Vacuum Filtration Technique

Vacuum Filtration

• A technique used in organic chemistry
• It isolates a solid from a solid/liquid mixture or removes impurities from a large liquid quantity
• Also known as suction filtration
• A porcelain Buchner funnel is placed onto a vacuum filter flask
• The filter flask connects to a vacuum aspirator through thick vacuum tubing
• Vacuum filtration begins with setup
• The filter flask is clamped to a stand and connected to the vacuum aspirator via a rubber tube
• The Buchner funnel is inserted onto the filter flask
• Circular filter paper is placed on the Buchner funnel and moistened with an appropriate ice-cold solvent
• The solid/liquid mixture is poured onto the filter paper
• The vacuum aspirator forces liquid through the filter paper, collecting it in the filter flask
• The solid compacts on the filter paper
• The solid is air-dried for several minutes
• Turning off the vacuum requires disconnecting the rubber tubing and closing the inlet

Heating Under Reflux

• Heating is done to generally increase the rate of most organic reactions
• Heating under reflux prevents solvent loss
• Heat the liquid at its boiling point
• Use a condenser with cold water rushing along the side to condense solvent vapors back into the reaction vessel
• Refluxing time starts when the reaction begins to boil
• Set the heat source for one solvent drop back into the flask per second

Reflux Setup Procedure

• Position the heat source on a stand
• Select an appropriately sized RBF, filling it no more than half full
• Securely clamp the flask to the stand
• Add reactants to the round bottom flask with a funnel
• Add boiling chips or a magnetic stirring bar
• Connect tubes to the condenser
• Place the condenser onto the RBF
• Connect the condenser's lower tube to the cold water source
• Place the upper tube in the drain, ensuring a secure fit to prevent water splashing
• Turn on the heat source, ensuring gentle boiling with a solvent drip rate of about one drop per second
• A visible reflux ring of condensing vapors should be present, reducing heat if it rises too high in the condenser
• Use a clamp to stabilize the condenser

Magnetic Stirring

• Stirring ensures proper heat transfer and efficient reactant contact in a reaction
• Use a magnetic stirrer on a hot plate set to "stir"
• Rotate and mix the solution by placing a flask with a magnetic stir bar on the stirrer

Experiment 3: SN2 Reaction on 2-Naphthol

• Synthesize 2-butoxynaphthalene (butyl naphthyl ether) through an SN2 reaction
• Utilize 2-naphthol extracted from a mixture
• React 2-naphthol with sodium hydroxide to generate 2-naphthoxide
• React 2-naphthoxide with 1-bromobutane to produce 2-butoxynaphthalene

Procedure

• Reweigh leftover 2-naphthol, consulting TAs if less than 0.5 g is available
• Do not exceed 1.0g of 2-naphthol; set aside any excess and record the mass used
• Set up the reflux apparatus
• Add ~0.56 g (14.0 mmol) of NaOH (about 5 pellets) and 2-naphthol to a flat-bottomed round bottom flask through a powder funnel
• Add 20 mL of ethanol (EtOH) and a magnetic stir bar to the flask
• Reflux the solution for 30 minutes, adjusting heat for approximately 1 drop/second from the condenser
• Conduct reflux on a hot plate with magnetic stirring at 345 rpm and a speed of 500
• The round bottom flask should be as close as possible to the hot plate without making contact
• After 30 minutes, remove the heat source and allow slight cooling
• Remove the condenser after boiling stops, then add 1.0 mL of 1-bromobutane (8.8 mmol)
• Quickly replace the condenser and reflux for another 30 minutes
• While refluxing, prepare a vacuum filtration apparatus with a Buchner funnel
• Place 100 mL of water in an ice bath
• Obtain the masses of recrystallized benzoic acid
• Before the second reflux ends, place 25 g of ice in a 250 mL beaker
• After the second reflux, remove the heat and cool the solution for 1 minute.
• Pour the flask contents onto 25 g of ice chips in a 250 mL beaker, mixing thoroughly
• Place the beaker with sample and ice on ice
• Remove the magnetic bar
• Rinse the round bottom flask with sufficient cooled water and add to the beaker, swirling until all ice melts
• Allow cooling and crystallization under the fume hood for 10-15 minutes
• Collect the product via vacuum filtration
• Rinse the beaker with ~30 mL of ice-cold water
• It is vital that the rinse water used be ice-cold
• Draw air through the product for 2-5 minutes
• Allow product to dry over multiple days