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Synthesis And Characterization Of Acetanilide

Purpose

The purpose of this experiment was to synthesize acetanilide with aniline and acetic anhydride. We recrystallized our acetanilide to purify it and we analyzed the melting point, HNMR, and TLC (thin layer chromatography). Our main objective was to familiarize ourselves with organic synthesis through purification and characterizing our compound with the use of techniques that isolate the compound in question.

 

Background Information

Acetanilide (N-phenylacetamide) is an obsolete analgesic and antipyretic agent, also known as antifebrin. It was abandoned long ago due to its excessive toxicity and low activity. The acetanilide can be synthesized in several ways. In this laboratory you will use aniline and acetic acid anhydride as key reagents.

The acetanilide is soluble in hot water (-5.5 g/100 mL) and scarcely soluble in cold (-0.5 g/100 mL). We will use this property to purify it by recrystallization.

 

Recrystallization is a common purification technique used in an organic chemistry laboratory. The desired, to be purified product should be as soluble as possible in hot solvent and as insoluble as possible in cold solvent. The selection of solvent is, therefore, critical to successful recrystallization. Recrystallization is a widely-used technique to purify a solid mixture. The desired product is isolated from its impurities by differences in solubility at various temperatures. Soluble impurities remain in the cold solvent after recrystallization. In case of acetanilide, water will be used.

As seen above, we were given a reaction mechanism of the acetanilide synthesis. Our two key reagents were aniline and acetic anhydride in nucleophilic substitution, or acetylation; a reaction mechanism in which an electron rich nucleophile attacks a more positively charged molecule in the place of a leaving group. (5) To create the product, we take acetic anhydride and one of the Oxygen attacks a floating hydrogen atom, this makes the Oxygen more protonated and positively charged. The aniline will then attack the double bond of that Oxygen with the electrons on the Nitrogen. The aniline and acetic anhydride become one and to finally create acetanilide, we deprotonate the Nitrogen and to get rid of the acetic acid the O-H group will carry its electrons to make a double bond- removing the acetic acid. There are technically two products, but in the case of this experiment the acetic acid was not one of the three Spector’s. This reaction is known as a substitution reaction mechanism, when an atom(s) take the place of the atom preceding it on a molecule.

 

Procedure

To a 4 ml. conical vial weadded 186 mg of aniline and a magnetic spin vane. Next, we added 2 ml. of water and stirred it on a magnetic stirrer (DO NOT HEAT IT). After that, we added 240 mg of acetic anhydride and we kept stirring. At some point, solid was formed.We noted any changes that occurred to the reaction mixture and the times at which they occurred. After 20 minutes, we cooled the reaction mixture in an ice bath to complete crystallization. We Isolated the product by vacuum filtration using Hirsch funnel, and we washed it with ice-cold water (using Pasteur pipette), and allowed it to dry on the funnel by pulling air through the solids for 5 minutes. We weighed our product and reported the obtained yield. Next. TA prepareda water bath. We transferredour product into small flask.

Using a minimal amount of hot water (from water bath, we added drop after drop) dissolving our acetanilide. We keptour flask on hot plate (be careful!) while dissolving the product. After we obtained a clear solution we removed our flask from hot plate and let it cool down to room temperature. Once reached, weplaced our flask into ice bath to further cooling. We kept it on ice for 5 minutes and then filtered it off using Hirsh funnel. We Air-dried the product (left it on a bench, protected from spilling).We determined the recrystallization yield (percent recovery) and recorded it in our lab notebook.

 

Product characterization

We performed the TLC analysis of our recrystallized product and compare it with commercial pure acetanilide and aniline as potential impurity (the solution of these samples was provided to us). As a developing solvent system we used 50% ethyl acetate in hexanes.

Next, we weighed 50 mg of our acetanilide and placed it into 1.5 mL microcentrifuge tube provided by TA. We handed the TA the sample. TA dissolved it in 400 μL of deuterated chloroform and we recorded the ‘H NMR spectrum (TA will insert the NMR tube into the spectrometer).We acquired the spectrum, processed it and printed it out. We compared our product’s ‘H NMR spectrum with starting materials.

We recorded the M.P. of our recrystallized product. The M.P. apparatus was set up by TA to

Cover the range of 80-150 “C.

