Iodine and chlorine

Iodine does not replace hydrogen from saturated hydrocarbons directly, as do both chlorine and iodine. 

The halogen fluorides are binary compounds of bromine, chlorine, and iodine with fluorine. Of the eight known compounds, only bromine trifluoride, chlorine trifluoride, and iodine pentafluoride have been of commercial importance. Properties and appHcations have been reviewed (1 7) as have the reactions with organic compounds (8). Reviews covering the methods of preparation, properties, and analytical chemistry of the halogen fluorides are also available (9). 

In the photolysis of difiuorodiazirine (218) a singlet carbene was also observed (65JA758). Reactions of the difiuorocarbene were especially studied with partners which are too reactive to be used in the presence of conventional carbene precursors, such as molecular chlorine and iodine, dinitrogen tetroxide, nitryl chloride, carboxylic acids and sulfonic acids. Thus chlorine, trifiuoroacetic acid and trifiuoromethanesulfonic acid reacted with difiuorodiazirine under the conditions of its photolysis to form compounds (237)-(239) (64JHC233). 

Direct bromination readily yields the 6-bromo derivative (111), just as with uracil. Analogous chlorination and iodination requires the presence of alkalies and even then proceeds in low yield. The 6-chloro derivative (113) was also obtained by partial hydrolysis of the postulated 3,5,6-trichloro-l,2,4-triazine (e.g.. Section II,B,6). The 6-bromo derivative (5-bromo-6-azauracil) served as the starting substance for several other derivatives. It was converted to the amino derivative (114) by ammonium acetate which, by means of sodium nitrite in hydrochloric acid, yielded a mixture of 6-chloro and 6-hydroxy derivatives. A modified Schiemann reaction was not suitable for preparing the 6-fluoro derivative. The 6-hydroxy derivative (115) (an isomer of cyanuric acid and the most acidic substance of this group, pKa — 2.95) was more conveniently prepared by alkaline hydrolysis of the 6-amino derivative. Further the bromo derivative was reacted with ethanolamine to prepare the 6-(2-hydroxyethyl) derivative however, this could not be converted to the corresponding 2-chloroethyl derivative. Similarly, the dimethylamino, morpholino, and hydrazino derivatives were prepared from the 6-bromo com-pound. ... 

Most of the substitution reactions of di-, tetra, and hexa-hydro-carbolines and of their oxo derivatives are similar to those of the parent indole or indolenine derivatives. Nitration and bromination of harma-line (l-methyl-3,4-dihydro-j8-carbolme) are referred to in Section IV, A, 1. Sulfonation and azO COupling ° proceed as expected for indole derivatives. The preparation of chlorinated and iodinated derivatives of 6-nitroharmaline has been reported,but their structures have not been established. 

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. 

Chlorine and iodine can be introduced into aromatic rings by electrophilic substitution reactions, but fluorine is too reactive and only poor yields of monofluoro-aromatic products are obtained by direct fluorinafion. Aromatic rings react with CI2 in the presence of FeCl3 catalyst to yield chlorobenzenes, just as they react with Bi 2 and FeBr3. This kind of reaction is used in the synthesis of numerous pharmaceutical agents, including the antianxiety agent diazepam, marketed as Valium. 

Some results are already described in the literature with nickel- or copper catalysts (refs. 3,71-78). It was us possible to develop this exchange and to show that it is under thermodynamic control the equilibrium lies about 60 to 40 % for bromine and iodine, and is much more shifted to the left (95 to 5 %) for chlorine and iodine. 

The same principle can be applied to chlorinations and iodinations (ref. 2) as well as to the benzylic bromination of toluenes and related substrates as intermediates to benzaldehydes and benzoic acids (ref. 6). 

The first step, as we have already seen (12-3), actually consists of two steps. The second step is very similar to the first step in electrophilic addition to double bonds (p. 970). There is a great deal of evidence for this mechanism (1) the rate is first order in substrate (2) bromine does not appear in the rate expression at all, ° a fact consistent with a rate-determining first step (3) the reaction rate is the same for bromination, chlorination, and iodination under the same conditions (4) the reaction shows an isotope effect and (5) the rate of the step 2-step 3 sequence has been independently measured (by starting with the enol) and found to be very fast. With basic catalysts the mechanism may be the same as that given above (since bases also catalyze formation of the enol), or the reaction may go directly through the enolate ion without formation of the enol ... 

