Chem 315 -Lab 2 -Recrystallization
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Transcript of Chem 315 -Lab 2 -Recrystallization
NamePartnersDrawer No.Course / Section
Katheryn SotoN/A#21CHEM 315/204
The purpose of this experiment is to purify and isolate a solid organic compound by recrystallization with an appropriate organic solvent and vacuum filtration.
Determine an appropriate organic solvent (water, methanol, or petroleum ether) for recrystallization of fluorene. Determine the mass of the impure fluorene sample by weighing. Recrystallize impure fluorene sample using the appropriate solvent. Isolate recrystallized fluorene by vacuum filtration. Air-dry the isolated fluorene sample for one week. Determine the mass of the purified fluorene sample by weighing. Calculate the percent recovery for the recrystallization. Determine the melting point of the purified fluorene sample using the Mel-Temp device.
Text Pavia, D.L., Lampman, G.M., Kriz, G.S., Engel, .G.R., 2011, Introduction to Organic Laboratory Techniques, A Small Scale Approach, GMU Edition, Chem 315/318, Cengage Learning: pp. 598-608; pp. 630-642; pp. 662-680 Slayden, S., Stalick, W., Roth, R, 2014, Organic Chemistry Laboratory Manual, 2nd Edition: Pearson Custom Publishing: pp. 31-34
Web Site URL Dr Schornicks Website: http:/mason.gmu.edu/~jschorni/recrystallization Vacuum Filtration Image: https://upload.wikimedia.org/wikipedia/commons/thumb/d/da/Vacuum-filtration-diagram.png/622px-Vacuum-filtration-diagram.pngCompound
2,2-Methylenebiphenyl (9H-Fluorene), CAS No. 86-73-7, CRC Handbook of Chemistry & Physics, 84th Edition, Lide, D.R., Editor-in-chief, 2003-2004, CRC Press, #5343, p. 3-272.
Proc # 1Determine SolventResultsUnk No.
B.P. (oC)Bath (oC)Methanol
The boiling point (B.P.) of the solvent must be less than the melting point (M.P.) of the sample
Tube #1Mass Fluorene:0.045gSolvent:
[email protected]:Very insoluble. All of sample settled at the bottom of the tube with agitationGood Solvent?:NOTube #2
Very soluble. Sample dissolved completely without agitation. Good Solvent?:
NOTube #3Mass Fluorene:
Slightly soluble. Particles suspended but did not dissolve completely with agitation.Good Solvent?:
YES*@R.T.= at room temperature
Observations: Methanol was chosen as the most suitable solvent for recrystallization because it is important that the solid be insoluble at room temperature but soluble when heated. Fluorine dissolved in methanol @ 65oC. No additional solvent was needed.
0.05g fluorene Solvents
petroleum ether 2 Beakers 2 Hot plates Eye dropper
3 small test tubes
Test tube rack
Spatula 3 thermometers
Fill 2 beakers halfway full with water. Place a thermometer in each water bath.
Heat one water bath on a hot plate to 65oC. Heat the second water bath on a hot plate to 95oC. Label three test tubes, one for each of the solvents Add 50mg of fluorene to each test tube. Add 0.5mL (10 drops) of each solvent to each of the appropriately labeled test tubes. Swirl each mixture using a clean dry spatula. If the fluorene is very soluble or very insoluble at room temperature in any of the solvents, it is not suitable for recrystallization. Choose the test tube containing the solvent in which fluorene is slightly soluble at room temperature and place it in the water bath of the appropriate temperature (see chart on right).
Insert a thermometer into the test tube to monitor the temperature.
Heat mixture to solvent boiling point (see chart on right) and remove from bath immediately to reduce evaporation. If solid sample remains, use a dropper to add solvent sparingly to the test tube until dissolved completely dissolved (max 2.0 mL total solvent). Continue to heat the mixture. If solid sample remains, choose a different solvent. If almost dissolved remove the sample from the hot water bath and cool at room temperature. Cool the sample in an ice bath 1 min to crystallize. If recrystallization does not occur scratch the surface of the mixture with a stirring rod to encourage the process. If still no recrystallization occurs, restart this process of heating, cooling and scratching. If still no crystals form, choose a different solvent.
