Reductive aqueous ammonia

Two different sets of experimental conditions have been used. Buu-Hoi et al. and Hansen have employed the method introduced by Papa et using Raney nickel alloy directly for the desulfurization in an alkaline medium. Under these conditions most functional groups are removed and this method is most convenient for the preparation of aliphatic acids. The other method uses Raney nickel catalysts of different reactivity in various solvents such as aqueous ammonia, alcohol, ether, or acetone. The solvent and activity of the catalyst can have an appreciable influence on yields and types of compounds formed, but have not yet been investigated in detail. In acetic anhydride, for instance, desulfurization of thiophenes does not occur and these reaction conditions have been employed for reductive acetylation of nitrothiophenes. Even under the mildest conditions, all double bonds are hydrogenated and all halogens removed. Nitro and oxime groups are reduced to amines. 

Besides direct reduction, a one-pot reductive amination of aldehydes and ketones with a-picoline-borane in methanol, in water, and in neat conditions gives the corresponding amine products (Scheme 8.2).40 The synthesis of primary amines can be performed via the reductive amination of the corresponding carbonyl compounds with aqueous ammonia with soluble Rh-catalyst (Eq. 8.17).41 Up to an 86% yield and a 97% selectivity for benzylamines were obtained for the reaction of various benzaldehydes. The use of a bimetallic catalyst based on Rh/Ir is preferable for aliphatic aldehydes. 

Thus, the technique can become counterproductive. A typical arrangement for selective non-catalytic reduction is shown in Figure 25.30. Aqueous ammonia is vaporized and mixed with a carrier gas (low-pressure steam or compressed air) and injected into nozzles located in the combustion device for optimum temperature and residence time10. NO, reduction of up to 75% can be achieved. However, slippage of excess ammonia must be controlled carefully. 

Rather than selective non-catalytic reduction, the reduction can be carried out over a catalyst (e.g. zeolite) at 150 to 450 C. This is known as selective catalytic reduction. Figure 25.31 shows a typical selective catalytic reduction arrangement10. Either anhydrous or aqueous ammonia can be used. This is mixed with air and injected into the flue gas stream upstream of the catalyst. Removal efficiency of up to 95% is possible. Again, slippage of excess ammonia needs to be controlled. 

Example 25.5 A gas turbine exhaust is currently operating with a flowrate of 41.6 kg s-1 and a temperature of 180°C after a heat recovery steam generator. The exhaust contains 200 ppmv NOx to be reduced to 60 rng rn 3 (expressed as N02) at 0°C and 1 atm. The NOx is to be treated in the exhaust using low temperature selective catalytic reduction. Ammonia slippage must be restricted to be less than 10 mgm 3, but a design basis of 5 mg-rn 3 will be taken. Aqueous ammonia is to be used at a cost of 300 -1 1 (dry NH3 basis). Estimate the cost of ammonia if the plant operates... 

Taurine is generally prepared from ox bile1 or the large muscle of the abalone.2 It has been synthesized from isethionic add through chloroethanesulfonic acid followed by the action of aqueous ammonia 3 from ethyleneimine and sulfur dioxide 4 from 2-mercaptothiazoline by oxidation with bromine water 5 from bromoethylamine and ammonium sulfite 6 and from acetaldehyde by a complex set of reactions involving sulfonation, formation of the aldehyde ammonia and the imido sulfonic add and finally reduction.7 The method given in the procedure has recently appeared in the literature.8 9... 

The Department of the Environment UK [155] has described a number of alternative methods for the determination of total oxidised nitrogen (nitrate and nitrite) in aqueous solution, while specific methods for nitrate and nitrite are also included. Among the methods for total oxidised nitrogen, one is based on the use of Devarda s alloy for reduction of nitrate to ammonia, and another uses copperised cadmium wire for reducing nitrate to nitrite, which is determined spectrophotometrically. Nitrate may also be determined spectrophotometrically after complex formation with sulfosalicylic acid or following reduction to ammonia, the ammonia is eliminated by distillation and determined titrimetrically. Other methods include direct nitrate determination by ultraviolet spectrophotometry, measurements being made at 210 nm, and the use of a nitrate-selective electrode. Details of the scope, limits of detection, and preferred applications of the methods are given in each case. 

Ketoximes and oximes of 2-oxo-acids are hydrogenated to amines by [CoH(CN)5]3-. The latter reaction allows the preparation of a-amino-acids by reductive amination of 2-oxo-acids in aqueous ammonia. At 40-50 °C and 70 bar H2 the yields are ca. 90% [146]. 

The reductive dehalogenation of polyfluoroarenes by zinc in aqueous ammonia gave products derived from the removal of one or two halogen atoms. A radical anion is suggested to form initially by direct electron transfer from the zinc to substrate which then fragments. Ceo undergoes single-electron reduction by the electron-rich. 

