Chlorination, alkane

Figure 10.2 Energy diagram for alkane chlorination. The relative rates of formation of tertiary, secondary, and primary radicals are the same as their stability order.

In contrast with alkane chlorination, alkane bromination is usually much more selective. In its reaction with 2-methylpropane, for example, bromine abstracts the tertiary hydrogen with greater than 99% selectivity, as opposed to the 35 65 mixture observed in the corresponding chlorination. 

The Lead-Off Reaction Addition of HBr to Alkenes Students usually attach great-importance to a text s lead-off reaction because it is the first reaction they see and is discussed in such detail. 1 use the addition of HBr to an alkene as the lead-off to illustrate general principles of organic chemistry for several reasons the reaction is relatively straightforward it involves a common but important functional group no prior knowledge of stereochemistry or kinetics in needed to understand it and, most important, it is a polar reaction. As such, 1 believe that electrophilic addition reactions represent a much more useful and realistic introduction to functional-group chemistry than a lead-off such as radical alkane chlorination. 

Drivers for Performing Alkane Chlorination in Micro Reactors... 

Beneficial Micro Reactor Properties for Alkane Chlorination... 

Alkane chlorinations usually give a complex mixture of products => they are not... 

A noticeable feature of alkane chlorination is the very low yield of chloro products. Using hexane as the alkane, it has been shown (84) that... 

Alkane chlorination is a stoichiometric reaction [such as Eq. (11)], and a Pt(IV) atom is lost each time a chloroalkane molecule is produced. Efforts to make it catalytic, by converting the Pt(II) formed back to Pt(IV), have so far been totally unsuccessful (86) added K3Fe(CN)6, RuCls, and Fe(OH)(OAc)2 are without effect. Certainly a very subtle... 

Compounds that undergo only vdW interactions (London plus Debye plus Keesom interactions) are commonly referred to as apolar. Examples include alkanes, chlorinated benzenes, and PCBs. 

Nanocrystalline MgO and CaO with high surface area are able to absorb large amounts of chlorine, which undergo dissociative chemisorption. These can serve as rather selective, catalytic alkane chlorination reagents, which suggests that trapped Cl atoms are involved in the reaction.295 Liquid-phase low-temperature chlorination of alkanes is also possible in the presence of various alkenes as inductors and AIBN [azobis(isobutyronitrile)] 296... 

Bintein and Devillers [3] developed a model for alkylbenzenes, PAHs, halogenated alkanes, chlorinated benzenes, PCBs, and acids and bases. Their model has been derived from 229 Kp values (with %OC >0.1) recorded for 53 compounds. A test was performed on 500 other Kp values for 87 compounds. The model requires the input of the system parameter %OC and of two compound properties, Kow and pKa ... 

PCBs > PAHs > chlorinated aliphatic alkanes > chlorinated aromatics > unsaturated chlorinated aliphatic compounds... 

Reactions of more electrophilic SC12 with fluoroolefins under thermolytic conditions are not selective they always produce a mixture of sulfenyl and thiosulfenylchlorides, sulfides, and polysulfides, along with substantial amounts of products of alkane chlorination [135]. 

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-... 

---