CHEMISTRY Organic Chemistry Laboratory II Spring 2019 Lab #3: Friedel-Crafts Acylation

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1 CHEMISTRY Organic Chemistry Laboratory II Spring 2019 Lab #3: Friedel-Crafts Acylation Purpose: In this lab you will predict and experimentally test the directing effects of substituent groups in an Electrophilic Aromatic Substitution (EAS) reaction between 2-chlorotoluene and acetylchloride. A series of reactions will yield one of four possible EAS products. You will first use your organic chemistry background to predict the major EAS product. Then, based on your lab skills in product isolation, purification and melting point determination, identify which one of the four possible EAS products was obtained. Important Notes: 1) You must have lab goggles and your Hayden-McNeil Lab Notebook as specified in the lab syllabus. The format for writing in your notebook is outlined below. 2) This is a two-week lab and your notebook pages will be submitted at the conclusion of Part II. 3) Format your lab notebook items I - IV as outlined below. I. Your name, the name of your lab instructor, the name of your lab partner. II. Title of the experiment and date. III. Table of Reagents (Parts I & II). Synthesis experiments require a table with the first column listing the Chemical Name of all reagents, roughly in the order in which they are used in the experimental procedure. That is followed by a column with the Chemical Formula, and a column of the Purpose of the reagent (i.e., reactant, drying agent, solvent, etc.). For everything you identified as Reactant, Product, or Solvent, you will also need columns for: structure, molecular weight, and physical properties (melting point, boiling point, density). Copy the sample table below into your notebook, and fill in the required information. Refer back to your previous reagent tables for assistance. Chemical Name Purpose chemical formula structure molecular (g/mole) melting point ( o C) boiling point ( o C) density (liquids) (g/ml) Methylene chloride N/A N/A 2-chloro toluene N/A Acetyl chloride N/A Aluminum trichloride N/A N/A N/A N/A Water N/A N/A Hydrochloric acid N/A N/A N/A N/A N/A Sodium carbonate N/A N/A N/A N/A N/A Ethanol N/A N/A Sodium hypochlorite N/A N/A N/A N/A N/A acetone N/A N/A Sodium hydroxide N/A N/A N/A N/A N/A IV. Background information and notes from the pre-lab assignment. You are expected to read this lab handout, prepare this notebook section with the following content, and review this information to prepare for a prelab quiz. 1) Goals. Based on your reading, what are the Experimental Goals for Parts I & II of this experiment? 2) Lab Safety Parts I & II. Copy the table outlined below into your lab notebook. Read over the experimental procedure for Parts I & II, then complete the table so that you have a thorough list of key lab safety topics specific to this lab. Parts of the table have been completed for you. Common Risk factors in the organic chemistry lab (cross out those that are not applicable to this lab) Hot plate What is the associated Hazard? (burn, sharp/cuts, solvent vapor, skin irritant, eye irritant, etc.) How will you limit Exposure to the hazard? SDS Section 2 summary SDS Section 8 summary

2 Hazardous chemicals Strong acids and/or bases Volatile solvents Glassware Melting point capillary tube Electrical equipment Vacuum filtration InfraRed Light Methylene chloride Health & Safety (look up SDS at Flinn website) Chemical exposure may result in irritation and or illness Cuts from broken glass Glassware implodes under vacuum Keep solvent covered; use in hood Look for frayed power cords; avoid spilling water 3) Reaction Equation. Under your reagent table draw the overall reaction based on the scheme detailed in this handout. 4) In Part I, you will conduct a Friedel-Crafts acylation reaction between 2-chlorotoluene and acetylchloride yielding one of four possible EAS products. In Part II, you will oxidize this EAS product into a solid carboxylic acid. The procedure gives reagent amounts in moles, so you need to covert to grams (solid reagents), and grams and ml (liquids). Record the calculation(s) and value(s). 5) The general structure of mono-substituted benzene is drawn to the right ( sub = substituent group). Look up the definition of the ortho, meta and para positions on a benzene ring, and/or watch this You Tube video: Draw this general structure in your notebook and label the 5 remaining positions as ortho, meta, and para (relative to the substituent). 6) Product Structures. In EAS reactions (Electrophilic Aromatic Substitution) you are adding an electrophile to a benzene ring. In this lab the electrophile is the acyl group that is added in Part I giving you a liquid product. The acyl group is then oxidized into a carboxylic acid group in Part II to give a solid product for melting point determination. In the reaction schemes given in this handout, the electrophile could go to one of the four possible open positions of 2-chloro toluene. Your challenge is to (1) PREDICT the product, and (2) run the reaction to see if your prediction was correct. Using the given chemical equations as a guide, draw the complete structures of the four possible products for Parts I & II. 7) In class we will cover how substituents can direct an electrophile to the ortho, meta and/or para positions in an EAS reaction. With one substituent on a benzene ring this is easy to predict, but more challenging with two substituents as in 2- chloro toluene. Your goal is to predict the products in Parts I & II from the structures you drew in question (6). As a general guide, the methyl group will increase the rate of electrophile addition, while the chloro group will decrease the rate of addition. The rate factors are summarized in the table below: Rate factors that activate (+) or deactivate (-) electrophilic addition to the ortho, meta and para positions for the methyl and chloro substituents of 2-chloro toluene. Substituent ortho meta para -CH 3 (+)25 (+)10 (+)700 -Cl (-)10000 (-)10000 (-)100 Copy this table into your lab notebook, and the structure of 2-chlorotolune drawn above. Based on the data in the table, label each of the four open positions with the proper rate factors for CH 3 and Cl. For example, the ring carbon with the dot is ortho to the CH 3 (+25), and meta to the Cl (-10000). Note that the net rate factor for that position is (-)9975. After you have labeled all four open positions with the rate factors, the one with the most positive net rate factor is most likely to add the electrophile. Look at the products you drew for Parts I & II and CIRCLE the one product for each that you PREDICT will be the major product. You do not need to justify your choice at this time. Your notebook is now prepared to start the lab period. Be sure to leave space in your notebook to take notes during the recitation period.

