Self-alkylation reaction

The actual research is focused on finding new types of zeolites or modifying already known ones (5), to selectively catalyze branching isomerization and self alkylation reactions in the gasoline fraction, while minimizing overcracking. Efforts have also been devoted to development of new active and selective matrices. 

Dimerization and trimerization of alkylbromocyanoacetates (a self-alkylation reaction) has been used for the synthesis of highly substituted cyclopropanes and dialkyl-( )-2,3-dicyanobutendioates (equation 71). The latter products are potentially very useful for the synthesis of a wide range of heterocyclic compounds. 

R1 = phenyl in compound 170, the acidity of the amino hydrogen is such that deprotonation is easily achieved using sodium carbonate as a base. Where R1 is aliphatic or alicyclic, a stronger base mixture of sodium hydroxide/potassium carbonate is used. Self-alkylation reactions of the esters 170 was avoided by using excess of the alkylation reagents 175 and high yields are generally achieved. 

The replacement of the hydrogen of the methylo1 compound with an alkyl group renders the compound much more soluble in organic solvents and more stable. This reaction is also cataly2ed by acids and usually carried out in the presence of considerable excess alcohol to suppress the competing self-condensation reaction. After neutrali2ation of the acid catalyst, the excess alcohol may be stripped or left as a solvent for the amino resin. 

Because of self-condensation under the conditions of the alkylation reaction, enamines derived from acetaldehyde or monosubstituted acetaldehydes cannot usually be alkylated 28) except when there is a bulky secondary amine used to produce the enamine 32a). In these cases C alkylation takes place in good yield. 

Water, which can be taken to a minimum by the use of molecular sieves, can produce a lactamide either through direct reaction with the aziridinone intermediate, or upon hydrolysis of oxazolidinone self-condensation products, previously obtained also in the presence of a strong non-nucleophilic base (H ) (ref. 17). The recently reported 0-self-alkylation compound H bears the (S,S)-configurations at the unreacted C-Br and newly formed C-0 bonds. The presence of bromine was expedient for the x-ray assessment of configuration at the two chiral centers of 11 which forms in high diastereoisomeric excess (ref. 5). 

With hydrofluoric acid (23,50), and to a lesser degree also with zeolites (14,81, 87-89), a significant fraction of the product stems from self-alkylation, which is sometimes also termed hydrogen transfer. The importance of this mechanism depends on the acid, the alkene, and the reaction temperature. Self-alkylation... 

The crucial step in self-alkylation is decomposition of the butoxy group into a free Brpnsted acid site and isobutylene (proton transfer from the Fbutyl cation to the zeolite). Isobutylene will react with another t-butyl cation to form an isooctyl cation. At the same time, a feed alkene repeats the initiation step to form a secondary alkyl cation, which after accepting a hydride gives the Fbutyl cation and an -alkane. The overall reaction with a linear alkene CnH2n as the feed is summarized in reaction (10) ... 

With propene, n-butene, and n-pentene, the alkanes formed are propane, n-butane, and n-pentane (plus isopentane), respectively. The production of considerable amounts of light -alkanes is a disadvantage of this reaction route. Furthermore, the yield of the desired alkylate is reduced relative to isobutane and alkene consumption (8). For example, propene alkylation with HF can give more than 15 vol% yield of propane (21). Aluminum chloride-ether complexes also catalyze self-alkylation. However, when acidity is moderated with metal chlorides, the self-alkylation activity is drastically reduced. Intuitively, the formation of isobutylene via proton transfer from an isobutyl cation should be more pronounced at a weaker acidity, but the opposite has been found (92). Other properties besides acidity may contribute to the self-alkylation activity. Earlier publications concerned with zeolites claimed this mechanism to be a source of hydrogen for saturating cracking products or dimerization products (69,93). However, as shown in reaction (10), only the feed alkene will be saturated, and dehydrogenation does not take place. 

Patents assigned to Mobil (217) describe the use of boron trifluoride supported on several porous carriers. BF3 supported on silica was found to exhibit a slightly higher performance with added water in the alkylation of a mixed alkene feed at 273 K. It was also shown that self-alkylation activity was considerably lower than that with HF as catalyst. Another patent (218) describes the use of a pillared layered silicate, MCM-25, promoted with BF3 to give a high-quality alkylate at temperatures of about 273 K. BF3 was also supported on zeolite BEA, with adsorbed water still present (219). This composite catalyst exhibited low butene isomerization activity, which was evident from the inferior results obtained with 1-butene. At low reaction temperatures, the product quality was superior to that of HF alkylate. 

In 1899 R. C. Guerbet discovered the self-condensation reaction of alcohols, which, via the aldehyde as an intermediate, lead to branched structures (2-alkyl alcohols) (Fig. 4.21) - the Guerbet alcohols. Starting with fatty alcohols from vegetable sources, such as octanol and decanol, the corresponding C1(, and C2o alcohols are produced (2-hexyldecanol and 2-octyldecanol, respectively). The reaction is carried out under alkali catalysis and high temperatures (>200 °C). Over the years, both products have proven to be efficient emollients, but are also used for other applications, such as plasticizers or components for lubricants (Fig. 4.21). 

These rate differences show that, over platinum on silica-alumina, two cyclization reactions occur simultaneously. One is catalyzed by the platinum metal it is the mechanism observed over platinum on silica. Acid catalyzed self-alkylation is the second reaction. The following steps are involved. 

The self-recombination reactions of HOj, CF3CFHO, and CF3O) have been studied using pulse radiolysis/time-resolved UV absorption spectroscopy.215 The addition of the cumylperoxy radical to a range of alkyl-substituted biphenyls has been studied and the rate constants compared with reactions with related monosubstituted benzenes.216... 

Generally, the preparation of symmetrical dialkylhalonium ions is simpler and the reactions are clean. Unsymmetrical dialkylhalonium ions undergo disproportionation and alkylation (self-condensation) reactions, even at low temperatures (about 30°C). 

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