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lab 42...

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Haloform Oxidation of 4’-Methoxyacetophenone

Amira Lazizi CHEM 222 Section 02 Lab 04 Student ID: 40096525 Partner: Vicky Barrera

TAs Gianna Di Censo Cynthia Messina

Date performed: October 19, 2018 Friday, October 26th 2018

Results Observations -

Bleach was of a light-yellow colour The solution of bleach, 4’-methoxyacetophenone and tricaprylmethylammonium drops was mostly clear with drops of oil at the top We weren’t able to keep temperature at 60C (varied from 70C) After adding HCl (10 mL), the mixture wasn’t at a pH of 2, so we added more until the total of hydrochloric acid added was of 14 mL After hydrochloric acid was added, the mixture was milky and thick During melting point analysis, the temperature went over 195 C with no melting occurring.

Table 1: Physical properties of reagants Compound

Molecular weight (g/mol) Quantity Moles Boiling point (C) Melting point (C)

NaOCl (6%)

74.4

4’4methoxyacetophenone methoxybenzoic acid 150.2 152.2

Chloroform

119.4

45 mL 0.0362 mol -

1.502 g 0.01 mol 15426

0.890 g 0.0585 mol 280

62

-

38

185

-63.5

Table 2: Starch-iodine test results Time (min) 10

Temperature (C)

NaOCl excess?

Comments

70

No

15 20 25 30 35

58 58 55 60 60

Yes Yes Yes No Yes

White, Added 1 mL NaOCl Black fringe Black fringe Black fringe Black fringe Added acetone

Table 3: Raw data Mass of 4’methoxyacetophenone used (g) Mass of watch glass (g) Mass of watch glass + product (g) Mass of product obtained (g) Melting point range of product obtained (C)

1.508 42.603 43.493 0.890 185-1861

Table 4: IR analysis of product obtained Wavenumber (cm-1)

2982.22 1685.88 1603.36 and 1449.95 1178.79

Expected wavenumber range (cm-1) 3200-2700 1780-1650 1600 and 1500-1430 1250-1050

Intensity

Type of bond

Medium Very strong Strong; Medium

C-H sp3 C=O C=C Benzene ring

Strong

C-O

Calculations Moles of NaOCl mass = 45mL x 1g/mL x 6% = 2.7g NaOCl mass molar mass

=

2.700 g = 0.0362 mol of NaOCl 74.4 g /mol

Mass of product obtained Mass watch glass + product = 43.493 g Mass watch glass = 42.603 g watch glass ¿ Mass product=Mass watch glass+ product −Mass ¿

product =43.493 g−42.603 g ¿ Mass¿ ¿ 0.890 g

Theoretical yield mol 4 ' methoxyacetophenone × MW 4−methoxybenzoic acid= yield g 0.01 mol ×152.2 =1.522 g mol

4’methoxyacetophenone is the limiting reagent in this reaction. Moles of 4-methoxybenzoic acid obtained

mass molar mass

=

0.890 g 152.2 g/mol

= 0.00585 mol of 4’-methoxyacetophenone

Percent yield obtained % yield = ¿

experimental mass × 100 % theoretical mass

0.890 g ×100 %=58.5 % 1.502 g

Discussion Objective: The objective of this experiment was to convert 4’-methoxyacetophenone into 4methoxybenzoic acid using laundry bleach, which was 6% NaOCl in its aqueous form. Procedure: The first step was to add 45mL of 6% NaOCl and six drops of tricaprylmethylammonium to 4’methoxyacetophenone. The reason we use bleach (NaOCl) is to trigger the formation of chloroform, a haloform, by going through a base-catalyzed halogenation, a nucleophilic acyl substitution and as a final step, an acid-base reaction. Tricaprylmethylammonium acts as a phase-transfer catalyst and is used to make ions cross the phase boundary in the reaction.

The second step was to stir vigorously for 30 minutes in a 60C water bath. The reason we stirred was to make sure that the reaction occurred, and the temperature had to be kept at 60C as to avoid unwanted by-products. Starch-iodine tests were conducted all throughout the 30 minutes, to ensure sodium hypochlorite was in excess (positive tests make the paper turn black/blue), but we added acetone at the end to remove any of this excess until the starchiodine paper tested negative (no black/blue colour). We transferred the mixture into a separatory funnel and washed it with ethyl ether to remove chloroform and any other by-products of the reaction. We discarded of the top (oily) layer in the funnel as it contained most of the chloroform. A total of 14 mL of 3M HCl (hydrochloric acid) is added to the aqueous layer while stirring, so that the pH of the solution reached a value of 2, to cause a precipitation in the product. To purify the product obtained, we carried out a vacuum filtration and recrystallization with aqueous ethanol. The latter was used because the solubility of benzoic acid changes with temperature. We measured the mass of the product obtained, its melting point range and were given an IR spectrum of it.

Results: The IR spectrum results showed some of the expected peaks of 4-methoxybenzoic acid, but not all of them. The C-O, C=O and benzene ring bonds all showed up on the spectrum at respectively 1178.79 cm-1, 1685.88 cm-1, and both 1603.36 cm-1 and 1449.95 cm-1 for the benzene ring. However, the expected O-H alcohol bond from carboxylic acid which is broadly estimated at a range of 3300 cm-1 to 2500 cm-1 did not appear on our spectrum. This leads one to think the product obtained contains impurities or that the reaction wasn’t conducted properly. The mass of 4-methoxybenzoic acid obtained was 0.890g, and the percent yield was 58.5%. Loss of product during transfer and unreacted substances caused the yield to be so low. It was impossible for us to measure our melting point, as the product was too wet at the time. The temperature kept increasing way over the expected value of 185 °C, with no melting occurring. Another group provided us with their melting point for the purpose of this experiment. Their measured melting point range was 185-186 C, which indicates a very pure product, as 4methoxylbenzoic acid’s melting point is 185C and the range obtained is very small. The most important cause of error in this experiment is the fact that we were unable to keep the temperature at 60C during the stirring/heating step. It fluctuated a lot, going from under 50 to over 70C, which may have altered our results, caused impurities to form or the reaction not to carry out properly and be the reason why our IR spectrum doesn’t show peaks for alcohol carboxylic acid bonds. Analyzing our compound while it was still wet also probably led to incorrect results. Improvements could be to use more precise apparatus and to avoid human error by being more careful while controlling the temperature. Quantities of substances being measured precisely and instruments being clean are also vital to a successful experiment.

Conclusion In conclusion, the experiment was not a success since the formation of 4-methoxylbenzoic acid using 4’-methoxyacetophenone and laundry bleach might not have occurred, since the melting point and IR spectrum gave no reliable results allowing us to affirm so. The percent yield which was 58.5%, which is low.

References: 1. Kalem L. ; and partner Chem 222 Experiment 42: Haloform Oxidation of 4’Methoxyacetophenone. Done at Concordia University, Montreal, Quebec, October 19, 2018 2. Lehman, John W. “Operational Organic Chemistry”. Fourth ed. New Jersey: Pearson Education, n.d. Print. Oct 14 2018....