Acid catalyzed Esterification - Test for Water formed

Demonstration Experiment on Video

Acid catalyzed Esterification - Test for Water (formed in this Reaction)

Objectives: Catalysis, Equilibrium, Le Chatelier's Principle

Peter Keusch

German version

Chemicals:
acetic acid 100 %
1-butanol
conc. sulfuric acid
CoCl₂ · 6 H₂0
ethanol

Apparatus and glass wares:
magnetic stirrer hotplate
magnetic stirring bar
water estimation apparatus (Dean & Stark) with stopcock - comprises a flat bottom flask, a reflux condenser and a graduated receiver with glass stopcock having sockets 19/26 & cone 24/29
test tube

Hazards and safety precautions:

Acetic acid is strongly corrosive and causes serious burns. Lachrymator

Ethanol is highly flammable.

Conc. sulfuric acid is extremely corrosive, causes serious burns. Highly toxic. Harmful by inhalation, ingestion and through skin contact. Ingestion may be fatal. Skin contact can lead to extensive and severe burns. Chronic exposure may result in lung damage and possibly cancer.

Cobalt(II) chloride is toxic. Risk of irreversible effects. May cause sensitization or allergic effects. May cause skin or eye irritation.

Safety glasses and protective gloves required. The experiment should be performed under a portable fume cupboard giving all-round visibility!

Experimental procedure:

Experiment set-up

The apparatus consists of a flat bottom flask (1) bearing a Dean-Stark trap (2) fitted with a reflux condenser (3).

25 mL of 1-butanol, 15 mL of acetic acid, 1 mL of conc. sulfuric acid and and some booling stones are placed in the bottom flask. Using a hotplate the reaction mixture will be heated to boiling.

Result:

The vapors ascend to the reflux condenser, condense and drip into the Dean-Stark receiver. The condensed mixture consists of two immiscible liquids (interface). The bottom layer is allowed to flow into a test tube containing a blue solution of cobalt(II) chloride in ethanol. The color of the solution turns pink.

Video clip (Download RealPlayer .rm Datei)

Discussion:

The acid catalyzed esterification is reversible:

In order to obtain a high yield of ester the equlibrium must be shifted toward the products. According to Le Châtelier’s Principle, adding an excess of one reactant (either butanol or acetic acid) to a system at equilibrium causes a shift in the reaction that favors product formation.

Another technique to upset the equilibrium is to remove the water as an azeotrope using a water trap Dean-Stark apparatus). When the homogenous vapor (63 % ester, 24 % water, 8 % alcohol) condenses two layers are fotmed in the Dean-Stark receiver. The upper layer consists of 86 % butylester, 11 % alcohol and 3 % water. The bottom layer is composed of 97 % water and traces of ester and alcohol. The upper layer is allowed to return to the reaction mixture. Thus the equilibrium can be upset and nearly 100 % of ester can be produced in the reaction flask.

CoCl₂ · 6 H₂0 is dissolved in ethanol to form a blue chloro complex. When water is added the chloro complex is converted to a pink hexaaqua complex.

Index of Lecture Experiments