Alkene industrial preparation

Although alkenes typically react with chlorine and bromine by addition at room tern perature and below (Section 6 14) substitution becomes competitive at higher tempera tures especially when the concentration of the halogen is low When substitution does occur It IS highly selective for the allylic position This forms the basis of an industrial preparation of allyl chloride... 

The key factor is the action of the metal on the peroxo group making one oxygen atom electrophilic. Whether or not the metal is bonded to the alkene in the intermediate is not known if so, this will depend strongly on the particular substrate and the catalyst. Later, in the discussion of the dihydroxylation reaction we will come back to this (section 14.3.2). In the example shown in Figure 14.2 the second product is t-butanol stemming from t-butylhydroperoxide (industrially prepared from isobutane and dioxygen). 

Trimethylaluminum cannot be prepared by any of the above processes, which rely on alkene insertion. The industrial preparation of trimethylaluminum is achieved by reaction of ground aluminum with chloromethane to yield the sesquichloride, Me3Al2Cl3, and subsequent reduction with sodium metal (equation 8). This procedure also works for the... 

Racemic 4-acetoxy-3-unsubstituted azetidinone 10 and homochiral (3R,4R)-3-(IR)-hydroxyethyl derivative 11, commercially available intermediates industrially prepared by the so-called CSI route , testify to the importance of this ring formation strategy. By using vinyl acetate as the olefin partner in the chlorosulfonylisocyanate-alkene cycloaddition, in 1974, Clauss et al. [10] laid down the basis of this approach in the field of p-lactam antibiotics. The most recent efforts have been directed to the key intermediate 11 and its synthetic equivalents 12, 13. Starting from methyl 3R-hydroxybutyrate [11], three independent methodologies have been realized, the main difference being the type (ether, thioether, ester) of enolate used. 

Among other applications olefin metathesis is useful in the synthesis of cyclic alkenes, the industrial preparation of propene, and in polymerization. 

One oxidation reaction that is of large industrial relevance is the oxidative dehydrogenation of light alkanes to the corresponding alkene (Scheme 3.20). This reaction has been reported to be promoted by r-GO as catalyst [29]. The importance of this reaction type is particularly high for the industrial preparation of propene from propane and butenes from butanes. Both reactions are carried out industrially in very large scale, because propene is the monomer of polypropene and also the starting material of propylene oxide, acrylonitrile, and other base chemicals. Butenes are mainly used for the preparation of 1,3-butadiene that is one of the major components of rubbers and elastomers. 

Alkylaluminium compounds are produced on a very large scale industrially. This is somewhat remarkable considering their extreme susceptibility to oxidation and hydrolysis, which makes handling hazardous. In 1975 about 20000 tonnes were produced worldwide for sale and a further 90000 tonnes were used as intermediates in the manufacture of linear alcohols and 1-alkenes. Their preparation depends on hydroalumination , or the addition of A1—H to an alkene. The key to the success of this method, which is much more suitable to industrial than to laboratory use, is the production of metal with an active surface. One way of achieving this is ball-milling the powder in contact with the metal alkyl. 

Dimerization in concentrated sulfuric acid occurs mainly with those alkenes that form tertiary carbocations In some cases reaction conditions can be developed that favor the formation of higher molecular weight polymers Because these reactions proceed by way of carbocation intermediates the process is referred to as cationic polymerization We made special mention m Section 5 1 of the enormous volume of ethylene and propene production in the petrochemical industry The accompanying box summarizes the principal uses of these alkenes Most of the ethylene is converted to polyethylene, a high molecular weight polymer of ethylene Polyethylene cannot be prepared by cationic polymerization but is the simplest example of a polymer that is produced on a large scale by free radical polymerization... 

The preparation and structure determination of ferrocene marked the beginning of metallocene chemistry Metallocenes are organometallic compounds that bear cyclo pentadiemde ligands A large number are known even some m which uranium is the metal Metallocenes are not only stucturally interesting but many of them have useful applications as catalysts for industrial processes Zirconium based metallocenes for example are the most widely used catalysts for Ziegler-Natta polymerization of alkenes We 11 have more to say about them m Section 14 15... 

Ethylene glycol and propy lene glycol are prepared industrially from the corre spending alkenes by way of their epoxides Someapplica tions were given in the box in Section 6 21... 

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