The Cyclic Hydrocarbons

Organic compounds are generally good insulators, and metals conduct electricity. However researchers have been successful in making organic compounds that are conductors. Acetylene can be polymerized in the presence of a catalyst to polyacetylene, a typical plastic that does not conduct electricity. 

This polymer appears as a black powder in the usual laboratory preparation and received little attention prior to 1970. In that year, a Korean university student, having trouble understanding his Japanese instructor, Hideki Shirakawa, prepared the polymer using an excessive amount of the catalyst. 

The result was a silver film that looked more like a metal than anything else. Furthermore, the polyacetylene film conducted electricity, which was a first for plastic materials. 

About the same time, Alan Mac-Diarmid at the University of Pennsylvania was working with an inorganic polymer of sulfur nitride (SN)jj that also looked like a metal and raised questions about the conductivity of polymers, MacDiarmid and Shirakawa met by chance at a seminar in Tokyo, and a collaboration was begun. Because Shirakawa knew that the optical properties of a polymer change on oxidation, they oxidized polyacetylene with iodine vapor. The product was raws-polyacetylene in which some electrons from the double bond had transferred to the iodine (to give I3). The result was that elec- 

In recognition of the significance of their work. Professors Shirakawa, MacDiarmid, and another collaborator, Alan J. Heeger of the University of California at Berkeley, received the Nobel Prize in chemistry in 2000. 

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Cyclic Hydrocarbons. The cyclic hydrocarbon intermediates are derived principally from petroleum and natural gas, though small amounts are derived from coal. Most cycHc intermediates are used in the manufacture of more advanced synthetic organic chemicals and finished products such as dyes, medicinal chemicals, elastomers, pesticides, and plastics and resins. Table 6 details the production and sales of cycHc intermediates in 1991. Benzene (qv) is the largest volume aromatic compound used in the chemical industry. It is extracted from catalytic reformates in refineries, and is produced by the dealkylation of toluene (qv) (see also BTX Processing). 

Omission of the hydroxyl group and one of the cyclic hydrocarbons from the acid moiety is apparently not inconsistent with biological activity. Thus, the ester from 2-phenylbutyryl chloride and diethyl-aminoethoxyethanol, butamirate (71), shows anti-spasmodic activity. In analogous fashion, reaction of the acid chloride from 72 with N-methyl-4-... 

Aromatic molecule a molecule based on the cyclic hydrocarbon benzene. 

The pattern of activity of the metals for the exchange of other hydrocarbons appears to be similar to that established for the exchange of ethane. For the exchange of methane (Table V), nickel behaves like palladium, but for the exchange of the cyclic hydrocarbons (Table X), nickel exhibits activity similar to that of rhodium. 

Interestingly, the related lithium derivative 1 -butyl-1-diphenylmethylcyclopropane, obtained by carbometallation of diphenylmethylenecyclopropane with BuLi, is stable and gives the cyclic hydrocarbon upon hydrolysis (equation 40)90. On the other hand, a-phenyl styrene reacts similarly with BuLi to give only ring-cleavage products. 

The activation energy t for the cyclic hydrocarbons on Ni—AI2O3 are practically independent of the number of methyl side groups (Nos. 1-3). For amines on Ni and Pd (Nos. 23-39) the are also quite constant. 

Certain cyclic ketones have been formed in this way, and from them, the cyclic hydrocarbons. 

The cyclic hydrocarbons, such as cyclohexane, act much in the same manner as the aliphatic hydrocarbons. A significant percentage of quantity inhaled may be metabolized to compounds with a lower order of toxicity. The unsaturated cyclic hydrocarbons generally are more irritating than the saturated forms. 

Cyclic Hydrocarbons. Some of the cyclic hydrocarbons found in the CHX coal extracts are shown in Table V. They were tentatively identified by capillary GC/MS except for the naphthalenes, for which authentic standards were available. Selected ion profiles were used to detect sesquiterpenes (m/e 206, 191), sesquiterpanes (m/e 208), o alkanes (m/e 141), alkyl benzenes (m/e 191, 163), steranes (m/e 217),... 

