Basic and Acidic Media

In some molecules, the loss of halogen is unexpectedly facile and may occur extensively even over platinum, as illustrated by reduction of the dihydro-2-benzazepine 4 to 5. The authors (5i) raised the possibility that such facile loss of halogen may involve neighboring-group assistance from the amide moiety. 

Nickel catalysts have been used for many dehydrohalogenations (30), but these catalysts are much more suspectible to poisoning by halide ion than are noble metals. As a result, the catalyst-to-substrate ratio must be much higher when using nickel, and reduction times are apt to be lengthy (36). Reductive deiodination of 6 to 7 was achieved over Raney nickel in methanol containing triethylamine. Despite massive loadings, the reduction was slow (20). 

A number of halogen acceptors, such as alkali and alkaline earth hydroxides, aceutes, ethoxides, amines, and ammonia, have been used successfully. The pyrida2ine 9 was prepared via dehydrohalogenation of 8 using sodium acetate as acceptor (37). 

Triethylamine was used as acceptor in dehydrochlorination of 10 to give the macrolide phoracantholide 1 (11) (44). 

Compounds containing a basic nitrogen, such as 2-chloroaniline. may function as their own hydrogen-halide acceptor (4). The rate of reduction is greatly retarded by added hydrogen chloride. 

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Calixarenes, the cyclic oligomers formed from condensation reactions between para-substituted phenols and formaldehyde, are inexpensive compounds that are stable to both basic and acidic media. ... 

Fig. 2 Surface behavior of alumina in basic and acidic media, respectively. (From Ref. [2].)...

PtMe(Tp)], a new alkyne protecting group, can be used under a variety of reaction conditions, including basic and acidic media and the environment required for catalytic hydrogenation and for chromate oxidation reaction.79... 

For the purpose of studying, e.g., protein subunits, the so-called urea-polyacrylamide gels are in use. The separation in the presence of urea can be done in basic and acidic media, and the solutions for preparation of both types of gels are naturally different. The alkaline gel system with urea-alkaline (for denatured protein subunits) is prepared in the following way (7.5% gel, pH 8.3). 

Iodine Monochloride This precursor is generated by the exchange IGl/Na I, which corresponds to an oxidation of iodide by cold iodine. It can also be obtained by oxidation with elemental GI2. Depending on the reaction conditions, pH, and solvent, the reagent is either IO or IOH and lOHj, respectively, in basic and acidic media. 

Liu, J. Barrio, J.R. Satyamurthy, N. Kinetics and mechanism of the defluorination of 8-fluoropurine nucleosides in basic and acidic media. J. Fluorine Chem. 2006, 127, 1175-1187. 

Fig. 2 Surface behavior of alumina in basic and acidic media, respectively.

In basic solution Fe(CO)6 and M(CO) (M = Cr, Mo, or W) catalyse the water-gas shift reaction (i.e. HgO + C0 C02 + H2). Ruthenium carbonyl compounds catalyse this reaction in both basic and acidic media mixed ruthenium-iron carbonyl catalysts e.g. [FeRu3H2(CO) 3] are considerably more active in basic solution than either ruthenium or iron carbonyls alone. [PtLg] (activity L = PPr 3>PEt3>PPh3) and KaPtCl4-SnCl4,5H20 also catalyse the water-gas shift reaction the proposed mechanism for the latter catalyst is shown in Scheme 1. ... 

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