Acetanilide synthesis is a representative acetylation reaction commonly performed in organic chemistry experiments.
In general, acetanilide is synthesized by acetylating the amino group of aniline, and the obtained crystals are purified by recrystallization.
In reports, the melting point after recrystallization, melting-point range, yield, crystal appearance, contamination by impurities, drying condition, and other factors are discussed comprehensively.
In a discussion of acetanilide synthesis, it is not sufficient simply to write that “white crystals were obtained” or “the melting point was close to the literature value.”
It is necessary to explain why recrystallization increases purity, why the yield decreases, and what may be considered when the melting point is low or the melting-point range is broad.
Unreacted aniline, impurities derived from acetic acid or acetic anhydride, recrystallization solvent, insufficient washing, and insufficient drying are also important points for discussion.
This article clearly explains how to interpret the results of acetanilide synthesis experiments, how to think about the melting point and yield after recrystallization, sources of error, points for improvement, and discussion examples that can be used in reports.
Note:
This article is a reference intended to assist with discussions of results obtained in chemistry experiments at universities and similar institutions.
For the actual synthesis procedures, handling of reagents, heating, cooling, recrystallization, filtration, drying, waste-liquid disposal, and safety precautions, always follow the instructions in your university’s laboratory manual and those given by your instructor or TA.
- What Is an Acetanilide Synthesis Experiment?
- Main Items to Include in the Results
- Discussion of the Acetylation Reaction
- Calculation and Discussion of Yield
- Causes of Low Yield
- Discussion When the Yield Is Too High
- Purpose of Recrystallization
- How to Interpret the Melting Point After Recrystallization
- Causes of a Low Melting Point
- Causes of a Broad Melting-Point Range
- Comparison of Melting Points Before and After Recrystallization
- Why the Yield Decreases During Recrystallization
- Relationship Between Improved Purity and Reduced Yield
- Effect of Unreacted Aniline
- Effects of By-Products and Residual Reagents
- Effects of Insufficient Washing
- Effects of Excessive Washing
- Effects of Insufficient Drying
- Discussion Based on Crystal Appearance
- Discussion Using an IR Spectrum
- Effect of the Amount of Recrystallization Solvent
- Cooling Rate and Crystal Size
- Loss During Filtration and Transfer
- When the Result Can Be Considered Good
- Example Discussion When the Experiment Did Not Go Well
- How to Write Points for Improvement
- Difference Between a Superficial Discussion and a Good Discussion
- Examples of Expressions That Can Be Used in Reports
- Points to Check When Discussing Acetanilide Synthesis
- Summary
What Is an Acetanilide Synthesis Experiment?
Acetanilide is an aromatic amide in which the amino group of aniline has been acetylated.
In an acetanilide synthesis experiment, aniline is reacted with an acetylating agent to obtain acetanilide containing an amide bond.
Because the crude product obtained after the reaction may contain unreacted substances, by-products, solvents, and acidic or basic impurities, it is purified by recrystallization.
Because acetanilide is obtained as a solid, its purity can be readily evaluated by melting-point measurement.
If the melting point after recrystallization is close to the literature value and the melting-point range is narrow, relatively pure acetanilide may have been obtained.
Example Discussion:
In this experiment, the amino group of aniline is considered to have been acetylated, producing acetanilide.
Recrystallization of the obtained crude crystals may have removed some impurities into the mother liquor and improved the purity of the product.
If the melting point after recrystallization is close to the literature value, the target compound, acetanilide, can be judged to have been obtained with relatively high purity.
Main Items to Include in the Results
In the results of an acetanilide synthesis experiment, record not only the mass and yield of the product but also the appearance before and after recrystallization, melting point, melting-point range, and condition of the crystals.
In particular, the melting point after recrystallization is central to purity evaluation.
Main Items to Include in the Results
- Amount of aniline used
- Amount of acetylating agent used
- Limiting reagent
- Appearance of the crude product
- Mass of the crude product
- Type and amount of recrystallization solvent
- Appearance of the crystals after recrystallization
- Mass of the product after drying
- Theoretical yield
- Yield
- Melting point before and after recrystallization
- Comparison with the literature value
- Width of the melting-point range
- Analytical results such as IR spectra
Example of How to Write the Results:
The crude product obtained after the reaction was recrystallized, yielding white needle-like crystals.
The mass of the product after drying was ○○ g, and the yield calculated from the theoretical yield was ○○%.
