Oxidations, lead dioxide

Phenylhydrazine Phosgene Phosphine Lead dioxide, oxidizers Aluminum, alkali metals, 2-propanol Air, boron trichloride, bromine, chlorine, nitric acid, nitrogen oxides, nitrous acid, oxygen, silver nitrate... 

In addition to the procedure given here for the oxidation of tert-octylamine to nitroso-tert-octane,2 the oxidation may be carried out with m-chloroperoxybenzoic acid or with a solution of peroxyacetic acid in ethyl acetate.4 The lead dioxide oxidation of alkyl hydrazines to alkyl radicals appears to have general application. In addition to tert-butylhydrazine, various secondary alkylhydrazines (e.g., bornylhydrazine and menthylhydrazine) have been used to good effect. The reduction of tri-tert-alkylhydroxyl amine to the di-tert-alkylamine has also been achieved with sodium in ammonia but the insolubility of the hydrophobic substrate makes this procedure difficult. The use of sodium naphthalenide gives higher yields and is more reproducible. 

Mixed carbonates Lead dioxide oxidizes A-hydroxycarbamates to nitroso-formates 0=N-C00R which react with alcohols and phenols to afford mixed carbonates. 

The writer prefers structure CLXIc for this necic acid by analogy with other acids derived from alkaloids of Senecio species, on the usual requirement of an a-hydroxyl for lead dioxide oxidation, and on the basis of possible biosynthesis (74). 

Prochiral carbon radicals have enantiotopic faces reaction with chiral nitroxides can result in two possible diastereomeric products (Scheme 9). Our laboratory has been investigating the ability of chiral nitroxides to differentiate between the two enantiotopic faces of a transient prochiral carbon radical. In many of the examples, the prochiral radical is generated by the lead dioxide oxidation of a secondary benzylic hydrazine. Early work utilized a camphor-derived nitroxide 27, which was coupled to a secondary benzylic prochiral carbon radical with low but reproducible stereoselectivity (Scheme 10) [26]. The stereoselectivity jumped dramatically upon moving to a conformationally rigid nitroxide in the form of the steroid doxyl radical... 

Experimentally, fra j(N)-RR, fr< w(N)-RS, A-c/j(N)-RR, A-ds(N)-RS, A-cis(N)-RR and A-ciy(N)-RS were chromatographically isolated from a reaction mixture obtained after lead dioxide oxidation (Dowex 1-X8, Cl form 0.07 mol/dm KCl or NaC104). The existence of mer-trans(li) isomers was excluded because of the general difficulty of meridional coordination of a linear 0,N,0-ligand. 

All Group IV elements form both a monoxide, MO, and a dioxide, MO2. The stability of the monoxide increases with atomic weight of the Group IV elements from silicon to lead, and lead(II) oxide, PbO, is the most stable oxide of lead. The monoxide becomes more basic as the atomic mass of the Group IV elements increases, but no oxide in this Group is truly basic and even lead(II) oxide is amphoteric. Carbon monoxide has unusual properties and emphasises the different properties of the group head element and its compounds. 

The white precipitate of lead hydroxide (or hydrated lead(ll) oxide) is then oxidised by the chloraie(I) lo the brown dioxide ... 

Laughing gas, see Nitrogen(I) oxide Lautarite, see Calcium iodate Lawrencite, see Iron(II) chloride Lechatelierite, see Silicon dioxide Lime, see Calcium oxide Litharge, see Lead(II) oxide... 

Manganese(II) can be titrated directly to Mn(III) using hexacyanoferrate(III) as the oxidant. Alternatively, Mn(III), prepared by oxidation of the Mn(II)-EDTA complex with lead dioxide, can be determined by titration with standard iron(II) sulfate. 

Hydroxylamine Barium oxide and peroxide, carbonyls, chlorine, copper(II) sulfate, dichromates, lead dioxide, phosphorus trichloride and pentachloride, permanganates, pyridine, sodium, zinc... 

Oxidative Fluorination of Aromatic Hydrocarbons. The economically attractive oxidative fluorination of side chains in aromatic hydrocarbons with lead dioxide or nickel dioxide in Hquid HF stops at the ben2al fluoride stage (67% yield) (124). 

