Pressure cyclic hydrocarbons

Cyclohexadiene and benzene form identical structures on Pt(l 1 1) at low pressures (Figures 7.23 and 7.24). 1,3-Cyclohexadiene dehydrogenates to form benzene on the surface, while benzene adsorbs molecularly. Figure 7.24b schematically shows the adsorbed benzene structure at low pressure. The STM images of the C6 cyclic hydrocarbons show three different adsorbed structures on Pt(l 1 1). Cyclohexene and cyclohexane partially dehydrogenate to form rc-allyl, 1,4-cyclohexadiene adsorbs in a boat configuration, and both 1,3-cylohexadiene and benzene adsorb as molecular benzene on the surface. 

FIGURE 2.2.4 Vapor pressure (liquid or supercooled liquid) versus Le Bas molar volume for aliphatic and cyclic hydrocarbons. 

Letcher, T.M., Marsicano, F. (1974) Vapour pressures and densities of some unsaturated C6 acyclic and cyclic hydrocarbons between 300 and 320 K. J. Chem. Thermodyn. 6, 509-514. 

In the case of pentanes, disproportionation to isobutane and hexane is pronounced. This undesirable side reaction can be suppressed by the addition of small amounts of cyclic hydrocarbons or by operation under hydrogen pressure (6). 

The hexanes undergo side reactions even more readily than do the pentanes. Although disproportionation and cracking can be suppressed to some extent by the addition of cyclic hydrocarbons, this treatment is not effective enough to ensure satisfactory catalyst life, and hydrogen at relatively high pressure must be used as the inhibitor. 

Thermal cyclooligomerizations of olefins and alkynes require severe and often dangerous reaction conditions and the yields of cyclic products are usually very low. Acetylene ean be trimerized to benzene at 500 °C [1] and butadiene (BD) dimerizes at 270 °C and under high pressure to give small amounts of 1,5-cyclo-octadiene [2]. Reppe s discovery in 1940 that acetylene can be cyclotetramerized to cyclooctatetraene (COT) using a nickel catalyst [3] shows that transition metals can act as templates for the synthesis of cyclic hydrocarbons from acetylenic or olefinic building blocks (Scheme 1). 

Concerning the details of this reaction there exist several different opinions detailed reviews are given by Anderson and Kemball (217) and Burwell (66). However, the cyclic hydrocarbons have been little investigated in this respect up to recent times. We took up this problem together with Gudkov, Fedorovich, and Savin (231-233). The exchange with deuterium was carried out on evaporated films at a low pressure with a mass spectrometric analysis of the products. 

This study on the contact conversion of cyclic hydrocarbons under hydrogen pressure gives grounds for the following conclusions on the characteristics of highly dispersed group VIII metals of the periodic system deposited in low concentrations on aluminum oxide, silica gel, or activated carbon ... 

Cyclic Hydrocarbons. Hajjar et al, ° studied the low-pressure compressibility of cyclohexane at various temperatures between 43 and 200 °C. The derived values of are appreciably more negative at lower temperatures than selected values. ... 

Polymerization of raw feedstock. Aliphatic hydrocarbon resins. Raw feedstock contains straight-chain and cyclic molecules and mono- and diolefins. The most common initiator in the polymerization reaction is AICI3/HCI in xylene. The resinification consists of a two-stage polymerization in a reactor at 45°C and high pressure (10 MPa) for several hours. The resulting solution is treated with water and passed to distillation to obtain the aliphatic hydrocarbon resins. Several aliphatic hydrocarbon resins with different softening points can be adjusted. 

C complexes, 32 185-186 CFjHCFjH, 39 340 chemisorption complexes, 32 170-172 CjH, enthalpies, 37 141, 143 "C-labeling studies, 25 166-172 commercial, 6 197 complex molecules, 30 58-72 medium-sized rings, 30 68-72 polymethylcycloalkanes, 30 59-65 substituted aromatics, 30 65-68 cyclic-acyclic product ratio, 30 8-9 cycloalkanes, 30 68-69 function, hydrogen pressure, 30 12, 15-16 hydrocarbon reaction models, 32 202-205 hydrogenolysis and, 23 93, 103 interconversion, 30 81-82 isopentane, 30 17 label scrambling, 30 7, 12-13 mechanism, 30 5-16 bifunctional, 30 4 catalyst particle size and, 30 72-85 concerted, 30 20... 

The contribution of the various classes of hydrocarbons to the formation of particulate organic compounds is a complex function of their relative ambient concentrations, gas-phase reactivity, and ability to form products whose physical properties, especially vapor pressures, are of prime importance in the physical mechanisms controlling the gas-to-aerosol conversion process. In view of the results discussed previously, cyclic olefins appear to be the most important class of organic aerosol precursors. This is due to their high gas-phase reactivity and their ability... 

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