Chapter 29. Organic Chemistry Experiment
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1. Reaction Vessels
⑴ Distillation Apparatus (aspirator)
① Vacuum Filtration Apparatus
⑵ Büchner Funnel (Büchner funnel)
① Equipped with a pump in the funnel itself for vacuum filtration.
⑶ Claisen Adapter
⑷ Dean-Stark Trap
① Efficiently removes water or low-boiling components formed during reactions
② Condition 1: Uses an azeotropic mixture: solvent and co-solvent are mixed to maintain a constant boiling point.
③ Condition 2: Boiling point of azeotropic mixture should be higher than that of the low-boiling solvent
④ Examples of solvents used in Dean-Stark Trap: Benzene (80.1 ℃), Toluene (110.6 ℃), Xylene (139.3 ℃)
⑸ Dropping Funnel
① Used to constantly and slowly add liquid reactants in a controlled manner.
⑹ Fractional Distillation
① Separates compounds with different boiling points
② Fractional Distillation Column: Column with many indentations.
③ The grooves in the fractional distillation column increase the surface area, allowing vapor-phase compounds to lose heat more easily, thereby enhancing the fractional sensitivity.
⑺ Reflux Condenser
① Prevents solvent evaporation
② It is designed to ensure that vapor-phase compounds lose as much heat as possible from the cooling water. In other words, the column is coiled.
⑻ Rotary Evaporator
① Vacuum + gentle heating + rotation (to increase evaporating surface area)
⑼ Separatory Funnel
① Used for separating polar and non-polar liquids
⑽ Simple Distillation Apparatus
① Used to separate liquids with significant boiling point differences
⑾ Suction Filtration
① Used for vacuum-assisted separation of solid filtrates
2. Experimental Equipment
3. Experimental Reagents
⑴ Extraction Solvents
① Polar Inorganic Solvent: Water
② Polar Organic Solvents: CH2Cl2, Acetone
③ Non-polar Organic Solvents: Benzene, Hexane, Dichloromethane, Diethyl Ether
⑵ Organic Solvents with Higher Density than Water: CS2, CCl4, CHCl3, CH2Cl2, CH3Cl, DMSO
① Purpose 1: Used in combination with separatory funnel
⑶ Organic Solvents with Lower Density than Water: Ethyl Acetate, Diethyl Ether, Benzene, …
⑷ Drying Agents: CaCl2, MgSO4, Na2SO4, CaSO4, K2CO3, Molecular Sieves, Zeolite
① Anhydrous salts that readily generate hydrated forms
② Purpose 1: Drying tube
③ Purpose 2: Used with Dean-Stark trap
④ Purpose 3: Used with separatory funnel
⑤ Purpose 4: Used for storing solvents after anhydrous solvent purification
4. Experimental Techniques
⑴ Recrystallization: Utilizes solubility differences
① Step 1: Heat the solution until it melts, then slowly cool
○ Slow cooling prevents supercooling
② Step 2: Wait for crystals to form
○ Providing seed crystals: If no crystals form, scrape the walls of the beaker with a glass rod
③ Step 3: Filtration using vacuum filtration apparatus (e.g., Büchner funnel)
④ Case 1: Precipitate is washed with EtOH, dried, and weighed: If interested in the precipitate
○ Why sprinkle a small amount of solvent onto the crystals?: To remove impurities on the crystal surface
⑤ Case 2: Solvent extraction using a vacuum rotary evaporator: If interested in the solution
⑥ Good solvents exhibit significant changes in solubility with temperature
⑵ Liquid-Liquid Extraction: Utilizes polarity differences
① Generally employs a separatory funnel
② Addition of NaCl increases the ionic strength of the aqueous layer, facilitating separation between the organic and aqueous layers
⑶ Fractional Distillation: Utilizes boiling point differences
Figure 1. Fractional Distillation Apparatus
⑷ Chromatography: Utilizes polarity differences
Figure 2. TLC Chromatography (left) and Column Chromatography (right)
