new diels sdfsdfsd diels-alder synthesis lab report

7/22/2019 New Diels Sdfsdfsd Diels-Alder Synthesis Lab Report

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Synthesis of the Diels-Alder Adduct

Purpose: To investigate the methods behind Diels-Alder chemistry through the synthesis of 4-

cyclohexene-cis- 1,2-dicarboxylic anhydride from butadiene sulfone and maleic anhydride. By using

a hands-on approach through laboratory synthesis, I hope to gain a better understanding of theconcepts governing Diels-Alder reactions.

Theory: The Diels-Alder reaction is a cycloaddition reaction that occurs between a conjugated

diene, a molecule with two alternating double bonds, and dienophile, an alkene, to form rings and

bicyclic compounds. Because it involves the interaction of four electrons that are supplied by the

diene and the two electrons supplied by the dienophile, the Diels-Alder reaction is often called [4 +

2] cycloaddition. In the reaction, two new bonds are formed and one bond is formed at the

expense of two bonds, which results in a cyclic product. Diels-Alder reactions are pericyclic

reactions, which are ones that take place in a single step, without intermediates, and that involve the

flow or redistribution of bonding electrons. The reaction proceeds through a cyclic transition state

and is concerted, meaning bonds in the transition state are simultaneously made or broken. The

Diels-Alder reaction is facilitated when the dienophile is the substituted with electron-withdrawing

groups such as nitriles, amines, and carbonyls and when it reacts with dienes that contain electron-

donating groups like alkyls and alkoxys groups.

Diels Alder reactions have unique characteristics and requirements. First, they are

stereospecific, meaning cis-alkenes form cis-substituted products and trans-alkenes form trans-

substituted products. The diene undergoes syn addition to the dienophile, and two new carbon-

carbon sigma bonds are formed on the same face of the diene ordienophile. Because Diels-Alder

reactions are stereospecific, the configuration of the dienophile is always retained in the product.

Secondly, the diene must acquire the s-cis conformation in order for a Diels-Alder reaction to take

place; those locked in the s-trans conformation cannot take place. The result of a Diels-Alder reaction

involving a cyclic diene is a bicyclic structure. Furthermore, dienes locked in the s-cis configuration,

such as those in rings, will react faster than those able to assume both s-cis and s-trans

configurations, such as those in open chains.

In this experiment, we applied the Diels-Alder reaction concepts to synthesize 4-

cyclohexene-cis-1,2- dicarboxylic anhydride from butadiene sulfone and maleic anhydride.The first

step was the generation of the butadiene in situ from butadiene sulfone. This was accomplished
http://web.chem.ucla.edu/~harding/IGOC/D/diene.htmlhttp://web.chem.ucla.edu/~harding/IGOC/D/dienophile.htmlhttp://web.chem.ucla.edu/~harding/IGOC/D/dienophile.htmlhttp://web.chem.ucla.edu/~harding/IGOC/D/diene.html


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through the heating, and butadiene sulfone decomposed into cis 1,3-butadiene and sulfur dioxide gas.

The reaction and balanced chemical equation for this step are shown below:

Step 1Decomposition of Butadiene sulfone to form 1,3-butadiene & sulfur dioxide

C4H6SO2C4H6+SO2

Sulfur dioxide gas and excess 1,3-butadiene are distilled out during the reflux process. The

1,3- butadiene still present in the mixture then reacts with maleic anhydride to form 4-cyclohexene-

cis- 1,2- dicarboxylic anhydride. This reaction and balanced chemical equation are shown below:

Step 2F ormation of 4-cyclohexene- cis- 1,2- dicarboxylic anhydride

C4H6SO2+C4H2O3C8H8O3+SO2

1,3 Butadiene Maleic anhydride 4-cyclohexene- cis- 1,2- dicarboxylic anhydride

Maleic anhydride is a highly reactive dienophile due to the two electron-withdrawing

carbonyl groups, which causes the two-carbon system to be electron deficient. This creates a

positive center that initiates the addition reaction with the butadiene formed. As a result of this

interaction, two new sigma bonds are formed from the two bonds to give the product shown above.

As previously stated, there are no intermediates formed in the reaction, and the configuration of the

dienophile is retained in the final product. In this case, the maleic anhydride is cis and consequently

so is 4- cyclohexene- cis- 1,2- dicarboxylic anhydride. There are no significant side reactions to

report for this preparation since the 1,3-butadiene was produced in situ from butadiene sulfone.

In the experiment, butadiene sulfone was used as an alternative reactant for 1, 3 butadiene.

Butadiene is a gas at room temperature, which makes it difficult to store and to handle when

performing the experiment. Also, Diels-Alder reactions involving butadiene generally have to be

carried out in a sealed pressure vessel, because the reaction temperature is greater thanbutadienes

boiling point. Thus, the alternative reagent is advantageous because it greatly reduces handling

difficulties and the potential for the formation of polymeric by-products, which typically accompany

the reaction that uses only 1,3- butadiene.


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There is also another method to prepare the product. First, 1,3-butadiene reacts with maleic

acid to form 4- cyclohexene- cis- 1,2- dicarboxylic acid. The product undergoes dehydration and 4-

cyclohexene- cis- 1,2- dicarboxylic anhydride is produced. Thus, the cyclic anhydride is formed by

the pyrolysis of the diacid.