Hydrocarbons. The hydrocarbons, as the name implies, are compounds containing carbon and hydrogen. If the carbon atoms lie in the same plane they are known as open-chain, or aliphatic hydrocarbons. If the carbon atoms form a ring structure they are known as cyclic hydrocarbons. The cyclic hydrocarbons are further differentiated into benzene benzenoid, or aromatic) and alicydic hydrocarbons. If there is another element present in the ring besides carbon, they are known as heterocyclic hydrocarbons. 

Introduction. The action of halogens on saturated open chain hydrocarbons, as for example, pentane or hexane, gives several monohaJogen derivatives. Since the separation of the isomeric monohalides is difficult in the laboratory, they are usually prepared from alcohols. Direct halogenation is used industrially. The cyclic hydrocarbons, such as cyclohexane and benzene, jdeld only one monohalide. The present experiment illustrates direct bromination of a hydrocarbon. Chlorination is more difficult it is described in the latter part of the text (page 229). The catalyst used for bromination is iron other substances which can be used for the same purpose are anhydrous aluminum chloride and pyridine. 

The cyclic hydrocarbons all have the positive properties of the alkanes with regard to thermal and chemical stability as well as good environmental properties. In addition, they have a higher octane number in comparison to alkanes. 

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. 

Table 4 Diffusion coefficients of the cyclic hydrocarbons in sUicalite-l measured by the FR method ...

To produce more reliable predictions of aromaticity, Hess and Schaad (following a suggestion of Dewar) calculated delocalization (resonance) energies of cyclic hydrocarbons by comparing the compounds Htickel-theory with a value calculated for a hypothetical acyclic conjugated polyene with the same number and kinds of bonds as in a localized structure of the cyclic hydrocarbon. [B. A. Hess and L. J. Schaad, J. Am. Chem. Soc., 93, 305, 2413 (1971) 94, 3068 (1972) 95, 3907 (1973) B. A. Hess, L. J. Schaad, and C. W. Holyoke, Tetrahedron, 28, 3657, 5299 (1972) Schaad and Hess,... 

Azeotropic distillation. A further development involves the addition of an entrainer, either another solvent or water, to the mixture of liquids to be separated. The purpose of this material is to form a selected azeotrope with one of the components. This results in a difference in relative volatility between the azeotrope and the non-azeotropic component allowing separation to be achieved. Typically the azeotrope will be of higher volatility and becomes the distillate, although the azeotrope can be such that it is removed as bottoms. An effective entrainer therefore must be selective for the solvent to be recovered, stable under the conditions of use, chemically compatible with all components, relatively inexpensive, readily available and must be easily separable from the desired product. Water is an ideal entrainer when used to form azeotropes with solvents which separate on condensation. Guidelines for entrainer selection have been provided by Berg and Gerster [28,29]. Many examples of azeotropic distillation can be cited [23]. Examples include the separation of benzene from cyclohexane by the azeotrope of the latter with acetone followed by liquid-liquid extraction with water to yield the cyclic hydrocarbon. Similarly the use of methylene chloride as an entrainer for separation of an azeotropic mixture of methanol and acetone is achieved by addition of methylene chloride followed by the distillation of the selective azeotrope between the alcohol and chlorinated hydrocarbon. 

The main products of this process are benzene, cyclohexane, and cyclohexane. The benzene was formed by direct hydrogenolysis from phenol, while the cyclic hydrocarbons were formed by hydrogenation of phenol via the intermediate cyclohexanol and cyclohexanone. 

The cyclic hydrocarbons, reported to be minor components of plant waxes (Kuksis, 1964 Mold et al., 1%6) could also be generated by elongation of the appropriate fatty acids followed by decarboxylation. The cyclic acids may originate by cyclization of a dicarboxylic acid derivative (Stumpf, 1%3) or from shikimic acid, as suggested for the biosynthesis of w-cyclo-hexyl fatty acids (De Rosaer al., 1972 Oshima and Ariga, 1975). The reader... 

The use of ROMP has been widely applied. Thus, cyclopentene can be polymerized by olefin metathesis to a linear pol5mier. In this reaction the cyclic hydrocarbon is opened up by the catalyst and joined together in a linear fashion (see Eq. 2.34). The catalysts that perform this operation are called ring-opening metathesis catalysts. 

The best known example of resonance in organic chemistry concerns the cyclic hydrocarbon benzene, CgHg, which can be described by two major resonance structures called Kekul structures (Figure 14.52). 

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