① Type 1: Thin Layer Chromatography (TLC): Used to monitor the progress of reactions
○ Principle: Interaction difference between the sample and silica gel
○ Purpose: Confirm reaction progress, determine reaction completion
○ Normal Phase Silica Gel: Strongly polar. Higher affinity between sample and gel with increasing sample polarity
○ Stationary Phase is silica gel (most polar), Mobile Phase is developing solvent (non-polar)
○ Definition of Rf: Distance moved by sample ÷ Distance moved by solvent
○ Comparison of Rf for different compounds
○ Acid, Base, Metal salt < Carboxylic acid, Amine, Amide < Alcohol < Aldehyde, Ketone < Alkyl halide < Ester < Alkene < Alkyne < Alkane
○ Trend 1: Higher sample polarity leads to stronger interaction with silica gel, resulting in smaller Rf
○ Trend 2: Amino and hydroxy groups are less polar than nitro, but due to hydrogen bonding, their Rf is smaller
○ Trend 3: trans Alkenes have smaller Rf than cis Alkenes (because of stronger interaction)
○ Example: Rf in Paper Chromatography and Chlorophyll Separation Experiment: Carotinoids > Xanthophyll > Chlorophyll a > Chlorophyll b
○ Comparison of Rf with organic solvents
○ Water < Acetic acid < Alcohol < Ethyl Acetate < CH2Cl2 < Toluene < CCl4 < n-Hexane
○ Trend 1: Higher polarity of the developing solvent leads to increased Rf
○ Ethyl Acetate: Representative polar solvent
○ n-Hexane: Representative non-polar solvent
② Type 2: Column Chromatography: Used for separation of mixtures
○ TLC can be thought of as a simplified chromatography
○ Factor 1: Faster migration with weaker interactions in the column: Columns are generally polar
○ Factor 2: Faster migration with stronger interactions with the developing solvent: Developing solvent is non-polar
○ Non-polar substances migrate faster. Gravity has little relevance
⑸ Qualitative Analysis: Uses visible characteristics for identification of specific functional groups in organic compounds
① Br2: Reddish-brown solution
○ Bleaching Reaction: Halogenation reaction results in colorless product
② FeCl3(aq): Yellow solution
○ Reacts with phenol to form Fe(OPh)3, producing color change (burgundy)
○ Fe(OH)2: Green rust
○ Fe(OH)3: Dark orange
③ AgNO3(aq): Colorless solution
○ Forms white precipitate AgCl if leaving group is Cl-
○ Forms yellow precipitate AgI if leaving group is I-
④ KMnO4(aq): Purple solution
○ Forms brown precipitate MnO2
⑤ AgNO3, KOH, NH4OH or Ag2O, NH4OH: Colorless solution
○ Silver mirror reaction or Tollens test: It does not react with ketones but reacts with aldehydes to precipitate metallic silver.
○ Ag2O acts as an Ag+ donor: Oxygen in water migrates to aldehydes, forming carboxylic acids.
Figure 3. Silver mirror reaction or Tollens test
⑥ Concentrated HCl, ZnCl2: Colorless solution
○ Reacts with alcohols to form alkyl chlorides, resulting in a cloudy solution or layer separation
○ In alcohol’s SN1 addition reactions, Cl- is less reactive than other nucleophiles like OH-, hence a catalyst like ZnCl2 is needed
⑦ Silver (Ag)
○ Reacts with hydrogen sulfide (H2S) to form black silver sulfide (Ag2S) precipitate
⑧ Chromium (Cr)
○ K2Cr2O7 is orange, Cr2(SO4)3 is bluish-green
○ K2Cr2O7 is used as an oxidizing agent, often used to measure COD
⑨ Ammonium Chloride (NH4Cl)
○ Reaction of gaseous HCl and NH3 results in a white ring
⑹ Optical Resolution
① The process of reacting a racemic mixture with a specific absolute configuration optical isomer to produce a diastereoisomer.
② Different physical properties allow for separation
③ Application 1: Acid-Base Reaction: Add a strong acid or strong base to separate the ionic bonds between the reactant and the additive.
④ Application 2: Mirror Image Chromatography
Input: 2019.03.29 15:18