Lab A: Synthesis of Salicylic Acid Flashcards
(64 cards)
what are 4 uses of salicylic acid?
- as a keratolytic agent
- as an antibacterial agent
- as an anti-dandruff agent
- as a precursor molecule
draw the reaction pathway for the synthesis of salicylic acid
draw the transformation of functional groups
draw the reaction for base promoted hydrolysis of methyl salicylate
hydrolysis is base ___, NOT base ___. and explain why
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 like a catalyst would be
what is the most common type of lipid?
triacylglycerol
draw the reaction and products of the hydrolysis of triacylglycerols
what are 4 facts about the hydrolysis of triacylglycerols?
- Each triacylglycerol is a triester containing three long hydrocarbon side chains (Typically, the R groups have 12-20 C’s) .
- Metabolism of a triacylglycerol: Cleavage of three ester bonds forms Glycerol and three long-chain fatty acids.
- Hydrolysis of a Lipid is the same as the Hydrolysis of an Ester Hydrolysis.
- This lipid hydrolysis is catalyzed by the enzyme lipases.
what is saponification?
base-promoted hydrolysis of triacylglycerols
theoretical yield
the yield of a reaction assuming 100% conversion of the limiting reactant to the product
limiting reagent
The reactant that is present in the smallest amount and would limit the amount of product possible
the moles of product (i.e. theoretical yield) is determined by the moles of “limiting reactant” on a molar equivalent basis
percent yield
% yield = actual yield / theoretical yield * 100
stoichiometry review: multistep synthesis (2 tips)
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? (Definition)
Convenient way to purify a solid organic compound by using a suitable solvent
an impure solid compound is COMPLETELY dissolved in a boiling solvent and then ALLOWED TO COOL SLOWLY to form beautiful pure crystals
- impurities not soluble at hot temp may be removed by hot gravity filtration
- impurities soluble at cold temp will remain in the bulk of the solution/filtrate
what is the technique/2 steps of recrystallization?
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 later, once substantial crystal formation is observed- cool in an ice-water bath)– allows for the formation of purer, larger crystals. This is because impurity molecules have sufficient time to return to the solution
why do you SLOWLY cool the solution for recrystallization and not RAPIDLY cool it?
slow cooling allows for the formation of purer and larger crystals since the impurity molecules have sufficient time to return to the solution
rapid cooling results in PRECIPITATION and the impurities are trapped due to the rapid formation of the lattice
- aka the impurities stay trapped by the solute molecules that are crystallizing as the solid lattice reforms
how does the “like dissolves like” concept relate to recrystallization?
the polarity of the solvent and the polarity of the compound being recrystallized should be similar
Q. What is the rule for selecting a good solvent for recrystallization? (Is it answer choice A or B?)
A. The solid you are trying to purify should be soluble in the hot solvent and insoluble in a cold or room temperature solvent.
B. The solid you are trying to purify should be insoluble in the hot solvent and soluble in a cold or room temperature solvent.
A. The solid you are trying to purify should be soluble in the hot solvent and insoluble in a cold or room temperature solvent
what is vacuum filtration? (definition)
a technique used to quickly and completely separate a solid from the liquid with which it is mixed
what are 4 technique points to keep in mind when doing a vacuum filtration?
Direction of Ring stand (front facing)
Vacuum filter flask is firmly clamped to prevent from tipping over
Uses an Adapter to ensure a tight seal between Buchner funnel and vacuum filter flask
Employs Heavy-walled rubber tubing to prevent the tubing from collapsing from atmospheric pressure on the outside when the vacuum is applied
what are the 2 sources of vacuum for vacuum filtration?
- water aspirator
- compressor-driven vacuum system
vacuum filtration: when washing the filtered crystals with solvent….
always use SMALL portions of solvent to avoid washing away small amounts of your product
vacuum filtration: to ensure efficient drying of the product, after the 1st round of filtration…
- empty the mother liquor from the vacuum filter flask and then connect the filter flask back to the vacuum line
- pull air only over the crystals inside the filter funnel
what are the steps for drying your product after vacuum filtration?
NOTE: your product is still wet even after vacuum filtration
1. weigh an empty watch glass
2. transfer the product to the water glass
3. weight the product and record this weight as WET mass in lab notebook
4. break down big clumps of product and leave to airdry in drawer until next lab
5. the following week: weight the DRY product and compare the WET and DRY mass of the product
