Faculty of Pharmacy Organic Chemistry Laboratory Study Guide

Faculty of Pharmacy Organic Chemistry Laboratory Overview

This laboratory course, prepared by Dr. Abdullah Ghawanmeh for the February 2026 term, provides students with essential tools and techniques for handling organic compounds. The curriculum is split into two primary segments. Part One focus on Tools & Techniques, covering six experiments directed at identification, purification, and isolation using physical properties like melting point (for solids), boiling point (for liquids), and solubility. Key techniques include recrystallization, distillation (simple, fractional, and steam), extraction, and chromatography. Part Two focuses on Chemical Testing & Chemical Reactions, where students identify functional groups (alcohols, phenols, aldehydes, ketones, and amines) and perform organic syntheses, including Fischer esterification, Aldol reactions, and saponification for soap production.

Laboratory Safety and Personal Conduct

Safety is the absolute priority in the organic chemistry lab. Personal safety requires appropriate dress: bare feet, sandals, shorts, short skirts, and tank tops are strictly prohibited. Long hair and loose clothing must be tied back, and synthetic fingernails should not be worn due to fire hazards. Personal items like book bags must be stored in designated areas and never on lab benches. Students are prohibited from working alone and must wear safety glasses or goggles at all times while in the lab. Any health conditions or allergies to chemicals must be reported to the instructor. Eating, smoking, drinking, or applying cosmetics is forbidden. In the event of a chemical spill on the skin, the area should be washed with soap and water for at least five minutes and reported immediately. Hands must be washed before leaving the laboratory. Tasting or purposely smelling chemicals is prohibited unless instructed otherwise. Students must know the location and operation of safety equipment, including the eyewash fountain, safety shower, and fire extinguisher. During emergencies, students should remain calm, turn off all heat sources (such as sand baths and melting-point instruments), and follow evacuation plans.

Hazard Communication and NFPA Rating System

The National Fire Protection Association (NFPA) diamond provides standardized hazard information. The Blue area represents Health Hazards: 4 (May be fatal on short exposure), 3 (Corrosive or toxic; avoid skin contact/inhalation), 2 (Harmful if inhaled or absorbed), 1 (May be irritating), and 0 (No unusual hazard). The Red area represents Flammability Hazards: 4 (Flammable gas or extremely flammable liquid), 3 (Flammable liquid with flash point below $100\,^{\circ}F$), 2 (Combustible liquid, flash point $100-200\,^{\circ}F$), 1 (Combustible if heated), and 0 (No unusual hazard). The Hazard Communication Standard (HCS) Pictograms alert users to Hazards through symbols in red borders: Health Hazard (carcinogen, mutagen, toxicity), Flame (flammables, pyrophorics), Exclamation Mark (irritant, acute toxicity), Gas Cylinder (gases under pressure), Corrosion (skin burns, eye damage), Exploding Bomb (explosives), Flame Over Circle (oxidizers), Environment (aquatic toxicity), and Skull and Crossbones (fatal or toxic).

Experiment 1: Melting Point Determination

The melting point (m.p.) is the temperature at which liquid and solid phases exist in equilibrium at atmospheric pressure. This physical property is used to identify solids and examine purity. Intermolecular forces—London forces (momentarily produced dipoles in non-polar compounds like heptane), Dipole-dipole interactions (permanent dipoles due to electronegativity differences, as in acetone), and Hydrogen bonds (strong dipoles when H is bonded to F, O, or N, as in methanol)—govern melting points. Generally, high melting point correlates with lower water solubility. A pure solid has a sharp melting point (range of $0.5-1.0\,^{\circ}C$). Insoluble impurities like sand or glass do not affect the melting point. Soluble impurities lower the melting point and broaden the range because they reduce vapor pressure. A eutectic mixture is a combination of two compounds that results in a distinct minimum melting point lower than either pure component.

Procedural steps for melting point determination include grinding the dry solid with a mortar and pestle and filling a capillary tube (6 cm long) to a depth of $2-4\,mm$. Using a Mel-Temp apparatus, students perform an initial rough run (heating at $5-10\,^{\circ}C/min$) followed by an accurate run. In the accurate run, the rate is slowed to $2\,^{\circ}C/min$ once within $20\,^{\circ}C$ of the expected melting point. The melting range is recorded from the appearance of the first liquid drop until the last crystal disappears. Factors affecting results include particle size, amount of solid, packing density, and heating rate.

Experiment 2: Boiling Point and Distillation

Boiling point is the temperature where a liquid's vapor pressure equals external pressure ($1\,atm = 760\,torr$). Vapor pressure increases with temperature due to increased kinetic energy. Factors affecting boiling point include intermolecular forces (e.g., 1-Hexanol has a higher b.p. than Dipropylether because of hydrogen bonding), molar mass (b.p. increases with weight: Methanol $65\,^{\circ}C$ vs. 1-Butanol $118\,^{\circ}C$), and branching (branching reduces forces, lowering b.p.; 1-Butanol $118\,^{\circ}C$ vs. tert-butanol $83\,^{\circ}C$). For solutions, total pressure ($P_T$) follows Dalton’s Law: $P_T = P_1 + P_2 + P_3 + \dots$ and Raoult’s Law: $P_A = \chi_A \times P^o_A$, where $\chi_A$ is the mole fraction and $P^o_A$ is the vapor pressure of the pure component.

