Condensation of alkanes

The key initiation step in cationic polymerization of alkenes is the formation of a carbocationic intermediate, which can then interact with excess monomer to start propagation. We studied in some detail the initiation of cationic polymerization under superacidic, stable ion conditions. Carbocations also play a key role, as I found not only in the acid-catalyzed polymerization of alkenes but also in the polycondensation of arenes as well as in the ring opening polymerization of cyclic ethers, sulfides, and nitrogen compounds. Superacidic oxidative condensation of alkanes can even be achieved, including that of methane, as can the co-condensation of alkanes and alkenes. 

Scheme 118 shows enantioselective condensation of alkanals and ni-tromethane promoted by a binaphthol-modified rare earth alkoxide in wet THF. Reaction of the initially formed metal /3-nitro alkoxide and acidic nitromethane, leading to the j8-nitro alcohol product and chiral metal nitronate, makes the C—C bond formation catalytic (284). 

Intramolecular condensation of alkane dialdehydes gives cycloalkenecarbaldehydes under conditions of acid or base cyclizations of symmetrical dialdehydes leading to five-, six- and seven-membered rings are depicted in equations (95)-(97)." "" ... 

Superacidic systems are able even to catalyze self-alkylative condensation of alkanes demonstrated here by the condensation of methane (63,78). The reaction requires the oxidative removal of hydrogen involving the pentacoordinate cation (17) (eq. 55). This can be attained by applying the oxidizing superacid Magic Acid (HSOsF-SbFs). The carbocationic pathway leading to C4-C6 alkanes also occurs through the involvement of pentacoordinate cations (18 eq. 56). 

Acid-catalyzed isomerization reactions of alkanes as well as alkylation and condensation reactions are initiated by protolytic ionization. Available evidence indicates nonlinear but not necessarily triangular... 

These reactions involve the intermediate formation of thiols, followed by condensation to the sulfides. The observation of isomerized products in suitable cases indicates the intermediate formation of carbocations, either by protolysis of alkanes by the superacid or reversible ionisation of the thiol products (149). 

By-Products. Almost all commercial manufacture of pyridine compounds involves the concomitant manufacture of various side products. Liquid- and vapor-phase synthesis of pyridines from ammonia and aldehydes or ketones produces pyridine or an alkylated pyridine as a primary product, as well as isomeric aLkylpyridines and higher substituted aLkylpyridines, along with their isomers. Furthermore, self-condensation of aldehydes and ketones can produce substituted ben2enes. Condensation of ammonia with the aldehydes can produce certain alkyl or unsaturated nitrile side products. Lasdy, self-condensation of the aldehydes and ketones, perhaps with reduction, can lead to alkanes and alkenes. 

Although the unsaturated nitrile oxides 124 can be prepared via the aldoxime route (see Scheme 8), the older procedure suffers from the disadvantage that a tenfold excess of allyl alcohol and two additional steps are required when compared to Scheme 15. Therefore, unsaturated nitro ether 123 that can be prepared by condensation of an aldehyde 120 and a nitro alkane followed by Michael addition of alcohol 122, was a useful precursor to nitrile oxide 124 [381. The nitrile oxide 124 spontaneously cyclized to ether 125. This procedure is particularly suitable for the synthesis of tetrahydrofurans (125a-h) and tetrahydropyrans (125i-k) possessing Ar substituents in 72-95% yield (Table 12). The seven-membered ether 1251 was obtained only in 30% yield on high dilution. The acetylenic nitro ether 126 underwent INOC reaction to provide the isoxazole 127. 

Table 11.5 Sequences for the separation of the mixture of alkanes, with pressure fixed for cooling water in condensers.

Co-condensation of rhenium atoms with benzene alone gave no isolable products at ambient temperature. It was not expected, however, when rhenium atoms were co-condensed with a benzene alkane mixture that l-alkylidene complexes, analogous to the l-arylidene complexes were formed. Thus, co-condensation of rhenium atoms with a 1 1 mixture of benzene... 

