Chlorine, Bromine and Iodine

Halogenation reactions with organometallic intermediates may be represented by the following general scheme [62]  

The reaction of iodine with lithium compounds proceeds rapidly, generally below —40 °C. The reaction of most Grignard derivatives with elemental iodine can be carried out conveniently at temperatures around 0 °C. Many chemists are intimidated by the aggressive nature of chlorine gas (attack of the organic solvent considerable chance of further reaction with the chlorination product) and therefore resort to chlorine donors, such as N-chlorosuccinimide (NCS) or hexachloroethane [196] which give off their chlorine under mild conditions  

There is some chance of side reactions with these chlorination reagents, particularly when RM is strongly basic and the temperature is not kept sufficiently low the organometallic intermediate can also attack the metallated succinimide resulting from the desired reaction. While 2-thienyllithium reacted rather smoothly at about +20 °C with tetrachlorethene to 2-chlorothiophene, chlorination with hexa-chloroethane proceeded at considerably lower temperatures. Hence, it should be possible to avoid the subsequent reaction with tetrachloroethene by working at low temperatures [9]. 

Halogenations of lithiated hetero-aromatic compounds may give less satisfactory results because of subsequent reactions, e.g. in the iodination of 3-lithiothiophene [9]  

Addition of iodine to a solution of 3-lithiothiophene in THF gave the expected 3-iodothiophene in a moderate yield together with two isomeric di-iodo compounds. We presume that 3-lithiothiophene lithiates 3-iodothiophene at the 2- and 5-positions respectively further reaction with iodine gives the di-iodo compounds. These yield-reducing side reactions could be suppressed completely by conversion of 3-lithiothiophene into the less reactive Grignard compound by addition of MgBr2. 

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White and red phosphorus combine directly with chlorine, bromine and iodine, the red allotrope reacting in each case at a slightly higher temperature. The reactions are very vigorous and white phosphorus is spontaneously inflammable in chlorine at room temperature. Both chlorine and bromine first form a trihalide ... 

Only chlorine forms a -t-3 acid, HCIO2. This is also a weak acid and is unstable. The - -5 acids, HXO3, are formed by chlorine, bromine and iodine they are strong acids. They are stable compounds and all are weaker oxidising agents than the corresponding +1 acids. 

Chlorine, bromine and iodine form halic(V) acids but only iodic(V) acid, HIO3, can be isolated. Solutions of the chloric) V) and bromic) V) acids can be prepared by the addition of dilute sulphuric acid to barium chlorate(V) and bromate(V) respectively, and then filtering (cf. the preparation of hydrogen peroxide). These two acids can also be prepared by decomposing the corresponding halic(I) acids, but in this case the halide ion is also present in the solution. 

The mix of inductive and resonance effects varies from one halogen to another but the net result is that fluorine chlorine bromine and iodine are weakly deactivating ortho para directing substituents... 

The most important of the halogenated derivatives of acetic acid is chloroacetic acid. Fluorine, chlorine, bromine, and iodine derivatives are all known, as are mixed halogenated acids. For a discussion of the fluorine derivatives see Fluorine compounds, organic. 

KrF+ AsF/, KrF+ SbF/, and KrF+ Sb2F, are moderately stable at room temperature. The KrF+ cation ranks as the most powerful chemical oxidizer known (120) and is capable of oxidizing gaseous xenon to XeF/, gaseous oxygen to O2, NF to NF, and chlorine, bromine, and iodine pentafluorides to... 

Tin does not react directly with nitrogen, hydrogen, carbon dioxide, or gaseous ammonia. Sulfur dioxide, when moist, attacks tin. Chlorine, bromine, and iodine readily react with tin with fluorine, the action is slow at room temperature. The halogen acids attack tin, particularly when hot and concentrated. Hot sulfuric acid dissolves tin, especially in the presence of oxidizers. Although cold nitric acid attacks tin only slowly, hot concentrated nitric acid converts it to an insoluble hydrated stannic oxide. Sulfurous, chlorosulfuric, and pyrosulfiiric acids react rapidly with tin. Phosphoric acid dissolves tin less readily than the other mineral acids. Organic acids such as lactic, citric, tartaric, and oxaUc attack tin slowly in the presence of air or oxidizing substances. 

