ACID / BASE EXTRACTION AND ISOLATION OF CAFFEINE FROM TEA

Submitted in partial fulfillment of the requirements for:

CHE 324Organic Chemistry Laboratory

Dr. Robert DuncanFall Semester 2010

Kendra SandersonTiffany Wade

Jordan HugheyOctober 30, 2010

Introduction:

Extractions are often used in organic chemistry to extract desired products.

These extractions are more specifically called liquid-liquid extractions because

they involve two immiscible liquid solvents. Often times extractions are used to

acquire organic chemicals that exist in nature. These natural products that exist in

plant or animal tissues

The two solvents must be completely immiscible for an effective separation.

This procedure requires that they form two separate phases. An extraction is

typically formed in a separatory funnel. When the two solvents form upper and

lower phases (or layers) this allows one phases to be drained from the stopcock and

the other decanted from the mouth of the funnel if necessary.

Also, in order for an extraction to work properly the solute must be more

soluble in the second solvent than in the first. This has to do with the distribution

coefficient, a constant, K. K = C2/C1, where C is the concentration at equilibrium

(1, pg. 165). When the two solvents are shaken the solute becomes distributed

throughout both solvents. What portion of the solute is in each solvent is

determined by its solubility in each. If K is greater than 1 the second solvent is

effective. The bigger K is the greater the efficacy of the second solvent. If K is less

than one then most of the solute will remain in the original solvent and the second

solvent will not be effective. Therefore, the equation for K allows extraction

efficacy to be determined. Often multiple extractions with the same second solvent

will be performed to draw out a maximum amount of product.

The majority of the time in organic chemistry one of the solvents used will

be an organic solvent and the other will be an aqueous solvent. To determine which

layer, organic or aqueous, will remain on the bottom, the densities must be

determined. The solvent that is denser will form the lower phase, regardless of

volume. The only problem is that sometimes the solute will greatly change the

density of the layer. An alternate method for determining which layer is aqueous is

to drop a few drops of water into the funnel. If the water forms droplets or a new

layer, that phase is the organic layer; whereas, if the water is immediately

absorbed, that phase is the aqueous layer.

The procedure for performing a separation with a separatory funnel is

relatively simple. First, the solvent with the desired solute is poured into the

separatory funnel whose stopcock is closed. Then, an appropriate solvent is added.

After the funnel has been stoppered a gentle rocking motion is made with the

funnel to allow movement between the layers. This is when the solute moves from

the first solvent to the second. If the rocking is done too vigorously sometimes an

emulsion may form. An emulsion is a colloidal suspension of one liquid in another

(1, pg. 181). This happens when droplets of the organic phase are surrounded by

aqueous solution. To break an emulsion many techniques can be used including:

stirring the solutions, swirling the funnel, adding a small amount of water soluble

detergent, or simply allowing the solution to stand for a while. As the rocking is

happening there is a build up of gas, often CO2, in the funnel. To release this

pressure the separatory funnel should be tilted so that the stopcock is pointed

upward, then the stopcock should be opened, pointed away from people or

equipment. The gas will rush out of the funnel making an audible noise. The

stopcock can then be closed and rocking resumed. This “burping” should be done

fairly often especially at the beginning. At the point that no audible whoosh can be

heard the separation is near complete. When finished rocking the separatory funnel

should be set in a ring stand and allowed to sit for a few moments so that the layers

might separate.

Because a separation involves interaction of the organic and aqueous layers,

some water usually dissolves into the organic layer. To remove the water the

solution must be “dried.” A drying agent such as calcium chloride accomplishes

this. Calcium chloride is an anhydrous inorganic salt; therefore, it will hydrate

whenever it comes in contact with water in the air or in a “wet” solution (1, pg.

178).

After the rocking process is complete, sometimes further extractions need to

be performed in order to remove impurities. Organic layers can be washed in order

to remove any highly polar impurities. This simply means performing an extraction

with the organic phase and water. If there is a basic impurity, a dilute acid (i.e. 1-

2M HCl) can be used to convert bases to salts making them water-soluble. Or, to

remove acid impurities, a dilute base (i.e. 5% sodium bicarbonate) can be used to

convert the acid impurities to their anionic salts. Anionic salts are usually soluble

in an aqueous phase so they can then be easily extracted.

There are now better possibilities for performing extractions. One of these is

the integration of a wet analysis system on a glass chip. The time for this method

of extraction “was about tenfold shorter than a conventional system using a

separatory funnel and mechanical shaker” (2). In addition to this, the often difficult

procedures such as “phase separation necessary for the conventional system could

be omitted” (2). This is obviously beneficial in many research and clinical

environment. However, in the organic laboratory, conventional separation and

extraction methods will be sufficient.

