Organic Chemistry Lab 318 Spring, 2012

DUE DATES Today –Banana Oil Report at beginning of lab –“Quiz” notebook copy of today’s experiment –At end of lab -- copy of the remainder of the laboratory notebook pages for today's experiment Next Week -Dibenzalacetone Report at beginning of lab

Synthesis of Dibenzalacetone This reaction is an example of an aldol condensation The reaction is also a mixed aldol, between and aldehyde and a ketone The product is quite stable because of conjugation (resonance stabilization), and so product formation is highly favored

Synthesis of Dibenzalacetone Only the ketone has an alpha-H that can be removed by OH - base to form the enolate: The carbonyl group in the aldehyde is more reactive than the carbonyl of the ketone:

Synthesis of Dibenzalacetone The tetrahedral intermediate from addition is protonated: Then dehydration occurs to give a stable conjugated product (  -unsaturated ketone):

Synthesis of Dibenzalacetone The reaction is repeated by removing the  -H from the ketone and the enolate reaction with the aldehyde, followed by dehydration: The product has two trans double bonds (more stable).

The Experiment The experiment is very simple – follow the instructions on p. 103 of the Manual. You will need to calculate the quantity of acetone to use based on the amount of benzaldehyde that is in your vial. Weigh the vial + contents; pour contents into smallest Erlenmeyer flask; weigh empty vial. Add the calculated volume of acetone to the flask

The Experiment Use another smallest Erlenmeyer flask to prepare a mixture of 95% ethanol and 10% NaOH Add half of the PhCHO/acetone mixture to the ethanol/base mixture Swirl for 15 min. Add the remainder of the PhCHO/acetone mixture to the reaction flask, and swirl for 15 min.

The Experiment Isolate the crude product by vacuum filtration and wash with 3 portions of distilled water (the dibenzalacetone is very insoluble in water). Recrystallize the crude product from 95% ethanol using about 10 ml of ethanol for every 4 g of crude product. Use cold ethanol to wash the filtered product. Put product in pre-weighed vial. Weigh vial + product (“wet” product – no m.pt. this week).

Experiment Notes Empty your vial containing the aldehyde/ketone unknown into the Waste container in the hood. Wash the vial. Clean-up: Tiffany Nguyen