Faculty of Pharmacy Organic Chemistry Laboratory Manual Notes

Faculty of Pharmacy Laboratory Manual: Organic Chemistry Introduction

• Foundational Goals of the Course: This laboratory course introduces essential tools and techniques for handling organic compounds. It is structured into two primary divisions.
• Part One: Tools and Techniques (6 Experiments):     * Identification: Based on physical properties including melting point (for solids), boiling point (for liquids), and solubility (linked to molecular polarity).     * Purification and Isolation: Essential for extracting crude products from natural sources (e.g., plants) or isolating reaction products.     * Standard Techniques: Includes recrystallization, distillation, extraction, and chromatography.     * Standard Apparatus: Distillation sets, separatory funnels, beakers, Erlenmeyer flasks, filtration flasks, round-bottom flasks, cylinders, thin-layer plates, and glass columns.
• Part Two: Chemical Testing and Reactions (6 Experiments):     * Functional Group Identification: Use of simple chemical tests to distinguish alcohols, phenols, aldehydes, ketones, and amines.     * Organic Syntheses:         * Fischer Esterification: Synthesis of esters with fruity aromas.         * Aldol Reaction: A common condensation reaction for medicinal compound synthesis.         * Saponification: Transforming vegetable oil into soap.

Safety in the Organic Chemistry Laboratory

• General Responsibility: Safety is the primary concern for the well-being of individuals and environmental protection.
• Personal Safety Protocol:     * Dress Code: No bare feet, sandals, shorts, short skirts, halter tops, or tank tops. Long hair and loose clothing must be tied back. Synthetic fingernails are prohibited as they are fire hazards.     * Workspace Management: Personal items (bags, books) must be stored in designated areas, never on lab benches.     * Conduct: Never work alone. Never smoke, eat, drink, or apply cosmetics. Concentrating on the task is mandatory; personal electronics (cell phones) are prohibited.     * Protective Equipment: Safety glasses or goggles must be worn at all times while in the lab. They are the first item to put on and the last to take off.     * Health Hazards: Students must inform instructors of health conditions or specific chemical allergies.     * Chemical Exposure: If spilled on skin, wash with soap and water for at least $5.0\,\text{minutes}$ and report to the instructor immediately. Never taste or purposely smell chemicals.
• Emergency Procedures:     * Location Awareness: Identify emergency exits, evacuation plans, eyewash fountains, and safety showers on the first day.     * Response: Remain calm. Before evacuating, turn off all heat sources (sand baths, melting-point instruments) if possible.
• National Fire Protection Association (NFPA) Rating System:     * Health Hazard (Blue):         * $4$: May be fatal on short exposure; specialized equipment required.         * $3$: Corrosive or toxic; avoid skin contact/inhalation.         * $2$: May be harmful if inhaled or absorbed.         * $1$: May be irritating.         * $0$: No unusual hazard.     * Flammability Hazard (Red):         * $4$: Flammable gas or extremely flammable liquid.         * $3$: Flammable liquid; flash point below $100.0\,^{\circ}\text{F}$.         * $2$: Combustible liquid; flash point between $100.0\,^{\circ}\text{F}$ and $200.0\,^{\circ}\text{F}$.         * $1$: Combustible if heated.         * $0$: No unusual hazard.
• Hazard Communication Standard (HCS) Pictograms:     * Consist of a symbol on a white background with a red border.     * Health Hazard: Covers carcinogens, mutagenicity, reproductive toxicity, and respiratory sensitizers.     * Flame: For flammables, pyrophorics, self-heating materials, and organic peroxides.     * Exclamation Mark: Irritants (skin/eye), skin sensitizers, acute toxicity (harmful), and narcotic effects.     * Corrosion: Skin corrosion/burns, eye damage, and metal corrosion.     * Skull and Crossbones: Acute toxicity (fatal or toxic).

