Test for ester
Although there is very little information on testing for ester using information for Essential A2 Chemistry Book I found that esters can be hydrolysed with NaOH when heated in a water bath. Subsequently if I add phenylalanine indicator to the NaOH before I use it to hydrolyse the ester then the mixture will turn pink. Furthermore when esters are hydrolysed with NaOH they produce an alcohol and a salt. Therefore hydrolysing the ester with this mixture of NaOH and phenylalanine indicator the colour should change from pink to colourless as the alcohol and salt have a neutral pH. The most important part of this information is that when hydrolysing an ester with NaOH and phenylalanine indicator the mixture will change frompink to colourless.
Safety
Organic compounds – Most organic compounds are volatile and easily flammable so during the wet tests we cannot use a Bunsen burner
Sodium – Sodium is highly flammable and corrosive. Because it reacts violently with water it must be stored in oil. It forms the highly flammable gas hydrogen when reacted with alcohol or water so reaction must be carried out in a fume cupboard with gloves.
Brady’s reagent – 2,4-dinitrophenylhydrazine is toxic and explosive. If contact is made with a combustible material it may cause fires. Because of its explosiveness avoid heat, friction or shock. If contact is made with the skin or if its swallowed it is very toxic. When contact has been made with the skin it stains it yellow which can be followed by dermatitis.
Fehling’s reagent – Fehling’s solution is extremely flammable, an irritant and harmful. This is because the vapours can catch fire at temperature above 30oC and it is irritating to the eyes, skin and respiratory systems.
Bromine water – Bromine is very toxic and corrosive. The vapour can be lethal if inhaled and the liquid causes severe burns to the eyes and skin, so reaction carried out must be done in a fume cupboard with gloves and goggles.
Iodoform - Iodoform is harmful by ingestion, inhalation and through skin contact. Eye, skin and respiratory irritant
Potassium Dichromate – Potassium dichromate is toxic and can be lethal if inhaled. It is classed as a carcinogen and may cause cancer by inhalation. It is harmful if in contact to the skin and can cause irritation. If swallowed it is very toxic.
Sulphuric acid – Being an acid sulphuric acid is very corrosive and can cause severe burns.
Apparatus
- Test tube
- Boiling tube
- Conical flask
- Measuring cylinder
- Pipette
- Beaker
- Kettle
- Filter paper
- Glass tile
- Scalpel
- Forceps
Method
Because of the corrosive chemicals you will be handing at all times you must wear goggles, gloves and a lab coat if necessary.
- Pour the unknown compound into a beaker with the approximate volume of how much you think you will need to use. If more is needed during the wets test you can go and refill the beaker
- Transfer the beaker to your working area
Reaction with Sodium
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Pour approximately 5cm3 of the unknown compound from the beaker into a measuring cylinder
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Pour this 5cm3 from the measuring cylinder into a test tube
- Put the test tube into a test tube rack in a fume cupboard
- Using a scalpel cut out a tiny amount of sodium the size of a grain of rice on a glass tile
- Using forceps put this sodium on a filter paper
- Transfer it to a balance using filter paper and measure it to approximately 0.05g
- Carry the sodium on the filter paper to the fume cupboard
- Put the 0.05g of sodium into the test tube in a fume cupboard using forceps
- Wait for several seconds to see whether there is a reaction
- If bubbles are produced then this is a positive result
- If nothing happens then there has been no reaction
- Because sodium is a very reactive metal to dispose of the sodium you have to add an excess of ethanol in a beaker and once the reactions have stopped carefully add the solution to a bucket of water and dispose down the foul water drain
Universal Indicator
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Pour approximately 5cm3 of the unknown compound from the beaker into a measuring cylinder
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Pour this 5cm3 from the measuring cylinder into a test tube
- Put the test tube into a test tube rack in your working area
- Using a pipette suck into the pipette a small amount of universal indicator and add approximately 5 drops of the liquid into the test tube
- Put a lid on the test tube and shake vigorously
- Wait to see a colour change if the mixture remains yellow then the compound has a pH of 7
- If the mixture turns red then it acid and has a lower than pH
- To dispose of this mixture dilute it with 10 litres of water in a beaker and pour id down the foul water drain
Reaction with bromine water
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Pour approximately 10cm3 of the unknown compound from the beaker into a measuring cylinder
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Pour this 10cm3 into a conical flask
- Move the conical flask to the fume cupboard
- In the fume cupboard using another beaker pour a tiny amount of bromine water into the beaker
- Pour all the bromine water in the beaker into the conical flask
- Shake the mixture of the unknown compound and bromine solution in the conical flask being careful not to spill any as it is corrosive
- If the mixture remains brown i.e. the colour of the bromine water then no reaction has taken place
- If the mixture decolourises or forms a white precipitate then a reaction has taken place
- To dispose of this mixture pour it into a beaker and add with stirring 1ml amounts of 500ml of 10% sodium carbonate solution and then pour down the foul water drain
Reaction with Brady’s Reagent
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Pour approximately 5cm3 of the unknown compound from the beaker into a measuring cylinder
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Pour this 5cm3 from the measuring cylinder into a test tube
- Put the test tube into a test tube rack in your working area
