Orgo Lab Exam III: Lab F (Fisher Esterfication)

Sulfuric acid

an oxidant and corrosive

Why is a graduated cylinder used to collect the product of distillation?

beaker is not used, because its width at the top allows vapors to escape and allows dirt to get into the distillate.

Simple Distillation

- Used to remove a low-boiling solvent from a high-boiling organic compound. -A liquid is vaporized by boiling, then condensed back to a liquid (distillate), and collected in a receiving flask.

Fractional Distillation

-A fractional distillation is used to separate two compounds whose boiling points are less than 50oC apart. -A fractionating column (Vigreux column) is inserted between the distillation flask & the distilling head - providing a larger surface area over which a number of separate liquid-vapor equilibria can occur. -Many vaporizations and condensations take place before the distillate is collected.

Vigreux Columns

-Efficiency of a fractionating column - expressed by number of theoretical plates -One Theoretical plate: Equivalent to one simple distillation cycle. -Efficiency sometimes reported as HETP (Height of a column that is Equivalent to one Theoretical Plate) - The lower the HETP - the more efficient the column.

Esters:

-Have pleasant fruity odors -Used as Flavoring agents and in the Perfume Industry

Thermometer Position

-In order to read an accurate boiling point, the thermometer must be placed correctly -Read the thermometer when the material starts collecting - not when the solution starts boiling. (ie, the red bulb thingy shold be below the perpendicular pipe)

joints for simple distillation should be tight because

-Loose joints will cause your product to escape! -You should use a Keck clip in this location (between joints lol)

Methods of Esterification include

-Reflux -Extractions -Simple Distillation

Vacuum Distillation

-Used for compounds that either boil at too high a temperature, or that decompose near their boiling points Under vacuum - compounds can be distilled at temperatures lower than their atmospheric boiling points. Only feasible solution - distilling compounds with BPs > 200 oC.

Advantages of a reflux

-maintains a constant temperature in the reaction flask. -reaction is able to reach equilibrium with minimal evaporation of material inside the reaction flask.

boiling for distillation

Always use boiling stones! Fill your distilling flask to only ½ to 1/3 full. Pour liquids into the distillation flask using a funnel - to prevent the liquid from contaminating the ground glass joints.

Reflux information

By choosing the appropriate solvent, you can adjust the temperature of the reaction without needing to worry about equilibrating an external bath. By using an excess of one of glacial acetic acid and refluxing for one hour, we will be able to drive the equilibrium reaction to the product side and attain a good yield of ester. After an initial purification by extraction, the crude product will be distilled to give pure isoamyl acetate.

Using the Variac

Heating mantle is connected to a variac VARIAC-variable voltage transformer- adjusts the voltage to the heating mantle (and hence the heat).

How do you minimize evaporation for substances being distilled?

If a volatile compound is being distilled, the receiver can be chilled in an ice bath to minimize loss of vaporization.

NORMAL BOILING POINT:

Is defined as the temperature at which a liquid's vapor pressure equals 1 atm.

What is done to make the most products????

Lower equilibrium barrier via acid catalyst. Reflux reaction to increase the rate of the reaction. rate will double for every 10°C increase in temperature.

Where to plug the Variac

OMG NOT IN THE WALL! -bottom right corner; the plug that is by the knob that adjusts the electricity flow Variac - the higher the boiling point, the greater the voltage required. Start at ~ 65

Equilibrium and how to get the products

The reaction is reversible, as the ester can react with the acid and water to go back to the starting materials. In order to get a good yield of the product, it is necessary to push the equilibrium by either removing water as it forms, or by using an excess of one of the reagents. ACID IS A CATALYST

Purpose of a Reflux

To heat a reaction mixture at its boiling temperature to form the product, without losing any material inside the reaction flask.

What does it mean for a solution to boil?

Vapor Pressure = Atmospheric Pressure

How does water flow for the extension for distillation?

Water out nearest the boiling source, water in nearest the distilled reservoir

Glacial acetic acid

flammable, corrosive

Reflux

is a technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations. It is also used in chemistry to supply energy to reactions over a long period of time.

Fischer esterification

is an acid-catalyzed equilibrium reaction between a carboxylic acid and an alcohol in the presence of a strong acid catalyst, usually sulfuric acid, to produce the corresponding ester and water as a by-product

Why should you not distill to dryness?

leaving a small amount of residue will prevent overheating and breaking the flask, and also prevent formation of pyrolytic tars that are difficult to wash out.

Acid catalyzed reaction

meaning that the acid is regenerated and is never consumed. Impossible to obtain a 100% yield. Acid is used to lower the equilibrium barrier

How to push equilibrium to the left?

remove products as formed, or use excess of one of the starting materials

when a reaction is refluxed in an organic solvent

the bp of the solvent is the temp of rnx (WHAT IS THE SOLVENt?!?!)

How did we move equilibrium?

used x2 needed amount of acetic acid; results in a small amount of isopentyl alcohol to remove, which can be used in simple distillation.

during reflux, how much will the rate increase per ever 10 deg C increase in temperature?

x2