The melting point after recrystallization was close to the literature value, and the melting-point range was relatively narrow.
From this, it is considered that impurities were removed by recrystallization and the purity of acetanilide improved.
Discussion of the Acetylation Reaction
In acetanilide synthesis, the amino group of aniline is acetylated.
Aniline is an aromatic amine, and acetylation of its amino group gives acetanilide with an amide structure.
Because the functional-group state differs between the starting material and product, the product can be confirmed by melting point, IR spectra, and similar analyses.
If the reaction is incomplete, unreacted aniline remains and affects the odor, melting point, spectrum, and purity of the product.
Therefore, formation of the target compound should be judged from multiple results rather than from appearance alone.
Example Discussion:
The amino group of aniline is considered to have been acetylated, producing acetanilide with an amide structure.
Unlike the starting material aniline, acetanilide is readily obtained as a crystalline solid and can be confirmed by melting-point measurement.
However, if unreacted aniline remains, the purity of the product decreases and may cause a lower melting point or a broader melting-point range.
Calculation and Discussion of Yield
In acetanilide synthesis, the theoretical yield is determined from the limiting reagent and compared with the mass of acetanilide actually obtained to calculate the yield.
Yield is a value indicating how much of the target product was obtained.
Yield (%) = Actual yield ÷ Theoretical yield × 100
However, in acetanilide synthesis, the target product may not be completely formed during the reaction, and some product may be lost during recrystallization, filtration, and washing.
Therefore, it is not unusual for the yield to be less than 100%.
Example Discussion:
The yield of acetanilide obtained in this experiment was lower than the theoretical value.
Possible causes include incomplete progress of the acetylation reaction, part of the acetanilide remaining dissolved in the mother liquor during recrystallization, and loss of crystals during filtration and transfer.
Therefore, the reduction in yield may have originated from both the reaction stage and the purification and recovery stages.
Causes of Low Yield
Causes of low yield in acetanilide synthesis are easier to organize by separating cases in which the reaction did not proceed sufficiently from cases in which the product was lost during recovery.
| Stage | Cause | Effect on Yield |
|---|---|---|
| Reaction | Incomplete acetylation | Amount of target product formed decreases |
| Reaction | Insufficient reaction time or temperature | Unreacted aniline remains |
| Side reaction | Starting material or product is consumed in another reaction | Amount of target product decreases |
| Recrystallization | Acetanilide remains in the mother liquor | Recovered amount decreases |
| Filtration | Fine crystals pass through | Actual yield decreases |
| Transfer | Adhesion to apparatus or spillage | Recovered amount decreases |
Example Discussion:
One major possible cause of the reduced yield is that part of the acetanilide remained dissolved in the mother liquor during recrystallization.
Recrystallization is effective for increasing purity, but because a certain amount of the target product also dissolves in the solvent, complete recovery is not possible.
Therefore, although purity improves after recrystallization, the recovered amount decreases and the yield may become lower.
Discussion When the Yield Is Too High
If the yield is too close to 100% or exceeds 100%, the measured mass may include components other than the target product.
In acetanilide synthesis, possible causes include residual water or solvent due to insufficient drying, unreacted aniline, by-products such as acetic acid, inorganic salts, and residual recrystallization solvent.
Even if the yield is high, low melting point, a broad melting-point range, residual odor, or extra peaks in the spectrum may indicate low purity.
Example Discussion:
One possible reason the yield was estimated to be high is insufficient drying of the product.
If water or recrystallization solvent remains on the crystal surface, the weighed mass includes components other than acetanilide.
Therefore, although the actual yield appears high, the purity of the product may be low.
Purpose of Recrystallization
The purpose of recrystallization after acetanilide synthesis is to remove impurities from the crude product and obtain acetanilide crystals of higher purity.
Recrystallization uses the property that acetanilide dissolves readily in the solvent at high temperature but less readily at low temperature.
Cooling causes acetanilide to precipitate as crystals while leaving some impurities in the mother liquor.
Example Discussion:
Recrystallization is considered to have removed impurities from the crude product into the mother liquor and improved the purity of acetanilide.
If the melting point after recrystallization approached the literature value and the melting-point range became narrower, this can be regarded as evidence of the purification effect.
On the other hand, because part of the acetanilide also remains in the mother liquor, the yield after recrystallization tends to decrease.
How to Interpret the Melting Point After Recrystallization
Because acetanilide is a solid, its purity can be evaluated by melting-point measurement.
