The Hive > Serious Chemistry

First published direct reduction of COOH to CH3

<< < (4/5) > >>

Rhodium:
Preparation of triethylsilane

Journal of the American Society, v69, page 2108 (1947)
Whitmore,Pietrusza, and Sommer.

"Triethylsilane-Preparation of this compound in 56.5% yield by the simulataneous addition of equivalent amounts of trichlorosilane and ethyl magnesium bromide has been reported. The following procedure is more convenient and give yields of 70-78%.

Ethylmagnesium bromide, 12.6 moles, was prepared in a 5-litre, three-necked flast, fitted with an efficient stirrer, dropping funnel and large bulb condenser, each connected to a trap, cooled in Dry Ice and acetone. A cold solution of trichlorosilane, 406.5 g., 3.0 moles, in 1200 cc. of anhydrous ethyl ether was added in six hours with cooling and vigorous stirring. The mixture was stirred for eight hours at room temperature and  then heated to reflux for five hours. Ether was removed from the reaction mixture through a 20-plate column and the residue was heated on the steam-bath for ten hours. With cooling, the solid residue was hydrolyzed with 180 cc. of water, followed by 372cc of contrated hydrochloric acid. The aqueous layer was sepearated and extracted twice with 500cc. portions of ether. The ether extracts and product were comobined, washeed with water, and then dried over 150g. of anhydrous potasssium carbonate for two hours.  Fractional distillation through the 20-plate column gave 270.3 g. of thriethylsilane, bp 107 at 733mm., ----- 77.5% yield"


ibid.
Kraus and Nelson

"Trichlorosilance. - edited

Preparations were made in a horizontal, electricallly heated, Pyrex tube, 3cm. in diamter and 45cm. in lenght, with its entrance connected to a uslric acid drying tower and calibrated flow meter. The exis was attached to a water- cooled condenser, which led to a flask cooled in salt-ice. As a precation against moisure and loss of material the flask connected to a trap immerser in Dry Ice and aceton, which led tta a sulfutic acid drying tower. The tube was chearged with 375g. granyular ferrosilicon, and the system was dried by passing nitrogen through it for twenty-four hours at a furnace temperature of 300 c. Dry hydrogen chloride was then passed in at 350 c until liquid condensed in the receiver. The temperature was then lowered and kept at 290-310 c, while maintaining the flow at 0.6-0.8 mole per hour. Nitrogen was passed through for ten minutes at approximately ten-hour intervals. In sixty hours, this 1370m of liquid product.______________  Fractionation of the liquid product through a column of about 15 theoritical plates gave 1045g. of trichlorosilance, bp 31.5-32 c at 729mm., 77%  of the crude liquid, the remainder being mainly silicon tetrachloride. ___"

Journal of the American Chemical Society, v.56, page 196 (1934)

"Triethylsilance.- ____ was first prepared by Ladenburg (Ann.164,300(1872)) by teating silicon tetraethyl ester with sodium and diethylzinc. Paper (Ann.222,354(1883)) prepared tripropylsilance by treating silicochloroform with dipropyulzinc.  Kahler (unpublished) has shown that triethylsilance may be prepared conveniently by the interaction of the ethyl Grignand reagent with silicochloroform. Sin the the is very connient and we ahve had occasion to lemploy it in preparing quatities of triethylsilance, it will be described briefly.

After adding the two reagents, the mixture is allowed to stand for fifteen hours and is then boiled with reflux condenser for twenty hours. Acidulated water was is added to deocompose the excess ehtymagnesium bromide, the ether layer is seperated, dried over calcium chlordie and the solvent diwstilled.

In our preparation the residue was fractionated through a long Eastman column and the product coming over from 100-125 c was refractionated, the fraction coming over at 107-110 c being retained. The average yield was 56.5%."

abc123:
As luck would have it I've been able to procure some of the funky fluoro compound.... However triethylsilane isn't available directly as of yet. I was wondering if it would be possiable to subsitute trimethylsilane in it's place in an equimolar amount. TMS is abundant as we use it for the NMR... Also TMS is more affordable and less suspicious than it's ethyl analog. I'm going to review your quoted reference and see what it has to say for myself, and see if I can gain any addtional insight. Perhaps there is a way to get around this existing  reagent problem. Let me know what you bees think and I'll keep you posted!

Yours in thought

Calamus

Rhodium:
What is usually used in NMR is tetramethylsilane (TMS), which is unreactive, and won't work in this reaction. Triethylsilane is Et3SiH.

abc123:
Rhodium,
Thanks for pointing out what I should have known.If TMS really was an acronym for trimethylsilane it couldn't be used in NMR because the protons on the molcule wouldn't be identical. I haven't had a chance to grab the article yet, but I'm guessing that the hydrogen attached to the silicone atom is essencial in the mechanism of this reduction. I better just read what I need to and quit talking before I put another foot in my mouth. Thanks for the info.

Calamus :-[

abc123:
I Think that perhaps if you reduced dopa first to an amphetamine via the subject method, and then reacted the amine with acetic anhydride as a protecting group, you could then perform your addtion of DCM to make a methelenedioxy structure. You could then remove the acetyl amide protecting group as you see fit to yeild the product of your choice.

Navigation

[0] Message Index

[#] Next page

[*] Previous page