Tetravalent lead is obtained when the metal is subjected to strong oxidizing action, such as in the electrolytic oxidation of lead anodes to lead dioxide, Pb02 when bivalent lead compounds are subjected to powerful oxidizing conditions, as in the calcination of lead monoxide to lead tetroxide, Pb O or by wet oxidation of bivalent lead ions to lead dioxide by chlorine water. The inorganic compounds of tetravalent lead are relatively unstable eg, in the presence of water they hydrolyze to give lead dioxide. 

Lead dioxide is electrically conductive and is formed ia place as the active material of the positive plates of lead-acid storage batteries. Because it is a vigorous oxidizing agent when heated, it is used ia the manufacture of dyes, chemicals, matches (qv), pyrotechnics (qv), and Hquid polysulfide polymers (42) (see Polypous containing sulfur). 

The standard potential for the anodic reaction is 1.19 V, close to that of 1.228 V for water oxidation. In order to minimize the oxygen production from water oxidation, the cell is operated at a high potential that requires either platinum-coated or lead dioxide anodes. Various mechanisms have been proposed for the formation of perchlorates at the anode, including the discharge of chlorate ion to chlorate radical (87—89), the formation of active oxygen and subsequent formation of perchlorate (90), and the mass-transfer-controUed reaction of chlorate with adsorbed oxygen at the anode (91—93). Sodium dichromate is added to the electrolyte ia platinum anode cells to inhibit the reduction of perchlorates at the cathode. Sodium fluoride is used in the lead dioxide anode cells to improve current efficiency. 

The most common white pigments are titanium dioxide, 2inc oxide, leaded 2inc oxide, 2inc sulfide [1314-98-3], and Hthopone, a mixture of 2inc sulfide and barium sulfate [7727-43-7]. The use of lead whites and antimony oxides has been decreasing steadily for environmental reasons. 

The preparation of triaryknethane dyes proceeds through several stages formation of the colorless leuco base in acid media, conversion to the colorless carbinol base by using an oxidising agent, eg, lead dioxide, manganese dioxide, or alkah dichromates, and formation of the dye by treatment with acid (Fig. 1). The oxidation of the leuco base can also be accompHshed with atmospheric oxygen in the presence of catalysts. 

The central carbon atom is derived from an aromatic aldehyde or a substance capable of generating an aldehyde during the course of the condensation. Malachite green is prepared by heating benzaldehyde under reflux with a slight excess of dimethyl aniline in aqueous acid (Fig. 2). The reaction mass is made alkaline and the excess dimethylaniline is removed by steam distillation. The resulting leuco base is oxidized with freshly prepared lead dioxide to the carbinol base, and the lead is removed by precipitation as the sulfate. Subsequent treatment of the carbinol base with acid produces the dye, which can be isolated as the chloride, the oxalate [2437-29-8] or the zinc chloride double salt [79118-82-4]. 

Diphenylmethane Base Method. In this method, the central carbon atom is derived from formaldehyde, which condenses with two moles of an arylamine to give a substituted diphenylmethane derivative. The methane base is oxidized with lead dioxide or manganese dioxide to the benzhydrol derivative. The reactive hydrols condense fairly easily with arylamines, sulfonated arylamines, and sulfonated naphthalenes. The resulting leuco base is oxidized in the presence of acid (Fig. 4). 

The most suitable oxidizing agent is potassium ferricyanide, but ferric chloride, hydrogen peroxide ia the presence of ferrous salts, ammonium persulfate, lead dioxide, lead tetraacetate or chromate, or silver and cupric salts may be useful. Water mixed, eg, with methanol, dimethylformamide, or glycol ethers, is employed as reaction medium. 

Fig. 1. Schematic representation of a battery system also known as an electrochemical transducer where the anode, also known as electron state 1, may be comprised of lithium, magnesium, zinc, cadmium, lead, or hydrogen, and the cathode, or electron state 11, depending on the composition of the anode, may be lead dioxide, manganese dioxide, nickel oxide, iron disulfide, oxygen, silver oxide, or iodine.

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