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Organic Chem SN2 Grignard
Transcript of Organic Chem SN2 Grignard
Aaron Garst Background Information Sn2 Reaction "Subsitution Nucleophilic Biomolecular" Alkyl halides undergo substitution reaction in which the leaving group is a halide and then is replaced by another atom or group. Grignard Reaction Named after scientist that synthesized first Grignard Reagent in 1900 Francios Auguste Victor Grignard An organometallic compound, also known as a Grignard Reagent, is prepared by mixing magnesium shavings and an alkyl halide in diethyl ether or THF under anhydrous conditions Dependant on what the reagent is mixed with, it can form one of two products. A Tertiary Alcohol
Ketone A Secondary Alcohol Aldehyde Summary of Procedure Assemble Reflux Apparatus Example from page 41 of Organic Chemistry Lab Manual To the round bottom flask, while stirring, add: 8.1 g of 1-pentanol
16 mL of 48% HBr
5.2 mL of concentrated sulfuric acid(slowly) Step 1 Reflux acid and alcohol for one hour Formation of two layers apparent Remove top acidic layer and wash remaining product, the
1-bromoalkane, with sodium bicarbonate twice to neutralize any remaining acid. Wash with water to ensure pure remaining product Add anhydrous sodium sulfate until clear to ensure dry bromoalkane organic layer. weigh and store until following week. Step 2 Mechanism Step 1 Data and Product Characterization 1-bromopentane Boiling Point: 124°C-127°C; correlates with the literature value of 130°C Flame Test: Green flame indicating presence of a halogen Density: 1.25 g/mL; correlates with literature value of 1.22 g/mol Theoretical Yield: Percent Yield: 14.05 g 37.4% Conclusion Step 1 Resulted in isolation of 1-bromopentane from the reaction of 1-pentanol and sulfuric acid in an HBr Solvent By refluxing the reaction for an hour then washing the bottom layer that was formed repeatedly with water and sodium bicarbonate, our product was ensured to be pure. This alkyl halide that was synthesized will be used in two seperate Grignard reactions with a carbonyl reagent for step two. Use saved alkyl halide, 1-bromopentane, synthesized in step 1 to set up Grignard Reaction The amounts of magnesium turnings, diethyl ether, and alkyl halide were calculated and placed in a round bottom flask initially. The formation of bubbles on the magnesium indicated a reaction which we allowed to carry itself to completion, while adding the remaining alkyl halide The solution was refluxed for 15 minutes and allowed to cool to room temperature. Add .049 moles of 3 pentanone to the addition funnel with a graduated cylinder, wash graduated cylinder with anhydrous ether and add to addition funnel as well. Lower round bottom flask into ice bath and turn stirring mechanism on. Add the solution from the addition funnel drop-wise into the flask over a period of 15 to 20 minutes. Reflux for 15 minutes Crushed ice and sulfuric acid were added to the solution and its contents were then transferred into a round bottom flask. The formation of two layers allowed us to obtain our product 3-ethyloctan-3-ol. Mechanism Step 2 Data and Product Characterization 3-ethylooctan-3-ol Boiling Point: 121°C Theoretical Yield: 5.52 g Percent Yield: 37.9% Step 2 The reflux reactions that were conducted during week 3 proceeded as normal except for the alkyl bromide ether solution being added all at once instead of slowly.
This could have adversely affected our expected product, 3-ethyloctan-3-ol.
Overall, our reaction worked as expected with the predicted product of 3-ethyloctan-3-ol.
Setbacks: -Group A added all of the alkyl bromide into the round bottom flask instead of adding in small increments. -One of the last steps of the final step is to slowly add the ketone to the solution, Group B added the ketone all at once instead of by drop wise. Overall Reaction Objective: Through Sn2 and Grignard Reaction, convert 1-propanol to 3-ethyloctan-3-ol.