8/14/2019 exp 22.pdf

http://slidepdf.com/reader/full/exp-22pdf 1/12

Fred Ernsberger

Chem 203, section 2

TA: Travis

Lap Report 6

Due 10/20/2010

Infrared and Mass Spectrum Analyses of Distillation products of Acid-catalyzed

Elimination Reactions of 2-Methyl Cyclohexanol and 4-Methyl Cyclohexanol

8/14/2019 exp 22.pdf

http://slidepdf.com/reader/full/exp-22pdf 2/12

Ernsberger 2

The purpose of this experiment was to perform an acid catalyzed elimination reaction of a

Cyclohexanol, as well as distillations and analyses of the product(s). Several runs of steam distillations

were used to help purify and increase the yield of the reaction. Mass Spectrum (MS) and infrared

spectrum (IR) analyses were used to determine the identity of the products and their relative abundances.

Purification of products formed from elimination reactions of secondary alcohols can be difficult

to achieve. The reason being the two products have very similar chemical properties. The only difference

 between them is where the double bond forms. Figure 1. shows how the bond can be formed on

neighboring bonds. When the hydrogen ion interacts with the alcohol group, it pulls the lone pair of

electrons off and forms water. This single molecule elimination reaction causes the water molecule to

separate from the molecule leaving behind a positively charged carbon atom. Since this molecule is

unstable (due to the carbocation), there will be bond rearrangements to establish stability. This will cause

the hydrogens on neighboring carbons to lose their bond. This allows for the formation of a double bond.

Since there are two neighboring carbons with hydrogens, both of them will be inclined to form double

 bonds in this manner. For the 2-methyl cyclohexanol there are two main products; methyl cyclohexene

and 3-methyl cyclohexene. Due to the possible substitutions, the 3-methyl cyclohexene is the most likely

substitution. This is due to the two chances (two hydrogen bonds) for substitution on the third carbon

from the methyl. The 1-methyl cyclohexene only has one possible substitution, the hydrogen attached to

the same carbon as the methyl group. Therefore it is expected that the 3-methyl cyclohexene would be

twice as likely as the as the 1-methyl cyclohexene. The expected ratio would be 66% 3-methyl

cyclohexene to 33% 1-methyl cyclohexene. The best way to remove the product is to distill it out of the

solution. As the product is removed from reaction, it will push the equilibrium to produce more products

according to Le Chatelier's principle. This will increase the yield of the product and will remove more of

the reactant from the organic layer. Thus when aqueous layer is removed there should be a higher

concentration of the products. Once the products are formed a mass spectrum and infrared spectrum

analysis can prove to be useful tools for determining the identity of the products and their ratios. The

8/14/2019 exp 22.pdf

http://slidepdf.com/reader/full/exp-22pdf 3/12

Ernsberger 3

mass spectrum allows the user to determine the molecular weight of the products and the mass of some of

the fragments. Thus a molecule can have a distinct molecular weight and molecular weight for its

fragments. The relative area of the peaks corresponding to the molecules and their fragments can show

the proportion of all of the components. The infrared analysis allows the analysis of molecular bonds by

irradiation with electromagnetic energy. When the bonds are irradiated they only accept a certain

frequency of radiation which then gives off a distinct infrared spectrum. Thus by interpreting the reaction

to the radiation the functional groups of the molecule can be determined. If the infrared spectrum (IR

spectrum) does not have a peak in the 3400-3650 cm-1

 range then there is no alcohol left and all of the

 products have been converted.

Materials And Methods

Synthesis of Methylcyclohexenes:

Mixed 15ml of 4-methylcyclohexanol and 4 ml of 85%phosphoric acid. Used the Hayden McNeil

setup for a steam distillation apparatus (Hayden McNeil et. al. page 139-140,145), distilled the heated

mixture until there were only a few millimeters of solution left. The temperature was not allowed to

exceed 120 degrees centigrade. A separatory funnel was used to drain off the aqueous layer. Then this

was washed twice with 5ml of saturated sodium chloride and twice again with 10 ml of .5M sodium

 bicarbonate. Then the organic layer was allowed to dry over anhydrous sodium sulfate for 10 minutes.

Purification of Methylcyclohexenes:

The product from the synthesis was then distilled again using the Hayden McNeil apparatus

(Hayden McNeil et. al. pg 139-140,145). The product was collected when the temperature stabilized

around 70 degrees Celsius. The distillation was not run to dryness.

8/14/2019 exp 22.pdf

http://slidepdf.com/reader/full/exp-22pdf 4/12

Ernsberger 4

Results:

Percent yield for the individual products based on GC/MS analysis:

Table 1: Relative abundance of products from 4-methyl cyclohexanol reaction. 

3-Methyl 1-Cyclohexene 16.5%

4-Methyl 1-Cyclohexene 16.5%

1- Methyl 1-Cyclohexene 38%

Table 1: Summary of the percent abundance from figure 3 A and B. Percent abundance readings from a

Gas chromatography analyses of an acid-catalyzed elimination reaction of 4-methyl cyclohexanol. The

synthesis reaction and purification was run with the steam distillation set up from the Hayden and McNeil

lab notebook pages 139-140,145. 

Table 2: Relative abundance of products from 2-methyl Cyclohexanol reaction: figure 5 A,

B, and C 

3-Methyl 1-Cyclohexene 34% figure 5c

Methylene Cyclohexane 21 % figure 5b

1-Methyl 1-Cyclohexene 42% figure 5a

Table 2: Summary of the percent abundance from figure 5 A, B, and C. Percent abundance readings from

a Gas chromatography analyses of an acid-catalyzed elimination reaction of 2-methyl cyclohexanol. The

synthesis reaction and purification was run with the steam distillation set up from the Hayden and McNeil

lab notebook pages 139-140,145.