Sublimation occurs when a solid passes directly into the vapor phase

without ever being a liquid. Sublimation is an effective method for purification

because after a solid is sublimed it can be resolidified and any impurity that has a

significantly lower vapor pressure will not. This can be easily accomplished using

a Petri dish and a hot plate. If the Petri dish is slowly heated with the cover on, the

solid will vaporize and then almost immediately resolidify in a purified form on the

cover of the dish. The major advantages of sublimation as a method for

O

OH

purification are that it is quick and does not require the removal of product from

another solvent. The only disadvantage is that sometimes, if too much solvent is

present in a sample, it will condense on the cooled surface and interfere with

sublimation (1, pg. 272)

Objectives:

For this experiment, we will use the principal of extraction to isolate certain solid

substances from solutions. We well perform an acid/base extraction as well as an

isolation method. Both of these procedures will enable us to explore the

effectiveness of this method

Table of Physical Constants:Substance MM

(g/mol)Density(g/mL)

MP C⁰

BP C⁰ Solubilityin H2O

Hazards

H

O

H

water

18.02 1.00 0 100 Complete ---

Benzoic acid

122.12 1.2659 122.35 249.2 Soluble Eye, skin, and respiratory irritant. May combust in air

Calcium Chloride

Ca2+

Cl- Cl-

110.98 1.835 782 1600 Soluble Respiratory, Skin, and Eye irritant. Harmful if inhaled.

Dichloromethane

Cl Cl

84.33 1.3266 -97.2 40 Slightly soluble in H2O

Harmful if swallowed, inhaled, or absorbed through skin. May cause cancer.

4-t-butylphenolOH

150.3 0.91 101 238 Insoluble Harmful if swallowed, inhaled or absorbed through the skin. Causes burns. Inhalation may be fatal.

1,4-dimethoxybenzene

O

O138.2 1.053 60 213 --- Eye, skin, and respiratory

irritant. May be harmful

Diethyl Ether 74.16 .731 -116 34.6 Slightly soluble Harmful by ingestion,

Oinhalation or through skin contact. Skin, eye and respiratory system irritant

Sodium Bicarbonate

Na+

HO

O

O-

83.995 2.16 270 --- Soluble Eye, skin, and respiratory irritant.

Sodium HydroxideNa+ OH-

40.00 2.13 318 1390 Mostly soluble Fatal if swallowed. Harmful if inhaled. Corrosive. Causes burns.

Sodium chlorideNa+ Cl-

58.44 2.16 801 1413 Slightly soluble Causes eye irritation.

Hydrochloric AcidH Cl

36.46 1.18 -74 53 Soluble Fatal. Corrosive. Harmful if swallowed, inhaled, or in contact with skin.

Sodium Carbonate

Na+Na+

-O

O

O-

105.99 2.53 851 decomposes

Slightly soluble May cause eye burns. Harmful if swallowed or inhaled.

Caffeine

O N

N

N

N

O194.19 1.23 238C 178C 1 gm in 46 mls

water.

Procedure:

Part 1: Extraction of Acids/Bases.

3.009g of a benzoic acid, 4-t-butylphenol, and 1,4-dimethoxybenzene

mixture was accurately weighed out. The mixture was dissolved into 30mL of

diethyl ether, which was then transferred into a 125mL separatory funnel. A few

extra mLs of diethyl ether were used to aid the transfer of the solution to the

separatory funnel.

For the first extraction, 10mL of saturated sodium bicarbonate was added to

the funnel. The extraction was performed following the standard procedure of

rocking gently and burping to prevent CO2 buildup. At the point no more pressure

was forming, the funnel was allowed to rest until the layers were completely

separated. The lower, organic layer was then drained into an Erlenmeyer flask

labeled “Flask 1”. This extraction was repeated once more and the contents of flask

one were noted.

For the second extraction, 15mL of 2.0M sodium hydroxide was added to the

separatory funnel. The same extraction procedures were followed as before, but

repeated three times and the lower layers were added to an Erlenmeyer labeled

“Flask 2”. Also, 5mL of water was added to separatory funnel and one final

extraction was performed and the lower layer was added to flask two. It was noted

what flask two contained.

