Haloalkanes and Haloarenes — Class 12 Chemistry Notes

Topics covered in Haloalkanes and Haloarenes

1. 1.Introduction of Haloalkanes and haloarenes and It's Classification

   Short Answer

   Haloalkanes and Haloarenes are organic compounds that have halogen atoms (such as Fluorine, Chlorine, Bromine, Iodine) attached to the carbon atoms of alkanes or arenes, respectively. They are classified based on the halogen type, the number of halogen atoms, and the carbon structure to which they are attached.

   Long Answer

   Haloalkanes and haloarenes are two categories of organic compounds that contain halogen atoms (fluorine, chlorine, bromine, iodine) attached to the carbon atoms of alkane or arene (aromatic) rings, respectively. These compounds are significant in various industrial applications, including as solvents, refrigerants, and in the synthesis of pharmaceuticals and agrochemicals. They are classified based on the type of carbon-halogen bond and the number of halogen atoms present in the molecule.

   Classification Based on the Number of Halogen Atoms

   1. Monohalogenated Compounds: These contain only one halogen atom in the molecule. Examples include chloromethane (CH₃Cl), bromobenzene (C₆H₅Br), etc.
   2. Dihalogenated Compounds: These have two halogen atoms. Depending on their positions, they can be vicinal (on adjacent carbons), geminal (on the same carbon), or on different parts of the molecule. Examples include 1,2-dichloroethane (ClCH₂CH₂Cl), 1,1-dichloroethane (CH₃CHCl₂), etc.
   3. Trihalogenated and Polyhalogenated Compounds: Containing three or more halogen atoms. Examples include trichloromethane (CHCl₃) and carbon tetrachloride (CCl₄) for tri and polyhalogenated compounds, respectively.

   Classification Based on the Type of Carbon-Halogen Bond

   1. Compounds Containing sp³ C—X Bond (X= F, Cl, Br, I): These compounds have their halogen atoms attached to sp³ hybridized carbon atoms. The halogen atoms can be attached to either primary, secondary, or tertiary carbon atoms. Examples include chloromethane (CH₃Cl), 2-bromopropane ((CH₃)₂CHBr), and 2-iodo-2-methylpropane ((CH₃)₃CI), respectively.

   2. Compounds Containing sp² C—X Bond: In these compounds, the halogen atom is bonded to an sp² hybridized carbon atom, typically part of an aromatic ring or an alkene. Examples include bromobenzene (C₆H₅Br), where the bromine is attached to a carbon atom in a benzene ring, and vinyl chloride (CH₂=CHCl), where the chlorine is attached to one of the sp² hybridized carbons of the ethylene (alkene) group.

   Reaction Examples

   • Substitution Reactions: Haloalkanes readily undergo nucleophilic substitution reactions where the halogen atom is replaced by another nucleophile. For example, the reaction of chloromethane with hydroxide ions (OH⁻) produces methanol (CH₃OH) and chloride ions (Cl⁻).

   • Elimination Reactions: Haloalkanes can also undergo elimination reactions to form alkenes. For example, the dehydrohalogenation of 2-bromopropane produces propene (CH₃CH=CH₂) and HBr.

   • Addition Reactions: Haloarenes, due to the nature of the aromatic ring, do not typically undergo addition reactions. Instead, they are more likely to undergo electrophilic aromatic substitution, where the halogen acts as a directing group.

   • Electrophilic Aromatic Substitution: An example is the nitration of bromobenzene, where it reacts with nitric acid in the presence of sulfuric acid to form ortho- and para-nitrobromobenzene, depending on the position of substitution on the aromatic ring.

   These classifications and examples provide a basic overview of the diversity and reactivity of haloalkanes and haloarenes, illustrating their importance in organic chemistry and industrial applications.

