What was green about this experiment? THEORY Electrophilic addition is the most

Question

What was green about this experiment? THEORY Electrophilic addition is the most characteristic reaction of A variety of electrophiles X-Y) will add across the double bond of an alkene to yield a saturated compound. If bromine (Br) is the electrophile, the resulting compound is a 1,2-dibromide (also called a vicinal dibromide) (2). I Y CEC X-Y (1) C C Br-Br (2) Br 1,2-dibromide (vicinal dibromide) Typically, electrophilic brominations of alkenes are carried out in methylene chloride (CH2Cl2 or carbon tetrachloride (CCIO. These solvents are ideal because they are non and will not interfere with the desired reaction. However, both solvents are volatile and toxic and both are suspected The traditional reagent used for these brominations, Brz, is also dangerous to handle because it is highly corrosive and causes severe burns upon contact with the skin. In this experiment, you will brominate (E-stilbene using alternative reaction conditions: pyridinium tribromide in ethano (EtOH) (3)

Explanation / Answer

An organic salt pyridinium tribromide is a sufficient alternative to liquid bromine. pyridinium tribromide is solid and significantly safer to handle, and the molecular bromine is generated in situ (which means “in the reaction mixture”). Generation of the active reagent occurs due to a chemical equilibrium between the pyridinium tribromide and molecular bromine.

Liquid bromine is hazardous whereas pyridinium tribromide produces molecular bromine and hence safe to handle. Hence it is green chemistry.

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