Reduction of 9-Fluorenone

Purpose To demonstrate the reduction of a ketone to an alcohol using sodium borohydride. 

Avoid contact of methanolic solutions of sodium borohydride with your skin they are highly caustic. If possible, wear latex gloves when handling these solutions. If these solutions accidentally get on your skin, wash the affected area first with a 1% acetic acid solution and then with copious quantities of water. 

Do not stopper flasks containing methanolic sodium borohydride the solution slowly evolves hydrogen gas, and a dangerous buildup of pressure could occur in a stoppered flask. 

Preparation Sign in at www.cengage.com/login to answer Pre-Lab Exercises, access videos, and read the MSDSs for the chemicals used or produced in this procedure. Review Sections 2.9 and 2.17. 

Apparatus A 25-mL Erlenmeyer flask, apparatus for vacuum filtration, and flameless heating. 

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In this experiment, you will examine the reduction of 9-fluorenone (10) using sodium borohydride to give 9-fluorenol (12), as shown in Equation 17.17. This reaction is mechanistically analogous to the reduction of imines with sodium borohydride (Sec. 17.3) and involves the transfer of hydride ion (H ) from borohydride ion, BH4, to the electrophilic carbonyl carbon with concomitant transfer of the electron-deficient boron atom to the carbonyl oxygen. Theoretically, all four of the hydrogen atoms attached to boron may be transferred in this way to produce the intermediate borate salt 11, which is decomposed upon addition of water and acid to yield 9-fluorenol (12). 

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