Is chloroform polar

Fabric examples

The halogenated hydrocarbons as a group of substances in organic chemistry contain a hydrocarbon and at least one halogen atom in their basic structure. Chloromethane is a simple representative of the group.

Name of the halogenated hydrocarbons

The molecules of the halogenated hydrocarbons contain a basic structure of a hydrocarbon in which hydrogen atoms are replaced by iodine, bromine, chlorine or fluorine atoms. They are mainly due to the chlorofluorocarbons CFC known. These are among the main causes of the ozone hole. But some other halogenated hydrocarbons also have this potential.


According to the IUPAC nomenclature, the name is given by placing the halogen atoms in front of the name of the hydrocarbon skeleton. If there are several halogen atoms in a molecule, they are listed in alphabetical order. With the chlorofluorocarbons CFC the reverse order is also common because it has become so common in everyday language. In the empirical formula, the C and H atoms are listed first, then the halogen atoms.


Examples of aliphatic Halogenated hydrocarbons

Chloromethane (methyl chloride)

Chloromethane is a colorless, slightly sweet smelling, poisonous gas that has a narcotic effect. The boiling point is −23.8 ° C. Inhaling the gas can cause severe nerve damage. Liver, kidney and heart failure ultimately lead to death. It is also suspected of having a carcinogenic effect. It is required in organic chemistry as an intermediate product for the production of other organic compounds. Chloromethane must not come into contact with alkali or alkaline earth metals, as this can cause an explosion.


Dichloromethane (methylene chloride)

Dichloromethane is a colorless, non-flammable liquid that is difficult to dissolve in water and easily soluble in alcohol. The boiling point is +40 ° C. The liquid already evaporates at room temperature. The vapors irritate the eyes; higher concentrations lead to intoxication and unconsciousness. Like chloromethane, it is suspected of having a carcinogenic effect. It damages the liver, blood and the central nervous system. According to recent research, like carbon tetrachloride, it can destroy the ozone layer. Dichloromethane is used as a solvent and extractant for oils, caffeine, resins, waxes and is contained in stain cleaners. Like bromomethane or dichloroethane, it is used as a fumigant in shipping containers to control pests. If such a container is opened, if it has not been thoroughly ventilated beforehand, this can lead to severe poisoning for shipyard workers or truck drivers. Dichloromethane reacts with alkali metals or with aluminum powder in an explosion. This reaction has already led to serious accidents in laboratories several times. The other haloalkanes can also react explosively with sodium or potassium. For example, sodium must not be used to dry haloalkanes.
Trichloromethane (chloroform)

Chloroform was previously used as a pesticide and as an anesthetic. These uses are now banned because it causes liver damage and is suspected of being carcinogenic. In addition, the anesthetic was at high risk: many patients died of cardiovascular failure during the anesthesia. In the laboratory, the sweet-smelling, colorless and non-flammable liquid is used as a solvent. When exposed to light, phosgene and hydrogen chloride are formed, so it is stored in brown bottles. The commercially available chloroform is stabilized with ethanol, which reacts with the phosgene produced and renders the gas harmless.
Carbon tetrachloride (carbon tetrachloride)
The haloalkane carbon tetrachloride is a colorless, non-flammable liquid that is only slightly soluble in water, well soluble in ethanol, ether or gasoline and dissolves fatty oils or resins well. Like chloroform, it is very damaging to the liver and is one of the substances with a possible carcinogenic potential. It is also harmful to aquatic organisms and damages the ozone layer. Carbon tetrachloride is very inert and is not attacked by acids and alkalis. When exposed to light and heat, the poisonous gas phosgene is produced, especially in the presence of moisture. Therefore, its use as a fire retardant is prohibited today. Mixtures with alkali metals such as sodium and potassium or with aluminum powder can explode violently. Carbon tetrachloride must no longer be used as a solvent due to the possible dangers.
Tetrachlorethylene (PER) 

The Halogenalken PER is also a colorless, non-flammable liquid and is used today in dry cleaning for textile cleaning. It is an excellent solvent for animal and vegetable fats and oils. Nevertheless, its use is very problematic: like the other halogenated hydrocarbons, it is liver-damaging and is one of the suspected carcinogenic substances. Any residues in textiles from dry cleaning are problematic. Garments from dry cleaning should therefore be well ventilated before wearing. Ventilation must not take place in living rooms or bedrooms. However, it is better to completely dispense with chemical cleaning. One look at the label when buying is enough to decide whether the garment can be washed yourself:


If a molecule contains two different halogen atoms, these are named in the order of the alphabet. The preceding numbers indicate the position of the halogen atoms:

Bromotrifluoromethane (Halon 1301)

Halon 1301 was previously contained in Halon fire extinguishers due to its fire retardant effect. The use of halons in fire extinguishers is no longer permitted in Germany today due to their ozone-damaging effects. As Halons all flame retardant halogenated hydrocarbons are designated, for example carbon tetrachloride (Halon 104), bromomethane (Halon 1001) or bromochlorodifluoromethane (Halon 1211).
Dichlorodifluoromethane (Frigen 12)

