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Lab report Experiment 7 Extraction of Usnic Acid Observations ********************************************* Extraction of Usnic Acid -Appearance of acetone

Lab report

Experiment 7 Extraction of Usnic Acid Observations


Extraction of Usnic Acid

-Appearance of acetone =clear colourless solvent

-Appearance of lichen = course green and brown fibrous material

-mass of ‘Old Man’s Beard’ lichen weighed = 5.01 g

-lichen + ~300 mL acetone in 500 mL Erlenmeyer Flask with stopper = course green and brown

fibrous slurry

-Extraction time was overnight, ~15 hours

Usnic Acid Recovery (by gravity filtration/roto-evaporation/recrystallization)

-lichen + acetone after solid liquid extraction = liquid is pale green in colour

-After gravity filtration =filtrate is pale green in colour, lichen discarded and appeared the same

as it started out, a course green and brown fibrous material

-Solvent removal by roto-evaporation = as acetone was removed, the concentrated solution went

very dark green.

-After roto-evaporation, a golden yellow green powder was seen coating the bottom of the round

bottom flask

after all acetone removed (yield not determined)

-Crude usnic acid recovered by adding a small amount of hot acetone and pouring the slurry into

a 50 mL Erlenmeyer flask

Usnic Acid Recrystallization Observations

-volume of hot acetone solvent used = ~40 mL

-volume of ethanol solvent used = 4 mL

-Appearance of crude usnic acid in hot acetone= yellow-greenish solution

-Slow cooled ‘saturated crude usnic acid in acetone’ for 1 hour to allow crystals to grow

-Placed on ice for chilling to 4 C to maximize crystal formation

Vacuum Filtration

-chilled ~30 mL of acetone on ice

-Assembled vacuum filtration apparatus with Buchner funnel and filter paper

-swirled and transferred crystals from recrystallization flask to Buchner funnel

-Washed harvested crystals with 2x 5 mL ice cold acetone

-Yield of pure usnic acid = 123 mg

-mp of pure usnic acid = 201-202 C (uncalibrated thermometer used)

-mmp of purified usnic acid = 202-203 C (uncalib. thermometer used)

Polarimetry (using digital Polax Polarimeter) with 2 dm long polarimeter tube

1. L-tartaric Acid (with ‘unknown’ optical rotation)

appearance of unknown L-tartaric acid = fine white powder

appearance of unknown L-tartaric acid solution (in dH2O) = clear colorless solution

concentration of unknown L-tartaric acid in distilled water = 5.8742 g / 25 mL

optical rotation of blank distilled water = 0.0 (autoset by instrument)

optical rotation of L-tartaric acid solution = + 6.0

specific rotation of L-tartaric acid solution = ? (you must do calc. to determine it)

2. Usnic Acid

appearance of usnic acid + Dichloromethane (DCM) = clear, yellowish/green solution

concentration of usnic acid in DCM = 0.0813 g / 25 mL

optical rotation of blank DCM = 0.0 (autoset by instrument)

optical rotation of usnic acid solution = + 2.1

specific rotation of usnic acid solution = ? (you must do calc. to determine it)

Both samples were + (d or dextrorotatory). This was noted in that the polarimeter was ‘darker on

right side’ (relative to the blank), and that the reading was a positive value when the observed

rotation was made.

Both were done at 22.5 degrees C (please note there is no thermal correction equation for optical

rotation measurements, like there is for refractive index).

Here are the specific rotations of (+) usnic acid and L-tartaric from R.C Weast, et al, 1984. CRC

Handbook of Chemistry and Physics, 65th ed., CRC Press Inc., Boca Raton, Florida.

D-(+)-usnic acid specific rotation or [alpha]D/20 is = +469 degrees.

Note: L-(-)-usnic acid specific rotation or [alpha]D/20 is = -480 degrees.

L-(+)-tartaric acid specific rotation or [alpha]D/20 is = +12.7 degrees.

Specific Optical Rotation Calculation Hints

The polarimeter tube is 20 cm or 2 dm long.

You must use the formula for calculating the ‘specific rotation of a solution’ (solute dissolved in a


specific rotation [alpha]D20 = (observed rotation alpha – blank)/ 2 dm x concentration (g/mL)

You maybe didn’t do a blank reading (water or tetrahydrofuran) in the lab, so assume it is 0.00.

i.e., They are both optically inactive and should give readings of 0. If you did do readings of

water or the THF blank, you must correct your observed readings.