Proc # 2Mass Impure Fluorene Results
MaterialsEquipmentMass Fluorene (g):
1.521gObservations: Fine white powder, difficult to weigh accurately because stuck easily to weigh boat
1.5 g fluorene Weigh boat
Electronic balance (0.001) 1 125 mL Erlenmeyer flask
Place a clean dry weigh boat on the electronic balance and close doors.
Tare the instrument. Use a spatula to add 1.5g of fluorene to the weigh boat. Record the sample mass to the precision limit of the balance (0.001) and dispense into a clean dry 125 mL Erlenmeyer flask.
Proc # 3RecrystallizationResults
MaterialsEquipmentObservations: A good deal of heat and additional methanol was required to dissolve the sample completely (20mL total). Temperature of water bath was increased to 75oC to aid in dissolving the sample.
1.521g fluorene Previously determined solvent (methanol) Ice bath 1 125 mL Erlenmeyer flask Hotplate
Add the solvent chosen (methanol) to the Erlenmeyer flask containing the fluorene sample. Use only enough to cover the sample. Swirl the flask to stir. Heat the solution for 1 min. to dissolve the fluorene. If solid remains, add 0.5 to 1.0 mL of solvent to the flask and continue to heat the solution. Repeat until a homogenous mixture has formed. Cool the solution to room temperature.
Transfer the flask to an ice bath to continue cooling. Cool the solution until it thickens but is still fluid (slurpee consistency). If too much recrystallization occurs, add more methanol and repeat the recrystallization process. If no recrystallization occurs, reheat the mixture to evaporate excess solvent.
Continue the process until the appropriate solvent to crystal ratio is obtained.
Proc # 4Vacuum filtrationResults
MaterialsEquipmentVacuum Filtration Apparatus
Observations: End product before drying had larger, more translucent white crystals and a fluffier, flakier consistency when compared to the impure fluorene sample.
Sample before air drying was fairly dry.
Filter paper 20mL Methanol (cold)
Fluorene solution 125 mL Erlenmeyer flask
1 Buchner funnel 1 Filter flask
Ring stand and clamp
Assemble the filtration apparatus (see diagram on right). Place the filter paper in the Buckner funnel and moisten with a few drops of cold methanol. Turn on the vacuum to tightly affix the filter paper to the funnel.
Dispense the purified fluorene solution on top of the filter paper. Rinse the Erlenmeyer flask with a small amount of solvent and swirl to transfer remaining solution to the funnel. Filter until no more liquid can be seen passing into the filter flask. Add 5mL of cold methanol solvent to the crystals to remove any remaining impurities. Wash crystals 3 times using the cold methanol, waiting until the filtrate stops dripping between each wash.
Use a spatula to transfer the purified crystals to a pre weighed vial. Leave the lid slightly ajar to allow air into the vial. Air dry sample for one week.
Proc # 5Mass Purified FluoreneResults
Mass vial + sample
15.588 - 14.920 =1.415gMass weigh boat
2.820gMass boat + sample
4.233 2.820 =1.413gAverage(1.415 + 1.413)/2 =
Dry purified fluorene sample in vial
Weigh boat Electronic balance (0.001) Spatula Calculator
Tare the balance with all doors closed to ensure an accurate measurement
Weigh the sample in the vial on the electronic balance.
Record mass to three decimal places.
Subtract the previously determined mass of the empty vial from the mass measurement to determine the mass of the fluorene sample
Mass of vial and sample (g) mass of empty vial(g) = mass of purified sample (g)Mass of weigh boat and sample (g) mass of empty weigh boat = mass of purified sample (g)
Proc # 6% RecoveryResults
MaterialsEquipment% recovery = (1.414/1.521) x 100 93.0%Grams lost = 1.521 1.4140.107g
Similar in theory to percent yield.
Used when no chemical reaction takes place.