Experiment 1: Melting Point Identification and Purity Examination

• Definition: The temperature where liquid and solid phases exist in equilibrium. Practically, it is the transition from solid to liquid at atmospheric pressure.
• Intermolecular Forces and Physical Properties:     * London Forces: Result from momentarily-produced dipoles; the only active forces in non-polar organic compounds (e.g., heptane).     * Dipole-Dipole Interactions: Attraction between permanent positive ($\delta+$) and negative ($\delta-$) poles (e.g., acetone).     * Hydrogen Bonds: A strong dipole-dipole interaction occurring when H is bonded to F, O, or N and attracted to a negative pole of F, O, or N on an adjacent molecule (e.g., methanol).
• Relationship to Purity:     * Pure Solids: Melt sharply within a narrow range ($0.5\,^{\circ}\text{C}$ to $1.0\,^{\circ}\text{C}$).     * Insoluble Impurities: (e.g., sand or glass) Do not affect the melting point.     * Soluble Impurities: Lower the melting point and broaden the melting range by reducing vapor pressure in the molten compound.
• Mixed Melting Points: If an unknown and a known compound (e.g., Benzoic acid) are the same, their mixture melts at the same temperature ($122.0\,^{\circ}\text{C}$). If different, they act as impurities for each other, depressing the melting point.
• Eutectic Mixture: A mixture with a distinct minimum melting point (eutectic point) lower than either pure compound.
• Practical Factors Affecting Melting Point: Particle size, amount of solid, packing density, capillary tube thickness, and heating rate.
• Procedure Highlights:     * Sample Prep: Solid must be dry and finely powdered (use mortar/pestle). Fill capillary tube to a depth of $2.0-4.0\,\text{mm}$.     * Heating Rate: For unknown samples, heat at $5.0-10.0\,^{\circ}\text{C/min}$. For accurate measurement, slow the rate to $2.0\,^{\circ}\text{C/min}$ when within $20.0\,^{\circ}\text{C}$ of the expected point.
• Reference Compounds and Melting Points:     * Acetanilide: $114.0\,^{\circ}\text{C}$     * Mandelic acid: $117.0\,^{\circ}\text{C}$     * 2-Naphthole: $121.0\,^{\circ}\text{C}$     * Benzoic acid: $122.0\,^{\circ}\text{C}$     * Urea: $132.0\,^{\circ}\text{C}$     * Cinnamic acid: $133.0\,^{\circ}\text{C}$     * Maleic acid: $135.0\,^{\circ}\text{C}$     * Adipic acid: $152.0\,^{\circ}\text{C}$     * Citric acid: $154.0\,^{\circ}\text{C}$     * Salicylic acid: $158.0\,^{\circ}\text{C}$     * Benzanilide: $161.0\,^{\circ}\text{C}$     * Sulfanilamide: $165.0\,^{\circ}\text{C}$     * p-Toluic acid: $182.0\,^{\circ}\text{C}$

Experiment 2: Boiling Point and Distillation

• Boiling Point Definition: The temperature at which the vapor pressure of the liquid equals the external pressure (usually $1.0\,\text{atm} = 760.0\,\text{torr}$).
• Vapor Pressure Dynamics: Molecules escape the liquid state due to kinetic energy. Equilibrium is reached when evaporation rate equals condensation rate.
• Factors Influencing Boiling Point:     * Intermolecular Forces: Stronger forces increase b.p. (e.g., 1-Hexanol b.p. $157.0\,^{\circ}\text{C}$ vs Dipropylether b.p. $57.0\,^{\circ}\text{C}$).     * Molar Mass: Higher mass increases b.p. (e.g., Methanol $65.0\,^{\circ}\text{C}$ vs 1-Butanol $118.0\,^{\circ}\text{C}$).     * Branching: More branching leads to lower b.p. (e.g., 1-Butanol $118.0\,^{\circ}\text{C}$ vs tert-Butanol $83.0\,^{\circ}\text{C}$).
• Solutions and Mathematical Laws:     * Dalton’s Law: Total vapor pressure $P_T = P_1 + P_2 + P_3 + \dots$     * Raoult’s Law: $P_A = \chi_A \times P^o_A$, where $\chi_A$ is the mole fraction ($\text{moles component} / \text{total moles}$).     * Solution Behavior: If a solute is less volatile than the solvent (e.g., sugar in water), the b.p. increases; if more volatile (e.g., acetone in water), the b.p. decreases.
• Distillation Techniques:     * Simple Distillation: For purifying liquids or separating mixtures where $\Delta \text{b.p.} \ge 80.0\,^{\circ}\text{C}$.     * Fractional Distillation: For mixtures with $\Delta \text{b.p.} < 80.0\,^{\circ}\text{C}$. A fractionating column provides surface area for repeated evaporation/condensation cycles.     * Vacuum Distillation: For high-boiling liquids or compounds that decompose at atmospheric pressure.     * Steam Distillation: Separates volatile, water-insoluble substances from non-volatile matter at temperatures below $100.0\,^{\circ}\text{C}$. Ideal for essential oils (cloves, anise, caraway) and Bromobenzene.
• Practical Distillation Rules:     * Flask should be no more than half full.     * Add boiling stones to prevent bumping.     * Grease ground joints to seal the system.     * Cooling water must enter at the lower end and exit at the upper end of the condenser.     * The thermometer bulb must be positioned below the side arm opening.

