Chloride displacements

The excess of thionyl chloride displaces the equilibrium to the left not only by removing the carboxylic acid (RCOOH + SOClj->RCOCl + SOj + HCl) but also by... 

The carrier stream consists of an acidic solution of Hg(SCN)2 and Fe +. When a sample containing chloride is injected into the carrier stream, the chloride displaces the thiocyanate from Hg(SCN)2. The displaced thiocyanate then reacts with Fe + to form the reddish colored Fe(SCN) + complex, the absorbance of which is monitored at a wavelength of 480 nm. Sampling rates of approximately 120 samples/h have been achieved with this system. 

These compounds perform a dual function in synthesis procedures. The introduction of a complex anion assists in the stabilization of the desired product and the generation of unique intermediates by chloride displacement, eg, silver hexafluorophosphate, AgPF, forms adducts with neutral diamagnetic organometaHics which can act as controUed sources of highly reactive cations (29). Silver hexafluoroantimonate, AgSbF, is an electrophilic... 

Reactive halogens in various series have been removed by catalytic hydrogenation with either platinum or palladium catalysts, and other nucleophiles which have been used in chloride displacements include hydroxide ion, alkoxides, hydrosulflde, hydrazine and toluene-p-sulfonylhydrazine, and trimethyl phosphite. 

In one example where a 2-Cl and 2 -F were present, only the chloride displacement product (548) was reported also the tetrafluoro-l,2-benzisoxazole (550) was prepared by heating the oxime (549) (Scheme 166) (79EUP2666, 71MI41600). 

Complexes 59 or 60 enter the chloride displacement reaction with sodium bromide and iodide. The products obtained are analogs of isomer 59. Pyiazole,... 

C2F4 displaces one ethene to give Rh(C2H4)(C2F4)(acac), as does hexa-fluorodewarbenzene, whereas other alkenes (e.g. propene, styrene, vinyl chloride) displace both ethenes. Comparison of the structures of two complexes (Figure 2.28) shows that the Rh-C bonds are shorter to tetra-fluoroethene, because C2F4 is a better 7r-acceptor, with concomitant strengthening of the Rh-C bond. 

Much was unknown for the halogenation for unreactive substrates until very recently, when the biosynthesis of the cyclopropyl amino acid side chain of coronatine was elucidated. This intriguing pathway, which involves /-chlorination of an enzyme-bound L-isoleucine followed by chloride displacement by the a-carbon, yields the cyclopropanated precursor... 

Acetamido-2-phenylethaneboronic acid, the boronic acid analog of. V-acetylphenyl-alanine and a good inhibitor of chymotrypsin, has been prepared via a stable silylated intermediate59, 62. Coordination with boron evidently facilitated the unusual chloride displacement by sterically hindered lithium hexamethyldisilazanide. 

Under the influence of ultraviolet irradiation, chloride displaced the nitro group of 2-(5 -nitro-2 -furanyl)benzothiazole to give a chlorofuran exhibiting intense violet fluorescence. This allowed the reaction to be used as an analytical process for chloride determination (80CPB939). 

Under biphase conditons (in dry dioxane) the activity of 46 for the reaction of 1-bromo-heptane with sodium phenoxide decreased with an increase in the length of aliphatic chains. Under triphase conditions, however, only catalyst 46 with n-octyl groups was active for chloride displacement reactions, and catalysts with groups smaller than n-butyl showed no activity 165). Polyacrylamides 46 with short aliphatic chains are too hydrophilic to act as catalysts under triphase conditions. Similar behavior has been observed for ammonium salts supported on dextran 95). 

The topical antifungal bifonazole (60-2) dispenses with virtually all but the imidazole ring the intermediate (60-1) is obtained by sequential reduction of 4-phenyl-benzophenone and then reaction of the alcohol with thionyl chloride. Displacement of chlorine by imidazole gives (60-2) [65]. 

Incorporation of a piperazine function on the heterocyclic ring leads to a compound in which bronchodilator activity predominates. Treatment of the amino-amide (73-1) with trimethyl orthoformate provides the additional carbon atom for the formation of the quinazolone ring in (73-2). Reaction with phosphoms oxychloride in effect converts the ring to its aromatic form (73-3) by locking in the former amide as an enol chloride. Displacement of the halogen with the isobutyryl urethane (73-4) from piperazine affords piquizil (73-5) [82]. 

At the ordinary temperature chlorosulphonic acid dissolves sodium chloride, displacing hydrogen chloride and forming sodium chloro-sulphonate,11 this reaction being due to its acidic nature. It is of interest that ammonium chlorosulphonate can be synthesised by the action of sulphuryl chloride on aminosulphonic acid at 100° C.12... 

The indirect hydrocyanation of butadiene as practiced by du Pont (/) involved the electrolysis of sodium chloride, formation of sodium cyanide from HCN using the NaOH, chlorination of butadiene to give 1,4-dichloro-but-2-ene, chloride displacement with sodium cyanide, and subsequent hydrogenation, as indicated in Eqs. (l)-(5), with the net result of Eq. 6. 

Another important function of protecting groups is to prevent a reagent from attacking itself. In the last chapter, when we discussed the synthesis of the bicyclic amine monomorine, we used the protected enone 12 but did not say how it was made. The chloroketone 9 is first made1 in 89-93% yield from the ketolactone 6 simply by reaction with HC1. Chloride displaces the protonated ester group 7 and the product 8 decarboxylates under the conditions of the reaction. 

Recently, the synthesis and evaluation of a new pyrazinone class of tryptase inhibitors has been reported. One step in the preparation of these compounds involved regioselective chloride displacements from a dichloropyrazinone scaffold using amines and anilines as nucleophiles. The aniline reactions required the use of microwave-assisted heating for 12 min at 120 °C, as illustrated in Scheme 23 [84]. Although the aniline-derived compounds (e.g., 50) were modest inhibitors, other compounds from this study, synthesized by classical heating methods, were shown to be highly potent tryptase inhibitors. 

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