Highly pure acetanilide is expected to have a melting point close to the literature value and a relatively narrow melting-point range.
If impurities are present, the melting point may decrease or the melting-point range may broaden.
In a report, it is preferable to write the melting point not as a single temperature but as the temperature range from the beginning of melting to complete melting.
Discuss whether the melting point is close to the literature value and whether the melting-point range is narrow.
Example Discussion:
The melting point of acetanilide after recrystallization was close to the literature value, and the melting-point range was relatively narrow.
This suggests that impurities were removed by recrystallization and the purity of the product improved.
However, because the structure cannot be completely determined from melting point alone, the result must be judged together with data such as the IR spectrum.
Causes of a Low Melting Point
If the melting point of acetanilide after recrystallization is lower than the literature value, impurities may be present.
If unreacted aniline, by-products, recrystallization solvent, water, or similar substances are contained in the crystals, the crystal lattice becomes disturbed and melting may begin at a lower temperature than for pure acetanilide.
Example Discussion:
One possible reason the measured melting point was lower than the literature value is the presence of impurities in the product.
If unreacted aniline, by-products, residual solvent, or similar substances are mixed in, the crystal lattice of acetanilide becomes disturbed and melting begins at a lower temperature than in the pure substance.
Therefore, a lower melting point provides a clue that the purity may still have been insufficient after recrystallization.
Causes of a Broad Melting-Point Range
If the melting-point range is broad, the sample may not consist of a single component and may contain multiple components.
Highly pure acetanilide melts over a relatively narrow temperature range, but if impurities are present, the temperature difference between the beginning and completion of melting becomes larger.
A broad melting-point range can be discussed as resulting from incomplete reaction, insufficient recrystallization, insufficient washing, insufficient drying, or contamination by impurities.
Example Discussion:
One possible reason the melting-point range was broad is that unreacted substances or by-products were mixed with the acetanilide.
When multiple components are present, their melting behavior overlaps, making it difficult to show a sharp melting point like a pure substance.
Therefore, a broadened melting-point range is considered to indicate that the purity of the product was insufficient.
Comparison of Melting Points Before and After Recrystallization
If melting points are measured before and after recrystallization, the purification effect can be discussed more clearly.
If the melting point approaches the literature value and the melting-point range becomes narrower after recrystallization, impurities are likely to have decreased.
On the other hand, if the melting point remains low or the range remains broad after recrystallization, recrystallization may have been insufficient.
| Change in Melting Point | Discussion |
|---|---|
| Approached the literature value | Purity may have improved |
| Melting-point range became narrower | Impurities may have decreased |
| Remained low | Impurities or solvent may remain |
| Range remained broad | Insufficient purification or insufficient drying may be involved |
Example Discussion:
Compared with before recrystallization, the melting point after recrystallization approached the literature value and the melting-point range also became narrower.
This is considered to be because recrystallization removed impurities such as unreacted substances and by-products and improved the purity of acetanilide.
On the other hand, because part of the acetanilide remained in the mother liquor during recrystallization, the yield may have decreased.
Why the Yield Decreases During Recrystallization
Recrystallization tends to improve purity while reducing yield.
Because acetanilide is not completely insoluble even at low temperature, part of it remains dissolved in the mother liquor after cooling.
Crystals may also be lost during filtration, washing, and transfer.
Therefore, a decrease in yield after recrystallization does not necessarily mean that the experiment failed.
It is easier to explain the result by considering that some of the target product was also lost during the purification operation used to increase purity.
Example Discussion:
One possible reason the yield decreased after recrystallization is that part of the acetanilide remained dissolved in the mother liquor.
Recrystallization improves purity by leaving impurities in the mother liquor, but a certain amount of the target product also dissolves in the solvent.
Therefore, recrystallization is effective for improving purity but tends to be accompanied by a decrease in yield.
Relationship Between Improved Purity and Reduced Yield
In acetanilide synthesis, recrystallization may improve purity while reducing yield.
If impurities are thoroughly removed, acetanilide is also more likely to be lost into the mother liquor or washing solution.
Conversely, if recrystallization or washing is insufficient in an attempt to maintain a high yield, impurities are more likely to remain.
Therefore, evaluation after recrystallization should consider not only whether the yield is high but also whether the purity is high based on the melting point.
Example Discussion:
Although the melting-point range became narrower after recrystallization, the yield decreased.
This result indicates that impurities were removed and the purity improved through recrystallization, while part of the acetanilide was lost into the mother liquor or washing solution.