Remember to use the actual symbols for specific rotation e.g., [alpha]D 20 -cannot be shown correctly in this e-mail.

Exp. 8 Synthesis of Cyclohexene


A. Reagent and Equipment Prep

-used a 25 mL grad. cylinder to measure 21mL cyclohexanol (clear and colorless) plus + 5 mL

conc. phosphoric acid (clear and colorless), used cyclohexanol product from Exp. 3 plus extra

from reagent bottle

-setup distillation apparatus and used 50 mL round bottom (r.b.) flask for receiver flask.

B. Reaction

-2:30 PM Mix reagents in 100mL r.b. flask and apply heat using heating mantle and rheostat

barometric pressure = ~700 mmHg

reaction mixture stays clear, gentle boiling beginning already

rheostat setting 6

-2:38 PM begin distillation (all following temps barometric. press. corrected) gentle boiling

beginning already

-2:40 PM 1st drop at 88 C

-2:41 PM distill. rate = 1drop/2s, temp 95 C, very gentle boiling

-2:45 PM distill. rate = 1drop/2s, temp 101 C, product in receiver flask clear and colorless

-2:50 PM incr. rheostat to 4.5, distill. rate = 1drop/s, temp 98 C

-2:55 PM distill. rate = 1drop/2s, temp 105 C

-2:56 PM temp drops to 97 C very slow 1 drop/10s, increased rheostat to 7

-3:15 PM temp drops to 110 C v.slow 1 drop/10s, reaction mix starting to produce cloudy vapors

C. Quenching the reaction

-3:15 PM temp 108 C, distillation pot almost still 1/8 full, whitish fumes seen, spent reaction

mixture orange-reddish in color. Halt distillation. (total distillation time = 37 min, distillate is

colorless but slightly cloudy in appearance)

-3:15-3:30PM lowered heat source and allowed system to cool off, observed ~35 mL distillate in

two layers (upper layer is larger) in 50 mL r.b. flask

D. Reaction Workup/Product Recovery

-3:35 PM Moved to work in fume hood. Cylcohexene smell very stinky!

added ~0.5 g solid NaCl to the distillate, swirled and when all dissolved, added another ~0.5 g

NaCl. A few crystals of NaCl remain at bottom of the flask. Upper layer has begun to clear.

-3:40 PM let added 20 drops of 10% Na2CO3, used glass rod to dip into lower layer in the

distillate flask, pH on pH paper shows alkaline pH of 9.0

-3:44 PM transferred distillate to separatory funnel, removed the bottom aqueous layer, retained

upper layer

-3:48 PM washed retained product layer with 10 mL saturated NaCl (brine) -pre-drying step,

drew off and discarded bottom layer of brine

-3:53PM transferred pre-dried product to 50 mL Erlenmeyer Flask.

-3:55 added 2.0 g of CaCl2 to 50 mL Erlenmeyer flask

E. Product Purification and Analysis

-wt. of receiver 25 mL r.b. flask = 24.30 g

-dried clean distillation apparatus in oven for 10 min.

-4:25 begin distillation rheostat setting 4.5 (prewarmed mantle)

-4:32 PM 1st drop at 75 C

-4:36 PM 77 C, distillation rate is 1 drop/s, product clear and colorless

-4:37 PM 81 C max, distillation pot almost dry. Halt distillation. product clear and colorless.

(total distillation time = 37 min)

-4:45 PM product transferred to sealed vial for later analysis

Refractive Index of product at 22 C = 1.4400

Infrared Spectrum taken of reagent and product -see next 2 pages for spectra to analyze)

final wt. of 25 mL rb flask and product = 33.78 g

yield of cyclohexene = 9.48 g

bp range of product (uncorrected) = 75.0-81.0 C

theoretical yield of cyclohexene (g) = (vol. cyclohexanol used x density / Mwt of cyclohexanol)

x Mwt cyclohexene

21 mL cyclohexanol x (0.963 g/mL) x (1mol/100.16g) x (1mol/1mol) x (82.15g/mol) = ____ g

% yield = (9.48 g/___ g) x 100% = ___%

The bp correction to use in this experiment is:

corr.bp(C) = obs.bp(C) + ((760 mmHg – obs.BP mmHg)/10 mmHg) x 0.5 C)


corr. = corrected

bp = boiling point

C = degrees Celsius

obs. = observed

BP = barometric pressure

Experiment 9 Synthesis of p-nitroacetanilide Observations


amt. of acetanilide = 7.00 g (white shiny flat crystals)

amt of glacial acetic acid used = as per lab manual = 7.0 mL

amt of sulfuric acid used = 4 mL, clear and colorless, very viscous liquid

amt of nitric acid used = 3 mL, clear and colorless, slightly viscous liquid

Procedureal Steps


1. Carefully add 3 mL of concentrated nitric acid (15 mol× L-1) to 4 mL of concentrated sulfuric acid (18 mol× L-1)

in a very clean smaller flask. Cool the resulting nitrating mixture to room temperature….

