aldehydes and carboxylic derivatives Flashcards
Tollens why cant we heat w bunsen burner
when adding aldehyde or ketones to supply reac w eneryg heat using a water bath. no bunsen burner as aldehydes and ketones are flammable
reduction of aldehydes and ketones
aldehydes make primary alcohols (2h) ketones make secondary alcohols
what is this and potassium cyanide and carbonyl groups an example of
nucleophillic addition
what can happen if we use an unsymmetrical ketone or aldehyde
we can make a mixture of enantiomers
using kcn
irritant dangerous if ingested or inhaled, when it reacts w moisture it can form toxic gases eg hcn. to reduce wear gloves safety goggles lab coat to prevent contamination and use a fume cupboard
In order to ensure that the oxidation to ethanoic acid is complete, the reaction is
carried out under reflux.
Describe what happens when a reaction mixture is refluxed and why it is necessary,
in this case, for complete oxidation to ethanoic acid.
A mixture of liquids is heated to boiling point for a prolonged time
Vapour is formed which escapes from the liquid mixture, is changed back into
liquid and returned to the liquid mixture
Any ethanal and ethanol that initially evaporates can then be oxidised
esterification conditions
sulfuric acid catalyst
acid hydrolysis vs base hydrolysis
acid with water and h+ catalyst. splits into a carboxylic acid and an alcohol using h2s04 or hcl under reflux. however w a base. reacts w oh- to make a carboxylate ion and an alcohol.
phenyl propanoate+ naoh
ch3ch2coo-na+ and phenyl
vegetable oils vs animal fats
unsaturated hydrocarbon chains that are not straight which means the chains cant pack together closely and so have low vdw forces and so lower mp and so liquid room temp. animal fat opposite saturated uniform pack together strong vdws, solids at rtp
carboxylic acids + carbonates- what does this reac produce
carboxyolate salt, water, co2
equilibrium
carboxylic acids are weak acids therefore they disasociate poorly so they partially ionise so equilibirum lies well over to the left so not much carboxylate ions and h+’s are formed.
ch3cooh+ na2co3 and nahco3 equations
2ch3cooh+na2co3–>2ch3coona+h2o+co2
ch3cooh+nahco3—>ch3coona+h20+co2
base hydrolysis vs acid hydrolysis. using an ester.
ethyl ethanoate+h20(h+ catalyst eg h2so4)–>–carboxylate ion+alcohol.
so the acid hydrolysis one has a lower yield of the cooh and alcohol since the reac is reversible but the base one is one way so higher yield. but the base one produces a carboxylate ion rather than the cooh so its more expensive to make a cooh but u could further react it
further reac to ensure base hydrolysis forms a cooh
salt eg ch3coo-na+ +hcl–>ch3cooh+ nacl
conditions for esterification
coohs can react w alcohols in the prescence of a strong acid catalyst to form esters. carried out under reflux.
why are acid anhydrides used rather than acyl chlorides
cheaper and safer to use, less corrosive and doesnt produce toxic hcl gas.however it is a slower reaction the reaction with acyl chlorides is faster.
Give one advantage of the use of propanoyl chloride instead of propanoic acid in the laboratory preparation of methyl propanoate from methanol.
faster reaction and also its not a reversible reac and so has a bigger yield.
The student purified the crude solid product, N−phenylethanamide, by
recrystallisation.
(i) Outline the method that the student should use for this recrystallisation
Dissolve the product in the minimum volume of water / solvent (in a
boiling tube / beaker)
If dissolving is not mentioned, CE = 0 / 4
Hot water / solvent
Steps must be in a logical order to score all 4 marks
Allow the solution to cool and allow crystals to form.
Filter off the pure product under reduced pressure
) Assume that the reaction goes to completion.
Suggest two practical reasons why the percentage yield for this reaction may
not be 100%
) Any two from:
Product left in the beaker or glassware
Sample was still wet
Sample lost during recrystallisation
The product of step 1 was purified by recrystallisation as follows.
The crude product was dissolved in the minimum quantity of hot water and the
hot solution was filtered through a hot filter funnel into a conical flask. This filtration
removed any insoluble impurities. The flask was left to cool to room temperature.
The crystals formed were filtered off using a Buchner funnel and a clean cork was
used to compress the crystals in the funnel. A little cold water was then
PhysicsAndMathsTutor.com
Page 7
poured through the crystals.
After a few minutes, the crystals were removed from the funnel and weighed.
A small sample was then used to find the melting point.
Give reasons for each of the following practical steps.
The minimum quantity of hot water was used
……………………………………………………………………….
The minimum quantity of hot water was used:
To ensure the hot solution would be saturated / crystals would form on cooling
The flask was left to cool before crystals were filtered off:
Yield lower if warm / solubility higher if warm
The crystals were compressed in the funnel:
Air passes through the sample not just round it
A little cold water was poured through the crystals:
To wash away soluble impurities
The melting point of the sample in part (b) was found to be slightly lower than a
data-book value.
PhysicsAndMathsTutor.com
Page 8
Suggest the most likely impurity to have caused this low value and an improvement
to the method so that a more accurate value for the melting point would be obtained.
