Preparatory Problems 44th
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Apparatus and Glassware • Balance (± 0.01 g precision or better) • Erlenmeyer flask, 125 mL • Hotplate/stirrer • Graduated cylinder, 10 mL • Büchner funnel • Filter flask and source of vacuum (e.g., water aspirator) • Silica gel-coated TLC plates and development chamber • Melting point apparatus • Spatulas Procedure 1. To the 125 mL Erlenmeyer flask add 0.35 g 2,2-dimethyl-1,3-diaminopropane, 2.2 g 2,4-di-tert-butylphenol, 10 mL ethanol, and a stirbar. Stir the mixture until it becomes homogeneous, then add 1.0 mL 37% aqueous formaldehyde solution. 2. Heat the mixture to a gentle boil, with stirring, on the hotplate/stirrer. Maintain at a gentle boil for 1.5 hr. Alternatively, the heating can be carried out in a round-bottom flask under a reflux condenser, using a heating mantle or oil bath to heat the flask, with the solution maintained at reflux for 1.5 hr. 3. Take the flask off of the hotplate, remove the stirbar from the solution, and allow the reaction mixture to cool to room temperature. If no solid has formed, scratch the inner sides of the flask with a spatula to initiate crystallization. After the solution has reached room temperature, chill the flask in an ice bath for at least 10 minutes. 4. Suction-filter the precipitate on the Büchner funnel. Wash the solid thoroughly with 10 mL methanol to remove any unreacted 2,4-di-tert-butylphenol. After the wash, leave the precipitate on the Büchner funnel with the vacuum on (to suck air through the precipitate) for at least 15 min. This serves to dry the solid by evaporating any residual methanol. 5. Scrape the solid into a tared container and measure the yield of product. 6. Characterize the product by its melting point (it is between 200–250 °C) and by thin layer chromatography (silica gel, eluting with 3:1 hexane:ethyl acetate (v/v)).
a) The 1H NMR spectra of the product, recorded in CDCl3 solution at 500 MHz at –40 °C and at 55 °C, are shown below. For each temperature, the full spectrum from 0–12 ppm is shown, then an expansion of the region from 1.5–4.5 ppm. Peak positions, where listed, are given in ppm. Some small impurities in the solvent are observable; they are marked with asterisks (*) and should be ignored. Based on these spectra, suggest a structural formula for the observed product. 
b) Suggest an explanation for the change in appearance of the 1H NMR spectra with temperature. c) Calculate a percent yield of product. d) Report the melting point and Rf value of the compound. Periodic Table of the Elements
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