Exp 4 Chm556.docx

RESULT AND OBSERVATION: Mass of 3-Nitrobenzaldehyde 0.7501 g Volume of Acetophenone 0.600 mL Mass of filter paper + wet product 2. 2983g Mass of wet product 1.3545 g Mass of product used for second 0.5 g recrystallization Mass of filter paper + Mass of product after 1.4097 g second recrystallization Mass of product after second 0.4144 g recrystallization Melting point of 3-Nitrochalcone 143 ̊C

ii. H-NMR result for 3-Nitrochalcone

Signal

Concentration ,ppm

2HA,doublet

7.8

2HB,triplet

7.0

1HC,triplet

6.8

1HD,doublet (15.6 Hz)

5.0

1HE, doublet

4.7

1HF, singlet

8.9

1HG,doublet

8.7

1HH,triplet

8.1

1HI,doublet

7.5

iii. FTIR result for 3-Nitrochalcone Bond

Theoretical wavenumber (cm-1)

C=O Stretch (Ketone )

1760-1740 (sharp peak)

C=C Stretch (Alkene)

1600-1680 (sharp peak)

C=C Stretch (Aromatic)

1450-1600 (weak – several)

C-H (Aromatic)

3100-3000 (weak)

OBSERVATION: 

After 0.6 mL of Acetophenone and 4 mL 95% ethanol were added, the solution was changed into yellow solution. After 0.5 mL NaOH was added, the yellowish solution forming reddish yellow solution for a while, and then started solidified into milky orange precipitate. After adding with 20 mL hot methanol, pale yellow solution formed.

CALCULATION: Molar mass of acetophenone = 120g/mol Molar mass of 3-nitrobelzaldehyde = 151g/mol Molar mass of 3-nitrochalcone = 253g/mol Density of acetophenone = 1.03g/cm3

C7H5NO3 + C8H8O (3-nitrobenzaldehyde) (acetophenone)

Mol of 3-nitrobenzaldehyde 0.7501 g = 151 g

= 4.97x10-3 mol

C15H11NO3 + (3-nitrochalcone)

H2O

Mol of acetophenone 0.6mL x1.03g/mL = 120g/mol

= 5.15x10-3 mol Limiting reagent: 3-nitrobenzaldehyde since having least number of mole 1 mol of 3-nitrobenzaldehyde produce 1 mol of 3-nitrochalcone ∴ 3-nitrobenzaldehyde produce

1

= 1 x 4.97x10-3 mol of 3-nitrochalcone = 4.97x10-3 mol of 3-nitrochalcone

Theoretical mass of 3-nitrochalcone = 4.97x10-3 mol x 253 g/mol =1.2574 g Percentage yield cannot be be determined since the product was wet. Since the experiment only use 0.5 g of 3-nitrochalcone for second recrystallization, Percent Recovery of 3-nitrochalcone 𝐹𝑖𝑛𝑎𝑙 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑝𝑟𝑜𝑑𝑢𝑐𝑡

= 𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 x100 =

0.4144𝑔 0.5𝑔

x 100

= 82.88%

DISCUSSION: The synthesis of chalcone was carried out via crossed Aldol or Claisen-Schmidt condensation of commercially available Acetophenone and Benzaldehyde in the presence of NaOH as a base in ethanol (Islamoghul, 2009). The reaction was initiated by removal of a proton from the 𝛼-carbon of Acetophenone to form a resonance-stabilized enolate ion by the base. This was followed by the nucleophilic enolate attacks on the electrophilic carbonyl carbon of benzaldehyde resulting in a new carbon-carbon bond formation. This reaction joined the 𝛼carbon of acetophenone to the carbonyl carbon of benzaldehyde to form intermediate. The final

step of this reaction was protonation and deprotonation by hydroxide ion to form an 𝛼, 𝛼unsaturated ketone, chalcone or 1, 3-diphenylpropenone as a light yellow solid (Attarde, 2014). The reaction mechanism for chalcone synthesis:

In this experiment, the product of 3-Nitrochalcone can be formed into two which Cis-3Nitrochalcone or Trans-3-Nitrochalcone. However, the product can be determined into major product or minor product by H-NMR method. The Trans-3-Nitrochalcone was more stable than Cis-3-Nitrochalcone due to steric hindrance (Attarde, 2014). In Cis 3-Nitrochalcone, the hygrogens were presented side by side. This gives rise to steric hindrance between the C=C making it less stable. Whereas in trans 3-Nitrochalcone, the hydrogens were presented on opposite sides, so steric hindrance was minimised in this making it more stable. Therefore, theoretically the trans 3-Nitrochalcone will be the major product while cis 3-Nitrochalcone will be minor product.

