MJMResearchReportSpring2013

=Research Report= Matthew McBride CHEM 496 - Senior Research Project Spring 2013 =Introduction= During this quarter, the research I conducted demonstrated the ability to use boiling point solubility predictions for a compound to choose a recrystallization solvent. The compounds examined were benzoic acid, trans-cinnamic acid and caffeine recrystallized from solvents such as n-hexane, cyclohexane, ethanol, toluene and water. Additionally, it was determined that compounds that have good solubility in ethanol should not be washed by pentane following a recrystallization from 1:1 ethanol/water. The pentane wash causes the product to become soluble and be lost through the filter. It was determined that pentane can be used as a wash to remove toluene from a sample, but is unable to remove water. =Experimentation= EXP351 investigated the ability of benzoic acid to be recrystallized from n-hexane using a sintered glass funnel to remove the solvent. The predicted solubility of benzoic acid at the boiling point of n-hexane is [|0.9 M], but this experiment found that the benzoic acid crystals did not dissolve into the boiling solution until the concentration was at 0.25 M. This lower solubility at the boiling point of n-hexane likely contributed to the lower recovery yield of 59%. The predicted recrystallization yield for 0.9 M solubility at the boiling point was 92%, but the predicted yield is reduced to 70% when the solubility at the boiling point is 0.25 M. Scheme for EXP351

EXP352 investigated the ability of trans-cinnamic acid to be recrystallized from cyclohexane using a sintered glass funnel to filter. The predicted solubility of trans-cinnamic acid at the the boiling point of cyclohexane is [|0.77 M], but this experiment measured the boiling point solubility to be 0.23 M. The yield of this recrystallization was 88% and this exactly matched the predicted yield with the solubility at the boiling point being 0.23 M and the solubility at room temperature being 0.029 M. Since cyclohexane has a boiling point under 80°C and the recrystallization yield was over 80%, this recrystallization of trans-cinnamic acid in cyclohexane is a good example of using solubility predictions to successfully choose a recrystallization solvent. Scheme for EXP352

EXP353 investigated the ability of trans-dibenzalacetone to be recrystallized from ethanol using the sintered glass funnel to filter. Trans-dibenzalacetone was predicted to have a solubility of 0.74 M at [|65°C] and this experiment found that the crystals of the 0.74 M solution went completely into the solution at 75°C. At 0.74 M, the recrystallization yield was predicted to be 87% and this experiment had a yield of 69%. Scheme for EXP353

EXP354 and EXP355 investigated the use of pentane washes to remove 1:1 ethanol/water from a product following a recrystallization. EXP354 found unsurprisingly that ethanol and pentane are miscible with one another. However, upon the addition of eight drops of water to this binary solvent system, the system separated into two layers of approximately equal volume. This means that the water was not only immicible with the pentane, but the addition of the water caused the ethanol to be immicible with the pentane layer as well. EXP355] showed that this separation of the ethanol can cause products, such as trans-cinnamic acid, that are soluble with ethanol to be lost. In [[EXP355, trans-cinnamic acid crystals were throughly mixed with a 1:1 ethanol/water mixture and then washed with pentane. As the pentane washes were applied to the crystals wet with the 1:1 ethanol/water mixture, the trans-cinnamic acid crystals were observed to enter the wash solution and pass through the filter. Based on the findings of EXP354, this increased solubility of the trans-cinnamic acid must be due to localized pockets of ethanol forming on the surface of the crystals as the pentane was added.

EXP358 investigated the ability of pentane to remove the higher boiling point solvent toluene from the product following the recrystallization of caffeine from toluene. A 0.24 M solution of caffeine in toluene was prepared and all the crystals entered the solution at the boiling point of toluene (110°C). The predicted recrystallization yield for a 0.24 M solution of caffeine in toluene was [|88%] and this experiment had an yield of 80%. This showed that, as predicted, toluene is a good solvent for recrystallizing caffeine. However, since toluene does have a higher boiling point (110°C), the removal of toluene can be a bit more difficult than solvents with boiling points under 80°C. In this experiment, the product crystals were washed with pentane 3x and then analyzed by HNMR spectroscopy to determine whether any toluene had remained in the product. The [|HNMR spectrum] of the product did not show the presence of toluene and so it can be concluded that the pentane washes successfully removed the toluene from the product crystals. Scheme of EXP358

EXP359 investigated the ability of pentane to remove the solvent water from the product following the recrystallization of benzoic acid from water. A 1.35 M solution of benzoic acid in water was prepared and all of the crystals entered the solution at the boiling point. At a concentration of 1.35 M, the predicted yield for this recrystallization was 98%, but the yield obtained in this experiment was 66%. This reduced yield was due to the pentane washes. The product crystals were washed with pentane 3x to determine whether the pentane was able to remove the water, but benzoic acid has a predicted room temperature solubility in pentane of 0.053 M and some of the crystals were observed to pass through the filter as these washes took place. From the [|HNMR spectrum] of the product crystals, a water peak was observed at 1.5 ppm indicating that the pentane washes were not able completely remove the water from the sample. This was expected as pentane is extremely non-polar while water is a polar molecule. Scheme of EXP359 =Conclusion= This research taught me valuable skills for planning and performing a recrystallization. It demonstrated that solubility is highly temperature dependent and that the solubility of a compound at the boiling point of the recrystallization solvent is important for determining the yield of the recrystallization. One of the major issues with a recrystallization, particularly those that use solvents with higher boiling points (>80°C), is the removal of the solvent from the product after the recrystallization has been completed. This research found that the lower boiling point solvent pentane is able to remove some high boiling point solvents, such as toluene. Additional recrystallization experiments can be found [|here].