Experiment VI. Part a: Fischer Esterification Of A Carboxylic Acid And Identification of The Product By GC, Micro-Boiling Point and IR spectroscopy. Reading assignment: Review the mechanism of Fischer esterification. See, for example, KPC Vollhardt and NE Schore, Organic Chemistry, 5th or 6th ed, Ch 19-9 or any introductory organic chemistry text. Techniques in Organic Chemistry pages: 56-58, 60-61, 33. IR: 225-240, 243-266. 3rd ed pages 58-63, 24,-25, 277-288, 291-307. Watch the video! It will help you in setting the experiment correctly. Topics and Techniques i) reaction mechanisms and reaction conditions, ii) reaction work-up, product isolation and purification, iii) infrared spectroscopy, iv) micro-boiling point determination of unknowns Introduction In a Fischer esterification reaction, a carboxylic acid is exposed to an alcohol and a strong acid catalyst that in turn yields an ester and water as the reaction products. The reaction is reversible and the composition of the reaction mixture or position of equilibrium is determined by thermodynamics. The reaction mechanism for formation of the ester is given below. There are a number of ways to obtain good yields of the product ester. Generally these methods involve the removal (or complexation) of water or the use a large excess of one of the reactants in order to favor the formation of the ester. Both procedures for obtaining good yields of ester exploit Le Chatelier's principle in that the removal of water or the addition of an excess of one of the reactants drives the reaction towards formation of the ester. In this experiment, an excess of carboxylic acid will be used. In this respect, the presence or addition of water is of some concern since, water will shift the composition of the reaction mixture away from formation of the ester and toward the formation of carboxylic acid, so use dry glassware.The Experiment (overview) In this experiment you will be given an "unknown alcohol" to react with acetic acid in an esterification reaction. You will isolate, purify, and identify your ester product by performing a microboiling point determination, GC and IR spectroscopy. Your product ester will be one of the esters below: n-propyl acetate isobutyl acetate isopentyl acetate hexyl acetate n-octyl acetate benzyl acetate Part A: Procedure, reaction conditions, isolation and purification of the ester Transfer 0.50 mL of your "unknown alcohol" into a dry 5.0 mL conical vial. Place a magnetic spin vane in the conical vial and add 1.5 mL of glacial acetic acid. Next, have your TA add one drop of concentrated sulfuric acid to the conical vial. Connect a reflux condenser equipped with a calcium chloride drying tube to the conical vial. Connect the condenser to the water. Which direction should the water be flowing through the condenser? Place the vial inside a sand bath. Turn-on both stirring and heating and heat the sand to about 160-180 °C. Note: you should observe refluxing of the alcohol in the condenser. Heating the sand bath to 160 - 180°C will assure you that the reactioncontents in the vial will be brought to a state of reflux, which should be noticeable upon careful inspection of the condenser. Following a 1 hour reflux, very carefully remove the sand bath, clamp the conical vial 1.5 inches above the magnetic stir plate and allow the conical vial and contents to cool (you may want to use a room temperature water bath to cool your reaction vial and contents more quickly). Figure 4.a Microscale reflux with stirring under anhydrous conditions When the conical vial and contents have approached room temperature continue rigorous stirring and add 1.5 mL of an aqueous 10% sodium carbonate solution to the reaction mixture. Make sure that the reaction contents have been mixed well. Following this, add 1.0 mL of MTBE to the neutralized reaction mixture with thorough mixing, but do not shake to vigorously. Allow the aqueous and organic phases of the reaction contents to separate. Which layer is the organic layer and which the aqueous layer? Which layer is your product in? Carefully remove the aqueous layer from the reaction vial with a pipette. Wash the organic layer 2 more times with 1.5 mL of aqueous 10% sodium carbonate. The last aqueous sodium carbonate wash should be basic to lithmus. If not, wash the organic layer an additional time or more until the aqueous layer is basic to lithmus. Why is the organic layer washed with additional 10% aqueous sodium carbonate? Do not discard the aqueous washes until you have isolated and characterized your product. Dry the organic phase for 15 minutes over anhydrous sodium sulfate. Construct a small chromatography column by filling a dry filter Pasteur pipet with a small plug of cotton followed by approximately 1 mm of sea sand, 5 cm of silica gel, and 2-3 mm of sea sand sequentially. Tare a 10.0 mL Erlenmeyer flask containing a boiling chip and place this below the silica gel filled filter pipet to act as a receiver. Apply 1.0 mL of methylene chloride to the column. Use a Pasteur pipette to add the crude product ester to the top of the column. Rinse the reaction vial twice with 0.5 mL portion of methylene chloride and add the methylene chloride rinse to the top of the column. Add anadditional 2.5 mL of methylene chloride to the column to ensure complete elution of the product. Evaporate the MTBE-methylene chloride solvent mixture from your product ester completely by gentlywarming the contents of the flask using a sand bath with a temperature of 80 - 100 0C. If the evaporation of solvent is not complete and solvent is present, what effect would this have on the percent yield? What effect would this have on the micro-boiling point? What effect would this have on the IR spectra? Remember use a fume hood whenever possible. Weigh the ester and calculate the experimental yield of the reaction. Your product ester should be sufficiently pure as isolated to allow the calculation of an experimental yield and characterization. Part B: Boiling Point Determination by the “Ultramicro Boiling-Point” Method. A common way to determine a boiling point of a liquid, is to use the Mel-Temp. Measuring the