Hydrogen, nascent

Tantalum. Above 300°C (570°F), the possibihty of reactivity of tantalum with all gases except the inert gases. Below 300°C (570°F), the possibility of embrittlement of tantalum by nascent (monatomic) hydrogen (but not molecular hydrogen). Nascent hydrogen is produced by galvanic action or as a product of corrosion by certain chemicals. 

Hydrogen. Nascent hydrogen (Zn + H2SO4) and H2PHO3 yield PH3. 

Bouveault-Blanc reduction The reduction of esters to alcohols by nascent hydrogen gen-... 

Place a few drops of nitromethane in a test tube, add about 3 times as much concentrated hydrochloric acid, and then a piece of granulated tin. The tin dissolves in the acid and the nascent hydrogen produced reduces the nitromethane to monomethylamine ... 

Both aliphatic and aromatic nitro-compounds can be readily reduced in acid solution to the corresponding primary amine. Thus when a mixture of nitrobenzene and tin is treated with hydrochloric acid, the tin dissolves to give stannous chloride, SnCh, which in these circumstances then reacts with more acid to give stannic chloride, SnCl, and the nascent hydrogen produced from... 

Mono and Di-iubstitution Derivatives. The enolic sodium derivative of ethyl acetoacetate (E) is prepared by mixing ethanolic solutions of the ester and of sodium ethoxide. It should not be prepared by the direct action of metallic sodium on the ester, as the reaction is slow and the nascent hydrogen evolved reduces some of the ester to ethyl p4iydroxy- butyrate, CH3CH(OH)CHjCOOEt. 

Another approach for the production of phosphine is an aqueous electrolytic process, whereby nascent hydrogen reacts with elemental phosphoms (70). Phosphine is produced at the cathode. 

In past years, metals in dilute sulfuric acid were used to produce the nascent hydrogen reductant (42). Today, the reducing agent is hydrogen in the presence of a catalyst. Nickel, preferably Raney nickel (34), chromium or molybdenum promoted nickel (43), or supported precious metals such as platinum or palladium (35,44) on activated carbon, or the oxides of these metals (36,45), are used as catalysts. Other catalysts have been suggested such as molybdenum and platinum sulfide (46,47), or a platinum—nithenium mixture (48). 

Nascent atomic hydrogen released at metal surfaces by chemical reactions between the process environment and the metal (corrosion or cathodic protection reactions)... 

Nascent atomic hydrogen released by a process reaction such as catalytic desulfurization... 

In many applications tantalum can be substituted for platinum and gold, and there are some environments in which tantalum is more corrosion resistant than platinum. Table 3.37 lists the main chemicals for which tantalum is not a suitable substitute for platinum and, conversely, those for wliich tantalum is better than platinum. Tantalum is rapidly embrittled by nascent hydrogen even at room temperature. Therefore, it is very important to avoid the formation of galvanic couples between tantalum and other metals. 

Arsine, AsHs, is formed when many As-containing compounds are reduced with nascent hydrogen and its decomposition on a heated glass surface to form a metallic mirror formed the basis of Marsh s test for the element. The low-temperature reduction of AsCls with LiAlH4 in diethyl ether solution gives good yields of the gas as does the dilute acid hydrolysis of many arsenides of electropositive elements (Na, Mg, Zn, etc.). Similar reactions yield stibine, e.g. ... 

Aldehydes are also formed by the action of nascent hydrogen (sodium amalgam) upon the chlorides of acid radicles or their oxides (the acid anhydrides) —... 

In the chemical process industry molybdenum has found use as washers and bolts to patch glass-lined vessels used in sulphuric acid and acid environments where nascent hydrogen is produced. Molybdenum thermocouples and valves have also been used in sulphuric acid applications, and molybdenum alloys have been used as reactor linings in plant used for the production of n-butyl chloride by reactions involving hydrochloric and sulphuric acids at temperatures in excess of 170°C. Miscellaneous applications where molybdenum has been used include the liquid phase Zircex hydrochlorination process, the Van Arkel Iodide process for zirconium production and the Metal Hydrides process for the production of super-pure thorium from thorium iodide. 

Alcohols react with nascent hydroiodic acid to form alkyl iodides. When the starting material is an alcohol ether sulfate, the resulting alcohol ethoxylate obtained by acid hydrolysis of the sulfate gives the corresponding alkyl iodides. The number of moles of diiodoethane equals the number of moles of ethylene oxide present in the alcohol ethoxylate. Diiodoethane decomposes or reacts with more hydrogen iodide to give iodine quantitatively in both cases. However,... 

In the past it had been a popular belief that the electrochemical reduction of any inorganic or organic substance involves the primary electrochemical formation of a special, active form of hydrogen in the nascent state (in statu nascendi) and subsequent chemical reaction of this hydrogen with the substrate. However, for many reduction reactions a mechanism of direct electron transfer from the electrode to the substrate could be demonstrated. It is only in individual cases involving electrodes with superior hydrogen adsorption that the mechanism above with an intermediate formation of adsorbed atomic hydrogen is possible. 

Since koumine has been reductively cleaved by nascent hydrogen (sodium-EtOH) to afford a C20 primary alcohol (39), the above deduction based on spectroscopic analysis is supported chemically (Scheme 6). 

The mechanism of activation is believed to be as follows. In an alkaline medium, hydrogen peroxide yields the perhydroxide anion (Scheme 10.22), which reacts with TAED (10.86) to form diacetylethylenediamine (10.87) and the peracetate anion (10.88) as in Scheme 10.30 [244]. At pH 8-9, the peracetate anion is in equilibrium with free peracetic acid, as in Scheme 10.31 [244]. The peracetic acid reacts with the peracetate anion to form nascent oxygen which is the active bleaching agent, as in Scheme 10.32 [244]. Further possible activators suggested by Kleber [244] include ... 

The uniqueness of arsine revolves primarily around its accidental formation (need for nascent hydrogen) resulting in relatively unexpected exposures. 

In the cell, chlorate and bromate are converted to chloride and bromide at the cathode by reduction with nascent hydrogen, although the chlorate reacts only partially. The chlorate remaining in the cell-liquor can be reduced with thiosulphate or another chemical reducing agent ... 

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