Acetylene-benzene conversion

Industrially, chlorine is obtained as a by-product in the electrolytic conversion of salt to sodium hydroxide. Hazardous reactions have occuned between chlorine and a variety of chemicals including acetylene, alcohols, aluminium, ammonia, benzene, carbon disulphide, diethyl ether, diethyl zinc, fluorine, hydrocarbons, hydrogen, ferric chloride, metal hydrides, non-metals such as boron and phosphorus, rubber, and steel. 

In the case of palladium particles supported on magnesium oxide, Heiz and his colleagues have shown,29 in an elegant study, a correlation between the number of palladium atoms in a cluster and the selectivity for the conversion of acetylene to benzene, butadiene and butane, whereas in the industrially significant area of catalytic hydrodesulfurisation, the Aarhus group,33 with support from theory, have pinpointed by STM metallic edge states as the active sites in the MoS2 catalysts. 

The points for Ag and Pd-Ag alloys lie on the same straight line, a compensation effect, but the pure Pd point lies above the Pd-Ag line. In fact, the point for pure Pd lies on the line for Pd-Rh alloys, whereas the other pure metal in this series, i.e., rhodium is anomalous, falling well below the Pd-Rh line. Examination of the many compensation effect plots given in Bond s Catalysis by Metals (155) shows that often one or other of the pure metals in a series of catalysts consisting of two metals and their alloys falls off the plot. Examples include CO oxidation and formic acid decomposition over Pd-Au catalysts, parahydrogen conversion (Pt-Cu) and the hydrogenation of acetylene (Cu-Ni, Co-Ni), ethylene (Pt-Cu), and benzene (Cu-Ni). In some cases, where alloy catalysts containing only a small addition of the second component have been studied, then such catalysts are also found to be anomalous, like the pure metal which they approximate in composition. 

Formation of cuprene is either by a free-radical chain reaction or by clustering around the parent ion (cluster size 20) followed by neutralization, which is not a chain process. The M /N value for decomposition of acetylene is about 20, giving the corresponding G value as 70-80, which is very large. The G value of benzene production is 5, whereas the G of conversion of monomers into the polymer is 60. 

In addition to the Hopf cydization of 176, there is a second pericydic reaction leading to 162, that is, the dehydro Diels-Alder reaction of butenyne with acetylene (Scheme 6.47). The theoretical treatment of this process by Johnson et al. [59] predicted a free reaction enthalpy and a free activation enthalpy, both at 25 °C, of -13.4and 42.0kcalmol-1, respectively. Ananikov [116] arrived at a similar result for the intramolecular case of non-l-en-3,8-diyne (202) and calculated the same quantities to be -15.3 and 30.9 kcal mol-1 for the formation of the isoindane 203. As already discussed regarding Scheme 6.40, the conversion of 162 into benzene and likewise that of 203 into indane have to be considered as a sequence of two [1,2]-H shifts 116, 117], whose highest transition state has a significantly lower energy than that for the formation of 162 and 203 by the dehydro Diels-Alder reaction. 

In order to obtain maximum catalytic TON, pyridine yields, nitrile conversions, as well as high pyridine/benzene ratios in the product, more than 60 [YCoL] complexes were systematically investigated for the catalytic cotrimerization of propionitrile and acetylene [Eq.(9)J [85AG264, 85AG(E)248]. 

The cobalt-catalyzed synthesis enables 2,2 -dipyridyl to be prepared directly from 2-cyanopyridine and acetylene in a 72% yield with a cyanopy-ridine conversion of 21%. The pyridine benzene ratio in the product is 2.7 1 [Eq.(18)]. 

Reaction X. (6) Catalytic Conversion o Simple Hydrocarbons into more Complex Hydrocarbons.—These reactions are usually accomplished at high temperatures in presence of catalysts. Acetylene, propylene and even methane can be converted into benzene. (E.P., 374,422 369,351 366,394.)... 

The photocycloaddition of cyclooctyne to benzene [72], producing bicy-clo[6.6.0]tetradeca-l,3,5,7-tetraene can be sensitized (with acetone) and quenched (with piperylene). The unsensitized reaction occurs with very high efficiency (56% yield at 66% conversion). Because transfer of triplet energy from acetone to benzene is improbable, the authors consider the possibility that the acetylene triplet may be the reactive species in the cycloaddition. 

Accordingly, a 0-1 molar solution of phthalic anhydride in benzene (100 ml.) was pyrolyzed at 690° under nitrogen at a steady rate of 30 ml/hr (Fields and Meyerson, 1965). The pyrolysis tube was Vycor, filled with Vycor beads contact time was 11 5 sec, which gave a 58% conversion of the phthalic anhydride. Acetylene was steadily evolved, along with carbon dioxide and carbon monoxide in a 1 1 ratio these were identified in the gas stream by mass-spectral analysis of samples taken at regular intervals. The benzene was distilled off and the products boiling over 180° (2 g) were analyzed by mass spectrometry on a Consolidated Model... 

