Lab A: Synthesis of Salicylic Acid Flashcards
What is one real life application of salicylic acid?
Found in many anti-dandruff shampoos as it helps loosen dry skin on the scalp and remove dry skin flakes
Draw the chemical formula that shows the synthesis of salicylic acid
In notes
What is the approx pKa of a phenol
10
What is the approx pKa of a carboxylic acid functional group?
3.5
Draw the base-promoted hydrolysis of methyl salicylate. Why is it base promoted and not base catalyzed?
Hydrolysis is base promoted, not base catalyzed – because the base (OH–)
is the nucleophile that adds to the ester and forms part of the product. It
participates in the reaction and is not regenerated later
Draw the hydrolysis of triacylgylcerols
Drawn in ntoes
How do you calculate % yield?
% Yield = Actual Yield / Theoretical Yield x 100
In a multistep synthesis, the overall percent yield is determined by
multiplying the yield of each step expressed as a decimal.
Multiply the answer by 100 to convert final value back to % yield
What is recrystallization?
A convenient way to purify a solid organic compound by using a suitable solvent
Step 1. Impure solid is dissolved in an appropriate hot solvent - the impure crystal lattice breaks down
Step 2. Slow cooling of the solution(first on bench top, undisturbed, and late, once substantial crystal formation is observed, cool in an ice-water bath) allows for the formation of purer, larger crystals.
Why does slow cooling allow of the formation of purer, larger crystals?
Impurity molecules have sufficient time to return to the solution. Rapid cooling results in precipitation where impurities are trapped due to rapid formation of the lattice(impurities stay trapped by the solute molecules that are crystallizing as the solid lattice reforms).
In recrystallization, the polarity of the solvent and that of the compound being recrystalllied should be
similar
What is the rule for selecting a good solvent for
recrystallization?
Rhe solid you are trying to purify should be soluble in
the hot solvent and insoluble in a cold or room
temperature solvent.
Draw a vacuum filtration schematic
Drawn in notes
Vacuum filtration is a technique used to
quickly and completely separate a solid form the liquid with which it is mixed
How do you neutralize waste acidic filtrates?
Use NaHCO3 and add it into the beaker until it is neutral . This should be done in the neutralizing hood
How can melting point capillary tubes be identified?
should be closed on one ed
sample height in a capillary tube
2-3 mm
What heating rate should be set on the Digital MeltTemp? why?
Heating rate to be maintained at 2 degrees celsius per minute. The sample has to be melted slowly for two reasons:
- Thermometer lag: occurs when the sample melts before the thermometer has a chance to reach that temperature
- Broad range: observed when melting too quickly
The observed melting point is always recorded as a _______.
Range
First reading on the range: temperature at which the solid block first begins to liquefy
Second reading of the range: temperature at which the solid completely melted
When using a Digital Melt temp, samples should never be
re-melted
How should MP capillary tubes be disposed off?
In the red sharps contianer
What happens when a melting point is determined?
Solid phase changes to liquid phase
loss of order in crystalline lattice
Does the presence of impurities increase or lower the observed MP range of a compound?
lowers the observed melting point range of a compound, meaning it broadens the range and makes the melting point appear lower than for a pure sample;
Impurities lower the melting point of a substance because they disrupt the orderly crystal lattice structure of a pure solid, creating defects that weaken the intermolecular forces holding the molecules together, thus requiring less energy to transition into a liquid phase,
When washing the filtered crystals with solvent, you should always
use small portions of solvent to avoid washing away your product
What are the two sources of vacuum
- Water aspirator
- Compressor-drivenvacuum system
To ensure the efficient drying of the product, what should you do after the 1st round of filtration?
Empty the mother liquor(filtrate) form the vacuum filter flask
pull air only over the crystals inside the filter funnel
What is used to ensure a tight seal between Buchner funnels nd vacuum filter flask?
adapter
Vacuum filtration employs heavy-walled rubber tubing. Why?
prevent the tubing from collapsing from atmospheric pressure on the outside when the vacuum is applied
what is methyl salicylate used for in real life?
used to flavour candy and perfumes
Bengal pain relieving ointment
Salicylic acid is a white crystalline solid that is found naturally in ________, which has been used as pain relievers since before Hippocrates
the extractors of willow bark
While salicylic acid served both as a pain reliever and an anti-inflammatory, it was also extremely irritating to the lining of the stomach. _______ found that by converting the phenol group in salicylic acid into an ______, he was able to obtain aspiring which had many of the same pain relieveing properties as salicylic acid but did not produce as sever gastrointestinal side effects
Felix Hoffman
acetyl group
What are the benefits of aspirin other than pain relief
reduce heart attack risk
anti-clotting activity
prevents ischemic strokes
The iron trichloride test is very sensitive but not very
specificSu
marine the chemical reaction that is the synthesis of salicylic acid
methyl salicylate is treated with sodium hydroxide in water to convert the methyl ester functional group into a carboxylic acid.
the conversion of an ester functional group into a carboxylic acid functional group with a base is termed
saponification or soap making
Why is an erelenmeyer flask used for the reaction?
the sloped sides help to reduce the amount of solvent that evaporates and to reduce loss of materials due to splashing during the reaction.
What is the hazard associated with methyl salicylate?
toxic in high doses
What is the hazard associated with salicylic acid
toxic in high doses
what is the hazard associated with sodium hydroxide and HCl
corrosive
What is the pKa of the phenol proton
13.6
How does the isolation of salicylic acid take advantage of the acidic properties of the molecules involved?
In the presence of a strong base, the protons on the phenols nd the carboxylic acid will be sremoved and the solution will have the very water soluble disodium sale/ In order to produce the salicylic acid, enough acid needs to be added to lower ht eps of the solution to below 3. After adding the 6M HCl, a large amount of white precipitate will form which will be the salicylic acid.
General procedure
- Mix methyl salicylate and NaOH
- Boil
- Ice water bath
- add HCl
- Vacuum filtration
- transfer precipitate and add water. Boil
- let sit and then ice water bath
- vacuum filtration
What happens to the waste acid filtrate
neutralized with NaHCO3
Once the salicylic acid has precipitated, how will it be further purified?
Recrystallization
an impure solid compound is completely dissolved in a boiling solvent and then allowed to cool slowly.
Why is it necessary to empty out the filtrate from the vacuum filter flask before pulling air over the crystals?
we wan to ensure that the entire vacuum pressure is being used to dry the product.
