Reactions involving unsaturated hydrocarbons

None of the chlorophosphetane is produced in the absence of the AICI3, and the amount of the latter employed has a marked influence on the product yield thus if the ratio of the three reactants alkene, PCI3 and AICI3 was 1 1 0.75 the yield was about 50%, the yield was about 80% if the ratio was 1 1 1 and 95% if it was 1 1 1.25. Replacement of the dichloromethane solvent by either a pure aliphatic or aromatic hydrocarbon prevented phosphetane formation, and the use of 1,2-dichloroethane gave some phosphetane together with some dimerized alkene. 

No phosphetane was obtained from 2,4,4-trimethylpent-l-ene 3,3-dimethylbut-l-ene afforded a 92% yield of a mixture of 16% cis- and 84% /ra 5 -l-chloro-2,2,3-trimethylphosphetane 1-oxide  

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Similar reactions are also known for other coordinated molecules. The majority of isomerization reactions involving unsaturated hydrocarbons are catalyzed by -electron metal complexes. In the transition state, hydrido complexes are usually formed ... 

Before ozone - and PAN were identified as specific phytotoxic components of the photochemical complex, researchers used a number of artificial chemical reaction systems to simulate the ambient photochemical-oxidant situation. These efforts involved a number of irradiated and nonirradiated reaction systems unsaturated hydrocarbon-ozone mixtures, unsaturated hydrocarbon-NOx mixtures, and dilute auto exhaust). Most research before 1960 involved one or more of these reaction systems. This research has been well reviewed " - 451.459.488.505 extenslvely covered here. Although the... 

Alkanes can be activated by both hard and soft transition metal complexes. Hard catalysts have been known for a long time, although examples involving alkanes are few in number, and all are from studies of recent years. Soft catalysts have become important and have been much studied during the past decade and are widely used for reactions of unsaturated hydrocarbons. It was the use of such soft catalysts that Halpem had particularly in mind when he spoke of the development to activate alkanes as an important and challenging problem. 

A major effort to study the chemistry of the zero oxidation state lanthanides on a preparative scale involved their reactivity with neutral unsaturated hydrocarbons 14, 60). This class of reagents was of interest because reactions of unsaturated hydrocarbons with metals constitute such an important component of organometallic chemistry and because species such as alkenes and alkynes were not common as ligands or reactants in organolanthanide chemistry at that time. 

Clearly, whether or not ozone is formed depends also on the rate at which it is destroyed, for example, by reaction with unsaturated hydrocarbons. Rates of reactions with alkanes are, as noted above, much slower than for reaction with OFI radicals, and reactions with ozone are of the greatest significance with unsaturated aliphatic compounds. The pathways plausibly follow those involved in chemical ozonization (Hudlicky 1990), and some of these are noted later. 

As has already been indicated hydrogen transfer reactions involving olefinic hydrocarbons lead to the formation of highly unsaturated compounds. These form addition complexes ( lower layer or sludge ) with the catalyst. In this way, crystalline aluminum chloride is converted to a red-brown liquid. Similar red to brown viscous products are obtained when sulfuric acid or hydrogen fluoride is employed. 

The investigation into thiyl-catalyzed isomerization of olefins eventually resulted in the measurement of relative rate coefficients for several CH3S + olefin reactions. These early relative rate studies relied on the interpretation of complex chemical systems to arrive at rate coefficients for the elementary reactions involving CH3S attack on the olefin double bond. More recently, the characterization of the CH3S laser induced fluorescence (LIF) spectrum [90,91] has led to direct measurements of rate coefficients for methyl thiyl radical reactions with unsaturated hydrocarbons. Reported relative rate coefficients are tabulated along with the recent direct measurements of Balia et al. [92] (see Table 6). This has been done to allow for observation of any reactivity trends that may be present and to facilitate qualitative discussion of proposed CH3S+olefin reaction mechanisms. 

