Halide-free

To determine which halogen is present, take 1-2 ml. of the filtrate from the sodium fusion, and add dilute sulphuric acid until just acid to litmus. Add about 1 ml. of benzene and then about 1 ml. of chlorine water and shake. A yellowish-brown colour in the benzene indicates bromine, and a violet colour iodine. If neither colour appears, the halogen is chlorine. The result may be confirmed by testing the solubility of the silver halide (free from cyanide) in dilute ammonia solution silver chloride is readily soluble, whereas the bromide dissolves with difficulty, and the iodide not at all. 

PREPAHATIQM OF HALIDE-FREE tCTHVLLITHIUM (Lithium, methyl-)... 

The reaction of lithium with methyl chloride in ether solution produces a solution of methyllithium from which most of the relatively insoluble lithium chloride precipitates. Ethereal solutions of halide-free" methyllithium, containing 2-5 mole percent of lithium chloride, were formerly marketed by Foote Mineral Company and by Lithium Corporation of America, Inc., but this product has been discontinued by both companies. Comparable solutions are also marketed by Alfa Products and by Aldrich Chemical Company these solutions have a limited shelf-life and older solutions have often deteriorated... 

Seven procedures descnbe preparation of important synthesis intermediates A two-step procedure gives 2-(HYDROXYMETHYL)ALLYLTRIMETH-YLSILANE, a versatile bifunctional reagent As the acetate, it can be converted to a tnmethylenemethane-palladium complex (in situ) which undergoes [3 -(- 2] annulation reactions with electron-deficient alkenes A preparation of halide-free METHYLLITHIUM is included because the presence of lithium halide in the reagent sometimes complicates the analysis and use of methyllithium Commercial samples invariably contain a full molar equivalent of bromide or iodide AZLLENE IS a fundamental compound in organic chemistry, the preparation... 

III Ti, Ti alloys Halide-free acids >0.0 >-0.32 Protection against weight loss... 

High-alloy steels with >16%Cr = Halide-free cold acids 0.2/1.1 -0.1/0.8 Protection against active and transpassive corrosion... 

All the halide exchange reactions mentioned above proceed more or less quantitatively, causing greater or lesser quantities of halide impurities in the final product. The choice of the best procedure to obtain complete exchange depends mainly on the nature of the ionic liquid that is being produced. Unfortunately, there is no general method to obtain a halide-free ionic liquid that can be used for all types of ionic liquid. This is explained in a little more detail for two defined examples the synthesis of [BMIM][(CF3S02)2N] and the synthesis of [EMIM][BF4]. 

However, formation of the metal carbene complex was not observed in pure, halide-free [BMIM][Bp4], indicating that the formation of carbene depends on the... 

Having retraced the remarkably efficient sequences of reactions which led to syntheses of key intermediates 14 and 15, we are now in a position to address their union and the completion of the synthesis of the spiroketal subunit (Scheme 6b). Regiocontrolled deprotonation of hydrazone 14 with lithium diisopropylamide (LDA), prepared from diisopropylamine and halide-free methyl-lithium in ether, furnishes a metalloenamine which undergoes smooth acylation when treated with A-methoxy-A-methylcarboxa-mide 15 to give the desired vinylogous amide 13 in 90% yield. It is instructive to take note of the spatial relationship between the... 

Alkenes can be acylated with an acyl halide and a Lewis acid catalyst in what is essentially a Friedel-Crafts reaction at an aliphatic carbon. ° The product can arise by two paths. The initial attack is by the acyl cation RCO (or by the acyl halide free or complexed see 11-14) at the double bond to give a carbocation ... 

Group-IIIB element-transition-metal compounds have been synthesized by means of anionic metal bases and halide-free group-IIIB compounds. The carbonylate anions of Mn and Re interact with BHj to give [HjBMfCOlj]", which are best isolated as the tetraalkylammonium or phosphonium salts ... 

For internal olefins, the hydroboration step is slower, taking days rather than hours, and in this case the boron-zinc exchange requires the use of Zn(Pr )2 (Scheme 5). The reaction is stereospecific, provided that the diisopropylzinc is metal halide free.29,30... 

