Direct alkane —> cycloalkane

The first mechanistic concepts of aromatization 16) originate from pregas-chromatography times. A direct alkane- cycloalkane reaction was proposed by Kazansky and co-workers 47). Several authors have interpreted the formation of six-membered rings over metal catalysts in terms of alkene-alkyl insertion (i.e., analogous to the Twigg mechanism) (7, 8, 14). 

Volter (66) reported that a part of Pt(IV) (which is present as a non-stoichiometric oxychlorinated complex over his alumina support after calcination) is reduced reversibly below 550°C to a Pt complex related to soluble platinum. Above this temperature, reduction to the metallic state is complete. He attributed direct alkane- cycloalkane cyclization to this platinum complex (24, 66). 

As you can see cycloalkanes are named under the lUPAC system by adding the prefix cyclo to the name of the unbranched alkane with the same number of carbons as the ring Substituent groups are identified m fhe usual way Their posifions are specified by numbering fhe carbon atoms of fhe ring m fhe direction fhaf gives fhe lowesf num ber to fhe subsfifuenfs af fhe firsf pomf of difference... 

The monofluoromethylene group and difluoromethyl group m 1H perfluoro-alkanes and -cycloalkanes are oxidized at the C-H bond to perfluoroalkyl and perfluorocycloalkyl fluorosulfates by anodic oxidation m fluorosulfonic acid [J, 4] Two modifications of the method are used ox idation by fluorosulfonyl peroxide generated pnor to the reaction [J] (equation 2A) and direct electrolysis m the acid [i, 4] (equabons 2B and 3)... 

Bromination and chlorination of alkanes and cycloalkanes can also take place by an electrophilic mechanism if the reaction is catalyzed by AgSbFs. " Direct chlorination at a vinylic position by an electrophilic mechanism has been achieved... 

RoCek et al. have also measured rate coefficients for a series of cyclo-alkanes, (CH2) (/i = 4 to 14), and find the analogue of kcHj in equation (25) to fluctuate with ring size in a manner corresponding exactly to the enthalpy of combustion of the cycloalkane concerned per methylene group, provided n is greater than five, i.e. there exists a direct correlation between reactivity and thermochemical strain. 

These are found in crude petroleum including bitumen in the Athabasca tar sands of Northern Alberta. They contain a complex mixture of saturated polycyclic live- and six-membered cycloalkanes with alkane and alkanoic acid substituents. Attention has been directed to the degradation of both commercially available products, and those that are produced during bitumen extraction. Although the former were degradable (Clemente et al. 2004), the higher molecular mass components of the latter were much more recalcitrant (Scott et al. 2005). 

In contrast to the results obtained with -alkanes and cycloalkanes, H2 elimination is found to be an unimportant process in the photolysis of neopentane [107]. At 7.6 eV the methane elimination and direct C-C bond cleavage to radicals are the predominant processes ... 

Bromination and chlorination of alkanes and cycloalkanes can also take place by an electrophilic mechanism if the reaction is catalyzed by AgSbF. "2 Direct chlorination at a vinylic position by an electrophilic mechanism has been achieved with benzenescleninyl chloride PhSe(0)Cl and AIC13 or AIBr3. n However, while some substituted alkenes give high yields of chloro substitution products, others (such as styrene) undergo addition of Cl2 to the double bond (5-26).113 Electrophilic fluorination has already been mentioned (p. 690). 

Mn- and Fe-tetraarylporphyrins catalyse the direct hydroxylation of saturated C-H bonds with 30% H O [27, 50-52]. Because of further oxidation, a mixture of alcohols and ketones is produced. With cycloalkanes, the hydroxylation is fast and selective. In n-alkanes and alkylbenzenes, the reaction stops after a few turnovers. 

As a result of their inertness no general suitable derivative exists for alkanes and cycloalkanes Characterization IS based only on the physical constants given in the Table melting and boiling points, index of refraction and density Any laboratory text-book will give adequate directions for the determination of these constants... 

The a-, P- or y- cyclodextrins that have been permethylated must be dissolved directly in appropriate polysiloxanes mixtures, and coated on the walls of a glass or fused quartz open tubular columns. The underivatized cyclodextrins, and those that have not been permethylated, can be coated directly onto the walls of the column. Many alcohols, diols, carboxylic acids, alkanes and cycloalkanes can be separated directly on such columns without derivatization. To improve the thermal stability of the mixed stationary phase, a phenylpolysiloxane can be included in the coating material. The presence of phenylpolysiloxane can also improve its stability towards oxidation at elevated temperatures, as cyclodextrin, being basically a sugar, is very susceptible to oxidation at high temperatures. Some methysiloxane, however, must be present to increase... 

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