Deoxygenation with hydrazine

An aldehyde or ketone 1 can react with hydrazine to give a hydrazone 2. The latter can be converted to a hydrocarbon—the methylene derivative 3—by loss of Na upon heating in the presence of base. This deoxygenation method is called the Wolff-Kishner reduction. ... 

Attempts at preparing 3-azidoisoquinoline from the 3-chloro precursor were unsuccessful due to the inertness of the chloro substituent. However, if 3-chloroisoquinoline was first converted into its AT-oxide, its susceptibility to nucleophilic substitution was enhanced. Thus, reaction of the iV-oxide with hydrazine gave the 3-hydrazine iV-oxide which, upon nitrosation and deoxygenation, gave the desired 3-azidoisoquinoline (367). This material was rather stable, with electrocyclization to (47) taking place only upon crystallization (Scheme 71) (76JHC881,81JOC843). 

Many hydroxypyrazine A oxides have been A(-deoxygenated to pyrazines with a variety of reducing agents which include heating with hydrazine hydrate in alcohols hydriodic acid and red phosphorus in acetic or phosphoric acid iodine and red phosphorus in refluxing acetic acid phosphorus tribromide in ethyl acetate sodium dithionite catalytic reduction with hydrogen over Raney nickel dry distillation with copper-chromite catalyst and titanium trichloride in tetrahydrofuran at room temperature. 

Deoxygenation of the carbonyl group of aldehydes and ketones via the intermediacy of their hydrazone derivatives, known as the Wolff-Kishner reduction,offers an alternative to the thioacetal desulfurization method. The Wolff-Kishner reduction in the presence of hydrazine and NaOH (or KOH) has been replaced largely by the Huang-Minlon method,where the deoxygenation is carried out with hydrazine in refluxing ethylene glycol. 

Hydroxide ion and heat differentiate the Wolff-Kishner reduction from ordinary hydrazone formation. Initially, the ketone reacts with hydrazine to form a hydrazone. After the hydrazone is formed, hydroxide ion removes a proton from the NH2 group. Heat is required because this proton is not easily removed. The negative charge can be delocalized onto carbon, which abstracts a proton from water. The last two steps are repeated to form the deoxygenated product and nitrogen gas. 

Ketones can be reduced to secondary alcohols by H and a catalyst or a complex metal hydride or by hydrogen transfer reagents. Deoxygenation with a strong base at 150°C (302°F) can form olefin. Ketones react with thiols to form thioacetals. Reaction with anhydrous hydrazine may be explosive. 

The deoxygenation of aldehydes and ketones to the corresponding hydrocarbons via the hydrazones is known as the Wolff-Kishner reduction.28 Various modifications of the original protocols have been suggested. One of the most useful is the Huang-Minlon modification, which substituted hydrazine hydrate as a safer and less expensive replacement of anhydrous hydrazine. In addition, diethylene glycol together with sodium hydroxide was used to increase the reaction... 

Dialkyl ditellurides (general procedure) Powdered Te (6.35 g, 50 mmol) is added to a stirred solntion of NaOH (3.0 g, 75 mmol) in deoxygenated H2O (20 mL). The mixture is cooled in a water bath, and 100% hydrazine hydrate (2.5 g, 200 mmol) is added over a period of 30 min and stirring is continned for an additional honr at room temperature. The aUcyl halide (50 mmol) is then added dropwise over a period of 2-3 h. Dnring the addition, the temperature is maintained at 15-20°C. The end-point of the alkylation is indicated by a sharp colour change from dark brown to nearly colourless. The mixture is then extracted with ether, the organic layer is washed with H2O, dried (Na2S04) and the solvent removed by slow distillation. The residue is distilled under vacuum. 

Oxygen is soluble in water to the extent of 9.4 ppm from air at 100 kPa and 20 °C, and 02 is the oxidant responsible for most metallic corrosion. Consequently, deaeration of water by purging with nitrogen or vacuum degassing may be desirable in some circumstances this should not be undertaken without circumspection, since deoxygenation may cause activation of otherwise passive metals or cause cathodic areas to become anodic (Chapter 16). At high temperatures, aqueous oxygen is consumed quite rapidly by hydrazine or sodium sulfite (Section 16.7). 

R = Ar,R2 = H), which were deoxygenated in one instance.19 Other N-oxides (133 R1 = Ar,R2 = H and R1 = R2 = Ph) were obtained directly by hydrazinolysis of the 4-chloropyridine 131b.126 Reaction of hydrazine with the pyridinium salt 134 caused replacement of the methoxy group with formation of 135 29 and, more unexpectedly, 3-carbethoxy-4-pyrrolylpyridine (136) and hydrazine afforded an almost quantitative yield of 137 by expulsion of the pyrrole nucleus.130... 

This explosive is more powerful than C-4 plastique explosive. With its high detonation rate and great bristance, it should find some use. It is more sensitive than most explosives obtained from AN, since it is not AN but hydrazine nitrate. This explosive liquid is very corrosive and this should be taken into affect when suitable containers are rounded up in which to place the explosive. Hydrazine is a hard chemical to find. Used as a rocket fuel, obtaining this chemical could arouse suspicion. It is used as a boiler deoxygenator and perhaps could be procured for this purpose. The manufacture is simple with the AN prills being dissolved in the hydrazine by small additions with good ventilation, as ammonia gas is produced by the reaction. 

Heteroatomic nucleophiles which also have been shown to undergo addition across the 3,4-double bond of quinazolines 5 and with which the addition products 6 were isolated include the methoxide anionand sodium hydrogen sulfite.(For addition of sodium hydrogen sulfite and hydrazine at the 4-position of quinazoline 3-oxides with concomitant deoxygenation of the A(-oxide group, cf p 105.) Equilibrium and rate constants have been determined at 25 °C for the covalent addition of water, the bisulfite ion, hydroxylamine, urea, 2-sulfanylethanol, and hydrogen sulfide to the 3,4-bond of the quinazoline cation. ... 

The synthetic potential of reductions by formate has been extended considerably by the use of ammonium formate with transition metal catalysts like palladium and rhodium. This forms a safe alternative to use of hydrogen. In this fashion it is possible to reduce hydrazones to hydrazines, azides and nitro groups to amines, to dehalogenate chloro-substituted aromatics, and to carry out various reductive removals of functional groups. For example, phenol triflates are selectively deoxygenated to the aromatic derivatives using triethylammonium formate as reductant and a palladium catalyst. - These recent af li-cations have been reviewed. 

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