Halohydrocarbon

A compound in which the hydrogen atom in a hydrocarbon molecule is replaced by a halogen atom

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The hydrogen atom in the hydrocarbon molecule is halogen Atomic substituted chemical compound It is called haloalkane, or halohydrocarbon for short. Halogenated General formula Is: (Ar) R-X, X is a halogen atom, which can be regarded as the functional group of halohydrocarbon, including fluorine, chlorine, bromine and iodine.^[1]

Chinese name: Halohydrocarbon
Foreign name: Haloalkane

Alias: Halohydrocarbon
General formula: (Ar)R-X

catalog

one name
two nature
three synthesis
four reaction

▪ Emergency treatment
eight Inspection method

name

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According to the difference of substituted halogens, they are called fluorohydrocarbon, chlorohydrocarbon, bromocarbon and iodocarbon respectively; It can also be based on the halogen in the molecule atom Is divided into monohalogenated hydrocarbon, dihalogenated hydrocarbon and Polyhalogenated hydrocarbon ； It can also be based on Alkyl group It can be divided into saturated halogenated hydrocarbon, unsaturated halogenated hydrocarbon and aromatic halogenated hydrocarbon. In addition, it can also be directly connected to halogen atoms according to carbon atom Is divided into primary halohydrocarbon RCH two X、 Secondary halohydrocarbon R two CHX and tertiary halohydrocarbon R three CX。^[2]

nature

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physical property

Halohydrocarbon

Basically different from hydrocarbon, CH three F、CH three CH two F、CH three Cl、CH three Br is a gas at room temperature, the others are liquid at lower level and solid at higher level. Their boiling point With the increase of the number of carbon atoms and halogen atoms in the molecule (except fluorohydrocarbon) and halogen Atomic number Increase with the increase of. density It decreases with the increase of the number of carbon atoms. The density of monofluorohydrocarbons and monochlorohydrocarbons is generally smaller than that of water, while the density of bromocarbons, iodocarbons and polyhalogenated hydrocarbons is larger than that of water. Most halogenated hydrocarbons are insoluble in or in water solubility Very small, but can dissolve in many Organic solvent Some can be directly used as solvents. Most halogenated hydrocarbons have a special smell. Polyhalogenated hydrocarbons are generally difficult or incombustible.

Halogenated Isomer The boiling point of Alkyl group The increase of the middle branch chain decreases. The boiling points of different halogenated hydrocarbons of the same hydrocarbon group vary with halogen Atomic Relative atomic mass Increase with the increase of.

chemical property

Halogenated hydrocarbons are a kind of important organic synthesis intermediates and raw materials for many organic synthesis. They can undergo many chemical reactions, such as Substitution reaction 、 Extinction reaction Etc. Halogens in haloalkanes are easily exposed to - OH, - OR, - CN, NH three Or H two NR substitution, generating corresponding alcohol 、 ether 、 nitrile 、 amine Etc.

The general reaction formula can be written as: R-X+: Nu ®-Nu+:X

Iodine alkanes are most likely to undergo substitution reactions, followed by bromine alkanes and chloroalkanes, Aryl group And vinyl halides due to carbon halogen Key connection It is firm and difficult to have similar reaction. Halogenated hydrocarbon can occur Extinction reaction , removed under the action of alkali Halogenation Hydrogen to carbon carbon double bond Or carbon carbon Triple bond , for example, Bromoethane And strong base Potassium hydroxide stay ethanol Under the condition of co heating ethylene 、 Potassium bromide And water. When the elimination reaction of halohydrocarbon occurs, follow saytzeff rule 。 In addition to the dehydrohalogenation reaction, the o-dihalogenated compounds zinc powder (or Nickel powder ）Dehalogenation reaction can also occur under the action of olefin 。

Aliphatic halogenated hydrocarbons can be used in alkaline aqueous solutions hydrolysis To generate alcohols, the elimination reaction takes place in alkaline alcohol solution to generate alkenes, while aromatic halogenated hydrocarbons are more difficult.

synthesis

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Simple halogenated hydrocarbons, such as chlorine methane 、 dichloromethane Etc., most of which are caused by alkane It is prepared by direct substitution reaction. The halogenated hydrocarbon with complex structure is mainly composed of alcohol or Unsaturated hydrocarbon Made.

For a halogenated hydrocarbon, alcohol and hydrocarbon are usually used to produce:

(1) Preparation from alcohol: it is a classic method commonly used. Common reagents include hydrohalide acid, phosphorus halide and Sulfoxide chloride （SOCl two , or Thionyl chloride ）。

A. Interaction between alcohol and halogen acid:

ROH+HX®RX+H two O

This is a reversible reaction. In order to make the reaction complete, try to constantly remove water from the reaction to improve the yield. For example, when preparing chlorinated hydrocarbons, dry them Hydrogen chloride The gas is passed into the alcohol in the presence of anhydrous zinc chloride; When preparing brominated hydrocarbon Sodium bromide And concentrated sulfuric acid Of mixture Co heating with alcohol; When preparing iodinated hydrocarbon, alcohol is mixed with Hydroiodic acid Return together. It is worth mentioning that this is not a good way to synthesize halohydrocarbon. This is mainly because some alcohols will rearrange in the reaction process and generate mixed products.