Therefore, recrystallization may involve a trade-off between improved purity and reduced yield.
Effect of Unreacted Aniline
If acetylation is incomplete, unreacted aniline may remain in the product.
Remaining aniline affects the odor, melting point, spectrum, and purity of the product.
Aniline is a liquid, and if it contaminates acetanilide crystals, it may lower the melting point or broaden the melting-point range.
Example Discussion:
One possible reason the melting point was lower than the literature value and the melting-point range was broad is that unreacted aniline remained in the product.
If aniline is mixed in, the crystal lattice of acetanilide becomes disturbed and melting begins at a lower temperature than for pure acetanilide.
Therefore, residual unreacted aniline is one possible cause of decreased purity.
Effects of By-Products and Residual Reagents
In acetanilide synthesis, by-products and residual reagents may contaminate the product depending on the reaction conditions and workup.
For example, residual acetic acid, unreacted acetylating agent, acidic components, water, or recrystallization solvent may affect the melting point, yield, and crystal appearance.
If these substances are present, the yield may appear high while purity is low.
Discuss them in relation to results such as a low melting point, broad melting-point range, or wet crystals.
Example Discussion:
If acetic acid, unreacted acetylating agent, recrystallization solvent, or similar substances remained in the product, the weighed mass would include components other than acetanilide.
Therefore, the yield could appear high while the melting point decreases and the melting-point range broadens.
From this, yield and purity must be evaluated separately.
Effects of Insufficient Washing
If washing is insufficient, mother liquor, acidic components, unreacted substances, recrystallization solvent, or similar materials may remain on the crystal surface.
As a result, the mass after drying may become larger and the yield may appear high.
However, because impurities remain, the melting point may decrease or the melting-point range may broaden.
Example Discussion:
If washing was insufficient, mother liquor or unreacted substances may have remained on the surface of the acetanilide crystals.
In this case, the mass of the product includes impurities, so the yield may appear high.
On the other hand, contamination by impurities may lower the melting point and broaden the melting-point range, so insufficient washing is a cause of decreased purity.
Effects of Excessive Washing
Washing is necessary to remove impurities, but excessive washing may dissolve and remove part of the acetanilide in the washing solution.
In particular, the yield tends to decrease when a large amount of washing solution is used, when its temperature is high, or when a solvent in which acetanilide has some solubility is used.
Example Discussion:
One possible reason the yield was low is that part of the acetanilide dissolved in the washing solution during washing.
Washing is necessary to remove mother liquor and impurities, but the target product is also more easily lost when a large volume of washing solution is used or the temperature is high.
Therefore, it is important to perform only the minimum amount of washing required to remove impurities.
Effects of Insufficient Drying
If the acetanilide crystals are not sufficiently dried, water or recrystallization solvent remains on the crystal surface and the measured mass becomes larger than the actual mass.
As a result, the yield is overestimated.
Residual solvent may also affect melting-point measurement and may cause a lower melting point or a broader melting-point range.
Example Discussion:
If drying was insufficient, water or recrystallization solvent may have remained in the acetanilide crystals and caused the measured mass to be too large.
Therefore, the yield would be estimated to be higher than the actual value.
In addition, residual solvent affects the melting behavior of the crystals and may cause a lower melting point or a broader melting-point range.
Discussion Based on Crystal Appearance
Acetanilide is often obtained as white crystals, but a white appearance alone does not prove high purity.
If the crystals are wet, uneven in color, very fine and powdery, or retain an odor, impurities or insufficient drying should be considered.
Appearance should be used as supplementary information and evaluated together with melting point and spectroscopic results.
Example Discussion:
Because white crystals were obtained after recrystallization, there may have been little colored impurity.
However, colorless impurities or residual solvent are difficult to judge from appearance alone.
Therefore, the purity should not be determined from crystal appearance alone but should be evaluated together with the melting point, melting-point range, IR spectrum, and other results.
Discussion Using an IR Spectrum
If an IR spectrum is measured, absorptions characteristic of the functional groups in acetanilide can be confirmed.
Because acetanilide has an amide structure, absorptions derived from the amide carbonyl group and N-H are targets for discussion.
Because the functional-group state differs from that of the starting material aniline, spectral changes before and after the reaction can be compared.
Example Discussion:
If an absorption corresponding to the amide carbonyl group of acetanilide was observed in the IR spectrum, this supports the possibility that acetylation of aniline proceeded and the target product formed.
