Naphthalene → Lithium Naphthalene

Participants

Reaction Steps

A rotator for a magnetic stirrer was placed in a 500-ml four-necked flask, and the mouths of the flask were equipped with ampoules containing 28.2 g of anhydrous naphthalene, 200 ml of anhydrous tetrahydrofuran, 40 ml of anhydrous isoprene and 1.38 g of metallic lithium, respectively. After completely replacing the atmosphere in the flask by nitrogen gas, the ampoule containing metallic lithium was opened by a magnetic hammer to allow the lithium to fall into the flask. Next, tetrahydrofuran and naphthalene were allowed to fall in the same manner as above. On mixing the contents in the flask at room temperature for 17 hours, a deep green complex of lithium-naphthalene was formed. After cooling to -70° C, isoprene was added, and the mixture was stirred at room temperature for 2 hours, whereby the reaction solution turned to yellow brown. The tetrahydrofuran was removed from the reaction solution under reduced pressure, and then 100 ml of anhydrous n-hexane and 100 ml of cyclohexane were added thereto under the stream of nitrogen gas. After cooling to -40° C, 95 ml of isoprene were added, and polymerization was carried out at 50° C for 3 hours. The metallic lithium was removed from the product, in the same manner as in Example 1, by washing the reaction mixture with an aqueous hydrochloric acid solution. After neutralization and washing with water, the separated oil layer was concentrated under reduced pressure in a rotary evaporator to give low molecular weight polyisoprene. By the analysis according to the Morero's method, the microstructure of the resulting polymer was found to consist of 85% of the cis-1,4 structure and 15% of the 3,4 structure. The molecular weight determined by means of a vapor pressure osmometer was 760.

Provenance & Evidence