Bromination and Debromination: Purification of CholesterolSmit Patel

October 21, 2009Aim: - To purify the cholesterol using the process of bromination and debromination.

Experimental Procedure: - A literature procedure1 was followed for the purification of cholesterol lab.

Table I Apparatus Cholesterol Dibromide Purified Cholesterol

DataTable II Experimental Value Table III Theoretical Value

Dibromide Cholesterol

1.424g

Cholesterol Temperature

149 °C

Recrystallize Cholesterol

.600 g

Result

Zinc DustEtherAcetic acid3 Erlenmeyer flaskPipetteStirring rod1.005 g CholesterolMethanolCalcium chlorideSeparatory funnel10% sodium hydroxide

Dibromide Cholesterol 1.2096g

Cholesterol Temperature

141 °C

Recrystallize Cholesterol

.612g

Sample Calculation % Recovery: - [abs (Theoretical Value – Experimental value)/Theoretical value)*100Dibromide Cholesterol % recovery = 15.06% Cholesterol Temperature % recovery = 5.37% Recrystallize Cholesterol % recovery =2.0%

Discussion: -the purpose was to recrystallize the cholesterol and find the melting point. Initial measurement was of cholesterol was 1 gram. Then the cholesterol and bromine was added to make dibromide cholesterol. When bromine was added to the cholesterol, the compound turns to yellow color and paste of dibromide promptly result. Sodium acetate was used as anhydrous of solution. Acetic acid was used to make the crystallize product clear by removing the yellow color. Acetic acid was used because dibromide cholesterol moist with the acetic acid. Experimental value of dibromide cholesterol was 1.2096 grams and the theoretical value for dibromide cholesterol was 1.424 grams. The percent error was 15.06% which is much higher than expected. The percent error was high because the product was wet this could be one of the reason. If we let the product there could be less error in our experiment. The other reason some product might have filtered out from the filtration paper. Third reason possible some product have been left on the filter paper. So this could be the reason for having percent error for dibromide cholesterol. The second part of the lab is to recrystallize dibromide cholesterol to pure cholesterol. In this lab zinc dust, sodium hydroxide, and calcium chloride was used. Zinc dust become white precipitate in the solution. Sodium acetate was used to remove excess hydrogen halide from the compound. Calcium chloride was used as anhydrous in solution. The final product of the recrystallization of cholesterol was .612 gram. The theoretical value was .600 gram. The percent error of the recrystallize cholesterol was only 2% which is very small. The value could have been improved by recrystallize the product one more time. The error could be because of the impurities did not filter through the filter paper. There could be some kind of impurity involved in the product which could not be recrystallized. The product might not be dry enough to measure it this could be possibly one reason. The final step to find out, how pure the compound is through the melting point. The experimental melting point was 141 °C and the theoretical melting point was 149°C. The error came out to be 5.37%. Since the compound was not pure so the error in the melting point was expected but the error came out to little higher than expected. The error is higher because the melting point apparatus was not calibrated so melting point value could be higher or lower. That could maximize or minimize the error in the experiment. But in spite of that there was still impurity present in the compound it could be because of filter paper. There might be something on filter paper before it has been used. There were a lot of places the experiment could have been done it better.

ConclusionThe percent recovery for dibromide cholesterol, cholesterol temperature, and recrystallize cholesterol was 15.06%, 5.37%, 2.0% respectively.

Reference 1. Williamson, K, Minard, R, & Masters , K, (2007). Macroscale And Microscale Organic

Experiments. New York, NY: Houghton Mifflin.