Science / Bromination Debromination Of Cholesterol

Bromination Debromination Of Cholesterol

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Autor:    03 April 2012
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Bromination/ Debromination of Cholesterol

Aim

To isolate Cholesterol from its impurities, like 5,7-Cholestadien-3β-ol, 7-Cholesten-3β-ol and 3β-Cholestanol, through bromination and debromination.

Equipment

flask Buchner funnel Filter flask Hot plate/stirrer

Melting point apparatus

Setup

Procedure

Refer to the handout Procedure for Bromination/Debromination of Cholesterol for the procedure of this experiment. However there were modifications to this experiment:

a. Mass was measured after bromination and after debromination in addition to initial measurements.

b. In the debromination step, 1mL of 6 mol NaOH and 1mL of water were used instead 2 mL of 10% sodium hydroxide and of4 mL of water.

c. Magnesium sulfate was used a drying agent instead of anhydrous calcium chloride.

Results

Table A: Bromination Table A: Debromination

Mass of standard cholesterol solid (mg) 203.3 Mass of solid after debromination (mg) 20.0

Melting point (˚C) 146-150 Melting point (˚C) 140-148

Mass of solid after bromination (mg) 136.2 Percent yield after bromination (%) 47.4

Melting point (˚C) 124-126 Percent yield after debromination (%) 20.7

Table C: Formulas

Percent yield after bromination [Final mass after bromination / [(initial mass X (1mol Cholesterol/ 386.7g Cholesterol) X (546.4g/mol dibromocholesterol)]]X100=[136.2/ (203.3 /(386.73)* 546.4)]*100= 47.4%

Percent yield after debromination [Final mass after debromination / [(Initial mass after bromination X(1mol dibromocholesterol/546.4g dibromocholesterol) X (386.7g Cholesterol/1mol)]] X100=[20/ (136.2*386.73/546.4)]*100 = 20.7%

Discussion

Mass was measured after bromination and after debromination in addition to initial measurements so that the percent yield could be calculated. Percent yield was calculated because only a portion of the crude product was isolated. Bromine usually has a brownish red color and lost some of its color when brominating the cholesterol because bromine formed bonds with the cholesterol.

The electron-seeking reagents are electrophiles. It’s hard to notice that the bromine can be an electrophile because both atoms are identical. However, the bromine molecule was very polarisable. When the bromine approached the cholesterol molecule, the nearer bromonium ion became slightly positive and therefore was the electrophile. The reagent that seeks positive charges is a nucleophile. The double bond of the molecule of cholesterol was the nucleophile and therefore initiated a reaction with the bromi ...



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