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Most alkyl and aryl halides have very low solubilities in water, but as we might expect, they are miscible with each other and with other relatively nonpolar solvents. Alkyl halides are formally derived from alkanes by exchanging hydrogen for halogen (fluorine, chlorine, bromine, and iodine).
In the generally accepted nomenclature of alkyl halides, the name of the alkyl residue is followed by the name of the halide, e.g. In the nomenclature of unsaturated alkyl halides, unsaturated bonds have a higher priority than halogen substituents. Some commonly used chlorinated organic solvents, such as carbon tetrachloride (tetrachloromethane), chloroform (trichloromethane) and methylene chloride (dichloromethane), are known more by their trivial name than by their IUPAC name. Organic Halides are divided into two different groups called haloalkanes and haloarenes. Their names are derived by naming the attached alkyl group to halogen and adding the name of the halide. Haloalkanes are not able to form hydrogen bonds with water and, even though they are polar in nature, they are practically insoluble in water. Haloarenes or aryl halides are named by adding the prefix 'halo' (fluoro, chloro, bromo, iodo) before the name of the aromatic hydrocarbon. Many synthetic organic compounds such as plastic polymers, and a few natural ones, contain halogen atoms; they are known as halogenated compounds or organohalogens. For example, chloride ions play a key role in brain function by mediating the action of the inhibitory transmitter GABA and are also used by the body to produce stomach acid. Adsorbable organic halides (AOX) are generated in the pulp and paper industry during the bleaching process. Physical, chemical and electrochemical methods reported to remove AOX compounds are not economically viable.
AOX (absorbable organic halide) and total organic halide (TOX) analyzers make up a small segment of the environmental analysis market. Organofluorides are very stable compounds that are nonflammable, have very limited toxicity, and do not react with other chemicals. Because of their low chemical reactivity, alkyl chlorides are useful in dissolving other chemicals, greases, and oils. Chlorofluorocarbons (CFCs) are compounds that contain both chlorine atoms and fluorine atoms bonded to carbon atoms.
Organobromides form highly reactive compounds when mixed with metals such as magnesium (Mg) or aluminum (Al); for this reason, they are used extensively in the manufacture of dyes, drugs, and other chemicals. The most chemically reactive of the organic halides are those that contain carbon atoms bonded to iodine atoms.
Free radical halogenation typically produces a mixture of compounds mono- or multihalogenated at various positions. Due to the different dipole moments of the product mixture, it may be possible to separate them by distillation. In hydrohalogenation, an alkene reacts with a dry hydrogen halide (HX) like hydrogen chloride (HCl) or hydrogen bromide (HBr) to form a mono-haloalkane. Alkenes also react with halogens (X2) to form haloalkanes with two neighboring halogen atoms in a halogen addition reaction. Tertiary alkanol reacts with hydrochloric acid directly to produce tertiary chloroalkane, but if primary or secondary alkanol is used, an activator such as zinc chloride is needed.
The most popular conversion is effected by reacting the alcohol with thionyl chloride in the "Darzen's process," which is one of the most convenient laboratory methods because the byproducts are gaseous. Alcohol may likewise be converted to bromoalkane using hydrobromic acid or phosphorus tribromide (PBr3).
Two methods for the synthesis of alkyl halides from carboxylic acids are the Hunsdiecker reaction and the Kochi reaction. There are two main preparatory routes for aryl halides.[1] The first is the Friedel-Crafts halogenation.
Direct halogenation of an aromatic compound is easy, and doesn't require light or high temperature.
Without Lewis acid catalysts, arenes with electron donating groups such as phenols and anilines may react with halogens. An agressive campaign is now being waged to remove CFCs from use as refrigerants because of danger to the ozone layer above the earth.
Haloalkanes are widely used as synthon equivalents to alkyl cation (R+) in organic synthesis. Short chain haloalkanes such as dichloromethane, trichloromethane (chloroform) and tetrachloromethane are commonly used as hydrophobic solvents in chemistry. Many organohalogen compounds in which the halogen is directly attached to a benzenoid ring occur naturally. The present invention relates to a catalyst for decomposing organic harmful substances such as organic halides.