2. 2.Nomenclature

   Short Answer

   Haloalkanes and Haloarenes are compounds containing halogen atoms (such as fluorine, chlorine, bromine, or iodine) attached to an alkane or arene (aromatic) hydrocarbon chain, respectively. Their nomenclature involves naming the carbon chain and indicating the position and type of halogen(s) present.

   Examples:

   • Haloalkanes: 2-bromopropane (a three-carbon chain with a bromine atom on the second carbon).
   • Haloarenes: chlorobenzene (a benzene ring with a chlorine atom attached).

   Long Answer

   Nomenclature of Haloalkanes and Haloarenes

   1. Identify the Longest Carbon Chain: For haloalkanes, find the longest continuous carbon chain. For haloarenes, identify the aromatic system.

   2. Number the Chain: Start from the end nearest to the halogen atom(s) in haloalkanes. For haloarenes, numbering typically starts from the halogen and proceeds around the ring to give substituents the lowest possible numbers.

   3. Name the Halogens as Prefixes: Use the prefixes "fluoro-", "chloro-", "bromo-", or "iodo-" for fluorine, chlorine, bromine, and iodine, respectively. If multiple different halogens are attached, list them in alphabetical order.

   4. Combine with the Hydrocarbon Name: For haloalkanes, append the alkane name of the carbon chain. For haloarenes, use the name of the aromatic compound.

   5. Multiple Halogens: If more than one of the same halogen is attached, use prefixes like "di-", "tri-", "tetra-" before the halogen name, and indicate their positions.

   Reaction Examples:

   • Substitution Reaction (for Haloalkanes): −2−+→−2−+R−CH2​−X+KOH→R−CH2​−OH+KX This shows a haloalkane (where R is an alkyl group and X is a halogen) reacting with potassium hydroxide (KOH) to form an alcohol and potassium halide.

   • Electrophilic Aromatic Substitution (for Haloarenes): 66+2→65+C6​H6​+Br2​→C6​H5​Br+HBr Here, benzene reacts with bromine in the presence of a catalyst (like FeBr_3) to form bromobenzene and hydrogen bromide.

   Applications in Real Life and Industries

   • Pharmaceuticals: Many drugs are synthesized using haloalkanes and haloarenes as intermediates.
   • Agricultural Chemicals: Pesticides and herbicides often contain these compounds.
   • Manufacturing of Plastics and Resins: Haloalkanes serve as solvents and reactants in the production of various polymers.

3. 3.Common and IUPAC Names of some Halides

   Below is a chart listing some common halides along with their common names, IUPAC names, and structural formulae. This should help you understand the difference between common and systematic naming conventions, and how the structure of these compounds is represented.

   Common Name	IUPAC Name	Structural Formula
   Methyl chloride	Chloromethane	CH₃Cl
   Ethyl chloride	Chloroethane	CH₃CH₂Cl
   Methylene chloride	Dichloromethane	CH₂Cl₂
   Chloroform	Trichloromethane	CHCl₃
   Carbon tetrachloride	Tetrachloromethane	CCl₄
   Freon-12	Dichlorodifluoromethane	CCl₂F₂
   Vinyl chloride	Chloroethene	CH₂=CHCl
   Allyl chloride	3-Chloropropene	CH₂=CHCH₂Cl
   Bromobenzene	Bromobenzene	C₆H₅Br
   Iodoform	Triiodomethane	CHI₃

   This table showcases a range of halides, from simple alkyl halides to more complex ones like halogenated aromatics and halogenated methanes. The IUPAC naming system provides a systematic way to name chemical compounds based on their structure, ensuring clarity and consistency in chemical nomenclature.

4. 4.Nature of C-X Bond

   Short Answer

   The C-X bond in haloalkanes and haloarenes is polar due to the difference in electronegativity between carbon and the halogen atoms. This polarity makes haloalkanes and haloarenes reactive, especially in nucleophilic substitution and elimination reactions.