Distillation is used for purification and separation. Simple distillation is effective if b.p. differences are $\ge 80\,^{\circ}C$. Fractional distillation uses a fractionating column to provide surface area for repeated evaporation/condensation, suitable for components with closer boiling points. Vacuum distillation is used for high-boiling or unstable compounds. Steam distillation isolates slightly volatile, water-insoluble substances (like essential oils from cloves or anise) at temperatures below $100\,^{\circ}C$. In steam distillation of immiscible liquids, $P_T = P_A + P_B = P^o_A + P^o_B$. The weight ratio in the vapor phase is defined by: $\frac{\text{mass of A}}{\text{mass of B}} = \frac{P^o_A \times MW_A}{P^o_B \times MW_B}$. Practical rules: flasks should be maximum half-full, boiling stones prevent bumping, joints must be greased, and cooling water must enter the bottom and exit the top of the condenser.

Experiment 3: Recrystallization

Recrystallization is a purification technique where a solid precipitates from a saturated solution. It relies on the fact that most solids are more soluble in hot solvents than cold ones. Purities are achieved by removing insoluble impurities via hot gravity filtration and soluble impurities which remain in the "mother liquor" during suction filtration. Solubility depends on relative polarities ("like dissolves like") and lattice energy (higher melting point often suggests lower solubility). A good solvent must have a high temperature coefficient (dissolve much solid when hot, little when cold), be non-reactive, non-toxic, and volatile. If one solvent is insufficient, a miscible "solvent pair" may be used.

Experimental steps include: 1. Solvent selection via solubility tests. 2. Preparing the hot solution using an Erlenmeyer flask with minimal solvent. 3. Decolorizing with charcoal (added after removing from heat). 4. Hot gravity filtration using a fluted filter paper and preheated funnel. 5. Slow cooling to room temperature followed by ice-chilling. 6. Collection via suction (Büchner) filtration, washing with ice-cold solvent, and drying. Percent yield is calculated as: $\frac{\text{Mass of purified}}{\text{Mass of crude}} \times 100$.

Experiment 4: Extraction

Extraction separates substances using a solvent that preferentially dissolves the target compound. Liquid-liquid extraction involves two immiscible phases (organic and aqueous) in a separatory funnel. The distribution coefficient ($K_D$) is defined as: $K_D = \frac{C_o}{C_w} = \frac{S_o}{S_w}$. Multiple extractions with smaller volumes are more efficient than a single large-volume extraction. For example, extracting 6 g of compound A ($K_D = 2$) with $100\,ml$ ether once recovers 66.6%, while two $50\,ml$ extractions recover 75%. "Salting-out" using $NaCl$ or $Na_2CO_3$ decreases the solubility of organic compounds in the aqueous phase and helps break emulsions. Emulsions can also be broken by gentle stirring or centrifugation. Anhydrous salts ($CaCl_2$, $MgSO_4$, or $Na_2SO_4$) act as drying agents to remove traces of water from the organic phase.

Acid-base extraction separates mixtures based on chemical property changes. Organic acids (like benzoic acid) react with bases (like $NaOH$) to form water-soluble salts: $RCOOH(org) + NaOH(aq) \rightarrow RCOO^-Na^+(aq) + H_2O(l)$. The aqueous layer is then neutralized with $HCl$ to precipitate the acid for collection: $RCOO^-Na^+(aq) + HCl(aq) \rightarrow RCOOH(s) + NaCl(aq)$. Caffeine extraction from tea involves boiling tea leaves with $Na_2CO_3$ to convert acidic tannins into salts, followed by extraction of the basic caffeine into dichloromethane ($CH_2Cl_2$).

Experiment 5: Chromatography

Chromatography is used for separation, identification, and purity examination. It involves a stationary phase and a mobile phase. Adsorption chromatography (TLC and column) depends on selective desorption. Partition chromatography (paper and gas) depends on solute distribution between phases. In TLC and paper chromatography, compounds are identified by the Retardation Factor ($R_f$): $R_f = \frac{\text{distance traveled by compound}}{\text{distance traveled by solvent}}$. In gas chromatography, retention time is used.

Thin-Layer Chromatography (TLC) uses silica gel or alumina search on glass. More polar eluents (mobile phases) have higher eluting power and result in higher $R_f$ values. The eluting power order is: Acetic acid > Ethanol > Acetone > Diethyl ether > Dichloromethane > Hexane. Spots are visualized via UV light, iodine vapor (forms complexes), or sulfuric acid (chars organic compounds). Paper chromatography can separate dyes, such as food coloring, while TLC can analyze the constituents of analgesic drugs (e.g., aspirin, phenacetin, salicylamide, caffeine, and acetaminophen) by comparing them to known standards.

Questions & Discussion

1. What is the effect of a non-volatile impurity on the boiling point? A non-volatile impurity lowers the vapor pressure of the liquid, which requires a higher temperature to reach atmospheric pressure, thus elevating the boiling point.

2. Why must cooling water enter at the lower end of the condenser? This ensures the condenser jacket is completely filled with water, providing maximum cooling efficiency.

3. Why is it critical to slow the heating rate near the melting point? Slowing the rate to $2\,^{\circ}C/min$ ensures that the thermometer and the sample are in thermal equilibrium, providing an accurate and sharp melting range.

4. What does it tell you if a mixture of two compounds melts sharply at the same temperature as the pure components? It indicates that the two compounds are identical. If they were different, they would act as impurities to each other, lowering and broadening the melting range.

5. In paper chromatography, which dye is more soluble in the solvent? The dye with the higher $R_f$ value identifies as the one more soluble/less strongly adsorbed by the mobile phase compared to the stationary phase.