Halocarbon

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(Redirected from
Halogenated compound
)

Halocarbon compounds are

organochlorides.[1]

Many synthetic organic compounds such as

trifluoromethyl
groups.

For information on inorganic halide chemistry, see halide.

Chemical families

Examples of organohalogens-chlorides

Halocarbons are typically classified in the same ways as the similarly

molecular sites of the halogen atoms in halocarbons. Among the chemical families are:[2]

The halogen atoms in halocarbon molecules are often called "substituents," as though those atoms had been substituted for hydrogen atoms. However halocarbons are prepared in many ways that do not involve direct substitution of halogens for hydrogens.

History and context

A few halocarbons are produced in massive amounts by microorganisms. For example, several million tons of

methyl bromide
are estimated to be produced by marine organisms annually. Most of the halocarbons encountered in everyday life – solvents, medicines, plastics – are man-made. The first synthesis of halocarbons was achieved in the early 1800s. Production began accelerating when their useful properties as solvents and anesthetics were discovered. Development of plastics and synthetic elastomers has led to greatly expanded scale of production. A substantial percentage of drugs are halocarbons.

Natural halocarbons

A large amount of the naturally occurring halocarbons, such as

thyroid gland and is an iodide. The highly toxic fluoroacetate is one of the rare natural organofluorides and is produced by certain plants.[3][4][5]

Organoiodine compounds, including biological derivatives

Main article:
Organoiodine compound

Organoiodine compounds, called organic iodides, are similar in structure to organochlorine and organobromine compounds, but the C-I bond is weaker. Many organic iodides are known, but few are of major industrial importance. Iodide compounds are mainly produced as nutritional supplements.[6]

The

iodized salt
.

Six mg of iodide a day can be used to treat patients with hyperthyroidism due to its ability to inhibit the organification process in thyroid hormone synthesis, the so-called Wolff–Chaikoff effect. Prior to 1940, iodides were the predominant antithyroid agents. In large doses, iodides inhibit proteolysis of thyroglobulin, which permits TH to be synthesized and stored in colloid, but not released into the bloodstream. This mechanism is referred to as Plummer effect.

This treatment is seldom used today as a stand-alone therapy despite the rapid improvement of patients immediately following administration. The major disadvantage of iodide treatment lies in the fact that excessive stores of TH accumulate, slowing the onset of action of

thioamides
(TH synthesis blockers). In addition, the functionality of iodides fades after the initial treatment period. An "escape from block" is also a concern, as extra stored TH may spike following discontinuation of treatment.

Uses

The first halocarbon commercially used was

Murex brandaris
marine snail.

Common uses for halocarbons have been as solvents, pesticides, refrigerants, fire-resistant oils, ingredients of elastomers, adhesives and sealants, electrically insulating coatings, plasticizers, and plastics. Many halocarbons have specialized uses in industry. One halocarbon, sucralose, is a sweetener.

Before they became strictly regulated, the general public often encountered

1,1,1,2-tetrafluoroethane
).

Haloalkenes have also been used as

PTFE
).

Haloaromatics include the former

askarel dielectrics
(mixed with PCBs, no longer used in most countries), and chemical feedstocks.

A few halocarbons, including acid halides like

molds
; or they may not be affected as much by sun exposure.

Hazards

The stability of halocarbons tended to encourage beliefs that they were mostly harmless, although in the mid-1920s physicians reported workers in

hydraulic oils containing polychlorinated biphenyl (PCB)s, the U.S. Navy found that skin contact caused fatal liver disease in animals and rejected them as "too toxic for use in a submarine" (Owens v. Monsanto 2001
).

Atmospheric concentration of several halocarbons, years 1978–2015.

In 1962 a book by U.S. biologist

global warming.[7]

Since the 1970s there have been longstanding, unresolved controversies over potential health hazards of trichloroethylene (TCE) and other halocarbon solvents that had been widely used for industrial cleaning (Anderson v. Grace 1986) (Scott & Cogliano 2000) (U.S. National Academies of Science 2004) (United States 2004). More recently perfluorooctanoic acid (PFOA), a precursor in the most common manufacturing process for Teflon and also used to make coatings for fabrics and food packaging, became a health and environmental concern starting in 2006 (United States 2010), suggesting that halocarbons, though thought to be among the most inert, may also present hazards.

Halocarbons, including those that might not be hazards in themselves, can present

corrosive byproducts such as hydrochloric acid and hydrofluoric acid, and poisons like halogenated dioxins and furans. Species of Desulfitobacterium are being investigated for their potential in the bioremediation of halogenic organic compounds.[8]

See also

Notes

  1. doi:10.1002/9780470682531.pat0011
  2. doi:10.1002/14356007.a06_233.pub2
  3. doi:10.1021/ar9701777
    .
  4. doi:10.1039/a900201d
    .
  5. ISBN 3-540-42064-9
    .
  6. doi:10.1002/14356007.a14_381
  7. ^ Climate Change 2007: The Physical Science Basis. Summary for Policymakers Archived 2007-02-03 at the Wayback Machine, page 3
  8. PMID 16911041
    .

References

External links

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