Alkyl alkanoates are reduced only at very negative potentials so that preparative scale experiments at mercury or lead cathodes are not successful. Phenyl alkanoates afford 30-36% yields of the alkan-l-ol under acid conditions [148]. Preparative scale reduction of methyl alkanoates is best achieved at a magnesium cathode in tetrahydrofuran containing tm-butanol as proton donor. The reaction is carried out in an undivided cell with a sacrificial magnesium anode and affords the alkan-l-ol in good yields [151]. In the absence of a proton donor and in the presence of chlorotrimethylsilane, acyloin derivatives 30 arc formed in a process related to the acyloin condensation of esters using sodium in xylene [152], Radical-anions formed initially can be trapped by intramolecular addition to an alkene function in substrates such as 31 to give aiicyclic products [151]. 

Condensation of Q—C4 alkanes to produce highly branched oligomeric and polymeric hydrocarbons41 was also achieved by their condensation in FSO3H—SbF5. Block methylene units in the polymeric chain were observed even when methane was brought into reaction with alkenes under similar conditions.42... 

Figure 6 shows the isotherms of the samples using different alkanes as expander. Except the sample obtained with nonane, the adsorption-desorption isotherms of all other compounds are type IV, characteristic of mesoporous materials according to the BDDT classification [21], Isotherms can be decomposed in three parts the formation of the monolayer, a sharp increase characteristic of the capillary condensation of nitrogen within the mesopores and finally a plateau indicating the saturation of the samples. From pentane to decane the relative pressure at which the capillary condensation occurs, increases from 0 30 to 0.60, indicating that the value of the pore diameter increases when the alkane chain length is raised since the p/po position of the inflection point is related to the pore diameter. From undecane, this value decreases to reach 0.40 for dodecane We can conclude that the value of the pore diameter drops from decane to dodecane... 

On the other hand, a remarkable difference between catalysis by Y and 13 zeolites has been found for the Claisen-Sohmidt condensation of acetophenone and benzaldehyde (Table 5). When the cross aldolic reaction is carried out in the presence of HY, together with the expected trans and ois chalcones 5, the 3,3-diphenylpropiophenone 6 is also formed, this product being not detected on 13 zeolites. A likely explanation for the absence of 6 using zeolite beta is that the crystalline structure of this zeolite exerte a spatial constraint making difficult the formation of a big size molecule like 6, especially in the smaller channel. Similar effects due steno limitations on 6 catalysis have been found for the formation of multi-branched products during the cracking of alkanes (ref 8). 

A large number of 5-deazaflavins (32 R1, R2 = H, alkyl, aryl R3, R4 = H, Cl, NO2, OH 48 examples in all), have been prepared in good yields via condensation of 6-substituted aminouracils with o-halo-benzaldehydes in DMF under reflux. The mechanism shown in Scheme 14 was proposed for this reaction.138 Several bis(5-deazaflavin-10-yl)alkanes (33 n = 6, 8, 10, 12) have also been prepared via the same route using bis(uracil-6-ylamino)alkanes.138 By an analogous reaction the substituted quinolines (34a) and (34b) were obtained in 87% and 50% yield, respectively, from enaminones (35a X = Y = NMe Z = O) and (35b X = Y = CH2 Z = Me2) and pentafluorobenzaldehyde in glacial acetic acid at reflux.139... 

The mass spectrometric analyses of the saturate fractions are reported in Table VI. These fractions appear to be composed mostly of alkanes and noncondensed cycloalkanes with smaller amounts of condensed cycloalkanes, mainly two- and three-ring systems. However, because of the presence of olefins in these fractions the analyses are only semiquantitative. In fact, an olefin should make a contribution to the cycloalkane group type which has the same molecular weight. That is, a monoolefin will contribute to the cycloalkanes, a diolefin or a cyclic olein will contribute to the bicycloalkanes, etc. However, to determine the extent of these contributions more analytical work is necessary. 

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