Hydrocarbons cyclopentane

C5 Cyclization of various alkanes 38, 38a) over platinum on carbon was first observed in 1954. Barron et al. 15a) postulated the formation of a surface C5 cyclic intermediate, which may desorb as a cyclopentanic hydrocarbon or may produce skeletal isomers without desorption. 

The first examples of skeletal rearrangements on metals were reported by the Soviet school of catalysis. A major step in hydrocarbon chemistry was the finding that platinum, unlike palladium and nickel, selectively catalyzes the hydrogenolysis of cyclopentane hydrocarbons. At about 300°C, on the classical Zelinskii platinum-charcoal catalyst, cyclopentane yields -pentane as sole reaction product (3, 4), while palladized charcoal is completely inactive (J) and nickel-alumina produces all the possible acyclic hydrocarbons, from methane to pentane (5-7). 

Cyclopentane Hydrocarbon canister, supplied air or hose mask rubber or plastic gloves chemical goggles or face shield. Remove to fresh air if breathing stops, apply artificial respiration and administer oxygen. Flush well with water, then wash with soap and water. Flush with water for at least 15 minutes call a physician. 

When dehydrogenation was carried out in a stream of hydrogen at 325°C, the yield of aromatic hydrocarbons formed in the dehydrogenation of cyclohexane and cyclohexene derivatives was 87—99%. As a result of side-reactions an insignificant amount of dealkylation products (benzene, toluene) was also formed. Decalin was most difficult to dehydrogenate, and in this instance, together with naphthalene, tetralin was also formed. Under these conditions isomerization of cyclopentane derivatives into cyclohexane hydrocarbons did not take place, and aromatic hydrocarbons were not formed from cyclopentane hydrocarbons. The process, however, was complicated by hydrocracking reactions. 

Hydrocarbons, compounds of carbon and hydrogen, are stmcturally classified as aromatic and aliphatic the latter includes alkanes (paraffins), alkenes (olefins), alkynes (acetylenes), and cycloparaffins. An example of a low molecular weight paraffin is methane [74-82-8], of an olefin, ethylene [74-85-1], of a cycloparaffin, cyclopentane [287-92-3], and of an aromatic, benzene [71-43-2]. Cmde petroleum oils [8002-05-9], which span a range of molecular weights of these compounds, excluding the very reactive olefins, have been classified according to their content as paraffinic, cycloparaffinic (naphthenic), or aromatic. The hydrocarbon class of terpenes is not discussed here. Terpenes, such as turpentine [8006-64-2] are found widely distributed in plants, and consist of repeating isoprene [78-79-5] units (see Isoprene Terpenoids). 

The term naphthenic acid, as commonly used in the petroleum industry, refers collectively to all of the carboxyUc acids present in cmde oil. Naphthenic acids [1338-24-5] are classified as monobasic carboxyUc acids of the general formula RCOOH, where R represents the naphthene moiety consisting of cyclopentane and cyclohexane derivatives. Naphthenic acids are composed predorninandy of aLkyl-substituted cycloaUphatic carboxyUc acids, with smaller amounts of acycHc aUphatic (paraffinic or fatty) acids. Aromatic, olefinic, hydroxy, and dibasic acids are considered to be minor components. Commercial naphthenic acids also contain varying amounts of unsaponifiable hydrocarbons, phenoHc compounds, sulfur compounds, and water. The complex mixture of acids is derived from straight-mn distillates of petroleum, mosdy from kerosene and diesel fractions (see Petroleum). 

Cycloparafficin Hydrocarbons Cyclopentane Methylcyclopentane Cyclopentane Methylcyclopentane... 

The use of radical cyclizations to make five-membered rings has become a very important tool for synthetic chemists Although there has been a virtual explosion of reports in the literature regarding the cyclization of 5-hexenyl radicals to cyclopentyl carbinyl radicals in all types of hydrocarbon systems [55], the use of this cyclization for the synthesis of fluorme-containing cyclopentanes has been largely ignored... 

Physical properties of cycloalkanes [49, p. 284 50, p. 31] show reasonably gradual changes, but unlike most homologous series, different members exhibit different degrees of chemical reactivity. For example, cyclohexane is the least reactive member in this family, whereas both cyclopropane and cyclobutane are more reactive than cyclopentane. Thus, hydrocarbons containing cyclopentane and cyclohexane rings are quite abundant in nature. 

Saturated cyclic hydrocarbons, normally known as naphthenes, are also part of the hydrocarbon constituents of crude oils. Their ratio, however, depends on the crude type. The lower members of naphthenes are cyclopentane, cyclohexane, and their mono-substituted compounds. They are normally present in the light and the heavy naphtha fractions. Cyclohexanes, substituted cyclopentanes, and substituted cyclohexanes are important precursors for aromatic hydrocarbons. 

Petroleum contains hydrocarbons other than the open-chain alkanes considered to this point. These include cycloalkanes in which 3 to 30 CH2 groups are bonded into closed rings. The structures of the two most common hydrocarbons of this type are shown in Figure 22.5 (p. 585). Cyclopentane and cyclohexane, where the bond angles are close to the ideal tetrahedral angle of 109.5°, are stable liquids with boiling points of 49°C and 81°C, respectively. 

Cycloalkane A saturated hydrocarbon containing a closed ring. General formula = C H2 , 584-585 Cyclopentane, 584 Cysteine, 622t... 