 

IUPAC Name	Cas#	Molecular mass unit	Melting point	Boiling point	Solubility in water	Density units	Amount used	Role of reagent
Acetic anhydride	103-24-7	102.09 g/mol	-73.0 C	139.8 C	Yes	1.08 g/mol	240 mg	Reagent
Aniline	62-53-3	93.13 g/mol	-6.0 C	184.1 C	Yes	1.02 g/mol	136 mg	Reagent
Water	7732-18-5	13.02 g/mol	0.00 C	100 C	Yes	1.00 g/mol	2 mL	Solvent
N-phenylacetamide	103-34-4	135.16 g/mol	114.3 C	304 C	Slightly	1.22 g/mol	50 mg	Product and solute
Acetic Acid	64-19-17	60.05 g/mol	17.2 C	117.8 C	Yes	1.06 g/mol	N/A	Product
Deuterated Chloroform	865-49-6	130.38 g/mol	-64.0 C	61.0 C	Slightly	1.50 g/mol	405 mL	Solvent
Ethyl acetate	141-78-6	33.11 g/mol	-83.5 C	75-78 C	Slightly	0.902 g/mol	N/A	Solvent
Hexane	110-54-3	68.18 g/mol	-95.0 C	69.0 C	No	0.655 g/mol	N/A	Solvent

 

Results and Discussions

 

Compound	Rf value	Distance travelled on plate
CA	0.056	0.25cm
P	0.067	0.3cm
A	0.378	1.7cm

 

 

CA- commercial acetanilide

 

P- Product we made of acetanilide

 

A- Aniline

Melting point of	Literature Value	Obtained value
recrystallized product	80-150	113

 

H NMR, acetic anhydride in CDCl3

 

Signal	Atom is a part of a group	Observed chemical shift	PeakMultiplicity	Peakintegral value	Chemical shift value(from literature ppm)
A	CH3	2.18 ppm	singlet	6.00	2.1-2.6

 

 

Signal	Atom is a part of a group	Observed chemical shift	Peak Multiplicity	Peak integral value	Chemical shift value (from literature ppm)
A	NH	8.51	singlet	1.00	5.5- 9.4
B	CH	7.28	triplet	6.70	6- 9.5
C	CH3	2.11	singlet	3.97	1- 5

 

Acetanilide yields

 

Recovery mass	Starting mass	Percent recovery yield	Theoretical yield	Recrystallization yield
137 mg	270 mg	50.7 %	270 mg	270 mg

 

Calculations

 

Calculations: the amount used mL (volume)

 

1. Acetic Anhydride 240 mg (g/1000 mg) (1ml/1.08g) = 0.222 mL

 

2. Aniline 136 mg x (1g/1000mg) x (1 mL/1.02g) = 0.182mL

 

3. Acetaniline 50 mg x (1g/1000 mg)x (1 mL/1.22) = 0.042 mL

 

Amounts used in mmol

4. Acetic Anhydride 240 mg x (1g/1000 m) x (1 mL/102.06g)x (1000 mmol/1 mol) = 2.35 mmol

 

5. Aniline 136 mg x (1g/1.000 mg)x (1 mol/93.13g) x (1000 mmol/1 mol) = 1.997 mmol

 

6. Water 2mL x (1g/1 mL) x (1 mol/18.02g) x (1000 mmol/1 mol) = 110.9 mmol

 

Theoretical yield calculations CH NH₂ +(CH3CO) ₂O→ C₂H5NH (COCH3) + CH3COOH

 

Aniline 136mg x (1g/1000mg) = 0.136g x (1 mol/93.13g) = 0.001997x (1mol/1 mol) = 0.001997 mol

Acetic Anhydride 240mg x (1g/1000mg) =0.24g x (1 mol/102.04g) = 0.002351 mol x (1mol/1 mol) = 0.00235

Aniline is limiting agent 0.002 mol x (135.16g/1 mol)= 0.27g x (1000 mg/1g) = 270 mg Acetadine

 

Discussion

For the experiment, we first performed a recrystallization reaction for acetanilide using aniline and acetic anhydride. Recrystallization is the process of dissolving an impure substance-that must be soluble- and cooling it to purify it.(1) The process works well in conditions where the amount of impurities is minimal and that it has a high melting point. Our crystallization went well while the aniline was in the magnetic spin vane, and the addition of acetic anhydride stirred in created the solidified form. We observed through the procedure the changes in our compound as the reaction was slowly occurring.

In the magnetic spin vane, white precipitate began forming and thickening. This was different when compared to the clear, yellowish liquid it was prior to placing it on the magnetic stirrer. The spin vane stopped only once while in the vial of the compound, but after using a spatula to loosen up the thickness it spun non- stop. It became a smoky white color soon after that and remained constant. When it became snow- like we removed it from the stirrer. We cooled the crystals slowly for the crystals to form more perfectly. The acetanilide appeared more in its form after the hot water bath. The filtration through the Hirsch funnel went smoothly and the final product of acetanilide was completed. Our recrystallization yield was 50.7% when calculated.

