The haloalkanes (also known as halogenoalkanes or alkyl halides ) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons , although the distinction is not often made. Haloalkanes are widely used commercially. They are used as flame retardants , fire extinguishants , refrigerants , propellants , solvents , and pharmaceuticals . Subsequent to the widespread use in commerce, many halocarbons have also been shown to be serious pollutants and toxins. For example, the chlorofluorocarbons have been shown to lead to ozone depletion . Methyl bromide is a controversial fumigant. Only haloalkanes that contain chlorine, bromine, and iodine are a threat to the ozone layer , but fluorinated volatile haloalkanes in theory may have activity as greenhouse gases . Methyl iodide , a naturally occurring substance, however, does not have ozone-depleting properties and the United States Environmental Protection Agency has designated the compound a non-ozone layer depleter. For more information, see Halomethane . Haloalkane or alkyl halides are the compounds which have the general formula "RX" where R is an alkyl or substituted alkyl group and X is a halogen (F, Cl, Br, I).
40-423: Trinitrobenzenesulfonic acid (C 6 H 3 N 3 O 9 S) is a nitroaryl oxidizing acid . Due to its extreme oxidative properties, if mixed with reducing agents including hydrides , sulfides , and nitrides , it may begin a vigorous reaction that culminates in almost immediate detonation. The aromatic nitro compounds may explode in the presence of a base such as sodium hydroxide or potassium hydroxide even in
80-567: A covalent bond between the two. Thus C–X is broken by heterolytic fission resulting in a halide ion, X . As can be seen, the OH is now attached to the alkyl group, creating an alcohol . (Hydrolysis of bromoethane, for example, yields ethanol ). Reactions with ammonia give primary amines. Chloro- and bromoalkanes are readily substituted by iodide in the Finkelstein reaction . The iodoalkanes produced easily undergo further reaction. Sodium iodide
120-405: A hydrohalic acid rarely gives a pure product, instead generating ethers . However, some exceptions are known: ionic liquids suppress the formation or promote the cleavage of ethers, hydrochloric acid converts tertiary alcohols to choloroalkanes, and primary and secondary alcohols convert similarly in the presence of a Lewis acid activator, such as zinc chloride . The latter is exploited in
160-489: A proton is abstracted from nitroalkane 1 to a carbanion 2 followed by protonation to an aci-nitro 3 and finally nucleophilic displacement of chlorine based on an experimentally observed hydrogen kinetic isotope effect of 3.3. When the same reactant is reacted with potassium hydroxide the reaction product is the 1,2-dinitro dimer. Chloramphenicol is a rare example of a naturally occurring nitro compound. At least some naturally occurring nitro groups arose by
200-420: A diatomic halogen molecule. Free radical halogenation typically produces a mixture of compounds mono- or multihalogenated at various positions. In hydrohalogenation , an alkene reacts with a dry hydrogen halide (HX) electrophile like hydrogen chloride ( HCl ) or hydrogen bromide ( HBr ) to form a mono-haloalkane. The double bond of the alkene is replaced by two new bonds, one with the halogen and one with
240-424: A free-radical mechanism. Alkenes also react with halogens (X 2 ) to form haloalkanes with two neighboring halogen atoms in a halogen addition reaction . Alkynes react similarly, forming the tetrahalo compounds. This is sometimes known as "decolorizing" the halogen, since the reagent X 2 is colored and the product is usually colorless and odorless. Alcohol can be converted to haloalkanes. Direct reaction with
280-420: A fully positive pressure self-contained breathing apparatus be used along with either foam or CO 2 extinguishers. Nitro compound In organic chemistry , nitro compounds are organic compounds that contain one or more nitro functional groups ( −NO 2 ). The nitro group is one of the most common explosophores (functional group that makes a compound explosive) used globally. The nitro group
320-513: A melting point of −183.6 °C. As they contain fewer C–H bonds, haloalkanes are less flammable than alkanes, and some are used in fire extinguishers. Haloalkanes are better solvents than the corresponding alkanes because of their increased polarity. Haloalkanes containing halogens other than fluorine are more reactive than the parent alkanes—it is this reactivity that is the basis of most controversies. Many are alkylating agents , with primary haloalkanes and those containing heavier halogens being
360-486: A nitronate hydrolyzes to a carbonyl and azanone . Grignard reagents combine with nitro compounds to give a nitrone ; but a Grignard reagent with an α hydrogen will then add again to the nitrone to give a hydroxylamine salt. The Leimgruber–Batcho , Bartoli and Baeyer–Emmerling indole syntheses begin with aromatic nitro compounds. Indigo can be synthesized in a condensation reaction from ortho -nitrobenzaldehyde and acetone in strongly basic conditions in