B. Alcohol reacts with phosphorus halide. Chlorinated hydrocarbon, brominated hydrocarbon and iodinated hydrocarbon can be prepared by the reaction of alcohol and phosphorus halide. Commonly used for preparing brominated hydrocarbon or iodinated hydrocarbon Phosphorus tribromide Or three Phosphorus iodide 。 For example:

3C two H five OH+PBr three ® 3C two H five Br+P(OH) three

3C four H nine OH+PI three ® 3C four H nine I+P(OH) three

The phosphorus trihalide used is reacted by adding red phosphorus and bromine or iodine directly into alcohol.

Generally, chlorinated hydrocarbon is not prepared by Phosphorus trichloride , often generated by Phosphite And the yield can only reach about 50%:

3ROH+PCl three ® P(OR) three +3HCl

Therefore, generally Phosphorus pentachloride It reacts with alcohol to produce chlorinated hydrocarbon.

ROH+PCl5®RCl+POCl three +HCl

C. Alcohols and thionyl chloride (SOCl two ）Role. This is one of the most commonly used methods for preparing chlorinated hydrocarbons.

ROH+SOCl two ®RCl+SO 2 +HCl

The by-products generated by the reaction are all gases, which are easy to remove, so the product has high purity and the yield can reach about 90%. industrial production This method is also commonly used.

(2) Preparation with hydrocarbon

A. Substitution reaction of saturated hydrocarbon: CH four + Cl two ® CH three Cl + HCl

B. Addition reaction of unsaturated hydrocarbon: CH two =CH two + HBr ® CH three CH two Br^[3]

reaction

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1. Substitution reaction

Because halogen atoms have great ability to attract electrons, the C-X bond in halohydrocarbon molecules has certain polarity. When C-X bond encounters other polar reagents, halogen atoms are replaced by other atoms or atomic groups.

(1) Substituted by hydroxyl

Halogenated hydrocarbons can react with water to form alcohols. In the reaction, the halogen atom in the halohydrocarbon molecule is replaced by the hydroxyl group in the water molecule:

R—X+HOH®R—OH+HX

The reaction is relatively slow and reversible. If the strong alkali aqueous solution is used for hydrolysis, the reaction can proceed to the right, because the hydrogen halide generated in the reaction is neutralized by the alkali, which is conducive to the reaction towards hydrolysis.

R—X+NaOH®R—OH+NaX

Halogenated aromatics linked by halogen and benzene ring are generally difficult to hydrolyze. For example, chlorobenzene can be hydrolyzed under high temperature and pressure.

(2) Substituted by alkoxy group

Halogenated hydrocarbon reacts with sodium alkoxide, and the halogen atom is replaced by alkoxy group (RO -) to form ether, which is a method for preparing mixed ether.

RX+R′ONa®ROR′+NaX

Example: CH three Br+CH three CH two ONa®H three C—O—CH two CH three (methyl ether)+NaBr

(3) Substituted by cyano group

The halogenated hydrocarbon is co heated with the alcohol solution of sodium cyanide (or potassium cyanide), and the halogenated atom is replaced by the cyano group to form nitrile.

RX+NaCN®RCN+NaX

The generated nitrile molecule has one more carbon atom than the original halohydrocarbon molecule, which is used as a method of carbon chain growth in organic synthesis.

2. Eliminate reaction

Heating haloalkanes in alkali alcohol solution can remove a hydrogen halide molecule to form olefins.

RCH two CH two X+KOH®RCH=CH two +KX+H two O

3. Interaction with metal

Halogenated hydrocarbons can interact with a variety of metals to produce organometallic compounds, among which Grignard reagent is the most important class of organometallic compounds and one of the most important reagents in organic synthesis. It is an organic magnesium compound formed by the interaction of haloalkanes with metal magnesium in anhydrous ether, and then coupled with active halogenated hydrocarbons such as allyl and benzyl halogenated hydrocarbons to form hydrocarbons.

RX+Mg®RMgX

CH two =CHCH two Cl+RMgCl®CH two =CHCH two R+MgCl two

C six H five CH two Cl+CH two =CH—CH two MgCl®C six H five CH two CH two CH=CH two +MgCl two

Alkanes can be formed by the reaction of haloalkanes with metal sodium, and higher alkanes can be prepared by this reaction.

