Hydride, sodium

Caviion. The same precautions outlined in the preparation of sodium dispersions (synthesis 2) must be observed. 

Equipment Cleanup. The same procedure employed for sodium dispersions is used (synthesis 2). 

Sodium hydride is a colorless to grayish-white, crystalline solid, consisting of sodium and hydride ions arranged in a lattice of the sodium chloride type (a = 5.53 A.). The density is 0.92 0 and the heat of formation 13.8 kcal./mol. Heating causes the solid to dissociate to sodium and hydrogen, the pressure of the latter being expressed by the equation1 

Between 400 and 430° the hydrogen pressure reaches 1 atm. The melting point (under pressure) is above 800°. Sodium hydride dissolves in fused sodium hydroxide and in fused alkali halides. It is insoluble in liquid ammonia. Water decomposes it immediately and completely to hydroxyl ion and hydrogen. Although sodium hydride is said to be stable in dry oxygen to 230°, traces of elemental sodium present may cause its ignition at lower temperatures. Copper, lead, and iron oxides are reduced by the compound to the free metals. Sulfur dioxide, carbon monoxide, and the halogens are reduced by the hydride to dithionite, formate, and halide ions, respectively. 

Dispersions of sodium hydride in oil are white or light gray and have roughly the same viscosity characteristics as sodium dispersions (synthesis 2). Such dispersions are useful as safe and convenient means of adding sodium hydride in such reactions as Claisen or Stobbe condensations, in preparations of complex hydrides, and in reductions of metal salts. 

Solubility decomposes in water insol all organic solvents insol liq NH3 sol molten sodium. 

Form Supplied in free-flowing gray powder (95% dry hydride) gray powder dispersed in mineral oil. 

Handling, Storage, and Precautions the dispersion is a solid and may be handled in the air. The mineral oil may he removed from the dispersion by stirring with pentane, then allowing the hydride to settle. The pentane/mineral oil supernatant may he pipetted off, but care should be exercised to quench carefully any hydride in the supernatant with a small amount of an alcohol before disposal. The dry powder should only be handled in an inert atmosphere. 

Sodium hydride dust is a severe irritant and all operations should be done in a fume hood, under a dry atmosphere. Sodium hydride is stable in dry air at temperatures of up to 230 °C before ignition occurs in moist air, however, the hydride rapidly decomposes, and if the material is a very fine powder, spontaneous ignition can occur as a result of the heat evolved from the hydrolysis reaction. Sodium hydride reacts more violently with water than sodium metal (eq 1) the heat of reaction usually causes hydrogen ignition. 

Sodium hydride in DMF is also used to deprotonate carbohydrate derivatives, for methylation or benzylation (eq 4).  

CONTACT WITH WATER LIBERATES HIGHLY FLAMMABLE 

Silvery needles the commercial product is a gray-white powder dec, 425°C.  

Flammable solid may ignite in moist air. Do not use water, carbon dioxide, dry chemical, or halogenated extinguishers. Extinguish frre by smothering with dry sand or class D extinguisher.2 

Reacts explosively with water, and violently with lower alcohols ignites spontaneously on standing in moist air.1 

Acetylene. Reacts vigorously in the presence of moisture even at -60°C.3 Air. The finely divided dry powder ignites in dry air.4 Dimethyl Sulfoxide. Mixture explodes if heated above 70°C.5 Halogens. Incandesces in chlorine or fluorine at room temperature and in iodine at 100°C.3 

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An alternative method for ascertaining the end of the reaction, which does not involve the removal of the cover, is to conduct the exit gas through an empty wash bottle (to eict as a trap in case of sucking back ) and then collect a sample in a test-tube over water. If an inflammable gas (hydrogen) is absent, the reaction may be considered complete. Under no circumstances should the reaction be stopped until all the sodium has completely reacted too early arrest of the reaction may result in the product containing sodium hydride, which appears to be partially responsible for the explosive properties of the impure substance ... 

