeast
- anaerobic conditions
why is the reaction of making alcohols from fermentation carried out in anaerobic conditions?
otherwise the ethanol is oxidised to vinegar
how is the ethanol separated from the mixture in the reaction of making alcohols from fermentation?
by filtering and then by distillation
(con)
what is a biofuel?
a fuel produced by a biological process
what are the cons for the reaction of making alcohols from fermentation?
- takes a long time
- filtering and distillation
- this process doesnt produce 100% concentrated ethanol as fermentation stops when the concentration of ethanol reaches around 15% bc at these levels enzymes in the yeast cease to function
what are the advantages and disadvantages of biofuels?
disadv:
- biofuels release less energy per gram compared to fossil fuels
- more people are required to produce biofuels compared to fossil fuels
- more land is required to be cleared to grow the plants which can lead to deforestation
- not really carbon neutral as dont take into account fuel needed to build factories, transport raw materials etc
adv:
- increased income for farmers
- helps lower fuel prices as biofuels limit the demand for fossil fuels
- renewable
- carbon neutral - bc even tho produce CO2, plants take it in
how can alcohols be made from alkenes?
CALLED A HYDRATION/ADDITION REACTION
- steam and ethene are passed over a catalyst of conc sulfuric or phosphoric acid
. H H H H
I I I I
C=C + H2O (g) —> H - C - C - O - H
I I I I
H H H H
what are the conditions for the addition reaction of making alcohols from alkenes?
- 300°C
- 60-70 atm
- concentrated sulfuric or phosphoric acid catalyst
what is the name of the reaction of making alcohols from alkenes?
addition reaction
what is the name of the reaction of making alcohols from halogenoalkanes?
nucleophilic substitution
what are the conditions for nucleophilic substitution (making alcohols from halogenoalkanes)?
- aqueous sodium hydroxide
- reflux/warm
what does an addition reaction mean?
there’s only one overall product
what are the 2 reactions of alcohols?
- dehydration/elimination
- oxidation reactions
what does the dehydration/elimination reaction form?
an alkene (from an alcohol)
what is the dehydration/elimination reaction?
- alcohol —> water + alkene
- dehydrate means to eliminate water
- if you dehydrate an alcohol, you lose the -OH group and an adjacent (next C over) hydrogen atom to make the eliminated water molecule
. I I I I /
- C - C - C - O - H —> - C - C =C
I I I I I \
what are the conditions for the dehydration/elimination reaction?
- concentrated sulfuric acid
- 170°C
can this alcohol be dehydrated?
.
I
- C -
I I I
- C - C - C - OH
I I I
- C -
I
no because the C adjacent to the C with the OH doesn’t have a H to lose
what happens during the oxidation reaction of alcohols?
- an oxidation reaction can be thought of a molecule that gains an oxygen atom or one that loses hydrogen
- loss of electrons - can be seen as colour changes in the oxidising agent
- main oxidising agent for AS is acidified potassium dichromate H+/K2Cr2O7 (sometimes referred to acidified dichromate which is the same reagent but missing out the potassium H+/Cr2O7 2-
- to make the oxidising agent we add potassium dichromate and sulfuric acid
- water is always produced
how do you make the oxidising agent in the oxidising reactions of alcohols?
add sulfuric acid and potassium dichromate (hence acidified potassium dichromate)
what are the two products that the oxidation reactions of PRIMARY alcohols make? how are they made?
- aldehydes - partially oxidised using acidified potassium dichromate under reflux (heating) and then distill it out
- carboxylic acid - full oxidation by heating under reflux with acidified potassium dichromate (not distilled)
what is the colour change from adding acidified potassium dichromate to an alcohol? (TEST FOR ALCOHOLS)
from orange to green
what are the conditions of the oxidising reaction from alcohols to aldehydes?
- acidified potassium dichromate
- heat followed by distillation
what are the conditions of the oxidising reaction from alcohols to carboxylic acids?