The boron trihalides are covalent in nature and exist as monomeric molecules having planar triangular geometry.
Since there are only six electrons in the valence shell of boron atom in boron trihalides, therefore, they have a great tendency to accept two more electrons in order to acquire a stable octet. The other halides of Group 13 elements have halogen bridged dimeric structures as shown below for aluminium (III) chloride, which exists as Al2Cl6. Boron halides do not form dimers because the size of boron is so small that it is unable to coordinate four large-sized halide ions.
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Note: The most reactive organic halide, organoiodide, is the element that is the lowest in period number on the periodic table and it appears to be the most reactive. Consequently, the carbon–halogen bond length increases and carbon–halogen bond strength decreases as we go down the periodic table (Table 1). As we shall learn in this chapter, the halogen atom of an alkyl halide can be easily replaced by other groups, and the presence of a halogen atom on a carbon chain also affords us the possibility of introducing a multiple bond. Compounds in which a halogen atom is bonded to an sp2-hybridized carbon are called vinylic halides or phenyl halides. The chemistry of vinylic and aryl halides is, as we shall also learn later, quite different from that of alkyl halides, and it is on alkyl halides. Dichloromethane (CH2Cl2, also called methylene chloride), trichloromethane (CHCl3, also called chloroform), and tetrachloromethane (CCl4, also called carbon tetrachloride) are sometimes used as solvents for nonpolar and moderately polar compounds.

Depending on the degree of substitution at the carbon atom carrying the halogen, alkyl halides are classified into primary, secondary and tertiary alkyl halides.
Halogens tend to form ionic compounds with metals such as sodium chloride and covalent compounds with nonmetals such as organohalogens, our main focus .
These are obtained when the hydrogen atom of an alkane and arene is replaced by a halogen atom (F, Cl, Br and I). The lower members like methyl chloride, methyl bromide and ethyl chloride are colorless gases while members having very high molecular masses are solids. With the increase in the size of halogen, the magnitude of Van der Waals forces increases and, consequently, the boiling points increase. In case of di-substituted compounds, the relative positions of the substituents 1,2; 1,3 and 1,4 are indicated by the prefixes ortho (o-), meta (m-) and para (p-) respectively. Chlorine is by far the most abundant of the halogens, and the only one needed in relatively large amounts (as chloride ions) by humans. Iodine is needed in trace amounts for the production of thyroid hormones such as thyroxine.
Different types of aerobic, anaerobic and combined biological treatment processes have been developed for treatment of pulp and paper industry wastewater. Halogenated organic materials are used to manufacture numerous industrial and consumer products, including pharmaceuticals, fine chemicals, plastics and solvents. Perfluorocarbons (PFCs) are alkyl fluorides that consist of chains of carbon atoms bonded only to fluorine atoms. Methylene chloride (CH2Cl2) is an alkyl chloride with a low molecular weight that is used in many paint and varnish removers.
Organoiodides are not used as extensively as organobromides or chlorides because they are expensive. In this reaction a hydrogen atom is removed from the alkane, then replaced by a halogen atom by reaction with a diatomic halogen molecule. It is possible to predict the results of a halogenation reaction based on bond dissociation energies and the relative stabilities of the radical intermediates. The double bond of the alkene is replaced by two new bonds, one with the halogen and one with the hydrogen atom of the hydrohalic acid.
Both phosphorus pentachloride (PCl5) and phosphorus trichloride (PCl3) also convert the hydroxyl group to the chloride. A catalytic amount of PBr3 may be used for the transformation using phosphorus and bromine; PBr3 is formed in situ.
In the presence of light or at high temperature, the alkyl positions tend to be halogenated first in the free radical halogenation.
For example, phenols and anilines react quickly with bromine water to give multiply-brominated benzene rings, which precipitate.
The Earth's ozone layer is formed by the action of sunlight on ordinary oxygen in the atmosphere, and that ozone is a strong absorber of ultraviolet light from the sun.
