Abia Polytechnic University Comparative Vertebrate Anatomy Discussion

ObservationVacuum tubing mass: 15.04g
Crude product mass :0.99g
Recrystallized product mass :0.51g
percent recovery= mass pf recrystallized/mass of crude*100
0.51/0.99*100=51.51
Melting point for crude product:128.5-146.6
Melting point for recrystallized product:172-178
Recrystallization of N-Bromosuccinimide
CHM 2012
Introduction:
Recrystallization is a simple and cost-effective laboratory technique for purifying solid
compounds. The process depends on solubility increasing as the temperature of the selected
solvent increases. Recrystallization begins by dissolving an impure crude solid in a minimal
amount of hot solvent. The compound of interest (pure compound) should only be soluble in the
heated solvent, while the impurities should be soluble in both cool and heated solvent. Thus,
once the hot saturated solution cools slowly the compound of interest will recrystallize out of
solution and the impurities will remain dissolved.
When selecting a solvent for recrystallization it is critical that the target compound to be purified
is soluble near the boiling point of the solvent. This target compound must also be poorly
soluble in the selected solvent when cooled to room temperature. In addition, the impurities
must remain soluble in the selected solvent at all temperatures. Once the target compound
recrystallizes from the cooled saturated solution it may be collected via vacuum filtration. The
collected pure product may only be washed with the cold solvent. In this way the impurities may
be solubilized (soluble in cold and hot solvent) without risking loss of the pure product (soluble
in hot solvent only) from the filter paper.
Recrystallization procedures are often performed in an Erlenmeyer flask rather than beakers or
other flat side-surfaced glassware. Erlenmeyer flasks prevent crystallization upward along the
sides of the glassware, making product transfer for vacuum filtration more feasible. Erlenmeyer
flasks also offer tapered neck designs which minimize the loss of solvent during the process.
The rate at which the saturated solution is cooled is also critical to the success of
recrystallization. Slowly cooling the mixture will promote greater crystallization. Crystals are
typically composed of one single compound and thus pure. Cooling the recrystallization mixture
too quickly can promote more precipitation than recrystallization. In the example of a precipitate,
it may not be reasonably pure.
Melting point determination is a useful tool for determining the success recrystallizations since
solids are being purified. The purer a sample is the higher its melting point, the narrower its
melting point range, and the closer its melting point range is to literature/expected value.
Percent recovery is also used to quantify the efficiency of the purification. Percent recovery may
be calculated using Equation 1 below:
𝑝𝑒𝑟𝑐𝑒𝑛𝑡 𝑟𝑒𝑐𝑜𝑣𝑒𝑟𝑦 =
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑟𝑒𝑐𝑟𝑦𝑠𝑡𝑎𝑙𝑙𝑖𝑧𝑒𝑑 𝑝𝑟𝑜𝑑𝑢𝑐𝑡
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑟𝑢𝑑𝑒 𝑝𝑟𝑜𝑑𝑢𝑐𝑡
× 100%
(1)
Objectives:
–
Purify N-Bromosuccinimide from a crude mixture of Succinimide using recrystallization.
Characterize the success of the purification using melting point range determination.
Succinimide
N-Bromosuccinimide
Figure 1. Chemical structures of the impurity Succinimide and the target compound NBromosuccinimide (NBS).
Procedure1:
1) Setup a vacuum filtration apparatus using a vacuum flask, Buchner funnel, and
filtration adapter. Clamp the vacuum flask to a vertical lattice support and
connect vacuum tubing.
2) Weigh the top half of the Buchner funnel with a filter paper inserted for use later
in the experiment. Once product is collected this setup may be weighed again
and the initial mass subtracted to easily calculate the mass of pure product.
3) Add approximately 50 mL of DI water to a 250 mL beaker and heat using a hot
plate.
4) Obtain approximately 1 g of crude product. Record the exact mass for use in
percent recovery calculations at the end of the experiment.
5) Add the crude product to a clean 50 mL Erlenmeyer flask.
6) Once the temperature of the DI water exceeds 95°C begin adding the solvent to
your crude product containing 50 mL Erlenmeyer flask with a pipette. Constantly
rotate between swirling and replacing the Erlenmeyer flask on the hot plate. If the
solvent is allowed to cool during this step there is a significant risk of adding too
much.
