Acids Isomerism

Heating with cuprous chloride in aqueous hydrochloric acid isomerizes 2-butene-l,4-diol to 3-butene-l,2-diol (98)] Various hydrogen-transfer catalysts isomerize it to 4-hydroxybutyraldehyde [25714-71-0] (99), acetals of which are found as impurities in commercial butanediol and... 

Maleic and fiimaric acids have physical properties that differ due to the cis and trans configurations about the double bond. Aqueous dissociation constants and solubiUties of the two acids show variations attributable to geometric isomer effects. X-ray diffraction results for maleic acid (16) reveal an intramolecular hydrogen bond that accounts for both the ease of removal of the first carboxyl proton and the smaller dissociation constant for maleic acid compared to fumaric acid. Maleic acid isomerizes to fumaric acid with a derived heat of isomerization of —22.7 kJ/mol (—5.43 kcal/mol) (10). The activation energy for the conversion of maleic to fumaric acid is 66.1 kJ/mol (15.8 kcal/mol) (24). 

Hydration and Dehydration. Maleic anhydride is hydrolyzed to maleic acid with water at room temperature (68). Fumaric acid is obtained if the hydrolysis is performed at higher temperatures. Catalysts enhance formation of fumaric acid from maleic anhydride hydrolysis through maleic acid isomerization. 

Analogously, tnflic acid isomerizes n-butane into 2 methylpropane [80, 81] Interestingly, perfluorobutanesulfonic acid, which is of similar strength as tnflic acid, does not catalyze the isomerization of n-butane [50]... 

The anhydride (35) with water gave an acid isomeric with (36), and complete hydrogenation of both acids followed by esterification gave the same compound (37). Four moles of hydrogen were absorbed and the benzyl group was split off. Only three moles of hydrogen... 

Azcpincs under acid conditions reportedly117-225 yield aniline derivatives although ring contraction to pyridines is more usual. Thus, highly substituted 3//-azepines, e.g. 28, with a vacant 7-position, formed by cycloaddition of 2//-azirines with cyclopentadienones, on heating in acetic acid isomerize rapidly to the correspondingly substituted anilines 29.117... 

A non-acidic isomerization catalyst system has unexpectedly emerged from recent studies by French workers [4] in the area of Mo-oxycarbides. Although at an early stage of development, these new materials exhibit high selectivities for the isomerization of paraffins such as n-heptane. An alternative non-carbenium ion mechanistic route to achieve isomerization of higher alkanes could potentially overcome some of the limitations of conventional solid acid based catalyst systems. 

Finally, a third route considers the possibility of removing the steric hindrance prior to desulfurization by including an acid (isomerizing/dealkylating) function on the catalyst so that the bulky substituents can be moved to a different, less harmless, position related to the S atom site. 

In the HTFT oil refinery the light oil and <345°C fraction of the decanted oil (obtained by passing the decanted oil through a vacuum flash drum) were clay treated. Clay treatment is similar to Bauxite treatment and is used to increase the octane number of the naphtha by acidic isomerization and to reduce the oxygenate content of the oil. Processing the LTFT and HTFT in separate (and different)... 

Acidic isomerization of the C5-C6 naphtha and some heavy alcohols from the aqueous product refinery (not shown in Figure 18.5) produced a reasonable-quality olefinic motor gasoline (Table 18.10). The octane value varied depending on the carbon number distribution of the feed, which could result in a product with an octane number up to ten units higher. 

Oxygenate refining was limited to chemicals recovery from the Fischer-Tropsch aqueous product and acidic isomerization of the C5-C6 naphtha. The naphtha and distillate range oxygenates were removed by hydrodeoxygenation (HDO) in hydrotreaters, before further refining. 

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. 

Under the same conditions, but at elevated temperatures, the C-2 -center is very likely to be inverted (aci-inversion) yielding a more acidic isomeric compound. 

Ethynylcycloheptatriene 195 when treated with acid isomerizes to phenylallene 26 [612] (Scheme 1.88). 

The catalytic homogeneous isomerization of olefins by protonic acids as well as by Lewis acids is well-known and there is little doubt that such isomerizations proceed through carbonium ion transition states or intermediates. Thus, strong acids isomerize 1-hexene to all possible hexene isomers, including cis and trans isomers where these are possible. The isomerization to 2-hexene may be written as a proton addition-elimination ... 

The submitters find phosphoric acid more convenient than boric acid or acetic acid. Acid isomerization to abietic acid did not occur under the conditions used here. 

Oxadiazole to furazan transformations are not limited to the oximes of keto substituents amidoximes and hydrazidoximes <92KGS969> also rearrange readily. For example, Z)-N,N,-6is-ubstituted amidoximes of l,2,4-oxadiazole-3-carboxylic acids on treatment with acid isomerize even at room temperature to the thermodynamically more stable (F)-isomers, which then rearrange to diaminofurazans <91KGS822>. 

Irradiation of 413 leads in high yield to 414 as the sole product. When heated in benzene solution containing / toluenesulfonic acid, isomerization to triquinane ketone 415 results... 

Two improvements have been introduced by the method described above (1) the abietic acid content of the rosin is increased by acid isomerization, and (2) a much better recovery of acid is obtained by applying the amine salt technique directly to the isomerized rosin, thus eliminating the step involving the acid sodium salt. 

They also reported the sensitized photoisomerization of the cis[10.10] precursor 73 to a 50 50 mixture of (Z) and ( ) isomers, and this mixture was said to be converted to virtually pure ( )[10.10] isomer on acid treatment. They attributed this facile isomerization to the thermodynamical stability of the ( ) isomers over the (Z) isomers. However, their third short communication 55c) showed that the course of this acidic isomerization had not followed the route reported in their preceding paper. 

Expecting that acidic isomerization involving a double Wagner-Meerwein rearrangement would transform the bicyclic olefin 74 into supposedly stable [10.10]betweena-nene and its (Z)[10.10] isomer, they treated 74 with H2S04-AcOH in benzene only to find that the product was an 85 15 mixture of 75 and 76. Solvolysis of the spiro compound 77 was also found to yield a 60 40 mixture of 75 and 76 which was totally free from the fused (Z)[10.10] and ( )[10.10] olefins. 

These unexpected findings prompted them to re-examine the acidic isomerization of the (Z)[10.10] precursor 73, and what they found was that the isomerization product was the fused trisubstituted olefin 78 instead of the previously reported [10.10]... 

Although these findings had seemed to resolve the conflicting situations, Nickon and coworker 57) reported an interesting ring-size effect directing the course of this acidic isomerization. 

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