3. Dicyclohexylamine is formed as a by-product of the reaction. How does the use

Question

3. Dicyclohexylamine is formed as a by-product of the reaction. How does the use of saturated ammonium chloride solution help to separate 8,8'-bicaffeine from the dicyclohexylamine? Hint: Consider the pH of the saturated ammonium chloride that you measured in lab during the workup. Consider the following estimates: The pKa of the conjugate acid of 8,8'-bicaffeine is 1.7, and the pKa of the dicyclohexylammonium ion is 11.4. pKa=-1.7 H+H pKa = 1 1.4 H + How would use of aqueous hydrochloric acid during the workup of the reaction have affected the isolation of the product? Hint: Estimate the pH of 10 M hydrochloric acid, and consider its significance during the extraction. 4. 45

Explanation / Answer

3. Dicyclohexylamine gets protonated in presence of saturated ammonium chloride solution. Therefore it dissolved in aqueous solution. Whereas 8,8'-bicaffeine remains as an insoluble compound in water under these conditions and can easily be separated out.

4. hydrochloric acid again is an acid which protonated dicyclohexylamine in the reaction which goes in water layer. The 8,8'-bicaffeine remains in organic layer and can be separated from the aqueous layer easily.

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