 

Following the recrystallization procedure to create our acetanilide, we performed our TLC analysis. TLC, or thin layer chromatography, is a technique utilized when confirming the purity of compounds in an experiment with a silica gel plate. We took a commercial acetanilide by our TA, our own product of acetanilide and a sample of aniline provided to us. After soaking in the solvent system of EtAc/hexane, we placed our TLC plate under the UV light to check how far our compounds travelled. UV light is an excellent way to ensure we are obtaining uncontaminated and concise results. The CA and our P were just identical in RF value, as shown on the TLC plate above, with only a 0.011 point difference. The CA was at 0.056 and the P was just slightly above it at 0.067.The aniline being more nonpolar rose to the top of the plate compared to the acetanilides- which have a stronger polar pull. This is because the carbonyl group on the acetanilide make it polar compared to aniline, which has a peptide bond that makes it have a less polar structure. (2)

 

Our TLC plate completed, we used the remainder of the sample to find the melting point and the H NMR spectra. The melting point was within our literature range of 80- 150, for it was

Melting point was another method in purifying our compound and the value obtained showed that our product was indeed the acetanilide, for the structure melts at this temperature range due to the aromatic ring and the amide, or carbonyl group.

 

Next, when we went to further observe the H NMR spectra, we noticed an impurity around 2.5 ppm. The impurity was a small peak as seen on the spectra that represents the three hydrogen’s coming from the acetic acid, not including the hydrogen from the -OH. The spectra altogether had 3 functional groups from the peaks evaluated; an amide, an aromatic ring, and a methyl group. Signal A was representing the H signal from the N-H, B represented the H signalson the aromatic ring, and C represented the methyl H signals. This proves our structure of acetanilide was the product made. As shown in the table above, the H NMR literature values were close and consistent with the values obtained.

 

According to our H NMR of acetic anhydride in CDCl3, there was one signal produced from the acetic anhydride: the H signals that share a signal from the two symmetrical methyl groups. The aniline H NMR spectra when observed had a zero ppm signal. This signifies a TMS(tetramethylsilane) reference signal from the CDCl3; it makes sure the spectra begins at zero and it is a standard in chemistry for most spectra. (3)

 

The most crucial aspect of the experiment was to ensure that we made the correct product. We had to find the recrystallization/recovery yield, percent yield, theoretical yield and the starting mass and recovery mass.We found the starting mass by weighing the Erlenmeyer flask and putting the product in the flask and subtracted the difference. This was the starting mass, then the recovery mass was found after recrystallization. After recrystallization, we noticed the mass go down. This was supposed to happen due to the removal of impurities within the sample. Our recrystallization yield was 50.7%, which was the same as our percent yield. We determined this could possibly be from the mass that we started with and how it was equal to the theoretical yield (270mg), so dividing made us calculate the same percent yield. The product yield was originally 270mg and it did match the theoretical yield. It was supposed to be the limiting factor, but as we reviewed the data, we came to find that the product yield was equal to the theoretical due to the synthesis of acetanilide going through like it was supposed to, without any impurities.

 

Conclusion

In conclusion, the overall experiment was successful in synthesizing acetanilide through nucleophilic substitution and we were able to obtain the perfect sample. Our objective was to purify a synthesis of acetanilide with the techniques of micro pipetting, analytical balance, Recrystallization, filtration, melting point analysis and TLC. Recrystallization was used in order to increase the chance our sample was fully purified with no impurities to ruin our yields. Our findings showed that acetanilide was the product we obtained by the melting point value being within the literature range, the H NMR was shown to have the ppm of each signal within the literature range, and the TLC plate. The plate was especially significant in that it was able to show where the CA and P spots would raise to and if they matched then we were looking at a successful experiment (which we had).

In error, throughout the experiment we could have made some minor mistakes that would have interfered with the original reaction. We could have not left our product forming on the stirrer for 20 minutes like we were told and the product would not have become the snow- like consistency in which it became, leaving just the original reagent(s) we started with. During our preparation for TLC analysis we spilled our product of acetanilide. As this is human error, we could have lost a substantial amount of product that would have been a terrible loss for our TLC plate which would have not shown the same values we obtained had we not put more product than we needed in the vial. We successfully completed the experiment and synthesized acetanilide through purification and multiple analyses. Our yield shows we had a 50.7% yield for both recrystallization and percent yield as well.

 

REFRENCES

 

1. Libretexts. Recrystallization.

 

2. https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_ Maps/Supplemental_Modules_ (Physical_and_Theoretical_Chemistry)/Physical_Properti es_of_Matter/Solutions_and_Mixtures/Case_Studies/RECRYSTALLIZATION (accessed Jun 16, 2019).
3. https://study.com/academy/lesson/polar-and-nonpolar-covalent-bonds-definitions-and-examples.html (accessed Jun 18, 2019).

 

4. Yawaryawar 59051025; bonbon 12.6k104380; long 10.4k2144. Why is tetramethylsilane (TMS) used as an internal standard in NMR spectroscopy? https://chemistry.stackexchange.com/questions/47913/why-is-tetramethylsilane-tms-used-as-an-internal-standard-in-nmr-spectroscopy (accessed Jun 18, 2019).

 

5. https://study.com/academy/lesson/substitution-reaction-examples-in-organic-chemistry.html (accessed Jun 19, 2019).

 

6. Nucleophilic substitution. https://en.wikipedia.org/wiki/Nucleophilic_substitution (accessed Jun 19, 2019).