SYNTHESIS OF UNDECANE

STEP 1: Place 9.53 g (0.05 mol) of copper(i) iodide in a two-necked, 500-m1 round-bottomed flask containing a glass-covered magnetic follower bar. 

STEP 2: Fit a rubber septum to one of the necks of the flask and connect the other neck to one arm of a three-way stopcock. 

STEP 3: Connect the second arm of the stopcock to a supply of dry, oxygen-free nitrogen and the remaining arm to a vacuum pump. 

STEP 4: Evacuate the flask by opening the stopcock to the vacuum pump (1) and then, with a rapid stream of nitrogen flowing, carefully open the stopcock to the nitrogen supply to fill the flask with nitrogen. Repeat this process twice; flame the flask gently on the final occasion it is evacuated. Maintain a static atmosphere of nitrogen in the flask throughout the reaction by passing a slow stream of nitrogen through the nitrogen line. Cool the flask in an acetone/Cardice bath and transfer 100 ml of dry tetrahydrofuran (2) to the flask via the septum using a hypodermic syringe (3). 

STEP 5: Stir the cooled (— 78 °C) suspension and add 52.0 ml of a 1.92 molar solution of butyllithium in hexane (4) from a hypodermic syringe. 

STEP 6: Stir the flask solution at — 78 °C for 1 hour, and then add a solution of 3.39 g (0.015 mol) of 1-iodoheptane in 10 ml of dry tetrahydrofuran dropwise from the syringe. 

STEP 7: Stir the solu­tion at —78 °C for 1 hour and then at 0 °C (ice bath) for a further 2 hours ((5) and (6)). 

STEP 8: Hydrolyse the reaction mixture by pouring it carefully into 100 ml of 1 M hydrochloric acid. 

STEP 9: Separate the upper organic layer and extract the aqueous layer with two 50 ml portions of pentane. 

STEP 10: Wash the combined organic layers with water (50 ml), dry over magnesium sulphate and evapor­ate the solvents on the rotary evaporator. 

STEP 11: Distil the residue at atmospheric pressure using a semimicro scale distillation unit fitted with a short fractio­nating side-arm packed with glass helices. 

STEP 12: Undecane has b.p. 194-197 °C; the yield is 1.24 g (53%).

Notes to keep in mind:

1. This operation should be carried out behind a safety screen.

2. Tetrahydrofuran should be freshly distilled from lithium aluminium hydride. It is convenient to store a supply of peroxide-free tetrahydrofuran under nitrogen over lithium aluminium hydride and distil appropriate quantities as required.

3. The syringes and long flexible needles can be obtained from Aldrich Chemical Co.

4. Solutions of butyllithium, and other lithium reagents, may be purchased from Aldrich.

5. The progress of the reaction may be conveniently followed by g.l.c. Remove samples (c. 2-3 ml) from the reaction mixture by means of a hypodermic syringe and submit them to a small-scale hydrolysis and extraction procedure similar to that described for the main reaction mixture. Analyse the organic layer on a 10 per cent squalane on Chromosorb W column held at 140 °C. Under these conditions 1-iodo­heptane has a slightly longer retention time than undecane.

6. Complete reaction of the alkyllithium can be tested by means of the Gilman test.