Ester Purification and Analysis Flashcards
Is it possible to obtain PURE ester from simple distillation DIRECTLY AFTER the ester synthesis reaction?
–> See the image
(Mixture of ester, carboxylic acid, catalyst, and H2O)
NO It is NOT possible
–> Because the boiling points of each component are too close to one another to allow for separation by distillation
What does the BP difference need to be between substances in a mixture to allow for separation of the substances by distillation?
The BP difference must be >50C!!!!
GREATER THAN 50 degrees celsius!!!!!
Why did we distill the ester product after extraction?
To remove any possible BYPRODUCTS!
That result from the catalyst (H2SO4) reacting with the reactants (and then the byproducts themselves) of the ester synthesis reaction!
What byproducts could be present in the ester product after extraction?
- Ethers –> Due to reaction of alcohol with H2SO4
- Alkenes –> Due to acid-catalyzed dehydration of alcohol
- OTHER alcohols –> Due to acid-catalyzed HYDRATION of alkene
What is the smallest RBF available to us?
5 mL
What is the range of temperature fluctuation for a collected fraction to be considered pure?
1-3 degrees C
What methodologies can be used to analyze the IDENTITY of a compound?
- Boiling point
- Infrared Spectroscopy
What methodoloy can be utilized to analyse purity? (of ester)
GAS CHROMATOGRAPHY
Vibrational Frequency calculation
m1 and m2 refer to the two different atoms in a bond
K only differs between bond types (single, double, triple)
For reduced mass, multiplication ontop!
IR Spectroscopy
Works by subjecting sample to IR light and seeing how much of it is absorbed by the sample
–> Different components (bonds) absorb at different frequencies due to different molecular properties
The frequency of absorption of a sample increases (absorbs at higher frequencies) as ___________ increases
DIPOLE MOMENT
–> The greater the dipole moment, the greater the frequency of absorption will be!
(because stronger dipole moments = more deshielding!)
List the following in increasing order of absorption:
Alkanes, alkenes, alkynes
- Alkanes (lowest freq)
- Alkenes
- Alkynes (highest freq)
(stronger bonds absorb at higher frequencies because the electrons are more concentrated between atoms = deshielding effect on the atoms involved)
Stronger bonds absorb at…
HIGHER frequencies
What are the two main regions of an IR spectrum?
1) Functional group region (1400 and up)
2) Fingerprint region (below 1400)
IR is mainly used to…
Identify the functional groups present in a molecule
What IR peaks should be seen for an ester?
3 main peaks:
1) C-H peak (left most)
2) C=O peak (middle)
3) C-O peak (fingeprint region)
If you get an IR and see that it has the following peaks:
1) C-H peak
2) C=O peak
3) C-O peak
what can you determine from this?
You POSSIBLY have an ester!
We can only say with certainty that certain groups are present but we can’t specifically say what ester is present!
(Cannot be said with absolute certainty just from the functional groups)
What can we definitively determine from an IR spectrum?
Functional groups present
IR says nothing about….
PURITY
Although IR does not tell us about purity, it can tell us about…
IMPURITIES that are present if they are present in large quantities!
Why does IR NOT tell us about purity?
Because the ABSENCE of functional groups other than the ones you are “supposed to find” does NOT tell us that the compound is pure
–> What if there is an impurity with the same functional groups as the desired molecule?
What do we need to use in IR to determine EXACT ester identity?
The FINGERPRINT REGION
(is unique for every ester!)
–> Therefore we can compare an experimental IR of an unknown ester to the IR in literature for every ester to find which one matches!
Why CANT we use the functional grp region of an IR to determine the exact ester identity?
The functional group region will be largely the same for ALL esters
–> The func. grp. region is good for us to determine that we have AN ester but NOT WHICH ester we have
What are the mobile and stationary phases of gas chromatography?
Mobile Phase = GAS (helium)
Stationary Phase = Liquid (Ex:non-polar silicone oil)