Determines quantity of product yielded from the quantity of product used in the filtration process.
Proc #7Melting PointResults
MaterialsEquipmentPurified Fluorene1st M.P. (oC)
2nd M.P. (oC)
113.0117.3115.2Observ:Larger more flaky translucent white crystals, fluffy consistency.
Purified fluorene sample
Capillary tubes Mel-Temp Apparatus
Use a watch glass and spatula to crush a small amount of purified fluorene sample.
Tap the sample with the open end of a capillary tube to load (2mm) Drop the capillary tube (closed end down) through the glass tubing so the sample is at the bottom of the tube. Insert the capillary tube closed end down into the Mel-Temp device.
Heat the sample increasing the temperature 2-3oC/ min to determine the rough melting point.
Record the 1st M.P. when the compound begins to melt.
Record the 2nd M.P. to when the sample is clear liquid. Record temperatures to one decimal place.
Cool the sample until solid. Reheat sample until approximately 10oC below the rough melting point.
Continue to heat the sample at a slower rate (0.5oC/min). Record a second M.P. range.
Summary of Results:
The solvent chosen for the recrystallization of fluorene was methanol. The mass of the impure fluorene sample before recrystallization was 1.521g. The mass of the purified fluorene sample was 1.414g. The percent recovery for the recrystallization of the fluorene sample was 93.0%. The average melting point for the purified fluorene sample was 113.0-117.3oC (Average 115.2oC).
Analysis & Conclusions:
The purpose of this experiment was to purify and isolate solid fluorene by recrystallization of an impure fluorene sample with an appropriate organic solvent and vacuum filtration.
First, three organic solvents: methanol, petroleum ether, and water were considered for fluorene recrystallization. An appropriate solvent for recrystallization is one in which the compound of interest is soluble at elevated temperatures, but only sparingly soluble at room temperature or lower. Since fluorene is a nonpolar organic compound, a polar solvent is the best bet for crystallization. In petroleum ether, a nonpolar organic solvent, fluorene was too soluble at room temperature, demonstrating the like-dissolves-like rule of chemistry. In water, a very polar organic solvent, fluorene was insoluble both at room temperature and at elevated temperatures. In methanol, fluorene was slightly soluble at room temperature, but very soluble when heated. Methanol is polar; however, because it is an alcohol, it contains both polar and nonpolar parts, which causes both polar and nonpolar substances to be soluble in it. The recrystallization was carried out using methanol as the solvent. After recrystallization of the compound, the sample was isolated from the mother liquor via vacuum filtration and allowed to air dry. After one week, the air-dried sample was weighed (1.414g) and the percentage recovery for the recrystallization was calculated (93%). The large percent recovery suggest careful lab technique was used in transferring the sample from container to container as to prevent additional loss
As with any recrystallization, it is impossible to achieve 100% product recovery due to the fact that some of the fluorene sample is soluble in the methanol solvent at any temperature; therefore, some fluorene remained dissolved in the mother liquor during filtration (0.107g of the 1.521g before recrystallization). To increase the percent recovery in future trials, a second recrystallization can be performed with the mother liquor by evaporation; however, this second recrystallization will produce a less pure product (marked by a lower and broader melting point) by comparison to the first due to a higher concentration of impurities after evaporating the solvent. Finally, the purity of the isolated fluorene was determined by testing its melting point (113.0-117.3oC; avg. 115.2oC). The melting point of the purified sample was very close to the literature value of 114.8oC, suggesting a fairly pure final product. In comparison to the impure product, the purified fluorene was fluffy, with larger more flaky crystals.
Literature Summary (Unknowns, Synthesized Compounds)
Synonyms9H-Fluorene, Fluorene, diphenylenemethane, o-Biphenylenemethane
Melting Point (oC)
Lit(113.0-116.0oC) 114.8oCExp(113.0-117.3oC) 115.2oCLit
Boiling Point (oC)
Refractive Index (nD20)Lit1.645Exp
Solubility(Rel to Water)Lit800g/L @ 25Exp
Rel to WaterLit1.203g/cm-3Exp