Organic Chemistry CHM 252 and CHM 254L
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Organic Chemistry CHM 252 and CHM 254L
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Work on the following problems and hand in with your exam. 1. Aspartame is used in artificial sweeteners such as NutraSweet and Equal. In fact, aspartame is 160 times as sweet as sucrose (table sugar). In order to simulate what happens in your stomach upon digestion, you proceed to the laboratory and place a sample of aspartame in round-bottom flask. You heat the sample at reflux for 1 hour in an aqueous HCl solution. What products do you expect to receive upon complete hydrolysis (a series of NAcS reactions)? You should generate three separate degradation products. Provide complete reaction mechanisms for your hydrolysis reactions being sure to clearly indicate the TAI. 2. Acetals are commonly ermployed as protecting groups for carbonyl functionalities (ketones and aldehydes). One routine method involves the acid catalyzed acetal formation using ethylene glycol. Shown below is a synthetic scheme that shows the protection of the ketone in the first step, followed by a Grignard reaction using ethylene oxide to form the ultimate target molecule. The cool part here is that the acetal protecting group can be introduced and released under acidic conditions (check out arrows #1 and #3). However, the acetal remains in tact under basic conditions (look at arrow #2 --- you have a carbanionic base here!). What I want you to do is to show the complete reaction mechanism for the protection of the ketone (step #1 ONLY) under acidic conditions. Be sure to discuss (as a group) why the acetal formation essentially stops at the TAI (carbonyl addition) and does not collapse releasing a leaving group (NAcS). |
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Timm A. Knoerzer Last Updated Saturday, April 07, 2001 01:00:42 PM |