7) Continue adding the hot DI water solvent while maintaining heat in the
Erlenmeyer flask until all crude product is dissolved. It is critical to add just
enough solvent to successfully recrystallize the NBS.
8) Once the crude mixture has completely dissolved turn off the hot plate and allow
the recrystallization mixture to cool slowly by placing the Erlenmeyer flask on the
benchtop in the fume hood.
9) Once cooled to room temperature, place the Erlenmeyer flask in an ice bath to
continue cooling. Place a DI bottle (or beaker containing DI water) in the ice bath
for use in later steps.
10) Filter the cold recrystallization mixture using the assembled vacuum filtration
apparatus. Turn the vacuum on and wet the filter paper with cold DI water before
filtering.
11) Slowly pour the recrystallization mixture onto the center of the filter paper to
avoid loss of product around the edges. Use small aliquots (single pipette
additions) of cold DI water to aid the transfer of pure product from the Erlenmeyer
flask to the filter paper.
12) After filtration wash the pure NBS product with two separate 5 mL aliquots of
cold DI water.
13) Allow the pure NBS product to air dry for approximately 15 minutes with the
vacuum on.
14) Record the mass of the pure NBS product as described in step #2.
15) Determine the melting point range of the dried, pure NBS product and calculate
percent recovery using Equation 1 above.
Waste:
–
Dispose of aqueous filtrate in general aqueous waste
Dispose of solids in the solid waste container
Discard melting point capillary tube in the sharps container
Data for the Report:
–
Percent Recovery
Experimental and literature melting point ranges of NBS
References:
1) Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Engel, R. G. A Small Scale
Approach to Organic Laboratory Techniques, 4th ed.; Cengage Learning:
Boston, 2016.
Recrystallization of N-Bromosuccinimide (NBS)
Author’s Name
Partner’s Name
Date
ABSTRACT: The purpose of this experiment was to Purify N-Bromosuccinimide from a crude mixture of an unknown
amount of NBS and succinimide. This was done via recrystallization: a technique using a hot solvent to dissolve the mixture.
The solution is then allowed to cool, making the target solute recrystallize out of the mixture. The solute is then separated
to analyze its purity. This was assessed by measuring the experimental melting point and then comparing it to the literature
melting point of NBS. The melting point obtained from the experiment suggests that the product was not pure, having a
range of 174-182.4oC. However, there may be some determinate errors that could be affecting the experimental melting
point range instead of impurities in product.
Introduction
Recrystallization is a technique of distilling an impure solid in
the minimum amount of a hot solvent and filtering out the
impurities. The most important part of this process is what
solvent is used. Crystal growth is affected by its solubility in the
compound. When considering what solvent to use, the target
compound must be completely soluble when the solvent is hot,
but poorly soluble when it is cold. The unwanted impurities
must be soluble at all solvent temperatures. This ensures that
the impurities do not recrystallize with the target compound.
The solvent is then allowed to naturally lower to room
temperature and the target solute recrystallizes out of the
mixture. The slow cooling ensures that impurities are not
trapped within the recrystallized compound. The process is a
simple, cheap, and effective process. However, it is not ideal if
you require a ~100% yield of the target compound because
some of the solute will still be dissolved in the solvent
regardless of how cool it gets.
The purpose of this experiment was to use recrystallization to
isolate N-bromosuccinimide from succinimide from a crude
mixture with deionized water. The structural formulas of NBS
and succinimide can be seen in Figure 1.1,2 The purity of the
sample was then assessed by analyzing the melting point range.
Mixtures of substances have a lower melting point than the
melting point of pure substances. So, the purer the NBS, the
closer the melting point is to the literature value.
Results
Table 1. The mass of the solid before and after the
recrystallization experiment. The percent recovery was
found with the formula from Figure 3.
Mass of Impure
Solid (g)
Mass of Recrystallized
Product (g)
Percent
Recovery
1.00
0.68
68.0 %
Table 1 shows the mass of the solid before and after the
recrystallization experiment. The percent recovery was found
with the formula from Figure 3.