400-509: A reaction known as the Baeyer–Drewson indigo synthesis . Many flavin -dependent enzymes are capable of oxidizing aliphatic nitro compounds to less-toxic aldehydes and ketones. Nitroalkane oxidase and 3-nitropropionate oxidase oxidize aliphatic nitro compounds exclusively, whereas other enzymes such as glucose oxidase have other physiological substrates. Explosive decomposition of organo nitro compounds are redox reactions, wherein both
440-463: A solution of sodium nitrite . Upon heating this solution with copper(I) chloride, the diazonium group is replaced by -Cl. This is a comparatively easy method to make aryl halides as the gaseous product can be separated easily from aryl halide. When an iodide is to be made, copper chloride is not needed. Addition of potassium iodide with gentle shaking produces the haloalkane. Haloalkanes are reactive towards nucleophiles . They are polar molecules:
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#1732790498834480-848: Is chloroethane ( CH 3 CH 2 Cl ). In secondary (2°) haloalkanes, the carbon that carries the halogen atom has two C–C bonds. In tertiary (3°) haloalkanes, the carbon that carries the halogen atom has three C–C bonds. Haloalkanes can also be classified according to the type of halogen on group 17 responding to a specific halogenoalkane. Haloalkanes containing carbon bonded to fluorine , chlorine , bromine , and iodine results in organofluorine , organochlorine , organobromine and organoiodine compounds, respectively. Compounds containing more than one kind of halogen are also possible. Several classes of widely used haloalkanes are classified in this way chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). These abbreviations are particularly common in discussions of
520-481: Is achieved using a mixture of nitric acid and sulfuric acid , which produce the nitronium ion ( NO + 2 ), which is the electrophile: The nitration product produced on the largest scale, by far, is nitrobenzene . Many explosives are produced by nitration including trinitrophenol (picric acid), trinitrotoluene (TNT), and trinitroresorcinol (styphnic acid). Another but more specialized method for making aryl–NO 2 group starts from halogenated phenols,
560-617: Is also found in members of the Annonaceae , Lauraceae and Papaveraceae . Despite the occasional use in pharmaceuticals, the nitro group is associated with mutagenicity and genotoxicity and therefore is often regarded as a liability in the drug discovery process. Nitro compounds participate in several organic reactions , the most important being reduction of nitro compounds to the corresponding amines: Virtually all aromatic amines (e.g. aniline ) are derived from nitroaromatics through such catalytic hydrogenation . A variation
600-513: Is also strongly electron-withdrawing . Because of this property, C−H bonds alpha (adjacent) to the nitro group can be acidic. For similar reasons, the presence of nitro groups in aromatic compounds retards electrophilic aromatic substitution but facilitates nucleophilic aromatic substitution . Nitro groups are rarely found in nature. They are almost invariably produced by nitration reactions starting with nitric acid . Aromatic nitro compounds are typically synthesized by nitration. Nitration
640-454: Is called a nitronate , and behaves similar to an enolate . In the nitroaldol reaction , it adds directly to aldehydes , and, with enones , can serve as a Michael donor . Conversely, a nitroalkene reacts with enols as a Michael acceptor. Nitrosating a nitronate gives a nitrolic acid . Nitronates are also key intermediates in the Nef reaction : when exposed to acids or oxidants,
680-413: Is formation of a dimethylaminoarene with palladium on carbon and formaldehyde : The α-carbon of nitroalkanes is somewhat acidic. The p K a values of nitromethane and 2-nitropropane are respectively 17.2 and 16.9 in dimethyl sulfoxide (DMSO) solution, suggesting an aqueous p K a of around 11. In other words, these carbon acids can be deprotonated in aqueous solution. The conjugate base
720-417: Is recommended that all direct contact be avoided and the compound be kept under extremely strict environmentally controlled conditions. In case of spillage it is recommended that a local fire department be called in advance prior to any attempt at cleaning. In case of fire it is recommended that the material be left to burn and the surrounding area be evacuated. If fire fighting is required it is recommended that
760-454: Is the Zinke nitration . Aliphatic nitro compounds can be synthesized by various methods; notable examples include: In nucleophilic aliphatic substitution , sodium nitrite (NaNO 2 ) replaces an alkyl halide . In the so-called Ter Meer reaction (1876) named after Edmund ter Meer , the reactant is a 1,1-halonitroalkane: The reaction mechanism is proposed in which in the first slow step
