Preparation of sec-butyl propionate with H2SO4 catalyst
The lab procedure in Vogel's Textbook of Practical Organic Chemistry, 5th ed, calls for use of anhydrous HCl as the catalyst when preparing sec-butyl acetate by Fischer esterification (1). HCl gas would be generated and bubbled into the alcohol until saturated. Presumably HCl is used instead of H2SO4 to avoid dehydration of the butan-2-ol to but-2-ene.
questioned if this extra step of gas generation is really necessary, when I could just use sulfuric acid catalyst as usual for Fischer esterifications, which is more convenient (Scheme 1). Secondary alcohols are generally compatible with sulfuric acid in esterifications, unlike tertiary alcohols, which are highly prone to elimination to an alkene. Even if any but-2-ene was formed, it would be easily removed in simple distillation because its boiling point is only 3.7 °C (2).
METHODs
To a 50 mL round bottom flask was added sec-butyl alcohol (20. mL / 0.22 mol), propionic acid (20. mL / 0.27 mL), and with rapid stirring, conc. sulfuric acid (0.7 mL / 0.01 mol / 5% mol equiv). The mixture was refluxed for 10 hours.
After reflux, the mixture was poured into a separatory funnel. First it was washed with a large arbitrary volume of water (about twice the volume). Next, the ester was washed with saturated sodium carbonate solution until gas production stopped. Next, it was washed with an equal volume of water. Lastly, it was washed with saturated sodium chloride. The crude ester was dried with anhydrous CaCl2 pellets in a beaker, then transferred into a 50 mL round bottom flask. The ester was purified by simple distillation.
RESULTS
The ester boiled 132.7 °C (literature value 133 °C) (3). I measured its density at 0.8412 g/mL (lit. value 0.8633 g/mL) (4). Yield was 14.30 g / 17.00 mL / 0.1098 mol / 49% yield.
Its aroma is same as sec-butyl acetate. Ethereal, solventy, grapey, nothing special.
The lab procedure in Vogel's Textbook of Practical Organic Chemistry, 5th ed, calls for use of anhydrous HCl as the catalyst when preparing sec-butyl acetate by Fischer esterification (1). HCl gas would be generated and bubbled into the alcohol until saturated. Presumably HCl is used instead of H2SO4 to avoid dehydration of the butan-2-ol to but-2-ene.
questioned if this extra step of gas generation is really necessary, when I could just use sulfuric acid catalyst as usual for Fischer esterifications, which is more convenient (Scheme 1). Secondary alcohols are generally compatible with sulfuric acid in esterifications, unlike tertiary alcohols, which are highly prone to elimination to an alkene. Even if any but-2-ene was formed, it would be easily removed in simple distillation because its boiling point is only 3.7 °C (2).
METHODs
To a 50 mL round bottom flask was added sec-butyl alcohol (20. mL / 0.22 mol), propionic acid (20. mL / 0.27 mL), and with rapid stirring, conc. sulfuric acid (0.7 mL / 0.01 mol / 5% mol equiv). The mixture was refluxed for 10 hours.
After reflux, the mixture was poured into a separatory funnel. First it was washed with a large arbitrary volume of water (about twice the volume). Next, the ester was washed with saturated sodium carbonate solution until gas production stopped. Next, it was washed with an equal volume of water. Lastly, it was washed with saturated sodium chloride. The crude ester was dried with anhydrous CaCl2 pellets in a beaker, then transferred into a 50 mL round bottom flask. The ester was purified by simple distillation.
RESULTS
The ester boiled 132.7 °C (literature value 133 °C) (3). I measured its density at 0.8412 g/mL (lit. value 0.8633 g/mL) (4). Yield was 14.30 g / 17.00 mL / 0.1098 mol / 49% yield.
Its aroma is same as sec-butyl acetate. Ethereal, solventy, grapey, nothing special.