Despite the extensive history of organozinc chemistry, the first solid-state structure of a Lewis base-free diorganozinc compound with cr-bound ligands, namely diphenylzinc, was not reported until 1990.37 Diphenylzinc was synthesized by the transmetallation of diphenylmercury with metallic zinc (Scheme 10) and, after multiple sublimations, obtained halide free in 67% yield. 

The essential factor which differentiates the monomeric and dimeric carbonylations seems to be the presence or absence of halide ion coordinated to the palladium. The dimerization-carbonylation proceeds satisfactorily with halide-free palladium phosphine complexes. Most conveniently, Pd(OAc)2 is used with PPh3. PdCl2(PPh3)2 can be used as a catalyst with addition of an excess of bases. The reaction is carried out at 1I0°C under 50 atm of carbon monoxide pressure in alcohol. Higher... 

The carbonylation was explained by the following mechanism. Formation of dimeric 7r-allylic complex 20 from two moles of butadiene and the halide-free palladium species is followed by carbon monoxide insertion at the allylic position to give an acyl palladium complex which then collapses to give 3,8-nonadienoate by the attack of alcohol with regeneration of the zero-valent palladium phosphine complex. When halide ion is coordinated to palladium, the formation of the above dimeric 7r-allylic complex 20 is not possible, and only monomeric 7r-allylic complex 74 is formed. Carbon monoxide insertion then gives 3-pentenoate (72). 

Efforts to tune the reactivity of rhodium catalysts by altering structure, solvent, and other factors have been pursued.49,493 50 Although there is (justifiably) much attention given to catalysts which provide /raor-addition processes, it is probably underappreciated that appropriate rhodium complexes, especially cationic phosphine complexes, can be very good and reliable catalysts for the formation of ( )-/3-silane products from a air-addition process. The possibilities and range of substrate tolerance are demonstrated by the two examples in Scheme 9. A very bulky tertiary propargylic alcohol as well as a simple linear alkyne provide excellent access to the CE)-/3-vinylsilane products.4 a 1 In order to achieve clean air-addition, cationic complexes have provided consistent results, since vinylmetal isomerization becomes less competitive for a cationic intermediate. Thus, halide-free systems with... 

The submitters used an ether solution of halide-free methyl-lithium, purchased from Foote Mineral Company, and the checkers prepared the compound from methyl chloride and lithium metal in ether according to the literature.2 The solution was standardized before use by the titration procedure described in a previous volume of this series.3 The checkers observed that use of a halide-containing ether solution of methyllithium resulted in a considerable decrease in yield of the product, principally due to difficulty in following the subsequent procedure described in the text. 

The compounds 2,6-Trip2H3C6AsCl2 and 2,6-Mes2H3C6AsCl2 can be reduced by magnesium and potassium, respectively, to give the halide-free... 

Alkenylzinc compounds have been prepared by a Te-Zn exchange reaction on vinyhc tellurides under halide-free conditions, with retention of the geometry of the starting tel-luride. ... 

H4Ru4(ri -C6H6)](BF4)2, that was not expected to be sensitive to poisoning by halide impurities showed a significant increase in the turnover rate when the cluster was immobilized in the halide-free [BMIM]BF4. 

Relative to the reductive carbonylation of methanol, the added recycle step is a disadvantage with dimethyl ketals. This disadvantage is offset by the lower pressure of operation and the noncorrosive halide-free catalyst, which permits cheaper materials of construction. 

This solvent- and halide-free oxidation of cyclohexene and cyclopentene is clean, safe, and reproducible, with conditions that are less corrosive than those of the nitric acid oxidation. No operational problems are foreseen for a large-scale version of this green process, and technical refinement should further increase the synthetic effi-... 

Many classical oxidations are frequently performed in aqueous media, using oxidants such as potassium permanganate, sodium periodate, or sodium or calcium hypochlorite (Hudlicky, 1990). Cyclohexene can now be oxidized directly to colorless crystalline adipic acid with aqueous 30 percent hydrogen peroxide under organic solvent-and halide-free conditions, as discussed earlier (Sato et al., 1998) (see fig. 6.1). 

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