synthesis of aspirin + salicylic acid

methyl salicylate structure

Functional group?

Describe

Functional Group: ester

liquid w/ minty smell

Salicylic Acid structure

Functional group?

Describe - impure vs pure form

Functional group: - Carboxylic acid

- phenol group

Solid

Impure -> white powder

Pure -> white, needle-shaped crystals

Draw Scheme 1 Synthesis of Salicylic Acid

Why do we say base promoted hydrolysis occurred versus base catalyzed hydrolysis for the synthesis of salicylic acid from Me Salicylate

Based (OH-) is the nuc that adds to the ester and forms part of the product. It participates in the rxn but is not regenerated later.

Saponification

the reaction between a fat and a strong base to produce glycerol and the salt of a fatty acid (soap)

% yield

actual/theoretical x100

Multistep synthesis % yield eq.

mult yields of each step as a decimal then mult. by 100

Recrystallization def

way to purify solid organic compound by using a suitable solvent

Recrystallization technique:

2 steps

Fast or slow cooling and why?

1. Melt impure solid in hot solvent -> breaks down impure crystal lattice

2. Slow cool (on bench top until substantial crystals formed then ice-water bath) -> leads to bigger, purer crystals because impurity molecules have enough time to return to the soln

Rule for selecting a good solvent

The solid you are trying to purify should be soluble in the hot solvent and insoluble in cold or room temp. solvent

vacuum filtration apparatus and why

(4)

- front facing

- clamped -> to keep from tipping over

- adapter used -> tight seal b/w Buchner funnel and vacuum filter flask

- heavy-walled rubber tubing -> prevent tubing from collapsing from atmospheric pressure on the outside when vacuum is applied

vacuum filtration use

quickly and completely separate a solid from the liquid with which it is mixed

Calc. melting point range

1st reading of range = temp @ which solid block first begins to liquefy

2nd reading range = temp. at which solid is completely melted

Impurities will ______ the observed MP of a compound

Lower

Thermometer lag

occurs when the sample melts before the thermometer has a chance to reach that temperature-leading to a depressed MP range

Melting point capillary tubes have ______ open ends

1 open and 1 closed end

Hazard label of NaOH

Corrosive

Hazard Label of HCl

Corrosive

At what approximate temperature will the reaction mixture containing methyl salicylate and 30 mL of an aqueous solution of 4M sodium hydroxide boil? (hint: aqueous)

100 degrees celsius

Why is it important to clamp your vacuum filter flask, even though it has a flat bottom?

to prevent it from tipping over

Salicylic acid has some solubility in water. What would happen if you washed your crystals with too much water, during vacuum filtration?

you may wash away or lose some product

Why is it necessary to empty out the the filtrate from the vacuum filter flask, before pulling air over the crystals being dried inside the Buchner funnel?

ensures vacuum's full pressure is being used to dry product

After adding NaOH to Me salicylate, what happens and why

solid white precipitate forms -> formation of disodium salt of SA

# of equivalents of NaOH

mmoles NaOH/mmoles MS

How do you know the disodium salt of SA is boiling

clear, homogenous solution hits a rolling boil and bubbles even when not stirred

What happens when you add 6M HCl to Erlen meyer flask w/ disodium salt?

Why do you do more than one increment of HCl?

heavy white precipitate forms (SA crashes out of the solution)

you check the pH (pink) and do more than one increment to ensure that precipitate doesn't disappear

Should 6M HCl or a similarly strong base be added while a flask is on a hot plate? Why or why not?

No because you still have residue heat from the hot plate will cause acidic content to spill over onto your gloves

why do we break down SA crystals

make them dry faster

Purpose of Lab A:

treat Me SA with NaOH and HCl to convert ester functional group to a carboxylic acid functional group

Aspirin structure

Functional group

Functional groups:

- ester

- carboxylic acid group

Scheme 2. Synthesis of Aspirin

what's important about the esterification rxn of SA into Aspirin? Why do we use excess acetic anhydride?

