Preparation of Isopentyl Acetate

Results and Discussion Isopentyl propanoate was prepared by refluxing isopentyl alcohol in excess propanoic acid and concentrated sulfuric acid. The ester was obtained by distillation in 62% yield, bp 140-150oC (lit. 156 oC [1]). GC analysis of the distillate revealed only traces of the starting alcohol (Figure 1). The ester's structure was confirmed using IR and 1H NMR spectroscopy. The IR spectrum (Figure 2) shows a strong absorption at 1741 cm-1 consistent with an ester C=O stretching vibration. The NMR spectrum (Figures 3 and 4) contains all of the signals expected for this compound. A triplet at 1. 18 ppm and a quartet at 2. 8 ppm are assigned to the propionyl methyl and methylene groups, respectively. A doublet at 0. 82 ppm is assigned to the two isopentyl methyl groups. A 6 line pattern at 1. 66 ppm is assigned to the methine group (9 lines are expected), and a triplet at 4. 08 and a quartet at 1. 48 ppm are assigned to the OCH2 and CHCH2 methylene groups, respectively. Experi mental Preparation of isopentyl propanoate. Isopentyl alcohol (4. 6 mL, 42 mmol), propanoic acid (40 mL, 530 mmol), and concentrated sulfuric acid (1 mL, 18 mmol) were refluxed for 66 minutes. The solution was diluted with water (60 mL) and extracted with ether (60 mL).The ether layer was washed with saturated aq. NaHCO3 (2 x 60 mL), dried with MgSO4, and distilled at atmospheric pressure to give isopentyl propanoate: 3. 8 g (62% from isopentyl alcohol), bp 140-150 oC (lit. 156 oC [1]); IR (ATR) cm-1: 2960 (vs, CH), 1741 (vs, C=O), 1189 (s, C-O); 1H NMR (C6D6, 400 MHz) ? : 0. 92 (d, 6H, J = 6. 8 Hz, CH(CH3)2), 1. 18 (t, 3H, J = 6. 6 Hz, CH2CH3), 1. 48 (q, 2H, J = 6. 6 Hz, CHCH2), 1. 66 (9 lines, 1H, J = 6. 8 Hz, CH), 2. 28 (q, 2H, J = 6. 6 Hz, CH2CO), 4. 08 (t, 2H, J = 6. 8 Hz, OCH2); GC (120 oC, right-hand column): isopentyl propanoate (4. 8 min), isopentyl alcohol (4. 4 min). References 1.Mordechai, U. ed. â€Å"Esther's Ester Handbook, 11th Ed. â€Å", Fruity Publishing, Boca R aton, 1984. E-factor Insert list and mass of consumed materials, product, and e-yield here. Figures [GC data, IR spectrum, and NMR spectrum; label each one as a numbered figure (see above) and give the figure an appropriate title; see appendix for additional instructions] NMR Exercise Choose one of the molecules listed below. Draw its structure (show all H) and label all protons as A, B, C, †¦ (apply the same label to ‘NMR equivalent' protons). Examine the online proton NMR spectrum (follow the link; the small upper spectrum is the carbon-13 NMR, ignore it).List all shifts associated with the compound; do not list shifts for solvent, TMS, etc. , and do not list integrals or coupling patterns. Assign each signal to a particular proton. Do this on your own; do not work with others. (If you are having trouble with the assignment and would like some help from others, work on a different spectrum from the one that you turn in). Turn in 1) the compound name provided below, 2) t he structural formula and H labels, 3) the list of shifts and assignments (write the label next to its shift). Do not turn in the spectrum