Alkanes polycondensation

This parallelism is reflected in the proposed mechanism for the ionization of methane which shows that (a) the second step of the scheme invoives attack of an ethyl cation on methane, but the reaction cannot stop there, and goes on to (b), the third step, which involves attack of a secondary-isopropyl cation on methane. The primary and secondary alkyl cations are very strongly acidic species and are unstable under the reaction conditions. The condensation reaction essentially terminates with the much more weakly acidic tertiary-butyl ion. Alkane polycondensation and olefin polymerization side reactions producing stable, less acidic, tertiary ions obscured the simple alkylation reactions of the primary and secondary alkyl cations. Implicit in this mechanism, however, is that it is possible to react an acidic energetic primary cation (such as the ethyl cation) with molecules as weakly basic as methane and thus, the door was opened to new chemistry through activation of the heretofore passive, weakly basic, "paraffins" (20-24). 

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. 

Lower alkanes such as methane and ethane have been polycondensed ia superacid solutions at 50°C, yielding higher Hquid alkanes (73). The proposed mechanism for the oligocondensation of methane requires the involvement of protonated alkanes (pentacoordinated carbonium ions) and oxidative removal of hydrogen by the superacid system. 

The main reactions of the MTG/MTO process can be summarized as follows the first is the dehydration of methanol to DME on acidic zeolite catalysts. The equilibrium mixture of methanol, DME, and water is then converted to light alkenes, which react further to form higher alkenes, n- and Ao-alkanes, aromatics, and naphthenes by hydrogen transfer, alkylation, polycondensation, isomerization, and other secondary reactions. 

A new class of polyamides containing dibenzo 18-crown-6-moieties and alkaline units in the main chain shows [75] varying complexing capabilities with 4-toluene sulfonates of Rb+, K+, Na+ and potassium salts of CH3C6H4SOj, SCNI-, Br-. The polyamide polycondensates are obtained from cis- or trans-4,4 -diaminodibenzo 18-crown-6-(DAC) and a 4,4 -diearboxy-a, cu-diphenoxy-alkane (DCA) (Fig. 25). 

An experimental attempt towards polycatenanes 9, based on a strategy related to the stepwise polycondensation approach, was reported in the seventies. Karagoumis et al. took advantage of the interface between a nonpolar phase (air, CC14) and a polar phase (H2O, Hg) to orient alkanes a,oj-disubstituted with polar groups (Scheme 9) [45], The successive addition of macrocycles of ring sizes 15-60 atoms and of difunctional species, susceptible to reaction with the a,o>disubstituted al-... 

These polysiloxanes were also found to be synthesized by the condensation reaction between organosilanes and organoalkoxysilanes with release of alkane as an inert by-product. For this polycondensation, B(C6F5)3 was used as an effective catalyst [88]. This process involves cleavage of C-0... 

The high conversion of monomers and the distribution of products in the time of reaction catalyzed by [RuHCl(CO)(PPh3)3], performed under mild conditions (toluene, 110°C or 80 °C), show that o.w-bis(dimethylvinylsiloxy)alkanes undergo silylative coupling cycllzation/polycondensation according to Scheme 3. 

Kricheldorf has reported the synthesis of lyotropic poly(amide-imide)s and poly(benzoxazole-amide)s. These were prepared by the polycondensation of N,N-bis(trimethylsilyl)-p-phenylenediamine or N,AT -bis(trimethylsilyl)-3,3 -dim-ethylbenzidine with the diacyl chloride of trimellitimide of p-aminobenzoic acid, or the imide formed from p-amino benzoic acid and terephthalic acid. Lyotropic behaviour was observed in cone, sulphuric acid solution [38]. A series of thermotropic poly(imide-amide)s was prepared based on trimellitimides formed from trimellitic anhydride and an a, -bis(4-aminophenoxy) alkane with carbon chain lengths 9-12. Melting points were in the range 250-300 °C. They formed smectic A phases and tended to degrade around the isotropisation temperatures (around 350 °C). Pendant methyl groups or occupied meta- groups tended to prevent mesophase formation [39]. Novel LC poly(imide-amides) have also been synthesised from new diamine spacers derived from linear diaminoalkanes and 4-nitrophthalic anhydride. A smectic and nematic phase were observed when 4,4 -biphenyl dicarboxylic acid was used as co-monomer [40]. 

