Preparation of Isopentyl Acetate

Category: Alcohol, Chemistry

Last Updated: 19 Apr 2023

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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 of [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. Experimental 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).