Water
Press the sample of crystals between filter papers
When T is heated with an excess of methanol, glycerol is formed together with a
PhysicsAndMathsTutor.com
Page 5
mixture of methyl esters.
(i) Give a use for this mixture of methyl esters.
biodiesel
Describe the experimental conditions and the practical method used to ensure
that the acid is obtained in a high yield. Draw a diagram of the assembled
apparatus you would use.
PhysicsAndMathsTutor.com
Page 6
Conditions …………………………………………………………………………………
…………………………………………………………………………………………………
Apparatus
Excess acidified potassium dichromate(VI)
Reflux (for some time)
In the diagram credit should be given for
• a vertical condenser
• an apparatus which would clearly work
) Describe the different experimental conditions necessary to produce propanal
in high yield rather than propanoic acid.
Distillation
Immediately (the reagents are mixed)
Propan-1-ol is a volatile, flammable liquid.
Give one safety precaution that should be used during the reaction to minimise this
hazard.
keep away from naked flames
You are provided with a small sample of pure aspirin in a melting point tube.
Describe briefly how you would determine an accurate value for the melting point of
aspirin.
Heat melting point tube in an oil bath
slowly near the melting point
Q6.Aldehydes can be prepared from acyl chlorides.
State how an aldehyde could be tested to show whether it is contaminated with traces of
unreacted acyl chloride.
State what you would observe
silver nitrate (solution) white precipitate
Explain the purpose of each underlined point.
Minimum volume ………………………………………………………………………………………..
…………………………………………………………………………………………………………………
Hot water ………………………………………………………………………………………………….
…………………………………………………………………………………………………………………
Filtered hot ………………………………………………………………………………………………..
…………………………………………………………………………………………………………………
Cooled in ice ……………………………………………………………………………………………..
…………………………………………………………………………………………………………………
Washed with cold water ……
Minimum volume and hot water:
to obtain saturated solution to increase yield / reduce amount left in solution enable crystallisation (on cooling)
Filtered hot: to remove insoluble impurities / to prevent crystals forming during
filtration
Cooled in ice: to increase amount of crystals that are formed
1
Washed with cold water: to remove soluble impurities
Haloalkanes such as CH3Cl are used in organic synthesis.
Outline a three-step synthesis of CH3CH2NH2 starting from methane. Your first step
should involve the formation of CH3Cl
In your answer, identify the product of the second step and give the reagents and
conditions for each step
CH3CN or ethan(e)nitrile or ethanonitrile not ethanitrile but allow correct formula with ethanitrile 1 for each step wrong or no reagent loses condition mark contradiction loses mark 1 Step 1 Cl2 uv or above 300 °C wrong or no reagent loses condition mark 1 Step 2 KCN 1 aq and alcoholic (both needed) allow uv light/(sun)light/uv radiation 1 Step 3 H2/Ni or LiAlH4 or Na/C2H5OH not CN– but mark on NOT HCN or KCN + acid, and this loses condition mark NOT NaBH4 Sn/HCl (forms aldehyde!) ignore conditions
Although Terylene is biodegradeable, it is preferable to recycle objects made from
Terylene.
Give one advantage and one disadvantage of recycling objects made from
Terylene.
Adv reduces landfill
saves raw materials
lower cost for recycling than making from scratch
reduces CO2 emissions by not being incinerated
not allow cost without qualification
ignore energy uses
1
Disad difficulty/cost of collecting/sorting/processing
product not suitable for original purpose, easily contaminated
use of esters
perfumes and food flavourings
solvents as polar can form hydrogen bonds w water
low bp can make glue
plasticisers
why are vegetable oils liquids at room temp
they have unsaturated hydrocarbon chains that are not straight which means the chains cannot pack closely together, so they have lower van der waals forces hence, lower melting points so their liquids at room temp
why are animal fats solids at room temp
they have saturated hydrocarbon chains that are straight and more uniform than oils which means that the chains can pack together closely and hence have much higher vdw forces so they have higher melting points and are solids at room temp
explain how carbon dioxide causes global warming
c=o bonds in co2 absorb infrared radiation
this does not escape
equation to show the role of aluminium chloride as a catalyst
AlCl4+ H+ –> Al3Cl +HCl
how would you draw a diagram to show how to filter crude oil under reduced pressure
side arm flask with flat bottomed funnel w filter paper clearly shown
you are provided with a small sample of pure aspirin in a melting point tube describe briefly how you wuold determine an accurate value for the mp
heat the melting point tube in an oil bath, slowly near the melting point.
suggest why excess naoh is used
suggest why an electric heater is used rather than a bunsen burner
suggest why reflux is used in this hydrolysis
suggest why sodium benzoate is soluble in cold water but benzoic acid is insoluble in cold water
to ensure that all the ester reacts
as the ethanol is flammable
reflux allows reactant vapours to be returned to the reaction mixture
sodium benzoate is soluble as it is ionic, benzoic acid is insoluble as despite the polarity of the cooh the benzene ring is non polar
describe the method the studebt should use to purify benzoic acid
dissolve crude product in hot water of minimum volume filter to remove insoluble impurities cool to recrystallise filter under reduced pressure wash with cold water and dry
