Isomers of butanol

Comparison of Three Isomers of Butanol

Introduction
An alcohol’s reactivity is determined based on the attachment of their hydroxyl functional group. The location of this hydroxyl functional group will impact the molecular structure of the alcohol, making it either primary (1° ), secondary (2° ), or tertiary (3° ). The purpose of this experiment is to observe and predict the reactions that take place between all three alcohols and an oxidizing agent, as well as to test our theories of how the molecular structure affects the chemical properties of the three isomers of butanol. I predict that the primary, secondary and tertiary alcohols will undergo substitution reactions, but only primary and secondary alcohols will undergo oxidation reactions due to their chemical properties and the theories learned in class.

Procedure

Three test tubes were placed in a test-tube rack. A clean eye dropper was used for each alcohol and 4 drops of 1-butanol were placed in the first tube; 4 drops of 2-butanol were placed in the second tube; and in the third tube, 4 drops of 2-methyl-2-propanol were placed. After the 4 drops of each alcohol were placed in the test tubes, the next step was to add 10 drops of concentrated hydrochloric acid (HCl) to each of the three test tubes. The mixtures were shaken very gently and the tubes were left to stand for 1 min while they were observed for evidence of cloudiness. Three more test tubes were set up for each alcohol to observe the reaction between the three alcohols and the KMnO4 solution. For each tube, 2ml of KMnO4 solution were carefully added then shaken gently. The test tubes remained standing for 5 min, with occasional shaking. After allowing adequate time for the reactions to occur, the test tubes were observed to determine if there was any colour change. Results

Table 1: Reactions of Alcohols with Lucas Reagent and KMnO4
Oxidizing Agent1-butanol (Primary Alcohol)2-butanol (Secondary Alcohol)2-methyl-2-propanol (Tertiary Alcohol)

Lucas
Reagent-Not cloudy after 5 minutes
-Not cloudy after 15 minutes
-Not cloudy after 5 minutes
-cloudy after 16 minutes-Turns cloudy
immediately
KMnO4-Very slow reaction
-Turns into dark purple
-Very quick reaction
-Turned from purple to brown instantly-No Reaction
-Remains the same colour (purple)

Table 2: Reactions of the Alcohols With the oxidizing agent 1 butanol (substitution reaction)
2 butanol
(substitution reaction)
2-methyl-2-propanol
(Substitution Reaction)
1 butanol (oxidation reaction)

2 butanol
(oxidation reaction)

2-methyl-2-propanol
(oxidation Reaction)

As observed in Table 1, when the primary alcohol was placed in the Lucas Reagent the mixture did not turn cloudy after five, and fifteen minutes. When the primary alcohol was placed in the KMnO4 solution, there was a very slow reaction and the mixture turned dark purple. When the secondary alcohol was placed in the Lucas Reagent, it turned cloudy after sixteen minutes. When the secondary alcohol was placed in the KMnO4 solution, there was a very quick reaction that turned the mixture from purple to brown. When the tertiary alcohol was placed in the Lucas Reagent, it turned cloudy immediately. When the tertiary alcohol was placed in the KMnO4 solution, there was no reaction as expected and the mixture stayed purple as it was before. As the catalyst that provided the reaction changed, the rate at which the reactions occurred also changed. Discussion

As seen in Table 1, each of the alcohols reacted very differently when mixed with a Lucas Reagent, and when mixed with KMnO4. The explanation for this is that the hydroxyl group on alcohols relates to their rate of reactivity. When the alcohols react with the Lucas Reagent, they produce an alkyl halide and water. The solubility of the resulting alkyl halide from the reaction is what determines the rate of reactivity. The catalyst that was used also affected the rate of the reaction, which I think is a result of the solubility of the Lucas Reagent and the KMnO4 solution with the alcohols. From theories studied in class, the results that took place were very accurate since the reactions happened almost exactly as they should have due to their chemical equations (see Table 2 for reactions).

The location of the hydroxyl functional group is what impacts the rate at which they react, and it also determines what type of alcohol it is. This difference in molecular structure of the alcohols is what regulates its chemical properties and therefore the colour of the products and speed of the reaction. The oxidation of alcohols provides a great way of carrying out a qualitative test for different types of alcohols because there is a clear and distinct colour change that is observable. If scientists are trying to determine whether any given alcohol is a primary, secondary, or tertiary alcohol, they can oxidize the alcohols with some form of a catalyst and be able to separate the alcohols from one another. This type of test is also easily done with students because the procedures are easy and fast so it is a good way of determining chemical and physical changes from the observable reaction in a classroom environment.

The sources of error in this lab could have been the time that we waited for the reaction to occur. For example, when we were observing the primary and secondary alcohols, we were limited by the duration of the lab and had to make conclusions based on what we saw in a short amount of given time. If we were given more time to observe the reactions, the results could have been different. Another source of error is that the original samples from each mixture could have been contaminated as people tried to use the eyedropper,which in return can affect the results of the lab.

Another source of error was the measurement of the quantity of each mixture. If the quantities were off by even a small amount, this could have affected the results. Also if the temperature and humidity of the room are different than the intended values, this may affect the results. My prediction based on the theories learned in class was correct in that the primary, secondary and tertiary alcohols will undergo substitution reactions, but only primary and secondary alcohols will undergo oxidation reactions due to their chemical properties and their molecular structures.