Condensation reactions halides

Most syntheses of nitrogen heterocycles involve substitution and/or condensation reactions of nitrogen nucleophiles with difunctional halides or carbonyl compounds. Common nitrogen reagents are ... 

In the polyetherification route the condensation reaction proceeds by reactions of types (1) and (2) where M is an alkali metal and X a halide. 

The cyclic sulfur imides readily undergo condensation reactions in the presence of a base, e.g., pyridine. For example, the reaction of S7NH with sulfur halides, S Cla or SOCI2, produces the series (S7N)2Sx (x = 1, 2, 3, 5), or (S7N)2S0, respectively. The bicyclic compound S11N2 (6.6) is obtained by treatment of 1,3-S6(NH)2 with The reaction... 

The chemistry of 1,2,5-thiadiazole systems (RC)2N2S has been extensively investigated. " In addition to the condensation reactions of sulfur halides with 1,2-diaminobenzenes, this ring system is obtained in high yields by the reaction of S4N4 with acetylenes (Section 5.2.6). For example, the reaction of S4N4 with diphenylacetylene produces 3,4-diphenyl-1,2,5-thiadiazole in 87% yield. 

There is no simple answer to this question, but the exact experimental conditions usually have much to do with the result. Alpha-substitution reactions require a full equivalent of strong base and are normally carried out so that the carbonyl compound is rapidly and completely converted into its enolate ion at a low temperature. An electrophile is then added rapidly to ensure that the reactive enolate ion is quenched quickly. In a ketone alkylation reaction, for instance, we might use 1 equivalent of lithium diisopropylamide (LDA) in lelrahydrofuran solution at -78 °C. Rapid and complete generation of the ketone enolate ion would occur, and no unreacled ketone would be left so that no condensation reaction could take place. We would then immediately add an alkyl halide to complete the alkylation reaction. 

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

Since amine-phosphorus(III) halide condensation reactions are well-established low-energy routes to phosphorus-nitrogen bonds, they provide a logical starting point for examination of skeletally stabilized molecule synthesis. For our initial studies, reactants that are phenyl substituted as opposed to alkyl substituted... 

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

Deliberate and stepwise increase of the nuclearity of polynuclear complexes is possible by condensation reactions between silyl-substituted heteronuclear complexes [Ln(R3Si)M]xM L m and metal halides. Two such examples are shown in Scheme 3 (reaction of MeCp(CO)2(MePh2Si)Mn-HgPh with PhHgCl, and reaction of [MeCp(CO)2(MePh2Si)Mn]2Hg with HgBr2) [18]. 

Perfluorohalogenoalkanesulfenyl halides readily undergo condensation reactions with numerous types of compounds this is due to their polarization R/S " "—HaP caused by the strong electron-withdrawing action of the fluorine atoms. Thus, the reaction of dimethylarsine with trifluoromethanesulfenyl chloride affords (CHs)2AsSCF3, (CHjjgAsCl, and trifluoromethanethiol ... 

For maximum yield, care must be taken to ensure that the rate of addition of the reagents is not excessive. If this occurs then the alkyllithium is generated in the presence of significant amounts of unchanged alkyl halide and the Wurtz condensation reaction may be favored. The rate of formation of the alkyllithium is proportional to the surface area of the lithium metal and so at a constant rate of addition the Wurtz condensation is reduced by an increase in the lithium surface available for reaction. 

Related synthetic routes include the redox condensation reaction of carbonylate anions with neutral carbonyls, e.g., Eq. (12) (55), metal exchange reactions between carbonylate anions, e.g., Eq. (13) (56), and direct reductive carbonylation of metal halides, e.g., Eq. (14) (57). The stoichiometry of the products are not rational, and the mechanisms clearly are very complicated, though once again these reactions, under experimental optimization, can provide very useful synthetic routes. 

Georgiev et al. [82] have described the preparation of novel adamantine-spiro-heterocyclic (3-lactams 34, 35, and 40. Grignard reaction of 2-adamantanone 31 with benzylmagnesium halide provided the compound 32, which on further dehydration afforded corresponding analogs 33. Condensation reaction of compound 33 with chlorosulfonyl isocyanate in ether afforded spiro-(3-lactams 34 and cycloaddition with chlorosulfonyl isocyanate resulted in the formation of spiro product 35 (Scheme 10). 

Although it may be expected that other mercury derivatives of pyrimidines will be applied in this general reaction, several limitations warrant consideration. Oddly enough, attempts to employ a mercuri derivative of uracil in this condensation reaction have thus far been unsuccessful.810 As has been pointed out, since many of the mercurypyrimidines are insoluble, it is both desirable and usually possible to prepare them in essentially quantitative yield by the use of stoichiometric proportions of the reactants (pyrimidine, alkali, and mercuric halide), in order to obtain a pure product.198 With uracil, however, it has not thus far been possible to prepare a pure mercury salt (that is, monochloromercuriuracil, diuracilmercury, or uracilmercury). Instead, mixtures, which probably contained some unreacted uracil, were obtained.811 Lack of a solution to this problem may account for the consistent failure to adapt uracil to the mercuri synthesis. 

These two synthetic methods have, therefore, the built-in feature which limits them to the synthesis of aldoglycosyl nucleosides having a trans relationship between Cl and C2 substituents. From the practical point of view, however, in any successful synthesis of a D-ribofuranosyl analog of ribonucleosides, the /S configuration of the product is assured. In contrast, where the 2-acyloxy function is absent (as in poly-O-acyl-2-deoxyglycosyl halides), stereochemical controls of the condensation reaction, by the mechanisms involved in the trans rule, are lacking, and both the a and the /3 nucleoside should be formed.219... 

Alkylation of / -ketoesters with ( -substituted alkyl halides is an efficient method for the synthesis of cyclic products577-580. In one such reaction sequence, the dianion of a / -ketoester was reacted with 2-(2-bromoethyl)-l,3-dioxolane, the co-substituent in this case being a masked aldehyde. Upon regeneration of the aldehyde functionality, a condensation reaction occurred to give the cyclohexanone as shown in equation 88577. 

Wurtz synthesis. The condensation reaction between two halides brought about by the action of metallic sodium, as in... 

Even simple metal halides have been used as sources of metal atoms for the condensation reactions of carbonyl metallates [e.g., Eq. (6)] (379). 

Two principle strategies have been employed for the synthesis of siloxide-containing molecular precursors. The first involves a silanolysis, or condensation, reaction of the Si - OH groups with a metal amido, alkyl, halide, or alkoxide complex. The second method involves salt metathesis reactions of an alkali metal siloxide with a metal halide. Much of our work has been focused on formation of tris(tert-butoxy)siloxide derivatives of the early transition metals and main group elements. The largely imexplored regions of the periodic table include the lanthanides and later transition metals. 

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