Equilibrium rxn

Excess acetic anhydride is used to drive the rxn towards completion and as a solvent

Phosphoric Acid Hazard

corrosive

acetic anhydride hazard

corrosive, combustible, flammable, acute toxicity

Why do we use aq. FeCl3 during our aspirin lab?

Control group

Conclusion based on results

Purity test

FeCl3 will produce a deep purple solution in the presence of a phenol group

SA has a phenol group. Pure aspirin does not.

Control: SA w/ FeCl3

Conclusion: If aspirin is purple, that means there is unreacted starting material in your final product

Why do you carry out the aspirin synthesis in an Erlenmeyer flask rather than a beaker?

Erlen flask has sloped sides so it prevents solvents from evaporating out of the flask too easily

Why do we use a powder funnel to transfer SA to erlen flask in Lab B?

Powder funnels are used for dry solids and never wet solids since wet solids will make us lose products since it'll get stuck in the stem

Why do you scratch the inside of Erlen flask in Lab B after the addition of SA, H3PO4, and acetic anhydride?

formation of a white paste due to

Small scale solvent test

two test tubes one w/ each solvent

the one that doesn't dissolve at room temp may be the better solvent of choice

based on lab B results what was the better solvent of choice for the recrystallization of aspirin

ethanol

impure aspirin

yellowish-white powder

pure aspirin

white, small, shiny, needle-shaped crystals

aq FeCl3 + pure aspirin would give

yellow solution

Immiscible

liquids that are not soluble in each other; can't form a homogenous solution

you must have two _________ liquids to carry out a liquid-liquid extraction

immiscible

extraction

technique used for the isolation and purification of organic compounds

layers settle depending on their

densities

more dense solvents go on the bottom

less dense float to the top

theory of extraction

better to do several smaller extractions than one big extraction to maximize amount extracted

% recovery

( dry mass of product isolated / initial mass used ) * 100%

partition coefficient

K = solubility of solute in organic layer/ solubility of solute in aqueous layer

when draining the separatory funnel, what position is the stopcock and glass stopper

vertical is open, stopcock is removed

what are drying agents

anhydrous salts (devoid of water) that combine with water that is mixed in with your product and retains it as water of crystallization

liquid (now free of water) passes through gravity filter paper leaving hydrated salts behind

when would you use gravity filtration vs vacuum filtration

what kind of funnel does each use

gravity

- solute is mixed w/ low-boiling solvent

- used to filter drying agents

- uses a powder funnel

vacuum

- when solute is mixed with high-boiling organic & water

- employers buchner funnel

why should vacuum filtration not be used for volatile or low-boiling solvents

solvent will evaporate during the filtration and contaminate the product crystals with impurities that have just been removed

rotary evaporator (3 benefits)

-The rotovap spins the round bottom flask to increase the surface area covered by the solvent.

-Applying vacuum reduces boiling point of the solvent being removed.

-Spinning flask helps prevent solvent from bumping.

what is in the solid after the filtration of the methyl salicylate synthesis

salicylic acid, H2O,

what is in the filtrate of the methyl salicylate synthesis

NaCl, MeOh, H2O, excess HCl

How would melting point be affected if you determined it before crystals were dry

lower b/c crystal lattice structure has more impurities making it break up faster

what is in the filtrate of the salicylic acid synthesis

acetic acid, H2O, H3PO4, acetic anhydride

what is in the solid of the salicylic acid synthesis

aspirin, water, trace salicylic acid

synthesis of aspirin performed NEAT (without solvent) and water was added later. If reaction was performed in water how would the results be different

• lower yield of aspirin b/c salicylic acid has low solubility in water

• aspirin could revert back to salicylic acid in water

why is it important to turn vacuum off when you aren’t using suction

• damage equipment results in weaker vacuum pressure

• could start to get backflow where filtrate goes into vacuum tube

what compounds will result in bright purple color with the addition of FeCl3

compounds with free OH group