Nitro compounds Alumina

Cerium(IV) ammonium nitrate, 67 Grignard reagents, 138 Other nitro compounds Alumina, 14 Nitrones... 

Aromatic hydrocarbons can be purified as their picrates using the procedures described for amines. Instead of picric acid, 1,3,5-trinitrobenzene or 2,4,7-trinitrofluorenone can also be used. In all these cases, following recrystallisation, the hydrocarbon can be isolated either as described for amines or by passing a solution of the adduct through an activated alumina column and eluting with toluene or petroleum ether. The picric acid and nitro compounds are more strongly adsorbed on the column. 

Hydroxylamines ordinarily do not accumulate in the reduction of aromatic nitro compounds for, with some exceptions, most systems in competition will reduce the hydroxylamine function preferentially. Nonetheless, systems have been found that afford the intermediate aromatic hydroxylamine in excellent yield. With hydrogen gas as a reductant and platinum-on-carbon or -on-alumina and about I wt % of DMSO based on nitro compound as a modifier, aromatic hydroxylamines can be formed in 90% yield under mild conditions. The reduction slows markedly after absorption of the second mole of hydrogen and should be stopped at this stage (80). 

The nitro compound in Et2NH (70 mol equiv) was either heated under reflux with (EtO)2PMe (2- 5 mol equiv) under N2, or the mixture was heated in an autoclave at 57°C, until the reaction was complete as shown by GC analysis of the reaction mixture (4-7d). The excess Et2NH was removed under vacuum and the residue was chromatographed (alumina) to give the product which was further purified by distillation or crystallization. 

The diastereoselectivity is observed in the Henry reaction using optical active nitro compounds or a-heteroatom substituted aldehydes. For example, the reaction of O-benzyl-D-lactal-dehyde with methyl 3-nitropropionate in the presence of neutral alumina leads to a mixture of three nitro-aldol products from which D-ribo isomer is isolated by direct crystallization. D-Ribo... 

Alternatively, Ballini devised a new strategy to synthesize tri-alkylated pyrroles from 2,5-dialkylfurans and nitroalkanes <00SL391>. This method involves initial oxidation of 2,5-dimethylfuran with magnesium monoperoxyphthalate to cA-3-hexen-2,5-dione (6). Conjugate addition of the nitronate anion derived from the nitro compound 7 to 6 followed by chemoselective hydrogenation of the C-C double bond of the resulting enones 8 (obtained by elimination of nitrous acid from the Michael adduct) completes the conversion to the alkylated y-diketones 9. Final cyclization to pyrroles 10 featured improved Paal-Knorr reaction conditions involving reaction of the diketones with primary amines in a bed of basic alumina in the absence of solvent. 

Intramolecular cycloadditions of alkenyl-substituted nitrile oxides produce bicyclic isoxazolines. When monocyclic olehns are used, tricyclic structures are obtained. This approach was pioneered by both Kozikowski s and Curran s groups. A typical case involves the cycloaddition of nitro compound 191 [mixture of diastereomers derived from pentenose pyranoside 190], which produced a diaster-eomeric mixture of isoxazolines that contain cis-fused rings (i.e., 192) in near quantitative yield (326) (Scheme 6.85). Further elaboration of this mixture led to epoxycyclopentano-isoxazoline 193, which was then converted to the aldol product in the usual manner. The hydrogenation proceeded well only when rhodium on alumina was used as the catalyst, giving the required p-hydroxyketone 194. This... 

The reaction is generally carried out by refluxing a stirred mixture of 0.014 mole of the nitro compound and 0.042 mole (8.5 gm) of thallium in 75 ml of ethanol for the periods shown in Table I. The cooled solution is decanted to remove unreacted thallium, 8 gm of potassium iodide is added, and the mixture is stirred for 1 hr at room temperature. The precipitated thallium iodide is filtered, and the filtrate concentrated under reduced pressure. The residue is dissolved in chloroform and then filtered through an alumina column (4 x 1 in.) to remove traces of inorganic salts. Chloroform is used as the eluent, and the resulting solution is concentrated under reduced pressure to afford the solid azoxy compounds. 