   Long Answer

   Nature of C-X Bond:

   1. Electronegativity and Polarity: Carbon is less electronegative than halogens, resulting in the electron density of the C-X bond being pulled towards the halogen. This makes the bond polar, with a δ+ charge on carbon and a δ- charge on the halogen.

   2. Bond Length and Strength: The bond length of the C-X bond increases from C-F to C-I due to the increasing size of the halogen atoms. Consequently, the bond strength decreases in the same order, making Iodine (I) compounds the most reactive towards nucleophilic substitution.

   Reaction Examples:

   1. Nucleophilic Substitution (SN2 reaction):

      • Example: Bromoethane (CH₃CH₂Br) reacting with hydroxide ions (OH⁻).
      • Reaction: CH₃CH₂Br + OH⁻ → CH₃CH₂OH + Br⁻
      • Structural Representation:
        • Before the reaction, bromoethane has a polar C-Br bond, with carbon having a partial positive charge.
        • Hydroxide ion, being nucleophilic, attacks the carbon, displacing the bromide ion and forming ethanol.

   2. Elimination Reaction (E2 reaction):

      • Example: 2-Bromopropane (CH₃CHBrCH₃) reacting with hydroxide ions (OH⁻) to form propene.
      • Reaction: CH₃CHBrCH₃ + OH⁻ → CH₃CH=CH₂ + H₂O + Br⁻
      • Structural Representation:
        • In 2-bromopropane, the polar C-Br bond is targeted by the base (OH⁻).
        • The base removes a hydrogen atom from the adjacent carbon, causing the electrons to form a double bond between the two carbon atoms, resulting in the formation of propene.

   Structural Representation of C-X Bond:

   • The C-X bond's polarity is represented by a delta positive (δ+) symbol near the carbon atom and a delta negative (δ-) symbol near the halogen atom in structural formulas.
   • In reactions, arrows are used to show the movement of electrons, indicating how nucleophiles attack positively charged carbon atoms or how bases remove hydrogen atoms in elimination reactions.

   Applications:

   • Synthesis in Organic Chemistry: The reactivity of the C-X bond is exploited in the synthesis of a wide range of organic compounds, including pharmaceuticals, agrochemicals, and materials.
   • Pharmaceuticals: Many drugs are synthesized using haloalkanes and haloarenes as intermediates due to the reactive nature of the C-X bond.
   • Pesticides and Herbicides: The stability and reactivity of the C-X bond in certain conditions make these compounds useful in the agricultural industry.

   The polar nature of the C-X bond, combined with the reactivity patterns observed in nucleophilic substitution and elimination reactions, underscores the importance of understanding these bonds in organic chemistry.

5. 5.Methods of Preparation of Haloalkanes

   Short Answer:

   Haloalkanes, also known as alkyl halides, are compounds containing a halogen atom attached to an aliphatic carbon chain. They can be prepared through various methods:

   1. From Alcohols: By reacting alcohols with halogen acids, phosphorus halides, or thionyl chloride.
   2. From Hydrocarbons:
      • (I) From alkanes through free radical halogenation.
      • (II) From alkenes by adding hydrogen halides or halogens.
   3. Halogen Exchange (Halide Exchange): Substituting one halogen atom in a haloalkane with another.

   Each method involves specific reagents and conditions to achieve the desired haloalkane.

   Long Answer:

   1. From Alcohols:

   Alcohols can be converted into haloalkanes by treating them with halogen acids (like HCl, HBr, or HI), phosphorus halides (PX3 or PX5), or thionyl chloride (SOCl2). The general reaction involves the replacement of the hydroxyl group (-OH) with a halogen atom.