Procedure The reaction apparatus was assembled as per the instructors model (Fig A). In a 25

mL round bottom flask, 2.0 g of butadiene sulfone, 1.2 g of maleic

anhydride, 0.8 mL of xylene, and 3 boiling chips was added. The

flask was assembled into the apparatus where it was gently heated,

and then the mixture was allowed to reflux for 30 minutes after all

starting materials dissolved and the first drops of reflux were

observed. After 30 minutes, the heating mantle was then removed,

and the reaction mixture was cooled for 5 minutes. Next, 12 mL of Toluene was added to the reaction

mixture in order to dilute the mixture and, the flask was

subsequently heated to dissolve any solid material. The hot

solution was then filtered through flutted filter paper into a 50

mL Erlenmeyer flask. The special apparatus used to collect the

filtrate is shown in Fig. B. Petroleum ether was then added in the

filtrate until the mixture appeared turbid. The solution was then rewarmed until it became clear, and the

Erlenmeyer flask was placed in an ice-water bath to crystallize the

product. After the product was crystallized, the product was collected

by vacuum filtration and allowed to dry on a sheet of filter paper. The

special apparatus used for this step is shown in Fig. C. Lastly, the yield

was determined by weighing a glass vile then weighing the vile plus

the product, and configuring the difference. The melting point of the product was taken twice, and the

average of the melting points was recorded.

Figure A

Figure C

Figure B


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Table of Reactants and Products:

Name Structure Mol.

Wt.

Amount

Used

Moles

Used

Eq. b/p

C

m/p

C

Density Solubility

Butadiene

sulfone(3-sulfolene)

118.2 2.0 g 0.0169 1.00 - 65-66 1.314g/

Solubility

in H2O:

130 g/L at20

C

Maleic

anhydride98.1 1.2 g 0.0122 1.38 200 52.8 1.314

Soluble in

water,

acetone,

ethyl

acetate,

chloroform,

and

benzene

4-

cyclohexene-

cis- 1,2-dicarboxylic

acid

anhydride

152 g - - 1.00 343 105-106 1.402 g/cm3

Xylene,

insoluble in

petroleum

ether

Mass of Vile 29.9916 g

Mass of Vile + Product 30.643 g

Mass of 4- cyclohexene- cis- 1,2-

dicarboxylic acid anhydrideproduced

0.6514 g

Number of Moles of 4-cyclohexene- cis- 1,2- dicarboxylicacid anhydride produced

.0122 mol

Observed Melting point of 4-cyclohexene- cis- 1,2- dicarboxylicacid anhydride product

Trial 1: 96.4Trial 2: 96.1

Actual Yield

(Mass of Vile + Product)(Mass of Vile ) = (30.64329.9916) = 0.6514 g

Theoretical Yield

( ) ( ) ( ) = 0.0169 mol 3-sulfolene used

( ) ( ) (

) ( ) .0122 mol MA

Yield Data

Actual Yield: 0.6514g

Theoretical Yield:

g

Percent Yield:35%

Melting Point 96.3 C


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Thus, maleic anhydride is the limiting reagent.

Mass of4- cyclohexene- cis- 1,2- dicarboxylic acid anhydride product

( ) ( ) = 1.86 g

%

Observations & Conclusions: During the heating of the diene and dienophile, the flask started

to smoke as the temperature increased, which could be indicative of sulfur dioxide gas bubbling out

of the mixture. The solution held a constant clear color throughout the heating and reflux process. I

was able to observe the importance of xylene in this experiment, because it is this solvents high

boiling point that allows the reaction to reflux at temperatures high enough for the reactions to take

place. In addition, the Diels-Alder product is soluble boiling xylene, but in soluble in cool xylene.

Also, upon cooling the solution, a faint, yellow-brown color was observed in the flask, but as the

purification process began with the addition of toluene, the solution became clear again. Toluene is a

nonpolar solvent and was added to dissolve any solid material or impurities in the solution. This

could account for the change to a clear color upon its addition to the mixture. Another observation

was that the solution became white and cloudy after adding petroleum ether, but turned clear again

after it was rewarmed. After the ether was added, the flask was put in an ice bath were it crystallized.

The crystals that were recovered had a soft, fluffy appearance and seemed to have a faint, brown tint

that gave the product an off-white color. Because of the solutions turbidity when added, it seemed

as though the petroleum ether played a role starting the crystallization process. The Diels product is

soluble in xylene, but relatively insoluble in the petroleum ether, thus by reducing the solubility, the

crystallization can take place.

Furthermore, the melting point for cis-4-cyclohexene-1,2-dicarboxylic anhydride (96.30C)

was quite lower than its literature melting range of 105-1060C. In addition, the percent yield was

35%. The low yield could be from the lossin product that occurred in the transfer of the product

from the filter paper in the Buchner funnel to vile to be weighed. Also, heating the mixture too

quickly could have resulted in the formation of butadiene gas, which doesnt react and form product.

Lastly, the solution could have not refluxed for long enough, and the butadiene sulfone did not

decompose all the way. All of these could account for the low yield of product in the experiment.


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Diels-Alder Synthesis of 4-Cyclohexene-cis- 1,2-Dicarboxylic Anhydridefrom Butadiene Sulfone and Maleic Anhydride.

new diels sdfsdfsd diels-alder synthesis lab report

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