The Diels-Alder Reaction is a reaction used in organic chemical science that builds rings really expeditiously ( 1 ) . this cycloaddition procedure allows for the stereoselective formation of cyclohexene rings possessing every bit many as four immediate stereogenic centres ( 3 ) . This reaction occurs without intermediates. in a individual measure. which explains the stereospecificity due to substituents non being given the opportunity to “switch around” . ( 1 ) These six membered rings are synthesized by responding a dienophile with a diene. organizing two new carbon-carbon sigma bonds in the signifier of the ring. The dienophile used in this experiment was Maleic anhydride ( a cyclic dienophile ) and the diene used was cyclopentadiene ( a cyclic diene ) . Due to the fact that more than one stereoisomer may organize. it is of import to cognize that the major merchandise will be the 1 with the passage province for the endo stereochemistry while the minor merchandise will be for the exo stereochemistry.
The ground for this is because the reaction favors the merchandise that involves the maximal convergence of pi negatrons in its passage province. which in this instance. is the endo isomer. To ease the concerns of orbital convergence between the HOMO ( Highest Occupied Molecular Orbital ) of cyclopentadiene with the LUMO ( Lowest Unoccupied Molecular Orbital ) maleic anhydride. reactants are used which possess negatron retreating groups on the dienophile ( maleic anhydride ) and electron donating groups on the diene ( cyclopentadiene ) . ( 2 ) Side reactions in this experiment include the reaction of cyclopentadiene with itself as it will dimerize to organize dicyclopentadiene if kept at room temperature every bit good as the exo isomer of the merchandise. Chemical reaction Mechanism:
Experimental ProcedureTo get down this experiment. a fractional distillment was set up in order to purify dicyclopentadiene. A 10 milliliter conelike phial was filled with 5 milliliters of dicyclopentadiene and so heated to a steady boiling point ( 40-42 C ) . Cyclopentadiene was so placed on ice while the staying reactant was prepared. . Maleic anhydride was so obtained ( 0. 2 g ) and dissolved in 1 milliliter of ethyl ethanoate. followed by add-on of 1 milliliter hexanes to this mixture. 0. 2 milliliter of the cyclopentadiene was eventually added and reaction was observed with the formation of the crystals. Following the formation of the crystals. the dissolver was removed via Pasteur pipette and so crystals were washed with cold crude oil quintessence. Crystals were so scraped onto a piece of filter paper to dry and so weighed. Finally. runing point was obtained and percent output was calculated. Table of Chemicals
Melting Point: -40 CToxicity: Irritant. make non inhaleMaleic anhydride
Melting Point: 52. 8 CToxicity: Irritant. flammable
Cis-Norbornene-5. 6-endo-dicarboxylic anhydride
Melting Point: 165 CToxicity: Corrosive. wellness jeopardyConsequences5 milliliter of distilled dicyclopentadiene enabled my spouse and I to obtain 0. 2 milliliter of cyclopentadiene for the reaction. 0. 2 g of Maleic acid was obtained and the merchandise yielded was 0. 168 g of Cis-Norbornene-5. 6-endo-dicarboxylic anhydride. The runing point of this merchandise was 138 C. The per centum output was so calculated: . 1572 g / 66. 1 g = . 00238 mols cyclopentadiene
. 2 g / 98. 06 g = . 00203 mols maleic anhydride ( Restricting Reagent ) . 168 g / 164. 16 g = . 00102 mols cis-norbornene-5. 6-endo-dicarboxylic anhydride. 00102 mols / . 00203 mols = 50. 25 % OutputDiscussionIn comparing to the literature value of the thaw point for cis-norbornene-5. 6-endo-dicarboxylic anhydride. 165 C. our existent thaw point was much lower at 138 C. There are many grounds why this may hold occurred some of which include defects in the distillment procedure. defects in commanding cyclopentadiene from dimerizing. non leting ample clip for reaction to happen. and deficient drying of crystals following ether wash.
Our per centum output for this reaction was besides rather low at merely 50. 25 % . It is conceivable that this could be due to non being able to full sum of crystals that were yielded because some remained stuck in the phial. If left at room temperature. cyclopentadiene will respond with itself ( dimerize ) to organize dicyclopentadiene. which is a side reaction with this reaction. In order to avoid this. cyclopentadiene is kept on ice to forestall dimerization. The coveted merchandise would hold been one that yielded crystals with a runing point much closer to the literature value of 165 C. runing between 161-169 C. this would hold meant a pure sample. Therefore. the coveted merchandise has non been attained in this experiment. Decision
The purpose of this experiment was to execute a Diels-Alder reaction between cyclopentadiene and maleic anhydride and place the merchandise. Although this is what my spouse and I did. it is really obvious based upon our consequences that the merchandise obtained is impure based upon runing point values. Many of the techniques performed in this lab can be applied to other state of affairss. the distillment setup is used rather frequently in organic chemical science labs every bit good as finding of runing point and percent output. For this ground. it is good that my spouse and I know how to get the better of the issues faced in this experiment in order to do certain the undermentioned experiments are performed with better technique in these countries. The coveted merchandise of a pure cis-norbornene-5. 6-endo-dicarboxylic anhydride has non been attained. despite the dross of our merchandise I feel that the overall facet of the experiment performed was understood really good and merchandise pureness could hold been improved had the above defects discussed been fixed.
1. Weldegirma. Solomon. “Diels-Alder Chemical reaction: Synthesis of cis-Norbornene-5. 6-endo- dicarboxylic anhydride. ” Experimental Organic Chemistry. Print. 2. Myers. Kyle. . Roark. James. Diels-Alder Synthesis of Exo-Norbornene-cis-5. 6-
Dicarboxylic Anhydride for Organic Chemistry Laboratory Instruction. Web.
& lt ; hypertext transfer protocol: //www. unk. edu/uploadedFiles/academics/gradstudies/ssrp/Myers. pdf & gt ;