Halogenated Derivatives - Organic Chemistry Tutor

The simple function combinations are equivalent with the substances containing one characteristic group of an organic function. The simplest formula of this combination is R-X, in which R is the rest of hydrocarbon (the radical) and X is the functional group. When several identical functional groups are found in the molecule, the respective combination has a multiple function (it is poly functional).

Structure and nomenclature

The organic halogenated combinations can be taken as deriving from a hydrocarbon by the substitution of one or more hydrogen atoms with halogen atoms. The number of halogenated derivates is known to be very big. The most used are, in decreasing order, the chloride derivates, the bromides and the iodides. The fluoride derivates also have a technical importance, especially in the refrigerating industry and some organic polymers.

The denomination of the halogenated derivates is formed from the name of the hydrocarbon (deriving from) preceded with a prefix indicating the number and the nature of the halogen atoms. For example, the chloride derivates of methane are called: CH₃Cl mono chloromethane, CH₂Cl₂ dichloromethane, CHCl₃ trichloromethane and CCl₄ tetra chloromethane. Also, in the case of molecules with more than one carbon atoms you must indicate, at the same time, the carbon atoms which the halogens are connected to. Hence, for example, if at the dichloroethane the two chlorine atoms are bound to a carbon atom CHCl₂-CH₃, the chloride derivate is called 1,1-dichloroethane; if the two chlorine atoms are connected to two carbon atoms CH₂Cl-CH₂Cl, the chloride derivate is called 1,2-dichloroethane.

According to the above demonstration, the denomination of the halogenated derivates is:
CCl₃-Cl₃ Hexachloroethane
CH₂Cl-CH₂-CH₂Cl 1,3-dichloropropane
CH₂Cl-CHCH₃-CH₃ 1-chlorine-2-methylpropane

Because of the formal look alike between the halogenated derivates of the hydrocarbons and the inorganic salts of the halogenated hydracids (the metal is being replaced by an organic radical), an older nomenclature, only sometimes used, expresses the halogenated combinations as the organic radicals halogen. For example, the mono chloromethane CH₃Cl is also named methyl chloride; the chloroethane C₂H₅Cl is also called ethyl chloride and the chloropropane C₃H₇Cl is also named propyl chloride.

The number of the halogenated derivates isomers is very big, taking into account the rich number of possibilities of substituting the hydrogen atoms, as well as the position the halogen occupies in the molecule. From methane and ethane (in which all the hydrogen atoms in the molecule are identical), you obtain only one mono halogenated derivate. On the other hand, at propane, there are two mono halogenated derivates:

CH₂Cl-CH₂-CH₃ (1-chloropropane or n-propyl chloride)
CH₃-CHCl-CH₃ (2-chloropropane or isopropyl chloride)

Obtaining methods

1. From alkanes

alkane + X₂

R-X + HX

Examples:
CH₄ + Cl₂

CH₃-Cl + HCl
CH₃-CH₂-CH₃ + Cl₂

CH₃-CH₂-CH₂-Cl + HCl

2. From alkenes

a) X₂ addition
R-CH=CH₂ + X₂

R-CHX-CH₂X (dihalogenated derivate)

b) HX addition
R-CH=CH₂ + HX

R-CHX-CH₃ (Markovnicov’s rule applies)

c) HBr reaction (on peroxides)
R-CH=CH₂ + HBr

R-CH₂-CH₂Br

d) X2 reaction (substitution in the allelic position - at 500 degrees)
CH₃-CH=CH₂ + Cl₂

CH₃-CCl=CH₂

3. From alkynes

a) X₂ reaction (addition) X=Cl,Br,I
R-C

C-R' + X₂

R-CX=CX-R' + X₂

R-CX₂-CX2-R' (tetra halogenated derivate)

b) HX reaction (addition) HX=HCl,HBr,HI / catalyser HgX2 la 170 grade
R-C

CH + HX

R-CX=CH₂ + HX

R-CX₂-CH₃ (dihalogenated derivate)

4. From arenes

a) With X₂ (substitution at the nucleus) X=Cl₂, Br₂
Ar-H + X₂

Ar-X + HX

b) With X₂ (substitution at the lateral chain) X=Cl₂, Br₂
Ar-CH₃ + Cl₂

Ar-CH₂-Cl + HCl
Ar-CH₃ + 3Cl₂

Ar-CCl₃ + 3HCl

5. From hydrocarbon derivates

a) From halogenated derivates (X=Br,I; X'=F,Cl)
R-X + NaX'

R-X' + NaX

b) From alcohol (HX=HCl,HBr,HI)
R-OH + HX

H₂0 + R-X

Chemical reactions

1. Hydrolyze reaction: H₂O in a basic environment

R-X + H₂O

R-OH + HX

2. The reaction with KCN or NaCN

R-X + KCN

KX + R-C

3. The reaction with NH3 and amines

R-X + NH₃

[R-NH₃]X + NH₃

R-NH₂ + NH₄X

4. The reaction with aromatic hydrocarbons

R-X + Ar-H

Ar-R + HX

5. The reaction with Hg

R-X + Mg

R-MgX

Use

» the halogenated derivates are used for obtaining synthetic rubber, plastic masses and herbicides
» the methyl chloride (CH3-CH3-Cl) is a refrigerant agent, and the carbon tetra chloride (CCl4) is a uninflammable liquid used for extinguishing fires
» the ethyl chloride (CH3-CH2-Cl) is a refrigerant agent; it is also used for obtaining tetra ethyl lead (gasoline aditive)
» chloroform (CHCl3) is a good solvent of lard and pitch; iodine is used in the rubber and oil industry; also used as a medicine
» the vinyl chloride (CH2=CH-Cl) is a monomer from which you obtain plastic masses (electro isolant, synthetic leather and synthetic fiber)
» mono chlorobenzene (C6H6Cl) is used to preparing the DDT insecticide

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