Isomerization byproduct reactions

An example of this type of reaction that does not produce a byproduct is isomerization (the reaction of a feed to a product with the same chemical formula but a different molecular structure). For example, allyl alcohol can be produced from propylene oxide5 ... 

One exception to the preservation of selectivity in microwave reactions was the C2 arylation of 2,3-dihydrofuran, which yielded an isomeric byproduct under the action of microwaves (2-phenyl-2,3-dihydrofuran/byproduct = 71/29), in contrast with the reported procedure using conventional heating (Eq. 11.4). The desired product could be isolated in 58% yield. Attempts to reduce the reaction time by using oil baths (125 °C or 150 °C) did not result in similar yields, but instead furnished complicated reaction mixtures, in definite contrast with the microwave procedure [17]. 

The analogous reaction with bromine was carried out in solution at — 78 °C and gave predominantly the cyclopropane derivative 3. Isomeric byproducts were the cyclobutane 4 and 3-bromo-2-(bromomethyl)propene (5, X = = Br) which were formed in 5-25% yield. ... 

Increasing the concentrations of CpCr(CO)3H and 1, or heating the reaction, shortens the reaction time but increases the extent of hydrogenation to 5. Increasing the hydrogen pressure increases the rate at which CpCr(CO)3 is converted to CpCr(CO)3H and thus increases (as we expect from Scheme 1.10) the ratio of the hydrogenation byproduct 5 to the isomerization byproduct 6. 

Auxiliaries (reaction) Substrates Byproducts Coupled products Loss of product Isomeric product(s)... 

In addition to separating product from catalyst, excess ligand and reaction solvent, one must also separate byproducts arising from the reactants or products. For example in hydroformylation, one must separate saturated hydrocarbon, isomerized alkene and aldehyde dimers and trimers. 

The free reaction is rather slow (pseudo-first-order rate constant k = 4.8 x 10 6s 1, t1/2 ca. 2 days) and produces a mixture of the four possible Diels-Alder adducts 103a—d along with the byproduct 104. Note that all acids isomerize under the basic reaction conditions to give the a,/i-unsaturated derivatives 105a—d. 

With this revision in our original plans, both alkenes and allenes were found to undergo efficient cycloadditions to produce cyclooctenone products in a new [6+2] cycloaddition process. This novel cycloaddition has been shown to proceed efficiently with alkenes tethered with sulfonamide, ether, or geminal diester Hnkers (Tab. 13.15, see page 294). Isomerization of the olefin, a potential competing reaction in this process, is not observed. Methyl substitution of either alkene in the substrate is well tolerated, resulting in the facile construction of quaternary centers. Of mechanistic importance, in some cases cycloheptene byproducts were isolated from [6+2] cycloaddition reactions in addition to the expected cyclooctenone products (that is, entries 3 and 4). 

It can be inferred from additional examples (Table 3) that the stereoselectivity and stereochemical outcome of the reaction strongly depend on the type of metal hydride and the leaving group. Furthermore, the reaction temperature is important in several cases67. The scope of the method is broad, however, varying amounts of isomeric alkyne isomers are formed as byproducts, sometimes accompanied by the corresponding alkenes. 

Byproducts include isomeric C4 and C5 hydrocarbons formed through C—C bond alkylation (alkylolysis). No 2,2-dimethylbutane, the main product of conventional acid-catalyzed alkylation, was detected, which is a clear indication of predominantly nonisomerizing reaction conditions. 

In an older version of the synthesis, propylene and chlorine react in an aqueous solution to form propylene chlorohydrin.192-194 The slightly exothermic reaction maintains the 30-40°C reaction temperature to yield isomeric propylene chlorohy-drins (l-chloro-2-propanol/2-chloro-1-propanol = 9 1). The main byproduct is 1,2-dichloropropane formed in amounts up to 10%. The product propylene chlorohydrin then undergoes saponification to propylene oxide with calcium hydroxide or sodium hydroxide. 

Hydrocarboxymethylation of Long-Chain Alkenes. An industrial process to carry out hydrocarboxymethylation of olefins to produce methyl esters particularly in the Ci2-Ci4 range for use as a surfactant feedstock was developed by Huels.183 A promoted cobalt catalyst in the form of fatty acid salts (preferably those formed in the reaction) is used. With high promoter catalyst ratio (5 1-15 1) at 180-190°C and pressure of 150-200 atm, the rate of alkene isomerization (double-bond migration) exceeds the rate of hydrocarboxymethylation. As a result, even internal olefins give linear products (the yield of normal products is about 75% at 50-80 % conversion). Secondary transformations of aldehydes (product of olefin hydro-formylation) lead to byproducts (ethers and esters) in small amounts. 

Laali et al.234 have developed a method to the highly selective pura-adamantylation of arenes (toluene, ethylbenzene, anisole) with haloadamantanes (1-chloro- and 1-bromoadamantane, l-bromo-3,5,7-trimethyladamantane) and 1-adamantanol promoted by triflic acid in butylmethylimidazolium triflate [BMIM][OTf] ionic liquid. In contrast to reactions mn in 1,2-dichloroethane, little or no adamantane byproduct was detected in [BMIM][OTf. Furthermore, no isomerization of para-tolyladamantane was observed supporting the intramolecular nature of the formation of meta isomers. In competitive experiments with benzene-toluene mixture (1 1 molar ratio), high substrate selectivities were found (kT/kB = 16-17) irrespective of the alkylating agent. This is in sharp contrast to values about unity measured in 1,2-dichloroethane. 

The metastable byproduct of [4+2] cycloaddition was detected when the reaction of cyclopentadiene with diphenylketene was (Equation (38)) was examined by low-temperature NMR experiment at — 30°C.67 The [4+2] cycloadduct was not observed at elevated temperature because easily isomerizes to [2+2] cycloaddition product via [3,3] sigmatropic (Claisen) rearrangement. This observation was supported by kinetic measurements NMR) and isolation of [4+2] cycloadduct.68 Mechanism proposed by Machiguchi and Yamabe was re-examined by Singleton.69... 

Catalytic Reforming A catalytic reaction of heavy naphtha(1) used to produce high-octane gasoline. The byproducts are hydrogen and light hydrocarbons the primary reaction is dehydrogenation of naphthenes to produce aromatics. Some reshaping of paraffins to produce aromatics and some isomerization of paraffins to produce isoparaffins also occur. 

Description Ethylene feedstream (plus recycle ethylene) and butenes feedstream (plus recycle butenes) are introduced into the fixed-bed, metathesis reactor. The catalyst promotes reaction of ethylene and 2-butene to form propylene and simultaneously isomerizes 1-butene to 2-butene. Effluent from the metathesis reactor is fractionated to yield high-purity, polymerization-grade propylene, as well as ethylene and butenes for recycle and small byproduct streams. Due to the unique nature of the catalyst system, the mixed C4 feed stream can contain a significant amount of isobutylene without impacting performance of the OCT process. A variation of OCT—Automet Technology—can be used to generate ethylene, propylene and the comonomer—hexene-1—by metathesis of n-butenes. 

Thus, good dispersion or mass transfer favors olefin isomerization (to isobutene), isobutene dimerization, and maximizes hydrogen transfer and primary alkylation reactions, i.e., yielding the greatest amount of high-octane-number trimethylpentanes, and minimizing low-octane-number byproducts from secondary reactions such os excess polymerization. 

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