Equation 1. Formula used to calculate the percent recovery
of NBS:
Table 2. Experimental & Theoretical Melting Point of NBS.3
Experimental Melting Point
of NBS (oC)
Theoretical Melting Point
of Pure NBS (oC)
174.0 oC – 182.4 oC
173.0 oC – 175 oC
Table 2 compares the theoretical melting point of NBS and the
experimental melting point of the recrystallized sample of
NBS.3
Figure 1. Structural formulas for N-bromosuccinimide
(left) and Succinimide (right).
Discussion
The recrystallization process recovered 68% of the mass of the
sample, determined using the formula in Figure 3.
Idealistically, this would mean that 0.68 g of the sample was
pure NBS. To confirm this, the melting point was analyzed. The
temperature at which a solid melts is known as the melting point
(MP) of that substance. The melting point is a physical property
of a solid and can be used to help identify a substance. The
purpose of the melting point analysis is to identify the actual
range of melting point range values to identify the presence of
impurities in a sample. Samples that contain impurities have a
lower melting point than the pure compound’s melting point.
According to Table 2, the initial melting point fell into the
range of NBS’s theoretical melting point. However, the final
temperature when the sample became liquid was 7.4 oC greater
than the theoretical value. This may be because some impurities
are trapped inside of the sample by not allowing it to cool to
room temperature before putting it in the ice bath. It is more
likely, however, that the sample was packed too tightly into the
capillary tube since the initial melting point found is within the
range of pure NBS’s melting point. This causes uneven heating
of the sample which alters the final melting point. This can be
improved by not packing samples in the capillary tube as
tightly. Another mistake would have been not using cold DIW
to wash the filtered NBS. Using warmer water would have
caused dissolvement of the target compound and lessened
recovery of the crystals. Allowing DIW to sit in a refrigerator
or ice bath longer can prevent the rinse from dissolving the
product.
Conclusion
Based on the results, the experiment was not successful. When
comparing it to the literature melting point of 173-175oC, our
experimental range of the sample is almost four times as wide
from 174.0-182.4oC. This indicates that there are some
impurities and errors in properly measuring the melting point of
the sample. In future tests, the experimenter should use more
capillary samples of the recrystallized product to ensure that it is
the impurities that are affecting the melting point instead of
systematic errors.
Experimental Section
First, 50 mL of DIW in a 250 mL beaker was heated on a
hotplate. Then, 1.00 g of impure NBS was weighed and put into
a 50 mL Erlenmeyer flask. When DIW reached 95-100oC, 1 mL
was transferred from the beaker to the flask via a plastic pipette.
This process was repeated while swirling the flask 4 times until
the impure NBS completely dissolved. The solution was
periodically heated for 3 seconds then swirled until there was
no solid visibly seen in the flask. The solution was then placed
on the counter and allowed to cool to room temperature. The
flask was then placed in an ice bath after reaching room
temperature for 5 minutes. The solution is then poured into the
vacuum filtration system. Leftover NBS inside the flask was
rinsed out with two 5 mL portions of cold DIW and poured into
the vacuum. The NBS was left on the vacuum to dry for 15
minutes. The NBS was then taken out of the Buchner funnel and
weighed. Finally, it was then packed inside a capillary tube to
estimate the melting point with a melting point apparatus, seen
in Figure 2. This was done by recording the temperature of
NBS started melting and the temperature NBS became fully
liquid.
Abbreviations
DIW, deionized water; NBS, N-bromosuccinimide.
References
1.UCLA Chemistry Department. Illustrated Glossary of Organic
Chemistry.http://www.chem.ucla.edu/~harding/IGOC/N/n_bromosuc
cinimide.html (Accessed February 2, 2020)
2.Millapore Sigma. Succinimide. 2020.
https://www.sigmaaldrich.com/catalog/product/sigma/s9381?lang=en
®ion=US (Accessed February 2, 2020)
3.National Center for Biotechnology Information. PubChem
Database. NBromosuccinimide,CID=67184,https://pubchem.ncbi.nlm.nih.gov
/compound/N-Bromosuccinimide (accessed on February 3, 2020).
4. Zubrick, J. W.The Organic Chem Lab Survival Manual: A
Student’s Guide toTechniques,9th ed.; Wiley: Hoboken, 2014.