Grignard experiment lab report PDF

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Post-lab report on Grignard reaction...

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Victoria Oh Lab section 1 group B

Dr. Hollabaugh, Thursday PM

Synthesis of triphenylmethanol Data & Calculations Table 1. Reagent quantities and appearances Reagent Magnesium Anhydrous diethyl ether Bromobenzene

0.3 mL

Benzophenone Hydrochloric acid

0.37 g 2 mL

Sodium chloride

Added until acid was removed Added until clumping stopped N/A

Sodium sulfate Crude Triphenylmethanol % yield Warm ether Ligroin Purified triphenylmethanol % yield

` 0.052 g 10.2 mL

Smallest amount 3.5 mL 56.6%

appearance Silver solid Clear and colorless liquid Clear and colorless liquid White solid Clear and colorless liquid White solid salt White solid salt Yellowish-white solid

Clear colorless liquid Clear colorless liquid

Table 2. Melting point determination Substance Purified triphenylmethanol

Trial 1 109.9 oC – 143 oC

Figure 1. IR spectroscopy

Table 3. IR spectroscopy data Wavenumber Relative -1 intensity (cm )

Shape

3465.01

weak

broad

Functional group/ hybridization O-H

3058.79 1958.17 1652.41 1596.36 1489.13

weak weak medium medium Medium

narrow broad narrow narrow narrow

C-H C-H C-H C-H C-H

Considerations, comments Intermolecular bond overtone aromatic aromatic Aromatic

Calculations: Theoretical yield calculation: Moles of Bromobenzene: (1.495 g/mL)(5.3 mL)/157.01g/mol)= 0.05mol Moles of Magnesium: (0.052g)/(24g/mol)= 0.0022 moles Moles of benzophenone: (0.37g)/(182.22 g/mol)= 0.0020 moles (limiting reagent)

0.37 g b enzophenone ×

1 mol b enzophenone 1 mol Triphenylmethanol 260.3 g Triphenylmethanol × × =0.53 1 mol B enzophenone 182.22 b enzophenone 1 mol Triphenylmethanol

Percent Yield calculation: Percent Yield=

Actual Yield ×100 ( Theoretical Yield )

Purified tryphenylmethanol=

0.3 g ×100=56.6 % ( 0.53 g)

Retention factor calculation: crude retention factor=

=0.15 cm ( 1.2cm 8 cm )

recrystallization r etention factor=

( 4.78 cmcm )=0. 59 cm

( 1.38 cmcm) =0.16 cm

Bromobenzene r etention factor=

( 0.58 cmcm) =0.06 cm

Bromobenzene r etention factor=

( 4.78 cmcm) =0. 59 cm

Bromobenzene r etention factor=

Product r etention factor=

( 0.86cmcm )=0.08 cm

Conclusion: Triphenylmethanol was successfully synthesized through the reduction of benzophenone, which was done through a Grignard reaction in 56.6 % yield (recrystallization) as a white solid. Although product did form, it was not pure. This is evident through the inaccurate melting point determination of 109.9-143 oC. However, the literature melting point of triphenylmethanol is 164.2 oC. Since the range of the product was not close to literature melting

point and was broad in range, it was concluded that the product was impure. For the melting point determination, only one trial was able to be conducted since the collected product immediately melted after adjusting the machine several times, as the predicted temperature was set too high. Additionally, this was done at the end of the lab and there was not enough time to conduct a second trial. The IR spectrum also showed that triphenylmethanol was produced. This is evident as the peaks were 3465.01, 1652.41, and 1596.36, which showed the presence of

alcohol, and aromatic C-H bonds respectively, which are all in the structure of triphenylmethanol. An additional evidence of impurity was shown in the TLC plate. The plate showed 1 spot for the crude product, 1 spot for the recrystallized product, 3 spots for the bromobenzene, and 1 spot for the purified product. The purified product had a spot that was similar to one of the bromobenzene spots. This shows that the purified product contained bromobenzene, which leads to the conclusion that the product was impure. Additionally, the recrystallized product had a spot similar to the bromobenzene as well, indicating that the recrystallized product contained bromobenzene. However, the TLC plate may not be the best evidence, since there were complications with during the plating procedure. The plate was touched before it was ran and the plate was also bumped in the mobile phase, which moved two of the spots on the bromobenzene. Additionally, eluent front was not marked immediately, which may have led to an inaccuracy regarding where the eluent front was. However, through the other evidence that was collected, it was concluded that the triphenylmethanol was synthesized, but it was impure. During the experiment, the triphenylmethanol collected, was at a 56.6% yield perhaps due to some product being lost due to having to transfer the mixtures multiple times during the experiment, leading to product being left in the previous containers, and due to the product

dripping out of the pipette. Other errors in the experiment were that the crude product was not weighed, leading to the percent yield unable to be found; the reaction may not have been able to run long enough, which may not have allowed the crystallization to occur; and adding too much ethanol during recrystallization. Changes that occurred during the experiment was that sodium sulfate was used instead of calcium chloride and mobile phase for the TLC was made beforehand, causing the amount of ligroin and methylene chloride to be unknown. In the future, better attempts should be made to collect all the product when transferring, placing the beakers closer when pipetting the product into them, weighing when necessary, allow reactions to run for a longer time, ensuring that an appropriate amount of reagent is added, not touching the TLC plate, carefully place the TLC plate in the mobile phase, and allowing enough time for melting point determination.

References: Hollabaugh, N; “Synthesis of triphenylmethanol”,

Zubrick, J; The Organic Chem Lab Survival Manual: A Student's Guide to Techniques, 10th Edition, Wiley

Pubchem.ncbi.nlm.nih.gov, magnesium, anhydrous diethyl either, bromobenzene, benzophenone, hydrochloric acid, triphenylmethanol, methyl-tert-butyl ether, sodium chloride, calcium chloride, ligroin, methylene chloride https://www.sigmaaldrich.com/technical-documents/articles/biology/ir-spectrum-table.html...