Lab B - Synthesis of Aspirin

What is the biological activity of aspirin?

analgesic, antipyretic (fever reducer), and anti-infalmmatory

What type of reaction is the synthesis of aspirin from salicylic acid?

esterification

What are the reagents in the aspirin synthesis lab and how much of each do you use?

salicylic acid - 90% of the product from last week (no less than 0.8g)

acetic anhydride - 3 equivalents

H3PO4 - 4-5 drops

Why do you use 3 equivalents of acetic anhydride to 1 equivalent of salicylic acid?

adding a lot more reactant to push to the equilibrium to the right and favor formation of product.

Theoretical yield of aspirin is calculated by finding

stoichiometric amounts of reactants in the balanced equation and the limiting reagent

-- remember only 90% of salicylic acid is used for the theoretical yield of aspirin

Percent yield of aspirin is calculated by

actual yield/theoretical yield x 100

What is recrystallization used for? How does it work?

purification of solid organics; as the solution is allowed to cool very slowly, it becomes saturated with the organic compound, then begins to crystallize out of solution. Impurities remain in the solution.

What are the characteristics of a good recrystallization solvent?

When the solid is insoluble in cold or RT solvent and soluble when solvent is hot.

What recrystallization solvent is used in the synthesis of aspirin lab?

Water

What does the aqueous FeCl3 test find? How does it work? What do the results mean?

checks for purity; phenols react with FeCl3 to produce a deep purple complex if you test it with 1ml Ethanol each, 3 drops of 0.02M FeCl3 and a little bit of your product; If a purple colored solution comes up, then there is a phenolic group in your product and the aspirin has some salicylic acid left; therefore, there is some uncreated starting material in the final product

The method used to characterize the sample in lab B is

melting point determination

Impurities will ___ the observed MP of a compound

lower

Advantages of the digital melt temp are

- the rate at which the temperature of the heating block increases can be programmed

- you can input the start temp, end temp, and ramp rate

Disadvantages of the analog melt temp are

- difficult to adjust the rate of heating

- heat transfer to the thermometer can be slow, leading to slower response time

What is thermometer lag? How will it affect melting points? How can you avoid thermometer lag? What is another problem with determining you melting point too quickly?

- occurs when a solution is heated too quickly for the thermometer to catch up

- will make observed mp lower

- can be avoided by heating the solution slowly (~2*C/min)

- another problem is that a broader range of temps will be observed if the temp continues to rise

Why are most reactions carried out in an Erlenmeyer flask instead of a beaker?

it has sloping sides that prevent evaporation and evaporation can occur in a beaker because it has flat sides

How should you prepare the MP tubes to do melting point determination?

- use tubes that are closed at one end

- make sure the solid is efficiently packed inside

When would you use gravity filtration over vacuum filtration?

Gravity is used for low boiling solvents and to filter drying ages; employs a powder funnel

Vacuum filtration is used for high boiling organic solvents and water and uses air and a Buchner funnel.

Give a general overview of the procedure for aspirin synthesis:

1. Using 90% of the product and 3 equiv worth of acetic anhydride, transfer into a 50 ml Erlenmeyer

2. Add drops of phosphoric acid into the mixture

3. let rxn sit then heat for 10 mins until homogenous

4. chill in ice water bath while scratching to break up solid

5. vacuum filter the crystals

6. recrystallize the compound from water - boil the water then dissolve the aspirin into that water. Use minimal solvent to dissolve.

7. Re-vacuum filter

8. Do aqueous fecl3 test

What do you do for waste disposal during this lab?

- the filtrate from the vacuum must be neutralized with sodium bicarb then flushed down the sink

- the solution with ethanol from the solvent tests must be in the CHO non halogenated containers

- The FeCl3 test fluid goes into its own container

Chemical toxicity: flammable (low flash point)

flash point is the lowest temp at which a liquid can from an ignitable mixture in air near the surface of the liquid

Chemical toxicity: corrosives

materials that can attack and chemically destroy exposed body tissues causing chemical burns

Examples: H2SO4, NaOH, HNO3, Ca(OH)2, Br2

Chemical toxicity: lachrymator

an irritant that causes tearing

Examples: thionyl chloride, acrolein, methacryloyl chloride

Chemical toxicity: carcinogen

a substance that can cause cancer

examples: benzene, arsenic, asbestos

Chemical toxicity: teratogen

Capable of interfering with development of a fetus

examples: phenol, benzene, dinitrotoluene, dioxane

Chemical toxicity: reactive

explode

Examples: Na metal, NaH, Ca carbide

What are NFPA ratings broken down into?

Blue - health hazard

Red - fire hazard; based on flash points

White - specific hazard

Yellow - reactivity hazard

The most dangerous of each of the labels are

Blue - 4- deadly

Red - 4 - flashpoint below 73F

White - W - water reactive

Yellow - 4 - may detonate

What are the NFPA ratings for phosphoric acid? Acetone? Bromine?

Phosphoric acid:

blue - 3

red - 0

yellow - 2

white - acid

Acetone:

blue - 1

red - 3

yellow - 2

Bromine:

blue - 4

red - 0

yellow - 0

white - oxy (oxidizing agent)

What are good sources of chemical information?

MSDS sheets

Use Merck Index

Aldrich Catalog