Addition to the Double Bond. Chlorine, bromine, and iodine react with aHyl chloride at temperatures below the inception of the substitution reaction to produce the 1,2,3-trihaLides. High temperature halogenation by a free-radical mechanism leads to unsaturated dihalides CH2=CHCHC1X. Hypochlorous and hypobromous acids add to form glycerol dihalohydrins, principally the 2,3-dihalo isomer. Dehydrohalogenation with alkah to epicbl orobydrin [106-89-8] is ofgreat industrial importance. 

Synthetic procedures are available for the preparation of fluoro, chloro, bromo and iodo compounds from the corresponding lithio derivatives. Perchloryl fluoride (FCIO3), N-chlorosuccinimide, bromine and iodine are examples of reagents which can be used to introduce fluorine, chlorine, bromine and iodine, respectively. 

Halogenation is one of the most studied electrophilic substitutions in the pyrazole series (67HC(22)1, B-76MI40402). The results concern chlorination, bromination and iodination since there is no report on direct fiuorination of pyrazoles (fiuoropyrazoles are prepared by other... 

As in the acid-catalyzed halogenation of aldehydes and ketones, the reaction rate is independent of the concentration of the halogen chlorination, bromination, and iodination all occur at the same rate. Fomnation of the enolate is rate-detemnining, and, once fomned, the enolate ion reacts rapidly with the halogen. 

Gases Molybdenum has a fair resistance to chlorine, bromine and iodine but not to fluorine and it has excellent resistance to a wide range of other gases (see Table 5.7). 

Halogens Although tantalum is severely attacked by flourine at room temperature it does not react with liquid chlorine, bromine and iodine up to 150°C and the metal suffers no appreciable attack in wet or dry bromine, chlorine and iodine below 250°C. It is virtually uncorroded by hydrogen bromide and hydrogen chloride below 370°C, attack starting at about 375 and 410°C respectively. 

But as argued in a recent book, once one accepts that the more correct ordering principle for the elements is atomic number the concept of triads makes a significant return, at least in about half of all conceivable triads in the modern table (6). Using the atomic numbers of chlorine, bromine, and iodine for example the middle element is not just the approximate mean of the atomic numbers of the flanking elements but the exact mean. 

Describe the preparation of elemental fluorine, chlorine, bromine, and iodine. 

Compare the reaction enthalpies for the halogenation of ethene by chlorine, bromine, and iodine. What trend, if any, exists in these numbers Use bond enthalpies to estimate the enthalpies of reaction. 

The halogens include fluorine, chlorine, bromine and iodine and all have been used in CVD reactions. They are reactive elements and exist as diatomic molecules, i.e., F2, CI2, etc. Their relevant properties are listed in Table 3.2. 

Wang, C. Y., Bunday, S. D., and Tartar, J. G., Ion Chromatographic Determination of Fluorine, Chlorine, Bromine, and Iodine with Sequential Electrochemical and Conductometric Detection, Ana/. Chem. 55, 1983, 1617-1619. 

C02-0002. Elemental bromine, chlorine, and iodine exist as diatomic molecules. Chlorine is a gas at room temperature, bromine is a liquid, and iodine is a solid. Draw molecular pictures that show the molecular distributions in samples of chlorine, bromine, and iodine. 

Chlorine, bromine, and iodine each form four different oxoanions that are distinguished by prefixes and suffixes. The nomenclature of these ions is illustrated for bromine, but it applies to chlorine and iodine as well BrO, hypohromite Br02, bromzte Br03, bromate and Br04, perbromate. 

Chlorinated, Brominated, and Iodinated Alkanes, Alkenes, and Alkanoates... 

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