CHM 2211L Practical #1

Recrystallization

Completely dissolve both the desired compound and any other organic impurities when the solvent is at boiling point.

Insoluble in the solvent at cold temperatures (ice bath), and the organic impurities must remain soluble when the solution is cooled.

They serve as nucleation sites where more molecules of the desired compound deposit themselves in layers.

It induces and maximizes crystal formation.

It is done to prevent the desired compound from crystallizing along with the impurities. It removes any insoluble impurities from the solution (rather than isolating the desired product).

With long-stemmed funnels, the crystals come out in the step as the solution cools, blocking up the funnel. Using a stemless funnel prevents this from happening.

Vacuum filtration. Any remaining impurities are removed from the desired compound.

A non-polar solvent. It is a colorless and flammable liquid.

HCl is used for the acid-base reaction rather than water becuase HCl's polarity contributes to a reaction driven to the right. It protonates the amine group, making it easy to dissolve.

It is used to buffer the reaction mixture because control of acidity is important in maximizing yield. Protonation activates acetic anhydride toward nucleophilic attack, but if the pH is too low the starting amine will will be converted to its conjugate acid.

Amide synthesis = formation of the amide bond & Williamson Ether = formation of the ether linkage.

Boiling sticks provide a large surface area and give the gas that forms from the hot liquid a place to form and then release. To summarize, it prevents bumping.

The temperature at which the solid phase is in equilibrium with the liquid phase of the compound.

Water because the solute is completely soluble at boiling point, but the crystals reappear when solution is placed in an ice bath.

Allows the reaction to be carried out at the boiling point of the solvent and yet it prevents loss of solvent or reagent due to evaporation. The vapors condense as they rise up the condenser and thus prevent them from escaping. We used it for Williamson Ether synthesis of acetophenetidin.

Synthesis of acetophenetidin by Williamson Ether synthesis produced purer crystals, but amide synthesis produced a larger crude mass (greener pathway). Recrystallizing the crude product formed from amide synthesis gave purer crystals that were identical to those formed by Williamson Ether synthesis. This is partly due to the fact that water is a good recrystallization solvent.

*Percent Yield = actual yield/theoretical yield x 100 *Percent Recovery = mass of recovered recrystallized product/mass of crude product used in recrystallization x 100

Extraction is a technique that chemists use to remove selected components from a mixture. The different types are solid-liquid extraction and liquid-liquid extraction.

It offers a greener alternative to other solvents, it is readily available, nonflammable, nontoxic, and safe for the environment. Ease of removal of solvent at the end of procedure, and it is relatively quick.

The two solvents that are chosen for the extraction must be immiscible (not soluble in each other). In addition, the compound to be extracted must have different affinities for the two solvents.

Because carboxylic acid is a relatively strong acid, it is strong enough to react with a weak base such as sodium bicarbonate to yield water-soluble carboxylate ions.

Because phenols are much less acidic, it is too weak to react with a weak base so it must react with a strong base such as sodium hydroxide in order to covert phenol to its water-soluble phenolate ion.

Neutralization must take place to regenerate the neutral organic compound. This is accomplished by adjusting the pH of the aqueous layer with HCl until the solution is acidic.

Brine. Even though the organic solvent is usually immiscible with water, they still tend to absorb some water during the mixing that occurs during extractions.

Placing it in contact with an anhydrous inorganic salt (anhydrous magnesium or sodium sulfate). The salt will absorb the water that is dissolved in the organic solvent.

Gravity filtration. (Filtered solution then sits so that organic solvent evaporates and only the extracted compound remains).

An aqueous layer (bottom) forms that is immiscible to the organic layer (top) and the aqueous solution.

The carboxylate ion is present. In order to regenerate the carboxylic acid it must be added to HCl in an ice bath to induce crystallization. To isolate the crystals, vacuum filtration is performed.

The phenol is present. There may be some water present in the solution so it must be dried with brine and anhydrous magnesium sulfate until it no longer clumps together. The drying agent is then separated from the organic solution through gravity filtration. Once this is done, the ether must be evaporated under reduced pressure so that the pure phenol solid is left in the flask.

Extraction is the process of pulling out the desired compound from a solution while washing is cleaning and purifying the extracted compound to eliminate contaminants from the parent solution.

When phenol loses a hydrogen, the electron pair will get delocalized and resonance will occur among the pi bonds in the phenyl ring. As a result, it is much more acidic while its conjugate base is weak. Cyclohexanol only consists of sigma bonds so delocalization cannot occur and the molecule is much less stable so it will be a weaker acid while its conjugate base will be much stronger.

It is a process used to isolate essential oils from plants and spices. The spice or herb is suspended in water, and as the water is boiled and vaporizes, it extracts the essential oils and carries them over into the collection flask. (High boiling points of these oils makes them difficult to isolate on their own without risking decomposition of the compound).

It will allow the water to penetrate the cloves and should allow more eugenol to be isolated from the cloves.

Vapors will form in the heated distillation flask. The condenser cools the vapors as they travel toward the collection vessel causing them to liquefy again and flow into the vessel. A filled condenser provides maximum cooling allowing maximum recovery of purified liquid during distillation.

To extract the eugenol from the water. This process is liquid-liquid extraction and the lower layer will be the dichloromethane along with the desired essential oil.

Add anhydrous magnesium sulfate to the solution.

Distillation is more advantageous than carbon dioxide extraction for cloves because a larger product yield is extracted. However, it takes time. Carbon dioxide extraction is also disadvantageous because the pressure build up from sublimation can cause the cap on the test tube to come off.

Helps expose fresh metal surface by removing some magnesium oxide on the exterior.

Cleaning the surface of the magnesium metal.

It is an important carbon-carbon bond forming technique that results in the formation of an alcohol.

Grignard reagents are sensitive to water,

Grignard reagents are sensitive to water so if diethyl either containing more water is used it will interfere with the formation of the Grignard reagent.

The acidic solution donates a proton to the negatively charged carbon forming an alcohol.

An aqueous layer forms (bottom) and an organic layer forms (top). The desired compound is dissolved in the organic layer (like dissolves like).

Dry the ether over anhydrous magnesium sulfate and remove the drying agent by gravity filtration.

Recrystallization using ethanol. The desired compound is soluble in ethanol at boiling point and is insoluble in ethanol when it cools.