Lead iodide formation

The fact that the cyclization is directed toward an acetylenic group and leads to formation of an alkenyl radical is significant. Formation of a saturated iodide could lead to a more complex product mixture because the cyclized product could undergo iodine atom transfer and proceed to add to a second unsaturated center. Vinyl iodides are much less reactive and the reaction product is unreactive. Owing to the potential... 

Oxidation of sulphonamides in the presence of bromide or iodide ions and sodium methoxide in methanol also leads to formation of the N-halogeno intermediate. The nitrogen-halogen bond in these intermediates is weak and will undergo themiolysis. At -10 °C, reaction proceeds by base catalysed elimination of hydrogen halide and ftirther steps lead to an a-amino acetal 20. The reaction is carried out in an undivided cell and renders a-aminoacetals readily available for the iso-... 

A highly modified methyl testosterone derivative also exhibits antiandrogenic activity. One synthesis of this compound involves initial alkylation of methyl testosterone (35) by means of strong base and methyl iodide to afford the 4,4-dimethyl derivative 6. Formylation with alkoxide and methyl formate leads to the 2-hydroxymethyl derivative 37. Reaction of this last with hydroxyl amine leads to formation of an isoxazole ring. There is then obtained azastene (38) . 

The electrochemical allylation of carbonyl compounds by electroreductivc regeneration of a diallyltin reagent from allyl bromide and a Sn species leads to formation of homoallylic alcohols in yields of 70-90 % even in methanol or methanol/water (Table 7, No. 12) Bisaryl formation is possible also from aryl iodides or bromides in the presence of electro-generated Pd phosphane complexes (Table 7, No. 13) In the presence of styrenes, 1,3-butadienes, or phenyl acetylene the products of ArH addition are formed in this way (Table 7, No. 14) . The electroreductivc cleavage of allylic acetates is also possible by catalysis of an Pd°-complex (Table K No. 15)... 

The displaced group X often is a halide ion (chloride, bromide, or iodide), and if the entering nucleophile Nu e is an alkynide anion, the reaction leads to formation of a carbon-carbon bond ... 

Precipitation reactions are processes in which soluble reactants yield an insoluble solid product that drops out of the solution. Formation of this stable product removes material from the aqueous solution and provides the driving force for the reaction. Most precipitations take place when the anions and cations of two ionic compounds change partners. For example, an aqueous solution of lead(II) nitrate reacts with an aqueous solution of potassium iodide to yield an aqueous solution of potassium nitrate plus an insoluble yellow precipitate of lead iodide ... 

It is possible to eliminate by-product lead metal formation in the PbXa-RM reaction without recourse to a low reaction temperature by simply conducting the reaction in the presence of an organic halide, preferably a bromide or iodide. This reaction was originally demonstrated by Gilman and coworkers 149,152) and is represented by the equations ... 

The reaction of trialkyl- and triaryl-phosphines with 1,3-benzodithiolylium salts leads to formation of phosphonium salts which are deprotonated by treatment with n-butyllithium to produce (69). The similar reaction of trialkyl phosphites in the presence of sodium iodide yields dialkyl phosphonates which can be deprotonated to (70). Both (69) and (70) can react further with ketones to give the 2-alkylidene-l,3-dithiole derivatives (71) (80AHC(27)151>. The ylide (72) has also been prepared (80H(l4)27l>. 

A nucleophilic attack by 4.7 on CH3I produces 4.8 and I. Conversion of 4.8 to 4.9 is an example of a carbonyl insertion into a metal alkyl bond. Another CO group adds onto the 16-electron species 4.9 to give 4.10, which in turn reacts with I to eliminate acetyl iodide. Formation of acetic acid and recycling of water occur by reactions already discussed for the rhodium cycle. Apart from these basic reactions there are a few other reactions that lead to product and by-product formations. As shown in Fig. 4.4, both 4.9 and 4.10 react with water to give acetic acid. The hydrido cobalt carbonyl 4.11 produced in these reactions catalyzes Fischer-Tropsch-type reactions and the formation of byproducts. Reactions 4.6 and 4.7 ensure that there is equilibrium between 4.7 and 4.11. 

From the argument above it follows that opposite action will shift the equilibrium in the opposite direction. Thus, for example, adding more iodine to the equilibrium system, or removing some of the hydrogen ions with a buffer, or removing iodide ions by precipitating them with lead nitrate in the form of lead iodide will shift the equilibrium towards the formation of arsenate. 

Sol-Gel. The sol-gel method is a variation on the gel method for producing single crystals of ionic materials (Brinker and Scherer, 1990). The gel method has been used for many years to produce single crystals of materials formed from ions, where direct combination results in instantaneous product formation and hence no large single crystals. A good example is the formation of lead iodide from and I. When these two are combined as aqueous solutions ... 

Reaction of hypochlorite with bromide and iodide leads to formation first of the other hypohalite and then, more slowly, of the halates. With bromide ion, between pH 10 and 14, formation of hypobromite is the only significant process , although the halates were detected at lower pH. The rate equation... 

Lead dissolves in liquid ammonia solutions of sodium giving a highly coloured liquid. The formation of pol) plumbides has been demonstrated by electrometrically titrating a solution of sodium in ammonia with one of lead iodide in ammonia the compounds formed are Na Pb and Na Pbg. The electrolysis of such a solution releases Na at the cathode and Pb at the anode. Evaporation gives [Na(NH3) ]4Pbg which loses NHg to leave pyrophoric Na Pbg. These compounds seem to possess a character between that of a true valency compound and an intermediate phase (Zintl, 1929),... 

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