Cyclohexanols isomerization

Higher alkanols, including the isomeric octyl alcohols (2-octanol and 2-ethylhexanol), cyclohexanol, lauryl and cetyl alcohols. Aliphatic alcohols have relatively poor foam control and have an odour that can be nauseous [536]. 

In the reactions of cis- and rrans-2-aminomethyl-l-cyclohexanol or -1-cycloheptanol or cis- and trans-2-hydroxymethyl-l-cyclohexylamine or -1-cycloheptylamine with ethyl 4-chlorobenzimidate, the stereo- and regio-isomeric derivatives and homologs 164 and 165 were prepared (79T799). The amidine intermediate 166 of the benzimidate ring closure was also... 

In chromic acid oxidation of isomeric cyclohexanols, it is usually found that axial hydroxyl groups react more rapidly than equatorial groups. For example, trans-4-t-butylcyclohexanol is less reactive (by a factor of 3.2) than the cis isomer. An even larger difference is noted with cis- and trans-3,3,5- trimethylcyclohexanol. The trans alcohol is more than 35 times more reactive than the cis. Are these data compatible with the mechanism given on p. 748 What additional detail do these data provide about the reaction mechanism Explain. 

Isomerization of oxepane (1) to cyclohexanol was found to occur in the presence of r-butyl hydroperoxide by a-cleavage of the oxepanyl radical intermediate (65) (76TL439). When a copper(I) chloride catalyst was present the major product was 2-(f-butyl-hydroperoxy)oxepane (77), probably also formed by a free radical pathway (Scheme 8) <80CR(291)223>. 

Cycloalkanes can be oxygenated when irradiated in the presence of nitrobenzene.196 A 50% yield of cyclohexanol and cyclohexanone is achieved from cyclohexane. Since the product ratio is independent of reaction time, the alcohol is not an intermediate in ketone formation. Isomeric 1,2-dimethylcyclohexanes give an identical mixture of the isomeric tertiary alcohols, indicative of conformational equilibration and the presence of a radical intermediate. 

The first tiiree types of isomerism are familiar and have been discussed previously. The conformational isomerism is very understandable if it is remembered tiiat axial and equatorial valences exchange upon chair-chair interconversion. For example, to draw die trans isomer of 3-metiiylcyclohexanol, one of the groups must be equatorial and die otiier axial. The otiier chair form must have die groups in opposite valences. Similarly frans-2-metiiyl-cyclohexanol has both groups equatorial in one chair form. The otiier chair form must therefore have both groups axial. 

Isomerization during hydrogenation may alter the functional groups present in the molecule. For instance, reduction of cyclohexen-2-ol over 5% platinum-on-carbon occurred with rapid absorption of 1 mole of hydrogen at substantially constant rate and quantitative formation of cyclohexanol. On the other hand, reduction over palladium ceased abruptly at about two-thirds of a mole, and the product was a mixture of cyclohexanol and cyclohexanone, the latter arising through double bond migration to the enol of cyclohexanone (29). 

Ethynyl caibinols on heating with formic acid are isomerized to olefinic ketones for example, isohexylmethylethynylcarbinol is taken to 3,7-dimethyl-3-octen-2-one (48%) and 1-ethynyl-1-cyclohexanol to 1-acety 1-1-cyclohexene (70%). Small amounts of unsaturated aldehydes may contaminate the product. 

Several factors such as the structure of the substrate, the catalyst, the solvent, the reaction temperature, the pressure of hydrogen and other reaction conditions determine the stereochemistry of the catalytic hydrogenation of cyclic ketones, and it is sometimes difficult to predict the major pn uct of catalytic hydrogenation. One reason for the complexity of the stereochemistry of the hydrogenation of cyclic ketones, at least in part, is related to the isomerization of the products under the reaction conditions. Some cyclohexanols were isomerized in the presence of platinum or nickel catalysts at room temperature or at higher temperature under a hydrogen atmosphere, and the isomerization reached a cis-trans equili-brium. For example, rranj-3,3,5-trimethylcyclohexanol isomerized in the presence of a nickel catalyst. 