The condensation of aldehydes and ketones with succinic esters in the presence of sodium ethoxide is known as the Stobbe condensation. The reaction with sodium ethoxide is comparatively slow and a httlo reduction of the ketonic compound to the carbinol usually occurs a shorter reaction time and a better yield is generally obtained with the more powerful condensing agent potassium ieri.-butoxide or with sodium hydride. Thus benzophenone condenses with diethyl succinate in the presence of potassium [Pg.919]

The formation of the above anions ("enolate type) depend on equilibria between the carbon compounds, the base, and the solvent. To ensure a substantial concentration of the anionic synthons in solution the pA" of both the conjugated acid of the base and of the solvent must be higher than the pAT -value of the carbon compound. Alkali hydroxides in water (p/T, 16), alkoxides in the corresponding alcohols (pAT, 20), sodium amide in liquid ammonia (pATj 35), dimsyl sodium in dimethyl sulfoxide (pAT, = 35), sodium hydride, lithium amides, or lithium alkyls in ether or hydrocarbon solvents (pAT, > 40) are common combinations used in synthesis. Sometimes the bases (e.g. methoxides, amides, lithium alkyls) react as nucleophiles, in other words they do not abstract a proton, but their anion undergoes addition and substitution reactions with the carbon compound. If such is the case, sterically hindered bases are employed. A few examples are given below (H.O. House, 1972 I. Kuwajima, 1976). 

Sodium hydride (9.3 g, 0.22 mol) was washed with petroleum ether and DMSO (200 ml) was added and the mixture was heated to 100°C. A solution of diethyl malonate (35.2 g, 0.22mol) in DMSO (50 ml) was then added and stirred for 10 min to give a clear solution. A solution of 4-bromo-3-nitrobenzophenone (30.6 g, 0.10 mol) in DMSO (100 ml) was added and the resulting dark solution kept at 100 C for 1 h. The solution was poured into water (3 1) and extracted (2x) with ether. The extract was washed with water, dried (NajSOj and concentrated in vacuo to give an oil which crystallized. The solid was recrystallized from isopropyl alcohol to give 35.4 g (92% yield) of the product. 

Sodium hydride was used as the base in this example It is often used instead of sodium ethoxide in these reactions... 

Binary Compounds of Hydrogen. Binary compounds of hydrogen with the more electropositive elements are designated hydrides (NaH, sodium hydride). 

Dimethylsulfoxide Acyl and aryl halides, boron compounds, bromomethane, nitrogen dioxide, magnesium perchlorate, periodic acid, silver difluoride, sodium hydride, sulfur trioxide... 

Glycerol Acetic anhydride, hypochlorites, chromium(VI) oxide, perchlorates, alkali peroxides, sodium hydride... 

Sulfur dioxide Halogens, metal oxides, polymeric tubing, potassium chlorate, sodium hydride... 

The imide proton N-3—H is more acidic than N-1—H and hence this position is more reactive toward electrophiles in a basic medium. Thus hydantoins can be selectively monoalkylated at N-3 by treatment with alkyl haUdes in the presence of alkoxides (2,4). The mono-A/-substituted derivatives (5) can be alkylated at N-1 under harsher conditions, involving the use of sodium hydride in dimethylform amide (35) to yield derivatives (6). Preparation of N-1 monoalkylated derivatives requires previous protection of the imide nitrogen as an aminomethyl derivative (36). Hydantoins with an increased acidity at N-1—H, such as 5-arylmethylene derivatives, can be easily monoalkylated at N-3, but dialkylation is also possible under mild conditions. 

Similarly, hydantoins can be arylated at N-3. For example, treatment of 5,5-diphenyIhydantoin (4), R = R = Cg (phenytoin), with -tolyUead triacetate in the presence of sodium hydride and a catalytic amount of copper(II) acetate (37) gives compound (7). 

Sodium Hydride. Sodium hydride [7646-69-7] decomposes to its elements without melting, starting at ca 300°C. Decomposition is rapid at 420°C. The dissociation pressure in kPa between 100 and 600°C for the decomposition range 15—90% NaH can be found from... 

Sodium hydride is insoluble in organic solvents but soluble in fused salt mixtures and fused hydroxides such as NaOH. It oxidizes in dry air and hydrolyzes rapidly in moist air. The pure material reacts violently with water ... 

