03-06-02 03:46
No 277800
Toluene can be selectivly alpha-lithiated with either sec-BuLi in PhMe/THF or with n-BuLi and TMEDA (N,N,N',N'-Tetramethylethylenediamine) at -78ºC in 95% yields. This would then be added to a solution of dry Acetonitrile in THF via cannula. Aqueous workup (NH4Cl, H2O) should afford the ketone.
This route will avoid the Wurtz coupling encountered in the preparation of Benzyl Magnesium Chloride, giving very low yields.
(Distinctive Doe)
03-06-02 12:43
No 277973
(Rated as: excellent)
Slappy
Where did you pull that one from? Got a reference??
Is it from here?
Organometallics, 4, 2117 (1985)
Good stuff
Patent US3534113
They perform a similar reaction here.
Patent US3663585
Example
Mixed 6ml Toluene, 5ml (1M)BuLi in n-hexane and 1ml (2M)TMEDA in n-hexane(I assume). Then allowed to stand under N2 for 3 days. Evap. to dryness yeilded 0.68g of yellow solid. They make some questionable judgements and say it yeilded 78%.
Here is some other interesting stuff
Patent US4006187
EXAMPLE I
Preparation of Benzyllithium
From 1-lithio-3-methylpentylbenzene
To 200 ml of sec-butyllithium in hexane (2.05 N) at -20.degree. C there is added 57.2 ml of TEA, followed by 47 ml (0.41 moles of styrene diluted with 30 ml of hexane. Then 43.5 ml of toluene (0.41 moles) is added and the resulting solution is placed in a constant temperature bath at 35.degree. C. Aliquots of the solution are removed periodically, treated with excess trimethylchlorosilane in diethyl ether, and analyzed by G.L.C. for 3-methylpentylbenzene, the amount of which hydrocarbon indicating the percentage of toluene metalated. The results are shown in the following tabulation:
______________________________________
Time (hrs) % Metalation
______________________________________
24 19.5
46 44
78 63
102 76
______________________________________
Metalation is essentially complete in 150 hrs. By contrast, n-butyllithium . TEA metalates toluene much more slowly, only about 10% metalation occurring in a period of 156 hrs at 35.degree. C.
Selective side chain lithiation of toluene and methylpyridines.
Screttas, Constantinos G.; Eastham, Jerome F.; Kamienski, Conrad W.
Chimia (1970), 24(3), 109-11.
Abstract
Benzyllithium (I) was prepd. free of ring-metalated by-products using n- or sec-BuLi and THF. 2- (II) and 4-Pyridylmethyllithium (III) were prepd. with THF and 2-thienyllithium. Solns. of II and III in 70:30 benzene-THF were stable 9 months under refrigeration. Reaction of picolyllithiums (a-, b-, g-) in THF with Ph2CO or PhCN gave 66-100% corresponding carbinols or phenacylpyridines. For example, THF (40 ml) was added to 18 ml (14.1 g) sec-BuLi in 180 ml toluene under N at -15 ± 1°. After addn. of 3/4 of the THF, the temp. rose to 0° and the mixt. solidified to a yellow cryst. mass (1:1 I-THF). The remaining THF and 10 ml extra dissolved the solid to give an orange-red soln., reaction time 3 hr, 98% yield PhCH2Li.
Lithiation of toluene in the presence of polycyclic aromatics and conjugated dienes.
Froehlich, Hans Otto; Scholz, Peter; Griehl, Volker; Stoye, Hartmut; Anton, Elisabeth.
Ger. (East) (1988), DD 256519 A1 19880511
Patent written in German.
Abstract
PhCH2Li was prepd. by addn. of a conjugated diene to a mixt. contg. 0.1-5 mol Li/L, 0.5-7.5 mol/L PhMe, 0.01-1 mol/L polycyclic arom., and 0.5-8 mol/L aliph. or cycloaliph. ether at (greater than or equal to)278 K followed by stirring at 283-340 K for 10-80 h. Thus, a mixt. of toluene 2, THF 2.7, Li 1.5, and naphthalene 0.1 mol in an autoclave at 268 K was treated with 7.5 mol butadiene at (greater than or equal to)278 K and the mixt. was stirred 48 h at 313 K to give 97% PhCH2Li.
Make a Difference Donate Now!! (http://www.lp.org/drugwar/)
(Hive Bee)
03-07-02 22:11
No 278776
(Rated as: excellent)
foxy,
Thanks for the links
, I will examine them thouroughly. Here is a list of the ref's that I was reffering to. I think that the second one is the most interesting. I would imagine that Diisopropyl Ether or Methyl tert-Butyl Ether would also help stabilize the carbanion as a cosolvent.Chimica, 1970, 29, p2928
- Lithiation with sec-BuLi in Toluene/THF. 95% yield.
Main Group Met. Chem., 21(12), 777-781, 1998
- Toluene and n-BuLi in a mixture of THF and 2-Methyl-THF. The mixed solvent system stabilizes
the carbanion. 98% Yield.
Chem. Ber., 122(12), 2303-9, 1989
- alpha-lithiation of Toluene with TMEDA, n-BuLi in THF/Et2O.
Organometallics, 8(1), 67-69, 1989
- TMEDA and n-BuLi.
J. Organomet. Chem., 280(2), 153-8, 1985
- TMEDA and n-BuLi in Benzene.
J. Organomet. Chem., 409(1-2), 93-101, 1991
- Benzyltributylstannane is lithiated with MeLi in THF. Bu3SnCh2Ph can be made from Benzyl Chloride and Tributylstannane.
The procedure should go like this:
All experiments should be performed under anarobic and anhydrous conditions for optimal yields. Alkyl Lithium reagents are more sensitive to decomosition than thier corresponding Grignard reagents.
A mixture of Toluene and Ether co-solvent (THF, Et2O, or 2-Me-THF/THF mix), both freshly distilled from Na or K metal, is taken to -78°C in a solid CO2/Acetone bath with vigerous magnetic stirring, and an appropriate amount of your Lithiating agent (n-BuLi, sec-BuLi, or TMEDA then n-BuLi) is added via syringe. It is let react for an appropriate time (~1-3h) while maintaining the temperature. Acetonitrile, freshly distilled from CaH, is added dropwise to the reaction mixture via cannula. After addition is complete, the mixture is allowed to warm to room temperature, and quenched with aq. NH4Cl. After distillation, you should have your ketone in high yields from PhMe/MeCN.
(Newbee)
06-12-02 13:09
No 320377
I have an aunt who is 73 years old and still not married. She keeps asking me the same question over and over again...
Is there a way to generate this (n-butyl lithium) in situ without using the nasty and very expensive metal?
I know that other "strong bases" can be electrochemically generated... any thoughts
I dunno, but I been told ... You never slow down, you never grow old!
(Chief Bee)
06-12-02 15:52
No 320460
n-Butyllithium is most often not made in the laboratory, but bought ready-made in hexane solution.
No, it cannot be made easily by any other means than Lithium metal and butyl (chloride).