Halogenoalkanes

Keynotes in Organic Chemistry, Second Edition. Andrew F. Parsons. 

The use of hashed and wedged line notation is discussed in Section 3.3.2 

The formation of bromobenzene from benzene is discussed in Section 7.2.1 

Although the C-l bond is not polar, it becomes polarised when a R nucleophile approaches It 

Halogenoalkanes have an sp carbon atom and so have a tetrahedral shape. 

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The alkoxide formed by attack of the carbonyl group of perfluorobutyrolactone opens the oxirane ring of hexafluoropropene oxide at the central carbon atom [37] (equation 33). A fluorinated sultone reacts with halogenoalkanes in the presence of metal fluoride [3S] (equation 34). 

There has been much interest recently in the reaction of a, o)-di-halogenoalkanes. 1,2-Dibromoethane reacts with phthalazine to give ethane 1,2-bis-phthalazinium dibromide (1), none of the mono salt being formed directly, but the same dibromo compound and a, a -dipyridyl give the cyclic compound 2. ... 

Alkanes react with halogens, such as chlorine and bromine, to form halogenoalkanes. 

Hydrogen halides alkenes add hydrogen halides across the double bond to form halogenoalkanes. 

Halogenoalkanes are compounds in which a halogen atom is bonded to a saturated carbon atom. 

Halogenoalkanes react with aqueous sodium (or potassium)... 

The mechanism of nucleophilic substitution in primary halogenoalkanes proceeds as follows, using 1-bromobutane as an example ... 

A nucleophile is a species that attacks electron-deficient sites and donates a lone pair of electrons to form a covalent bond. Halogenoalkanes get more reactive as the C-X bond gets longer and therefore weaker. Iodoalkanes therefore react fastest and fluoroalkanes slowest. 

Once the halogen atom has left the halogenoalkane as the halide ion, X-, silver nitrate solution can be used to identify the halide as in inorganic chemistry. The three essential steps are ... 

Many of these so-called halogenoalkanes are used as solvents. For example, dichloromethane is used as a solvent in paint stripper (Figure 14.6). 

Halogenoalkanes Organic compounds in which one or more hydrogen atoms of an alkane have been substituted by halogen atoms such as chlorine. 

These involve addition of a halogenoalkane to a carbonyl compound. 

The most important means of introducing an alkyl group into an aromatic ring is the Friedel-Crafts reaction. In its simplest form, this is the reaction of an alkyl halide (halogenoalkane) with an aromatic compound, such as benzene, in the presence of a Lewis acid, commonly aluminium chloride (Scheme 3.1). 

The alkyl halides (halogenoalkanes), thiols and amines are at the same oxidation level as the alcohols, while acyl halides, thioacids and amides are similarly related to the carboxylic acids. Like oxygen, sulfur can be inserted into a chain to generate the equivalent of an ether such as the thioether... 

As a model system for elucidating the reactivity of silylene towards electrophiles the reaction of 3 with halogenoalkanes was chosen. Stirring a solution of 3 with three equivalents of iodomethane in toluene for seven days at room temperature afforded siliconium ion 5a in 90% yield (Eq. I). Analogously, 5b and c were obtained. 

In case of the direct reaction of the natural oil or lower alkyl ester of natural fatty acid and the amine the reaction method for producing the amide derivatives is as follows That is, about 1 mol of the said oils and 1 to 100 equivalent mols of the said amines are mixed in the absence or presence of solvents such alcohols as methanol, ethanol or the like, such aromatic hydrocarbons as benzene, toluene, xylene or the like, such halogenoalkanes as methylene chloride, chloroform, carbon tetrachloride or the like, and such alkenes or alkanes as petroleum ether, benzene, gasoline, ligroin or cyclohexane, such ethers as tetrahyrofuran, dioxane and the like, or a mixture thereof, and the mixture is subjected to the reaction in the absence or presence of catalyst amount or equimolar amount to the amine of an auxiliary agent of condensation, such as alkoholate of alkali metal, i.e. lithium, methylate, lithium ethylate, sodium methylate, sodium ethylate, potassium-t-butylate and the like, or acidic auxiliary agents, i.e. p-toluenesulfonic acid and the like, thereby to yield the amide derivatives. In this reaction, a formal alcohol may be removed from the reaction system. 

Many mechanisms in organic chemistry start with an acid/base reaction. This may be just a simple Bronsted-Lowry protonation of a hydroxyl group, which results in the activation of a C-OH bond or it may be a Lewis acid/base reaction as, for example, when aluminium trichloride complexes with a halogenoalkane in the first step of the Friedel-Crafts reaction. In each case, the initial intermediate usually reacts further and leads to the desired product. In inorganic chemistry, the acid/base reaction may be all that is of interest, e.g. the treatment of a carbonate with an acid to liberate carbon dioxide. However, it is unusual in organic chemistry for the acid/base reaction to be an end in itself. It is for this reason that acid/base characteristics are normally considered as a property of the molecule, similar to the nucleophilic and electrophilic properties to which they are closely related, rather than as a fundamental reaction type as is the case in inorganic chemistry. 

We have seen that primary and secondary halogenoalkanes when attacked by a hydroxide anion normally undergo inversion at the carbon centre at which substitution occurs, because they proceed via an SN2 pathway. In the case of l-chloro-2-hydroxyalkanes, it is observed that when treated with a hydroxide... 

Abstract Room temperature ionic liquids (ILs) have attracted considerable attention as novel reaction media over the last decade. By virtue of their unique properties, ILs have been proposed as alternative solvents. Structurally, most of the ILs that have been investigated to date are based on imidazolium, pyridinium and ammonium cations, associated with polyatomic anions such as chloroaluminates, tetrafluoroborate, hexafluorophoshate and bis-triflimide. Although these salts have positive properties, imidazole, pyridine and halogenoalkanes come from petroleum feedstocks that are neither green nor sustainable. Renewable resources may represent a valid alternative to synthesized new ILs an alternative able to take into accounts both the ecological and economic requirements. 

From the application point of view, there are many reasons to favour the development of the IL chemistry and many reasons for considering new non-imidazolium" and "non-pyndimum ILs. Although these salts have positive properties, imidazole, pyridine and halogenoalkanes come from petroleum feed-stocks that are neither green nor sustainable. 

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