From the NMR result the 1H doublet signal was observed with frequency of 15.6Hz. From the literature review, the frequency of signal for trans compound was between 12-18Hz, so that it was proven that the compound yield was trans-compound. This frequency was compared to ciscompound frequency that was lower, 6-12Hz. FTIR spectrum was used to confirm the 3Nitrochalcone. The functional groups that appeared were C=C stretch (aromatic) with 14501600cm-1, N=O stretch(Nitro) with 1300-1500cm-1, C=O stretch(ketone) with 1690-1740cm-1, C=C stretch(alkene) with 1600-1680cm-1 and C-H(aromatic) with 3000-3100cm-1. Ethanol was added into the reaction of 3-Nitrobenzaldehyde and Acetophenone because it has lower boiling point than the water and the by-product with impurities can dissolve in ethanol. When the ethanol is vaporized, the by-product together with the impurities will evaporate too and leaving only the pure product. The purity of the product yield can be confirmed, the melting point of the product were taken and been compared with the theoretical

value. The closer value of the experimental melting point product to the theoretical melting point range of 3-Nitrochalcone, the higher the purity of the product. The confirmation also been done by 1H NMR spectrum that will give the structure of the compound. Besides, NaOH was used as a base to attack the Acetophenone to become enolate which will attack 3-Nitrobenzaldehyde to form the product. The ice water was used to make the solution reached freezing point which formed crystal and can be weighed. Furthermore, in second recrystallization, hot methanol was used to dissolve any contamination of product to form the purest 3-Nitrochalcone. From the calculation, the limiting reagent was the 3-Nitrobenzaldeyde. The theoretical mass was calculated by referring to the mole of the 3-nitrochalcone. The percentage yield cannot be calculated because the product formed was in wet form which contained water but the purity of 3-Nitrochalcone can be tested from the second recrystallization product by using Cole-Parmer High Resolution Digital Melting Point Apparatus, 230 V. From the result obtained, the product were pure and not contaminated since the experimental melting point was 143°C while the theoretical melting point range of 3-Nitrochalcone was around 143-145°C (National Center for Biotechnology Information). The percentage recovery of 3-Nitrochalcone for second recrystallization was 82.88% which shows that almost whole 3-nitrochalcone was recovered back after dry process but 17.12% of 3-nitrochalcone was lost during the experiment was conducted. There are some precautions step when doing this experiment. Firstly, we must properly make sure that the solid we want to dissolved must be completely dissolved before proceeding with the next step. Next, we must filtrate the solution carefully and make sure that the filter paper not have any hole during filtration process. Then, we should handling the chemical in the fume hood because the chemical may be have bad smell and can be harmed . If there was a chemical spilled on our hands, wash our hand immedietly with water until the chemical was removed. Fot the error to be overcame in the future, it was a good idea to carefully conduct the experiment. We also need to to make sure the reactions between 3-Nitrobenzaldehyde and Acetophenone was fully reacted in order to recover the highest percent yield as possible. In order there was no error in weighing the product, the solid must be dry at least overnight to evaporate all the water moisture. Last but not least, the product must be washed thoroughly when transferring from conical flask to filter paper for filtering process in order to recover the highest yield of product.

CONCLUSION: In conclusion, the product yield from this experiment was 3-nitrochalcone that proven with the H1 NMR and FTIR spectrum. The percentage yield cannot be determined because of wet product but the percentage recovery of 3-Nitrochalcone can be calculated which 82.88% and the melting point of the product was 143 °C. REFERENCES: F. Islamoglu, A.Usta(2009); Determination of the protonation constants of some chalcones by the potentiometric method in non-aqueous solvents, 153-161 M. Attarde, A. Vora, A. Varghese and Y. Kachwala (2014). Synthesis and evaluation of chalcone derivatives for its alpha amylase inhibitory activity. Organic Chemistry, 10(5) National Center for Biotechnology Information. PubChem Compound Database; CID=5369664, https://pubchem.ncbi.nlm.nih.gov/compound/5369664 (accessed Oct. 20, 2018).