Hydrogen generator, sodium hydride

A schematic illustration of a typical inlet apparatus for separating volatile hydrides from the analyte solution, in which they are generated upon reduction with sodium tetrahydroborate. When the mixed analyte solution containing volatile hydrides enters the main part of the gas/liquid separator, the volatiles are released and mix with argon sweep and makeup gas, with which they are transported to the center of the plasma. The unwanted analyte solution drains from the end of the gas/liquid separator. The actual construction details of these gas/liquid separators can vary considerably, but all serve the same purpose. In some of them, there can be an intermediate stage for removal of air and hydrogen from the hydrides before the latter are sent to the plasma. 

Fig. 2 Apparatus for hydrogenation with hydrogen generated from sodium boro-hydride.

The actual mechanism is rather complicated. Hydrogen gas is evolved, but in reality free sodium hydride is never generated. See McGill and Rappa (1988). 

A better hydrogenation catalyst was generated by reaction of alkene metathesis ruthenium catalyst, with sodium hydride, after the RCM reaction was performed. In that case, hydrogenation can be performed under 1 bar of H2 at 20 °C [86]. Thus, cyclopentanols can be selectively prepared in one pot by RCM of the parents dienes, followed by addition of NaH and hydrogenation [86] (Scheme 40). 

The anion 19 or 20 has most generally been prepared by removal of the hydrogen bonded to a carbon a to the cyano group by a base such as phenyllithium in ether-dioxan at —10 to — 20° or by a base such as sodium hydride at the temperature of refluxing xylene. Recent work, however, has shown that these anions can be generated and caused to react at room temperature by use of sodium hydride in dimethyl-formamide. " ... 

Caution. Since hydrogen gas is generated by the action of sodium hydride, a well-ventilated fume hood is required, as is the exclusion of all open flames near the work area. 

The mixture is stirred at ambient temperature until the generation of hydrogen can no longer be observed ( 2 days). The sodium chloride and utueacted sodium hydride are removed by filtration, the solvent is removed under vacuum, and the residue is distilled under high vacuum using the short-path distillation apparatus described in this volume. " The yield of / .P -methanetetraylbis [N,A ,A , A , A ",A "-hexamethylphosphoranetriamine] [[(CH3)2N]3P=C=P [N(CH3)2l3] is 6.4 g (86%), bp 87° (5 X 10" torr). It is a colorless liquid that crystallizes to a solid that melts at 51° P H NMR (d-THF) 8 27.7. 

It may be destroyed in several ways. One method is as follows (Aldrich 1995). The solid or its solution is dissolved or diluted in large volume of water. Diluted acetic acid or acetone is then slowly added to this solution in a well-ventilated area. Hydrogen generated from decomposition of borohydride should be carefully vented out. The pH is adjusted to 1. The solution is then allowed to stand for several hours. It is then neutralized to 7, and the solution is then evaporated to dryness. The residue is then buried in a landfill site approved for hazardous waste disposal. Sodium borohydride may be destroyed in the laboratory by alternative methods mentioned for other hydrides. 

The ylide was prepared by refluxing a mixture of 0.04 mol sodium hydride, 5.12 g (0.04 mol) trimethyloxosulfonium chloride, and 30 mL dry tetrahydrofuran under nitrogen until the evolution of hydrogen ceased ( 2 h). With the reaction mixture held at 55°C, a solution of 3.18 g (0.03 mol) benzaldehyde in 30 mL dry tetrahydrofuran was slowly added dropwise with stirring over a period of 1.5 h and the reaction mixture was then stirred at 55°C for an additional hour. The mixture was concentrated under reduced pressure (generated by a water aspirator) to a volume of 10 mL, then 50 mL water was added. The mixture was extracted with pentane (some resinous material remained in the aqueous phase). The combined pentane extracts were dried over anhydrous sodium sulfate and evaporated the pale yellow residue was evaporatively distilled at 80°C (5.0 mmHg) to yield 2.0 g of colorless styrene oxide, in a yield of 55.6%. 

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