Organochloride

An organochloride, organochlorine compound, chlorocarbon, chlorinated hydrocarbon, is an covalently bonded atom of chlorine as the dominant functionality, of which chloroalkane and chlorinated solvent as examples are major members. Their wide structural variety and divergent chemical properties lead to a broad range of names and applications. Many such compounds are controversial because of the effects of these compounds on the environment and on human and animal health.

Contents

  • Physical and chemical properties 1
  • Natural occurrence 2
  • Preparation 3
    • From chlorine 3.1
    • Reaction with hydrogen chloride 3.2
    • Other chlorinating agents 3.3
  • Reactions 4
  • Applications 5
    • Vinyl chloride 5.1
    • Chloromethanes 5.2
    • Pesticides 5.3
    • Insulators 5.4
  • Toxicity 6
  • See also 7
  • References 8
  • External links 9

Physical and chemical properties

alkylating agents because chloride is a leaving group.

Natural occurrence

Many organochlorine compounds have been isolated from natural sources ranging from bacteria to humans.[1][2] Chlorinated organic compounds are found in nearly every class of biomolecules including epibatidine, an alkaloid isolated from tree frogs, has potent analgesic effects and has stimulated research into new pain medication.

Preparation

From chlorine

Alkanes and aryl alkanes may be chlorinated under free radical conditions, with UV light. However, the extent of chlorination is difficult to control. Aryl chlorides may be prepared by the Friedel-Crafts halogenation, using chlorine and a Lewis acid catalyst.

The haloform reaction, using chlorine and sodium hydroxide, is also able to generate alkyl halides from methyl ketones, and related compounds. Chloroform was formerly produced thus.

Chlorine adds to the multiple bonds on alkenes and alkynes as well, giving di- or tetra-chloro compounds.

Reaction with hydrogen chloride

Alkenes react with hydrogen chloride (HCl) to give alkyl chlorides. For example, the industrial production of chloroethane proceeds by the reaction of ethylene with HCl:

H2C=CH2 + HCl → CH3CH2Cl

Secondary and tertiary alcohols react with the Lucas reagent (zinc chloride in concentrated hydrochloric acid) to give the corresponding alkyl halide; this reaction a method for classifying alcohols:

Other chlorinating agents

In the laboratory, alkyl chlorides are most easily prepared by reacting alcohols with thionyl chloride (SOCl2) or phosphorus pentachloride (PCl5), but also commonly with sulfuryl chloride (SO2Cl2) and phosphorus trichloride (PCl3):

ROH + SOCl2 → RCl + SO2 + HCl
3 ROH + PCl3 → 3 RCl + H3PO3
ROH + PCl5 → RCl + POCl3 + HCl

In the laboratory, thionyl chloride is especially convenient, because the byproducts are gaseous.

Alternatively, the Appel reaction:

Reactions

Alkyl chlorides are versatile building blocks in organic chemistry. While alkyl bromides and iodides are more reactive, alkyl chlorides tend to be less expensive and more readily available. Alkyl chlorides readily undergo attack by nucleophiles.

Heating alkyl halides with sodium hydroxide or water gives alcohols. Reaction with alkoxides or aroxides give ethers in the Williamson ether synthesis; reaction with thiols give thioethers. Alkyl chlorides readily react with amines to give substituted amines. Alkyl chlorides are substituted by softer halides such as the iodide in the Finkelstein reaction. Reaction with other pseudohalides such as azide, cyanide, and thiocyanate are possible as well. In the presence of a strong base, alkyl chlorides undergo dehydrohalogenation to give alkenes or alkynes.

Alkyl chlorides react with magnesium to give Grignard reagents, transforming an electrophilic compound into a nucleophilic compound. The Wurtz reaction reductively couples two alkyl halides to couple with sodium.

Applications

Vinyl chloride

The largest application of organochlorine chemistry is the production of vinyl chloride. The annual production in 1985 was around 13 billion kilograms, almost all of which was converted into polyvinylchloride (PVC).

Chloromethanes

Most low molecular weight chlorinated hydrocarbons such as chloroform, dichloromethane, dichloroethene, and trichloroethane are useful solvents. These solvents tend to be relatively non-polar; they are therefore immiscible with water and effective in cleaning applications such as degreasing and dry cleaning. Several billion kilograms of chlorinated methanes are produced annually, mainly by chlorination of methane:

CH4 + x Cl2 → CH4−xClx + x HCl

The most important is dichloromethane, which is mainly used as a solvent. Chloromethane is a precursor to chlorosilanes and silicones. Historically significant, but smaller in scale is chloroform, mainly a precursor to chlorodifluoromethane (CHClF2) and tetrafluoroethene which is used in the manufacture of Teflon.[7]

Pesticides

The two main groups of organochlorine insecticides are the DDT-type compounds and the chlorinated alicyclics. Their mechanism of action differs slightly: The DDT like compounds work on the peripheral nervous system. At the axon's sodium channel, they prevent gate closure after activation and membrane depolarization. Sodium ions leak through the nerve membrane and create a destabilizing negative "afterpotential" with hyperexcitability of the nerve. This leakage causes repeated discharges in the neuron either spontaneously or after a single stimulus.[8]:255

