Dehydration of Alcohols Essay Example for Free

Dehydration of Alcohols Essay Abstract The dehydration of cyclohexanol to cyclohexene can be done through fractional distillation. Once the fraction has been collected it must then be dried. The dried distillate is finally tested to determine whether or not it has been dehydrated. The three tests used were infrared spectroscopy, Bromine chemical test and Bayer’s chemical test. The infrared spectroscopy showed a large narrow peak at 3062. 12(cm-1) and 3020. 71(cm-1) which indicates that there is a double bond present. To assure the results were correct the chemical tests were done. The Bromine test was found to be positive for cyclohexene. The OH group was removed from the cyclohexanol and replaced with a double bond found around 3062. 12(cm-1) and 3020. 71(cm-1) and the dehydration was successful. Introduction Fractional distillation can be used when trying to dehydrate alcohols. Dehydrating an alcohol consists of taking away an OH group. Fractional distillation separates the initial compound into separate compounds; depending on what their boiling point is. Cyclohexanol can be dehydrated to form cyclohexene. Infrared spectroscopy is used to analyze a compound and can give a breakdown of what chemicals the original mixture is composed of. An example of this is the long broad peak around 3200 (cm-1) which signifies an OH group in the compound. This technique is very useful to help determine what a compound is made of and it can also be used with NMR to give a chemical structure. Since infrared spectroscopy can be used to analyze a compound it can also be used to verify that you have the correct compound. Another way to do this is to use a chemical test. There are multiple chemical tests that can be used, one of them being the bromine test. A bromine test is used to verify whether an OH group is present or not. Another test is used with KMNO4 to test whether and alkene is present or not. Using both chemical tests and infrared spectroscopy to analyze the substance it will be clear if fractional distillation and the drying agent were able to work together in the process of dehydrating the alcohol. Materials and Methods For this experiment, 5. 0-mL of cyclohexanol were weighed and placed in a 25-mL recovery flask. A magnetic stir bar was added to the flask. 2. 5-mL of 9 M sulfuric acid was added to the same flask and mixture was swirled. The fractional distillation apparatus was set up with steel wool in the column. A 10-mL receiving flask was placed in an ice-water bath. Fractional distillation was started making sure to maintain the head temperature between 80 and 85Â °C, making sure it did not go over 90Â °C. Heating was stopped once the mixture turned dark brown and a deep green condensate formed. Distillate was then collected and transferred to a 25-mL Erlenmeyer flask. Anhydrous potassium carbonate was added with a spatula to the 25-mL Erlenmeyer flask. Flask was swirled occasionally for about 15 min while adding more anhydrous potassium carbonate until liquid no longer looked cloudy. The mixture left that was not distilled was neutralized by adding bicarbonate to the solution, slowly, until foam stops forming. Dried liquid was then transferred with a Pasteur pipet into a 10-mL recovery flask containing a stir bar for simple distillation. Another 10-mL recovery flask was used as the receiver and a calcium chloride drying tube was connected with a vacuum adaptor. The more pure compound was collected by maintaining heat from 80 to 85Â °C, making sure it did not go over 90Â °C. Distillate was weighed and percent yield of cyclohexene was determined. An infrared spectroscopy was run on the distillate by taking a drop of distillate and putting it in between two salt plates. Closed the salt plates with metal holders and then put it into the infrared spectroscopy machine. First an infrared spectroscopy was run on the cyclohexanol. Then an infrared spectroscopy was run on the cyclohexene. The Bromine chemical test was run by adding 2 drops of distillate to a test tube. 0. 1 M of bromine in dichloromethane was added to the same test tube. Then added drops of dichloromethane until color appeared if color disappeared the test would have been positive. If the color did not go away the test would have been negative. Finally a Bayer test was run by adding 2-mL of 95% ethanol to a test tube. Two drops of distillate were added to the test tube. Then KMnO4 was added drop wise until color persisted. Results Table 1. Mass of starting solution, sulfuric acid, and ending product formed. Solution| Mass (g)| Cyclohexanol| 4. 512| Sulfuric Acid| 3. 384| Cyclohexene| 1. 217| Table 2. Chemical tests done to determine whether or not the product was cyclohexene. Result seen by changes in color. Type of Test| Color of Starting Reactant| Color of Reactant plus Product| Bromine| Bromine was red| Mixture went from red to clear | Baeyer| KMnO4 was purple| Mixture went from purple to dark brown | Table 3. Infrared spectroscopy peak values representing different structures found for cyclohexanol and cyclohexene. Solution| Alcohol| Single Bonds (sp3 C-H)| Double Bonds(sp2 C=C)| Ring Structure| Cyclohexanol| Peak 13339. 25 cm-1| Peak 2-32930. 94cm-1, 2854. 63cm-1| N/A| Peak 51450. 92cm-1| Cyclohexene| N/A| Peak 8 and 112923. 83cm-1, 2658. 55cm-1| Peak 6-73062. 12cm-1, 3020. 71cm-1| Peak 281438. 15cm-1| The original weight of the cyclohexanol added was 4. 512 g. The original weight of cyclohexanol with sulfuric acid was 7. 896 g. The original weight of the sulfuric acid alone was 3. 384 g. The weight for the product, assumed to be cyclohexene, was 1. 217 g. The percent yield for cyclohexene was calculated to be 26. 97%. Cyclohexanol was distilled fractionally to produce 4-mL of cyclohexene at 88? C. The original cyclohexanol was put through infrared spectroscopy and was found to have a large broad band at 3339. 25(cm-1) indicating the presence of an OH group, large narrow bands at 2930. 94(cm-1) and 2854. 63(cm-1) indicating single bonds between carbon and hydrogen, and a large narrow band at 1450. 92(cm-1) indicating a ring. The cyclohexene was put through infrared spectroscopy which showed that there was no OH group now. This time there was a double bond between carbons at 3062. 12(cm-1) and 3020. 71(cm-1), single bonds between hydrogen and carbon at 2923. 83(cm-1) and at 2658. 55(cm-1), and a ring at 1438. 15(cm-1). The bromine chemical test gave a positive result for cyclohexene after one drop of dichloromethane was added, which changed the liquid from a red color to a clear color. The Bayer test made the substance stay purple after 1 drop showing it was negative for an alkene. Doing the bromine chemical test and the Bayer test on cyclohexanol gave negative results for both. Discussion The fractional distillation was used to dehydrate cyclohexanol collected fraction allowed it to be separated and then was dried. Only 4-mL of cyclohexene was collected from the distillation. Infrared spectroscopy was then used to determine whether the substance retrieved from the distillation was dehydrated and had turned to cyclohexene. Looking at the infrared spectroscopy of the distilled substance there was no broad peak which signifies that there is not an OH in the substance anymore and the substance is not cyclohexanol anymore. To make sure the substance was cyclohexene two different chemical tests were given. The bromine test had a positive result after 1 drop. The Bayer test had a negative result after one drop was added. There was a discrepancy between the two tests but by viewing the IR we can conclude that the substance was no longer cyclohexanol. This could be attributed to error such as the cyclohexanol not being distilled correctly, leaving impurities. The fractions may have been heated too quickly and the fractions may have mixed. There may not have been enough drying agent added to the mixture. Some future possible changes to the experiment would be to have more time to not feel rushed. This way it would be easier to heat more slowly and make sure that everything is clean leaving little to no impurities.