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Using a pipette suck into the pipette a small amount of Brady’s reagent (2,4-dinitrophenylhydrazine) and add approximately 5cm3 of the solution into the test tube
- Put a bong on the test tube and shake vigorously
- If the unknown compound is a ketone or aldehyde then an orange precipitate will be formed
- If there is no formation of an orange precipitate then no reaction has occurred
- To dispose of the Brady’s reagent you have to dilute it with 10litres of water and pour it down the foul water drain
Reaction with Fehling Reagent
- Pour water into a kettle and heat the water
- Once the water as been heated pour it into a into a large beaker and let it cool
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Pour approximately 5cm3 of the unknown compound from the beaker with the unknown compound into a measuring cylinder
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Pour this 5cm3 from the measuring cylinder into a boiling tube
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Using a pipette suck into the pipette a small amount Fehling’s reagent and add approximately 5cm3 of the solution into the boiling tube
- Put the boiling tube into the beaker and warm the unknown compound in a water bath
- If there is a colour change from blue to red then the unknown compound is an aldehyde
- If there is no change then a reaction has not taken place
Reaction with Acidified Potassium Dichromate
- Pour water into a kettle and heat the water
- Once the water as been heated pour it into a into a large beaker and let it cool
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Pour approximately 5cm3 of the unknown compound from the beaker with the unknown compound into a measuring cylinder
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Pour this 5cm3 from the measuring cylinder into a boiling tube
- Put the boiling tube into a test tube rack in your working area
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Using another measuring cylinder pour 5cm3 of sulphuric acid into the measuring cylinder
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Pour this 5cm3 of sulphuric acid into a beaker
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Using yet another measuring cylinder pour 5cm3 of potassium dichromate into the measuring cylinder
- Pour this potassium dichromate into the same beaker which contain the sulphuric acid making acidified potassium dichromate
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Using a pipette suck into the pipette approximately 5cm3 of the acidified potassium dichromate solution which is orange in colour and put it into the boiling tube with the unknown compound
- Put this boiling tube into the beaker with warm water to warm in a water bath
- If the mixture turns from orange to green then the unknown compound is a primary alcohol
- If the mixture remains orange then a reaction has not taken place
- To dispose of this mixture pour into a beaker and dissolve it in 2M of hydrochloric acid, allow to stand for a few hours and then dilute it with excess water and pour it down the foul water drain
Iodoform test
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Pour approximately 5cm3 of the unknown compound from the beaker into a measuring cylinder
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Pour this 5cm3 from the measuring cylinder into a test tube
- Put the test tube into a test tube rack in a fume cupboard
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In the fume cupboard using a pipette put into the test tube with the unknown compound inside 2cm3 of 2M sodium hydroxide
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Using another pipette in the fume cupboard put 3cm3 of the 10% of iodine in KI into the test tube
- If a yellow crystalline precipitate is formed then a reaction has taken place and the unknown compound is a methyl ketone
- If the mixture remains clear then no reaction has taken place
- To dispose in the fume cupboard ass to 250ml of 1M (25%) sodium thiosulphate solution. When the solution is colourless, add the contents to a bucket of water and pour down the foul water drain
Reaction with Lucas reagent
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Pour approximately 5cm3 of the unknown compound from the beaker into a measuring cylinder
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Pour this 5cm3 from the measuring cylinder into a test tube
- Put the test tube into a test tube rack in your working area
- Using a pipette put into the test tube 5cm3 of Lucas reagent
- Put a lid on the test tube and shake vigorously
- If a cloudy emulsion is formed then the unknown compound is a tertiary alcohol
- If the mixture remain clear then a reaction has not taken place
- To dispose dilute 10litres of water and pour down the foul water drain
Hydrolysing with NaOH
- Pour water into a kettle and heat the water
- Once the water as been heated pour it into a into a large beaker
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Pour approximately 5cm3 of the unknown compound from the beaker with the unknown compound into a measuring cylinder
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Pour this 5cm3 from the measuring cylinder into a boiling tube and put the boiling tube into the water bath
- Hydrolyse the unknown compound for several minutes and wait for a colour change
- After 10 minutes if there is colour change then the unknown compound is an ester
- If after 10 minutes if there is no change in colour then no reaction has taken place
Analysis of compound A
Reaction with Bromine water:-
The first wet test in my flow chart was the reaction of compound A with bromine water. There was no reaction, as compound A did not decolourise the bromine water nor did a milky emulsion form in the test tube. This therefore meant that my unknown compound was not an alkene or a phenol and instead it can be a primary alcohol, tertiary alcohol, aldehyde, ketone, carboxylic acid or an ester. If it was an alkene the C=C bond would have decolourised the bromine water.
