Alkane direct alkylation

Alkylation Using Alkanes. Direct alkylation of pyridines and quinolines using simple alkanes and terf-butyl peroxide as oxidant was developed. This C-C bond forming reaction was carried out by using Sc(OTf)3 as a Lewis acid to increase the reactivity of pyridine and quinoline derivatives (eq 37). Scandium triflate demonstrated the best catalytic activity among the Lewis acids tested. While bis-alkylation product was obtained using quinoline, only mono-alkylation products were afforded when isoquinoline was used. Cycloheptane, cyclohexane, and norbornane were determined to be suitable reaction partners. 

On the other hand, under superacidic conditions, alkanes are readily alkylated via front-side CJ-iasertion by carbocationic alkylating agents. The direct alkylation of the tertiary C—H CJ-bond of isobutylene with isobutane has been demonstrated (71). The stericaHy unfavorable reaction of tert-huty fluoroantimonate with isobutane gave a Cg fraction, 2% of which was 2,2,3,3-tetramethylbutane ... 

For the non-oxidative activation of light alkanes, the direct alkylation of toluene with ethane was chosen as an industrially relevant model reaction. The catalytic performance of ZSM-5 zeolites, which are good catalysts for this model reaction, was compared to the one of zeolite MCM-22, which is used in industry for the alkylation of aromatics with alkenes in the liquid phase. The catalytic experiments were carried out in a fixed-bed reactor and in a batch reactor. The results show that the shape-selective properties of zeolite ZSM-5 are more appropriate to favor the dehydroalkylation reaction, whereas on zeolite MCM-22 with its large cavities in the pore system and half-cavities on the external surface the thermodynamically favored side reaction with its large transition state, the disproportionation of toluene, prevails. 

Theoretically, even the direct alkylation of carbenium ions with isobutane is feasible. The reaction of isobutane with a r-butyl cation would lead to 2,2,3,3-tetramethylbutane as the primary product. With liquid superacids under controlled conditions, this has been observed (52), but under typical alkylation conditions 2,2,3,3-TMB is not produced. Kazansky et al. (26,27) proposed the direct alkylation of isopentane with propene in a two-step alkylation process. In this process, the alkene first forms the ester, which in the second step reacts with the isoalkane. Isopentane was found to add directly to the isopropyl ester via intermediate formation of (non-classical) carbonium ions. In this way, the carbenium ions are freed as the corresponding alkanes without hydride transfer (see Section II.D). This conclusion was inferred from the virtual absence of propane in the product mixture. Whether this reaction path is of significance in conventional alkylation processes is unclear at present. HF produces substantial amounts of propane in isobutane/propene alkylation. The lack of 2,2,4-TMP in the product, which is formed in almost all alkylates regardless of the feed (55), implies that the mechanism in the two-step alkylation process is different from that of conventional alkylation. 

Simple aliphatic nitriles, aldehydes, ketones and esters are not readily alkylated under liquiddiquid phase-transfer conditions. Direct alkylation of aldehydes under even mildly basic phase-transfer conditions has to compete with aldol and Cannizzaro reactions and yields are low and variable [e.g. 6], a,a-Disubstituted aldehydes are C-alkylated, e.g. formylcyclohexane has been alkylated (>70%) with a range of reagents using benzyltrimethylammonium isopropoxide as the basic catalyst [7], whereas a-unsubstituted alkanals tend to undergo aldol condensation under basic liquid liquid two-phase conditions [8]. 

The yield of the alkane-alkene alkylation in homogeneous HF-TaF5 depending on the alkene-alkane ratio has been investigated by Sommer et al.149 in a batch system with short reaction times. The results support direct alkylation of methane, ethane, and propane by the ethyl cation and the product distribution depends on the alkene-alkane ratio (Figure 5.14). 

An increase in the alkene-alkane ratio results in a significant decrease in single-labeled propane ethylene polymerization-cracking and hydride transfer become the main reaction. This labeling experiment carried out under conditions where side reactions were negligible is indeed unequivocal proof for the direct alkylation of an alkane by a very reactive carbenium ion. 

