Oxidations green oxidants

Due to the rich development of oxidation reactions in recent years there was a need for a book covering the area. The purpose of this book on Modem Oxidation Methods is to fill this need and provide the chemistry community with an overview of some recent developments in the field. In particular some general and synthetically useful oxidation methods that are frequently used by organic chemists are covered. These methods include catalytic as well as non-catalytic oxidation reactions in the science frontier of the field. Today there is an emphasis on the use of environmentally friendly oxidants ( green oxidants) that lead to a minimum amount of waste. Examples of such oxidants are molecular oxygen and hydrogen peroxide. Many of the oxidation methods discussed and reviewed in tliis book are based on the use of green oxidants. 

Cobali in) fluoride, C0F3. Brown powder (C0F3 plus F2) also forms a green hydrate by electrolytic oxidation. C0F3 is widely used in the fluorinalion of organic derivatives. Gives complexes e.g. MjCoFg. 

Cobali [[) oxide, CoO. Olive green solid (heat on Co(OH)2 or cobalt(Il) oxyacid salt in absence of air) with NaCl structure. 

Rinmann s green, ZnCojO. A spinel formed when cobalt nitrate solution is placed on zinc oxide and the mixture heated to redness. The green colour forms a delicate test for Zn. 

Vanadium oxide dichloride, VOCI2. Green crystals VOCI3 plus H2. 

White phosphorus is very reactive. It has an appreciable vapour pressure at room temperature and inflames in dry air at about 320 K or at even lower temperatures if finely divided. In air at room temperature it emits a faint green light called phosphorescence the reaction occurring is a complex oxidation process, but this happens only at certain partial pressures of oxygen. It is necessary, therefore, to store white phosphorus under water, unlike the less reactive red and black allotropes which do not react with air at room temperature. Both red and black phosphorus burn to form oxides when heated in air, the red form igniting at temperatures exceeding 600 K,... 

The + 2 oxidation state is achieved by more drastic reduction (zinc and acid) of the -1-5. -I- 4 or -t- 3 states thus addition of zinc and acid to a solution of a yellow vanadate(V) gives, successively, blue [VOfH O) ]", green [VCl2(H20)4] and violet [VfH O)... 

The O oxidation state is known in vanadium hexacarbonyl. V(CO)(,. a blue-green, sublimable solid. In the molecule VfCO), if each CO molecule is assumed to donate two electrons to the vanadium atom, the latter is still one electron short of the next noble gas configuration (krypton) the compound is therefore paramagnetic, and is easily reduced to form [VfCO, )]. giving it the... 

It is a green powder, insoluble in water and in acids (cf. aluminium oxide, AI2O3). It is not reduced by hydrogen. 

Nickel forms yellow anhydrous halides NiXjlX = F. Cl. Br) and a black iodide Nil2 all these halides are made by direct combination of the elements, and the chloride by reaction of sulphur dichloride oxide with the hydrated salt. All dissolve in water to give green solutions from which the hydrates can be crystallised the solutions contain the ion [NifHjOls], and the chloride crystallises as NiCl2.6H2O, nickel(II) chloride hexahydrate. 

Addition of an alkali metal hydroxide solution to an aqueous solution of a nickel(II) salt precipitates a finely-divided green powder. nickel(II) hydroxide NilOHfj on heating this gives the black oxide. NiO. which is also obtained by heating nickel(II) carbonate or the hydrated nitrate. Black nickel(II) sulphide, NiS, is obtained by passing hydrogen sulphide into a solution of a nickel(II) salt. 

Oxidation, (i) Dissolve 5 g. of potassium dichromate in 20 ml. of dil. H2SO4 in a 100 ml. bolt-head flask. Cool and add 1 ml. of methanol. Fit the flask with a reflux water-condenser and warm gently a vigorous reaction soon occurs and the solution turns green. The characteristic pungent odour of formaldehyde is usually detected at this stage. Continue to heat for 3 minutes and then fit the flask with a knee-tube (Fig. 59, p. 100) and distil off a few ml. Test the distillate with blue litmus-paper to show that it is definitely acid. Then apply Test 3 p. 350) for formic acid. (The reflux-distillation apparatus (Fig. 38, p. 63) can conveniently be used for this test.)... 

It has been stated that many halogen-free compounds, e.g., certain derivatives of pyridine and quinoline, purines, acid amides and cyano compounds, when ignited on copper oxide impart a green colour to the dame, presumably owing to the formation of volatile cuprous cyanide. The test is therefore not always trustworthy. The test is not given by duorides. 

When a solution of, say, 1 g. of hydroquinone in 4 ml. of rectified spirit is poured into a solution of 1 g. of quinone in 30 ml. of water, qulnhydrone C,HA.C,H (0H)3, a complex of equimolecular amounts of the two components, is formed as dark green crystals having a gfistening metallic lustre, m.p. 172°. In solution, it is largely dissociated into quinone and hydroquinone. Quinhydrone is more conveniently prepared by the partial oxidation of hydroquinone with a solution of iron alum. 

Praseodymium is soft, silvery, malleable, and ductile. It is somewhat more resistant to corrosion in air than europium, lanthanum, cerium, or neodymium, but it does develop a green oxide coating that spalls off when exposed to air. As with other rare-earth metals, it should be kept under a light mineral oil or sealed in plastic. 

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