ORGANIC CHEMISTRY I

LABORATORY

220L-Tue 1-4pm

Extraction of Caffeine from Tea

Kathleen Swanson

11/01/2013

Introduction:

Chemical Extractions have been a part of human lives for centuries. While this procedure is

used by many laypersons to brew coffee, tea it is also a process commonly employed by

chemists and biochemists in order to target and separate desired products used for making

medications like quinine, morphine and menthol, perfumes. Extractions can be either solid-

liquid, or liquid-liquid, depending upon the desired compound. In both types, a liquid solvent

is used to isolate the compound. Scientists often perform extractions of organic material,

utilizing an inorganic solvent in order to better separate the organic compound from the

typical byproducts and starting materials. In these types of liquid-liquid extractions it is

important to choose an appropriate solvent that will not dissolve in water, have a low boiling

point so it can be easily removed; it should not react with the solute or other solvent. Ideally,

a well-chosen organic solvent when mixed with the mixture containing the liquid compound,

will create two immiscible layers; one containing the extraneous materials in the aqueous

layer, and the compound to be extracted in the organic layer.

This laboratory exercise, caffeine is first extracted in a solid-liquid extraction from tea leaves

into boiling water (a polar, inorganic solvent). Then the caffeine in the water is extracted using

dichloromethane (an organic solvent) in a liquid-liquid extraction procedure (carried out in a

separatory funnel). Caffeine, a naturally occurring stimulant belonging to a class of

compounds known as alkaloids (based on the amine, Purine). It is found in many beverages

and often addicting, especially for those that consume caffeine daily to promote attentiveness

and increase energy levels. While caffeine is a naturally white, slightly bitter, crystalline solid,

when extracted from tea leaves, the water turns a brownish color demonstrating that other

impurities are present in the solid-liquid extraction. When the caffeine dissolves in the organic

dichloromethane, extracted from the confounding impurities the mixture is clear in

appearance, leaving behind the brown in the aqueous solution. The solubility of caffeine in

water is 2.2 mg/mL at 25°C, 180 mg/mL at 80°C, and 670 mg/mL at 100°C. It is quite soluble in

dichloromethane, the solvent used in this experiment to extract the caffeine from water.

In addition to caffeine, tea leaves also contain a number of colored compounds, a small

amount of decomposed chlorophyll, and tannins, a weakly acidic phenol with a Pk of 10.0.

Tannins are slightly soluble in dichloromethane, the solvent used in the liquid-liquid phase of

the extraction, so to eliminate and neutralize these weak acids, sodium carbonate (NaCO3) is

added to convert the phenols to their salts (phenol anions) by deprotonation of the –OH

group, which remain in the H2O. The basic property of alkaloids comes from the lone pair of

electrons found on at least one of the nitrogen. When phenol is converted to phenolic salts

(by adding NaCO3) creates a more basic environment decreasing the solubility of caffeine in

water by causing it to take on its neutral form (C8H10N4O2), making it only somewhat polar. In

this way the basic N in caffeine can be used to increase or decrease its water solubility. In

contrast to the basic alkaline conditions, acidic conditions will form the conjugate acid salt

(C8H9N4O2 + H3O+) giving caffeine increased water solubility as a cation. This cation form would

make it very difficult to draw the caffeine from the aqueous layer into the organic layer.

Compounds Used:

Phenol (tannins) Caffeine Magnesium Sulfate Sodium Carbonate

Compound MW Density Vol. Mass mol Hazard

(g/mol) (g/mL) (mL) (g)

Caffeine(C8H10N4O2)

194.2 g/mol 1.23 g/mL3.35 mL

(calculated)4 g

(2 tea bags)0.0206

skin contact or eye contact (irritant),

ingestion, of inhalation.

DichloromethaneCH2Cl2

84.92 g/mol 1.33 g/mL74 mL

(7x 10mL +2x 2mL)

98.42 g(calculated)

1.159

eye and skin, and respiratory tract

irritation; Harmful if swallowed; May be

harmful if inhaled; May cause central nervous

system effects.

Sodium Carbonate(NaCO3)

105.99 g/mol 2.532 g/mL0.79 mL

(calculated)2 g 0.0189

skin contact (irritant), ingestion, of inhalation

(lung irritant)

MagnesiumSulfate (MgSO4)

120.38 g/mol Not available -non

specified amount

-

Ingestion; Slightly hazardous in case of skin

contact or eye contact (irritant), of inhalation.

Phenol(C6H5OH)

*from tannins/tea94.11 g/mol 1.057 g/mL

non specified amount

skin contact (corrosive, irritant), of eye contact

(irritant), of ingestion, of inhalation

Water(H2O)

18.02 g/mol 1.00 g/mL35 mL

(15 +20 mL)35 g

(calculated)1.94 none

Table 1: Table of Physical Properties

Beverage (8 oz.) Caffeine (mg)

coffee 50 – 200 mg

decaffeinated coffee 1 – 5 mg

tea 30 to 75 mg

soft drink 20 – 50 mg

Table 2: common beverages and caffeine content

Experimental:

The solid/liquid phase was conducted first, using a beaker with (15mL) boiling water to extract

the caffeine from 2 tea bags. Additional quantities of water, totaling 20 mL of water, were

added to maintain the initial volume of water while evaporation occurred during boiling. As

previously discussed, 2 grams of sodium carbonate (NaCO3) was added to the boiling water to

help ensure the Caffeine would remain a free base when mixed with water and other

compounds in the tea leaves. NaCO3 neutralizes the slightly acidic ph. of the tannins

(containing phenol, a weak acid). After allowing the concentrated solution to cool to room

temperature, an ice bath was used to further cool the mixture in preparation for the

liquid/liquid extraction procedure.