Sodium hydride is manufactured by the reaction of hydrogen and molten sodium metal dispersed by vigorous agitation ia mineral oil (4). 

Preparation. Sodium borohydride is manufactured from sodium hydride and trimethyl borate ia a mineral oil medium at about 275°C (26),... 

J. Plesek and S. Hermanek, Sodium Hydride Its Use in the Eaboratoy and in Technology, trans. by G. Jones, Academic, Prague, 1968. 

A AlI lation. 1-Substitution is favored when the indole ring is deprotonated and the reaction medium promotes the nucleophilicity of the resulting indole anion. Conditions which typically result in A/-alkylation are generation of the sodium salt by sodium amide in Hquid ammonia, use of sodium hydride or a similar strong base in /V, /V- dim ethyl form am i de or dimethyl sulfoxide, or the use of phase-transfer conditions. 

Sodium hydride, sodium amide, or other strong bases also can be used. The reagent can be generated in the presence of an appropriate carbonyl compound that reacts direcdy. 

Fig. 3. Synthesis of fluoxetine (31). 3-ChIoro-I-phenyl-I-propanol reacts with sodium iodide to afford the corresponding iodo derivative, followed by reaction with methylamine, to form 3-(methyl amin o)-1-phenyl-1-propan 0I. To the alkoxide of this product, generated using sodium hydride, 4-fluorobenzotrifluoride is added to yield after work-up the free base of the racemic fluoxetine (31), thence transformed to the hydrochloride (51)...

Isoquinoline can be reduced quantitatively over platinum in acidic media to a mixture of i j -decahydroisoquinoline [2744-08-3] and /n j -decahydroisoquinoline [2744-09-4] (32). Hydrogenation with platinum oxide in strong acid, but under mild conditions, selectively reduces the benzene ring and leads to a 90% yield of 5,6,7,8-tetrahydroisoquinoline [36556-06-6] (32,33). Sodium hydride, in dipolar aprotic solvents like hexamethylphosphoric triamide, reduces isoquinoline in quantitative yield to the sodium adduct [81045-34-3] (25) (152). The adduct reacts with acid chlorides or anhydrides to give N-acyl derivatives which are converted to 4-substituted 1,2-dihydroisoquinolines. Sodium borohydride and carboxylic acids combine to provide a one-step reduction—alkylation (35). Sodium cyanoborohydride reduces isoquinoline under similar conditions without N-alkylation to give... 

Lithium hydride is perhaps the most usehil of the other metal hydrides. The principal limitation is poor solubiUty, which essentially limits reaction media to such solvents as dioxane and dibutyl ether. Sodium hydride, which is too insoluble to function efficiently in solvents, is an effective reducing agent for the production of silane when dissolved in a LiCl—KCl eutectic at 348°C (63—65). Magnesium hydride has also been shown to be effective in the reduction of chloro- and fluorosilanes in solvent systems (66) and eutectic melts (67). 

Hydrogen and sodium do not react at room temperature, but at 200—350°C sodium hydride is formed (24,25). The reaction with bulk sodium is slow because of the limited surface available for reaction, but dispersions in hydrocarbons and high surface sodium react more rapidly (7). For the latter, reaction is further accelerated by surface-active agents such as sodium anthracene-9-carboxylate and sodium phenanthrene-9-carboxylate (26—28). 

The reaction is displaced to the right by dissociation of sodium hydride and Hberation of hydrogen. This dissociation is favored under vacuum or when the reaction 2one is swept with an inert gas to remove the hydrogen (24,25). In this manner, sodium monoxide substantially free of sodium and sodium hydroxide is produced. In the more compHcated reaction between sodium metal and anhydrous potassium hydroxide, potassium metal and sodium hydroxide are produced in a reversible reaction (42,43) ... 

Aromatic aldehydes (100), eg, cinnamaldehyde, and ketones (101) react ia a similar manner (eq. 4). Ketones containing reactive methyl or methylene groups give with succiaates, ia the presence of sodium hydride, both the Stobbe condensation and the formation of diketones by a Claisen mechanism (102) (eq. 5). 

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