rganisches Praktikum CP II Wintersemester 2009/10 Versuch 23 Stabiles Bromonium-Ion Betreuer: Hinweise: Susanne Kümmel Bei 2-Adamanton beginnen! Chemikalien: 2-Adamanton: Tomahogh Zink Tomahogh Titan(IV)-chlorid Nachtraum THF abs. Tomahogh Brom Nachtraum Hinweise: Bei 2-Adamanton beginnen.
Michael Seitz (room 33.1.23, Tel.: 943-4647) Preparation of a stable Bromonium-Salt Reactions: conc. H 2 S 4 TiCl 4, Zn THF Br 2 Br CH 2 Cl 2 Br 3
1. xidation of Adamantane: 2-Adamantanone conc. H 2 S 4 80 C, 5 h + H Literature: H.W. Geluk, V.G. Keizer rg. Synth., Coll. Vol. 6, 1988, 48. Procedure: A 100 ml-ns14-flask, equipped with an efficient stir bar and a reflux condenser, is charged with 70 ml conc. sulfuric acid. Finely powdered adamantane (3.82 g, 28.0 mmol) is added with vigorous stirring and the external temperature is raised to 75-76 C (note 1). Then the temperature is raised slowly over the course of 2 h to 85-86 C. Stirring is continued for additional 2 h (note 2) before the mixture is cooled and poured onto 100 g of crushed ice. The suspension is extracted with 4*100 ml tert.-butyl methyl ether. The combined organic layers are washed with 2*50 ml water and 50 ml brine. Drying (Na 2 S 4 ) and evaporation of the solvent under reduced pressure gives a brown solid, that is purified by sublimation (p < 20 mbar, oil bath 150-160 C) to give a mixture of the title compound, 1- adamantanol and adamantane. Ask your tutor if further purification is neccessary. Analysis: 1) The flask should only be immersed up to the level of the sulfuric acid. therwise too much solid will sublime in the upper part of the flask or the condenser. 2) From time to time sublimed material is scratched back into the reaction mixture from the glass wall of the flask. 13 C-NMR
2. McMurry-Reaction: Adamantylideneadamantane TiCl 4, Zn THF, reflux, 20 h Literature: D. Lenoir Synthesis 1989, 883-897. Procedure: A 100 ml three-necked flask, equipped with a reflux condenser, a dropping funnel (note 1) and a Schlenk-adapter, is dried by heating under vacuum and cooled down under dry nitrogen. Under a nitrogen-atmosphere it is charged with 30 ml THF (note 2) and cooled with an external ice bath. 1.2 ml (10.9 mmol, 2.06 g, 1.07 eq) TiCl 4 was added very carefully (note 3). After the addition is complete, the dropping funnel is removed and the yellow solution is treated with 1.46 g (22.4 mmol, 2.2 eq) zinc dust. A new dropping funnel is attached and after 5 min a solution of 1.53 g (10.2 mmol, 1.0 eq) 2-adamantanone in 10 ml dry THF is added dropwise to the green suspension. The mixture is heated to reflux for 20 h. Cooling down the black suspension is followed by slow addition of 22 ml of an aqueous K 2 C 3 -solution (10% by weight) and 30 ml cyclohexane. The suspension is stirred at room for 60 min and filtered (note 4). The phases are separated and the aqueous layer is extracted with 4*20 ml cyclohexane. The combined organic phases are washed with 2*50 ml water, dried (Na 2 S 4 ) and evaporated under reduced pressure. The crude product (note 5) is recrystallized from EtH (99%) and a small amount of cyclohexane to yield a colourless solid (mp 189-190 C). 1) The dropping funnel should be suitable for very slow addition. 2) THF is dried over Na in bulk for 3-4 people. Ask your tutor. 3) CAUTIN: The reaction of THF with TiCl 4 is very exothermic and can get very vigorous upon too fast addition! 4) If the Ti/Zn-slurry is too pasty additional water and cyclohexane can be added. 5) The main side reaction is the reduction of 2-adamantanone to 2-adamantanol. This is completely removed by recrystallization. Analysis: 13 C-NMR, mp
3. Bromination of Adamantylideneadamantane: Stable Bromonium-Ion Br 2 Br CH 2 Cl 2 Br 3 Literature: H. Slebocka-Tilk, R.G. Ball, R.S. Brown J. Am. Chem. Soc. 1985, 107, 4504-4508. Procedure: To a solution of 400 mg (1.49 mmol, 1.0 eq) adamantylideneadamantane in 20 ml CH 2 Cl 2 is added a solution of 0.19 ml (3.28 mmol, 524 mg, 2.2 eq) bromine in 20 ml CH 2 Cl 2. The immediately formed yellow precipitate is filtered, washed with 3*2 ml CH 2 Cl 2 and then dried in vacuo for about 15 min to give the product (mp 160-162 C) (Note 1). Analysis: 1) The product can be recrystallized from CH 3 CN, if necessary. mp