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Experiment 7 CHEM 613 Experimental Organic Chemistry 2013 Anastazija Ristovska

Post-Lab Haloform Reaction

The purpose of this experiment was to prepare benzoic acid from acetophenone using NaOCl, sodium hypochlorite, HCl, and NaOH. Acetophenone has the structural formula of an acetyl functional group attached to a benzene ring. The purpose of the reaction is to substitute the methyl group of acetophenone with a hydroxyl group. Therefore the experiment procedure will have the hard task of breaking only one carbon bond while leaving the rest intact, and then creating a carbon-hydrogen bond. The reaction is called a haloform reaction even though a halogen element is not present anywhere in the final desired product (benzoic acid) because a CHX3, in this case CHCl3 gas is released during a halogenation of a methyl ketone in the presence of base. The procedure consisted of adding 20ml 5% NaOCl solution to 560mg acetophenone. This step produced replaced the methyl group of acetophenone with covalently bound sodium monoxide NaO- unit. This step successfully severs the carbonyl carbon – methyl C-C bond and creates a carbon-oxygen bond. The reaction is C6H5-CO-CH3 + 3NaOCl  C6H5-COONa + CHCl3 + 2NaOH. Chloroform is released. The sodium hypochlorite solution is not miscible with acetophenone, and in order for this reaction to take place they must be heated while swirling in a heat bath. It took 42min for acetophenone to dissolve in sodium hypochlorite at 90°C. After it had dissolved completely, 30 drops of acetone were added in order to destroy any remaining sodium hypochlorite by forming sodium acetate with it (which was removed during purification). The next step is acidulation with hydrochloric acid; 37% HCl was added slowly until it was observed using litmus paper that the solution has turned acidic. Every drop of HCl added formed a white-yellowish precipitate. The container of the solution was moved to an ice bath to form even more of this precipitate which was then isolated using vacuum filtration. What happened during this step is a salt metathesis reaction: C6H5COONa + HCl  C6H5COOH + NaCl. The theoretic yield of benzoic acid was 514mg, and only 20mg were obtained. The percent yield was therefore 3.9%. There can be many theories why the reaction had such low yield, one of which is, in the first step which was the rate determining step, and was indeed a very slow step, the reaction was either carried out for too short, or the temperature was too low. The temperature was precisely controlled using thermometer, but perhaps increasing the temperature even more could have both increased the reaction rate as well as increased the yield. 1

The MS analysis of the starting organic reactant shows the molecular ion peak at 120m/z, and the strongest peak is at 105m/z. The 105m/z peak is due to the breaking off of the methyl group, leaving only a benzene ring (phenyl group) attached to a –C=O carbonyl group. The second strongest peak is at 77m/z and this is the peak of the benzene ring ion by itself. There’s also a peak at 43m/z from the fragment that occurs when only the benzene ring is removed from the molecule, leaving behind only the carbonyl and methyl groups bound together.

The first absorption we should be looking for in the IR spectral analysis of acetophenone is the characteristic carbonyl peak in the 1665-1760cm-1 area, and we do see it at 1695cm-1. At 3000-3100cm-1 we see the aromatic C-H stretches, and at 1600cm-1 the aromatic –C=C- in-ring stretches can be noticed. At 1760cm-1 the aromatic C-H ‘oop’ stretch is seen.

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The molecular ion peak in the benzoic acid mass spectrum appears at 122cm-1, whereas the strongest peak is at 105cm-1 and it comes from the fragment left over when the methyl group – carbonyl group bond is severed and the methyl group is cleaved off from the molecule. The third strongest peak is at 77m/z and it comes from the ion fragment that contains only a benzene ring with nothing else attached to it other than the five phenyl protons of benzoic acid.

The benzoic acid carbonyl peak is seen at 1695cm-1, the same position as in acetophenone. The aromatic C-H ‘oop’ peak is seen at 705cm-1 and in that area there is now only one peak as opposed to thee that were seen for acetophenone, so we assume that the two additional peaks in acetophenone came from the methyl group C-H bond vibrations. This time the aromatic C-H stretches in the 3000-3100cm-1 region are overlapped by a broad carboxylic acid O-H bond stretch from 2500cm-1 to 3200cm-1. 3

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