Cyclohexanes alkyl-substituted—

The term naphthenic acid, as commonly used in the petroleum industry, refers collectively to all of the carboxyUc acids present in cmde oil. Naphthenic acids [1338-24-5] are classified as monobasic carboxyUc acids of the general formula RCOOH, where R represents the naphthene moiety consisting of cyclopentane and cyclohexane derivatives. Naphthenic acids are composed predorninandy of aLkyl-substituted cycloaUphatic carboxyUc acids, with smaller amounts of acycHc aUphatic (paraffinic or fatty) acids. Aromatic, olefinic, hydroxy, and dibasic acids are considered to be minor components. Commercial naphthenic acids also contain varying amounts of unsaponifiable hydrocarbons, phenoHc compounds, sulfur compounds, and water. The complex mixture of acids is derived from straight-mn distillates of petroleum, mosdy from kerosene and diesel fractions (see Petroleum). 

In 5-alkyl-substituted 1,3-dioxanes, the 5 substituent has a much smaller preference for the equatorial position than in cyclohexane derivatives the A values are much lower. This indicates that the lone pairs on the oxygens have a smaller steric requirement than the C—H bonds in the corresponding... 

Although the suspended catalysts under boiling and refluxing conditions were active for dehydrogeno-aromatization of alkyl-substituted cyclohexanes, the levels of reaction rates were unsatisfactorily low. A breakthrough toward low catalytic activities was accomplished by our introduction of "superheated liquid-film concept" (vide infra) [30]. 

A different stereochemical pattern is evident in the hydrogenation over a platinum catalyst of 2-, 3-, or 4-alkyl-substituted methylene-cyclohexanes (57,63,64). With these compounds increasing, the pressure of hydrogen decreases the proportion of the more unstable saturated isomer in the product (cis-1,2-, tmn -l,3-, or cis-l,4-dialkylcyclohexane), a result which is not consistent with a mechanism involving an isomerization to an olefin which yields a proportion of cis and trans isomers different from that given by the methylenecyclohexane. For such a mechanism implies that the hypothetical olefin would yield a larger portion of the more unstable saturated isomer than is obtained from the initial reactant. 

In contrast to pyridine derivatives, aryl- and alkyl-substituted A -phosphorins cannot be protonated by strong, non-oxidizing acids such as trifluoroacetic acid. Addition of trifluoroacetic acid to cyclohexane solutions of various A -phosphorins fails to produce any change in the UV spectra Similarly, alkylation by such strong agents as oxonium salts or acylation by acylchlorides cannot be induced at the P atom or any ring C atom. This behavior has also been discussed theoretically 55a)... 

In a series of papers, Koltunov, Repinskaya, and co-workers have reported the ionic hydrogenation of isomeric naphthols and dihydroxynaphthalenes with alkanes in the presence of aluminum halides. 1-Naphthol and substituted derivatives undergo regioselective reduction under mild conditions in excess alkane and aluminum halides with the involvement of various reactive intermediates to yield a-tetralone derivatives874 [Eq. (5.322)]. Byproducts are 3-, 6-, and 7-alkyl-substituted derivatives. Mechanistic studies875 with cyclohexane-di2 showed that deuterium incorporation takes place exclusively at C(4), indicating the involvement of super-electrophilic dication 263.2-Naphthol is much less reactive and complete conversion cannot be achieved.876... 

Branched paraffins react somewhat differently to the normal paraffins during cracking processes and produce substantially higher yields of olefins having one fewer carbon atom that the parent hydrocarbon. Cycloparaffins (naphthenes) react differently to their noncyclic counterparts and are somewhat more stable. For example, cyclohexane produces hydrogen, ethylene, butadiene, and benzene Alkyl-substituted cycloparaffins decompose by means of scission of the alkyl chain to produce an olefin and a methyl or ethyl cyclohexane. 

With the alkyl-substituted cyclohexane derivatives there are also variations in the course of ctsw an ctbi 2-methyl compound (X) is not bitter up to a concentration of 20 mmol/1, whereas a 3-methyl group (XI) or a 4-methyl group (XII) decreases c-tbi in comparison with the unsubstituted compound IV. Whereas a 4-ethyl group (XIII) abolishes sweet taste, it lowers ctkj even further, in comparison with the methyl compound XII. The 4-tert.-butyl derivative XIV is neither sweet nor bitter. 

However, it is difficult to reconcile the observed relative reactivities of hydrocarbons with a mechanism involving electron transfer as the rate-determining process. For example, n-butane is more reactive than isobutane despite its higher ionization potential (see Table VII). Similarly, cyclohexane undergoes facile oxidation by Co(III) acetate under conditions in which benzene, which has a significantly lower ionization potential (Table VII), is completely inert. Perhaps the answer to these apparent anomalies is to be found in the reversibility of the electron transfer step. Thus, k-j may be much larger than k2 for substrates, such as benzene, that cannot form a stable radical by proton loss from the radical cation [Eqs. (224) and (225)]. With alkanes and alkyl-substituted arenes, on the other hand, proton loss in Eq. (225) is expected to be fast. 

Balandin and co-workers have examined the cyclohexane-benzene-hydrogen system as well as the alkyl substituted cyclohexanes and their adsorption rates on platinum, palladium, and nickel (17,23,24,27). As... 

The hydroxylation of cyclohexane, of potential interest for the production of cyclohexanone, is exceedingly slow at near room temperature and has low selectivity at 100 °C [27, 28]. Tertiary C—H bonds yield tertiary alcohols, with little or no oxidation observed at the secondary carbons that may be present in the alkyl chain t-C—H sec-C—H (Table 18.3). The steric constraints introduced by alkyl substitution strongly favor the competition of side reactions, at the expense of hydroxylation. On arylalkanes, oxidation occurs on both the aromatic ring and the alkyl chain, with a general preference for the latter. Consistently, the competitive hydroxylation of benzene and n-hexane or cyclohexane mainly occurs on the alkane. However, benzylic methyls, despite the relative weakness of their C—H... 

Little is known of the chemistry of alkyl-substituted cycloalkanes such as C6H11CH3. The presence of one tertiary C—H bond will not noticeably increase the overall rate of radical attack because of the abundance of secondary C—H bonds. Attack at a ring C—H position will tend to give a similar product distribution to that observed for cyclohexane with high yields of the various isomeric cyclohexenes at most temperatures between 600 and 1000 K. Loss of a hydrogen atom at the /3 position to the R group would induce homolysis to give cyclohexene and R radicals, particularly at temperatures above 800 K. 

Excitation Energies of Ethylene (1) and its Alkyl-Substituted Derivatives (A) in the Gas Phase (207a) and (B) in Cyclohexane (208)... 

Ring-opening of alkyl-substituted cyclohexanes is slower and much less selective selectivity was only about 5% with platinum, although Ir/A Os gave 87% C7 alkanes. Lower values were found with n-butylcyclohexane. ... 

The temperature-dependent NMR spectra of cyclohexane itself were investigated more than 25 years ago by NMR using several methods and solvents The barrier for chair-to-chair interconversion was determined to be 10.25 kcal mol Subsequently, simple alkyl-substituted derivatives were examined by NMR, for example methylcyclohexane and 1,2-dimethylcyclohexane (Figure 9). The chemical shifts observed in the low-temperature region are in line with the steric interactions and the conformational increments discussed in Section ILB.4. 

---