Ammonia formation reduction

As first demonstrated by Stork,the metal enolate formed by metal-ammoni reduction of a conjugated enone or a ketol acetate can be alkylated in liquic ammonia. The reductive alkylation reaction is synthetically useful since ii permits alkylation of a ketone at the a-position other than the one at whicf thermodynamically controlled enolate salt formation occurs. Direct methyl-ation of 5a-androstan-17-ol-3-one occurs at C-2 whereas reductive methyl-... 

In systems of conjugated double bonds catalytic hydrogenation usually gives a mixture of all possible products. Conjugated dienes and polyenes can be reduced by metals sodium, potassium, or lithium. The reduction is accomplished by 1,4-addition which results in the formation of a product with only one double bond and products of coupling and polymerization. Isoprene was reduced in 60% yield to 2-methyl-2-butene by sodium in liquid ammonia [357]. Reduction of cyclooctatetraene with sodium in liquid ammonia gave a... 

The in-series two-step pathway described above is able to account for the temporal evolution of the product which is observed during the reduction of stored NO, with nearly complete N2 selectivity at the beginning of the reduction process and significant ammonia formation near the end of the regeneration step (see Figure 13.17). 

Pyrroles are not reduced by sodium in liquid ammonia, but the Birch reduction of 2-furoic acid with lithium in liquid ammonia gives the 2,5-dihydro derivative in 90% yield (780PP94). Sodium-liquid ammonia-methanol reduction of thiophene gives a mixture of A2- and A3- dihydrothiophenes together with butenethiols. Reductive metallation of 1,3-diphenylisobenzofuran results in stereoselective formation of the cis- 1,3-dihydro derivative (Scheme 36) (80JOC3982). 

In the reduction of nitrite, Horold found that supports with lower surface areas showed improved selectivity for nitrogen over ammonia. The same study found that silica supports had much higher selectivity (i.e. much less ammonia formation) than alumina supports. (Horold et al. 1993)... 

If a reacting solution is acid quenched then a small amount of hydrazine, derived probably from an intermediate reduction product, is formed. The rate of ammonia formation is linear in PN2 and depends on the square of vanadium concentration, but the actual rate is a function of dioxygen pressure, metal contaminants, etc. The mechanism is believed to follow the pattern discussed above, with dinitrogen bound between two dinuclear pairs of vanadium(II) ions (232, 233), but the precise identity of the fixing species remains a mystery. 

Hydrazine is an intermediate in the formation of ammonia from reduction of N2 by titanium(m) in the presence of molybdenum compounds. Hydrogen is also produced by reaction of the titanium(iv) with the methanol solvent. Activation energies were determined for the formation of these three products.120 The preparation and n.m.r. spectra of Mg, Zn, and Cd derivatives of nonahydrohexaboratobis(cyclopenta-dienyl)titanium(m) have been reported.121... 

A large excess of ammonia suppresses formation of di- and trialkylamines. With a rhodium-on-carbon catalyst in process conditions of 75°C and 50 psig plus continuous removal of ammonia, the reduction of propionitrile with hydrogen proceeds with greater than 85% selectivity for di-n-propylamine, with 2 to 5% mono-n-propylamine coproduct. Several companies produce amines in the C 2 to Ci8 range from fatty nitriles by this route116. 

Finally, the hydrazine reduction reaction is unaffected by either dihydrogen or dideuterium, i.e., under either, there is no inhibition of ammonia formation, and under dideuterium, there is no HD production. Assuming that bound hydrazine reacts in the same manner as added hydrazine, then the dihydrogen and dideuterium effects must occur prior to the formation of bound hydrazine, and again a diimide-level species is implicated. 

A cortisone synthesis using remote functionalization at an unactivated carbon centre has been achieved.97 Cortexolone (224) was converted into the 5a-H,3j3-OH derivative (formation of the bismethylenedioxy-compound followed by lithium-ammonia-ethanol reduction). Inversion98 of 3)8- to 3 -OH followed by esterification with m-iodobenzoic acid produced (225), which on irradiation in methylene chloride containing phenyl iodide dichloride gave the 9 a -chloro-derivative (not isolated). This was dehydrohalogenated and saponified by methanolic potash to yield (226) (75%) and thence, by further known steps, cortisone acetate. 

In practice, the reduction temperature is raised stepwise by using the exothermic heat of ammonia formation. The progress of the reduction is controlled according to the catalyst temperature and the water concentration by adjustment of the synthesis gas flow. As a rough guideline, the water content of the gas effluent from the catalyst should not exceed 2-3 g/m3 (STP). Under these conditions, depending on its size and operating pressure, a synthesis converter with a fresh load of oxidic catalyst attains its full production capacity in 4-10 d. 

Open-chain acetylenes yield pure trans alkenes on reduction with alkali metal in liquid ammonia. However, reduction of cyclodecyne (111) with sodium in liquid ammonia led to a mixture of cis- (112, > 90%) and /rn/w-cyclodecene (113, > 4%y -The formation of the cis isomer (112) was attributed to the reduction of 1,2-cyclo-decadiene (114) formed by a rapid isomerization of the starting cycloalkyne, while the formation of the trans isomer (113) was ascribed to the direct reduction of 111. 

Controlled-current methods can be of particular value when the process being studied is the background process, such as solvated electron formation in liquid ammonia or reduction of quaternary ammonium ion in an aprotic solvent. A simple method for determination of the thickness of metal films is by anodic stripping at constant current. Working with background processes in a controlled-potential mode is often difficult. 

Reduction of nitrates Denitrifying bacteria Nitrite formation Ammonia formation Possible production of chloramines and odour... 

During the regeneration of the NOx trap, two major routes are commonly admitted for the ammonia formation. The first one is the direct reaction of stored NOx with hydrogen, as described in reaction (19.1) [13, 17]. This route was proposed over Pt-Ba/Al203 material, when H2 is used as the reductant [18]. Artioh et al. [19] observed that, depending on the gas feed composition, ammonia is emitted together with CO2 consumption, as reported in reaction (19.2). 

The direct ammonia formation mechanism (reactions 19.1 and 19.3), when only H2 is used as reductant, was studied in Ref. [11]. Authors proposed that hydrogen reacts firstly with the platinum surface on which oxygen species (Oa), resulting from the reduction of NO2, remain adsorbed (reaction 19.4). 

The nature of the basic storage phase also affects the ammonia formation. For instance, the comparison of usual Pt-Ba/Al203 catalyst with Pt-K/Al203 sample (with similar molar amount of basic element, i.e., Ba or K) evidences a higher N2 selectivity during the reduction step with H2 for the NOx stored over the K phase [17]. Authors report a similar reactivity for the H2 + nitrate and NH3 + nitrate... 

Le Phuc N, Corbos EC, Courtois X, Can F, Marecot P,.Duprez D (2009) NOx storage and reduction properties of Pt/CexZrl —x02 mixed oxides Sulfur resistance and regeneration, and ammonia formation. Appl. Catal. B. 93 12-21... 

This theory covers the formation of pit growth inhibiting species. It is basically linked with the ammonia formation theory. The NH4-i--formation in the pit tip appears to happen quicker than the OH—formation due to oxide reduction at the pit entrance. 

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