800-760: Is used as a catalyst . Haloalkanes react with ionic nucleophiles (e.g. cyanide , thiocyanate , azide ); the halogen is replaced by the respective group. This is of great synthetic utility: chloroalkanes are often inexpensively available. For example, after undergoing substitution reactions, cyanoalkanes may be hydrolyzed to carboxylic acids, or reduced to primary amines using lithium aluminium hydride . Azoalkanes may be reduced to primary amines by Staudinger reduction or lithium aluminium hydride . Amines may also be prepared from alkyl halides in amine alkylation , Gabriel synthesis and Delepine reaction , by undergoing nucleophilic substitution with potassium phthalimide or hexamine respectively, followed by hydrolysis. In
840-675: Is used as a detonator for certain other explosive compounds. It is also used to induce colitis in the colon of laboratory animals in order to model inflammatory bowel disease and post-infectious irritable bowel syndrome . The primary hazard of working with 2,4,6-trinitrobenzenesulfonic acid is the risk of instantaneous explosion. 2,4,6-Trinitrobenzenesulfonic acid is an extremely sensitive compound especially when mixed with other compounds, exposed to heat, or exposed to rapid temperature or pressure changes. The toxicological properties of this compound have not been investigated, so all health effects are unknown. To best prevent bodily harm or injury it
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#1732790498834880-414: Is used. To reduce confusion this article follows the systematic naming scheme throughout. Haloalkanes can be produced from virtually all organic precursors. From the perspective of industry, the most important ones are alkanes and alkenes. Alkanes react with halogens by free radical halogenation . In this reaction a hydrogen atom is removed from the alkane, then replaced by a halogen atom by reaction with
920-642: The Lucas test . In the laboratory, more active deoxygenating and halogenating agents combine with base to effect the conversion. In the " Darzens halogenation ", thionyl chloride ( SOCl 2 ) with pyridine converts less reactive alcohols to chlorides. Both phosphorus pentachloride ( PCl 5 ) and phosphorus trichloride ( PCl 3 ) function similarly, and alcohols convert to bromoalkanes under hydrobromic acid or phosphorus tribromide (PBr 3 ). The heavier halogens do not require preformed reagents: A catalytic amount of PBr 3 may be used for
960-553: The Mitsunobu reaction , the reagents are any nucleophile , triphenylphosphine, and a diazodicarboxylate ; the coproducts are triphenylphosphine oxide and a hydrazodiamide . Two methods for the synthesis of haloalkanes from carboxylic acids are Hunsdiecker reaction and Kochi reaction . Many chloro and bromoalkanes are formed naturally. The principal pathways involve the enzymes chloroperoxidase and bromoperoxidase . Primary aromatic amines yield diazonium ions in
1000-404: The R synthon , and readily react with nucleophiles. Hydrolysis , a reaction in which water breaks a bond, is a good example of the nucleophilic nature of haloalkanes. The polar bond attracts a hydroxide ion, OH (NaOH (aq) being a common source of this ion). This OH is a nucleophile with a clearly negative charge, as it has excess electrons it donates them to the carbon, which results in
1040-857: The R synthon. Alkali metals such as sodium and lithium are able to cause haloalkanes to couple in Wurtz reaction , giving symmetrical alkanes. Haloalkanes, especially iodoalkanes, also undergo oxidative addition reactions to give organometallic compounds . Chlorinated or fluorinated alkenes undergo polymerization. Important halogenated polymers include polyvinyl chloride (PVC), and polytetrafluoroethene (PTFE, or teflon). Nature produces massive amounts of chloromethane and bromomethane. Most concern focuses on anthropogenic sources, which are potential toxins, even carcinogens. Similarly, great interest has been shown in remediation of man made halocarbons such as those produced on large scale, such as dry cleaning fluids. Volatile halocarbons degrade photochemically because
1080-414: The carbon to which the halogen is attached is slightly electropositive where the halogen is slightly electronegative . This results in an electron deficient (electrophilic) carbon which, inevitably, attracts nucleophiles . Substitution reactions involve the replacement of the halogen with another molecule—thus leaving saturated hydrocarbons , as well as the halogenated product. Haloalkanes behave as
1120-451: The environmental impact of haloalkanes. Haloalkanes generally resemble the parent alkanes in being colorless, relatively odorless, and hydrophobic. The melting and boiling points of chloro-, bromo-, and iodoalkanes are higher than the analogous alkanes, scaling with the atomic weight and number of halides. This effect is due to the increased strength of the intermolecular forces —from London dispersion to dipole-dipole interaction because of
1160-417: The halide could be further replaced by other functional groups. While many haloalkanes are human-produced, substantial amounts are biogenic. From the structural perspective, haloalkanes can be classified according to the connectivity of the carbon atom to which the halogen is attached. In primary (1°) haloalkanes, the carbon that carries the halogen atom is only attached to one other alkyl group. An example