3 Reaction for Part I: Reaction for Part II: Qualitative Observations. You are expected to record detailed observations for all steps in this experiment. You will be graded on the accuracy and completeness of these observations, which you will use to answer post-lab questions. Experimental Procedure Part I. Add a circular stir bar to a DRY 10 ml round bottom flask followed by 2 ml of methylene chloride (CH 2Cl 2). While stirring, add (in this order) mole of 2-chlorotoluene (liquid), mole of acetyl chloride (liquid), and mole of DRY AlCl 3 (solid). Cap the reaction mixture and stir at room temperature for 90 minutes. If no red-orange color appears after 30 minutes, try adding an additional mole of AlCl 3. If this does not yield a reddish color, your instructor may have you start the reaction over. While you are waiting start work on the tables for the Quantitative Observation. CAUTION: Be careful when opening the reaction vial at any time as HCl(g) is a by-product and can exist as a corrosive vapor. Always open the reaction vial in the hood if you have to add more AlCl 3. Cool the reaction in an ice-water bath and slowly add 3 ml of ice-cold water. Again, be careful in case there are any corrosive vapors. Stir this mixture with a glass rod, and add one ml of concentrated HCl to dissolve any aluminum salts which may have precipitated. Mix thoroughly, then remove the aqueous layer and wash the CH 2Cl 2 layer with 5 ml of water, followed by 5 ml of 5% Na 2CO 3 solution, and then twice more with water. Do your best to remove any remaining water as it will affect your crude yield in Part I. Transfer the CH 2Cl 2 solution to a pre-weighted 25 ml Erlenmeyer flask, and evaporate the solvent at approximately C in the solvent evaporation station. You should obtain your Part I product as a crude yellow oil. Determine the of this crude material, then cover your product and leave in your lab drawer for next week. Complete the information needed for Section V of Part I and ask your instructor to briefly look at your notebook. V. Quantitative Observations. Using the suggested format below, build Data, Result and IR tables in your lab notebook. Immediately after your tables show all calculations with clearly labeled headings. These tables will be completed in Parts I & II. Data Table for Lab #3 Part I Friedel Crafts Molecular Sample (g/mole) 2-chlorotoluene acetylchloride Aluminum trichloride (total amt) Crude product (Part I) Exact (grams) Volume (ml) Moles Limiting reagent? (place an X) Calculations:

4 Data Table for Lab #3 Part II Friedel Crafts Molecular Sample (g/mole) Crude product (Part I) Sodium hypochlorite (NaOCl) Dry, purified product (Part II) Exact (grams) Volume (ml) Moles Limiting reagent? (place an X) Calculations: Results Table for Lab #3 Parts I & II Friedel Crafts Theoretical Sample yield (grams) Crude product (Part I) Dry, purified product (Part II) Theoretical yield (moles) % Recovery % Yield Melting point range ( o C) Literature melting range ( o C) Calculations: IR Data Table for Lab #3 Part II Friedel Crafts (Complete after Part II of this lab). Sample Structure Key functional groups and IR bands (predicted or observed) 2-chlorotoluene (Predicted IR) (Predicted) Part I Product (Predicted IR) Part II Product (Predicted IR) Part II Product (Observed IR) (Predicted) (Predicted) (Observed) Post-Lab Questions for Part I. (1) Which step in the Part I procedure gave you the most trouble and why? (2) Using complete sentences and your observations, data and results, discuss your evidence that a reaction occurred which produced a neutral organic compound. (3) % Yield is calculated by taking the or moles of product, divided by the theoretical or moles of product (x100). What type of useful information can you get from the % Yield? Lets assume that your Part I % Yield was 117%. What is this result telling you about the Part I product? (4) Read over Part II of this lab. You will not tear out your notebook pages for Part I. However, before you leave lab you must have your lab instructor check your notebook and initial the last page.

