Lab B: Synthesis of Aspirin Flashcards
write the reaction scheme for synthesis of aspirin
- the synthesis of aspirin is an example of what type of reaction?
esterification reaction
an equivalent (definition)
the experimental ratio in which reactants are added to thh reaction
what is the stoichiometric ratio for acetic anhydride and salicylic acid?
Acetic anhydride and salicylic acid react in a 1:1 ratio
HOWEVER…to favor the formation of Aspirin, the reaction is optimized by using 3.0 equivalents of acetic anhydride to 1.0 equivalent of salicylic acid
- aka three times the number of moles of acetic anhydride compared to the moles of salicylic acid
stoichiometric ratio is used to calculate what?
stoichiometric ratio is used to calculate the percent yield
equation to calculate the theoretical yield of salicylic acid
moles methyl salicylate x mol ratio (SA/ Methyl salicylate) x Mol. Wt. Salicylic acid (g/mol) = Y g of Salicylic acid
equation to calculate the volume (mL) of acetic anhydride needed for the synthesis of aspirin
0.9 x Xg SA/MW (g/mol SA) x 3mol Acetic anhydride/1mol SA x MW (g/mol) Acetic anhydride/Density (g/mL) Acetic Anhydride = Z (mL) of Acetic anhydride
- molecular weight of aspirin: 180.16g/mol
equation for the overall % yield for aspirin synthesis
% yield from Lab A x % yield from Lab B x 100
describe the small scale solvent test for the recrystallization of aspirin
Sample of crude Aspirin (transfer a small amount using a
spatula) to two test tubes + 1/3rd of the test tubes filled
with solvent (H2O or Ethanol (C2H5OH)) respectively
–> for this experiment, water is the better solvent (should observe that aspirin stays undissolved in water at room temp; whereas aspirin dissolves in ethanol at room temp)
describe the purity test/check with Aq. FeCl3 solution and steps
PHENOLS react with FeCl3 (aq) to produce a DEEP PURPLE solution
Separately test each of the following in a test tube, with 1 mL of Ethanol and
3 drops of 0.02 M aq. FeCl3 solution:
1. A small quantity (tip of spatula) of Salicylic acid (as a control) and
2. A small quantity (tip of spatula)of Aspirin
a QUALITATIVE test that indicates the presence of unreacted starting material (in this case, salicylic acid) in your final product (aspirin)
what does a purple colored solution indicate in the purity test with FeCl3 solution?
indicates the presence of a phenolic OH group
in this experiment: it signifies traces of Salicylic acid are present in the Aspirin product
safety precautions for acetic anhydride and concentrated H3PO4?
acetic anhydride: corrosive and irritant (to the nose)
- keep compound covered inside the hood at all times
concentrated H3PO4: corrosive
- flush contaminated area with copious amounts of water
what types of chemicals go into the non-halogenated waste container?
chemicals containing ONLY C, H, and O
what types of chemicals go into the halogenated waste container?
chemicals containing C, H, O, and halogens
waste disposal for waste acidic filtrates procedure?
first: neutralize the acidic filtrates with NaHCO3
second: pour down the sink (unless otherwise instructed)
waste disposal for solvent tests (ethanol and water) and solutions from the FeCl3 (aq) test procedure?
the solution containing ethanol must be emptied out into the non-halogenated container; the test tube containing water can be disposed down the drain
FeCl3 (aq) tests must be poured out into a specially labeled container “Aq FeCl3 waste”
what are the 6 classifications for chemical hazards?
- flammable (low flash point)
- corrosives
- lachrymator
- carcinogen
- teratogen
- reactive
definition and examples of (1) flammable compounds
compounds with low flash points (the lower the flash point, the easier it is to ignite the material)
ex: diethyl ether (-45C), tBut methyl ether (-33C), acetone (-17.2C)
flash point definition
the lowest temp at which a liquid can form an ignitable mixture in the air near the surface of the liquid
corrosive compounds definition and examples
Corrosives are materials that can attack and chemically destroy exposed body tissues, causing chemical burns.