Direct Alkyl Chloride Reductions. It was previously pointed out that at 40° in HF-TaF5 methyl- and ethyl-chloride do not form the expected alkylation product with alkanes, expected that is, assuming traditional carbenium ion chemistry, but rather underwent an independent reaction. The second part of this paper will describe in more depth what reactions do take place when alkyl chlorides react in the presence or absence of the lower alkanes under our reaction conditions of 40°C. 

Parent radical cations derived from alkanes and alkyl chlorides can be directly observed in the nanosecond time domain by time-resolved spectroscopy such as laser flash photolysis and electron pulse radiolysis. Especially the latter one enables the direct ionization of the solvents independently on the optical properties of the sample and a well-defined electron transfer regime according to Eq. (2) or (3). Representative examples of the radiolyfic generation of solvent radical cations are given in Eqs. (4) and (5a) for the cases of 1-chlorobutane and -decane. ... 

Olah and coworkers - have observed that alkyl fluoride-SbFj complexes, such as MeF-SbFj and EtF SbFs, or stable prepared alkylcarbenium hexafluoroantimonate salts directly alkylate alkanes (equations 125 and 126). 

Lewis superacid-catalyzed direct alkylation of alkanes is also possible with alkyl cations prepared from alkyl halides and SbFs in sulfuryl chloride fluoride solution. " Typical alkylation reactions are those of propane and butanes by 2-butyl and ZerZ-butyl cations. The ClfU-Sbfs and C2H5F-SbF5 complexes acting as incipient methyl and ethyl cations besides alkylation preferentially cause hydride transfer. Since intermolecular hydride transfer between different carbocations and alkanes are faster than alkylation, a complex mixture of alkylated products is usually formed. A significant amount of 2,3-dimethylbutane was, however, detected when propane was propylated with the 2-propyl cation at low temperature [Eq. (6.36)]. No 2,2-dimethylbutane, the main product of conventional acid-catalyzed alkylation, was detected, which is a clear indication of predominantly nonisomerizing reaction conditions. 

Very weak adducts of metal complexes with alkanes (or alkyl groups), in which the C-H bond is directly coordinated to the metal (I-l, 1-2) or its ligands (1-3), do not necessarily lead to subsequent cleavage of the C-H bond. However,... 

In the last two decades, hundreds of papers reported the use of NHPI for promoting the homogeneous selective oxidation of a wide range of organic substrates (including alcohols, ketones, ethers, amines, amides, silanes, alkynes, alkenes, alkanes, and alkyl aromatics) and the one-pot free-radical synthesis of complex molecules, involving molecular oxygen, directly or indirectly [4]. 

Li s copper-catalyzed oxidative difunctionalization of enol ethers with a-amino carbonyl compounds was recently reported (Scheme 2.9) [41]. This protocol allows rapid synthesis of 2-amino-3,4-dioxy carbonyl products. Significantly, metal-fiee, DTBP-mediated direct alkylation of a-amino carbonyl compounds with C—H bond of simple alkanes was developed by Cheng and co-workers [42]. 

Alkanes are poorly adsorbed, and the alkyl parts of molecules containing chemical groups susceptible to form bonds with the photocatalyst surface are oriented away from the surface. Accordingly, alkanes and alkyl parts [63] are thought to be prone to react with OH radicals rather than directly with holes. 

Substitutive nomenclature of alkyl halides treats the halogen as a halo—(fluoro chloro bromo or lodo ) substituent on an alkane chain The carbon chain is numbered m the direction that gives the substituted carbon the lower number... 

Chlorine gas reacts directly and highly exothermically with alkanes, giving rise to alkyl chlorides and hydrogen chloride, e.g., for addition to methane. 

The two propagation steps shown above for X2 are those that lead directly to the principal products (RX and HX), but many other propagation steps are possible and many occur. Similarly, the only termination step shown is the one that leads to RX, but any two radicals may combine. Thus, products like H2, higher alkanes, and higher alkyl halides can be accounted for by steps like these (these are for... 

Note that the main difference between zirconium hydride and tantalum hydride is that tantalum hydride is formally a d 8-electron Ta complex. On the one hand, a direct oxidative addition of the carbon-carbon bond of ethane or other alkanes could explain the products such a type of elementary step is rare and is usually a high energy process. On the other hand, formation of tantalum alkyl intermediates via C - H bond activation, a process already ob-... 

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