Stoichiometric double salts

Many stoichiometric double salts (citrates, oxalates) are suitable as precursors for mixed oxides. If stoichiometries are needed in an oxide for which no double salts are available, coprecipitation of hydroxides can yield a precursor that has the metal ions atomically mixed in the proper amounts so that no excessive reaction times are necessary in the calcining step. 

We return now to the mercuro-de-diazoniation. Nesmeyanov s school continued the work on metallo-de-diazoniations from 1929 to 1953 (see summary by Nesmeyanov, 1972). A major discovery was made at the very beginning, namely the influence of copper powder (Nesmeyanov, 1929 b Nesmeyanov and Kahn, 1929). With this addition metallic mercury was not required instead the double salt of the diazonium chloride and mercuric chloride was used. The copper reacts stoichiometrically as an electron donor. Therefore, either arylmercuric chlorides (Scheme 10-87) or diarylmercury compounds (Scheme 10-88) can be obtained. These reactions are called Nesmeyanov reactions. Specific examples are the syntheses of di-2-naphthyl-... 

Magnesium sulfate forms several double salts having varying stoichiometric compositions. When gaseous ammonia is bubbled through magnesium sulfate solution, several hydrated double salts are obtained by crystallization. 

Manganese(ll) chloride forms double salts with alkah metal chlorides when mixed in stoichiometric amounts. Such double salts, which can decompose in water, may have compositions like KMnCls or K2MnCl4. 

An agitated, moderately concentrated aqueous solutionofSnClgis rapidly mixed with a KI solution of about the same concentration containing half the stoichiometric amount of KI. If a larger quantity of KI is added, a yellow double salt coprecipitates with the red SnI 2 and is difficult to separate. After filtering the Snig, additional product may be obtained from the mother liquor by addition of the second half of the stoichiometric amount of KI. This method yields a preparation which, in general, is less pure than that obtained via method I. Purification and dryii of the product are as in I. 

Wittig reactions are versatile and useful for preparing alkenes, under mild conditions, where the position of the double bond is known unambiguously. The reaction involves the facile formation of a phosphonium salt from an alkyl halide and a phosphine. In the presence of base this loses HX to form an ylide (Scheme 1.15). This highly polar ylide reacts with a carbonyl compound to give an alkene and a stoichiometric amount of a phosphine oxide, usually triphenylphosphine oxide. 

All these reactions are promoted by Pd(II) species, and can be stoichiometric (Eq. 10) or catalytic (Eqs. 11-13, in the presence of Cu(II) salts or other oxidizing agents). 3-Chloropropionyl chloride from ethylene is conceivably formed through PdCl2 addition to the double bond followed by CO insertion and reductive elimination (Scheme 2). 

Kinetic studies established that tetra-n-butylammonium borohydride in dichloromethane was a very effective reducing agent and that, by using stoichiometric amounts of the ammonium salt under homogeneous conditions, the relative case of reduction of various classes of carbonyl compounds was the same as that recorded for the sodium salt in a hydroxylic solvent, i.e. acid chlorides aldehydes > ketones esters. However, the reactivities, ranging from rapid reduction of acid chlorides at -780 C to incomplete reduction of esters at four days at 250 C, indicated the greater selectivity of the ammonium salts, compared with sodium borohydride [9], particularly as, under these conditions, conjugated C=C double bonds are not reduced. 

The stoichiometric equivalents of halogen fluorides, i.e. chlorine monofluoride, bromine monofluoride and iodine monofluoride, have found a wide application in addition reactions to double bonds. The equivalents are obtained by reacting A -haloamides or free halogens in combination with hydrogen fluoride or its salts as the source of fluoride ions. The reactions proceed under mild conditions at — 80 to 20 "C in anhydrous hydrofluoric acid or diethyl ether, tetrahydro-furan, dichloromethane or chloroform mainly by electrophilic addition with Markovnikov-type regioselectivity (anti addition).26-28... 

Alkylcobalts form in stoichiometric reactions of pentacyanocobalt(III) hydride and alkenes. This reaction occurs both for halogenated alkenes such as tetrafluoroethylene and for alkenes that contain other electron-withdrawing groups such as carbonyls, nitriles and arenes as substituents (see Table 6) . The addition is regiospedfic, forming the more substituted alkylcobalt. Prior coordination of alkene to cobalt to form an alkene(hydrido)cobalt complex, an intermediate in hydrometalation reactions, is not important. This reaction is a radical process however, by NMR, additions of [HCo(CN)5 ] " to diastereomeric alkenes such as fumaric and maleic add salts lead to a cr-alkylcobalt by stereospecific cis addition of Co and H to the double bond . The overall reduction is not stereospecific. (r-Alkylcobalt bond formation proceeds by either a concerted addition or a rapid collapse of a radical cage. 

Two commercial stoichiometric Sp powders (Mg Alsl.0) were used. The first (labeled here Nl) is derived from A1 and Mg hydrated sulfate salts, using solution chemistry it is supplied by Baikowski (La Balme de Silligny, France). The calcination temperature is of-1100°C. The second, produced by Nanocerox (Ann Arbor, Ml, USA) was synthesized by flame-spray pyrolysis from a double Al-Mg alkoxide precursor. The synthesis product is calcined at 650°C. 

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