For the third extraction, 15mL of brine water was added to the funnel and the

same extraction procedures were followed. The lower, aqueous layer was drained

from the funnel and discarded. The upper ether layer was carefully poured off into

an Erlenmeyer labeled “Flask 3” so that no water was transferred. Calcium

chloride pellets were used to assure dryness of the organic layered. Pellets were

added until there was no more clumping. It was noted what flask 3 contained.

The contents of flasks one and two were acidified using ~6-7mL HCl drop

wise or until the solutions were very acidic and no more white precipitate was

forming. pH paper was also used to test the acidity of the solution. The flasks were

then placed into ice baths to cool the solutions. The solutions were vacuum filtered

through a piece of pre-weighed filter paper seated with water. The precipitates and

filter paper were then placed on a pre-weighed watch glass and allowed to dry until

the next lab period. After drying, the weights were found and recorded.

The dried ether solution in flask three was decanted into a pre-weighed round

bottom flask and extra ether was used to wash the drying pellets. This extra ether

was also decanted to assure maximum transfer. The flask was the placed on a

rotary evaporator until all of the solvent had evaporated off and only a white,

precipitate was left. The flask was weighed and recorded.

From the weights of the crystals from each extraction, the percent of each

product of the total recovered weight and total percent recovered were calculated.

Melting points for the crystal products from each extraction were obtained

using a Mel-temp apparatus. The temperature was corrected for thermometer

calibration. The crystals were saved in appropriately labeled vials for future use.

For cleanup, aqueous layers, washes, and filtrates were combined for

neutralization. This mixture was then poured down the drain with a great deal of

water. Calcium chloride pellets were allowed to dry and then were trashed.

Part 2: Isolation of Caffeine.

4 family sized tea bags, 20.076g of sodium carbonate, and ~250mLs of

boiling water were placed into a 600mL beaker. The initial weight of the family

size tea bags was recorded. The mixture was swirled and allowed to steep for 7

minutes. The solution was then decanted into a 500mL Erlenmeyer flask. ~75mL

of hot water was added to the beaker with the tea bags and then immediately

decanted into the same E. flask. The solution was then allowed to cool to room

temperature.

The same extraction procedure as was used in the first part was followed for

this part. The first extraction was difficult because a large emulsion formed. A

stirring rod and swirling were used to break up most of the emulsion. The

extraction was performed three additional times with much slower shaking to

prevent emulsions. Dichloromethane forms the lower, organic layer and is

therefore drained from the stopcock of the separatory funnel. The lower layers

from each extraction were drained into the same Erlenmeyer flask. Calcium

chloride was added as a drying agent until some of the pellets would float free

when the flask was swirled.

The solution was then filtered into a pre-weighed round bottom flask via

gravity filtration and the pellets were washed with extra dichloromethane and

added to the filtrate. The solvent was evaporated off using the rotary evaporator.

Crude caffeine product was the only thing left in the round bottom flask. The

weight of the flask and product was recorded.

The crude yield, percent caffeine extracted, and melting point were

determined. Mel-temp apparatus was used to determine the melting point and a

small amount of crude product was saved in a vial.

The remaining crude caffeine was then transferred to the bottom of a Petri

dish. The cover of the Petri dish was pre-weighed and placed on top. This was

placed on a hot plate and the temperature setting was gradually increased to 4.5-5.

This caused the caffeine to sublime and purified product gathered on the cover.

When the cover could hold no more product, the dish was cooled, the covered

removed and the product was carefully scraped onto a pre-weighed watch glass.

The cover was then replaced and the process was repeated twice more, until no

more caffeine sublimed. Both the Petri dish cover and the pre-weighed watch glass

with product were weighed and recorded. From these numbers the total mass of

purified product was determined. Then the percent of purified caffeine recovered

from crude products and the percent of purified caffeine obtained from initial tea

were calculated. The melting point of purified caffeine was also obtained via Mel-

temp apparatus and sealed capillaries. Both melting points were corrected for

thermometer calibration. The remainder of the purified caffeine was saved in a

vial.

The dichloromethane waste was placed in the halogenated waste container,

the aqueous tea layer was poured down the drain, the drying agent was allowed to

dry and thrown away, and the tea bags were placed in the non-hazardous solid

waste container.