Experiment 3: Recrystallization

• Theory: Solvent-based purification where a solid precipitates from a saturated solution as crystals. Based on the fact that solids are more soluble in hot solvents than cold.
• Solubility Principles:     * Polarity: "Like dissolves like." Polar groups (OH, $NH_2$, COOH) dissolve in water or alcohols (up to $4-5$ carbons).     * Lattice Energy: Reflected by melting point; higher m.p. compounds are generally less soluble.
• Solvent Requirements:     * High solubility of solute at high temps; low solubility at room temp.     * Dissolves impurities easily at low temps or not at all at high temps.     * Chemically inert with the solute.     * Highly volatile for easy removal from crystals.
• The Recrystallization Sequence:     1. Selection: Performed via solubility tests.     2. Solution Prep: Use minimum volume of hot solvent. Add decolorizing charcoal if colored impurities are present (remove from heat first).     3. Hot Filtration: Gravity filtration removes insoluble impurities and charcoal. Use a fluted filter paper and short-stem funnel.     4. Cooling: Allow to reach room temperature undisturbed to form large crystals.     5. Collecting: Use suction filtration (B™chner funnel). Wash with ice-cold solvent.     6. Drying: Use an oven or air-dry on paper.
• Common Solvents: Water ($100.0\,^{\circ}\text{C}$), Methanol ($65.0\,^{\circ}\text{C}$, flammable/toxic), Ethanol ($78.0\,^{\circ}\text{C}$, flammable), Chloroform ($61.0\,^{\circ}\text{C}$, toxic), Acetone ($56.0\,^{\circ}\text{C}$).

Experiment 4: Extraction

• Principles: Separation based on preferential solubility in a specific solvent. Includes solid-liquid (e.g., caffeine from tea) and liquid-liquid (using a separatory funnel).
• Distribution Coefficient ($K_D$): At equilibrium, $K_D = C_o / C_w = S_o / S_w$. Multiple small-volume extractions are mathematically more efficient than a single large extraction.     * Efficiency Example: One $100.0\,mL$ extraction ($66.6\%$) vs. two $50.0\,mL$ extractions ($75.0\%$).
• Salting-out: Saturating the aqueous phase with salt (NaCl) to decrease the solubility of organic compounds and help break emulsions.
• Emulsions: Challenging two-phase mixtures that don't separate cleanly. Resolved by gentle stirring, salting-out, or centrifugation.
• Drying Agents: Anhydrous $CaCl_2$, $MgSO_4$, or $Na_2SO_4$ are added to the organic phase to remove residual water.
• Acid-Base Extraction: Organic acids/bases are converted to water-soluble salts via neutralization.     * Caffeine Extraction: Caffeine is an alkaloid. Sodium carbonate ($Na_2CO_3$) is used to convert acidic tannins into water-soluble salts while caffeine remains in the organic phase (extracted with dichloromethane).     * Benzoic Acid Separation: Separated from neutral compounds like naphthalene using $5\%$ NaOH to form water-soluble sodium benzoate. The acid is then recovered by acidifying the aqueous layer with HCl.

Experiment 5: Chromatography

• Core Concepts: Involves a mobile phase and a stationary phase. Used for separation, purification, and identification.     * Adsorption Chromatography: TLC and Column chromatography. Based on selective desorption from a solid adsorbent.     * Partition Chromatography: Paper (liquid-liquid) and Gas-liquid chromatography.
• Analysis Metrics:     * Retardation Factor ($R_f$): $R_f = \text{distance traveled by compound} / \text{distance traveled by solvent}$.     * Retention Time: Used in gas-liquid chromatography.
• Thin-Layer Chromatography (TLC):     * Stationary Phase: Typically Silica Gel ($SiO_2 \times H_2O$) or Alumina ($Al_2O_3 \times H_2O$).     * Eluting Power Order: Acetic acid > Ethanol > Acetone > Diethyl ether > Dichloromethane > Hexane.     * Visualization: UV light for colorless spots, Iodine vapor (complexes show as brown spots), or Sulfuric acid (carbonizes compounds black).
• Specific Applications:     * Nitroanilines: Ortho and para isomers separated by DCM on TLC.     * Analgesic Drugs: Identifying components like Aspirin, Phenacetin, Salicylamide, Caffeine, and Acetaminophen using a mixture of Benzene: Ether: Acetic acid ($2:1:0.3$).     * Green Food Coloring: Separates into yellow and blue components on filter paper using Isopropyl alcohol: Water ($2:1$).