Chlorine substitution reactions

Rghei HO, Eiceman GA. 1985. Effect of matrix on heterogeneous phase chlorine substitution reactions for dibenzo-p-dioxin and hydrochloric-acid in air. Chemosphere 14 167-172. 

DegussaAG Methallylchloride (MAC) Isobutylene, chlorine Substitution reaction of isobutylene and chlorine, high yield NA NA... 

The influence of solvent molecules on the stereochemical course of hot substitution reactions in the condensed phase has also been studied in some detail. Of particular interest is whether there is a significant directing effect on the course of these cagelike reactions due to structural features or electronic interactions between solvent molecules and reaction intermediates. A careful study of the chlorine substitution reaction in... 

J. F. Durana and J. D. McDonald, Infrared chemiluminescence studies of chlorine substitution reactions with brominated unsaturated hydrocarbons, J. Chem. Phys. 64 2518 (1976). 

It is a typically aromatic compound and gives addition and substitution reactions more readily than benzene. Can be reduced to a series of compounds containing 2-10 additional hydrogen atoms (e.g. tetralin, decalin), which are liquids of value as solvents. Exhaustive chlorination gives rise to wax-like compounds. It gives rise to two series of monosubstitution products depending upon... 

Addition to double bonds is not the only kind of reaction that converts an achiral molecule to a chiral one Other possibilities include substitution reactions such as the formation of 2 chlorobutane by free radical chlorination of butane Here again the prod uct IS chiral but racemic... 

Chlorine Addition. Chlorine addition and some chlorine substitution occurs at normal or slightly elevated temperatures in the absence of catalysts. The chlorination of molten naphthalene under such conditions yields a mixture of naphthalene tetrachlorides, a monochloronaphthalene tetrachloride, and a dichloronaphthalene tetrachloride, as well as mono- and dichloronaphthalenes (35). Sunlight or uv radiation initiates the addition reaction of chlorine and naphthalene resulting in the production of the di- and tetrachlorides (36). These addition products are relatively unstable and, at ca 40—50°C, they decompose to form the mono- and dichloronaphthalenes. 

Substitution reactions on dialkyl peroxides without concurrent peroxide cleavage have been reported, eg, the nitration of dicumyl peroxide (44), and the chlorination of di-/ fZ-butyl peroxide (77). Bromination by nucleophilic displacement on a-chloro- or a-hydroxyalkyl peroxides with hydrogen bromide produces a-bromoalkyl peroxides (78). 

Electrophilic substitution reactions of diarylamines are easily accompHshed since the amino group activates the aromatic ring. Thus, DPA reacts with bromine or chlorine to form the 2,2H,4 tetrahalo derivative nitration usually produces the trinitro compound. 

The aromatic nature of lignin contrasts with the aliphatic stmcture of the carbohydrates and permits the selective use of electrophilic substitution reactions, eg, chlorination, sulfonation, or nitration. A portion of the phenoUc hydroxyl units, which are estimated to comprise 30 wt % of softwood lignin, are unsubstituted. In alkaline systems the ionized hydroxyl group is highly susceptible to oxidative reactions. 

Substitution Reactions on the Methyl Group. The reactions that give substitution on the methyl group are generally high temperature and free-radical reactions. Thus, chlorination at ca 100°C, or in the presence of ultraviolet light and other free-radical initiators, successively gives benzyl chloride, benzal chloride, and benzotrichloride. 

If the production of vinyl chloride could be reduced to a single step, such as dkect chlorine substitution for hydrogen in ethylene or oxychlorination/cracking of ethylene to vinyl chloride, a major improvement over the traditional balanced process would be realized. The Hterature is filled with a variety of catalysts and processes for single-step manufacture of vinyl chloride (136—138). None has been commercialized because of the high temperatures, corrosive environments, and insufficient reaction selectivities so far encountered. Substitution of lower cost ethane or methane for ethylene in the manufacture of vinyl chloride has also been investigated. The Lummus-Transcat process (139), for instance, proposes a molten oxychlorination catalyst at 450—500°C to react ethane with chlorine to make vinyl chloride dkecfly. However, ethane conversion and selectivity to vinyl chloride are too low (30% and less than 40%, respectively) to make this process competitive. Numerous other catalysts and processes have been patented as weU, but none has been commercialized owing to problems with temperature, corrosion, and/or product selectivity (140—144). Because of the potential payback, however, this is a very active area of research. 

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. 

Treatment of coal with chlorine or bromine results in addition and substitution reactions. At temperatures up to 600°C chlorinolysis produces carbon tetrachloride, phosgene, and thionyl chloride (73). Treatment with fluorine or chlorine trifluoride at atmospheric pressure and 300°C can produce large yields of Hquid products. 

In the case of phenazine, substitution in the hetero ring is clearly not possible without complete disruption of the aromatic character of the molecule. Like pyrazine and quinoxa-line, phenazine is very resistant towards the usual electrophilic reagents employed in aromatic substitution reactions and substituted phenazines are generally prepared by a modification of one of the synthetic routes employed in their construction from monocyclic precursors. However, a limited range of substitution reactions has been reported. Thus, phenazine has been chlorinated in acid solution with molecular chlorine to yield the 1-chloro, 1,4-dichloro, 1,4,6-trichloro and 1,4,6,9-tetrachloro derivatives, whose gross structures have been proven by independent synthesis (53G327). 