A separatory funnel was used for the liquid/liquid phase of the extraction. It is important to

adequately grease the stop cock and joints of the funnel. 10mL of dichloromethane was added

to the funnel along with the mixture containing water and the caffeine and other extracted

contents from the tea bags. The funnel was shaken gently back and forth, three times, at

which point the building vapor pressure was expelled by inverting the funnel and opening the

stopcock. (a significant decrease in the boiling point of compounds is inversely proportionate

to vapor pressure). Shaking allows the caffeine the opportunity to leave the aqueous layer,

extracted into the organic, dichloromethane layer found at the bottom of the funnel due to its

density +.33 g/mol, that of water. After allowing the layers time to separate, the funnel was

slowly drained of the dichloromethane layer only (containing caffeine). The organic layer was

clear, and the inorganic layer a dark brown color. Vigorous shaking caused extreme amounts

of emulsions to be formed, as evidenced by a third, lighter brown layer wedged between the

aqueous and the organic layers. In order to the process of adding 10mL of solvent (CH2Cl2) was

repeated 7 times, as opposed to 2. Which each addition of 10mL solvent, the organic layer

was subsequently drained in an effort to extract the highest yield of caffeine possible. Each

extraction was added to a larger beaker. While the original lab called for 2 x 10mL extractions

with dichloromethane, Extractions are most effective when repeated several times with small

volumes of solvent rather than once with a large volume.

After the liquid-liquid extraction the combine extracts contain very minute amounts of water,

so in order to thoroughly dry the mixture of all aqueous solvent, anhydrous magnesium

sulfate was added to the extracts until the powder persistently floated (as opposed to

clumping and sinking which denotes the presence of water in the sample). Using

gravity/vacuum filtration, the sample was washed two times, each with 2mL portions of

dichloromethane and allowed to evaporate to dry. Once completely dry of aqueous and

organic solvent the remnants, crude caffeine were transferred to weigh paper and the mass of

the extracted caffeine recorded.

Mass: filter paper + flask + crude caffeine 29.54g

Mass: filter paper + flask 29.47g

Mass of Crude Caffeine: 0.07g

** 1 tea bag contains 30-75 mg caffeine; average of 52.5 mg was used for actual value

2 x52.5mg(mean)=105mg=0.105gcaffeine (available for extraction)

% yieldcaffeine= .07 g.105g

x100=66.66%

Discussion:

It was estimated based upon mean reported values, which the two tea bags used provided a

potential 0.105 g of caffeine available for extraction. The total volume of water was held at 15

mL throughout the extraction of caffeine from the tea bags. Considering a rate of 670 mg/mL

at boiling (100 °C), it is assumed that all of the 0.105 grams were extracted into the water.

Based upon these values, the percent yield was calculated to be 66.66% with 0.07 grams of

crude caffeine obtained. There were several factors in addition to standard human error that

are believed to have had an impact on the crude caffeine yields following extraction. During

the liquid/liquid phase of extraction, the separatory funnel was inadvertently shaken very

vigorously causing a thick layer of emulsion to form between the aqueous and organic layers.

In an attempt to recover as much available caffeine as possible, the original protocol of 2 x 10

mL of dichloromethane was increased to 7 x 10mL of dichloromethane, extracting the organic

layer each time. At completion of the 7th trial, there was still a heavy layer of emulsions,

indicating that there was still a large amount of caffeine that would not be available for

recovery.

The percent yield was performed based upon the total weight of one tea bag (2 g) multiplied

by the two tea bags used, however tea leaves are composed of many other compounds other

than caffeine (tannins, colored compounds and small amounts of chlorophyll). Consideration

of the 4 grams of tea leaves as the total mass of caffeine available for extraction is a

misrepresentation of the true amount; however information regarding the mass or

percentages of other compounds contained in a single tea bag were not available for use in

percent yield calculations.

In addition to the above, many protocols for caffeine extraction by this Macroscale method

indicate the crude caffeine residue should be left a number of days to ensure the sample is

completely dry. This laboratory called for recording of mass within the single lab period,

making it impossible to obtain a mass of a dry sample of crude caffeine. It is believed that

some of the recorded mass (0.07 g) consists of small amounts of undetected CH2Cl2, remaining

in the sample.

This lab exercise successfully demonstrated both types of extractions, and allowed for visual

demonstration of organic methods for separation of two liquids in a mixture. In addition to

learning a fundamental concept needed in many types of chemical laboratories across vast

numbers of industries, this exercise offered many opportunities for application of several

concepts (of densities, polarities, boiling points, acid/base interactions, etc.) in the context of

a multiplayer, multifaceted framework. It is clear that not only are extraction techniques some

of the longest held chemical procedures known to scientists and non-scientists alike, but also

the true necessity and potential possibilities for extraction procedures.

Resources:

Macroscale and Microscale Organic Experiments, Williamson, K.L., 2nd Edition. D.C. Health and Company

UC Davis Chem Wiki, http://chemwiki.ucdavis.edu/Organic_Chemistry/Phenols/Phenols/Acidity_of_Phenols