Haloalkane - Wikipedia. Tetrafluoroethane (a haloalkane) is a colorless liquid that boils well below room temperature (as seen here) and can be extracted from common canned air canisters by simply inverting them during use.
The haloalkanes (also known, as halogenoalkanes or alkyl halides) are a group of chemical compounds derived from alkanes containing one or more halogens. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely used commercially and, consequently, are known under many chemical and commercial names. 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 which contain chlorine, bromine, and iodine are a threat to the ozone layer, but fluorinated volatile haloalkanes in theory may have activity as greenhouse gases.
Elimination Reactions of Alkyl Halides; Elimination Reactions 1. The Zaitsev Rule is a good predictor for simple elimination reactions of alkyl chlorides, bromides and iodides as long as relatively small strong bases are used. The Chemistry of Alkyl Halides Solutions to In-Text Problems 9.1 (b) The product is ethylammonium iodide. Secondary alkyl halides with no b- substituents (B) react more slowly than.
Reactions of Alcohols. OH KMnO 4, b a s e O OH H OH O CuO, 30 0 o C. Nucleophilic Substitution of Alkyl Halides. Submitted by Matt on July 19, 2011. S N 1, S N 2, E 1 and E2 Reactions Whether an alkyl halide will undergo an S N 1, S N 2, E 1 or an E2 reaction depends upon a number of factors. Some of the more common factors include the natures of the substrate carbon.
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 .
Chloroethane was produced synthetically in the 1. The systematic synthesis of such compounds developed in the 1. 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 the halide could be further replaced by other functional groups. While most haloalkanes are human- produced, non- artificial- source haloalkanes do occur on Earth, mostly through enzyme- mediated synthesis by bacteria, fungi, and especially sea macroalgae (seaweeds). More than 1. 60. 0 halogenated organics have been identified, with bromoalkanes being the most common haloalkanes.
Brominated organics in biology range from biologically produced methyl bromide to non- alkane aromatics and unsaturates (indoles, terpenes, acetogenins, and phenols). Specific dehalogenase enzymes in bacteria which remove halogens from haloalkanes, are also known. Classes. An example is chloroethane (CH3.
Characteristic reactions, nucleophilic substitution. Alkyl halide Classification of alkyl halides C R H H C X R R H C X R R R. 224 CHAPTER 7 Alkyl Halides and Nucleophilic Substitution.
CH2. Cl). 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 the environmental impact of haloalkanes. Properties. Their boiling points are higher than the corresponding alkanes and scale with the atomic weight and number of halides.
This is due to the increased strength of the intermolecular forces. Thus carbon tetraiodide (CI4) is a solid whereas carbon tetrafluoride (CF4) is a gas.
As they contain fewer C. 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. Many are alkylating agents, with primary haloalkanes and those containing heavier halogens being 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.
The oceans are estimated to release 1- 2 million tons of bromomethane annually. An estimated one fifth of pharmaceuticals contain fluorine, including several of the most widely used drugs. The beneficial effects arise because the C- F bond is relatively unreactive. Fluorine- substituted ethers are volatile anesthetics, including the commercial products methoxyflurane, enflurane, isoflurane, sevoflurane and desflurane.
Fluorocarbon anesthetics reduce the hazard of flammability with diethyl ether and cyclopropane. Perfluorinated alkanes are used as blood substitutes. Chlorinated or fluorinated alkenes undergo polymerization. Important halogenated polymers include polyvinyl chloride (PVC), and polytetrafluoroethene (PTFE, or Teflon).
The production of these materials releases substantial amounts of wastes. Nomenclature. 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).
For unambiguity, this article follows the systematic naming scheme throughout. Production. From the perspective of industry, the most important ones are alkanes and alkenes. From alkanes. In this reaction a hydrogen atom is removed from the alkane, then replaced by a halogen atom by reaction with a diatomic halogen molecule. The reactive intermediate in this reaction is a free radical and the reaction is called a radical chain reaction. Free radical halogenation typically produces a mixture of compounds mono- or multihalogenated at various positions. It is possible to predict the results of a halogenation reaction based on bond dissociation energies and the relative stabilities of the radical intermediates.
Another factor to consider is the probability of reaction at each carbon atom, from a statistical point of view. Due to the different dipole moments of the product mixture, it may be possible to separate them by distillation. From alkenes and alkynes. The double bond of the alkene is replaced by two new bonds, one with the halogen and one with the hydrogen atom of the hydrohalic acid. Markovnikov's rule states that in this reaction, the halogen is more likely to become attached to the more substituted carbon. This is an electrophilic addition reaction.
Water must be absent otherwise there will be a side product of a halohydrin. The reaction is necessarily to be carried out in a dry inert solvent such as CCl. The reaction of alkynes are similar, with the product being a geminal dihalide; once again, Markovnikov's rule is followed. Alkenes also react with halogens (X2) 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 . This reaction is exploited in the Lucas test. The most popular conversion is effected by reacting the alcohol with thionyl chloride (SOCl. Both phosphorus pentachloride (PCl.
PCl. 3) also convert the hydroxyl group to the chloride. Alcohols may likewise be converted to bromoalkanes using hydrobromic acid or phosphorus tribromide (PBr. A catalytic amount of PBr. PBr. 3 is formed in situ. Iodoalkanes may similarly be prepared using red phosphorus and iodine (equivalent to phosphorus triiodide). The Appel reaction is also useful for preparing alkyl halides. The reagent is tetrahalomethane and triphenylphosphine; the co- products are haloform and triphenylphosphine oxide.
From carboxylic acids. The principal pathways involve the enzymes chloroperoxidase and bromoperoxidase. By Rydons method. An alcohol on heating with halogen in presence of triphenyl phosphate produces haloalkanes or alkyl halides. Reactions. They are polar molecules: 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. Haloalkanes behave as 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. As can be seen, the OH is now attached to the alkyl group, creating an alcohol. Reaction 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 is used thus as a catalyst.
Haloalkanes react with ionic nucleophiles (e. 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 the Staudinger reduction or lithium aluminium hydride. Amines may also be prepared from alkyl halides in amine alkylation, the Gabriel synthesis and Delepine reaction, by undergoing nucleophilic substitution with potassium phthalimide or hexamine respectively, followed by hydrolysis. In 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 reagents to give magnesium salts and an extended alkyl compound. Mechanism. In this case, the slowest (thus rate- determining step) is the heterolysis of a carbon- halogen bond to give a carbocation and the halide anion. The nucleophile (electron donor) attacks the carbocation to give the product. SN1 reactions are associated with the racemization of the compound, as the trigonal planar carbocation may be attacked from either face. They are favored mechanism for tertiary haloalkanes, due to the stabilization of the positive charge on the carbocation by three electron- donating alkyl groups.
They are also preferred where the substituents are sterically bulky, hindering the SN2 mechanism.