General Methods for Preparation of Rieke Zinc

A wide variety of zinc salts and various reducing agents have been tried, but the aforementioned conditions seem to lead to the most active zinc. The addition of other alkali salts such as KI, Nal, Lil, KBr, LiBr, or LiCl prior to the reduction step does affect the activity of the zinc. 

A far superior method of preparing the highly reactive zinc is to use lithium metal as the reducing agent along with an electron carrier such as naphthalene (Method 2). This approach is considerably safer as there is no rapid burst of heat. The dark green lithium naphthalenide also serves as an indicator, signaling when the reduction is over. 

Rieke zinc is prepared by placing lithium metal (10 mmol), a catalytic amount of naphthalene (1 mmol), and 12-15 ml of THF in one flask placed in an ice bath. Once this mixture has stirred for about 30-60 s, it will turn dark green, indicating the formation of lithium naphthalenide. Zinc chloride dissolved previously in 12-15 ml of THF is then cannulated dropwise (ca. 3 s per drop) into the lithium naphthalenide, and stirring is continued for 30 min after the transfer is complete. This method is not only safer due to the use of lithium 

Chemical Synthesis Using Highly Reactive Metals, First Edition. Reuben D. Rieke. 2017 John Wiiey Sons, Inc. Pubiished 2017 by John Wiley Sons, Inc. 

Finally, the most reactive Rieke zinc yet prepared is generated by the reduction of Zn(CN)2 with lithium using an electron carrier such as naphthalene. Some of this zinc s chemistry will be described later in the text. The reaction details are the same as Method 2. 

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