Prelab and Observations

Prelab and Observations Prelab To be recorded in the lab notebook before coming to lab and to be submitted to the Teaching Fellow (TF) at the end of each lab session. Data and observations To be recorded in the lab notebook while performing the experiment and to be submitted to the TF at the end of each lab session. Pre-lab The most critical part of the lab report is completed before performing the experiment. The goal of advance preparation is to develop a good understanding of the required operations, a sense for their proper timing, and familiarity with the reactions, substances, and instruments involved. The pre-lab should include: • The title of the experiment. • The purpose of the experiment and how the product will be analyzed. • The main reaction, if any, under study, along with side reactions, all expressed in chemical symbology. • The reaction mechanism, if any, expressed in chemical symbology. (Not needed for all labs) • A list of instructions which records the experimental procedure in as much or as little detail as required so that you can execute the lab exclusively from pre-lab notes. The procedure should include drawings of equipment needed. The pre-lab should be sufficiently complete so that it is not necessary to refer to the lab text during lab. The presence of the lab text on the lab bench will be taken as an indication of poor preparation and will result in grade reduction. The procedure should be written on the left half of pages in your notebook. The right half is used to record data and observations next to the appropriate step of the procedure. Data and observations The ability to clearly record the phenomena observed in the course of the experiment is an important skill: such phenomena frequently indicate significant chemical events. Examples of observations to be noted are color changes; the evolution of heat; the liberation of gas; the physical state and appearance of starting materials, intermediate reaction mixtures, and crude and purified products. All such information should be recorded on the right half of pages in your notebook next to the appropriate step in the procedure. Data will be largely quantitative in nature and should be recorded using appropriate units. Examples include melting and boiling point ranges; quantities of materials used and products obtained; percent yields; reaction times, etc. All such information should be recorded on the right half of pages in your notebook next to the appropriate step in the procedure. Example: Text of the experiment in the lab manual THE MANNICH REACTION: SYNTHESIS OF A β -AMINO KETONE Introduction Reactions that form carbon–carbon bonds are of the highest importance in organic chemistry. One such reaction is the Mannich reaction in which a ketone, a secondary (2º) amine, and formaldehyde combine to form a β-amino ketone. The reaction takes place in three stages. First, the ketone isomerizes to an enol. Next, formaldehyde and the 2º amine react to produce an imine. Finally, the enol attacks the imine to create a new carbon–carbon bond. Note in the reaction mechanism shown below that the formation of both the enol and of the imine are acid-catalyzed. O R OH H CH3 HO H R H H R H H –H a ketone an enol a 2º amine H N R1 O H OH H H formaldehyde H H OH2 HO H R2 H N H R2 R1 H H N R1 H R2 – H 2O N H an imine R1 R2 S a m p l e Prelab/Observations THE MANNICH REACTION Submitted by Vladimir Markovnikov Teaching fellow: Hermann Kolbe Purpose: To conduct a Mannich reaction to make a new amino ketone and to analyze its NMR and melting point. Main reaction O O CH3 H N + O CH3 + CH3 H H H H N H H H CH3 + H CH3 2O Reaction mechanism Enol formation OH OH O H H H+ H H H H H –H H + Imine formation H+ O H OH H H H H H2 O H N H CH3 CH3 H CH3 N H CH3 OH N – H 2O H CH3 HO H H H H CH3 CH3 H ±H + N H CH3 CH3 N CH3 Product formation H O HO H H H + H CH3 N CH3 H H O H H N CH3 H H CH3 –H + H H CH3 N CH3 Experimental procedu re and data/observatio ns Place Dimethylamine hydrochloride and paraformaldehyde are colorless crystalline solids. 15 g acetophenone 13 g dimethylamine hydrochloride 5 g paraformaldehyde Acetophenone is oily colorless liquid having a strong odor of perfume; measured it out by volume. 1 mL conc. HCl 20 mL 95% ethanol in 250-mL Erlenmeyer Density of acetophenone = 1.03 g/mL, so 15 g = 14.6 mL Heat flask on steam bath 2 hr. Begin heat 1:24 P.M. End heat 3:05 P.M. Mixture started clear. Began to turn yellow at about 2:00 P.M. Very dark yellow after about 2:30 P.M. No more perfume smell! It’s GROSS!!! Remove flask from steam bath. Add 100 mL acetone while flask is still warm. Cool flask in ice bath until crude product precipitates. Solid started to accumulate at bottom of flask at 3:25 P.M. Separate precipitate from liquid by gravity filtration. Crude product is light yellow solid. Liquid is deep yellow color and stinks. Weigh crude. Mass of crude = 18 g