5 CHEMISTRY Organic Chemistry Laboratory II Spring 2019 Lab #3 (Part II): Friedel-Crafts Acylation Purpose: In this lab you will predict and experimentally test the directing effects of substituent groups in an Electrophilic Aromatic Substitution (EAS) reaction between 2-chlorotoluene and acetylchloride. A series of reactions will yield one of four possible EAS products. You will first use your organic chemistry background to predict the major EAS product. Then, based on your lab skills in product isolation, purification and melting point determination, identify which one of the four possible EAS products was obtained. Important Notes: 1) You must have lab goggles and your Hayden-McNeil Lab Notebook as specified in the lab syllabus. Note that there is no pre-lab work for Part II. 2) This is a two-week lab and your notebook pages will be submitted at the conclusion of Part II. 3) Format your lab notebook items I - IV as outlined below. I. Your name, the name of your lab instructor, the name of your lab partner. II. Title of the experiment and date. III. Table of Reagents. (Just review your Part I table) IV. Background information and notes from the pre-lab assignment. You are expected to read this lab handout. There is no other pre-lab preparation for Part II. Experimental Procedure Part II: The Haloform Reaction. The purpose of this Part II reaction is to oxidize the acyl (ketone) substituent group of your crude product from Part I to a carboxylic acid substituent group. This also converts the Part I product from a liquid into a solid, making it easier to purify and to identify based on its melting point. Qualitative Observations. You are expected to record detailed observations for all steps in this experiment. You will be graded on the accuracy and completeness of these observations, which you will use to answer post-lab questions. Dissolve the yellow oil from Part I in 5 ml of ethanol, add a stir bar, and then slowly add mole of 6.50% NaOCl (Clorox bleach, 6.50 g/100ml) over the course of one minute. Then stir the mixture at 50 o C for 2 minutes to complete the Haloform reaction. At this point, the reaction should be finished, but you probably have excess ClO -. Add 1 ml of acetone and stir the mixture at 50 o C for 2 more minutes to destroy the excess ClO-. Be sure to record observations in your notebook throughout the steps. You have now transformed the Friedel-Crafts acylation product into a water soluble carboxylate salt. Acidification of this aqueous reaction mixture will precipitate one of the four Part II carboxylic acid products, which will be isolated and purified. Cool the reaction mixture on ice and SLOWLY and carefully add 3 ml of concentrated HCl (CAUTION STRONG ACID!) to your reaction mixture. You should observe the formation of a precipitate. Record your observations! This crude product should be isolated by vacuum filtration, and washed with 1-2 ml of ice-cold water. The wet solid is transferred to a 5 ml reaction vial and dissolved in 1-2 ml of 1 M NaOH. Not all of the solid will dissolve, but what does dissolve is the conjugate base of your product. Any remaining solid that you observe is mostly by-product and needs to be removed by pipet filtration. Make a pipet filter by pushing a pinch of cotton into a short-stem Pasteur pipette, using a long-tip pipette to gently push in the cotton. This will act as a crude, but effective filter. Use the long-tip pipet to add the cloudy reaction solution into the pipet filter and allow the filtrate to drip into a clean 25 ml Erlenmeyer flask. You can use a pipet bulb to force the liquid through the cotton. When all of the reaction solution has passed through the filter, rinse the pipet filter with 1 ml of water and add this to the filtrate. You now need to convert the water-soluble carboxylate salt into its insoluble acid form. Cool the filtrate in ice, then acidify with concentrated HCl by carefully adding 5 drops at a time and checking the ph of the water layer to see if it is acidic. You should get a white precipitate of pure product.

6 Cool the mixture in an ice-water bath for 10 minutes, collect your product by vacuum filtration on a Hirsh funnel, and wash with 2 ml of ice-cold water. Scrape your product onto a pre-weighed watch glass and dry at 100 o C for minutes. Determine the of your dried product, an accurate melting point, and IR spectrum. The melting points for the four possible Part II products are listed below: 2-chloro-3-methyl benzoic acid (141 o C) 3-chloro-4-methyl benzoic acid (201 o C) 4-chloro-3-methyl benzoic acid (209 o C) 3-chloro-2-methyl benzoic acid (159 o C) V. Quantitative Observations. Complete the Data, Result and IR tables you started in Part I of this lab. Don t forget to show all calculations with clearly labeled headings. Post-Lab Questions for Part II. (1) Using complete sentences and your observations, data and results, discuss your evidence that the product you synthesized is a pure compound. (2) % Recovery is calculated by taking the of pure product, divided by the of crude product (x100). What type of useful information can you get from the % Recovery? Based on that answer, what is your % Recovery telling you? (3) % Yield is calculated by taking the or moles of product, divided by the theoretical or moles of product (x100). What type of useful information can you get from the % Yield? Based on that answer, what is your % Yield telling you? Use the data in the Part II table to calculate to % Yield for Part II. (4) Draw the structure of your predicted product and of the actual product based on your melting point. Did you successfully predict the actual product structure? Discuss whether the IR spectrum is consistent with your Part II product structure, and staple the IR to your report.