Ch5b-handlingOMcmps

Ch5b-handlingOMcmps - Development of Techniques for...

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Development of Techniques for Handling Organometallic Compounds . as with other physical sciences, development is strongly coupled with advances in techniques: NMR, ir, X-raY crYstallograPhY . Many organometallic are air-sensitive, so technique development in handling compounds in vacuum or an inert atmosphere are central . Increasing degree of sophistication. ..exclusion of 02 and H2O- simple funnel with N2 flow over flask, filter frit, etc' glove bag Schlenk tubes* cannula methods inert atmosphere boxes (several types)* high vacuum line(*) *depends uPon PuritY of inert gas . Historical: 1900- Alfred Stock developed chemical vacuum line for handling aolatile non- metal hydrides (boranes, silanes, efc.). Rotafi oil-filled vacuum pumP had just been developed. ..improved vacuum. Used soft glass; not able to withstand thermal shock; Hg pools used. on stopcocks. Stock's death was a result of Hg poisoning. 7920- others (Anton Berg; HC Brown) pick up on Stocks design, add their own wrinkles. ' Starting about L960- new materials (silicones, teflon, flexible metal lines and connectors) led to better lines . Glove bag to vacuum atmosphere's system. .. plexiglas, Al, stainless steel types of procedures for maintaining Pure inert gas. ..gas types (He, NZ, Ar) Na/K; supported 02 removing materials circulating pathways and effectiveness of Oz/HzO removal dessiccants: LNz(10-23 Torr); CaH2.4A MS(10-3 Torr), Al2O3, CaCl2 (0.2 Torr)
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Z Mer6ury yg;yg Rubbet lubing 8o ll beoring +To vocuum regulotot ond vocuum pump To nitrogen lin e Boll beoring ---\\ Mercury seol (see Fi9. Z.4) Sleom lnerl gos (nilrogen) Sle om Fig.7.1. Three-neck reaction flask with dropping funnel, stirrer, and reflux condenser. This type of setup is frequently used for Grignard and similar reactions. (By permission from Fieser and Fieser, York, 1967.) Woter G loss he Iices Nitrogen filled bolloon (b) Fig.7.2- (a) Distillation under inert atmosphere: Note that the complete apparatus should be purged initially, but a florv through the apparatus during distillation reduces the efficiency of separation. The sidearm arlorvs one to primp out the stoppered flask and fill it with nitrogen before it is attached to the still. Also, it allorrs one to maintain a brisk nitrogen florv over the solvent lvhen it is removed from thc still. (b) Distillation at reduced pressure r.ith minimum exposure to the atmosphere: The nitrogen-filled balloon may be replaced by a hose connected to a nitrogen source. During the vacuum distillation the three-rvay stopcock is turned so the upper and lorver sections communicate, but nitrogen does not enter. The ot_her stopcocks are open. The reflux ratio is adjusted by turning the cold finger. \\'hen a sample is to
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This note was uploaded on 01/03/2012 for the course CH 102 taught by Professor Hill,m during the Fall '08 term at Caltech.

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Ch5b-handlingOMcmps - Development of Techniques for...

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