Data:

Flask 1: Flask 2: Flask 3:

Calculations:

Discussion:

Part 1: Acid Base Extraction

3.009g of a mixture of benzoic acid, 4-t-butylphenol, and 1,4-

dimethoxybenzene was dissolved into 30mL of diethyl ether and placed into a

125mL separatory funnel. 10mL of sodium bicarbonate was added to the

separatory funnel and a separation was performed. The layers were allowed to

separate so that the benzoate ion was in the lower aqueous phase. This occurs

because the benzoic acid that was in the original solution was pulled into the

aqueous layer by the sodium of the sodium bicarbonate base. The upper phase was

organic. The lower phase was then drained from the separatory funnel. This

extraction was repeated once more, and the second lower layer, containing more

benzoate ion, was added to the first lower layer. This was Flask #1.

Next, 15mL of 2.0M sodium hydroxide was added to the separatory funnel

and another separation was completed. When the layers separated, 4-t-

butylphenoxide was drawn to the lower aqueous layer and this layer was

subsequently drained into Flask #2. This extraction was repeated two times, adding

each lower layer to the first. 5mL of water was added to the separatory funnel and

it was shaken. The lower, aqueous layer was added to Flask #2 to ensure a

maximum amount of product and aqueous solution was obtained.

A final separation was performed by adding 15mL of brine water to the

separatory funnel. This aided in drying – removing trapped aqueous solution in the

organic layer. The lower brine water layer was drained and discarded. The

remaining ether layer, containing 1,4-dimethoxybenzene, was poured into Flask

#3. Calcium chloride pellets were used to remove any remaining water.

Flasks #1 and #2 were acidified by adding HCl drop wise, approximately 6-7mL in

each. This converted the miscible benzoate ion into immiscible benzoic acid, and

miscible 4-t-butylphenoxide into immiscible 4-t-butylphenol. At this point, white

precipitate formed in each flask. The flasks were cooled in an ice bath so that

maximum product would precipitate, and the solutions were vacuum filtered

through pieces of pre-weighed filter paper (0.225g and 0.215g, respectively). To

improve purity, the precipitates were washed with cold water. Then, the

precipitates and filter papers were placed onto a pre-weighed watch glasses

(39.700g and 51.455g, respectively). After drying until the next lab period, the

total weight of the benzoic acid precipitate, filter paper, and watch glass was

40.699g, making the weight of the benzoic acid precipitate 0.774g. After drying,

the total weight of the 4-t-butylphenol precipitate, filter paper, and watch glass was

52.415g, making the weight of the 4-t-butylphenol precipitate 0.745g.

The ether organic solution was decanted (to leave behind the calcium

chloride) into a 100mL pre-weighed round bottom flask (48.323g). Extra ether was

used to wash the calcium chloride pellets to assure complete decanting. The

rotovap evaporate all of the solvent leaving behind 1,4-dimethoxybenzene

precipitate. The final weight of the round bottom flask and product was 49.360g.

The percents of benzoic acid, 4-t-butylphenol, and 1,4-dimethoxybenzene

out of the total crystals obtained were 32.6%, 31.4%, 36.0%, respectively. The

total mass of crystal obtained was 2.372g. Compared with the original mixture

mass shows a percent yield of 78.83%.

Melting point ranges for benzoic acid, 4-t-butylphenol, and 1,4-

dimethoxybenzene precipitates were 119.0-120.0°C, 96.4-98.1°C, and 34.5-38.1°C

respectively. These were corrected for thermometer calibration. The corrected

temperatures are 119.4°C, 98.0°C, and 39.5°C for benzoic acid, 4-t-butylphenol,

and 1,4-dimethoxybenzene precipitates respectively.

Part 2: Isolation of Caffeine

Four family sized teabags, 20.076g of sodium carbonate, and

approximately 250mL of boiling water were placed into a 600mL beaker and

stirred. After steeping for seven minutes, the liquid was decanted. 75mL of hot

water was poured over the tea bags and also decanted. The decanted solution was

cooled and poured into a separatory funnel. Three separations were performed with

25mL of dichloromethane each time. Because caffeine is more soluble in

dichloromethane than water, it leaves the water layer and enters the lower

dichloromethane layer. Dichloromethane forms the lower layer because it has a

higher density than water.

Calcium chloride pellets were used to dry the drained solution. The solution

was gravity filtered into a pre-weighed round bottom flask (96.801g). The solvent

was evaporated via rotovap. The final mass of the round bottom flask and crude

caffeine product was 97.327g, giving a yield of 0.526g crude caffeine. The percent

crude caffeine extracted from the initial mass of tea was 1.79%. The melting point

was determined, using Mel-temp apparatus, to be 218.1-220.7°C. After

thermometer calibration, the corrected temperature was 217.6°C. This shows a lack

of purity because the literature value for melting point of caffeine is 227-228°C.

