From a Halide

The process whereby aldehydes are produced from arylmethyl (also alkyl and other) halides by the action of hexamine is known as the Sommelet reaction. The reaction is essentially the conversion of an amine into an aldehyde the hexamine serves the dual role of converting the halide into the amine and the amine into the aldehyde, but its function is different in the two steps. When starting from a halide, the reaction proceeds in three stages —... 

Probably the most common aromatic nucleophilic displacement reactions involve the displacement of Hal from a halide activated by electron-withdrawing groups, e.g. (80) ... 

These include the simplest ion-association systems in which bulky cations and anions are extracted as pairs or aggregates without further coordination by solvent molecules. An example of this type of system is the extraction of manganese or rhenium as permanganate or perrhenate into chloroform by association with the tetraphenylarsonium cation derived from a halide salt... 

The El spectra of the A Sn compounds reveal some further interesting features51-54. For m- and / -substituted halophenyl (F, Cl) aromatics, there are noticeable peaks corresponding to Sn(halogen)+ that have been identified as originating from a halide migration in the fragmentation process as shown in equation 5. 

On the other hand, aromatic monomers containing a boronic acid function apart from a halide function, i.e. haloarene boronic acids, undergo coordination homopolycondensation in the presence of transition metal-based catalysts, which results in the formation of poly(arylene)s [2] ... 

As in the malonic ester synthesis, you should identify the structural fragments of the target compound. The acetoacetic ester synthesis converts an alkyl halide to a methyl ketone ("substituted acetone"). The methyl ketone component comes from acetoacetic ester the other component comes from a halide. 

These mechanisms give us some idea of the kind of behavior to expect from a halide of a particular structure its reactivity under a given set of conditions, the likelihood of racemization or of rearrangement, the extent of elimination. They tell us how to change the experimental conditions—concentration, solvent, the nucleophilic reagent—to achieve the results we want to speed up reaction, to avoid racemization or rearrangement, to minimize elimination. 

The term Heck reaction summarizes catalytic C-C-coupling processes, such that a vinylic hydrogen is replaced by a vinyl, aryl, or benzyl group, with the latter being introduced from a halide or related precursor compound (cf. eq. (3)) [9 a, 14-16]. Therefore, the final step of product formation is the elimination of a hydrogen halide, and a base is thus required to bind the acid. The olefinic (vinylic) double bond is retained throughout the Heck reaction. Palladium is practically the only catalyst metal used, in the form of certain Pd and Pd" salts or complexes normally 1-5 mol % of catalyst is administered. 

Oximes. Halides are converted to oximes when heated with an alkyl nitrite and (BUjSn). In this reaction the nitroso group is transferred to the carhon radical derived from a halide. Previously, the more undesirable tributylstannyl nitrite was used as NO donor. 

A great many ionic liquids are prepared by a metathesis reaction from a halide or similar salt of the desired cation. The general metathesis reaction can be divided into two categories (Scheme 2) depending on the water solubility of the target ionic liquid metathesis via (1) Free acids or group 1 metals/ammonium salts, or (2) Ag salt metathesis. 

When a photon is absorbed by a silver halide grain, an electron is ejected from a halide ion and temporarily held at some site in the crystal. A silver ion can migrate to the site and combine with the electron to form a silver atom. The atom is not stable it can decompose back into a silver ion and a free electron. However, during its lifetime, the atom can trap a second electron if one becomes available. If this second electron remains trapped tmtil the arrival of a second silver ion, a two-atom cluster forms. This buildup of a silver cluster can continue as long as photoelectrons are available. The smallest cluster corresponding to a stable latent image speck is believed to consist of three or four silver atoms. Specks of this size or greater on the crystal surface can catalyze the subsequent action of a developer. 

In this context it should be noted that there is quite a difference between an ionic liquid made in a metathesis step from a halide ionic Hquid, with subsequent removal of residual halide by washing, and one where no alkyl halide was involved during the course of its synthesis. 

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