   Examples:

   1. Reaction with Hydrogen Halides:
      • CH3CH2OH+HCl→CH3CH2Cl+H2OCH3​CH2​OH+HCl→CH3​CH2​Cl+H2​O
   2. Reaction with Phosphorus Halides:
      • CH3CH2OH+PCl3→CH3CH2Cl+H3PO3CH3​CH2​OH+PCl3​→CH3​CH2​Cl+H3​PO3​
   3. Reaction with Thionyl Chloride:
      • CH3CH2OH+SOCl2→CH3CH2Cl+SO2+H2OCH3​CH2​OH+SOCl2​→CH3​CH2​Cl+SO2​+H2​O
   4. Reaction with HBr (in the presence of an acid catalyst):
      • CH3CH2OH+HBr→CH3CH2Br+H2OCH3​CH2​OH+HBr→CH3​CH2​Br+H2​O
   5. Reaction with HI:
      • CH3CH2OH+HI→CH3CH2I+H2OCH3​CH2​OH+HI→CH3​CH2​I+H2​O

   2. From Hydrocarbons:

   (I) From alkanes by free radical halogenation: Alkanes can react with halogens under conditions of UV light or heat to form haloalkanes through a free radical mechanism.

   (II) From alkenes: Alkenes can be converted to haloalkanes by the addition of hydrogen halides (HX) or halogens (X2).

   Examples:

   • From Alkanes:

     1. CH4+Cl2→UV lightCH3Cl+HClCH4​+Cl2​UV light​CH3​Cl+HCl
     2. C2H6+Br2→UV lightC2H5Br+HBrC2​H6​+Br2​UV light​C2​H5​Br+HBr

   • From Alkenes: 3. CH2=CH2+HCl→CH3CH2ClCH2​=CH2​+HCl→CH3​CH2​Cl

     1. CH2=CH2+Br2→CH2BrCH2BrCH2​=CH2​+Br2​→CH2​BrCH2​Br
     2. CH3CH=CH2+Cl2→CH3CHClCH2ClCH3​CH=CH2​+Cl2​→CH3​CHClCH2​Cl

   3. Halogen Exchange (Halide Exchange):

   This method involves the replacement of one halogen atom in a haloalkane with another, more reactive halogen atom. This can be achieved using a halide salt and a suitable catalyst.

   Examples:

   1. CH3CH2Cl+KBr→CH3CH2Br+KClCH3​CH2​Cl+KBr→CH3​CH2​Br+KCl
   2. CH3CH2Br+KI→CH3CH2I+KBrCH3​CH2​Br+KI→CH3​CH2​I+KBr
   3. CH3CH2I+NaCl→CH3CH2Cl+NaICH3​CH2​I+NaCl→CH3​CH2​Cl+NaI
   4. C2H5Br+NaF→C2H5F+NaBrC2​H5​Br+NaF→C2​H5​F+NaBr
   5. C2H5I+AgF→C2H5F+AgIC2​H5​I+AgF→C2​H5​F+AgI

   These methods allow for the synthesis of a wide range of haloalkanes, each useful in various chemical reactions and industrial applications, including as solvents, intermediates in organic synthesis, and in the production of pharmaceuticals and agrochemicals.

6. 6.Preparation of Haloarenes

   Short Answer:

   Haloarenes are aromatic compounds where at least one hydrogen atom in the aromatic ring is replaced by a halogen (fluorine, chlorine, bromine, or iodine). They can be prepared by:

   1. From Hydrocarbons by Electrophilic Substitution: Haloarenes are synthesized from aromatic hydrocarbons like benzene through reactions with halogen in the presence of a Lewis acid catalyst such as FeCl3 or AlCl3.
   2. From Amines by Sandmeyer’s Reaction: This method involves converting an amine into a diazonium salt, which then reacts with halide ions in the presence of copper salts (CuCl, CuBr) to form haloarenes.

   Long Answer:

   1. From Hydrocarbons by Electrophilic Substitution:

   In this method, an aromatic hydrocarbon like benzene reacts with halogens (Cl2, Br2) in the presence of a Lewis acid catalyst (FeCl3, AlCl3) to produce haloarenes. The halogen acts as an electrophile, substituting a hydrogen atom on the aromatic ring.

