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
