Preparation of Calcium Hydride

Put not more than 1-2 g of freshly cut metallic calcium shavings into iron or porcelain boat 4, place the latter into the middle of reaction tube 5, and again test the tightness of the apparatus (in the presence of your instructor .  

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The preparation of calcium bis[tetrahydroborate(l —)] described here is recommended because high yields of pure product are usually obtained without difficulty. If the material should be contaminated by impurities from the calcium hydride, then it may be extracted with THF. Needles of Ca[BH4]-2THF11,21,22 may be obtained from this solution. The THF can then be readily removed by heating and pumping. 

The reaction of calcium hydride with water can be used to prepare hydrogen gas ... 

USE To prepare rare metals by reduction of their oxides as a drying agent for liquids and gases to generate hydrogen 1 g of calcium hydride in water liberates 1 liter of hydrogen at STP in organic syntheses. 

Lithium cyanotrihydridoborate reduces aldehydes in hot dioxan, e.g., pyrenecarbaldehyde in 85% yield, but does not affect aliphatic or aromatic ketones.380 Of the alkaline-earth boron hydrides, only calcium hydridotrimethoxyborate has been mentioned it is prepared from calcium hydride and trimethyl borate and its preparative use for reduction of carbonyl compounds has been investigated by Hesse and Jager.381... 

Both the triethylstannyl (19) and the trimethylsilyl (20) derivatives of cyanoacetylene (1) were prepared several years ago. Derivative 19 is available by reacting bis(triethylstannyl) ether with 1 in the presence of calcium hydride in benzene [27], and 20 can be obtained from 19 by trimethylsilyl bromide treatment in hmmethylphosphoramide (HMPA) [28] [Eq. (6)]. 

Synthesis of (+)-lactacystin Lactacystin 7 is one of the most important biologically active pyrrolidinone-based natural products found in nature. It was isolated from the culture broth of a Streptomyces in 1991, and since that time, it has generated an enormous interest as a consequence of its highly selective and irreversible inhibition of the 20S pro-teasome. Its synthesis was first reported by Corey and Reichard, and an alternative more recent approach is based on the preparation of an oxazoline 8 that is produced via formation of a 2-ethynyl-allyl epoxide 10 via Sharpless asymmetric epoxidation of the allyl alcohol 9 (Scheme 34.3). The reaction was carried out in the presence of catalytic amounts of calcium hydride and silica gel (whose role is not described in the paper) at —40°C to — 18°C obtaining the desired product 10 in 89% yield and >95% ee determined by integration of the F resonances of the corresponding Mosher ester derivative. 

Calcium hydride is prepared on a commercial scale by heating calcium metal to about 300°C in a high alloy steel, covered cmcible under 101 kPa (1 atm) of hydrogen gas. Hydrogen is rapidly absorbed at this temperature and the reaction is exothermic. 

TiH2 is prepared on an industrial scale by dkect combination of hydrogen and the metal (sponge, ingot, scrap, etc) at 200—650°C, followed by cooling in an H2 atmosphere. An alternative method is the reduction of the oxide using calcium hydride under hydrogen ... 

MetaHic potassium and potassium—sodium alloys are made by the reaction of sodium with fused KCl (8,98) or KOH (8,15). Calcium metal and calcium hydride are prepared by the reduction of granular calcium chloride with sodium or sodium and hydrogen, respectively, at temperatures below the fusion point of the resulting salt mixtures (120,121). 

Hydrogen can be prepared by the reaction of water or dilute acids on electropositive metals such as the alkali metals, alkaline earth metals, the metals of Groups 3, 4 and the lanthanoids. The reaction can be explosively violent. Convenient laboratory methods employ sodium amalgam or calcium with water, or zinc with hydrochloric acid. The reaction of aluminium or ferrosilicon with aqueous sodium hydroxide has also been used. For small-scale preparations the hydrolysis of metal hydrides is convenient, and this generates twice the amount of hydrogen as contained in the hydride, e.g. ... 

Mallinckrodt anhydrous diethyl ether was purified by refluxing with calcium hydride under nitrogen for at least 2 hours and distilling under nitrogen immediately before use. For use in the preparation of the propenyllithium, approximately 650 ml. of ether should be collected in a dry 1-1. graduated flask capped with a serum stopper. 