The chain and branched chain saturated hydrocarbons make up a family called the alkanes. Some saturated hydrocarbons with five carbon atoms are shown in Figure 18-11. The first example, containing no branches, is called normal-pentane or, briefly, n-pentane. The second example has a single branch at the end of the chain. Such a structural type is commonly identified by the prefix iso- . Hence this isomer is called /50-pentane. The third example in Figure 18-11 also contains five carbon atoms but it contains the distinctive feature of a cyclic carbon structure. Such a compound is identified by the prefix cyclo in its name—in the case shown, cyclopentane. 

As the number of carbon atoms increases, the number of possible isomers becomes larger. Whereas there are only two isomeric butanes, there are three isomeric pentanes. With hve carbons, in addition to the open-chain compounds shown, a stable ring compound known as cyclopentane is also possible. Five- and six-membered carbon rings are very stable because the bonds between carbon atoms in these size rings are close to the 109° angle preferred by carbon. Three- and four-membered hydrocarbon rings are also known, but they are less stable because of the required distortion of the bond angle. 

Likewise it is possible to differentiate between substituted and unsubstituted alicycles using inclusion formation with 47 and 48 only the unbranched hydrocarbons are accommodated into the crystal lattices of 47 and 48 (e.g. separation of cyclohexane from methylcyclohexane, or of cyclopentane from methylcyclopentane). This holds also for cycloalkenes (cf. cyclohexene/methylcyclohexene), but not for benzene and its derivatives. Yet, in the latter case no arbitrary number of substituents (methyl groups) and nor any position of the attached substituents at the aromatic nucleus is tolerated on inclusion formation with 46, 47, and 48, dependent on the host molecule (Tables 7 and 8). This opens interesting separation procedures for analytical purposes, for instance the distinction between benzene and toluene or in the field of the isomeric xylenes. 

Cyclopentane has the low chemical reactivity which is typical of saturated hydrocarbons, while 2-pentene is much more reactive. Similarly, ring structures containing double bonds, called cyclo-alkenes, can be shown to be isomeric with alkynes. 

Fig. 12.4. Vapor-to-water transfer data for saturated hydrocarbons as a function of accessible surface area, from [131]. Standard states are 1M ideal gas and solution phases. Linear alkanes (small dots) are labeled by the number of carbons. Cyclic compounds (large dots) are a = cyclooctane, b = cycloheptane, c = cyclopentane, d = cyclohexane, e = methylcyclopentane, f = methylcyclohexane, g = cA-l,2-dimethylcyclohexane. Branched compounds (circles) are h = isobutane, i = neopentane, j = isopentane, k = neohexane, 1 = isohexane, m = 3-methylpentane, n = 2,4-dimethylpentane, o = isooctane, p = 2,2,5-tri-metbylhexane. Adapted with permission from [74], Copyright 1994, American Chemical Society...

Figure 4b Summary of the reactions of rhenium atoms with cyclic saturated hydrocarbons. Rhenium atoms were co-condensed with the indicated substrates at -195°C (i) Cyclopropane (ii) cyclopentane (iii) cyclohexane.

In alicyclic hydrocarbon solvents with aromatic solutes, energy transfer (vide infra) is unimportant and probably all excited solute states are formed on neutralization of solute cations with solute anions, which are formed in the first place by charge migration and scavenging in competition with electron solvent-cation recombination. The yields of naphthalene singlet and triplet excited states at 10 mM concentration solution are comparable and increase in the order cyclopentane, cyclohexane, cyclooctane, and decalin as solvents. Further, the yields of these... 

As previously mentioned, Davis (8) has shown that in model dehydrocyclization reactions with a dual function catalyst and an n-octane feedstock, isomerization of the hydrocarbon to 2-and 3-methylheptane is faster than the dehydrocyclization reaction. Although competitive isomerization of an alkane feedstock is commonly observed in model studies using monofunctional (Pt) catalysts, some of the alkanes produced can be rationalized as products of the hydrogenolysis of substituted cyclopentanes, which in turn can be formed on platinum surfaces via free radical-like mechanisms. However, the 2- and 3-methylheptane isomers (out of a total of 18 possible C8Hi8 isomers) observed with dual function catalysts are those expected from the rearrangement of n-octane via carbocation intermediates. Such acid-catalyzed isomerizations are widely acknowledged to occur via a protonated cyclopropane structure (25, 28), in this case one derived from the 2-octyl cation, which can then be the precursor... 

Miscible in many hydrocarbons including cyclopentane, methylcyclopentane, cyclohexane, hexane, and 2-methylhexane. 

Reaction of linear conjugated dienes with la at —10 °C in hydrocarbon solvent in the presence of McsSiCl/AlCls affords stereospecific tra i-l-silyl-3-vinyl-cyclopentanes, indicating a [3 + 2] cycloaddition of the allyl group of la with a carbon arbon double bond of the diene [Eq. (9)]. In the [3 + 2] annulation reaction, of greater significance is the tram conformation of the trimethylsilyl group and vinyl groups. 

Highly enantioselective intermolecular C-H insertion into cyclohexane and cyclopentane is possible using the Rh2(S-DOSP)4 carbenoids generated from aryl diazoacetates 172 to form 173 (Eq. 21) [121, 130]. The enantioselectivity is enhanced when the reactions are conducted at lower temperatures, without any deleterious effect on the catalytic activity or product yield [130]. Extending the reaction to other cyclic and acyclic hydrocarbons has revealed a dehcate balance required between the steric environment and the electronic state of the carbon undergoing C-H insertion [130]. The decreasing enantioselectivity and yield of C-H insertion into adamantane 174 (67% yield, 90% ee). 

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