Reaction with Brady’s reagent:-
The second wet test in my flow chart was the reaction of compound A with Brady’s reagent, which is a mixture of 2, 4 dinitrophenylhydrazine. In this experiment a positive reaction occurred as an orange precipitate formed, which indicated the presence of an aldehyde or a ketone. This consequently meant that my unknown compound was not a primary alcohol, tertiary alcohol, carboxylic acid or an ester instead it was either an aldehyde or a ketone.
Reaction with Tollen’s reagent:-
Due to the second wet test in my flow chart which confirmed the presence of an aldehyde or a ketone in my unknown compound, I will now warm my unknown compound with Tollen’s reagent, to help me distinguish between an aldehyde and a ketone.
When compound A reacted with Tollen’s reagent no reaction occurred and this meant that mu unknown compound was a ketone, as if it was an aldehyde a silver mirror layer would have formed inside the test tube, but instead there was no reaction.
Though my wet tests have indicated that my unknown compound is a ketone, I will also however, use the three spectrums to help me identify which ketone it is and to also support my wet test finding results even more.
Infrared spectrum
The infrared spectrum for compound A showed that it has alkyl groups because of the peaks at the wavelengths 3000cm-1, but this does not help us identify the compound because most organic compound contain alkyl groups. However because there is also an absorption peak at 1750cm-1 this shows that there is also a C=O in compound which tells us its either a carboxylic acid, ester, amide, aldehyde or ketone as these all contain the C=O. Subsequently because:
there is no broad absorption peak at 2500-3300cm-1 it tells us it is not a carboxylic acid an this indicates there is no –OH bond as found in carboxylic acids
there is no absorption peak at 1250-1 it tells us it is not a ester as this indicates there is no C-O bond as found in esters
there is no absorption peak at 3300-3500cm-1 it tells us it is not a amide as this indicates there is no N-H bond as found in amides
there is no absorption peak at 2800cm-1 it tells us it is not an aldehyde as this indicates there is no C-H aldehyde bond in aldehydes
Therefore it is a ketone as none of the above absorption peaks are present. Consequently because my wets tests indicated that compound A was a ketone I believe what the infrared spectrum is telling me is correct as I expected to find the absorption peaks for the bonds found in ketones which the C=O, which was present in the IR spectrum.
Mass Spectrum
The mass spectrum can be used to identify a molecules structure as it tells you the molecular ion produced and its mass/charge ratio which is equivalent to the Mr of the molecule. In addition to this it also tells you the fragments produced which helps you to identify which of the several isomers the molecules could be. For compound A the molecular ion which is furthest to the right tells us that the Mr of the ketone I have is 59, this tells me that in the organic compound I have there is 3 carbons, 6 hydrogens and 1 oxygen. However this suggests that the Mr of the ketone is 58 when the mass spectrum tells me its 59 this must mean that one of the carbons in the compound is the isotope 13C, which I will try and prove using the fragments that the mass spectrum also shows.
The largest fragment the base peak has a mass/charge ratio of 44 which tells us that the ketone split homolytically as the electrons in the single bond were shared equally making the molecular ion produced have 2 carbons, 3 hydrogens and 1 oxygen. However as before this suggests the Mr should be 43 but because of the 13C its Mr is 44.
The second largest fragment has a mass/charge ratio of 58 which tells us that again the single bond split homolytically to produce a molecular ion which has a Mr of 58 meaning it has 3 carbons, 5 hydrogens and 1 oxygen. Again because of the 13C isotope this molecular ion has an increased mass. Finally the third largest fragment has a mass/charge ratio of 15 which tells us that the single bond has split hetrolytically because for this molecular ion occur both electrons must remain with the larger fragment because it has the positive ion. Therefore by splitting hetrolytically the smaller will have a positive charge and the large a negative. In addition to this the mass/charge ratio of 15 tells us the molecular ion has 1 carbon and 3 hydrogens which means that this fragment does not have the 13C isotope.
In conclusion the mass spectrum has shown me that the compound has a structure of CH3COCH3 because this is the only possible structure for a ketone with 3 carbons as ketones cannot be on the end of the chain. Additionally this agrees with the iodoform test I did which told me the ketone I had was a methyl ketone as this is a methyl ketone. Furthermore for base peak to occur and form the molecular ion CH3CO+ the C-C bond must have split and for the CH3+ molecular ion to occur the same bond must have but hetrolytically.
NMR
The NMR tell us the environments the hydrogens in the compound are in and I believe I can use this to tell me whether the structure I proposed for the ketone I believe to have is accurate. The chemical shift of 2.1 shows that the type of hydrogen in that environment is R-COCH3 this means that there will be no splitting of the peak because there is no hydrogens on a carbon adjacent to the hydrogens on the CH3. In addition to this because the nmr tells use that there are 6 hydrogens in this environment the Are group must be another CH3. Therefore the structure of the ketone I have is CH3COCH3 as I proposed above. Consequently unknown compound A is the ketone propanone otherwise better known as acetone.