Dueling Pericyclics: Cheletropic Cycloreversion and Diels-Alder Cycloaddition Re

Question

Dueling Pericyclics: Cheletropic Cycloreversion and Diels-Alder Cycloaddition Reading: Carey 10th Ed pp 553-560 (IR spectroscopy), 397-403 (Diels-Alder Reaction). Introduction The Diels-Alder reaction is the most famous example of a a pericyclic reaction, i.e. a reaction that involves neither a nucleophile or an electrophile. Discovery of this novel type of reactivity led to a Nobel Prize for Otto Diels and Kurt Alder in 1950. This reaction is controlled by favorable overlap of tt orbitals between a conjugated 1, 3 diene and an olefin (called the dienophile, because it likes dienes). Since then, a vast number of different types of pericyclic reactions have been discovered (as you will discover in Chem 12C). In this experiment, you will perform a combination of a Diels-Alder cycloaddition and a "cheletropic cycloreversion". A cheletropic reaction is a subclass of the Diels-Alder reaction whereby both new bonds are made to the same atom. As you are aware from class, pericyclic reactions are reversible, so the cycloreversion reaction merely means that we will perform the reverse of a cycloaddition. The compound sulfolene is a diene surrogate, i.e. it can form 1, 3-butadiene upon heating by expelling gas molecule. You will perform the combination process and analysis the two mechanisms present in the reaction. The Material Safety Data Sheets (MSDS) for all the chemicals involved in this lab are on iLearn. Read these and answer the following questions: Which chemical is the most dangerous in this lab? Explain why you chose your answer for part a), and the safety precautions you will take when handling this material. Fill in the reaction table below. Make sure you correctly calculate the molar amounts of your reactive materials. Based on your answers to Q2, which is the limiting reagent in this reaction? Calculate the Theoretical Yield of your product, i.e. the mass you would expect to recover, assuming 100 percentage conversion to product.

Explanation / Answer

1. (a) maleic anhydride is very hazardous.

(b) This is because maleic anhydride is very hazardous in case of ingestion. Hazardous in case of skin contact (irritant, permeator), of eye contact (irritant), of inhalation. Corrosive to eyes and skin. The amount of tissue damage depends on length of contact. Eye contact can result in corneal damage or blindness. Skin contact can produce inflammation and blistering. Inhalation of dust will produce irritation to gastro-intestinal or respiratory tract, characterized by burning, sneezing and coughing. Severe over-exposure can produce lung damage, choking, unconsciousness or death.

For safety wear do not touch with you bare hands. use a glove and goggles. If the chemical got onto the clothed portion of the body, remove the contaminated clothes as quickly as possible, protecting your own hands and body. wash the sffected part with water and soap. Seek medical attention.

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