A new class of diamine spacer was synthesised from a,co-diaminoalkanes and 4-nitrophthalic anhydride the resulting a, -bis(4-aminophthalimido)alkanes were polycondensed with one of the following acid chlorides terephthaloylchlo-ride, 2-phenylthioterephthaloylchloride, naphthalene-2,6-dicarboxylic acid or 4,4 -biphenyldicarboxylic acid chloride [40]. Thermotropic behaviour was con-... 

There are several reports in the literature on significant acceleration of reaction rates in monolayers. Such increase in reactivity is usually attributed either to enforced juxtaposition of the reactive functional groups in the ordered environment, or to the favourable orientation of the reactive group. Nakahara and coworkers found that long-chain alkane esters of aminoacids polycondense unexpectedly rapidly at the air-water interface, probably because of the close proximity of the amino and ester groups in the monolayer (equation 18)397. 

Mixture of nitric and sulfuric acid (mixed acid) used extensively in nitration of aromatic hydrocarbons, is generally unsuitable for nitration of alkanes, since primary nitroalkanes are rapidly hydrolyzed by hot sulfuric acid and secondary and tertiary nitroalkanes form tars (in all probability via rapid alkene-forming elimination and subsequent polycondensation, polymerization, etc.). It is, however, significant to point out that it is not necessarily the lack of reactivity of paraffins with mixed acid that makes the nitration of saturated hydrocarbons unsuitable, but that fast secondary reactions of any nitro products formed (as well as oxidative side reactions) can take place. This difficulty can be, at least in part, overcome by using preformed nitronium salts as nitrating agents. 

G. A. Olah, R. H. Schlosberg, Chemistry in super acids. I. Hydrogen exchange and polycondensation of methane and alkanes in FSOjH-SbFs ( magic acid ) solution. Protonation of alkanes and the intermediacy of CHJ and related hydrocarbon ions. The high chemical reactivity of paraffins in ionic solution reactions, /. Am. Chem. Soc., 1968, 90, 2726-2727. 

G. A. Olah, G. Klopman, R. H. Schlosberg, Super acids. HI. Protonation of alkanes and intermediacy of aUcanonium ions, pentacoordinated carbon cations of CHJ type. Hydrogen exchange, protolytic cleavage, hydrogen abstraction, polycondensation of methane, ethane, 2,2-dimethylpropane and 2,2,3,3-tetramethylbutane in FSOsH-SbFs, J. Am. Chem. Soc., 1969, 91, 3261-3268. 

The polymers of Series I-III were prepared by step-wise polycondensation of a,a)-bis(A-hydroxybenzoyloxy)alkane derivatives with the appropriate diacid chloride While samples 1 were obtained... 

Polycondensation of alkanes over HS03F SbF5 has also been achieved by Roberts and Calihan. Several low-molecular-weight alkanes such as methane, ethane, propane, butane and isobutane were polymerized to highly branched oily oligomers with a... 

Unlike polycondensation polymers, polymers of addition polymerization such as polyethylene and polypropylene when depolymerized in inert atmosphere (39) or in supercritical water (37) do not convert to just the monomer, but a homologous series of oligomers (alkanes and alkenes). Compared to pyrolysis in argon, for polyethylene, the portion of the lighter products increases in supercritical water depolymerizations conducted at 693 K and water densities of 0.13 and 0.42 g/cm. The 1-alkene to n-alkane ratio also increases in supercritical water and with density. These are shown in Figure 11. These results are attributed to the fact that in argon pyrolysis, the reaction proceed in the molten state of the polymer, whereas in supercritical water, some of degradation products... 

The polycondensation reactions of sebacoyl chloride with alkane diols has been investigated and found to be independent of chain length. 

The pillar[5] arene dimer described above formed relatively strong host-guest complexes with Unear alkanes, whereas the complexation ability of the corresponding monomeric pillar[5] arene towards linear alkanes was too weak to determine the association constants or stoichiometry of any potential interactions. The dimerization of this pillar[5] arene system therefore enhanced its host-guest ability. Stoddart et al. synthesized one-dimensional tubular assemblies by the polycondensation reaction of pillar[5]arene with A-B units [47]. It is noteworthy that this strategy allowed for the successful formation of one-dimensional tubular arrays containing between two and nine piUar[5]arene molecules (i.e., 2-mer to 9-mer) (Fig. 19.10b). 

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