Calciothermic reduction of samarium oxide, in the presence of cobalt powder, yields samarium-cobalt alloys in the powder form. The process is popularly known as reduction diffusion. Samarium oxide, mixed with cobalt powder and calcium hydride powder or calcium particles, is heated at 1200 °C under 1 atm hydrogen pressure to produce the alloys. Cobalt oxide sometimes partly replaces the cobalt metal in the charge for alloy preparation. This presents no difficulty because calcium can easily reduce cobalt oxide. A pelletized mixture of oxides of samarium and cobalt, cobalt and calcium, with the components taken in stoichiometric quantities, is heated at 1100-1200 °C in vacuum for 2 to 3 h. This process is called coreduction. In reduction diffusion as well as in coreduction, the metals samarium and/or cobalt form by reduction rather quickly but they need time to form the alloy by diffusion, which warrants holding the charge at the reaction temperature for 4 to 5 h. The yield of alloy in these processes ranges from 97 to 99%. Reduction diffusion is the method by which most of the 500 to 600 t of the magnetic samarium-cobalt alloy (SmCOs) are produced every year. 

In the preparation of anhydrous DMSO by a literature method [1], an explosion occurred during distillation from anhydrous magnesium perchlorate [2], This may have been due to the presence of some free methanesulfonic acid as an impurity in the solvent, which could liberate traces of perchloric acid. It is known that sulfoxides react explosively with 70% perchloric acid, (but several metal perchlorates also form unstable solvates with DMSO) The alternative procedure for drying DMSO with calcium hydride [3] seems preferable, as this would also remove any acidic impurities. 

The iron(II) chloride7 is prepared from 1.5 g. (0.0268 mol) of iron powder (hydrogen-reduced, 100-mesh), 6.0 g. (0.370 mol) of anhydrous sublimed iron(III) chloride (Matheson, Coleman and Bell, reagent-grade), and 150 ml. of tetrahydrofuran (THF) freshly distilled under nitrogen from lithium tetrahydroaluminate or preferably calcium hydride. 

The 1,2-dimethoxyethane (Ansul Chemical Co.) was predried for several days over calcium hydride, filtered, and stored over lithium aluminum hydride prior to its distillation at atmospheric pressure immediately before use. For a larger-scale preparation it is expeditious to distil simultaneously from two 5-1. flasks rather than from a single large one. Under these conditions, distillation of the glyme can be completed in 8-10 hours. 

The use of acid chlorides in the preparation of amides has been reviewed.7 The diethylamine was distilled from calcium hydride prior to use. 

General. Toluene, chlorobenzene, and o-dichlorobenzene were distilled from calcium hydride prior to use. 4-Dimethylaminopyridine (Aldrich Chemical Co) was recrystalled (EtOAc), and the other 4-dialkylaminopyridines were distilled prior to use. PEG S, PEGM s, PVP s, and crown ethers were obtained from Aldrich Chemical Co., and were used without purification. BuJ r and BU. PBr were recrystallized (toluene). A Varian 3700 VrC interfaced with a Spectraphysics SP-4000 data system was used for VPC analyses. A Dupont Instruments Model 850 HPLC (also interfaced with the SP-4000) was used for LC analyses. All products of nucleophilic aromatic substitution were identified by comparison to authentic material prepared from reaction in DMF or DMAc. Alkali phenolates or thiol ates were pre-formed via reaction of aqueous NaOH or KOH and the requisite phenol or thiophenol in water under nitrogen, followed by azeotropic removal of water with toluene. The salts were transferred to jars under nitrogen, and were dried at 120 under vacuum for 20 hr, and were stored and handled in a nitrogen dry box. 

Dibutyl boron trlflate was prepared according to the method of Mukaiyama. It Is also available from Aldrich Chemical Company, Inc. as a solution in dichloromethane or diethyl ether, but results with this material are inconsistent. It should be used within 2 weeks of preparation or after redistillation. Triethylamine Fisher Scientific Company) was distilled from calcium hydride immediately prior to use. 

Monomeric styrene is destabilized as in Example 3-1 and pre-dried with calcium chlo-ride.The monomer is now allowed to stand over calcium hydride for 24 h and then distilled under reduced pressure of nitrogen into a previously flamed-out Schlenk tube. Pure 4-vinylpyridine is distilled twice over KOH pellets in vacuum.lt is then vacuum distilled under nitrogen through a column packed with Raschig rings into a previously flamed out Schlenk tube (bp 62 °C/12 torr).The closed Schlenk tubes containing the monomers are stored in a refrigerator until required.The preparation of the initiator solution (sodium naphthalene) is described in Example 3-19. 

Calcium hydride may be prepared from its elements by direct combination of calcium and hydrogen at 300 to 400°C. It also can be made by heating calcium chloride with hydrogen in the presence of sodium metal ... 

Alternatively, calcium hydride may be prepared by the reduction of calcium oxide with magnesium in the presence of hydrogen ... 

Titanium hydride is prepared by heating titanium dioxide with calcium hydride at 600°C in the presence of hydrogen. 

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