Ammonium fluoride reduction

While the emphasis here has been on the reduction of the amount of waste sludges, it is also equally important to address the problem of regulating the effluents and emissions. In this context, special mention may be made of ammonia which must be carefully regulated. The procedure for processing ammonium fluoride or ammonium sulfate containing solutions begins with lime treatment. The filtrates are fed continuously into a column and stripped with live steam and upgraded. In this way it is possible (with improved equipment and carefully controlled operation) to attain ammonia contents of less than 50 ppm in the effluent. 

Evidently, an increase in steric hindrance around the reduced fragment requires the presence of ammonium fluoride in the reaction mixture. It should be noted that potassium fluoride has no effect. It is highly probable that ammonium fluoride is required for slow elimination of HF, which gradually desilylates the nitroso acetal fragment thus facilitating its reduction. As can be seen from Scheme 3.284, many reduction products are derivatives of unnatural amino acids. Since the initial nitroso acetals can be prepared by silylation of simple acyclic AN, possibilities have been opened for the synthesis of unnatural amino acids from available AN. 

M. D. Drew, N. J. Lawrence, W. Watson, S. A. Bowles, The Asymmetric Reduction of Ketones Using Chiral Ammonium Fluoride Salts and Silanes , Tetrahedron Lett. 1997, 38, 5857-5860. 

Nitroarenes are reduced to anilines (>85%) under the influence of metal carbonyl complexes. In a two-phase system, the complex hydridoiron complex [HFe,(CO)u]2-is produced from tri-iron dodecacarbonyl at the interface between the organic phase and the basic aqueous phase [7], The generation of the active hydridoiron complex is catalysed by a range of quaternary ammonium salts and an analogous hydrido-manganese complex is obtained from dimanganese decacarbonyl under similar conditions [8], Virtually no reduction occurs in the absence of the quaternary ammonium salt, and the reduction is also suppressed by the presence of carbon monoxide [9], In contrast, dicobalt octacarbonyl reacts with quaternary ammonium fluorides to form complexes which do not reduce nitroarenes. 

One method of obtaining beryUium metal is by chemical reduction, whereby beryllium oxide is treated with ammonium fluoride and some other heavy metals to remove impurities while yielding berylhum fluoride. This beryllium fluoride is then reduced at high temperatures using magnesium as a catalyst, which results in deposits of pebbles of metallic beryllium. 

Lanthanum in purified metallic state may be obtained from its purified oxide or other salts. One such process involves heating the oxide with ammonium chloride or ammonium fluoride and hydrofluoric acid at 300° to 400° C in a tantalum or tungsten crucible. This is followed by reduction with alkali or alkaline earth metals at 1,000°C under argon or in vacuum. 

Reduction The asymmetric reduction of a series of aryl alkyl ketones with quaternary ammonium fluorides and silanes was reported by Drew and Lawrence [55]. In these reactions, the best catalysts (e.g., 6f) were from the qui ni ne/quinidine series in fact, a fluoride salt prepared from cinchonine gave no induction. The use of trimethoxysilane resulted in faster rates but lower enantioselectivites when compared with tris(trimethoxy)silane. It is interesting that, with the... 

The hydrosilylation of carbonyl compounds with polymethylhydrosiloxane (PMHS) or other alkoxysilanes can be catalyzed by TBAF, at high efficiency [9]. The asymmetric version of this process has been developed by Lawrence and coworkers using chiral ammonium fluoride 7c prepared via the method of Shioiri [10]. The reduction of acetophenone was performed with trimethoxysilane (1.5 equiv.) and 7c (10 mol%) in THF at room temperature, yielding phenethyl alcohol quantitatively with 51% ee (R) (Scheme 4.6). A slightly higher enantioselectivity was observed in the reduction of propiophenone. When tris(trimethylsiloxy)silane was used as a hydride source, the enantioselectivity was increased, though a pro-... 

The asymmetric organocatalytic transformation of a ketone into an alcohol may be realized with the combination achiral silanexhiral phase-transfer catalyst, such a quaternary ammonium salt. The final alcohol is then recovered by an additional hydrolytic step. The asymmetric reduction of aryl alkyl ketones with silanes has been reported (ee-values up to 70%), the catalysts utilized being ammonium fluorides prepared from the quinine/quinidine series (e.g., 18 in Scheme 11.6) [19]. (For experimental details see Chapter 14.21.1). The more appropriated silanes were (Me3SiO)3SiH or (MeO)3SiH (some examples are... 

The protactinium(IV) fluoro complexes have been prepared either by hydrogen reduction of a pentavalent complex at 400°C or by heating together appropriate amounts of MF and PaF4 in sealed vessels. The reaction between ammonium fluoride and protactinium tetrafluoride to yield (NH4)4PaFg, the only octafluoro complex known, takes place when the component halides are ground together at room temperature (4,114). 

The enolate that is required for the aldol reaction can be generated in other ways, too. For example, trimethylsilyl enol ethers react with TBAF (tetrabutyl-ammonium fluoride, Bu4N" F ) to give the corresponding enolates. Enolates may also be prepared by the dissolving metal reduction of a,)3-unsaturated ketones (see Chapter 5). 

We have considered that in the presence o-f sodium methoxide the M3aromatic nitro compounds probably v i a ]l3tetrabutyl ammonium fluoride can catalyze the reduction of nitrobenzenes to anilines by Fe3i2 significantly... 

Reduction with Chiral Ammonium Fluoride Salts as Activators... 

Drew M. The asymmetric reduction of ketones using chiral ammonium fluoride salts and silanes. Tetrahedron Lett. 1997 38 5857 5860. 

Reduction of Beryllium Fluoride with Magnesium. The Schwen2feier process (11) is used to prepare a purified, anhydrous beryUium fluoride [7787-49-7], Bep2, for reduction to the metal. BeryUium hydroxide is dissolved in ammonium bifluoride solution to give a concentration of 20 g/L... 

Ammonia solutions are significantly more efficient than ammonium acetate as washing reagents. The process of fluorine content reduction is related to subsequent hydrolysis of fluoride and oxyfluoride contaminants by ammonia. 

A bromide was introduced in the reaction instead of a fluoride in performing the anodic oxidation of a-stannyl ethers in dibromomethane solvent with tetrabutyl-ammonium perchlorate as the electrolyte (Scheme 19) [28]. The bromide ion was generated by the reduction of the solvent at the cathode of an undivided cell. 

Yttrium oxalate is then ignited to its oxide, Y2O3. The oxide is heated at 750°C in a stream of anhydrous hydrogen fluoride to yield yttrium fluoride, YF3. Alternatively, the oxide is mixed with ammonium hydrogen fluoride NH4HF2 and heated at 400°C in a stream of dry air or helium. Yttrium metal may be produced from its fluoride either by metallothermic reduction or electrolysis. The more common metallothermic reduction involves reducing the fluoride with redistilled calcium in 10% excess over the stoichiometric amounts at elevated temperatures ... 

Beryllium (Glucinum) Fluoride, BeF2, mw 47 01, colorless, poisonous pdr, sp gr 2.0l at 15°, mp 800° bp — sublimes v sol in w sol in ale, acids and alkalies. Can be prepd by thermal decomph (at 900—950°) of ammonium beryllium fluoride. Used in production of beryllium metal by reduction with Mg metal Refs 1) Gmelin-Kraut System Number 26(1930), 105 2) Hackh sDict (1944), 123-R 3) Cond-... 

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