CHM 2211L Practical #2

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How do substituents on aromatic rings affect electrophilic aromatic substitutions?

Electron withdrawing groups (EWG) – direct incoming groups to positions that are meta to the groups. Electron donating groups (EDG) – direct incoming groups ortho and para to the groups.

What kind of EAS (electrophilic aromatic subtitution) did we observe in our experiment?

Iodination of an aromatic compound.

What is a greener method of carrying out an iodination reaction?

Sodium Iodide (NaI) as a source of iodine & sodium hypochlorite (NaOCl) as an oxidizer. (Iodine is the least reactive of the halogens and requires an oxidizer)

What happens to the reaction mixture after NaOCl is added?

The reaction mixture turns a pale yellow. (Indicates the presence of iodine)

Why is sodium thiosulfate added to the reaction mixture after it turns yellow?

To remove any residual or excess iodine from the solution.

What was the substitution pattern on the aromatic ring?

The substituents present on the aromatic ring are EWGs so the iodine came into the meta position.

Make sure you understand the mechanism for EAS, the product that forms, and the separate reaction that takes place to form the iodine electrophile.

Salicylamide is an active ingredient in BC powder, a common OTC remedy. What is its purpose?

It significantly enhances plasma levels of aspirin with potential therapeutic implications.

Which diacetylferrocene product (if any) forms when ferrocene is reacted with acetic anhydride?

It differed between each lab team, but only ferrocene and acetylferrocene was produced when I conducted the experiment.

What kind of acetylation procedure did we perform in this experiment?

Friedel-Crafts acylation (we will generate acylium ion electrophile using acetic anhydride).

What compound is referred to as the "superaromatic" (very reactive) compound?

Ferrocene.

What is chromatography?

A term that refers to techniques for separating, analyzing, and identifying compounds.

What are the different types of chromatography?

-Thin layer (TLC) -Gas (GC) -High Performance Liquid (HPLC) -Column

What types of chromatography will we be using in this experiment?

Thin layer (TLC Plate) & Column

TLC Terms:

Mobile phase = liquid or solvent (eluent) Stationary phase = silica gel (TLC plate) that contains adsorbent Solvent front = leading edge of solvent

How do you construct a developing chamber for the TLC plate?

Place the TLC plate in a beaker and cover the top of the beaker with a watch glass. Inside the beaker should be filter paper and a small amount of eluent.

How does the eluent move up the TLC plate?

Capillary action

How do you calculate the Rf value?

Rf = distance from origin to center of the spot/distance from origin to the solvent front

Explain TLC chromatography

The compounds will separate as the mobile phase passes through the origin. Compounds that are least polar will adhere to the mobile phase and travel much further up the plate while compounds that are most polar will adhere to the stationary phase and travel much slower (Rf value much smaller).

How could we speed up how fast each compound travels?

By using a polar solvent as the mobile phase. (Rf values would be greater)

Explain column chromatography

The stationary phase is packed into a glass tube (column), that is equipped with a stopcock. The sample is loaded on the top of the column. The column is eluted by adding solvent to the top of the column and collecting the solvent and component as they come through the stopcock as fractions. The least polar compound will elute first.

Why is it important not to dilute the initial sample before it has been loaded onto the chromatography column?

It is important to ensure that the entire sample enters the column in as compact of a band as possible.

Which compound would you expect to elute first from the column: ferrocene, acetylferrocene, or diacetylferrocene?

Ferrocene (unreacted) because it it the least polar compound.

What did we use as our mobile phase in the TLC chromatography?

Methylene chloride

Why must the column have a piece of cotton placed in it?

To support the packing material and keep it from clogging the stopcock during elution.

What is the order of each layer in the column before adding the sample solution?

Cotton -> sand -> silica -> sand -> solvent (fills the whole column, but hovers at the top)

What did we use as our mobile phase for column chromatography?

Ligroin = ferrocene (yellow) Ligroin & Ethyl acetate = acetylferrocene (orange) Ethyl acetate = diacetylferrocene (red)

Which diacetylferrocene isomer forms?

1,1′-Diacetylferrocene because since the acetyl group is an EWG it will favor the meta formation.

Polymer

A large molecule that is made up of many smaller molecules, called monomers.

How are polymers formed?

Through a synthetic process called polymerization where monomers are chemically linked together.

What kind of polymerization reactions did we observe in our experiment?

-Condensation -Chain addition -Slime (cross-linked polymer)

What is an example of a synthetic polymer? A natural polymer?

Polystyrene, cotton

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