Organohalides

The gases released during volcanic eruptions contain large amounts of organohalides, including chloro-methane, chloroform, dichlorodifluoromethane, and many others. 

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2 Preparing Alkyl Halides from Alkanes Radical Halogenation 

3 Preparing Alkyl Halides from Alkenes Allylic Bromination 

Now that we ve covered the chemistry of hydrocarbons, it s time to start looking at more complex substances that contain elements in addition to C and H. We ll begin by discussing the chemistry of organohalides, compounds that contain one or more halogen atoms. 

If a double or triple bond is present, the parent chain must contain it. 

Some alkyl halides are named by first citing the name of the alkyl group and then citing the halogen. 

Alkyl halides have approximately tetrahedral geometry. 

Bond lengths increase with increasing size of the halogen bonded to carbon. 

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Still other halo-substituted compounds are providing important leads to new medicines. The compound epihatidine, for instance, has been isolated from the skin of Ecuadorian frogs and found to be more than 200 times as potent as morphine at blocking pain in animals. 

Alkyl halides are encountered less frequently than their cxygen-containing relatives alcohols and ethers, but some of the kinds of reactions Ihey undergo—nucleophilic substitutions and eliminations—are encountered frequently. Thus, alkyl halide chemistry acts as a relatively simple model for many mechanistically similar but structurally more complex reactions found in biomolecules. VVeTl begin in this chapter with a look at how to name and prepare alkyl halides, and weTl see several of their reactions. Then in the following chapter, we U make a detailed study of the substitution and elimination reactions of alkyl halides—two of the most important and well-studied reaction types in organic chemistry. 

Electrochemical methods are preferred in analysis of phenols and halogenated organics since often there is no need for extensive separation. However direct determination on noble metal electrodes is not favored due to high over-potentials. Electrochemical oxidation of phenols readily occurs on unmodified electrodes, but oxidation results in the formation of dimers which poison the electrodes, decreasing the oxidation currents. In order to improve sensitivity and selectivity, chemically modified electrodes are employed. In this regard M-N4 complexes have shown remarkable catalytic activity towards the detection of phenols and other species when either employed as homogeneous catalysts or when adsorbed to electrodes. 

In general, phthalocyanines, porphyrins and corrins catalyze the reduction of organohalides and the overall reaction is shown by Equation (7.3) .  

The reduction of benzyl bromide mediated by vitamin B12r, CoTSPc, and Co(salem) in a microemulsion under homogeneous conditions, resulted in products derived from the resulting radicals and anions . The reactions were mediated by Co species . Priyantha and Tambalo employed GCE coated with Co TPP or Ee TPP as electrocatalytic amperometric sensors for the detection of herbicides including 2,3-dichlorophenoxyacetic acid  

M-N4 complex Electrode Method of Analyte (V) Medium 0/R References 

CoTPP Pt Solution Benzyl chloride -1.38 DMSO/TBAP R [69] 

Insertion into more challenging substrates such as aryl iodides or bromides requires more active zinc. Highly active zinc prepared by the reduction of zinc 

FIGURE 7.10 Some organohalide compounds that are, or have been in the past, potential air pollutants. 

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Figure 16.18 Some coordination environments of Se and Te in their organohalides.

Heck reaction, palladium-catalyzed cross-coupling reactions between organohalides or triflates with olefins (72JOC2320), can take place inter- or intra-molecularly. It is a powerful carbon-carbon bond forming reaction for the preparation of alkenyl- and aryl-substituted alkenes in which only a catalytic amount of a palladium(O) complex is required. 

Copper(ll) chloride, aromatic iodination and, 551 Coproslanol, structure of, 304 Coral, organohalides from, 352 Corn oil, composition of. 1062 Cornforlh. John Warcup. 1085 Coronene, structure of, 532 Cortisone, structure of. 107 Couper, Archibald Scott, 7 Coupled reactions. 1128-1129 ATP and, 1128-1129 Coupling (NMU), 460... 

Organohalide(s), 332 biological uses of, 352 naturally occurring, 351-352 number of, 351... 

The transition metal catalyzed cross coupling of an organohalide with a boronic acid derivative, the Suzuki-Miyaura coupling, has become one of the most popular ways of preparing biaryls.3 The reaction is very robust and can easily be scaled to provide multigrams of material.4... 

EPA. 1997e. Methods and guidance for analysis of water. Method 508.1 Determination of chlorinated pesticides, herbicides, and organohalides by liquid-solid extraction and electron capture gas chromatography. U.S. Environmental Protection Agency, Washington, DC. EPA 821-C-97-001. 

Bellar TA, Lichtenberg JJ, Kroner RC. 1974. The occurrence of organohalides in chlorinated drinking waters. Journal of American Water Works Association 66 703-706. 

May HD, LA Cutter, GS Miller, CE Milliken, JEM Watts, KR Sowers (2006) Stimulatory and inhibitory effects of organohalides on the dehalogenating activities of PCB-dechlorinating bacterium o-17. Environ Sci Technol 40 5704-5709. 

In this way, Davies and co-workers proved that for monomeric organohalide carbonylation, the catalyst was homogeneous, although Pd/C was used as pre-catalyst. This fact was in addition supported by the catal5fiic activity observed with related polymeric halides [30]. 

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