On the other hand, if absorptions derived from the starting material aniline remained strongly, unreacted aniline may have been mixed in because of incomplete reaction or insufficient purification.
Therefore, the IR spectrum provides a clue for judging formation and purity of the target product.
Effect of the Amount of Recrystallization Solvent
The amount of solvent used for recrystallization affects both yield and purity.
If too much solvent is used, more acetanilide remains dissolved in the mother liquor even after cooling, reducing the yield.
On the other hand, if too little solvent is used, the crude product may not dissolve completely and separation of impurities may be insufficient.
Example Discussion:
One possible reason the yield after recrystallization was low is that too much recrystallization solvent was used.
When a large amount of solvent is used, more acetanilide remains dissolved in the mother liquor even after cooling.
Therefore, the amount recoverable as crystals decreases and the yield may be reduced.
Cooling Rate and Crystal Size
In recrystallization, the cooling rate affects crystal size and purity.
Rapid cooling causes the degree of supersaturation to increase quickly, making it easier for many nuclei to form at once.
As a result, many small crystals form and may more readily trap mother liquor or impurities.
With slow cooling, a smaller number of nuclei have more time to grow, making it easier in some cases to obtain relatively large and highly pure crystals.
Example Discussion:
One possible reason the obtained crystals were fine is that cooling was too rapid.
Rapid cooling caused the degree of supersaturation to rise quickly and many nuclei to form at once, making it difficult for each crystal to grow large.
In addition, fine crystals tend to retain mother liquor and may lead to impurity contamination or a broader melting-point range.
Loss During Filtration and Transfer
Acetanilide crystals after recrystallization are recovered by filtration.
During this process, if crystals adhere to the filter paper or apparatus or are spilled during transfer, the recovered amount decreases.
Fine crystals may also pass through together with the filtrate.
Example Discussion:
One possible reason the yield decreased is that some acetanilide crystals were lost during filtration or transfer.
If crystals remained attached to the filter paper, beaker, glass rod, or other apparatus and were not recovered, the mass of the product after drying would become smaller.
Therefore, mechanical loss during recovery operations is also one cause of reduced yield.
When the Result Can Be Considered Good
A good result in acetanilide synthesis is indicated when white crystals are obtained after recrystallization, the melting point is close to the literature value, and the melting-point range is narrow.
Furthermore, if the yield is not extremely low and results corresponding to the amide structure are obtained in the IR spectrum or similar analyses, formation of the target product is more strongly supported.
Example Discussion:
The product after recrystallization was white crystals, the melting point was close to the literature value, and the melting-point range was relatively narrow.
This suggests that impurities were removed by recrystallization and acetanilide was obtained with relatively high purity.
Although the yield did not reach 100%, this is considered to be due to part of the target product remaining in the mother liquor during recrystallization and losses during filtration and washing.
Example Discussion When the Experiment Did Not Go Well
If acetanilide synthesis does not go well, causes can be considered from results such as low yield, excessively high yield, low melting point, broad melting-point range, wet crystals, remaining odor, or absorptions derived from the starting material remaining in the IR spectrum.
It is easier to write the discussion by separately organizing incomplete reaction, losses during recrystallization, insufficient drying, and contamination by impurities.
Example Discussion:
In this experiment, the melting point after recrystallization was lower than the literature value, and the melting-point range was also broad.
Possible causes include residual unreacted aniline, by-products, or recrystallization solvent in the product.
In addition, if water or solvent remained because of insufficient drying, this could also lead to a lower melting point and overestimation of the yield.
Therefore, the reaction conditions, recrystallization, washing, and drying operations are all considered to have affected the results.
How to Write Points for Improvement
In a discussion of acetanilide synthesis, including points for improvement as well as sources of error makes the report easier to organize.
Improvements are easier to organize by dividing them into improvements for allowing the reaction to proceed sufficiently, improvements for increasing purity, and improvements for increasing yield.
Improvements for Allowing the Reaction to Proceed Sufficiently
- Ensure an appropriate reaction time
- Maintain the temperature conditions specified in the laboratory manual
- Measure reagent amounts accurately
- Mix the reaction mixture sufficiently
- Check for unreacted substances after the reaction
Improvements for Increasing Purity
- Select an appropriate recrystallization solvent
- Use neither too much nor too little solvent
- Avoid rapid cooling and allow crystallization to proceed slowly
- Wash the mother liquor from the crystal surface appropriately
- Dry sufficiently before measuring the melting point
- Confirm purity using melting point and IR spectra
Improvements for Increasing Yield
- Reduce the amount of acetanilide remaining in the mother liquor
- Avoid losing crystals during filtration or transfer
- Do not use more washing solution than necessary
- Allow the crystals to precipitate sufficiently before filtration
- Adjust cooling conditions so that the crystals do not become excessively fine
Example of How to Write Points for Improvement:
To improve both yield and purity, the acetylation reaction must first be allowed to proceed sufficiently, followed by appropriate recrystallization conditions.
