Dehydration of Alcohols

1 January 2017

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.

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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 85°C, making sure it did not go over 90°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 85°C, making sure it did not go over 90°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. . 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.

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