Separation of Stereoisomers Part I Formation of a Diastereomer Place 15.6 g of (

Question

Separation of Stereoisomers

Part I

Formation of a Diastereomer

Place 15.6 g of (+)-tartaric acid, 210 mL of methanol, and a stirring bar in an Erlenmeyer flask and heat the mixture to boiling using a hotplate.

To the stirred hot solution, cautiously add 12.5 g of racemic 1-phenylethanamine in 35.0 mL of methanol. The density of 1-phenylethylamine is 0.94 g/mL.

Allow the solution to cool slowly to room temperature and to stand undisturbed until the next class period.

Part II

The amine hydrogen tartrate should separate in the form of white prismatic crystals. If the salt separates in the form of needlike crystals, the mixture should be reheated until all the crystals have dissolved and then allowed to cool slowly. If any prismatic crystals of the salt are available, use them to seed the solution.

Collect the crystals of the amine hydrogen tartrate by vacuum filtration using a Buchner funnel.

Wash with a small volume of cold methanol.

Weigh the crystals.

Dispose of the filtrate in the waste container.

Dissolve the crystals in four times their weight and add 8 mL of 14-M sodium hydroxide solution.

Extract the resulting mixture with 25 mL portions of diethyl ether.

Discard the aqueous layer in the waste container.

Wash the combined ethereal extracts with 25 mL of saturated aqueous sodium chloride.

Dray the ethereal solution over several spatula-tips full of anhydrous sodium sulfate for 10-15 min.

Swirl the flask; if the solution remains cloudy after this period of time, add additional portions of sodium sulfate.

Decant the dried solution into a beaker at the front of the desk.

Your instructor will run the sample through the rotary evaporator.

The instructor will place the sample in the polarimeter.

Measure the volume of the methanolic solution accurately.

Measure the mass of the solution.

Determine the density of the solution. It is the mass, in grams, of the 1-phenylethanamine divided by the volume of the solution, in mL, that provides the concentration c in g/mL.

Measure the observed rotation and determine the specific rotation of the sample and determine the specific rotation of the sample using the following Equation.

           l x c           l x d

Data Sheet Separation of Stereoisomers

Observed Rotation of a racemic mixture of 1-phenylethanamine

Observed Rotation of (S) 1-phenylethanamine 25

Mass of solution 8.14 g

Volume of solution 10 mL

Density of solution 0.814 g/mL

Length of sample tube 20 cm

Temperature 19.7 C

Specific Rotation of (S)-1-phenylethanamine -37.0 to -41.0 degrees (neat)

Literature value of (S)-1-phenylethanamine

Enantiomeric Excess

Is (S)-1-phenylethanamine dextrorotatory or levorotatory?

Discussion

Explain how (S)-1-phenylethanamine was separated from the racemic mixture (do not restate the procedures)

Discuss the specific rotation of (S)-1-phenylethanamine.

Discuss the presence of (R)-1-phenylethanmine in the purified solution.

Explanation / Answer

this is simply resolution method

1-phenylethanamine is a racemic mixture and we know that racemic mixture is having same physical and chemical process except their rotation in plane polarized light.

once you reacted with tartaric acid each enantimer will react with tartaric acid and form the diastereomers

once these are become a distereomers these can have different physical properties

one of his physical property crystalization only S isomer can form crystal and R isomer wiil be in the solution form

now we can separate directly with hand then you hydralyze with NaOH we will get the (S)-1-phenylethanamine.

specific rotation of (S)-1-phenylethanamine. - 37.0 - 41.0 º

(R)-1-phenylethanmine in the solution isolate in to organic layer concentrate it then do NaOH treat ment you will get the (R)-1-phenylethanmine separately with same optical rotation with -ve sign.

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