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 R_f: Distance moved by sample ÷ Distance moved by solvent

○ Comparison of R_f 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 R_f 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 R_f

○ 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 S_N1 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

⑺ Spectroscopy

Input: 2019.03.29 15:18

1444

Chapter 29: Organic Chemistry Experiment

1. Reaction Vessels

2. Experimental Equipment

3. Experimental Reagents

4. Experimental Techniques

results matching ""

No results matching ""