Preparation of Stilbenediol Acetonide

(1,2-dimethyl-1,5-dioxolane)

Abstract

In the preparation of stilbenediol acetonide, the first step was the synthesis of hydrobenzoin (1,2-diphenylethane-1,2-diol) by the reduction of benzil (dissolved in ethanol) with sodium borohydride, then heating the solution and adding water. The product crystallized in the reaction mixture, was washed with cold water twice to purify and isolated by filtration. The second step was reacting hydrobenzoin with acetone (reactant and a solvent) and iron (III) chloride (Lewis acid and catalyst), then heating the solution to synthesize cyclic stilbenediol acetonide. The solution was poured over water containing 3M potassium carbonate (a base) to react with the acid; the product was then extracted with methylene chloride, dried and evaporated to give stilbenediol acetonide. It was recrystallized in hexane to purify. Verification for both products included Infrared Spectroscopy, H NMR, and melting-point determination. We determined, from analyses, that we made the correct products.

Balanced Equations for Synthesis

Preparation of Hydrobenzoin from Benzil

Preparation of Stilbenediol Acetonide from Hydrobenzoin

OO OH

OH

NaBH4

OHOH

CH3 CH3

O

CH

CH

O O

CH3CH3

FeCl3

+

+ H2O

Procedures

Preparation of Hydrobenzoin

• Add .5g of dry benzil to a 50-ml flask• Add 5ml of 95% ethanol• Swirl contents to dissolve• Cook the solution in an ice bath until a fine

suspension appears • Add .1g NaBH4 to flask and swirl contents

for two to three minutes• Let the flask sit for 10 minutes with periodic

stirring• Add 5ml of water; heat the flask until

solution boils• Add 10ml water and allow to cool to room

temperature• Vacuum dry the crystals; wash several

times (with cold water) and dry the crystals• Transfer product to a watch glass and allow

to dry completely

Preparation of Stilbenediol Acetonide

• Dissolve .3g of hydrobenzoin in 9ml acetone• Add .1g FeCl3• Reflux the mixture for 20 minutes using an

esterification apparatus• Transfer the mixture to a flask containing

12ml water (more water may be added) and 3ml 3M potassium carbonate solution

• Extract the product with at least 9ml methylene chloride

• Wash extract with 7.5ml of water; dry the solution over anhydrous calcium chloride and evaporate dry (or dry under vacuum)

• Dissolve crude product in .9-1.5ml hexane; cool in ice and vacuum dry the product

DataCompound Molecular

WeightDensity Melting

Point Boiling Point

Solubility

(in H2O)

Benzil 210.23 g/mol 1.23g/cm3 94.5-95.08°C

346-348 °C Insoluble

Sodium Borohydride

37.83 g/mol 1.07 g cm-3 400 °C (decomposes)

500 °C Soluble

Hydrobenzoin 214.25 g/mol N/A 137°C N/A Slightly

Soluble

Acetone 58.08 g/mol .79 g/cm³ −94.9 °C 56.53 °C Miscible

Stilbenediol

Acetonide

254.3 g/mol N/A 147°C N/A N/A

Benzil to Hydrobenzoin(.5g benzil)(1 mol benzil/210.23 g benzil)(1 mol hydrobenzoin/1 mol benzil)(214.25g hydrobenzoin/1 mol hydrobenzoin)(1000mg/1g)= 527.9mg hydrobenzoin

Hydrobenzoin to Stilbenediol Acetonide(300mg hydrobenzoin)(1g/1000mg)(1 mol hydrobenzoin/214.25 g hydrobenzoin)(1 mol stilbenediol acetonide/1 mol hydrobenzoin)(254.3g stilbenediol acetonide/1 mol stilbenediol acetonide)(1000mg/1g)= 356.1 mg stilbenediol acetonide

Calculations for Starting MaterialTo get 300mg final product

Melting Point Data and Calculations

Hydrobenzoin

• Melting point

- Expected: 137°C

- Experimental 130-131°C

• Percent Yield - Theoretical Yield

(.5g benzil)(1 mol benzil/210.23 g benzil)(1 mol hydrobenzoin/1 mol benzil)(214.25g hydrobenzoin/1 mol hydrobenzoin)(1000mg/1g)= 527.9mg hydrobenzoin

- Actual Yield

-Crude Product:

.411g actual/.5279g theoretical= 78% crude

- Pure Product

.359g actual/.5279g theoretical=68% pure

Stilbenediol Acetonide

• Melting point - Expected: 147°C

- Experimental:140°C

• Percent Yield - Theoretical Yield

(300mg hydrobenzoin)(1g/1000mg)(1 mol hydrobenzoin/214.25 g hydrobenzoin)(1 mol stilbenediol acetonide/1 mol hydrobenzoin)(254.3g stilbenediol acetonide/1 mol stilbenediol acetonide)(1000mg/1g)= 356.1 mg stilbenediol acetonide

- Actual Yield

-Crude Product:

.321g actual/.3561g theoretical= 90% crude

- Pure Product

.289g actual/.3561g theoretical=81% pure

OHOH

Functional Group Class ExpectedBand Positions and Intensities of

Absorption

ExperimentalEquivalents

O-H 3200-3650 cm-1 (broad) 3369 cm-1, 3312 cm-1

Benzene/Aromatics 3030 cm-1, 1660-2000 cm-1 (both weak) and 1450-1600 cm-1 (medium)

3056 cm-1 , 1449 cm-1, 1494 cm-1, 1578 cm-1, 1591 cm-1

C-O 1050-1150 cm-1 (strong) 1173 cm-1

OHOH

Type of Hydrogen Expected Chemical Shift Experimental Equivalents

Aromatic 6.5-8 ppm 7.2 ppm

Alcohol (OH) 2.5-5 ppm(variable)

3.3 ppm

Alcohol (HO-CH)

3.3-5 ppm 4.6, 5.2 ppm

CH

CH

O O

CH3CH3

Functional Group Class ExpectedBand Positions and Intensities of

Absorption

ExperimentalEquivalents

Benzene/Aromatics 3030 cm-1, 1660-2000 cm-1 (both weak) and 1450-1600 cm-1

(medium)

3028 cm-1, 2999 cm-1, 1496 cm-1, 1453 cm-1

C-O 1050-1150 cm-1 (strong) 1046 cm-1, 1080 cm-1, 1153 cm-1

CH

CH

O O

CH3CH3

Type of Hydrogen Expected Chemical Shift Experimental Equivalents

Aromatic 6.5-8 ppm 7-8 ppm

Ether (CO-CH)

3.3-5 ppm 3-3.5 ppm

Methyl .7-2.7 2.5 ppm

Conclusions• Our experiment was the two-phase sythesis of stilbenediol acetonide. The first

phase involved the reduction of benzil (in ethanol) with sodium borohydride, then heating the solution and adding water to produce hydrobenzoin. After purification and drying, we determined our crude yield to be 78% and our pure yield to be 68%. Verification included IR spectroscopy, H NMR, and melting point analysis. We concluded that our product was pure through the closeness of the expected and experimental melting points, and what was expected and obtained in our spectral analyses.

• The second phase involved the synthesis of stilbenediol acetonide from our hydrobenzoin, by reacting it with acetone (both a reactant and solvent), and adding the acid catalyst iron (III) chloride. The solution was poured into water and potassium carbonate (a base) to react with the acid; the product was then extracted with methylene chloride. After purification and drying, we determined our crude yield to be 90% and our pure yield to be 81%. Verification included IR spectroscopy, H NMR, and melting point analysis. We concluded that our product was pure through the closeness of the expected and experimental melting points, and what was expected and obtained in our spectral analyses.