   Examples:

   1. Chlorobenzene Preparation:

      • C6H6+Cl2→FeCl3C6H5Cl+HClC6​H6​+Cl2​FeCl3​​C6​H5​Cl+HCl

   2. Bromobenzene Preparation:

      • C6H6+Br2→FeBr3C6H5Br+HBrC6​H6​+Br2​FeBr3​​C6​H5​Br+HBr

   The use of a Lewis acid catalyst is crucial as it enhances the electrophilic nature of the halogen, making the substitution process more efficient.

   2. From Amines by Sandmeyer’s Reaction:

   Sandmeyer’s reaction is a two-step process that converts an amine into a haloarene. First, the amine reacts with nitrous acid to form a diazonium salt. Then, this salt reacts with a halide ion in the presence of copper salts to produce the haloarene.

   Examples:

   1. Preparation of Chlorobenzene from Aniline:

      • First Step: Aniline to Diazonium Salt
        • C6H5NH2+HNO2+HCl→C6H5N2Cl+2H2OC6​H5​NH2​+HNO2​+HCl→C6​H5​N2​Cl+2H2​O
      • Second Step: Diazonium Salt to Chlorobenzene
        • C6H5N2Cl+CuCl→C6H5Cl+N2C6​H5​N2​Cl+CuCl→C6​H5​Cl+N2​

   2. Preparation of Bromobenzene from Aniline:

      • First Step: Aniline to Diazonium Salt
        • Same as above.
      • Second Step: Diazonium Salt to Bromobenzene
        • C6H5N2Cl+CuBr→C6H5Br+N2C6​H5​N2​Cl+CuBr→C6​H5​Br+N2​

   Sandmeyer’s reaction is notable for its versatility in synthesizing various haloarenes from the same aromatic amine precursor by simply changing the halide ion and copper salt.

   These methods illustrate how haloarenes, important in pharmaceuticals, agrochemicals, and materials science, can be synthesized from more basic organic compounds through specific and targeted chemical reactions.

7. 7.Physical Properties

   Short Answer:

   Haloalkanes and Haloarenes have unique physical properties due to the presence of halogen atoms. They are generally denser than water, have higher boiling points compared to their parent hydrocarbons, and are less soluble in water but soluble in organic solvents. Haloalkanes are used in refrigerants, solvents, and as intermediates in organic synthesis. Haloarenes, on the other hand, find applications in the manufacture of dyes, medications, and pesticides.

   Long Answer:

   Physical Properties:

   1. Boiling Points: Haloalkanes and haloarenes have higher boiling points than their corresponding alkanes and arenes due to the polar nature of the C-X bond, where X is a halogen. The boiling point increases with the size of the halogen atom due to increased van der Waals forces.

   2. Density: Most haloalkanes and haloarenes are denser than water. This is because the halogen atoms are significantly heavier than hydrogen atoms they replace in the hydrocarbon framework.

   3. Solubility: They are generally insoluble or less soluble in water but are soluble in organic solvents like chloroform, ether, and benzene. This is due to their non-polar or slightly polar nature which does not mix well with water, a polar solvent.

   4. Reactivity: Haloalkanes undergo nucleophilic substitution reactions, while haloarenes, being more stable due to the aromatic ring, usually undergo electrophilic substitution reactions.

   Examples and Applications:

   1. Haloalkanes:
      • Refrigerants: Chlorofluorocarbons (CFCs), although now limited due to their environmental impact, were widely used in air conditioning and refrigeration.
      • Solvents: Trichloroethane is used as a solvent in the production of a variety of chemical products.
      • Anesthetics: Halothane, a fluorinated alkane, was widely used as an inhalation anesthetic.

   Reaction Example:

   • Nucleophilic Substitution (SN2 reaction):
     • CH3CH2Br+OH−→CH3CH2OH+Br−CH3​CH2​Br+OH−→CH3​CH2​OH+Br−
   • This reaction is used in the conversion of haloalkanes to alcohols.

