Halogenation is a chemical unit process, which is the process of introducing halogen atoms into organic compound molecules. The most common is to introduce halogen atoms into hydrocarbon molecules to form "halohydrocarbon". Because halohydrocarbon is quite active, it is easy to be replaced by other atoms or "radicals", so it is often used in the process of organic synthesis and manufacturing intermediates.Halogenation can also refer to the process of introducing halogen atoms into inorganic compounds (such as metals).
The route and chemical dosage of halogenation and the characteristics of its chemical structure, functional groups of organic compounds or halogenatedHalogen group elementIt all matters.Halogen is the general name of five elements: fluorine, chlorine, bromine, iodine and astatine. Therefore, halogenation is also divided into fluorination, chlorination, bromination and iodization.Iodine is much more expensive than chlorine and bromine, so chlorination and bromination are the most commonly used methods in chemical production.The commonly used chlorinating agent is chlorine or hydrogen chloride.Because fluorine is too oxidizing, it usually directly oxidizes and decomposes the reactants, so the corresponding fluorinating agent is generally used for fluorination.
Examples of halogenation are acetylene chlorinated by hydrogen chloride, which can generate vinyl chloride and become plasticspolyvinyl chlorideRaw materials;Benzene is chlorinated to produce hexachlorobenzene, etc.
Halogenation of organic compounds has many reaction paths, including free radical halogenation, keto halogenation, electrophilic halogenation and haloaddition reaction.
Free radical
A typical saturated hydrocarbon is halogenated through free radicals without halogens, instead of replacing the hydrogen atom with halogens.Halogenation is often determined by the relatively weak C-H bond in regional chemistry.This reaction tends to be in the position of the second and third carbon, because the more stable the structural music will lead to the reaction of free radicals and transition energy levels.Free radical halogenation is used in the industrial manufacture of methane chlorides.
The addition halogenation of alkenes will produce intermediate halogen ions.In particular, this intermediate can be separated.
Aromatic compound
Aromatic compoundThe halogenation of is an electrophilic halogenation reaction.
RCsixHfive+ Xtwo→ HX + RCsixHfourX
This halogenation mechanism is subject toHalogen group elementFluorine and chlorine are relatively electrophilic and are relatively strong halogens. Bromine is relatively weak halogens compared with fluorine and chlorine, but iodine is the weakest among them.The mechanism of dehydrogenation and halogenation follows a reverse trend: iodine is the most easily removed from organic matter and organic fluoride has the highest stability.
Other methods
Hunsdiecker reaction is a short refining halide proposed from carboxylic acid. The first one will produce silver salt, which will be oxidized with halogen elements later.
RCOtwoAg + Brtwo→ RBr + COtwo+ AgBr
Sandmeyer reaction is obtained from aromatic halide diazonium salt, which is obtained from aniline.
Hello – Volhard – Zelinsky halogenation refers to the halogenation of carbon on α in acid condensation.[2-3]
Yihalogens
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fluorination
Fluorine reacts with saturated or unsaturated organic compounds, which is fast and explosive.This reaction needs to be carried out in a professional environment.In practical applications, organic compounds are often electrochemically halogenated.Recently, it has been found that hydrogen fluoride can be used as the source of fluorine at the cathode. This method is called electrochemical fluorination (ECF).In addition to electrochemical generation of fluorine, there are various applications of fluorinated reagents such asXenon difluorideAnd cobalt fluoride.
chlorination
Chlorination produces an exothermic reaction.All saturation orUnsaturated compoundIt will react directly with chlorine.This composition often requires UV light to help split chlorine atoms.Chlorination is often used in industry to make 1,2-Dichloroethane(PVC) and ethane as solvent.The other is oxychlorination with hydrogen chloride and oxygen, which must be directly chlorinated (with Cltwo）Good job.
Oxychlorination
Oxychlorination is a mixture of hydrogen chloride (HCl) and oxygen (Otwo）Chlorination of hydrocarbons is very popular in industry because hydrogen chloride is cheaper than chlorine.The most common reactant is alkene.
CHtwo=CHtwo+ 2 HCl + ½ Otwo→ ClCHtwoCHtwoCl + HtwoO
At the beginning of this reaction, copper chloride (CuCltwo, a kind of1,2-Catalyst produced by dichloroethane), sometimes CuCltwoWill besilicon dioxideAsCocatalystHelp to generate KCl, LaClthree, or AlClthree。In addition to silica, bauxite, diatomite or pumice can also be used as an auxiliary reaction.Because these reactions will release high energy (238kJ/mol), the catalytic temperature must be controlled to avoid warm solution.Catalysis plays an important role in the double bond chlorination of hydrocarbons because CuCltwoIt is one of the compounds that provide double bonds of chlorine atoms.
CHtwo=CHtwo+ 2 CuCltwo→ 2 CuCl + ClHtwoC-CHtwoCl
Copper chloride will be successivelyCuprous chlorideIt reacts with oxygen and then reacts with hydrogen chloride.
ClCHtwoCHtwoCl → CHtwo=CHCl + HCl
2 HCl + CHtwo=CHtwo+ ½ Otwo→ ClCHtwoCHtwoCl + HtwoO
HCl is subjected to oxychlorination by the above steps, and the reactants will produce by themselves, which is also the reason why the industry prefers oxychlorination to chlorination.
Bromination
Bromination is more selective than chlorination because less energy is released in the reaction. Generally, bromination is Br additiontwoAs for alkenes, saturated hydrocarbons andAromatic compoundTo form organic brominated compounds.The commonly used catalyst is bromine peroxidase, which combines bromine and oxygen to form an oxidant.An example of bromination is thatTrichloroethyleneThe anesthetic halothane was prepared by organic synthesis.
Organic bromine compounds are the most common halogenated compounds in nature. Their formation is catalyzed by bromine peroxidase.It is estimated that the ocean will release 1-2 million tons of bromoform and 56000 tons of methyl bromide every year.
Iodization
Iodine is the weakest halide and is the most difficult to react with most organic compounds.Iodine and alkenes addition is an analytical method called iodine, which is used to measure the degree of unsaturated fat.The iodoform reaction coating will degradeMethyl ketone。[4]
inorganic chemistry
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Elements other than argon, neon and helium will directly react with fluorine to form fluoride.Chlorine has strong selectivity, but it can still react with most metal elements and heavier non-metallic elements.According to the trend, the activity of bromine is weak, while that of iodine is the weakest.Possible reactions like chlorination of gold produce gold chloride.Direct chlorination of metals is less important in industry because it is easiermetallic oxideAnd hydrogen halide to carry out halogenation.imagePhosphorus trichlorideandSulfur monochlorideIt is an example of large-scale direct halogenation of inorganic compounds.[5]
