Branched alkanes chlorination

In 1949, the development of a catalyst based on a combination of platinum and an acidic component (e.g. A1203, A1C13) allowed the use of lower reaction temperatures than with the early catalysts.6 However, problems were still encountered with chlorine corrosion. In the 1960s, Universal Oil discovered that the addition of rhenium to a bifunctional Pt/Al203 catalyst resulted in slower deactivation by carbon deposition, and other dopants have since been found to modify the catalyst acidity and resistance to poisons, e.g. Cl, Sn, Ir. More recently, catalysts based on zeolites and noble metals have been shown to be more resistant to nitrogen and sulphur compounds, while giving a high activity and selectivity to branched alkanes. 

The most widely applied isomerization catalysts are platinum-promoted solid acids, namely chlorinated alumina1,2 and mordenite.3 5 The former catalysts require the continuous addition of chlorine-containing compounds, are moisture-sensitive and are poisoned by sulfur impurities.6 They are also highly corrosive and hence, environmentally hazardous. Zeolite catalysts are significantly less active and have to be operated at higher temperatures (500-550 K). As a consequence of thermodynamic limitations only relatively low yields of the target branched alkanes can be achieved under these conditions. 

Well over 100 compounds have been determined in seawater (and sediments) using a considerable variety of techniques (Table 2). Methods include n-and branched alkanes (up to about C20, pristane/ phytane), alkenes and aromatic compounds (up to the disubstituted naphthalenes), halocarbons and chlorinated aromatic species, low relative molecular mass alcohols, organic sulfur compounds (notably dimethyl sulfide, a major product of some phytoplankton species, but ranging up to dimethyl trisulfide), and freons (11, 12, and 113 used in studies of oceanic mixing). 

When chlorination or bromination of alkenes is carried out in the gas phase at high temperature, addition to the double bond becomes less significant and substitution at the allylic position becomes the dominant reaction.153-155 In chlorination studied more thoroughly a small amount of oxygen and a liquid film enhance substitution, which is a radical process in the transformation of linear alkenes. Branched alkenes such as isobutylene behave exceptionally, since they yield allyl-substituted product even at low temperature. This reaction, however, is an ionic reaction.156 Despite the possibility of significant resonance stabilization of the allylic radical, the reactivity of different hydrogens in alkenes in allylic chlorination is very similar to that of alkanes. This is in accordance with the reactivity of benzylic hydrogens in chlorination. 

C27H35CIN2O2, Mr 453.02, dark red powder. An anti-neoplastic antibiotic from the actinomycete Strepto-myces griseoviridis. R. has a novel structure composed of pyrrole and furan rings with a branched, long-chain alkane bridge. Another pyrrole pigment with three pyrrole units but without the furan system and the chlorine atom is prodigiosin. 

A substantial number of investigations have been devoted to this isomerization reaction and a number of reviews are available The isomerization is an equilibrium reaction that can be catalyzed by various strong acids. In the industrial processes, aluminum chloride and chlorinated alumina are the most widely used catalysts. Whereas these catalysts become active only at temperatures above 80-100 °C, superacids are capable of isomerizing alkanes at room temperature and below. The advantage is that lower temperatures thermodynamically favor the most branched isomers. 

Consider a regression for a set of 66 halogenides and their boiling points [116]. The molecules considered include branched and cyclic halo-alkanes and several halo-alkenes involved as heteroatoms chlorine, bromine, and iodide. All the molecules and their boiling points, which cover the range from -24°C (chloromethane) to... 

FIGURE 6.7 Regression for a set of 66 halogenides and their boiling points. The molecules considered include branched and cyclic halo-alkanes involving chlorine, bromine, and iodine. 

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