Lab 9- Cinnamaldehyde Lab 6845p

Cinnamaldehyde Isolation by Steam Distillation IR Spectroscopy Introduction: Infrared radiation is the part of the electromagnetic spectrum between 4000 and 400 cm-1. IR spectra result from molecular vibrations (stretching and bending) of bonds in an organic molecule. Only vibrations that result in a change in the dipole moment of the molecule are observed by IR. The intensities of these vibrations can be expressed as transmittance or absorbance. We will look at transmittance. The following table (Table 1) gives values for commonly encountered molecular vibrations. Infrared Absorption Frequencies of Common Structural Units Structural Unit

Frequency, cm-1

alcohols (-OH)

3200-3600

carboxylic acids (-OH)

2500-3600

amines (-NH)

3350-3500

sp alkynes (-CH)

3310-3320

sp2 alkenes (-CH)

3000-3100

sp3 alkanes (-CH)

2850-2950

sp2 (-C-O)

1200

sp3 (-C-O)

1025-1200

sp2 alkenes (-C=C)

1620-1680

sp2 carbonyl (-C=O) aldehyde and ketone

1710-1750

carboxylic acid

1700-1725

acid anhydride

1800-1850 & 1740-1790

acyl halide

1770-1815

esters

1730-1750

amides

1680-1700

sp alkynes (-CC)

2100-2200

sp nitrile (-C)

2240-2280

Table 1: Stretching frequencies of commonly encountered groups.

A picture of the IR in our lab is shown below in Figure 1. A background will need to be obtained before any samples are analyzed. To do this, make sure there are no chemicals on the sample plate. Lower the ATR clamp by turning the blue knob. Then press “obtain background” on the IR in the ATR mode. Now a sample is placed on the plate shown (either a drop of liquid or small amount of sample, if solid). Make sure the sample covers the crystal located at the center of the plate. Next, turn the blue knob to put the ATR clamp in place. On the computer press “obtain sample”. Then, press “% transmittance” and finally print your IR.

Figure 1: Pictures of the ATR IR instrument in the lab.

Steam Distillation Introduction: Steam distillation is a good way to separate two immiscible liquids (liquids that do not mix together). Oil (cinnamaldehyde) and water are examples of immiscible liquids - one floats on top of the other. When doing steam distillation the mixture is stirred or agitated in some way so that the two liquids are broken up into drops, this is an example of a colloid. At any one time there will be drops of both liquids on the surface. Assuming that the mixture is being agitated, both of the liquids will be in equilibrium with their vapours. Liquids boil when their vapour pressure becomes equal to the external pressure. This means that such a mixture would boil at a temperature just a shade less than 98°C - in other words lower than the boiling point of pure water (100°C) and much lower than cinnamaldehyde (248°C). Agitated mixtures of immiscible liquids will boil at a temperature lower than the boiling point of either of the pure liquids. Their combined vapour pressures are bound to reach the external pressure before the vapour pressure of either of the individual components get there. In the presence of water, cinnamaldehyde (or any other liquid which is immiscible with water) boils well below its normal boiling point. This has an important advantage in separating molecules like this from mixtures. Normal distillation of these liquids

would need quite high temperatures. On the whole these tend to be big molecules. Quite a lot of molecules of this sort will be broken up by heating at high temperatures. Distilling them in the presence of water avoids this by keeping the temperature low. Chemical Procedure: In a 10 mL round bottom flask, add ~1 g of cinnamon from ground cinnamon sticks and 4 mL of water with a boiling stone and magnetic stirrer. Attach the flask to a Hickman still as shown in the apparatus in Figure 2.

Figure 2: Apparatus used for Steam Distillation The apparatus is wrapped in aluminum foil below the t connection between the Hickman Still and the round bottom flask. The thermometer should be inserted into the round bottom flask to get a more accurate temperature reading. It is best if a digital thermometer is used. The hot plate and stirred are now turned on. Heat the flask until boiling occurs. Distillate should collect in the Hickman Still. Remove the cloudy distillate from the side arm of the Hickman Still using a Pasteur pipette and place in a centrifuge tube. As distillate is removed, unscrew the condenser from the Hickman Still and add more water to the round bottom flask via Pasteur pipette. Reattach the condenser. Keep collecting distillate until 5-6 mL has been removed, add more water to the round bottom flask as needed. To the distillate in the centrifuge tube, extract three times with 2 mL portions of methylene chloride. After each extraction place the methylene chloride layer (bottom layer) in a 25 mL Erlenmeyer flask. Dry the combined methylene chloride layers with anhydrous sodium sulfate. Transfer the dried methylene chloride solution to a tared 5 mL conical vial, rinse the sodium sulfate with methylene chloride and add to the conical vial. Evaporate off the methylene chloride in the hood on a hot plate. Weigh the vial and calculate the percentage of cinnamaldehyde extracted from the original sample of cinnamon. Obtain an

IR spectrum of cinnamaldehyde. Compare the IR spectrum obtained of cinnamaldehyde to the reference spectrum of cinnamaldehyde.

Assigned Questions: 1- Discuss the IR of product obtained in relation to the IR of the reference spectrum for cinnamaldehyde. Do the two spectra seem to contain the same peaks, which peaks correspond to which functional groups? 2- List two advantages of steam distillation as a method of purification. 3- Explain why the distillate collected from the steam distillation of cinnamon is cloudy.

Reference Spectrum of Cinnamaldehyde: Obtained from:

http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/cre_index.cgi?lang=eng