NITRATION OF p-methylacetanilide Experiment 17: NITRATION OF p-methylacetanilide

Objectives: To synthesize methylnitroacetanilide isomers using an electrophilic aromatic substitution. To purify product by recrystallization. To identify and determine purity of product by melting point, TLC and HPLC analysis. To characterize product by analysis of 1H-NMR and 13C-NMR spectra.

Before coming to lab… Review these techniques: TLC analysis Recrystallization Suction filtration HPLC analysis Melting Point Analysis

CHEMICAL EQUATION

ELECTROPHILIC AROMATIC SUBSTITUTION This reaction takes place in two steps: 1. Initial reaction of an electrophile, E+ with the aromatic ring. 2. Loss of H+ from the resonance stabilized carbocation intermediate to regenerate the aromatic ring.

MECHANISM (Preliminary steps…) Reaction of the aromatic compound with nitric acid alone is slow and potentially hazardous. It is safer and faster to use a catalytic amount of sulfuric acid. Sulfuric acid reacts with nitric acid to form the nitronium ion, a powerful electrophile. Sulfuric acid protonates the hydroxyl group of nitric acid, allowing it to leave as water and form a nitronium ion.

MECHANISM (Nitration of Aromatic Ring…) Electrophilic aromatic substitution by the nitronium ion gives the nitro product. Attack on the electrophile forms the sigma complex… …loss of proton to water… …gives the aromatic nitro product.

Overview… 1st Day Synthesize nitro acetanilide isomers. Isolate crude solid by vacuum filtration. Prepare TLC and HPLC samples of crude solid. Neutralize and extract liquid filtrate. Prepare TLC and HPLC samples of liquid filtrate. Recrystallize crude solid to purify. Isolate pure solid by vacuum filtration. Prepare TLC and HPLC samples of pure solid. Submit all 3 HPLC samples for analysis. Secure pure solid and TLC samples until next period.

Overview…2nd Day After Quiz #1, reweigh pure solid to obtain final product mass. Analyze HPLC results. Perform TLC analysis on 3 samples. Obtain experimental melting point of pure solid.

Day 1: Synthesis Mix p-methylacetanilide and acetic acid in 50 mL Erlenmeyer flask. Prepare nitrating mixture in small test tube (CAUTION!). *IMPORTANT!* Cool this tube in ice water! Add nitrating mixture drop wise while swirling. Allow to react at room temp for 15 minutes. Add cold deionized water.

Day 1: Crude Product Isolation Prepare suction filtration apparatus, seating filter with cold deionized water. Pour crude product slowly into center of funnel. Rinse with cold deionized water. Prepare CRUDE PRODUCT TLC and HPLC samples in small sample vials. Set crude solid aside to purify by recrystallization.

Day 1: Preparation of Filtrate Samples Transfer 2 mL filtrate to a small test tube. Add 10% NaOH drop wise until neutral (check every 5 drops with pH Hydrion paper). Add 3 mL ethyl acetate. Cork tube and shake to mix. Allow layers to separate. Prepare HPLC and TLC samples of FILTRATE using 5 drops of this solution for each. Remember to add appropriate sample solvent for each! Filtrate

Day 1: Purification Transfer CRUDE PRODUCT to 50 mL flask. Dissolve in hot 90:10 ethanol/water. Cool to room temp, then to 0oC. Suction filter. Seat filter paper w/90:10 ethanol/water. Prepare RECRYSTALLIZED PRODUCT TLC and HPLC samples.

Day 1: Sample Submission Transfer small filter paper and product to a preweighed large filter paper and submit to instructor to dry until next lab period, along with all TLC samples. At the end of lab, you should have: Submitted to lab instructor… 3 TLC samples, labeled in vials (crude solid, liquid filtrate, pure solid) 1 packet of pure solid product Submitted for HPLC analysis… 3 HPLC samples (crude solid, liquid filtrate, pure solid)

Experimental melting range (oC) Table 17.1 Theoretical yield (g) Lab 1: Calculate this value based on how much reactant you ACTUALLY used, not just what the MANUAL SAYS to use. Actual yield (g) Lab 2: Calculate this value after you have retrieved your dry product next lab! Percent yield Experimental melting range (oC) Lab 2: Record this value as a Ti-Tf range Product appearance Lab 1: Record COLOR and PHYSICAL STATE of product.

