Substitution alkane chlorination

Until recently, halogen substituted alkanes were thought to be inert to xenon difluoride, but detailed examination has shown that common solvents such as dichloromethane (3) and chloroform (4) undergo fluorine-chlorine and fluorine-hydrogen exchange at room temperature due to hydrogen fluoride catalysis.15... 

Problem 5.2 Alkane chlorination is not a generally useful reaction because most alkanes have several different kinds of hydrogens, causing mixtures of chlorinated products to result. Draw and name all monochloro substitution products you might obtain by reaction of 2-methylpentane with Cl2-... 

Rh(CNneopentyl)(Tp )(L)] reacts with chloro-substituted alkanes giving primary C-H oxidative addition products (Fig. 8.14). If the alkane has chlorine substitution 3 to the methyl group, then activation is followed by rapid -elimination to give [RhHCl(Tp )(L)] and the corresponding olefin.156-158... 

Radical-catalyzed chlorination and bromination occur readily on alkanes and substituted alkanes, both in the gas phase and in solution. Both thermal and photochemical generation of the halogen atoms are employed for chlorinations, sulfuryl chloride in the presence of an initiator such as dibenzoyl peroxide is also used (Scheme 4.17). 

Because the reaction has radical intermediates and repeating propagation steps, it is called a radical chain reaction. This particular radical chain reaction is called a radical substitution reaction because it substitutes a chlorine for one of the hydrogens of the alkane. 

Methane ethane and cyclobutane share the common feature that each one can give only a single monochloro derivative All the hydrogens of cyclobutane for example are equivalent and substitution of any one gives the same product as substitution of any other Chlorination of alkanes m which the hydrogens are not all equivalent is more com plicated m that a mixture of every possible monochloro derivative is formed as the chlo rmation of butane illustrates... 

Bromine reacts with alkanes by a free radical chain mechanism analogous to that of chlorine There is an important difference between chlorination and brommation how ever Brommation is highly selective for substitution of tertiary hydrogens The spread m reactivity among pnmary secondary and tertiary hydrogens is greater than 10 ... 

The haloform reaction of unsymmetrical perfluoroalkyl and co-hydroper-fluoroalkyl trifluororaethyl ketones gives the alkane corresponding to the longer alkyl chain [54] (equation 53) If the methyl group contains chlorine, the reaction can take different pathways, leading to loss of chlorine (equation 54), because of the variable stability of the chlorine-substituted methyl carbanions in alkali. 

Depending on the relative amounts of the two reactants and on the time allowed, a sequential substitution of the alkane hydrogen atoms by chlorine occurs, leading to a mixture of chlorinated products. Methane, for instance, reacts with CI2 to yield a mixture of CH3CI, CH2CI2, CHCI3, and CCI4. We ll look at this reaction in more detail in Section 5.3. 

---