Conversion of the benzophenone (ketone)

At room temperature, the time necessary to complete the conversion of benzophenone (ketone) to diphenylmethanol was determined in this lab. To accomplish this inquiry, the reaction product was isolated and examined at various stages of reduction. Infrared spectroscopy provided a practical way of analysis. The experiment here focuses on the IR spectra of the starting material as well as the crude product at various periods of reduction. The spectra are studied and contrasted as well. It was discovered that the optimum time required to perform the decrease under reaction conditions is 2.5 minutes.

Introduction In general, the alcohols having the hydrogen adjacent to a group of hydroxyls (OH) can easily be oxidized to form a compound of carbonyl (Lederer 1982). Upon the oxidation, if the alcohol is primary, an aldehyde is produced, which is further oxidized to form the carboxylic acid (Eriksson 1988). On the other hand, the secondary alcohol’s oxidation will result in the formation of ketone. However, no problem is presented with further oxidation (Zimowski 2015). Even though several agents of oxidization are known and easily available in the field of organic chemistry, some of them are made of transitional metals which are often toxic and expensive (Roth 1993). In this case, such agents of oxidization present problems of disposal. However, there is an excellent alternative that involves the use of sodium hypochlorite (Abbot 1984). Sodium hypochlorite is environmentally friendly since it possesses lower toxicity.

Secondary alcohols can be oxidized by the use of common household bleach or aqueous sodium hypochlorite ketones (Office 2015). The presence of the acidic condition makes the reaction to occur rapidly. For this reason, it is believed that the actual agent of oxidization is hypochlorous acid, that the acid-base reaction between the acetic acid and the sodium hypochlorite generates (Hoare and Waters 1962). In trying to ensure the complete occurrence of the oxidation, one has to use an excess of sodium hypochlorite. Markedly, it is possible to vary the concentration of the sodium hypochlorite in the bleach. Also, the solution of the starch-iodide helps in performing the test for the excess hypochlorite (Deitrich 2011).

Figure 1: The Reaction of the Ketones with Sodium Borohydride to Produce Diphenylmethanol

In a solution that is acidic, hypochlorite oxidizes iodide to iodine. Afterward, the starch reacts with iodine for the production of the characteristic colour of the starch-iodine complex (Littler and Waters 1959). The reaction of the ketones with the sodium borohydride results in their reduction to secondary alcohols. It is possible to see the intensity of the peak of absorption of hydroxyl as it increases relative to that of the carbonyl peak that is original (Wells and Husain 1970). Such process is possible by comparing the crude reaction product’s IR spectrum at various intervals of time (Fridman 2004).

Experimental Procedure

Ethanol (10 ml) and benzophenone (0.005 moles, 1 gram) were added to a 250 ml conical flask. This mixture was swirled until it dissolved. In a separate small beaker, a solution of sodium borohydride (250 mg) was made in water (2 ml). Afterward, a mixture of ice water (80 ml) that contains 2M of hydrochloric acid (20 ml) was prepared in a 250 ml beaker before storing it in an ice bath. When the stopwatch was ready, the sodium borohydride solution was added in one go to the solution of benzophenone in the conical flask. Immediately, the timing was started for quenching the reaction by precipitating out the product of the crude reaction of the cold mixture of acidified water.

The contents of the conical flask were then transferred to a 250 ml separating funnel before washing it with the use of an aliquot of diethyl ether (50 ml). Subsequently, the layer of the aqueous was run into a clean beaker. At this time, the organic ether layer was collected in a conical flask. Again, the aqueous layer was replaced into the separating funnel and before re-extracting it with the use of a second fresh diethyl ether aliquot (50 ml). Furthermore, the spent aqueous layer was discarded and the ether layer combined in the separating funnel.

A fresh aliquot of distilled water (about 50 ml) was used to wash the ether layer, after which, the washing was removed. Also, the organic layer was transferred into a clean 250 ml conical flask. The organic layer was then dried over anhydrous sodium or magnesium sulfate. Afterward, the drying agent was filtered off through a fluted filter paper, and the filtrate was collected directly in a round bottom flask. Finally, the method of rotary evaporation was used to remove the ether solvent under the reduced pressure.

Results and Discussion

There are different reduction products (i.e., for 10, 30, and 2.5 minutes) in this lab. For the 2.5 minutes, the IR appears to have mainly two special frequencies. For example, there is no asymmetric stretch from 650 to 2,750 cm-1. Also, there is no symmetry stretch from 2,700 to 3,500. Clearly, the optimum time needed for effecting the reduction under the conditions of reaction used is 2.5 minutes. The other two graphs, for 10, and 30 minutes produces the almost similar spectrum. The IR for the 2.5 minutes induced medium peaks around 2,900 cm-1 which indicates the presence of C-H stretches. The peak of 1,709 shows carboxylic acid which probably shows C=O. The possibility of the low frequency is due to the resonance through the adjacent bond of C=C. This crude has a strong peak at 1,267cm-1.

Figure 2: The Structure of the Lithium Aluminum Hydride (Source: Morlock 2015)

Figure 3: The Reduction of Butanol using Lithium Aluminum Hydride

The name of the reaction product includes the aldehyde and the ketone. Also, the ethyl ethanoate is reduced to form ethanol (Becker and Beattie 1982). This ethyl ethanoate destroys the hydride during its reduction to ethanol. The alkaline condition is required for the reduction of the cyclohexene to form cyclohexane. Some of the reagents include the hydroxide and the hydrogen hydroxide. Phosphoric acid is only used as a catalyst. Finally, there has to be the presence of sodamide for the Pent-2-yne to be reduced to cis-pent-2-ene (Cova 1960). In the process of reduction, some of the reagents include the acetylene, methyl iodide, and the ethyl iodide.

Conclusion

In summary, the objective of the lab was achieved. It was possible to determine the time required for effecting the complete conversion of the benzophenone (ketone) to diphenylmethanol. It is now clear that there are various conditions and reagents that the lithium aluminum hydride needs to reduce some products as in the case of ethanol and ethanoic acid.

References

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