Final Lab Report - Alcohols
Essay by francesmanuel • November 7, 2015 • Thesis • 2,463 Words (10 Pages) • 1,729 Views
Alcohols are organic molecules containing a hydroxyl group (-OH). Phenols on the other hand are molecules that contain a hydroxyl group and are attached to a benzene ring. The structures of the two causes them to differentiate in chemical properties. Through performing different experimental tests, these chemical properties were verified and analyzed.
Alcohols may be oxidized by oxidizing agents such as chromate and dichromate ions. In this case, potassium permanganate was used because KMnO4 can be utilized to oxidize a wide range of organic molecules. Its chemical reaction with MnO4 depends on the organic contaminants present. In an acidic solution, MnO4 is reduced to a colorless +2 oxidation state of manganese (II) ion (See eq.1). On the other hand, MnO4 is reduced to a green +6 oxidation state of manganate ion when reacted with a basic solution (See Eq.2). Correspondingly, in a neutral solution, MnO4 is reduced to a brown +4 oxidation state of manganese dioxide (See eq3) (Wikipedia, n.d.). This was somehow validated by the results obtained from Table 1. NaOH, being a strong base, oxidized with MnO4, resulting in a color green reaction. Contrariwise, results have been slightly inaccurate. This is due to the absence of a colorless and brown color reaction in test tubes 1 and 3, which are a neutral and acidic solution, respectively; both resulting into a change of pink solution (Refer to Table 1).
Eq. 1 8 H++ MnO4− + 5 e− → Mn2+ + 4 H2O
Eq. 2 MnO4− + e− → MnO42−
Eq.3 2 H2O + MnO4− + 3 e− → MnO2 + 4 OH−
Table 1. Comparison of Oxidizing Conditions | |
Observations | |
1 (Ethanol + H2O + KMnO4) | >Initial Color: cloudy white >Final Color: pink |
2 (Ethanol + H2O + NaOH + KMnO4) | Formation of 2 layers: |
3 (Ethanol + H2O + H2SO4 + KMnO4) | Formation of 2 layers: |
Alcohols can be classified based on whether the alcohol carbon is attached to one, two or three alkyl groups as primary, secondary, or tertiary. This classification is important, because the different classes of alcohols react differently. Theoretically, it is stated that primary alcohols can be oxidized to either aldehydes or carboxylic acids depending on the reaction conditions (University of Arkansas, n.d.). With KMnO4 being the oxidizing agent, primary alcohols can be oxidized more efficiently to carboxylic acid since there will be no over oxidation occurrence in the reaction proven by the chemical equation:
[pic 1]Eq. 4
Similar applies with secondary alcohols that oxidize to ketones presented in the equation:
[pic 2]
Eq.5
Tertiary alcohols on the other hand cannot be oxidized because of the absence of hydrogen atoms in the alcohol carbon.
Another test is introduced to authenticate the premise claimed in the comparison of oxidizing conditions through the use of four compounds namely, ethanol, isopropyl alcohol, ter-butyl alcohol, and phenol, each representing primary, secondary, tertiary, and phenols, respectively. Similar to the initial test made in comparing oxidation reactions in either basic or acidic reaction, a positive reaction of oxidization shows a green result in color. It has been obtained from the experiment that test tubes 1 and 2 (ethanol and isopropyl alcohol, respectively), are oxidized (Refer to Table 2). This is proven by the change of color from clear to mint green for both test tubes. Thus, positive in reaction. This is reaction is supported by Equation 4, where Ethanol is oxidized to a carboxylic acid. Whereas, Isopropyl alcohol, is oxidized to a ketone (Eq.5). tert-butyl did not show any presence of green because of its tertiary characteristics. Phenol, on the other hand turned from salmon pink to brown also due to the positive reaction of oxidation. Phenols do not have any hydrogen atoms attached to the alcohol carbon making the reaction with oxidizing agents distinct from alcohols. Oxidation from KMnO4 of Phenols result to benzoquinones, as presented in the chemical equation:
[pic 3]
Eq.6
Table 2. Comparison Rates of Alcohol | ||
Observations | ||
Initial Color | Final Color (after adding H2SO4 and Potassium dichromate) | |
1 (With Ethanol) | Clear | Mint green |
2 (With Isopropyl) | Clear | Mint green |
3 (With Tert-butyl) | Clear | Orange |
4 (With Phenol) | Salmon pink | Brown |
Aside from the oxidizing rates, the presence of alcohol was also concluded through the Ceric Nitrate test. Ceric nitrate is also an oxidizing agent that reacts with alcohols and phenols. A positive test gives a red color of alkoxy cerium(IV) when ceric nitrate is reacted with alcohols, while phenols give a brown to greenish precipitate (California State University Northridge, n.d.) This was evident in the results presented in Table 3. ethanol, isopropyl, and tert-butyl are deduced to be alcohols because of its positive reaction. H2O on the other hand stands as a controlled variable for the comparison among the test tubes. This reaction can be justified by the equation:
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