Isomerism/isomerization

Isomerization. Isomerization is a catalytic process which converts normal paraffins to isoparaffins. The feed is usually light virgin naphtha and the catalyst platinum on an alumina or zeoflte base. Octanes may be increased by over 30 numbers when normal pentane and normal hexane are isomerized. Another beneficial reaction that occurs is that any benzene in the feed is converted to cyclohexane. Although isomerization produces high quahty blendstocks, it is also used to produce feeds for alkylation and etherification processes. Normal butane, which is generally in excess in the refinery slate because of RVP concerns, can be isomerized and then converted to alkylate or to methyl tert-huty ether (MTBE) with a small increase in octane and a large decrease in RVP. 

Isomerization. Isomerization of any of the butylene isomers to increase supply of another isomer is not practiced commercially. However, their isomerization has been studied extensively because formation and isomerization accompany many refinery processes maximization of 2-butene content maximizes octane number when isobutane is alkylated with butene streams using HF as catalyst and isomerization of high concentrations of 1-butene to 2-butene in mixtures with isobutylene could simplify subsequent separations (22). One plant (Phillips) is now being operated for this latter purpose (23,24). The general topic of isomerization has been covered in detail (25—27). Isomer distribution at thermodynamic equiUbrium in the range 300—1000 Kis summarized in Table 4 (25). 

Isomerization. Isomerization of low octane and / -paraffins in gasoline streams into higher octane branched isomers is an important... 

Examples of first-order reversible reaetions are gas phase eis-trans isomerization, isomerizations in various types of hydroearbon systems, and the raeemization of a and (3 glueoses. An example of a eatalytie reaetion is the ortho-para hydrogen eonversion on a niekel eatalyst. 

Isomerization of ( /Z) isomers is another important transformation. Isomerization of ( ) and (Z-) conjugated amides is effected photochemically " (photo-isomerization " ). There is a rather high energy barrier for the excited state required for (E/Z) isomerization. Isomerization of the C=C units in dienes is also induced photochemically. " Isomerization of cyclic alkenes is more difficult but cyclooctene is isomerized photochemically. " Conjugated aldehydes have been isomerized... 

Having a weak O—O bond, peroxides split easily into free radicals. In addition to homolytic reactions, peroxides can participate in heterolytic reactions also, for example, they can undergo hydrolysis under the catalytic action of acids. Both homolytic and heterolytic reactions can occur simultaneously. For example, perbenzoates decompose into free radicals and simultaneously isomerize to ester [11]. The para-substituent slightly influences the rate constants of homolytic splitting of perester. The rate constant of heterolytic isomerization, by contrast, strongly depends on the nature of the para-substituent. Polar solvent accelerates the heterolytic isomerization. Isomerization reaction was proposed to proceed through the cyclic transition state [11]. 

Ethylbenzene Isomerization Isomerization of EB requires both metal and acid function. Hydrogenation results in an intermediate naphthene. The acid function is required to isomerize the naphthene to a methyl-ethyl-substituted five-mem-bered ring species that can further convert to a dimethyl-substituted six-membered ring naphthene. This can be dehydrogenated by the metal function to a xylene isomer, OX in the example shown in Figure 14.9. 

ENZYME COMMISSION NOMENCLATURE ISOMERIZATION Isomerization mechanisms,... 

Isomerization A refinery process used to produce branched compounds from straight-chain molecules. Butane, pentane, and hexane are isomerized to branched, higher-octane compounds through isomerization. Isomerization reactions are catalyzed through the use of aluminum chloride and other metal catalysts. 

Ammino-derivatives op Cobalt Salts—Cobaltous Salt Ammines—Cobaltic Salt Ammines—Mononuclear Cobalt-ammines containing One Atom of Cobalt in the Molecule—Cobaltic Salts with Trivalent Cation—Cobalt-ammines Containing Divalent Cation—Cobalt-ammines containing Monovalent Cation—Cobalt-ammines consisting of Non-dissociable Complex— Cobalt-ammines containing Monovalent Anion—Cobalt Salts containing Trivalent Anion—Polynuclear Cobalt-ammines containing Two or more Cobalt Atoms in the Molecule—Cobalt-ammines of Unknown Constitution— Ionisation Metamerism—Polymerisation Isomerism—Valency Isomerism —Co-ordination Position Isomerism—Isomerism due to Asymmetric Cobalt Atoms. 

Pentane Isomerization—Isomerization of n-C5 appears to be the most attractive for the C4-C7 paraffins. By recycling n-C5 the unleaded RON... 

Coordination isomerism isomerism in a coordination compound in which the composition of the coordination sphere of the metal ion varies. (20.4)... 

Geometrical (cis-trans) isomerism isomerism in which atoms or groups of atoms can assume different positions around a rigid ring or bond. (20.4 22.2)... 

Linkage isomerism isomerism involving a complex ion where the ligands are all the same but the point of attachment of at least one of the ligands differs. (20.4)... 

Octet rule the observation that atoms of nonmetals tend to form the most stable molecules when they are surrounded by eight electrons (to fill their valence orbitals). (13.10) Optical isomerism isomerism in which the isomers have opposite effects on plane-polarized light. (20.4)... 

Structural isomerism isomerism in which the isomers contain the same atoms but one or more bonds differ. (20.4 22.1) Subcritical reaction (nuclear) a reaction in which less than one neutron causes another fission event and the process dies out. (21.6)... 

Isomerism.—Isomerism in the case of the acids is of the same character as that of the alkyl halides and the alcohols if we consider the acids as mono-carboxyl substitution products of the hydrocarbons. In the five carbon acids, the pentanoic or valeric acids, we have one compound which possesses an asymmetric carbon atom. It is the 2-methyl butanoic-i acid. According to the van t Hofif-LeBel theory this compound should exist in three forms, dextro lew and inactive. By oxidation of the fermentation amyl alcohol which is a mixture of 2-methyl butanol-1 and 2-methyl butanol-4 there is obtained a mixture of two of the valeric acids, viz., the 2-methyl butanoic-i acid and the 2-methyl butanoic-4. This same mixture is found naturally in the roots of Valeriana officinalis. By separating out the 2-methyl butanoic-4 acid the 2-methyl butanoic-1 acid is obtained. This acid is inactive, but has nevery with certaintyy been separated into its optical components, though it is claimed that a dextro form has been obtained. 

Isomerism.—Isomerism in the esters may be due to several causes analogous to those given in the case of the ethers and the ketones. 

Because the rate of alkene hydrogenation generally decreases as the number and size of the substituents on the double bond increase, the least hindered double bond should be hydrogenated preferentially in the competitive hydrogenation of olefin mixtures. This selectivity, however, is not always observed either because of diffusion constraints or the presence of concurrent double-bond isomerization. Isomerization modifies the olefin structure, which changes the alkene reactivity and makes reaction selectivity difficult to attain. 

Thermally Neutral (Isomerization). Isomerization, represented by the vertical line in the diagram, involves skeletal rearrangement of molecules but no change in the molecular weight. Thus, the reaction does not cause any cooling or heating of the feed stream. 

Isomerization Isomerization of safrole to isosafrole, of 2,3-dimethyl-1-butene and of 3,5-vinylbicyclo[2.2.1]heptene Isomerization of 1,2-propadiene to propyne Na/NaOH/AljO, K2O/AI2O3... 

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