Metal—atom reactor

Preparation of a Typical Au-Acetone Colloid. The metal atom reactor has been described previously. (39,59, 60) As a typical example, a W-A1 0 crucible was charged with 0.5Qg Au metal (one piece). Acetone (300 mL, dried over K2C0 ) was placed in a ligand inlet tube and freeze-pump-thaw degassed with several cycles. The reactor was pumped down to 1 x 10 Torr while the crucible was warmed to red heat. A liquid N2 filled Dewar was placed around the vessel and Au (0.2g) and acetone (80g) were codeposited over a 1.0 hr period. The matrix was a dark purple color at the end of the deposition. The matrix was allowed to warm slowly under vacuum by removal of the liquid N2 from the Dewar and placing the cold Dewar around the reactor. 

Fig. 3. Metal atom reactor. From Reference 1. Reproduced by permission.

A detailed drawing of a simple metal atom reactor, largely build from commercially available parts, is given in Fig. 2. The main reaction chamber consists of a 3000-mL reaction flask and a four-necked top section. This reactor is suitable for all the experiments described in this chapter, with the possible exception of the molybdenum compounds. For syntheses of a practical scale with refractory metals (vaporization temperature greater than 2000°, e.g. Re, Mo, and W) a larger diameter reactor (140-178 mm) with a standard wall thickness (about 3.5 mm) is recommended to improve heat dissipation. 

The maximum pressure that should be tolerated in a metal atom reactor is a point of controversy among various workers in this field. High pressures favor reaction in the gas phase with respect to those in the matrix. Where different products are obtained from the gas and condensed phases, the former products begin to appear at pressures of 10 4 torr. The molybdenum atom syntheses described in this volume are best carried out under 10 4 torr and with apparatus described in synthesis number 16. Skell and co-workers consider this apparatus necessary and appropriate for all work. 

A Teflon-coated magnetic stirring bar is placed in the reactor flask, and the metal atom reactor is assembled and pumped down to less than IX 10 3 torr as described in Section 11. Thirty milliliters (20 mmole) of l,3-bis(trifluoromethyl)-... 

Fig. 1. Detail of reaction zone of the metal-atom reactor. Suitable reactor dimensions are 15-18 cm diameter, 5 mm wall thickness and 36-46 cm depth. The water-cooled electrodes are 7.5 cm apart. The central substrate inlet tube, a 6 mm od Pyrex slightly constricted at the end, extends 5 cm below the liquid nitrogen level. A 14 mm od Pyrex tube which serves as a substrate deflector is positioned 5 cm below the inlet nozzle and is suspended horizontally between the electrodes. A built-in Pyrex syphon tube extends to the bottom of the reactor for the removal of air sensitive products under an inert atmosphere.

A solution metal atom reactor (after Timms), as shown in Figure 3, offers the opportunity to evaporate metal atoms... 

Lithium atoms produced in a metal-atom reactor react with simple alkenes at 700-800°C to give mixtures of dilithiobutenes in low yield ". ... 

Cadmium slurries, formed from codeposition of Cd vapor with a solvent at 77 K followed by warming to RT, are sufficiently reactive toward RI in hexane, toluene, THF, dioxane or diglyme. Reactions do not proceed well with RBr e.g., only a 10% yield of propylcadmiums is obtained on refluxing in diglyme overnight. The presence of KI increases the reactivity of the slurries. Ethyl iodide reacts at — 196°C with a Cd slurry, obtained from simultaneous evaporation of PhMe and Cd in a metal-atom reactor" the yield of nonvolatile EtCdl is 55 %. 

Figure 4. Schematic of a rotatable metal atom reactor for dual electron beam vaporization and cocondensation or liquid phase reaction.

Figure 5b. Rotatable cold finger photochemical metal atom reactor (after Billups et al. [30]).

A metal atom reactor is often used in a variety of "dirty" and "clean" operations. Accordingly, it should be remembered that radiation, adventitious water, oxygen, hydrocarbons, metallic particles and so on, can affect the properties of the isolated products. In the case of minute magnetic structures it is important to determine clearly the role of such agents in affecting volume and surface magnetic properties. Incorporation of a high vacuum Schlenk manifold such as the one described by Wayda in this book, should be considered an important supplement to the VS equipment. 

Figure 8. Rotatable metal atom reactor for conducting liquid phase metal atom induced polymerizations of organic monomers.

It is a pleasure to acknowledge helpful discussions with Mr. V. E. Lamberti, Dr. A. L. Wayda, and Professors G. A. Ozin and K. J. Klabunde. The technique for alkali metal atom induced anionic polymerization was developed in collaboration with Ms. S. A. Heffner and Dr. M. E. Galvin. Thanks are due to Torrovap Industries and G. V. Planar Ltd. for providing technical information about their metal atom reactors. 

Heated Inlet System for Cocondensation Metal Atom Reactor... 

Recovering Air-Sensitive Products from Metal Atom Reactors... 

Slurries of finely divided Mg are prepared in TIIF at -1 IO C by v tpori/ing Mg in a rotary metal atom reactor. The resulting pyrophoric Mg clusters are "dean, alkali halide free, and extremely reactive 11311. In their Grignard reactions, there is immediate initiation. Reactions tend to be complete in short times (in the case of isopentyl bromide in THF at 2() C. a minimum time for the addition of RBr to the Mg slurry plus <1 min) and they give 100% yields of RH l rom isopenlyl bromide or f )tr/o-5-(2 -haIoeihyl)-2-norbornene]. alter quenching with 10% aqueous HCI. in reactions at temperatures from -80 to 20 C I3I. In no case have products of c (e g.. RR) been found. 

An active form of cadmium metal and zinc metal slutried in several solvents can be pFQ>ared by codeposition of metal vapors (atoms) and excess solvent on the walls of a metal atom reactor at 77°K. The slurries are sometimes so fine that they can be handled with a syringe. 

Dimethylfulvene and 250 mg nickel vapor were co-deposited at — 196°C in a conventional metal atom reactor, and 130 mg of 6,6-dimethylMvene dimmer was isolated upon sublimation of the residue. 

Fig. 10.1 Metal atom reactor. A - Glass reaction vessel. B - Electron beam furnace, model EBSl, G.V. Planer Ltd. C - Vapour beam of metal atoms. D - Co-condensate of metal and substrate vapours. E - Heat shield. F - Furnace cooling water pipes. G - Electrical lead for substrate solution dispersion device. H - Furnace electrical leads. J - Substrate inlet pipe (vapour). K - Substrate inlet pipes (solution). M - Rotation of reaction vessel. N - To vacuum rotating seal, service vacuum lead troughs and pumping systems. 0-Level of coolant (usually liquid nitrogen). P-Capped joint for product extraction. 0-Substrate vapour dispersion device. R-Substrate vapour beam. (From Green, M.L.H., 1980, /. Organomet. Chem., 300, 119.)...

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