Halogenated hydrocarbons halogen-substituted aromatics

Colourless solids. Carbohydrates simple phenols high rnoLwt. carboxylic adds, their salts and amides sulphonic adds, their salts and amides simple imides polyhydric alcohols Mgher mol.wt. esters polyhalogeno-aromatic hydrocarbons halogen substituted aromatic acids, their salts and amides bisulphite compounds of aldehydes and ketones aldehyde-anunonias condensation products of aldehydo- and keto-compounds. 

An exact match is obtained in the search for the Arochlor 1254 and interestingly, the four closest matches, with significantly reduced scores, are also Arochlors (Table 7). All the other compounds in the list are halogen substituted aromatic hydrocarbons. The key point in this example is that priority has been given to the materials of common generic type. 

Halogenated chemicals Polycyclic aromatic hydrocarbons Aliphatics Substituted benzenes Halogenated aliphatics Dioxins and furans... 

The introduction of the halogens onto aromatic rings by electrophilic substitution is an important synthetic procedure. Chlorine and bromine are reactive toward aromatic hydrocarbons, but Lewis acid catalysts are normally needed to achieve desirable rates. Elemental fluorine reacts very exothermically and careful control of conditions is required. Molecular iodine can effect substitution only on very reactive aromatics, but a number of more reactive iodination reagents have been developed. 

Solvents can be classified into three categories according to their polarity namely, polar protic, dipolar aprotic and non-polar. Most of the common solvents fall under one of following chemical classes Aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, phenols, ethers, aldehydes, ketones, carboxylic acids, esters, halogen-substituted hydrocarbons, amines, nitriles, nitro-derivatives, amides and sulfur-containing solvents (Marcus, 1998). In certain cases a mixture of two or more solvents would perform better than a single solvent. 

Organohalides (Figure 1.17) exhibit a wide range of physical and chemical properties. These compounds consist of halogen-substituted hydrocarbon molecules, each of which contains at least one atom of F, Cl, Br, or I. They may be saturated (alkyl halides), unsaturated (alkenyl halides), or aromatic (aryl halides). The most widely manufactured organohalide compounds are chlorinated hydrocarbons, many of which are regarded as environmental pollutants or hazardous wastes. 

Considering what was said about stabilization energies in our previous discussion of thermochemical mimics, we now turn to aryl halides. There are several conceptual approaches to their thermochemistry one can take. The first is to consider halogenated derivatives of benzene, then of naphthalene, then of the isomeric anthracene and phenan-threne, etc. This approach, perhaps more appropriate for a study of generally substituted aromatic hydrocarbons, is immediately thwarted. Although there are many appropriate derivatives of benzene worthy of discussion, thermochemical data on halogenated naphthalenes are limited to the isomeric 1- and 2-monosubstituted derivatives, and halogenated derivatives of other aromatics remain thermochemically unstudied. 

Halogen Acids Yield Aromatic Halides.— When a water solution of a diazonium salt is heated with a halogen acid the halogen substitution product of the corresponding hydrocarbon is obtained, the diazo group being replaced by the halogen. 

There are in principle three possibilities for reaction of halogens with aromatic hydrocarbons, namely, addition, substitution in the nucleus, and substitution in a side chain. The last of these is discussed on pages 152 and 157. Substitution of benzene by chlorine or bromine is an ionic reaction,114 whereas photochemical or peroxide-catalyzed addition of these halogens involves a radical-chain mechanism.115 Substitution in the side chain also proceeds by a radical mechanism,116 addition rather than side-chain substitution being favored by higher chlorine concentrations.115... 

Halo-substituted unsaturated hydrocarbons behave like aromatic hydrocarbons towards saturated halides in the presence of aluminum chloride.93 Suitable acceptors are the halogen substitution products of ethylene in particular, chloromethanes, and best of all chloroform and methylene chloride... 

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