Table 3: Percent yield values from 4-methyl hexanol products:

RT Value area total area percent

3.47 8567 11291 8567/11291= 75.9

4.17 774 11291 6.8

9.15 1950 11291 17.3

Table 4: Percent yield values from 2-methyl hexanol products:

RT Area Total area Percent yield

3.58 685 11681 5.864

4.34 10708 11681 91.6716.06 165 11681 1.41

16.34 123 11681 1.053

8/14/2019 exp 22.pdf

http://slidepdf.com/reader/full/exp-22pdf 5/12

Ernsberger 5

Figure 1. Synthesis of 1-Methyl Cyclohexene and 3-Methyl Cyclohexene from 2- Methyl

Cyclohexane.

The addition of hydrogen to the mixture draws off the lone pair of electrons from the oxygen on the hydroxyl group.

When this happens water is formed and the bond holding the water molecule to the cyclohexane breaks. From there,

the reaction proceeds in two possible directions. With a positive charge formed on the second carbon in the ring, one

of the hydrogens loses its bond which allows the formation of a double bond. This causes bond between either the

first and second carbon, or the second and third carbon.

8/14/2019 exp 22.pdf

http://slidepdf.com/reader/full/exp-22pdf 6/12

Ernsberger 6

Figure 2. GC Analysis of the Relative Abundance of products and reactants of acid-catalyzed

elimination of 4-methyl Cyclohexanol 

The above figure shows a gas chromatography analysis of the products and reactants from an acid-catalyzed

elimination of 4-methyl Cyclohexanol. The products were synthesized with a steam distillation apparatus from the

Hayden McNeil Lab book. The products were then purified at a constant temperature to give the final distillate.

Percent yield of all of the products was determined by subtracting the starting alcohol material and dichloromethane

 percentages from 100 percent. Data from Group 2 and 3 (Chem 203, Fall 2011).

8/14/2019 exp 22.pdf

http://slidepdf.com/reader/full/exp-22pdf 7/12

Ernsberger 7

Figure 3 (A and B). GC Analysis of Relative Abundance of the products for an acid-basedelimination reaction of 4-methylcyclohexanol.

A.

8/14/2019 exp 22.pdf

http://slidepdf.com/reader/full/exp-22pdf 8/12

Ernsberger 8

B.

Figure 3 A and B show the Gas chromatograph analysis of the acid based elimination of 4-methyl Cyclohexanol.

The relative abundance of each of the products and their fragments can be determined from the figures. The products

were synthesized with a steam distillation apparatus from the Hayden McNeil Lab book. The products were then

 purified at a constant temperature to give the final distillate. Data from Group 2 and 3 (Chem 203, Fall 2011).

8/14/2019 exp 22.pdf

http://slidepdf.com/reader/full/exp-22pdf 9/12

Ernsberger 9

Figure 4. GC Analysis of the Relative Abundance of products and reactants of acid-catalyzed

elimination of 2-methyl Cyclohexanol 

The above figure shows a gas chromatography analysis of the products and reactants from an acid-catalyzed

elimination of 2-methyl Cyclohexanol. The products were synthesized with a steam distillation apparatus from the

Hayden McNeil Lab book. The products were then purified at a constant temperature to give the final distillate.

Percent yield of all of the products was determined by subtracting the starting alcohol material and dichloromethane

 percentages from 100 percent. Data from Group 2 and 3 (Chem 203, Fall 2011).

8/14/2019 exp 22.pdf

http://slidepdf.com/reader/full/exp-22pdf 10/12

Ernsberger 10

Figure 5 A, B, and C. GC Analysis of Relative Abundance of the products for an acid-basedelimination reaction of 2-methylcyclohexanol 

A.

B.

8/14/2019 exp 22.pdf

http://slidepdf.com/reader/full/exp-22pdf 11/12

8/14/2019 exp 22.pdf

http://slidepdf.com/reader/full/exp-22pdf 12/12

Ernsberger 12

cyclohexene, 5.864% 3-methyl cyclohexene, 1.41% methylene cyclohexane (based off table 4 and 2). The

fourth product was the original alcohol. There were two products that were not shared between the two

elimination reactions. Methylene cyclohexane was only synthesized through the 2-methyl cyclohexnol

reaction (table 2). Whereas, 4-methyl cyclohexene only formed from the 4-methyl cyclohexanol reaction

(table 1). Given the results, it would be advisable to only use either 2-methyl cyclohexanol or 4-methyl

cyclohexanol if the goal would be the formation of their respective unique products. If either the 3-methyl

cyclohexene or the 2-methyl cyclohexene are the desired product, then 2-methyl cyclohexanol would be

the advised starting reactant, it has a higher overall percent yield and specific yield for the two common

 products. Some of the problems with isolating and purifying the products came from the setup of the

steam distillation apparatus. The temperature was difficult to control, often it would require temperatures

close to the 120 degree limit in order to get the distillate to travel to the condenser tube without

condensing too soon and dripping back down into the heated mixture. However, when the temperature

rose to the upper limit of 120 degrees, the solution ran the risk of running a heavy boil which could affect

the quality of the product. If the temperature was too low, no distillate would form at all. Future

experiments should use a longer condenser tube with a smaller diameter. This would increase the cooling

surface area to heated vapor volume ratio. This would allow for a faster cooling of the distillate which

may increase the speed of the system.