During recrystallization, using too much solvent causes acetanilide to remain in the mother liquor and lowers the yield.
On the other hand, because rapid cooling makes it easier for crystals to trap impurities, slowly cooling the solution and allowing the crystals to grow is effective for improving purity.
Difference Between a Superficial Discussion and a Good Discussion
In a discussion of acetanilide synthesis, simply writing that “the melting point was close” or “the yield was low” results in a superficial discussion.
Relating the results to recrystallization, loss into the mother liquor, unreacted aniline, impurities, and insufficient drying produces a more persuasive discussion.
| Superficial Discussion | Good Discussion |
|---|---|
| The melting point was close to the literature value. | Because the melting point after recrystallization was close to the literature value and the melting-point range was also narrow, impurities are considered to have been removed and the purity of acetanilide improved. |
| The yield was low. | Possible causes of reduced yield include incomplete acetylation, part of the acetanilide remaining in the mother liquor during recrystallization, and loss of crystals during filtration and washing. |
| The melting-point range was broad. | Possible reasons the melting-point range was broad include contamination by unreacted aniline, by-products, or residual solvent. When multiple components are present, the sample does not readily show a sharp melting point like a pure substance. |
Examples of Expressions That Can Be Used in Reports
The following expressions can be used when writing the results and discussion of an acetanilide synthesis experiment.
Adjust the necessary parts according to your own experimental results.
- The amino group of aniline is considered to have been acetylated, producing acetanilide.
- Because the melting point after recrystallization was close to the literature value, the purity of the product is considered relatively high.
- The narrow melting-point range provides a clue that the amount of impurities was small.
- Possible causes of the low melting point include contamination by unreacted aniline or residual solvent.
- Although recrystallization removes impurities, part of the acetanilide remains in the mother liquor, so the yield may decrease.
- Possible causes of reduced yield include incomplete reaction, losses during recrystallization, and losses during filtration and washing.
- If the yield is too high, the mass may have been overestimated because of insufficient drying or impurity contamination.
- If washing is insufficient, mother liquor or unreacted substances remain on the crystal surface and may reduce purity.
- Insufficient drying can cause overestimation of the yield and broadening of the melting-point range.
- Yield and melting-point results should be considered together so that the amount and purity of the product are evaluated separately.
Points to Check When Discussing Acetanilide Synthesis
Checking the following points before writing the report makes the discussion easier to write.
- Have you confirmed the limiting reagent and theoretical yield?
- Is the yield calculation correct?
- Have you considered the causes of reduced yield separately for the reaction and purification stages?
- Have you compared the melting point after recrystallization with the literature value?
- Have you related a broadened melting-point range to impurities?
- Have you explained the improvement in purity and reduction in yield caused by recrystallization?
- Have you considered contamination by unreacted aniline?
- Have you considered the effects of residual solvent and insufficient drying?
- Have you considered both insufficient washing and excessive washing?
- Have you avoided judging purity from crystal appearance alone?
- If an IR spectrum was measured, have you related the result to changes in functional groups?
- Do the points for improvement correspond to the sources of error?
Summary
In an acetanilide synthesis experiment, aniline is acetylated to obtain acetanilide.
The crude acetanilide produced is purified by recrystallization, and its purity is evaluated from the melting point and melting-point range after recrystallization.
If the melting point is close to the literature value and the melting-point range is narrow, relatively pure acetanilide may have been obtained.
On the other hand, because part of the acetanilide remains dissolved in the mother liquor during recrystallization, the yield tends to decrease.
Losses during filtration, washing, and transfer, incomplete reaction, contamination by unreacted aniline, and insufficient drying also affect the yield and melting point.
In a report, rather than writing “the melting point was close” and “the yield was low” separately, explain the relationship between improved purity and reduced yield caused by recrystallization.
A persuasive acetanilide synthesis report can be produced by relating the melting point, melting-point range, yield, crystal appearance, impurities, and drying condition.