Experimental Atom Economy (%) Table 17.2 Atom Economy (%) Lab 1: Review Exp. 13 or Appendix I to review calculation! Experimental Atom Economy (%) Lab 1: Be sure to calculate this value using actual weights/volumes that YOU used, not just what the MANUAL SAYS to use! “Eproduct” Lab 2: You need the PERCENT YIELD for this calculation! Cost per Synthesis ($) Lab 1: Be sure to calculate this value using actual weights/volumes that YOU used, not just what the MANUAL SAYS to use! Costs of stock bottles are given on p. 150. Cost per Gram ($/g) Lab 2: You need the final ACTUAL YIELD value to calculate this!

Day 2: Product Analysis TLC Analysis HPLC Analysis Prepare TLC plate with 6 lanes. Apply 3 provided standards along with samples of crude product, filtrate, and recrystallized product. Develop in 2:1 ethyl acetate/hexane. Visualize with UV lamp. Identify compounds and calculate Rf value. HPLC Analysis Compare sample chromatograms to provided standard to identify compounds in each sample submitted. Melting Point Analysis Obtain the experimental melting point of your purified product. Compare to the literature value to determine degree of purity.

4-methyl-2-nitroacetanilide 4-methyl-3-nitroacetanilide Table 17.3 Compound TLC Rf values Standards Crude sample Filtrate Recrystallized p-methylacetanilide All Rf values are unitless! All Rf values are 2 decimal places ONLY! If reactant present in this lane, it explains product loss! 4-methyl-2-nitroacetanilide If major product present in this lane, it explains product loss! 4-methyl-3-nitroacetanilide

Table 17.4 Compound Standards Crude Sample Filtrate Recrystallized Retention times (min) Area % p-methylacetanilide 4-methyl- 2-nitroacetanilide 3-nitroacetanilide All samples are submitted for analysis during 1st lab period. Samples will be run, and chromatograms returned during 2nd lab period!

Product Analysis (NMR Spectroscopy)

Table 17.5 Enter chemical shifts ONLY based on the spectra on pages 139 and 147.

SAFETY CONCERNS Nitric acid and sulfuric acid are very corrosive! Use EXTREME caution when in use! Ethanol is flammable! Be careful when heating!

WASTE MANAGEMENT Place all liquid waste from experiment into the bottle labeled “LIQUID WASTE”. Place solid waste in bottle labeled “SOLID ORGANIC WASTE”. Place all used TLC spotters and melting point capillaries in broken glass container, NOT trashcan!

CLEANING Clean all glassware with soap, water, and brush if necessary. Rinse all glassware with wash acetone before returning to lab drawer. DO NOT return any glassware dirty or wet to lab drawer! All hotplates and MelTemps must be unplugged from outlets, with cords wrapped neatly.

LABORATORY NOTEBOOK (Pre-lab) OBJECTIVE (Must clearly state…) What compounds will be made and how How the compounds will be purified How the purity of the product will be determined CHEMICAL EQUATION Include the chemical equation from page 143. TABLE OF PHYSICAL DATA (Complete the following table using a site listed on WWW Links ONLY. Wikipedia is unacceptable!) REFERENCE TO PROCEDURE (Must include…) full title including edition and author names page numbers where actual procedure can be found Compound MW (g/mol) mp(oC) bp(oC) d (g/mL) HAZARDS p-methylacetanilide X Nitric acid Sulfuric acid Acetic acid Ethanol Ethyl acetate Hexane

LABORATORY NOTEBOOK (In-lab) DATA/CALCULATIONS Initial weight of p-methylacetanilide HPLC vial slot #s (should have 3) Theoretical yield calculation (not just value!) Volume of 90:10 ethanol/water used for recrystallization Weight of small & LARGE filter paper Weight of small filter + large filter + recrystallized dry product Weight of recrystallized dry product Physical state and color of product TLC diagram Example TLC Rf value calculation (not just value!) Experimental melting point range Atom economy calculation (not just value!) Experimental atom economy calculation (not just value!) “Eproduct” calculation (not just value!) Cost per synthesis calculation (not just value!) Cost per gram calculation (not just value!) EXPERIMENTAL PROCEDURE In paragraph form, describe the procedure that you actually followed during the lab. Paragraph must be written in PAST TENSE, PASSIVE VOICE. Include any volumes or weights of chemicals used during the experiment. Include any mistakes, accidents, or observations if applicable.

Quiz #1 will be given at the beginning of day 2 of this experiment! For next lab… Quiz #1 will be given at the beginning of day 2 of this experiment! Bring a calculator! Cell phones cannot be out during quiz!