1200-461: The halogen as a prefix to the alkane. For example, ethane with bromine becomes bromoethane , methane with four chlorine groups becomes tetrachloromethane . However, many of these compounds have already an established trivial name, which is endorsed by the IUPAC nomenclature, for example chloroform (trichloromethane) and methylene chloride ( dichloromethane ). But nowadays, IUPAC nomenclature
1240-463: The hydrogen atom of the hydrohalic acid. Markovnikov's rule states that under normal conditions, hydrogen is attached to the unsaturated carbon with the most hydrogen substituents. The rule is violated when neighboring functional groups polarize the multiple bond, or in certain additions of hydrogen bromide (addition in the presence of peroxides and the Wohl-Ziegler reaction ) which occur by
2,4,6-Trinitrobenzenesulfonic acid - Misplaced Pages Continue
1280-651: The hydroxide ion HO abstracts a hydrogen atom. A Bromide ion is then lost, resulting in ethene , H 2 O and NaBr. Thus, haloalkanes can be converted to alkenes. Similarly, dihaloalkanes can be converted to alkynes . In related reactions, 1,2-dibromocompounds are debrominated by zinc dust to give alkenes and geminal dihalides can react with strong bases to give carbenes . Haloalkanes undergo free-radical reactions with elemental magnesium to give alkyl-magnesium compound: Grignard reagent . Haloalkanes also react with lithium metal to give organolithium compounds . Both Grignard reagents and organolithium compounds behave as
1320-443: The increased polarizability. Thus tetraiodomethane ( CI 4 ) is a solid whereas tetrachloromethane ( CCl 4 ) is a liquid. Many fluoroalkanes, however, go against this trend and have lower melting and boiling points than their nonfluorinated analogues due to the decreased polarizability of fluorine. For example, methane ( CH 4 ) has a melting point of −182.5 °C whereas tetrafluoromethane ( CF 4 ) has
1360-538: The most active (fluoroalkanes do not act as alkylating agents under normal conditions). The ozone-depleting abilities of the CFCs arises from the photolability of the C–Cl bond. An estimated 4,100,000,000 kg of chloromethane are produced annually by natural sources. The oceans are estimated to release 1 to 2 million tons of bromomethane annually. The formal naming of haloalkanes should follow IUPAC nomenclature , which put
1400-488: The oxidant (nitro group) and the fuel (hydrocarbon substituent) are bound within the same molecule. The explosion process generates heat by forming highly stable products including molecular nitrogen (N 2 ), carbon dioxide, and water. The explosive power of this redox reaction is enhanced because these stable products are gases at mild temperatures. Many contact explosives contain the nitro group. Alkyl halide Haloalkanes have been known for centuries. Chloroethane
1440-471: The oxidation of amino groups. 2-Nitrophenol is an aggregation pheromone of ticks . Examples of nitro compounds are rare in nature. 3-Nitropropionic acid found in fungi and plants ( Indigofera ). Nitropentadecene is a defense compound found in termites . Aristolochic acids are found in the flowering plant family Aristolochiaceae . Nitrophenylethane is found in Aniba canelilla . Nitrophenylethane
1480-451: The presence of a base, haloalkanes alkylate alcohols, amines, and thiols to obtain ethers , N -substituted amines, and thioethers respectively. They are substituted by Grignard reagent to give magnesium salts and an extended alkyl compound. In dehydrohalogenation reactions, the halogen and an adjacent proton are removed from halocarbons, thus forming an alkene . For example, with bromoethane and sodium hydroxide (NaOH) in ethanol ,
1520-453: The presence of water or organic solvents because of the explosive tendencies of aromatic nitro compounds which increase in the presence of multiple nitro groups. Not much is known about this compound, but it is used as a peptide terminal amino group neutralizer and is currently being investigated for its effects on the immune system. Its primary usage is primarily to neutralize peptide terminal amino groups in scientific research. Occasionally it
1560-499: The transformation using phosphorus and bromine; PBr 3 is formed in situ . Iodoalkanes may similarly be prepared using red phosphorus and iodine (equivalent to phosphorus triiodide ). One family of named reactions relies on the deoxygenating effect of triphenylphosphine . In the Appel reaction , the reagent is tetrahalomethane and triphenylphosphine ; the co-products are haloform and triphenylphosphine oxide . In
1600-574: Was produced in the 15th century. The systematic synthesis of such compounds developed in the 19th century in step with the development of organic chemistry and the understanding of the structure of alkanes. Methods were developed for the selective formation of C-halogen bonds. Especially versatile methods included the addition of halogens to alkenes, hydrohalogenation of alkenes, and the conversion of alcohols to alkyl halides. These methods are so reliable and so easily implemented that haloalkanes became cheaply available for use in industrial chemistry because
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