   1. Haloarenes:
      • Dyes and Pigments: Many dyes are synthesized using haloarenes as intermediates.
      • Pharmaceuticals: Several drugs, including some antipyretics and analgesics, are derived from haloarenes.
      • Pesticides: DDT, a chlorinated arene, was widely used as a pesticide.

   Reaction Example:

   • Electrophilic Substitution (Friedel-Crafts Acylation):
     • C6H5Cl+CH3COCl→AlCl3C6H5COCH3+HClC6​H5​Cl+CH3​COClAlCl3​​C6​H5​COCH3​+HCl
   • This reaction is used to attach acyl groups to the aromatic ring, forming ketones.

   These physical properties and reactions highlight the versatility of haloalkanes and haloarenes in both industrial applications and synthetic organic chemistry.

8. 8.Chemical Reactions of Haloalkanes

   Short Answer:

   Haloalkanes undergo various chemical reactions, showcasing their versatility in organic chemistry:

   1. Nucleophilic Substitution: A nucleophile replaces the halogen atom in the haloalkane, forming a new compound.
   2. Elimination Reactions: The removal of a halogen atom and a hydrogen atom from adjacent carbon atoms in the haloalkane, creating a double bond and forming an alkene.
   3. Reaction with Metals: Haloalkanes react with metals, such as in the Wurtz reaction, to form alkanes by coupling two alkyl halides.

   Long Answer:

   1. Nucleophilic Substitution:

   There are two main types of nucleophilic substitution reactions: SN1 and SN2.

   • SN1 (Substitution Nucleophilic Unimolecular): This reaction involves two steps. First, the haloalkane forms a carbocation intermediate. Then, a nucleophile attacks the carbocation, forming a new compound. This reaction is common with tertiary haloalkanes.

     Example:

     • R-Cl→R++Cl−→R-OHR-Cl→R++Cl−→R-OH
     • Here, an alcohol is formed when water acts as the nucleophile.

   • SN2 (Substitution Nucleophilic Bimolecular): This is a one-step process where the nucleophile attacks the haloalkane and the halogen leaves simultaneously. This reaction is stereospecific and results in inversion of configuration. It's common with primary haloalkanes.

     Example:

     • CH3CH2Br+OH−→CH3CH2OH+Br−CH3​CH2​Br+OH−→CH3​CH2​OH+Br−
     • Here, bromoethane is converted to ethanol.

   2. Elimination Reactions:

   Elimination reactions in haloalkanes can lead to the formation of alkenes. This process involves the removal of a halogen atom and a hydrogen atom from adjacent carbon atoms.

   • E2 (Bimolecular Elimination): Involves the simultaneous removal of a proton and a halogen, leading to the formation of a double bond.

     Example:

     • CH3CH2Cl+OH−→CH2=2+H2O+Cl−CH3​CH2​Cl+OH−→CH2​=CH2​+H2​O+Cl−
     • Here, ethyl chloride is converted to ethylene (ethene).

   3. Reaction with Metals:

   • Wurtz Reaction: This is a coupling reaction where two alkyl halides react in the presence of sodium metal in dry ether, leading to the formation of a new alkane with a longer carbon chain.

     Example:

     • 2R-Cl+2Na→R-R+2NaCl2R-Cl+2Na→R-R+2NaCl
     • Two molecules of an alkyl halide are coupled to form a new alkane.

   These reactions of haloalkanes are essential in organic synthesis, allowing the transformation of simple molecules into more complex ones, useful in pharmaceuticals, materials science, and as intermediates in chemical manufacturing.

