Discussion: In this experiment a ketone, 9-fluorenone is reduced to and alcohol. The are two possible ways by which this reduction can occur. One is by a catalytic hydrogenation, this uses a catalyst such as palladium or nickel, hydrogen gas, and heat/pressure. This can reduced an alkane to alkene. This catalytic process is preferred in industrial practices because the cost is low in the long run and more importantly there is little to no waste expense. However, hydrogen gas is dangerous due to being very flammable/combustible. Therefore, a reducing agent will be used in this experiment instead.
There are multiple types of reducing agents that reduce different types of functional groups and thus selection of the proper reducing agent is crucial. Two major hydride reducing agents are sodium borohydride and lithium aluminum hydride. These two reagents produce a hydride ion, hence the name “hydride”. They are versatile in the types of functional groups they can reduce as well. However, proton sources are of concern when using hydride reducing agents because proton sources will reduce or destroy a reducing agent and as a result also produce hydrogen gas.
Therefore aprotic solvents are usually used to prevent proton sources from being present in the solvent. Lithium aluminum hydride and methanol is not an acceptable combination due to methanol being a proton source for the reducing agent, however, sodium borohydride and methanol is a useable combination. The reasoning behind this is that that the aluminum is bigger than boron, therefore the valence shell electrons are further away from nucleus which contains protons and neutrons. Thus, since there is less attraction between electrons and protons and electrons will be more readily given up.
This explains the importance of electronegativity in dealing with reducing agents. The electronegativity difference in sodium borohydride is approximately 0. 1 V and therefore is weaker than LAH, however, this means that there are functional groups that it cannot reduce such as esters and carboxylic acids whereas LAH can. Nonetheless, this means that sodium borohydride can be used to selectively reduce certain functional groups such as an aldehyde in the presence of an ester, as only the aldehyde would be reduced and the ester would be left alone.
It is also a much safer reducing agent, thus this is the reducing agent used to reduce 9-fluorenone. The initial product resulting from the addition of sodium borohydride to 9-fluorenone is the boroxide salt. It is important to note that one sodium hydride can reduce up to four 9fluorenones because the are four equivalent hydride ions for every sodium borohydrides. To create the alcohol a dilute sulfuric acid is added to release the final product. It is important to minimize contact of sodium borohydride with air so that the reducing agent is not destroyed.
The reaction can be observed as successful as 9-fluorenol is bright yellow, whereas 9-fluorenol is a white color. Approximately 100 mg of crude product is obtained through this experiment. Recrystallization occurs, however there is not one pure solvent that allows for recrystallization of 9-fluorenol. Thus, multiple solvents will be added together, water and methanol, the ratio of water to methanol must be determined for this to occur. Therefore, 1 mL of methanol will be added to the crude product in a test tube that is then taken to a boil in a water bath. Once boiling, water is added dropwise until the solution turns cloudy.
The water must be added at the same temperature as methanol. Precipitate should form around the droplet of water added that then dissolves. Once the precipitate stops dissolving. At this point if methanol is added it should dissolve, therefore, this point is the correct ratio of water to methanol. However, in this experiment the reaction is stopped once the solution is cloudy and methanol is not added to make the solution clear. Product analysis involves melting point, IR analysis, and percent yield. The IR spectrum should show the disappearance of a carbonyl group thus confirming the product.
An alcohol peak should not be present as the product is a solid and since solides typically have small hydrogen bonding, if one is present the product should be dried more. The reaction works well and thus percent yield should be around 70%, however, even small mistakes in microscale experiments can often cause a very low percent yield so typical percent yield is around 20-50%. Analysis: The IR spectrum must be evaluated to determine whether or not the product isolated is 9-fluorenol, in other words whether or not the IR spectrum obtained is consistent with what is expected in terms of functional group peaks and the fingerprint regions.
The functional group regions expected should most notably be aromatic carbon carbon double bond bending at around 1600-1700 cm-1, and there should also be a aromatic CH stretch at approximately 3030 cm-1. It is important to note that while there should be an alcohol present in the final product, since the product is a solid there will likely not be an OH peak present as solids have much less hydrogen bonding than do liquids.
The fingerprint region, which is a complex and messy regions that represents all the various benign and vibrations present in the product is evaluated against a reference IR spectra of 9-fluorenol to see if it matches up with in reason to confirm the product. Thus, using the reference IR spectra of 9-fluorenol it is expected that in the fingerprint region there should be high transmittance stretch around 600 cm-1 and a less high shorter peak at around 1050 cm-1.
In evaluating the functional group region of IR spectrum obtained, a sharp peak is observed at 1656 cm-1 which corresponds to the aromatic carbon carbon double bond stretching that is expected. There is also a small peak at 3017. 3 cm-1 which corresponds to the aromatic C-H stretch that is expected. There is also no presence of a peak that corresponds to carbonyl functional group, which would appear at around 1750 cm-1. There is no presence of an alcohol peak, as is expected in the IR of a solid alcohol compound such as 9fluorenol.
The fingerprint region of the IR spectra obtained shows a sharp peak at 687. 5 cm-1 as well as a relatively sharp peak at 1015. 58 cm-1. Thus, this peaks corresponds with the two most notably peaks of the fingerprint in the fingerprint region at 600 cm-1 and 1050 cm-1. There various other peak in the fingerprint region seem to align well although transmittance values obtained seemed to be higher than that of the reference IR. Nonetheless, the combination for the functional group region aligning with the expected peaks as well as the fingerprint region roughly aligning allows for the confirmation that the product isolated is 9-fluorenol.
The percent yield of the product is also taken to determine the relative success of the experiment. The amount of final product obtained was 0. 403, and the initial amount amount of product was. 908. Thus, the percent yield is (0. 403/0. 908)*100, or 44. 38%. This is relatively low percent yield as a good percent yield for this experiment is around 70%, however, considering the experiment is done at a microscale level a percent yield from 40-50% is typically seen due to the ease of mistakes and thus the percent yield is acceptable.
The melting point was taken using a melting point apparatus, thus a melting point of 151°C was observed. The actual melting point of 9-fluorenol is 155-157°C, therefore the melting point is within reason for confirmation of 9-fluorenol. Conclusion: The goal of this experiment was to carry out a reaction to produce 9-fluorenol from 9-fluorenone and to confirm the product through analysis using an IR spectrum and melting point. The IR spectrum functional group region aligned well with what is expected in 9-fluorenol as there were peaks at 1656 cm-1 and 3017. cm-1 indicating aromatic C-C double bond stretching and C-H stretching respectively.
There was also no presence of a carbonyl (ketone) group indicated by the IR spectrum. The fingerprint region also aligned within reason to the reference IR spectrum of 9-fluorenol. The melting point observed was 151°C when in relatively the melting point of 9fluorenol is 155-157°C. Therefore, with the combination of the IR spectrum that aligns with what is expected in 9-fluorenol as well as a melting point that aligns with 9-fluorenol melting point allows for the confirmation that the product isolated through this experiment is 9-fluorenol.
The error or variation in the melting point is likely due to observational error from the experiment, however, it is very close to the actual melting point. The percent yield of 44. 38% is low, however, this experiment was done at a microscale level so 40-50% yield is often seen due to small errors such as leaving a small amount product in the filter after vacuum filtration which can have a large impact of the percent yield. Overall, this experiment was carried out successfully as 9-fluorenone was transformed to 9-fluorenol as confirmed through IR spectroscopy and melting point.