In the case of substituted phenazine fV-oxides some activation of substituents towards nucleophilic substitution is observed. 1-Chlorophenazine is usually very resistant to nucleophilic displacements, but the 2-isomer is more reactive and the halogen may be displaced with a number of nucleophiles. 1-Chlorophenazine 5-oxide (56), however, is comparable in its reactivity with 2-chlorophenazine and the chlorine atom is readily displaced in nucleophilic substitution reactions. 2-Chlorophenazine 5,10-dioxide (57) and 2-chlorophenazine 5-oxide both show enhanced reactivity relative to 2-chlorophenazine itself. On the basis of these observations, similar activation of 5- or 6-haloquinoxaline fV-oxides should be observed but little information is available at the present time. 

These effects can be attributed mainly to the inductive nature of the chlorine atoms, which reduces the electron density at position 4 and increases polarization of the 3,4-double bond. The dual reactivity of the chloropteridines has been further confirmed by the preparation of new adducts and substitution products. The addition reaction competes successfully, in a preparative sense, with the substitution reaction, if the latter is slowed down by a low temperature and a non-polar solvent. Compounds (12) and (13) react with dry ammonia in benzene at 5 °C to yield the 3,4-adducts (IS), which were shown by IR spectroscopy to contain little or none of the corresponding substitution product. The adducts decompose slowly in air and almost instantaneously in water or ethanol to give the original chloropteridine and ammonia. Certain other amines behave similarly, forming adducts which can be stored for a few days at -20 °C. Treatment of (12) and (13) in acetone with hydrogen sulfide or toluene-a-thiol gives adducts of the same type. 

Chlorination generally exhibits second-order kinetics, first-order in both alkene and chlorine. The reaction rate also increases with alkyl substitution, as would be expected for an electtophilic process. The magnitude of the rate increase is quite large, as shown in Table 6.3. 

Chlorobutyl rubber is prepared by chlorination of butyl rubber (chlorine content is about 1 wt%). This is a substitution reaction produced at the allylic position, so little carbon-carbon double unsaturation is lost. Therefore, chlorobutyl rubber has enhanced reactivity of the carbon-carbon double bonds and supplies additional reactive sites for cross-linking. Furthermore, enhanced adhesion is obtained to polar substrates and it can be blended with other, more unsaturated elastomers. 

The haloform reaction of unsymmetrical perfluoroalkyl and co-hydroper-fluoroalkyl trifluororaethyl ketones gives the alkane corresponding to the longer alkyl chain [54] (equation 53) If the methyl group contains chlorine, the reaction can take different pathways, leading to loss of chlorine (equation 54), because of the variable stability of the chlorine-substituted methyl carbanions in alkali. 

It is thus apparent that the selectivity of a reagent toward thiophene and benzene can differ appreciably, and this difference in selectivity is also strongly noticeable in the proportions of 2- and 3-isomers formed. Although in certain reactions no 3-isomer has been detected, appreciable amounts have been found in other reactions. Thus 0.3% of the 3-isomer has been found in the chlorination of thiophene.- Earlier results indicated that 5-10% 3-nitrothiophene is formed in the nitration of thiophene and a recent gas-chromatographic analysis by Ostman shows that the mononitrothiophene fraction contains as much as 16% of the 3-isomer. It appears that gas-chromatographic analysis should be very useful for the detection of small amounts of 3-isomers in other substitution reactions. However, from routine analyses of IR spectra, it appears to the present author that the amount of 3-isomers formed in acylation, formylation, and bromina-tion of thiophene are certainly less than a few per cent. 

The substitution reactions of 3-acetamidothiophene have been extensively investigated. From the bromination with A-bromosuc-cinimide and from the chlorination with sulfuryl chloride or A-chloro-succinimide only the 2-isomers were obtained, the structure of which... 

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. 

Millan and coworkers (99-101) also studied the effect of tacticity on the nucleophilic substitution reactions of PVC. Sodium thiophenate and phenol were used for these reactions. The central chlorine in isotactic triads and, to a lesser extent, in heterotactic triads was found to be most reactive. It was concluded that initiation of degradation may occur by normal structures, and polyene build-up may be favored by syndiotic sequence. This... 

It may not be appropriate to compare the thermal stability characteristics of VC/VAc copolymer to that of a VC homopolymer (PVC). The copolymerization would involve different kinetics and mechanism as compared to homopolymerization resulting structurally in quite different polymers. Hence, copolymerization of VC with VAc cannot be regarded as a substitution of chlorines in PVC by acetate groups. To eliminate the possibility of these differences Naqvi [45] substituted chlorines in PVC by acetate groups, using crown ethers (18-crown-6) to solubilize potassium acetate in organic solvents, and studied the thermal stability of the modified PVC. Following is the mechanism of the substitution reaction ... 

Chlorination of benzene is an electrophilic substitution reaction in which CL serves as the electrophile. The reaction occurs in the presence of a Lewis acid catalyst such as FeCls. The products are a mixture of mono- and dichlorobenzenes. The ortho- and the para-dichlorobenzenes are more common than meta-dichlorobenzene. The ratio of the mono-chloro to dichloro products essentially depends on the benzene/chlorine ratio and the residence time. The ratio of the dichloro-isomers (0- to p- to m-dichlorobenzenes) mainly depends on the reaction temperature and residence time ... 

As an example of an industrially useful radical reaction, look at the chlorination of methane to yield chloromethane. This substitution reaction is the first step in the preparation of the solvents dichloromethane (CHoCl ) and chloroform (CHCI3). 

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. 

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