Chlorinated cyclodienes include aldrin, dieldrin, endrin, heptachlor, chlordane and endosulfan. A 2- to 8-hour exposure leads to depressed central nervous system (CNS) activity, followed by hyperexcitability, tremors, and then seizures. The mechanism of action is the insecticide binding at the GABAA site in the gamma-Aminobutyric acid (GABA) chloride ionophore complex, which inhibits chloride flow into the nerve.[8]:257

Other examples include dicofol, mirex, kepone and pentachlorophenol. These can be either hydrophilic or hydrophobic depending on their molecular structure.[9]

Insulators

Polychlorinated biphenyls (PCBs) were once commonly used electrical insulators and heat transfer agents. Their use has generally been phased out due to health concerns. PCBs were replaced by polybrominated diphenyl ethers (PBDEs), which bring similar toxicity and bioaccumulation concerns.

Toxicity

Some types of organochlorides have significant toxicity to plants or animals, including humans. Dioxins, produced when organic matter is burned in the presence of chlorine, and some insecticides, such as

Chemical bonds to carbon
Core organic chemistry Many uses in chemistry
Academic research, but no widespread use Bond unknown
CH He
CLi CBe CB CC CN CO CF Ne
CNa CMg CAl CSi CP CS CCl CAr
CK CCa CSc CTi CV CCr CMn CFe CCo CNi CCu CZn CGa CGe CAs CSe CBr CKr
CRb CSr CY CZr CNb CMo CTc CRu CRh CPd CAg CCd CIn CSn CSb CTe CI CXe
CCs CBa CHf CTa CW CRe COs CIr CPt CAu CHg CTl CPb CBi CPo CAt Rn
Fr CRa Rf Db CSg Bh Hs Mt Ds Rg Cn Uut Fl Uup Lv Uus Uuo
CLa CCe CPr CNd CPm CSm CEu CGd CTb CDy CHo CEr CTm CYb CLu
Ac CTh CPa CU CNp CPu CAm CCm CBk CCf CEs Fm Md No Lr
  • "Formation of Chlorinated Hydrocarbons in Weathering Plant Material" article at SLAC website
  • "The oxidation of chlorinated hydrocarbons" article from The Institute for Green Oxidation Chemistry at the Carnegie Mellon University website

External links

  1. ^ a b Gordon W. Gribble (1998). "Naturally Occurring Organohalogen Compounds".  
  2. ^ Gordon W. Gribble (1999). "The diversity of naturally occurring organobromine compounds".  
  3. ^ Kjeld C. Engvild (1986). "Chlorine-Containing Natural Compounds in Higher Plants".  
  4. ^ Gribble, G. W. (1994). "The Natural production of chlorinated compounds". Environmental Science and Technology 28 (7): 310A–319A.  
  5. ^ Gribble, G. W. (1996). "Naturally occurring organohalogen compounds - A comprehensive survey". Progress in the Chemistry of Organic Natural Products 68 (10): 1–423.  
  6. ^ Public Health Statement - Chloromethane, Centers for Disease Control, Agency for Toxic Substances and Disease Registry
  7. ^ M. Rossberg et al. "Chlorinated Hydrocarbons" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2
  8. ^ a b J R Coats (July 1990). "Mechanisms of toxic action and structure-activity relationships for organochlorine and synthetic pyrethroid insecticides.". EHP (National Center for Biotechnology Information) 87:: 255–262. Retrieved 26 February 2015. 
  9. ^ Robert L. Metcalf "Insect Control" in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Wienheim, 2002. doi:10.1002/14356007.a14_263
  10. ^ Connell, D.; et al. (1999). Introduction to Ecotoxicology. Blackwell Science. p. 68.  
  11. ^ Pless, Tanja; Boettger, Michael; Hedden, Peter; Graebe, Jan (1984). "Occurrence of 4-Cl-indoleacetic acid in broad beans and correlation of its levels with seed development". Plant Physiology 74 (2): 320–3.  
  12. ^ Magnus, Volker; Ozga, Jocelyn A; Reinecke, Dennis M; Pierson, Gerald L; Larue, Thomas A; Cohen, Jerry D; Brenner, Mark L (1997). "4-chloroindole-3-acetic and indole-3-acetic acids in Pisum sativum".  
  13. ^ MDL Drug Data Report (MDDR), Elsevier MDL, version 2004.2
  14. ^ Marine Mammal Medicine, 2001, Dierauf & Gulland

References

  • Organic halide

See also

Arctic areas, particularly high levels are found in marine mammals. These chemicals concentrate in mammals, and are even found in human breast milk. In some species of marine mammals, particularly those that produce milk with a high fat content, males typically have far higher levels, as females reduce their concentration by transfer to their offspring through lactation.[14]

However, the presence of chlorine in an organic compound does not ensure toxicity. Some organochlorides are considered safe enough for consumption in foods and medicines. For example, peas and broad beans contain the natural chlorinated plant hormone vancomycin, the antihistamine loratadine (Claritin), the antidepressant sertraline (Zoloft), the anti-epileptic lamotrigine (Lamictal), and the inhalation anesthetic isoflurane.[13]

[10]

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