1/17/2015 1

Isolation of Caffeine Overview

An aqueous Vivarin/Sodium Carbonate mixture is extracted with Dichloromethane (Methylene Chloride)

The organic fraction is separated from the aqueous solution and evaporated to dryness

The product is recrystallized from Acetone The mass and % recovery of the product are

determined Confirmation of product is verified by Melting

PointReferences:Slayden: pp. 47- 49Pavia: pp. 24, 73 – 84 Note: These pages are not in the GMU version of the

Pavia text sold in the book, only in the primary text that we do not use anymore.

1/17/2015 2

Isolation of Caffeine Background

Caffeine is a bitter, white crystalline alkaloid (derivative of Xanthine) that acts as a stimulant drug

Caffeine is synthesized from the purine nucleotides AMP, GMP, and IMP in plants. These in turn are transformed into Xanthosine and then Theobromine, the latter being the penultimate precursor of Caffeine

1/17/2015 3

Isolation of Caffeine The two Amide groups exist as

zwitterionic resonance structures where the Nitrogen and Carbon atoms are double bonded to each other so that both of the Nitrogen atoms are essentially planer (in sp2 orbital hybridization)

A zwitterion is a neutral molecule with a positive and a negative electrical charge (not dipoles) at different locations within that molecule

Zwitterions are sometimes also called inner salts

The fused ring system therefore contains a total of ten pi () electrons and hence according to Huckel’s rule is aromatic

1/17/2015 4

Isolation of Caffeine

Zwitterionic Resonance

1/17/2015 5

Isolation of Caffeine Chemical Properties

Caffeine acts as a general nervous system stimulant, warding off drowsiness

Caffeine is considered a “psycho active” substance, but is generally legal and unregulated

Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, acting as a natural pesticide by paralyzing and killing insects

Sources for human use include coffee plants, tea leaves, and kola nuts

1/17/2015 6

Isolation of Caffeine Procedure

Obtain 2 Vivarin tablets noting % of active ingredient

Determine the mass of the tablets Obtain and determine mass of

approximately 8 g of Sodium Carbonate Crush the tablets with a pestal & mortor Add the crushed sample to a 150 mL

beaker Add 60 mL of Distilled Water Add the Sodium Carbonate (Na2CO3) to the

solution Add a Teflon boiling chip Heat solution to boiling on a hot plate –

maintain boiling point for 2 minutes

1/17/2015 7

Isolation of Caffeine Procedure (Cont’d)

Allow the hot mixture to settle slightly - some solid particles will remain undissolved

Attach an iron ring to a ring stand Insert a 125 ml Separatory Funnel

into the iron ring using a clay triangle if necessary to support funnel

Adjust height of iron ring so that stem of separatory funnel fits just inside a 150 ml beaker

Place a glass funnel into the neck of the separatory funnel

Make a boat of glass wool and place in the bottom of glass funnel

1/17/2015 8

Isolation of Caffeine Procedure (con’t)

Decant the sample solution into the bottom of the glass wool boat in the glass funnel allowing the liquid to drain into the 125 mL Separatory Funnel

Rinse the beaker with a small amount of distilled water and pass the water through the glass funnel into the separatory funnel

Allow the filtrate in the Separatory Funnel to cool to room temperature

1/17/2015 9

Isolation of CaffeineLiquid–liquid Extraction, also known as solvent extraction and partitioning, is a method to separate two immiscible liquids, usually an aqueous component and an organic solvent component

The process involves the extraction of a substance from one liquid phase into the other liquid phase utilizing a separatory funnel

Use the following steps to extract the Caffeine from the aqueous phase into the organic phase consisting of Methylene Chloride solvent (density – 1.33 g/ml)

You will do three (3) extractions

1/17/2015 10

Isolation of Caffeine Procedure (Cont’d)

Add 8.0 mL of Dichloroethane (Methylene Chloride) to the mixture in the separatory funnel

Place the stopper in the top opening and make sure it is secure, i.e. won’t leak

Invert the funnel pointing the stopcock end away from your face

Use “gentle”, (not vigorous swirling to avoid formation of an emulsion) for 15-20 seconds

Slowly open the stopcock to relieve any pressure

1/17/2015 11

Isolation of Caffeine Close the stopcock and continuing swirling

with venting every 15 seconds until no more gas is released (two or three times should be sufficient)

Continue the swirling for a total of 5 minutes

Replace the separatory funnel in the ring stand and allow the mixture to settle for a few minutes

Remove the stopper from the Separatory Funnel

Open the stopcock slowly and collect the clear bottom (organic) layer into a clean 150 mL beaker

Repeat the extraction process two more times with new 8.0 mL aliquots of Methylene Chloride, but reduce the total swirling time to 2 minutes

Each time, add the clear bottom layer to the 150 mL beaker

1/17/2015 12

Isolation of Caffeine Procedure (Cont’d)

With the help of the instructor, add Anhydrous Sodium Sulfate as a drying agent

Leaving the particles settled on the bottom of the beaker, slowly pour (decant) the liquid into a clean, dry, 50 mL beaker

Rinse the beaker containing the drying agent particles on the bottom with one additional small portion of Dichloromethane and add to the sample beaker

Evaporate the mixture to dryness in the hood

Note: Set hot plate setting to about 3

Note: Crude yield at this point is roughly 90%

1/17/2015 13

Isolation of Caffeine Procedure (Cont’d)

Recrystallization using a mixed solvent of Acetone and Petroleum Ether Dissolve the dried product in 12-15 mL cold

Acetone (from ice/water bath) Heat solution gently on hot plate If solution is incomplete, remove beaker from

hot plate and add more Acetone in 2 mL increments

Up to 20 mL of additional Acetone may be required until a clear pale-yellow solution is obtained

Remove solution from hot plate and allow to cool slightly

Add Petroleum Ether, drop by drop, with swirling from a full plastic pipet until the first appearance of pervasive cloudiness throughout the solution

1/17/2015 14

Isolation of Caffeine Procedure (Cont’d)

Continue cooling until crystallization is complete

Note: Maximum yield is obtained when the addition of Petroleum Ether is stopped at the first appearance of a pervasive cloudiness throughout the solution

It may be necessary to evaporate some of the solution to effect recrystallization

Separate the crystals from the solution by Vacuum Filtration rinsing the beaker and crystals in the funnel with small amounts of Petroleum Ether

Immerse beaker in an ice-water bath for about a minute

1/17/2015 15

Isolation of Caffeine Air-dry the sample from the evaporation

procedure or the vacuum filtration procedure on a pre-weighed weighing tray for one week

Compute the mass of the purified sample Compute the percent recovery of the product

relative to the amount of caffeine indicated in the tablets

Determine melting point - 236 oC

Note: Decomposition of this crude material occurs beginning at 236oC over a range of 5oC or so