A gentle stream of air was passed over the solution, using the air flow hose in the fume hood, in the 25 mL Erlenmeyer flask to allow the liquid to evaporate. The flask was warmed with a hand until all of the solvent evaporated, and yellow solid remained. The solution was set to dry for 5 minutes.
During recrystallization, 1 mL of acetone was added for every 50 mg of yellow solid. The solution was allowed to cool to room temperature, then the solution was placed in an ice-water bath for an additional 15 minutes. The solution was filtered via vacuum filtration and the crystals were collected on a small Hirsch funnel. The funnel was lifted slightly to cover the crystals with 1 mL of ice-cold acetone, and the filter was placed back down to further vacuum filtration. Air was allowed to pass over the crystals for a few minutes and they were then scraped onto a tared piece of paper. The crystals were allowed to dry to a constant weight. A small sample was saved to dry further and obtain a melting point.
During hydrolysis, 60 mg of the yellow solid, which is now identified as trimyristin, was weighed and transferred to a clean RB flask using a funnel. 2 mL of 6 M sodium hydroxide, 2 mL of 95% ethanol, and a few boiling chips were added and the solution was refluxed for 45 minutes on sand bath. The rest of the trimyristin was recrystallized a second time while the solution refluxed; allowing the solution to cool to room temperature for 10 minutes before cooling in the ice bath. A minimum amount of acetone was used to dissolve the crystals at the boiling point of the solution. The product was collected using vacuum filtration, and allowed to dry to a constant weight. The melting points of the once recrystallized solid and twice recrystallized solid were compared.
After hydrolysis, the flask was allowed to cool to room temperature. The contents were then poured into a 50 mL beaker containing 8 mL of water. Drop wise, 2 mL of hydrochloric acid were added as the solution was constantly stirred. The solution was filtered and the funnel was lifted 3 times to add very small portions of water (just enough to submerge all of the recovered crystals). The solid was allowed to dry overnight, and a melting point and % yield was taken.
Results:
Starting nutmeg mass: 1 g
Starting material(trimyristin): 0.473 g
After first recrystallization: 0.131 g MP: 53-54 ℃
After second recrystallization: 0.80 g MP: 54 ℃
Myristic acid mass: 0.046 g MP: 52-54 ℃
Myristic acid yield: 76.8%
Discussion:
The starting material nutmeg underwent multiple reactions in this lab and the final yield was calculated to be 76.8%. This is the yield of Myristic acid from 60 mg of starting material after undergoing hydrolysis. Initially 1 g of nutmeg was started with to make .473 g of trimyristin, then a recrystallization was done and 0.131 g were recovered and the product had a melting point of 53-54 ℃.. The product of the second recrystallization had a mass of 0.080 g and had a melting point of 54 ℃. The MP were below the theoretical MP of trimyristin, which means the trimyristin created in this lab contained some impurities decreasing the melting point. Also the range of the MP is important, the higher MP range means the presence of more impurities. The myristic acid from hydrolysis had a mass of 0.046 g which is a percent yield of 76.8 %. The melting point of the myristic acid was 53-54 ℃, which is very close to actual melting point which is 54.4 ℃. This means the myristic acid was very pure and was easily identified as myristic acid. The yield of the myristic acid and the trimyristin could have been decreased or affected by human error such as letting the mixture boil over and spilling. Other human errors may have contributed to lack of precision and overall error.
Post-Lab Questions
1. A saturated fatty acid is one where hydrogen atoms are attached at all maximum possible locations. This means that each carbon to carbon bond is a single bond. A fatty with one double bond is a monosaturated fatty acid; a polysaturated fatty acid is one in which there is more than one double bond. Trimyristin is all single carbon to carbon bonds, which would make it a saturated fatty acid.
2. The old procedure differs from the new procedure in the fact that a lot of the ether soluble components in the nutmeg will remain in the acetone solution. If the solution is cooled to room temperature before being put into the ice bath, they ether soluble components would be allowed to dissolve further before being put into the ice bath.
3. (1.8 g of tristearin)*(1 mol tristearin/891.48 g tristearin)*(3 mol stearic acid/1 mol tristearin)*(284.48 g stearic acid/1 mol stearic acid) = 1.723 g stearic acid
4. The mixture is a high boiling mixture. The mixture needs to be refluxed. Reflux occurs when a mixture is heated at a high temperature for a certain amount of time, which allows vapor to be produced and cooled in a condenser dripping back into the round-bottomed flask. This allows for a high separation.
5. If the mixture were heated at that temperature for 45 minutes, there would not be as high of a separation achieved from the reflux. Heat speeds up a chemical reaction, if the solution were allowed to reflux at that temperature for a longer period of time, then the solution may achieve the chemical reaction that is wanted.
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