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calculate theoretical yield info is given Resolution of (+)-trans-1,2-cyclohexanediamine The resolution of a racemic mixture requires more than a physical process (distillation etc.) because the
calculate theoretical yield
info is given
Resolution of (+)-trans-1,2-cyclohexanediamine The resolution of a racemic mixture requires more than a physical process (distillation etc.) because the physical properties of enantiomers are identical except for the direction in which they rotate the plane of polarised light. The racemic modification can be resolved by interaction with a chiral reagent to form a pair of diastereomers which, necessarily, do have different physical properties. Once the diastereomers have been separated each is treated chemically to release the component enantiomers of the original racemic modification. In this experiment the (-)-enantiomer of trans-1,2-cyclohexanediamine 2 will be obtained by the use of naturally occurring (+)-tartaric acid 3 as the resolving agent. The reaction involved is ammonium salt formation and one diastereomer of the salt 4 will crystallise from the reaction mixture and will be purified by recrystallisation. HOC CO2H NH2 NH2 NH2 NH och HO OH 3 NH2 "NH2 NH2 "NHS OC H2O, ACOH OH 2 Procedure? Add (+)-tartaric acid (1.87 g, 0.0125 mol) to a 100 mL beaker, add a spin bar, and dissolve in water (7 mL). While stirring this solution, add (+)-1,2-trans-diaminocyclohexane (actually a 38:62 cis/trans mixture) (3.00 mL, 2.85 g, 0.025 mol) in a steady stream using a 5 mL syringe. Care: this is an exothermic reaction. The solution will be cloudy at first but will clear as the mixture warms. Heat gently, if necessary, to get a clear solution. When it is homogeneous add acetic acid (1.3 mL) using a syringe and the product will begin to precipitate. Cool the thick creamy suspension in an ice- water bath for at least 20 min. (During this time heat approx. 100 mL of water in preparation for the recrystallisation.) Filter off the product under suction using a Hirsch funnel and wash with ice cold water (1 mL) and with methanol (4 x 1 mL). A second crop of product can be obtained by adding a little more methanol (2 ml) to the filtrate. I Recrystallise from the minimum volume nearly boiling water to obtain the (-)-(RR)-1.2- diammoniumcyclohexane mono-(+)-tartrate salt as a white crystalline solid. (Allow the hot solution to return to near room temperature slowly and then cool in an ice water bath; add methanol (0.5 mL) if crystals do not form.) Filter off the product under suction using a Hirsch funnel and dry thoroughly under suction Calculate the yield bearing in mind the percentage of trans isomer in the starting diamine. Any product in excess of that needed in the next step should be transferred to a properly labelled vial and retained for submission at the end of the semesterStep by Step Solution
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