Acetaldehyde decomposition, reaction pathway control, 14-15 Acetylene, continuous catalytic conversion over metal-modified shape-selective zeolite catalyst, 355-370 Acid-catalyzed shape selectivity in zeolites primary shape selectivity, 209-211 secondary shape selectivity, 211-213 Acid molecular sieves, reactions of m-diisopropylbenzene, 222-230 Activation of C-H, C-C, and C-0 bonds of oxygenates on Rh(l 11) bond-activation sequences, 350-353 divergence of alcohol and aldehyde decarbonylation pathways, 347-351 experimental procedure, 347 Additives, selectivity, 7,8r Adsorption of benzene on NaX and NaY zeolites, homogeneous, See Homogeneous adsorption of benzene on NaX and NaY zeolites... 

The first alkynyliodonium salt, (phenylethynyl)phenyliodonium chloride, synthesized in low yields from (dichloroiodo)benzene (3) and lithium phenylacetylide (equation 1), was reported in 196526. This chloride salt is unstable and readily decomposes to a 1 1 mixture of chloro(phenyl)acetylene and iodobenzene. It was not until the 1980s, however, that alkynyliodonium salts became generally available. This was made possible by the introduction of sulfonyloxy-/l3-iodanes as synthetic reagents46 and by the recognition that iodosylbenzene (4) can be activated either with boron trifluoride etherate or with triethy-loxonium tetrafluoroborate31. These reagents are now widely employed for the conversion of terminal alkynes and their 1-silyl and 1-stannyl derivatives to alkynyliodonium salts (equations 2 and 3). A more exhaustive survey of iodine(III) reagents that have been... 

The interaction between benzene or cyclohexadienes and activated silica forms acetylene as an intermediate. Its catalytic hydrogenation will be examined first. Figure 16 shows the conversion of the first dose (curves A) of acetylene (50 cm3) at 200°C (181). Ethylene and ethane are formed simultaneously. 

The spiltover hydrogen can simply be added to benzene (forming cyclohexane and cyclohexene) in a noncatalytic reaction which exhausts entirely this hydrogen species, as shown below. Also, in order to have a clearcut picture, the reaction of benzene is carried out after evacuation of silica, which has been activated. The evacuation desorbs the spiltover hydrogen. Figure 17 shows the conversion at 170°C of benzene (8 cm3) with hydrogen (1000 cm3) into ethane and initially into acetylene (182). 

Sometimes the metallic catalyst exerts a more or less powerful tendency to break down the molecule, hydrogen being added not only to the initial substance, but also to its fission-products. Examples are the conversion of benzene at 300° C. into methane of acetylene at 200° C. into a liquid resembling American petroleum, above red heat into one like Caucasian petroleum, and at red heat into a product similar to a mixture of the two varieties. 

Thermal reactions of acetylene, butadiene, and benzene result in the production of coke, liquid products, and various gaseous products at temperatures varying from 4500 to 800°C. The relative ratios of these products and the conversions of the feed hydrocarbon were significantly affected in many cases by the materials of construction and by the past history of the tubular reactor used. Higher conversions of acetylene and benzene occurred in the Incoloy 800 reactor than in either the aluminized Incoloy 800 or the Vycor glass reactor. Butadiene conversions were similar in all reactors. The coke that formed on Incoloy 800 from acetylene catalyzed additional coke formation. Methods are suggested for decreasing the rates of coke production in commercial pyrolysis furnaces. 

Lighter hydrocarbons such as acetylene and 1,3-butadiene were metered at atmospheric pressure to the tubular reactors at a flowrate of about 30 mL/min. Benzene was introduced to the reactor in a mixture containing benzene and helium helium was bubbled through liquid benzene maintained at approximately 25 °C to produce a mixture containing about 12% benzene by volume. The flowrates of the inlet feed streams were such that the residence times of the hydrocarbons in the heated section of the tubular reactors varied from about 25 to 30 sec. The variations of residence times were caused primarily by the differences in the temperature levels used in the reactor and by the variations in the conversions. 

Copper sulfate, CuS04 5H20, is used for the oxidative coupling of terminal acetylenes [5S] for the conversion of a-hydroxy ketones (acyloins) into a-diketones [351, 352] and, in cooperation with potassium peroxy-disulfate, for the selective oxidation of methyl groups on benzene rings to aldehyde groups [355],... 

A CaC03 supported Pd-Pb alloy catalyst was found to be more selective in alkyne hydrogenation than the Lindlar catalyst.23 Styrene was produced in over 95% selectivity by the hydrogenation of phenyl acetylene over this catalyst (Eqn. 16.12). Further hydrogenation to ethyl benzene was significantly less than that observed using Lindlar s catalyst. The Z (cis) alkene was formed in >99% selectivity at 100% conversion in the hydrogenation of 11-hexadecynyl acetate Eqn. 16,13).23... 

This direct conversion of acetylene to benzene C Hg) was first found to... 

Rucker TG, Logan MA, Muetterties EM, Somorjai GA (1986) Conversion of acetylene to benzene over palladium single-crystal surfaces. 1. The low-pressure stoichiometric and the high-pressure catalytic reactions. J Phys Chem 90 2703... 

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