Unlike alkyl and vinylic halides, for which marine origins are the most common, aryl halides are found in a variety of sources. More specifically, the present invention relates to a catalyst for decomposing harmful organic halides including dioxins in an exhaust gas generated with burning of urban garbage or industrial waste; or a treatment of plastic materials to make them harmless. Examples include methane or ethane, with one or more halogens linked, such as chlorine or fluorine. In these halides boron assumes sp2 hybrid state and the three B-X bonds are formed by axial overlap of sp2 hybrid orbital of boron and p-orbital of halogen. They rapidly combine with electron donors such as NH3, F- ion, amines, ether, sulphides or phosphorus. In the dimeric structure each aluminium atom accepts a lone pair of electrons from the chlorine atom bonded to the other aluminium atom. As a consequence of its strong Lewis acid character, BF3 is used as a catalyst in several industrial processes. Of the five elements in the group, fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) are used in biologicalmolecules. The aryl halides are compounds where the halogen is attached directly to an aromatic ring and have the general formula ArX, where Ar is an aromatic group.
Maps of electrostatic potential (see Table 1) at the van der Waals surface for the four methyl halides, with ball-and-stick models inside, illustrate the trend in polarity, C-X bond length, and halogen atom size as one progresses from fluorine to iodine substitution. The compound CH2=CHCl has the common name vinyl chloride, and the group CH2=CH- is commonly called the vinyl group.
Many chloroalkanes, including CH2Cl2, CHCl3, and CCl4, have a cumulative toxicity and are carcinogenic, however, and should therefore be used only in fume hoods and with great care.
The IUPAC nomenclature (shown in brackets in the illustration below), considers an alkyl halide a substituted alkane, i.e. Also, for the same halogen atom, the boiling points of haloalkanes increase with increase in the size of alkyl groups.
On the other hand, neither fluorine nor bromine are believed to be essential for humans, although small amounts of fluoride increases the strength of tooth enamel.
As the by-products of the production and degradation of synthetic substances, organic halides are deposited in the environment in the form of liquids, sludges, slurries, tars and solids. Flutriafol, another aryl fluoride, is a fungicide used to stop diseases on the grains used in the manufacture of various cereals.
It is used in portable fire extinguishers and in airplanes to stop engine fires while in flight.
Alkyl iodides react with metals such as lithium (Li) or mercury (Hg) to make useful chemicals in the manufacture of pharmaceutical and organic intermediates. The reactive intermediate in this reaction is a free radical and the reaction is called a radical chain reaction. Another factor to consider is the probability of reaction at each carbon atom, from a statistical point of view. Markovnikov's rule states that in this reaction, the halogen is more likely to become attached to the more substituted carbon. This is sometimes known as "decolorizing" the halogen, since the reagent X2 is colored and the product is usually colorless. Iodoalkanes may similarly be prepared using using red phosphorus and iodine (equivalent to phosphorus triiodide). The diazo compounds readiliy undergo nucleophilic attack by copper(I) chloride or halide to give a haloarene.

The benzylic carbon (Ph-C) tends to undergo free-radical halogenation first, due to the stabilization of the benzyl free radical by the aromatic ring. Halides are good leaving groups in nucleophilic substitution reactions and are good nucleophiles. The major problem with CFCs is that they tend to be unreactive near the surface, and being lighter than air, travel to the upper atmosphere if released.
The systematic synthesis of such compounds developed in the 1800s in step with the development of organic chemistry and the understanding of the structure of alkanes.
They are known under many chemical and trivial names such as fluorocarbons, chlorocarbons, and chlorofluorocarbons (CFC), etc. Anhydrous aluminium chloride is used as a catalyst in several organic reactions (Friedel - Craft's reaction).
The last and largest halogen,astatine (At), is radioactively unstable and not found in nature.