2RBr+2Na ®R—R+2NaBr^[4]

application

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Important halogenated hydrocarbon Freon

Many halogenated hydrocarbons can be used as fire extinguishing agents (e.g carbon tetrachloride ）Refrigerant (such as Freon ）, cleaning agents (common dry cleaning agents, machine detergent), anesthetics (such as chloroform , no longer used), pesticides (such as six six six , now prohibited), and raw materials of polymer industry (such as vinyl chloride 、 Tetrafluoroethylene ）。 In organic synthesis, halogenated hydrocarbons can be converted into other types of compounds due to their active chemical properties, such as substitution reaction, elimination reaction, etc. Therefore, the introduction of halogen atoms is often the first step to change the molecular properties and plays an important role in organic synthesis. For example:

1. Introduction into hydrocarbon molecules hydroxyl 。 E.g. made from benzene phenol 。 Use benzene first chlorine Preparation by substitution reaction in the presence of iron filings chlorobenzene , chlorobenzene in use sodium hydroxide And high temperature steam Phenol is obtained by hydrolysis reaction; Another example is the production of ethylene glycol from ethylene. First use ethylene and chlorine Addition reaction System 1, 2 - Dichloroethane Then, 1, 2-dichloroethane is hydrolyzed in sodium hydroxide solution to produce ethylene glycol.

2. Introduce halogen atoms onto specific carbon atoms. For example, 1 - bromine butane Prepare 1,2-dibromobutane. First cause 1 - Bromobutane The elimination reaction produces 1-butene, and then the addition of 1-butene and bromine produces 1,2-dibromobutane.

3. Change some functional group Location of. For example, from 1 to Butene Prepare 2-butene. First cause 1 - Butene Addition with hydrogen chloride yields 2 - Chlorobutane And then the elimination reaction of 2-chlorobutane produces 2-butene; If by

1-bromopropane to 2-bromopropane. First cause 1 - Bromopropane Preparation by elimination reaction propylene And then adding propylene and hydrogen bromide to obtain 2-bromopropane; From 1 - Propanol Prepare 2-propanol. Propylene is prepared by the elimination reaction of 1-propanol, and then 2 - Chloropropane Finally, 2-propanol is obtained by hydrolysis of 2-chloropropane.

4. And Bromoethane be similar.

(1) Hydrolysis reaction.

(2) . Eliminate the reaction.

toxicity

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Halogen is strong toxicity Halogenated hydrocarbons are generally more toxic than parent hydrocarbons. After being absorbed by the skin, halogenated hydrocarbons may invade the nerve center or act on internal organs, causing poisoning. Generally speaking, iodocarbons are the most toxic, and bromocarbons, chlorinated hydrocarbons and fluorohydrocarbons are less toxic in turn. Low grade halogenated hydrocarbon is more toxic than high grade halogenated hydrocarbon; Saturated halohydrocarbon is more toxic than unsaturated halohydrocarbon; Polyhalogenated hydrocarbons are more toxic than halogenated hydrocarbons with less halogens. The workplace where halogenated hydrocarbons are used shall be well ventilated.

poisoning

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clinical manifestation

(1) Mild poisoning: exposure to low concentration of chloroprene may cause strong irritation symptoms, including conjunctival congestion, tears, cough, chest pain, headache, dizziness, lethargy, nausea, vomiting and other symptoms.

(2) Severe poisoning: inhalation of high concentration of chloroprene may cause severe vomiting, irritability, excitement, convulsions, blood pressure drop, pulmonary edema, and shock. In serious cases, they quickly fell into a coma.

(3) Long term contact may cause hair loss, contact dermatitis, conjunctivitis, corneal peripheral necrosis, anemia and kidney damage. Laboratory examination: the obvious decrease of glutathione (GSH) in blood can be used as a reference for the diagnosis of poisoning. In addition, protein can appear in the urine, red blood cells, white blood cells and platelets in the peripheral blood can decrease, and reticulocytes increase.

Emergency treatment

1. Quickly move away from the poisoning site and clean the contaminated skin.

2. Oxygen inhalation.

3. If necessary, give respiratory stimulants. Those who have stopped breathing should immediately take mouth to mouth artificial respiration.

4. 10ml of 10% sodium thiosulfate was injected intravenously.

5. Timely prevent and treat pulmonary edema and protect liver. Pay attention to symptomatic treatment.

Inspection method

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① Mix (heat) halogenated hydrocarbon with excess NaOH solution, fully shake and stand still;

② Then add excess dilute HNO3 to the mixed solution to neutralize the excess NaOH;

③ Finally, AgNO3 solution is added to the mixed solution. If there is white precipitation, it is proved to be chlorinated hydrocarbon; If there is light yellow precipitation, it is proved to be brominated hydrocarbon; If there is yellow precipitation, it is proved to be iodinated hydrocarbon.

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