The subject of particle size effects in heterogeneous catalysis, in particular the dependence or otherwise of catalytic activity and selectivity on metal particle size in the range 1-10 nm, is of interest to both industrial and academic circles. General trends that have emerged suggest that transformations such as those involving the reactions of unsaturated hydrocarbons, e.g., catalytic hydrogenation and isomerisation, are independent of metal particle size, i.e., are... 

In several papers dealing with catalytic reactions involving hydrogen and unsaturated hydrocarbons the observed self-poisoning of nickel or its alloys has been quite properly attributed to the presence of carbonaceous... 

The nature of dangerous reactions involving organic chemicals depends on the saturated, unsaturated or aromatic structures of a particular compound. Saturated hydrocarbons are hardly reactive, especially when they are linear. Branched or cyclic hydrocarbons (especially polycyclic condensed ones) are more reactive, in particular as with oxidation reactions. With ethylenic or acetylenic unsaturated compounds, the products are endothermic . 

Both heterogeneous and homogeneous catalysts have been found which allow the hydroamination reaction to occur. For heterogeneously catalyzed reactions, it is very difficult to determine which type of activation is involved. In contrast, for homogeneously catalyzed hydroaminations, it is often possible to determine which of the reactants has been activated (the unsaturated hydrocarbon or the amine) and to propose reaction mechanisms (catalytic cycles). 

Neutral-neutral reactions are also involved in the synthesis of hydrocarbons, but here the evidence is less clear since, even for those systems studied in the laboratory, reaction products are rarely available. Unlike reactions involving O atoms, those involving C atoms and unsaturated hydrocarbons appear to be rapid, at least at room temperature and above.46,47 If the products of these reactions are analogous to ion-molecule insertion reactions, they can lead to molecular synthesis for example ... 

A second major class of ion-molecule reactions that is relatively poorly studied consists of systems involving very unsaturated hydrocarbon neutrals, especially radicals. The unsaturated nature of the organic chemistry in interstellar clouds leads to sizeable abundances of very unsaturated hydrocarbons such as the polyacetylenes HC H, the carbenes H2C , the radicals C H, and the clusters Cn. Although some work has been done on the chemistry of such species, much of the relevant ion-molecule chemistry involving ions such as C+, CH3, and even C2H2 must be guessed at from generalizations based on a small number of studied systems. 

The mechanisms of explosions in solidified gas mixtures at low temperatures containing unsaturated hydrocarbons and oxides of nitrogen is discussed. Fast radical addition of nitrogen dioxide to double bonds is involved, and with dienes it is a fast reaction of very low energy of activation. Possibilities of preventing explosions are discussed. 

Reactions involving lithium appear to be particularly good candidates for ultrasonic acceleration. The reduction of some highly unsaturated cyclic hydrocarbons by lithium was not only accelerated but pushed to completion by ultrasonic irradiation(19) ... 

Reactions, under irradiation, involving the addition to unsaturated hydrocarbons of nitrogen and phosphorus compounds and of silanes have been summarized by Spinks and Woods (1990). Some cycloaddition reactions have also been reviewed. These will not be detailed here. 

The gas-phase reaction of cationic zirconocene species, ZrMeCp2, with alkenes and alkynes was reported to involve two major reaction sequences, which are the migratory insertion of these unsaturated hydrocarbons into the Zr-Me bond (Eq. 3) and the activation of the C-H bond via er-bonds metathesis rather than /J-hydrogen shift/alkene elimination (Eq. 4) [130,131]. The insertion in the gas-phase closely parallels the solution chemistry of Zr(R)Cp2 and other isoelec-tronic complexes. Thus, the results derived from calculations based on this gas-phase reactivity should be correlated directly to the solution reactivity (vide infra). 

Many other ion-molecule reactions involving highly unsaturated hydrocarbon ions and neutral olefins or the equivalent strained cycloalkanes have been studied by mass spectrometry98. For example, we may mention here the addition of ionized cyclopropane and cyclobutane to benzene radical cations giving the respective n-alkylbenzene ions but also isomeric cyclodiene ions such as ionized 8,9-dihydroindane and 9,10-dihydrotetralin, respectively. Extensive studies have been performed on the dimerization product of charged and neutral styrene4. 

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