Experiment 19:

OXIDATION OF 9-FLUORENOL

OH

HOCl

O

Objectives: To synthesize a ketone from a secondary

alcohol using household bleach. To monitor the reaction progress using

TLC analysis. To purify product using simple extraction. To analyze the purity of the product

using TLC and melting point analysis. To characterize reactants and products

using IR analysis.

Before coming to lab… Review these techniques:

TLC analysis

Acid-base Extraction

Drying over MgSO4

Melting Point Analysis

TYPICAL OXIDATION VS. GREEN OXIDATION

OHNa2Cr2O7

H2O, CH3CO2H, heat O

OH ONaOCl, CH3CO2H

acetone

Typical oxidation using chromium compound

Greener oxidation using household bleach

THE OXIDIZING AGENTNaOCl + CH3CO2H HOCl + CH3CO2Na Sodium acetic hypochlorous sodiumHypochlorite 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.

PROPOSED MECHANISM

HOClH3O+

OH Cl

H

+

OHH OH

Cl

H

- H2O

OH H

OH

ClOH H

O

+ H3O+

+ Cl-

- H3O+

- H3O+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.

1

2 3

45

OH

HOCl

O

Reason for difference in Rf values

The 9-fluorenol can DONATE hydrogen bonds to the silica gel on the TLC plate, resulting in a lower TLC Rf value!

1 32xx x

The 9-fluorenone can ACCEPT hydrogen bonds, but not donate to the silica gel on the TLC plate, resulting in a higher TLC Rf value!

Reason for difference in color

OH

HOCl

O

• The more conjugated a compound is, the higher the wavelength of light it absorbs.

• The visible region of the spectrum is the 400-700 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.

1 32xx x

Complete reaction!!!

PRODSTD

YOUR RXN

RCT STD

EXPERIMENTAL PROCEDURE

(PURIFICATION) Transfer liquid to separatory

funnel.

Extract product into diethyl ether 2X.

Wash organic layer with 5% NaHCO3 and Saturated NaCl.

Transfer organic layer to clean flask.

Dry over MgSO4.

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 400mL

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 150mL 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

EXPERIMENTAL PROCEDURE(PRODUCT ANALYSIS)

Place LABELED 150mL 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

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 (oC)Compare to lit value of 81-85oC.

Product Appearance Physical state and color of product

Table 19.2

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

Compound

TLC Rf values

Standards Sample

9-fluorenone

Rf values are UNITLESS!

Rf values are 2 decimal places ONLY!

If more than one TLC experiment is performed, record data from final TLC plate!

9-fluorenol

IR Spectroscopy

OH O9-fluorenone9-fluorenol

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

3196

1031

3041

1716

3060

Table 19.4Functional

GroupBase Values

(cm-1)9-fluorenol 9-fluorenone

OH stretch3200-3400

C-O stretch1000-1200

C=O stretch1705-1725

sp2 CH stretch 3000-3100

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.