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. 

Similar electron accessibility generates similar chemical behavior. For example, iodine has many more electrons than chlorine, but these two elements display similar chemical behavior, as reflected by their placement in the same group of the periodic table. This is because the chemistry of chlorine and iodine is determined by the number of electrons in their largest and least stable occupied orbitals 3 S and 3 p for chlorine and 5 S and 5 p for iodine. Each of these elements has seven accessible electrons, and this accounts for the chemical similarities. 

Chlorine and iodine have been used extensively since their introduction as disinfecting agents in the early 19th century. Preparations containing these halogens such as Dakin s solution and tincture of iodine were early inclusions in many pharmacopoeiae and national formularies. More recent formulations of these elemens have improved activity, stability and ease of use. 

On another sheet of paper, write out the electron configurations for carbon, hydrogen, nitrogen, oxygen, bromine, chlorine, and iodine. 

On the basis of the number of holes and the electron configurations, identify the different colored balls as carbon, hydrogen, nitrogen, and oxygen. Label them in Data Table 1. (The colors of bromine, chlorine, and iodine have already been recorded for you.)... 

EXAMPLE 13.1. What are the oxidation numbers of chlorine and iodine in ICl, ... 

Iodination versus chlorination. Three distinct classes of halogenation reactions are observed with various substituted methoxybenzenes and IC1 when carried out under an identical set of conditions, i.e., exclusive iodination, exclusive chlorination, and mixed chlorination and iodination. For example, equimolar mixtures of anisole, 2,5-dimethyl-1,4-dimethoxybenzene and 1,4-dimethoxybenzene and iodine monochloride (kept in the dark) yield p-iodoanisole, chloro-2,5-dimethyl- 1,4-dimethoxybenzene, and a (4 6) mixture of chloro- and iododimethoxybenzene, respectively, in nearly quantitative yields,225 i.e.,... 

A careful analysis of the reaction mixtures establishes the stoichiometries for exclusive chlorination and iodination in equations (78a) and (78b). 

A comprehensive review covers stability relationships and reactions of these explosive compounds and their derivatives. Bromine, chlorine and iodine azides all explode violently in contact with magnesium, zinc or white phosphorus. 

Bromine is a very reactive nonmetallic element, located between chlorine and iodine in the periodic table. Bromine gas fumes are very irritating and toxic and will cause severe burns if spdled on the skin. 

Smith EM, Plewa MJ, Lindell CL, Richardson SD (2010) Comparison of byproduct formation in waters treated with chlorine and iodine relevance to point-of-use treatment. Environ... 

The natural glucocorticoid is hydrocortisone (cortisol). Semi-synthetic 9a-bromohydrocortisone 21-acetate was found to be less active as an anti-inflammatory agent than hydrocortisone 21-acetate by a factor of three, and 9a-iodohydrocortisone 21-acetate was also less active by a factor of 10. However, 9a-fluorohydrocortisone 21-acetate (fludrocortisone acetate) was discovered to be about 11 times more active than hydrocortisone acetate. Although the bromination sequence shown is equally applicable to chlorine and iodine compounds, fluorine must be introduced indirectly by the P-epoxide formed by base treatment of the 9a-bromo-lip-hydroxy analogue. 

When vaporized at 100°C iodine monochloride decomposes to chlorine and iodine ... 

Iodine trichloride is used in organic synthesis as a chlorinating and iodi-nating agent to introduce chlorine and iodine into organic compounds producing their halogen derivatives. It also is used as a topical antiseptic. 

Disinfection by-products (DBPs) form an undesired species in the chlorine disinfection processes of waters (performed with chlorine, chlorine dioxide, and chloramines). The high priority DBPs include brominated, chlorinated, and iodinated species of halomethanes, brominated, and chlorinated forms of haloacetonitriles, haloketones, haloacids, and halonitromethanes, as well as analogues of 3-chloro-(4-dichloromethyl)-5-hydroxy-2(5//)-furanone. All the high priority DBPs included in the Nation-wide DBP occurrence study are listed in Table 18.1 together with other contaminants. 

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