- Most corrosives are strong oxidizers and they are mostly either strong acids or strong bases
examples: H2SO4, NaOH, HNO3, Ca(OH)2, Br2
lachrymator compound definition and examples
lachrymator: an irritant that causes tearing (aka water of the eyes)
examples: thionyl chloride, acrolein, methacryloyl chloride
carcinogen compound definition and examples
carcinogen: a substance that is capable of causing CANCER
examples: benzene, arsenic, methylene chloride, dichloromethane (DCM)
teratogen compound definition and examples
teratogen: a drug or other substance capable of interfering with the development of an embryo fetus that may lead to birth defects or developmental malformations
examples: phenol, benzene, dinitrotoluene, dioxane
reactive compounds definition and examples
definition: things that go BOOM!
examples: Na metal, sodium hydride, calcium carbide
what are the 4 categories of the national fire protection association (NFPA) ratings?
blue: health hazard
red: fire hazard
white: specific hazard
yellow: reactivity hazard
number of ratings for the blue: health hazard
4 - deadly
3 - extreme danger
2 - hazardous
1 - slightly hazardous
0 - no health threat
number of ratings for the red: fire hazard
Flashpoints
4 Below 73 F
3 Below 100F
2 Below 200F
1 Above 200F
0 Will not burn
number of ratings for the white: specific hazard
W Water reactive
OX Oxidizing agent
ACID Acid
CORR Corrosive
number of ratings for the yellow: reactivity hazard
4 May detonate
3 Shock or Heat may detonate
2 Violent chemical reaction; water reactive
1 Unstable if heated
0 Stable
what does d and nD represent in the Merck Index?
d = density of molecule
nD = refractive index (a value calculated from the ratio of the speed of light in a vacuum to that in a second medium of greater density)
hazard ratings for phosphoric acid, acetone, and bromine
phosphoric acid: extreme health danger
- blue (3)
- red (0)
- yellow (2)
- white: acid
acetone: flammable
- blue (1)
- red (3)
- yellow (2)
- white: blank
bromine: extremely corrosive
- blue (4)
- red (0)
- yellow (0)
- white: OXY (oxidizing agent)
sources of chemical information?
- MSDS sheets: good resource for chemical info
- how to look up the following info: physical properties (MP, density), chemical properties (solubility, etc), toxicity
- merck index link
- sigma-aldrich catalog
3 characteristics about acetylsalicylic acid (aka aspirin)
- analgesic (reduce pain)
- antipyretic (prevent/reduce fever)
- anti-inflammatory
Patented by Bayer in 1893
One of the oldest and most consumed drugs
(American consumption = 16,000 tons/year = 80 million pills/ year)
what should IMPURE aspirin solid look like?
white or yellowish-white powder
what should PURE aspirin solid look like?
white small shiny need-shaped crystals
why do you want to bring the solution to a boil quickly and limit the amount of time you are boiling the crystals in solvent for? (recrystallization)
to avoid losing product/yield
what are the safety hazards for salicylic acid, acetic anhydride, and phosphoric acid?
salicylic acid: corrosive, irritant, health hazard (toxic)
acetic anhydride: irritant, corrosive
phosphoric acid: corrosive
what is a thermometer lag?
the thermometer takes a bit longer to display the actual temp of the solution –> the thermometer is display a lower melting point temp that actuality and to prevent this, we should heat the solution slowly
what is a good recrystallization solvent?
a solvent that will dissolve the solute when HOT but NOT dissolve it when the solvent is cold or room temp
- this helps the solution crystallize with as little impurities as possible as the solution cools slowly
what is the boiling point of acetic anhydride?
138 degrees C
where do you dispose the test tube containing water from the solvent test?
down the drain (sink)
where do you dispose the test tube containing ethanol from the solvent test?
C, H, O non-halogenated container
where do you dispose of the solutions from the FeCl3 test?
a specially labeled container called “Aq FeCl3 waste”
esterification definition
Esterification - a chemical reaction in which an acid (often an organic carboxylic acid) and an alcohol combine to form an ester and water
why is excess acetic anhydride needed for the synthesis of aspirin reaction?
Excess acetic anhydride is needed to push equilibrium to products
Excess acetic anhydride serves as solvent
what is the stoichiometric ratio of acetic anhydride to salicylic acid?
what is the equivalent ratio of acetic anhydride to salicylic acid?
1:1
3 AA: 1 SA
is salicylic acid or acetic anhydride the limiting reagent in the reaction for the synthesis of aspirin?
salicylic acid is limit reagent (1 mol of SA to 3 mol of AA)
how do you avoid thermometer lag?
Avoid thermometer lag by knowing the approximate melting point and bringing the temp to ~20ºC below the expected mp and then slow rate to 2ºC/min
what is melting point determined by?
mp is determined by the strength of the IMFs (intermolecular forces)
what 2 characteristics are associated with higher melting points?
large molecular surface area and symmetry are associated with higher mps
do impurities increase or decrease melting point?
impurities decrease melting points