*nitrating mixture very hot to touch after mixing two reagents. Solution clear and colorless.

2. Place 10 mL of concentrated (i.e., 18 mol× L-1) sulfuric acid contained in a 125-mL Erlenmeyer flask and cool in

an ice-water bath.

*sulfuric acid viscous, clear and colorless.

3. Dissolve about 7.0 g of the acetanilide in 7 mL of glacial (i.e., 100%) acetic acid by warming the two substances

together in a small Erlenmeyer flask in a fume hood …. Cool the solution until crystals just begin to form, then

warm slightly to redissolve.

* white shiny crystals begin to dissolve immediately. Need to heat until hot to touch to dissolve all

crystals. Solution is clear and slightly yellow colored upon cooling.

…and then pour the solution slowly, with stirring, into 10 mL of concentrated (i.e., 18 mol× L-1) sulfuric acid

contained in the 125-mL Erlenmeyer flask, which is being kept cool in an ice-water bath … Continue to cool the

solution to about 5o C (this can take ~30 min)….

* Solution warmed to 20 C upon mixing. Solution is clear and slightly deeper yellow colored upon cooling.

4. Use a Pasteur pipette to slowly transfer the nitrating mixture prepared in step 1 to the Erlenmeyer flask containing

the acetanilide solution prepared in step 3. Swirl the flask continuously during the addition and keep the

temperature of the mixture below 20o C by cooling in an ice-water bath.

*With each addition of nitrating reagent to the acetanilide (in sulfuric and acetic acid) solution, the mixture

warmed to ~ 20-25 C and the product deepened in color to a darker yellow. At first the additions had to be very

slow as cooling of the reaction took place after each addition. Addition of all the nitrating reagent took 20 min to

complete. Towards the end, additions occurred quicker as the exothermic nitration reaction seemed to slow.

5. When all the nitrating mixture has been added, allow the reaction mixture to stand at room temperature for 30


*product is a darker yellow, but clear solution.

6. Add the reaction mixture slowly, with stirring, to a mixture of 100 mL of water and 25 g of ice in a 400-mL


* product is a frothy, pale-yellow slurry.

7. Collect the solid by suction filtration (refer to Experiment 2, if necessary). Break up the solid with a spatula,

being careful not to tear the filter paper, and wash the solid with cold water.

*Product is a yellow precipitate.

8. Remove the solid from the Büchner funnel and transfer it to a 400-mL beaker. Add 100 mL of distilled water and

stir vigorously. Collect the solid by suction filtration and again wash with cold water.

*Yellow color is lessening and being washed away in the filtrate. Product losses occurring on the filter paper.

10. When the wash water is no longer acidic, press the solid between two filter papers until it is as dry as possible

and then allow it to dry in air.

*Filtrate pH ~6.0 after 4 washes.

11. Determine the mass of crude p-nitroacetanilide obtained. Recrystallize the product using a 4:1 mixture of

ethanol and water. You should expect to use about 100-150 mL of solvent. Remember that using either too much or

too little solvent will reduce your final yield.

*Crude not weighed. Crystals still slightly wet and not enough time to dry them before beginning

the recrystallization.

Used 125 mL of 80:20 Ethanol:distilled H2O solvent to recrystallize. Solvent yellow in color.

12. When your product is dry, determine its yield and melting point.

*Product is a light yellow ‘fluffy” cane like’ crystalline solid.

Mass = 3.89 g, mp = 212.5 -213.4 C.

Starting with 7.0 g of acetanilide = 7.0 g/135.17 g/mole = 0.052 moles

Starting with 3mL of conc. nitric acid = 0.003L  ́ 15.4 M = 0.0462 moles

Theoretical Yield (g product) = 180.16 g/mole  ́ 0.0462 mole = 8.32 g

See next 2 pages for infrared spectra of reagent and product to analyze.

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