Frigen 12 is a non-flammable gas that was previously widely used in refrigerators as a compressed gas and as a propellant in aerosols. Hydrocarbons with chlorine and fluorine atoms are called CFC or chlorofluorocarbons. These substances have proven to be the main cause of the destruction of the vital ozone layer in the stratosphere.
2-bromo-2-chloro-1,1,1-trifluoroethane (halothane) 

Today, halothane replaces the previously used chloroform as an anesthetic. It is a volatile, non-flammable liquid with a boiling point of 50 ° C. For anesthesia, the liquid is evaporated and inhaled. Repeated use can, however, lead to liver damage.
2,3,3,3-tetrafluoropropene (R-1234yf)

The Halogenalken R-1234yf is a gaseous refrigerant for refrigerators and air conditioning systems. It does not attack the ozone layer and decomposes relatively quickly in the atmosphere. Therefore, it is not considered to be harmful to the climate. However, the toxic fluorine compound trifluoroacetic acid is formed as a degradation product. When used in vehicle air conditioning systems, the refrigerant can ignite and cause fires.

Manufacturing of halogenated hydrocarbons

Halocarbons can be produced by a substitution reaction of an alkane with a halogen. For example, bromine reacts with hexane when it is heated and irradiated with UV light. Bromhexane and hydrogen bromide are formed HBr.


When bromine is dissolved in hexane, a yellow-brown solution is formed. This solution comes with
UV light irradiated. The solution gradually becomes discolored when exposed to light and when shaken.


Another production possibility is the addition reaction of a halogen to an alkene or to an alkyne. For example, if ethene is passed into bromine or bromine water, the bromine disappears without the need for UV light. This reaction proves the multiple carbon bond. The double bond in ethene is broken and two bromine atoms add to the molecule, so that the only reaction product obtained is 1,2-dibromoethane.

When ethene is introduced into bromine, this is used up.


Another way of producing the haloalkanes is the addition reaction of hydrogen bromide to an alkene in the gas phase or in a non-polar solvent:
HBr + propene 1-bromopropane

properties of halogenated hydrocarbons

Most halogenated hydrocarbons have good solvent power for organic solvents. Since the carbon-halogen bond is polar, the haloalkanes have a higher boiling point than a corresponding alkane. Since they are not flammable, they are also flame retardant. Many are highly toxic, damage the liver, or can cause cancer. Some are narcotic. CFCs and some others destroy the ozone layer.

The halogen atoms in the halogenated hydrocarbons can be used to produce other organic substances. An elimination reaction can be used, for example, to recreate ethene from 1,2-dibromoethane and zinc powder. Even though this reaction is of no technical importance because ethene can be produced much cheaper in other ways, it is often used in chemistry classes as an example of a typical elimination. Since 1,2-dibromoethane is carcinogenic, the experiment may no longer be carried out in schools:

C.2H4Br2 + Zn C.2H4 + ZnBr2
1,2-dibromoethane + zinc Ethene + zinc bromide

The halogen atoms can also be replaced by a substitution reaction. For example, if iodomethane is heated with sodium hydroxide, methanol and sodium iodide are obtained. The iodine atom is replaced by a hydroxyl group:

CH3I + Na+OH   CH3OH + Na+I.
Iodomethane + sodium hydroxide Methanol + sodium iodide

Use of halogenated hydrocarbons

Halogenated hydrocarbons are used as solvents, propellants, coolants, anesthetics and also for flame retardancy. Due to their dangerous potential, the use of most substances for experiments in schools is very limited!

Old name: dichlorodiphenyltrichloroethane
IUPAC: 1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane
Old name: Gammexan
IUPAC: γ-hexachlorocyclohexane

Insecticides such as DDT or lindane are also halogenated hydrocarbons. DDT is an aromatic halogenated hydrocarbon, while lindane is a cyclic one. The use of the two substances is now prohibited in the EU and Switzerland. DDT is a powerful insecticide for mosquitoes and other vermin. Lindane was used in wood preservatives, as an ant poison or to combat moths. It can harm babies through breast milk. Long-term ingestion of small amounts can cause chronic damage to the central nervous system.

Importance of the Grignard connections

For the production routes of organic chemistry, the halogenated hydrocarbons are important intermediate products for the production of other organic compounds. They are of great importance for organic syntheses Grignard connectionsmade from monohaloalkanes. Magnesium, for example, reacts with monochloromethane in ethereal solution to form methylmagnesium chloride:
CH3Cl + Mg CH3MgCl

Methyl magnesium chloride is a classic Grignard reagent that can "attack" and convert a large number of organic compounds. With water, for example, the reagent forms methane and magnesium bromide hydroxide in a substitution reaction:

CH3MgCl + H2O CH4 + Mg (OH) Br

The reaction with ethanal results in the secondary alcohol propan-2-ol (isopropyl alcohol). The tertiary butyl alcohol 2-methyl-2-propanol can be produced with propanone.

Create book individually: basic text halogenated hydrocarbons


> Table of Contents