Rapid reduction of aromatic nitro compounds into amines has been described using sodium hypophosphite and FeSC>4-7H20. The reactions showed best results in terms of yields and purity, when the substrates were pre-absorbed on alumina and irradiated by microwaves under solvent-free conditions. The reaction is chemoselective and does not affect functional groups such as CN, OH, COOH, CONH2 or halogens. In addition, oximes were not reduced under the given reaction conditions, but were dehydrated to the corresponding nitriles instead (Scheme 4.32)57. 

Vass, A., Dudas, J., T6th, J. and Varma, R.S., Solvent-free reduction of aromatic nitro compounds with alumina-supported hydrazine under microwave irradiation, Tetrahedron Lett., 2001, 42, 5347-5349. 

Keywords aromatic nitro compound, hydrazine hydrate, alumina, microwave irradiation, aromatic amine... 

Redox processes involving 178 have also been studied.Anodic oxidation of thianthrene has been eifected in a wide variety of solvents. Use of trifluoracetic acid gives stable solutions of 178 and, if perchloric acid is included, the solid perchlorate salt may be isolated on evaporation of the solvent after electrolysis. Dichloromethane at low temperatures has been used and, at the opposite extreme, fused aluminum chloride-sodium chloride mixtures. " Propylene carbonate permits the ready formation of 178, whereas the inclusion of water in solvent mixtures gives an electrochemical means of sulfoxidizing thianthrene. Reversible oxidation of 178 to thianthrenium dication may be brought about in customary solvents such as nitriles, nitro compounds, and dichloromethane if the solvent is treated with neutral alumina immediately before voltammetry addition of trifluoracetic anhydride to trifluoracetic acid equally ensures a water-free medium. The availability of anhydrous solvent systems which permit the reversible oxidation and reduction of 178 has enabled the determination of the equilibrium constants for the disproportionation of the radical and for its equilibria with other aromatic materials. ... 

Addition of 1-5% Re increased the activity of Pd for the hydrogenation of nitro-compounds, e.g., nitrobenzene but more Re had an adverse effect due to an increase in palladium crystallite size alumina was a better support than MgO, TiOj. ... 

Catalytic hydrogenation of oximes to amines requires conditions resembling those for catalytic hydrogenation of nitro compounds and nitriles.20d The catalyst should be as active as possible, e.g., Raney nickel101 (if necessary, platinized), platinum oxide,102 palladium-charcoal,103 palladium-barium sulfate,104 or rhodium-alumina.105 This rhodium catalyst also serves for reduction of an amidoxime to the amidine.106 Hydrogenation may be effected under pressure, but the temperature should be kept as low as possible to avoid formation of secondary amines. 

Reduction of Aromatic Nitro Compounds to Amines with Alumina-supported Hydrazine... 

Varma and his coworkers have described a simple and eflRcient procedure wherein aromatic nitro compounds are readily reduced to the corresponding amino compounds in good yields with hydrazine hydrate supported on alumina in the presence of iron(III) chloride (FeCls 6H2O), Fe(III) hydroxide, or Fe(III) oxides (Scheme 8.60) [159]. 

Scheme 8.60. Reduction of nitro compounds to amines with alumina-supported hydrazine.

Oximes can be converted to their corresponding nitro compounds with Oxone and refluxing acetonitrile (eq 58). They can also be cleaved to their parent carbonyl compounds by Oxone in conjunction with glacial acetic acid, or silica gel/alumina and microwave irradiation (eq 58). Ketoximes and aldoximes are both converted to carbonyl compounds in high yields using the microwave and alumina procedure. Several of the above transformations are highlighted in the oxidative decarboxylation of a-amino acids to form ketones and carboxylic acids. ... 

An interesting topological effect is the increased terminal chlorination of fatty acids when they are adsorbed and aligned on alumina Silicon disulfide and particularly boron sulfide have been used with advantage instead of phosphorus pentasulfide to replace carbonyl oxygen by sulfur The addition of sulfur monochloride to olefins followed by reduction of the adduct with sodium sulfide provides a convenient inexpensive route to a large number of episulfides A direct conversion of ar. nitro compounds to isothiocyanates has been reported Sec. phosphines add easily to olefins under UV-irradiation Advances in peptide synthesis include the use of acyloxyphospho-nium salts prepared with hexamethylphosphoramide a simple synthesis with triphenyl phosphite , and the use 4-picolyl esters at the... 

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