The crude caffeine was placed into a glass Petri dish. The Petri dish was covered

and slowly heated on a hot plate. This caused caffeine to sublime, leaving a pure

product on the cover of the Petri dish. When the Petri dish was cooled, purified

caffeine from the pre-weighed cover (44.843g) was scraped onto a pre-weighed

watch glass (46.500g). The sublimation process was repeated until no more

caffeine could be sublimed. The total weights of the watch glass and product, and

the cover and product were 46.525g and 44.826g respectively, giving a total of

0.044g of purified product. Not all of the product could be removed from the

cover, therefore it was added in the calculations. The percent of caffeine recovered

from the crude product was 8.4%. 0.15% of purified caffeine was obtained from

the initial mass of tea. Again using the Mel-temp apparatus, the melting point of

the purified caffeine was determined to be 221.0-225.0°C. After thermometer

calibration, the corrected temperature was 221.8°C. This shows a slight increase in

purity of the product because the melting point temperature increased over the

crude caffeine melting point.

Conclusions:

Part 1: Acid Base Extraction

It can be assumed that sodium bicarbonate, sodium hydroxide, and brine water are

good solvents for separation because they are all immiscible in diethyl ether.

Sodium bicarbonate is also effective as a secondary solvent to draw out benzoic

acid because it is significantly more soluble in sodium bicarbonate than diethyl

ether. The reason it is more soluble is due to the acid/base reaction yielding sodium

and benzoate ion in the aqueous layer. 4-t-butylphenol is more soluble in sodium

hydroxide making it an effective extraction agent. Again it is more soluble in

sodium hydroxide because of the acid/base reactions yielding sodium ion and 4-t-

butylphenoxide. The reason these acid/base reactions are effective at creating

extractions is because they polarize the desired molecules making them more

soluble in the aqueous layer. The brine water is effective at drying the remaining

diethyl ether for obvious reasons and it is more dense than and immiscible in

diethyl ether (as are the other two solvents) so that is will form the lower layer and

be easily drained through the stopcock. Also, 1,4-dimethoxybenzene, the

remaining desired product, is soluble in the diethyl ether and not in the brine

therefore it will not be extracted.

The acidification process was successful to ultimately convert the miscible

benzoate ion into immiscible benzoic acid, and miscible 4-t-butylphenoxide into

immiscible 4-t-butylphenol. It was clear that the conversion was carried out

successfully and to completion in that the white precipitate began to form, and

acidification was carried out until no more precipitate formed. The reason why

adding HCl to the miscible intermediate states transforms them back into their

original forms is because of the second part of each set of the reaction equations

for this lab: nRCO2- Na+ + HCl ® RCO2H + NaCl, nArO- Na + + HCl ®

ArOH + NaCl, and nRNH2 + HCl ® RNH3+Cl- which leads to nRNH3+Cl-

+ NaOH ® RNH2 + NaCl + H2O. These equations show how acidification

causes ions to return to their more stable forms.

Part 2- Isolation of Caffeine

In the separation of caffeine, Sodium carbonate was added to prevent the

formation of tannins, which would inhibit successful extraction. Dichloromethane

was used for this separation because caffeine is much more soluble in

dichloromethane than it is in water. Because of the differences in density, a layer

formed after each of the three extractions with dichloromethane, the more dense

liquid, in position to be drained out of the funnel. This layer contained the caffeine.

Three, smaller extractions were performed rather than one large because this leads

to a larger distribution coefficient and better extraction of the solute.

After drying , gravity filtration, and rotary evaporation, the percent crude yield

from the initial mass of tea was 1.79%. Once the crude caffeine was sublimed for

further purification, the percent yield dropped to 0.15%. This smaller amount of

caffeine had a much purer composition due to the sublimation that was performed

on it. Sublimation proved to be a fast and efficient way to retain anhydrous

caffeine because unlike crystallization, no extra solvent is added and therefore

none has to be removed. This purity is evidenced in the raised melting point of the

sublimed caffeine from 217.6 to 221.8°C.

Literature Cited

1. L., Donald, Gary M., and George S. Microscale and macroscale techniques in the organic laboratory. BrooksCole Pub Co, 2002. 165, 178, 181, 272. Print.

2. Minagawa T, Tokeshi M, Kitamori T. Integration of a wet analysis system on a glass chip: determination of Co(ii) as 2-nitroso-1-naphthol chelates by solvent extraction and thermal lens microscopy. Lab Chip. 2001 Sep; 1(1):72-5. Epub 2001 Aug 9.