- acidified potassium dichromate
- reflux
if the aldehyde is not distilled out, can the aldehyde be further oxidised to a carboxylic acid?
yes
aldehyde functional group:
. O
//
R - C
\
H
carboxylic acid functional group:
. O
//
R - C
\
OH
what does [O] represent?
the oxidising agent (e.g acidified potassium dichromate)
what is the product that the oxidation reactions of SECONDARY alcohols made?
- ketones
what are the conditions for the oxidising reaction of making ketones?
- acidified potassium dichromate
- reflux
ketone functional group:
. O
I II I
- C - C - C -
I I I
how are ketones different to aldehydes?
as the C=O in ketones are bonded to 2 other carbons
while in aldehydes, the C=O is bonded to 1 other C atom and 1 hydrogen
what is the name endings for aldehydes?
- al
(e.g ethanal)
what is the name endings for ketones?
- one (own)
e.g butan-2-one
how do you test for primary and secondary alcohols?
add acidified potassium dichromate under reflux
orange —> green
(doesnt work for tertiary alcohols)
why can’t you test for tertiary alcohols using APD?
(for the scope of A level, tertiary alcohols are resistant to oxidation)
so adding acidified potassium dichromate under reflux has NO EFFECT
what is the name ending for a carboxylic acid?
-oic acid
e.g ethanoic acid
what are the 2 ways of testing for a carboxylic acid?
- add a carbonate
- add a hydrogencarbonate
how does the test for carboxylic acids bu adding a carbonate work?
- add a carbonate (e.g sodium carbonate)
- this produced bubbles/effervescence (of carbon dioxide gas)
how does the test for carboxylic acids by adding a hydrogencarbonate work?
- add a hydrogencarbonate (e.g sodium hydrogencarbonate NaHCO3)
- this produces bubbles/effervescence (of carbon dioxide gas)
what is seen when carboxylic acids are reacted with bases?
no VISIBLE reaction is seen
what is the formula and charge of a hydrogencarbonate?
HCO3 -
how are esters formed?
from reactions of carboxylic acids with alcohols
- the carboxylic acid loses an -OH group and the alcohol loses a H. this combines to make wager as a by-product
what is the type of reaction that occurs between alcohols and carboxylic acids called?
esterification
(opposite of hydrolysis)
what are esters described as?
sweet smelling compounds
is esterification reversible?
yes
so le chatelier applies
what are the conditions for esterification?
- concentrated H2SO4 or concentrated HCl catalyst
- reflux
in order to increase the yield of ester in esterification, what can you do?
remove the water produced
so equilibrium shifts to replace it so increases yield of ester
how do you name esters?
- name the section that came originally from the alcohol first, then the bit that came from the carboxylic acid
- esters end in -oate
name the ester:
. O
II
C CH3
/ \ /
H3C O
methylethanoate
what is the general formula of alcohols?
CnH2n+1OH
how do you name alcohols if the -OH group is not the main functional group in the chain?
it is referred to as a ‘hydroxyl-‘ group
e.g 2-hydroxybutanoic acid
are smaller chain alcohols miscible (mixes with water easily)?
yes due to their ability to hydrogen bond with water molecules
what are some uses of alcohols?
- ethanol has been used as the active ingredient in alcoholic drinks
- ethanol is used as a biofuel and used as a petrol substitute in countries where oil supplies are low
what are the results of primary, secondary and tertiary alcohols with litmus paper?
primary - blue to red
secondary - remains blue
tertiary - remains blue
explain how ethanol can be separated from water?
ethanol and water have different boiling points so they can be separated by distillation
- the mixture is heated until the ethanol evaporates
- the ethanol vapour enter the condenser where they condense and run into a beaker
in an industrial process where the forwards reaction is exothermic, so a high yield would be favoured by a low temperature, why isnt a low temperature used?
as this would give a slow rate of reaction, so a compromised temperature is used
in an industrial process where a high yield is favoured by a high pressure, why isnt a high pressure used?
as a too high pressure is expensive to maintain
are carboxylic acids strong or weak?
they are weak acids
carboxylic acid + alcohol ⇌
ester + water
alcohols react with carboxylic acids to form esters.
a method used to separate the product from the liquid mixture is distillation.
state which property of an ester allows this method of separation to be used? [1]
the boiling temperature of ester is lower than alcohol/acid
