Experiment 19: OXIDATION OF 9-FLUORENOL

Objectives:  To synthesize a ketone from a secondary alcohol using household bleach.  To purify product using simple extraction.  To identify and analyze the purity of the product using TLC and melting point analysis.  To characterize reactants and product using IR analysis.

Before coming to lab…  Review these techniques: TLC analysis Acid-base Extraction Drying over MgSO 4 Melting Point Analysis

Typical oxidation vs. Green oxidation Typical oxidation using chromium compound Greener oxidation using household bleach

Forming the oxidizing agent… NaOCl + CH 3 CO 2 H  HOCl + CH 3 CO 2 Na Sodium acetic hypochlorous sodium Hypochlorite acid acid acetate Sodium hypochlorite is the main ingredient in bleach. It must first be converted to hypochlorous acid in order to oxidize the alcohol. HOCl is a source of a positive Cl, which has 2 fewer electrons than a chloride anion. Remember, oxidation is the loss of H or the addition of O.

CHEMICAL EQUATION From reaction of bleach with acetic acid!

PROPOSED MECHANISM Although complex, the mechanism results in the exchange of a Cl + with a H + on oxygen, followed by subsequent elimination of HCl to form the ketone. 1. Bleach is reacted with acetic acid to produce hypochlorous acid. 2. Electropositive chlorine atom undergoes nucleophilic attack by oxygen of alcohol to form O-Cl bond… 3. Water abstracts a proton from the oxygen bearing the chlorine… 4. …followed by another attack on the proton of the carbon bearing the oxygen. 5. Both electrons from the C-H bond form the  bond of the carbonyl, and a chlorine atom is eliminated to form the neutral product ketone

OVERVIEW  React ketone, acetic acid, and bleach dissolved in acetone to synthesize product.  Follow the reaction progress using TLC analysis.  Neutralize acid and perform extraction to purify product and isolate from unreacted starting materials.  Evaporate solvent to yield solid product.  To reweigh to obtain product mass and calculate % yield.  Perform melting point analysis to identify and determine product purity.

Why are the R f values different? The 9-fluorenol can DONATE hydrogen bonds to the silica gel on the TLC plate, resulting in a lower TLC R f value! The 9-fluorenone can ACCEPT hydrogen bonds, but not donate to the silica gel on the TLC plate, resulting in a higher TLC R f value!

Why does the color change? The more conjugated a compound is, the higher the wavelength of light it absorbs. The visible region of the spectrum is the nm wavelength range. If a compound absorbs light close to 400 nm, it will appear as a yellow color. More conjugated Less conjugated

EXPERIMENTAL PROCEDURE (SYNTHESIS)  Add Fluorenol to 50 mL flask with stir bar.  Add acetone and stir of until dissolved.  Add acetic acid and bleach while stirring. Place a small cork in top of flask to reduce decomposition of bleach.  Stir 10 minutes.  Perform TLC experiment to check for completion. If oxidation is incomplete, add more acetic acid and bleach, react for 10 additional minutes and repeat TLC experiment. If oxidation is complete, proceed to purification steps. Complete reaction!!! PROD STD YOUR RXN RCT STD

EXPERIMENTAL PROCEDURE (PURIFICATION)  Transfer liquid to separatory funnel.  Extract product into diethyl ether 2X.  Wash organic layer with 5% NaHCO 3 and Saturated NaCl.  Transfer organic layer to clean flask.  Dry over MgSO 4.  Transfer liquid to preweighed 150 mL beaker w/3 boiling chips. 125 mL 150 mL

EXPERIMENTAL PROCEDURE (PURIFICATION)  Prepare a tap water bath using your 400 mL beaker.  Place the water bath on a hotplate and heat the water on a setting of 3 (NO HIGHER) until just above room temp.  Remove water bath from hotplate.  Slowly place the 150 mL beaker containing diethyl ether into the water bath to evaporate the liquid solvent.  If the solution boils too rapidly, remove it immediately until it ceases to boil! 150 mL 400 mL DO NOT PLACE BEAKER OF ETHER DIRECTLY ON HOTPLATE! *DANGER*

EXPERIMENTAL PROCEDURE (PRODUCT ANALYSIS)  Place LABELED 150 mL beaker in oven for 10 minutes to dry. Reweigh.  Repeat if %yield is greater than 100%!  Reweigh to obtain final product mass and calculate % yield.  Perform melting point analysis. YOUR NAME HERE

Table 19.1: Experimental Results Theoretical yield (g) Calculate based on 9-fluorenol ONLY! Bleach is used in excess! Actual yield (g) (Beaker + product weight) – (empty beaker weight) % yield (Actual yield/theoretical yield) X 100 Melting Range ( o C) Compare to lit value of o C. Product Appearance  Physical state and color of product

Table 19.2: Green Chemistry Results Atom Economy (%)  Should be calculated based on 9-Fluorenol and hypochlorous acid (HOCl), NOT bleach (NaOCl)  Review Experiment 13 for calculation. Cost per Synthesis ($)  Remember to calculate COST PER SYNTHESIS using 9-Fluorenol, bleach, acetic acid and acetone.  Cost of stock bottles on p. 167! Cost per gram ($/g)  COST PER SYNTHESIS/ACTUAL YIELD

Table 19.3: TLC Results Compound TLC R f values StandardsSample 9-fluorenone  R f values are UNITLESS!  R f values are 2 decimal places ONLY!  If more than one TLC experiment is performed, record data from final TLC plate! 9-fluorenol

IR Spectroscopy Remember to concentrate on the types of bonds that indicate the CONVERSION from reactant to product!

Table 19.4: IR Analysis Functional GroupBase Values (cm -1 ) 9-fluorenol9-fluorenone OH stretch C-O stretch C=O stretch sp 2 CH stretch

SAFETY CONCERNS DIETHYL ETHER IS EXTREMELY FLAMMABLE! NEVER place diethyl ether directly on a hotplate! Acetic acid is corrosive!

WASTE MANAGEMENT  “LIQUID WASTE” container: any/all liquid waste from extraction and TLC experiment.  “SOLID WASTE” container: any/all solid waste from synthesis and purification.  BROKEN GLASS box: Place used TLC and melting point capillaries.

CLEANING  Clean all glassware with soap, water, and brush if necessary.  Rinse all glassware with wash acetone before returning to lab drawer.  DO NOT return any glassware to lab drawer dirty or wet.

In-lab Question (The following question should be answered in laboratory notebook.)  Using the mechanism proposed in this experiment, draw the product, and a complete mechanism for its formation, for the following reaction: