Sequential displacement reactions

Reactions of this type are defined as sequential or single-displacement reactions. They can be either of two distinct classes ... 

Fig. 17. Schematic illustration of the preparation of dendrimer-encapsulated bimetallic clusters by three different methods. Displacement reaction, co-complexation, and sequential loading...

An alternate and more controlled approach to the synthesis of phenothiazines involves sequential aromatic nucleophilic displacement reactions. This alternate scheme avoids the formation of the isomeric products that are sometimes observed to form from the sulfuration reaction when using substituted aryl rings. The first step in this sequence consists of the displacement of the activated chlorine in nitrobenzene (30-1) by the salt from orf/io-bromothiophenol (30-2) to give the thioether (30-3). The nitro group is then reduced to form aniline (30-4). Heating that compound in a solvent such as DMF leads to the internal displacement of bromine by amino nitrogen and the formation of the chlorophenothiazine (30-4). Alkylation of the anion from that intermediate with 3-chloro-l-dimethylaminopropane affords chlorpromazine (30-5) [31]. 

Sequential displacement reactions of Pd(CF3COCHCOCF3)2 with triarylformazans provides the highly colored chelates Pd(CF3COCHCOCF3)[(aryl)3CN4] and Pd[(aryl)3CN4]2.250... 

Other workers have concurrently developed the extensive acid-base chemistry of palladium and platinum /l-diketonates.44 452 Sequential displacement reactions also occur with Pt(CF3COCHC-OCF3)2, Pt(CF3COCHCOMe)2 and Pd(CF3COCHCOMe)2. Pdtetrakis(aniline)2+ diketonates are... 

Among other chemistries being developed, the synthesis of heterocychc molecules has proved a popular option both from chemical and biological perspectives. Two approaches employed are the modification of existing heterocyclic systems and the construction of the heterocycle dining the reaction ofinterest. Whitten et al. [14] have exemplified the former in sequential halide displacement reactions of dichlorotriazines with amines. 

This experiment allows you to carry out the sequential conversion of copper metal to copper(II) nitrate to copper(II) hydroxide to copper(II) oxide to copper(II) sulfate and back to copper metal. This conversion is carried out using synthesis, decomposition, single displacement, and double displacement reactions. 

The use of aminosulfites in the synthesis of o.p. sulfoxides was described for the first time in 1973 by Wudl and Lee,98 using ephedrine as chiral auxiliary. In 1991, Benson and Snyder reported a modification of the Wudl and Lee procedure, obtaining o.p. sulfoxides in high yield by sequential displacement reactions of organometallic reagents on the 1,2,3-oxathiazolidine-S-oxide (aminosulfite 70), obtained from ephedrine and thionyl chloride.99... 

Many such reactions transfer a functional group, such as a phosphoryl or an ammonium group, from one substrate to the other. Those that are oxidation-reduction reactions transfer electrons between substrates. Multiple substrate reactions can be divided into two classes sequential reactions and ionhle-displacement reactions. 

The results summarized in Table III suggest that the enzymes that catalyze phosphoryl transfer via an inversion of configuration do so with an in-line transfer in a sequential mechanism. The mechanistic pathway is prevalent in the phosphokinases. Although this information does not provide direct evidence for an associative or Sn2 mechanism in contrast to a dissociative mechanism, if the latter process does occur then there is insufficient room at the catalytic site for the metaphosphate to rotate or dissociate and to cause racemization. The observation of a secondary 0 isotope effect less than 1.00 indicates that a dissociative transition state occurs with yeast hexokinase (57). The enzymes that demonstrate retention of configuration do so via double-displacement reactions. Mutases exclusively use this mechanistic pathway. 

Core-shell catalyst materials may also be prepared by non-electrochemical routes. Core-shell nanoparticles may be produced in solutimi using colloidal methods, by sequential deposition of the core and shell components [33], or Pt layers may be deposited chemically or via displacement reactions onto preprepared core nanoparticles, but in cmitrast to approaches described in Sect. 19.3.1, no applied potential is required typically core particles or colloidal core-shell particles are deposited onto carbon supports. 

Polymerization was carried out via the one-pot method, but selective fluorine displacement was sequentially followed by nitro displacement. Fluorine displacement of 5-fluoro-2-nitrobenzotrifluoride with l,l,l-tm(4-hydroxyphenyl)ethane was carried out in DMSO at 80 °C for 4h in the presence of K2CO3, and then the reaction mixture was subjected to the nitro displacement reaction at 170°C for 6h. The polymerization proceeded homogeneously without gelation or precipitation at a concentration of lOwt.% monomers. Both A3+BC and A2C polymerization at a higher monomer concentration (25 wt.%) produced a gel. 

Scheme 2.17 Synthesis of hb poly(arylene ether)s from monomers containing nitro group (a) via selective and sequential S vjAr (preferential fluorine displacement followed by nitro displacement) reaction of As-and BC-type monomers (b) via nitro displacement reaction of A2C-type monomer. Taken from Ref. [76],...

Amino-3-deoxy-sucrose has been synthesized from sucrose by sequential oxidation at C-3 by Agrobacterium tumefaciens (40% yield), peracetylation, reduction of the C-3 ketone to an a//o-configured product (H2, Pt), trifluoro-methanesulfonylation, displacement by azide with inversion, deacetylation and hydrogenation. 4-Amino-4-deoxy-sucrose was obtained from a sucrose hepta-pivaloate by double inversion at C-4 by sequential triflate displacement reactions, first with nitrite then azide ion. Various 4-alkylamino-2,4-dideoxy-L-r/ireo-pentopyranosides 15, components of the calicheamicins, were synthesized from... 

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