Fluoromethane is highly polar and has the shortest C-X bond length and the strongest C-X bond. Vinylic halide, therefore, is a general term that refers to a compound in which a halogen is attached to a carbon atom that is also forming a double bond to another carbon atom. Some of them show a tendency to bioaccumulate while some are proven carcinogens and mutagens. However, as these processes are designed specifically for reducing COD and BOD of wastewater, they do not ensure complete removal of AOX. Two years later, scientists replaced the blood in a laboratory rat with a solution of oxygen dissolved in PFCs. The well-known pesticide, DDT, is an aryl chloride that was first used in 1939 to kill the mosquitoes that transmitted malaria.
There ultraviolet radiation can break off a chlorine, and that chlorine atom can react with an ozone (O3) molecule to form chlorine monoxide (ClO). At one time, natural l-thyroxine extracted from the thyroids of animals was used to treat patients with thyroxine deficiencies, but today almost all of the l-thyroxine used to treat thyroid disorders is synthetic.
AOX discharge from closed landfills was generally lower than that from operating landfills. The chlorides, bromides and iodides are essentially covalent compounds with low melting points. Halogens tend to form ionic compounds with metals such as sodium chloride and covalent compounds with nonmetals to create organohalogens, our main focus. Iodomethane is much less polar and has the longest C-X bond length and the weakest C-X bond. The name of the halogen is followed by the name of the alkane, for example, iodomethane and chloromethane. This paper reviews the anaerobic biological treatments developed for pulp and paper industry wastewater and also reviews the specific micro-organisms reported to degrade AOX compounds under anaerobic conditions, their nutritional and biochemical requirements. CFCs are also employed in the manufacture of various hard foams that are used under the siding in buildings and around dish washers and refrigerators for insulation and sound proofing. The reagent is tetrahalomethane and triphenylphosphine; the co-products are haloform and triphenylphosphine oxide.
The similar Schiemann reaction uses the tetrafluoroborate anion as the fluoride donor; copper(I) fluoride does not yield the desired product. The ClO can react with oxygen to release the Cl to react again, destroying another ozone molecule. Especially versatile methods included the addition of halogens to alkenes, hydrohalogenation of alkenes, and the conversion of alcohols to alkyl halides. Phenyl halides belong to a larger group of compounds that we shall study later, called aryl halides.
If an alkyl halide contains more than one halogen, the halogen names are noted in alphabetical order, such as 1-chloro-2-iodobutane.
It is imperative to consider these specific micro-organisms while designing an anaerobic treatment for efficient removal of AOX. In 1990, the Food and Drug Administration (FDA) approved the use of Fluosol-DA, a PFC solution licensed to Green Cross Corporation, as an oxygen carrier during the medical process of cleaning heart arteries with a balloon.
However, DDT is also poisonous to fish and birds; as a result, the Environmental Protection Agency (EPA) stopped its use in 1972. Since CFCs are excellent at dissolving oil and grease, they are a primary component of dry cleaning solutions. The reaction is necessarily to be carried out in a dry inert solvent such as CCl4 or directly in the gaseous phase. It is estimated that a chlorine can remain in the upper atmosphere for years, destroying thousands of O3 molecules, degrading our shield against harmful ultraviolet radiation.
Aryl chlorides, such as chlozolinate and quintozene, are used to stop the growth of fungus on fruits and vegetables.
The reaction of alkynes are similar, with the product being a geminal dihalide; once again, Markovnikov's rule is followed.
PFC chains are the foundation of many products used to repel water, oil, and dirt from carpets and upholstery. The chlorofluorocarbon, dichlorodifluoromethane (CCl2F2), is not poisonous and is employed as the carrier gas in asthma and allergy inhalers.
This compound is mixed with ethylene oxide, and the resulting gas is used to sterilize medical equipment and materials that are sent into outer space. In 1971, scientists determined that CFCs were accumulating in the atmosphere; they later showed that this "build up" was destroying the ozone layer, a level of the stratosphere that absorbs much of the harmful ultraviolet rays from the Sun.
The Antarctic ozone hole was discovered in 1985, prompting the international community to sign the Montreal Protocol. The agreement between 24 nations limited the production of CFCs with the intention of ceasing production by the year 2000.

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