Reductions with zinc are carried out in aqueous [160 as well as anhydrous solvents [163 and at different pHs of the medium. The choice of the reaction conditions is very important since entirely different results may be obtained under different conditions. While reduction of aromatic nitro groups in alkali hydroxides or aqueous ammonia gives hydrazo compounds, reduction in aqueous ammonium chloride gives hydroxylamines, and reduction in acidic medium amines (p. 73). Of organic solvents the most efficient seem to be dimethyl formamide [164 and acetic anhydride [755]. However, alcohols have... 

There is one report of reductive cleavage of the imidazole ring. Treatment of 122 with sodium dithionate in aqueous ammonia yielded amidine 123, which on hydrolysis with acid gave 124. Compound 124 was obtained directly on reduction with sodium dithionate in aqueous ethanolic sodium bicarbonate (83JHC1003). 

A second way of synthesizing it is from 2 -carboxy-4-chlorobenzophenone (21.3.21), which during reduction with zinc in acetic acid transforms into 3-(4 -chlorophenyl)phthalide (21.3.27). Sulfonylchlorination of this gives the corresponding snl-fonylchloride (21.3.28), which upon reaction with phosphorous pentachloride is chlorinated into 3-(4 -chlorophenyl-3 -chlorosulfo)-3-chlorophtalide (21.3.25). This is reacted with aqueous ammonia in the aforementioned manner, and it rearranges into chlorothalidone (21.3.26) [50]. 

Somei et al. reported the total synthesis of the cytotoxic and antiviral 5-cyano-6-methoxy-ll-methylindolo[2,3-fl]carbazole (357) starting from indigo (1458) (786,787). A reduction of indigo (1458) with tin in acetic acid/acetic anhydride afforded 3-acetoxy-2,2 -bisindolyl (1459) in 88% yield. Heating of 1459 with dichloroacetyl chloride in ethyl acetate under reflux provided 3-acetoxy-3 -dichloroacetyl-2,2 -bisindolyl (1460), which was treated with aqueous ammonia in methanol/DMF at room temperature to give the indolo[2,3-fl] carbazole derivative 1461. N-Methylation... 

When the dibromodideoxy-o-mannono-1,4-lactone (2) (Scheme 7) was treated with aqueous ammonia the 3,6-dideoxy-3,6-imino-D-allonamide (22) was formed as the only product [20]. Conversion to the ethyl ester and subsequent reduction of the ester with sodium borohydride transformed 22 into the known l,4-dideoxy-l,4-imino-L-allitol (23) [20]. 

Thus, the Co(NH3)6 complex is quite stable in the presence of excess aqueous ammonia and, indeed, Co(NH3)6 " undergoes spontaneous and rapid air oxidation to Co(NH3)6 ". a polarogram for the reduction of Co(NH3)6 " in an aqueous buffer consisting of 2.5 M ammonia and 0.1 M ammonium chloride exhibits two waves, the first corresponding to a one-electron reduction. 

Ozonolysis of acridine and reduction of the resulting dialdehyde with sodium borohydride gives the diol (179). This is esterified with excess methanesulfonyl chloride and the resulting diester reacts with aqueous ammonia to give the dihydropyrroloquinoline (180). This furnishes the pentacycle (181) with a quantitative yield for the final step (Scheme 55) (75JOC2140). 

The reductive defluorination of perfluoronaphthalene by the zirconocene-aetivated magnesium system in tetrahydrofuran gives mainly the dihydro product 8 in good yield (for the procedure see Section 2.I.I.I.).159-160 When zinc in aqueous ammonia is used as the reducing agent, the dihydro derivative 8 also results as a main product in ea. 30% yield.164... 

Pentafluorophenyl)methanol (3) is successfully reduced at the para position with zinc in aqueous ammonia at ambient temperatures in high yield to give 4.164 Despite the high selectivity. the reduction is apparently much more difficult than that of perfluorobenzoic acid 64 possessing an electron-accepting group at the position para to the bond selectively reduced (vide supra). 

The reduction of perfluoronaphthalene-2-carboxylic acid by zinc in aqueous ammonia takes place as readily164 as the reduction of perfluorobenzoic acid to give the product of hydrodefluorination at position 6 in high yield (Table 3). The carboxylic group thus activates the same position for the reduction (i.e., 6) as the C2 hydrogen in 2//-heptafluoronaphthalenc159160... 

This method involves the reduction of compound 1 in the presence of Raney nickel, aqueous ammonia, and methanol resulting in 2, followed by condensation of 2 with 3 in the presence of pivalic acid, cyclohexane, and isopropyl... 

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