9. 9.Polyhalogen Compounds

   Polyhalogen compounds contain multiple halogen atoms attached to carbon. These compounds exhibit diverse physical and chemical properties, making them useful in numerous applications, ranging from solvents and anesthetics to refrigerants and insecticides. Let's delve into more detailed explanations of some notable polyhalogen compounds:

   1. Dichloromethane (Methylene Chloride)

   • Chemical Formula: CH2Cl2
   • Physical Properties: Dichloromethane is a colorless, volatile liquid with a slightly sweet aroma, a high vapor pressure, and moderate solubility in water. It has a boiling point of about 40°C (104°F).
   • Chemical Properties: It is relatively stable but can undergo hydrolysis in the presence of water and bases to form hydrochloric acid and formaldehyde.
   • Uses: Dichloromethane serves as an efficient solvent in the pharmaceutical industry for the formulation of drugs. It is also used in the manufacturing of plastic products and as a paint stripper due to its ability to dissolve a wide range of polymers and resins.

   2. Trichloromethane (Chloroform)

   • Chemical Formula: CHCl3
   • Physical Properties: Chloroform is a dense, colorless liquid, with a sweet smell and a boiling point of 61.2°C (142.2°F). It is sparingly soluble in water but mixes well with most organic solvents.
   • Chemical Properties: Chloroform can be decomposed by light and air, producing toxic and corrosive products like phosgene, chlorine, and hydrochloric acid, hence it is stored in dark-colored bottles.
   • Uses: Beyond its historical use as an anesthetic, chloroform finds applications in the synthesis of refrigerants and as a solvent for fats, oils, rubbers, and alkaloids in the pharmaceutical industry.

   3. Triiodomethane (Iodoform)

   • Chemical Formula: CHI3
   • Physical Properties: Iodoform is a yellow crystalline solid with a distinct odor, poorly soluble in water but readily soluble in ether and ethanol. It has a melting point of about 119°C (246°F).
   • Chemical Properties: It exhibits antiseptic properties due to its slow release of iodine in contact with wound exudates.
   • Uses: While its use as an antiseptic has decreased, iodoform is used in laboratories for the iodoform test, which is a qualitative test for the presence of methyl ketones or secondary alcohols oxidizable to methyl ketones.

   4. Tetrachloromethane (Carbon Tetrachloride)

   • Chemical Formula: CCl4
   • Physical Properties: Carbon tetrachloride is a heavy, colorless liquid with a sweet, ether-like smell. It has a boiling point of 76.7°C (170.1°F) and is practically insoluble in water.
   • Chemical Properties: It is a non-flammable solvent but is highly toxic, affecting the liver and central nervous system upon inhalation or ingestion.
   • Uses: Its use has been largely phased out due to environmental and health concerns, though it was formerly used in fire extinguishers and as a solvent for greases, oils, and resins.

   5. Freons

   • General Formula: CnH2n+2-xClxFx
   • Physical Properties: Freons are colorless, odorless, nonflammable, and non-toxic in their typical usage forms. They exist as gases or liquids under room temperature depending on the specific compound.
   • Chemical Properties: Chemically stable and inert, which contributed to their widespread use. However, their stability allows them to reach the upper atmosphere, where they contribute to ozone depletion.
   • Uses: Used in refrigeration, air conditioning, and as propellants in aerosol cans. The Montreal Protocol has significantly restricted their use to protect the ozone layer.

   6. p,p’-Dichlorodiphenyltrichloroethane (DDT)

   • Chemical Formula: C14H9Cl5
   • Physical Properties: DDT is a colorless, tasteless, and almost odorless crystalline chemical compound. It has a low solubility in water but is highly soluble in fats and oils, with a melting point of 108.5°C (227.3°F).
   • Chemical Properties: It is highly persistent in the environment, bioaccumulating in animal and human tissues, leading to long-term ecological and health impacts.
   • Uses: Once widely used as an effective insecticide against malaria and typhus, the environmental persistence and potential health risks of DDT have led to bans and restrictions in many countries.

   Polyhalogen compounds play critical roles in various industries due to their unique properties. However, environmental and health concerns have led to increased regulations and a search for safer alternatives for some of these compounds.