Alkanes from alkenes

Dehydrogenation (Reforming)17-20—to increase octane number of gasoline, to produce alkenes from alkanes [Eq. (1.2)], as well as aromatics, such as benzene, toluene, and xylenes [Eq. (1.3)] ... 

In Eq. (3) [S]o and [S]f are starting and ending substrate concentrations. S approaches [S] when substrate consumption is minimal, and S is substituted for [S] to correct for excess substrate consumption. In these analyses, however, substrate inhibition can be a problem if the product has a similar affinity to the substrate. Fortunately, most P450 oxidations produce products that are less hydrophobic than the substrates, resulting in lower affinities to the enzymes. There are exceptions, including desaturation reactions that produce alkenes from alkanes (10) and carbonyl compounds from alcohols. These products have hydrophobicities that are similar or increased relative to their substrates. 

Results from these studies are important for the ongoing debates on the existence and utility of Sn/Pt alloy phases in bimetallic Pt-Sn supported catalysts. For example, our observation of dramatically decreased carbon buildup on the alloy surfaces from acetylene (a coke-precursor), and the enhanced yield of aromatics and alkenes from alkane dehydrogenation mimics important aspects of the chemistry of commercial Pt-Sn supported catalysts used for reforming. On the contrary, it seems unlikely that Sn/Pt alloy phases are solely responsible for the high selectivity observed in crotonaldehyde hydrogenation using Pt-Sn bimetallic catalysts. 

The formation of alkenes from alkanes is an elimination reaction, a reaction in which a combination of atoms is removed from two adjacent carbon atoms forming an additional bond between the carbon atoms. The atoms that are eliminated usually form stable molecules, such as H2O, HCl, or H2. Ethene, an important starting material in the chemical industry, is produced by the elimination of two hydrogen atoms from ethane. A reaction that eliminates two hydrogen atoms is called a dehydrogenation reaction. Note that the two hydrogen atoms form a molecule of hydrogen gas. 

Most of the published theoretical and practical applications of ED have been in the separation of hydrocarbons (alkenes from alkanes, toluene from naphthenes, benzene from paraffins, etc.) where, even... 

As the reaction occurs, the purple color of the permanganate ion is replaced by the brown precipitate of manganese dioxide. Because of this color change, the reaction can be used as a chemical test to distinguish alkenes from alkanes, which normally do not react with potassium permanganate. 

The regeneration of olefins with hydrochloric add provides a method for the separation of alkenes from alkanes. The hydrocarbon mixture is... 

Renneke RF, Pasquali M, Hill CL (1990) Polyoxranetalate systems for the catalytic selective production of nonthermodynamic alkenes from alkanes. Nature of excited-state deactivation processes and control of subsequent thermal processes in polyoxometalate photoredox chemistry. J Am Chem Soc 112 6585-6594... 

One can start building up a list of MM3 parameters by use of the TINKER analyze command. Don t expect to build up the entire set, which occupies about 100 pages in the MM3 user s manual, but do obtain a few representative examples to get an idea of how a parameter set is constr ucted. From previous exercises and projects, you should have input and output geometries for an alkene, an alkane, and water. From these, the object is to determine the stretching and bending parameters for the C—C, C=C, C—H, and O—H bonds. The C—H bond parameters are not the same... 

Another name for aromatic hydrocarbons is arenes Arenes have properties that are much different from alkanes alkenes and alkynes The most important aromatic hydrocarbon... 

As with alkyl and alkenyl substituents derived from alkanes and alkenes, respectively, alkynyl groups are also possible. 

Concerning consecutive reactions, a typical example is the hydrogenation of alkynes through alkenes to alkanes. Alkenes are more reactive alkynes, however, are much more strongly adsorbed, particularly on some group VIII noble metal catalysts. This situation is illustrated in Fig. 2 for a platinum catalyst, which was taken from the studies by Bond and Wells (45, 46) on hydrogenation of acetylene. The figure shows the decrease of... 

The injected sulfonyl chlorides decompose instantaneously to give peaks of monochloroalkanes and 1-alkenes from alkanesulfonyl chlorides and dichloro-alkanes, and monochloro- 1-alkenes from monochloroalkane sulfonyl chlorides ... 

To obtain alkanes and alkenes from ahphatic hydrocarbon fractions, argentation PLC was proposed that utihzed sihca-gel-60-precoated plates impregnated with 5% or 10% of AgNOj [37,80,99,100]. In some applications, TLC plates impregnated... 

Many Pseudomonas strains accumulate MCL-PHAs from alkane, alkene, al-kanoate, alkenoate, or alkanol [5,6,14,96]. The composition of the PHAs formed by the pseudomonads of the rRNA homology group I is directly related to the structure of the carbon substrate used [6]. These results suggested that MCL-PHAs are synthesized from the intermediates of the fatty acid oxidation pathway. In almost all pseudomonads belonging to the rRNA homology group I except Pseudomonas oleovorans, MCL-PHA can also be synthesized from acetyl-CoA through de novo fatty acid synthetic pathway [97]. The -oxidation pathway and de novo fatty acid synthetic pathway function independently in PHA biosynthesis. 

Chain propagation is started from a methylene group and terminated by desorption of 1-alkenes or alkanes. Propeller-type mobility of the olefin ligand renders possible CH3 branching of the growing chain, as demonstrated by the scheme. The growth probability is determined by the ratio of rates of formation of the alkyl intermediate and of the desorption of 1-alkenes, and to a minor extent of alkanes. 

Low-pressure discharges tend to produce much more intense chemiluminescence from alkenes than from alkanes. This has been attributed to the addition of N to the double bond, as illustrated for ethylene,... 

Figure 19.9. Hydrogen transfer from alkanes to alkenes...

Addition reactions form the basis for tests that distinguish alkenes and alkynes from alkanes. Bromine, Br2, has a deep reddish-brown colour. When bromine is added to an alkene or alkyne, an addition reaction takes place. As the bromine is used up, the brown colour of the bromine disappears. Since alkanes cannot undergo addition reactions, no reaction takes place when bromine is added to an alkane. 

Mechanism for protonation of alkenes was previously discussed in Section 13.5.1. In general, protonation of alkenes is an exothermic process. Protonation of alkanes was discussed in Section 13.5.2. There wiU be further discussion on this step in Section 13.8.4 within the context of alkane cracking mechanisms. The formation of a penta-coordinated carbonium ion from alkane protonation is typically an endothermic process, the reverse being true for deprotonation. 

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