The conversion of cyclohexanol on acid sites in zeolites and boralites is composed of two steps dehydration (to cyclohexene and water) and consecutive reactions of cyclohexene skeletal isomerization and disproportionation. Our IR and catalytic studies have shown that the dehydration occurs on both strong and weak Bronsted sites. On the other hand, only the strong Bronsted acid sites are required for isomerization and disproportionation. This observation may be used to propose a new ipethod for investigation of heterogeneity of acid sites in zeolites by a simple catalytic test. 

The results obtained in this study indicate that in Al-ffee H-boralite (BOR 1) only weak BrOnsted acid sites (Si—OH—B) are present. They are active only in cyclohexanol dehydration. Their catalytic activity is, however, relatively low. The insertion of A1 into the framework results in the creation of strong Bronsted acid sites. Most probably they are Si—OH—Al, the same as in zeolites. The IR band which could be characteristic of such Si—OH—Al (at about 3610 cm ) was not seen in the spectrum because of the very low concentration of these hydroxyls. The catalytic activity of Si—OH—Al is much higher that of Si—OH - B. Contrary to Si—OH -B, Si—OH— A1 are active in consecutive reactions of cyclohexene (isomerization and disproportionation). Cyclohexene isomerization (to methylcyclopentenes), a typical carbenium ion reaction is catalysed by strong Brdnsted acid sites even at temperatures as low as 450 K. The same strong Bronsted acid sites catalyse also cyclohexene disproportionation (to cyclohexane, methylcyclopentane and coke). Our earlier... 

Because chair cyclohexane has two kinds of positions, axial and equatorial, we might expect to find mo isomeric forms of a monosubstituted cyclohexane. In fact, we don t. There is only one methylcyclohexane, one bromocycloliexane, one cyclohexanol (hydroxycyclohexane), and so on, because cyclohexane rings are confonnationally mobile at room temperature. Different chair conformations readily interconvert, exchanging axial and equatorial positions. This interconversion, usually called a ring-flip, is shown in Figure 4.11. 

The reaction of Clj with a number of mixtures including butan-l-ol and butan-2-ol cyclohexanol, cyclohexanone, and hexachlorocyclohexane and phenol, chlorobenzene and dichlorobenzene (isomeric mixture) proceeded similarly. Many other similar types of mixtures are likely to undergo COCl /CCl formation under such severe conditions. Indeed, this system can be extended under such forcing conditions (550-660 "C and 80-300 atmospheres) to the reaction of Clj with mixtures of CO, CO or HjO with benzene, chlorinated benzenes, hexachlorocyclohexanes, trichloroethane, trichloroethene, or tetrachloroethene [1714]. The hydrogen in the system appears as HCl, and some perchlorinated compounds tend to be formed, but the principal carbon-containing products are COCl and CCl. ... 

Isomerization of ethynylcarbinols. Rupe12 first observed that ethynylcarbinols when refluxed in formic acid (90%) are isomerized to unsaturated carbonyl compounds, which he considered to be aldehydes. Chanley13 later investigated the reaction in detail and found that the predominant product is an a,/ -unsaturated ketone. Thus 1-ethynyl-l-cyclohexanol (1) is converted mainly into 1-acetyl-l-cyclohexene (2), with onLy traces of (3) being formed. 

There are other significant differences between the ene reactions using these auxiliaries. For example, in the ene reaction with the isomeric butenes, /rn .v-2-phenylcyclohexanol affords a higher level of antijsyn selectivity than with the Z-isomer, although lower than observed with the oxoacetate of 5-methyi-2-(l-methyl-1 -phenylethyl)cyclohexanol (see Table 4. entries 3, 4 see also 8, 9). Furthermore, and again in contrast to the reactions using the oxoacetate of... 

Figure 14.22 Chiral GC trace with odour descriptors for the isomeric mixture of l-methyl-3-(2-methylpropyl)cyclohexanol...

H, A. Smith University of Tennessee)-. Dr. Siegel (Lecture 4) suggests that his experiments indicate that a cyclohexene-type intermediate is formed in the catalytic hydrogenation of benzene. Further evidence for this is found in the hydrogenation of phenols, for when these are reduced under a variety of conditions and over a number of catalysts, cyclohexanone is formed as an intermediate and is readily isolated. The best explanation for this appears to be the addition of two moles of hydrogen per mole of phenol to form a cyclohexenol which isomerizes to cyclohexanone before further hydrogenation takes place. The cyclohexanone is desorbed from the catalyst, and may be subsequently reduced to cyclohexanol. 

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