Protonic acids reactions with olefins

The acid-induced reaction of aryldiazomethanes with olefins gives arylcyclo-propanes in addition to olefins and esters. The cyclopropanes are formed stereo-specifically and their yields are largest in reactions with olefins which on cation addition give secondary carbonium ion centres. The use of deuteriated acids leads to partial incorporation of deuterium in the cyclopropane adducts, whereas the use of [a- H]-phenyldiazomethane leads to partial loss of deuterium, suggesting a slow proton transfer from the acid to the diazo-compound a carbenoid rather than a free carbene appears to be involved. 

Either concentrated sulfuric acid or anhydrous hydrofluoric acid is used as a catalyst for the alkylation reaction. These acid catalysts are capable of providing a proton, which reacts with the olefin to form a carbocation. For example, when propene is used with isohutane, a mixture of C5 isomers is produced. The following represents the reaction steps ... 

Strong protonic acids can affect the polymerization of olefins (Chapter 3). Lewis acids, such as AICI3 or BF3, can also initiate polymerization. In this case, a trace amount of a proton donor (cocatalyst), such as water or methanol, is normally required. For example, water combined with BF3 forms a complex that provides the protons for the polymerization reaction. 

The Lewis acid-Lewis base interaction outlined in Scheme 43 also explains the formation of alkylrhodium complexes 414 from iodorhodium(III) meso-tetraphenyl-porphyrin 409 and various diazo compounds (Scheme 42)398), It seems reasonable to assume that intermediates 418 or 419 (corresponding to 415 and 417 in Scheme 43) are trapped by an added nucleophile in the reaction with ethyl diazoacetate, and that similar intermediates, by proton loss, give rise to vinylrhodium complexes from ethyl 2-diazopropionate or dimethyl diazosuccinate. As the rhodium porphyrin 409 is also an efficient catalyst for cyclopropanation of olefins with ethyl diazoacetate 87,1°°), stj bene formation from aryl diazomethanes 358 and carbene insertion into aliphatic C—H bonds 287, intermediates 418 or 419 are likely to be part of the mechanistic scheme of these reactions, too. 

The reactions covered in Scheme 2 are initiated by protonation but a hydride could form on the metal as intermediate. In some instances, cationic metal hydrides have been shown to be actually involved. See, for example, the addition of [HNi (POEt)3 4+] to butadiene (54) or of [HNi(Ph3P)3(7r-C3H5)] to olefins (10c, Vol. II, p. 25). Thus the reaction of olefins or dienes with acids in the presence of zero-valent nickel may be considered proton-promoted as well as hydride-promoted. 

In concluding this paper dedicated to our distinguished octogenarian, it is especially appropriate to mention the heuristic practical value which our ring-expansion theory has had, since he has always been intent upon applications and practical uses. It was the ring-expansion theory which led the senior author to imagine that the acid-catalysed reactions of cyclic formals with olefins would be insertion reactions [21]. In his view they involve the insertion of an olefin into the 0-1, C-2 bond of a protonated (or alkylated) 1,3-dioxacycloalkane ... 

Once formed, the radical intermediate (R ) can couple to afford a dimer (R2), can disproportionate to give an alkane (RH) and an olefin (R(—H)), or can accept a hydrogen atom from a donor (such as the solvent, SH) to give an alkane. A carbanion (R ) can be protonated by the solvent (or a deliberately added acid, HB) to yield an alkane. In addition, RX can undergo E2 and Sn2 reactions with B , and R can attack RX to form a dimer. 

An interesting effect of pH was found by Ogo et al. when studying the hydrogenation of olefins and carbonyl compounds with [Cp Ir(H20)3] (Cp = ri -CsMej) [89]. This complex is active only in strongly acidic solutions. From the pH-dependence ofthe HNMR spectra it was concluded that at pH 2.8 the initial mononuclear compound was reversibly converted to the known dinuclear complex [(Cp Ir)2(p-OH)3] which is inactive for hydrogenation. In the strongly acidic solutions (e.g. 1 M HCIO4) protonation of the substrate olefins and carbonyl compounds is also likely to influence the rate ofthe reactions. 

Other Reactions of Olefinic Steroids.—Reaction of cholest-5-en-3-one with air and acetic acid shows that isomerization to the A -3-oxo-compound is accompanied by autoxidation to the 6a- and 6/8-hydroxy-3-oxo-A -compounds and the 3,6-dioxo-A -compound. The oxidation appears to be controlled by heterolysis of the 4/3-proton and formation of the intermediate ion pair (73). Sitosterol was autoxi-dized at C-7 to give the 7-oxo- and the epimeric 7-hydroxy-derivatives. Oxidation of a 17-methylene steroid with Pb, Tl" , and Hg acetates in methanol gave a wide variety of products. The reaction with Pb(OAc)4 gave the rearranged products (74), (75), and (76) whereas the Tl and Hg products retained the... 

The process involves reacting butenes and mixtures of propenes and butenes with either a phosphoric acid type catalyst (UOP Process) or a nickel complex-alkyl aluminum type catalyst (IFP Dimersol Process) to produce primarily hexene, heptene, and octene olefins. The reaction first proceeds through the formation of a carbocation which then combines with an olefin to form a new carbocation species. The acid proton donated to the olefin initially is then released and the new olefin forms. Hydrotreatment of the newly formed olefin species results in stable, high-octane blending components. 

Ion 24 can either lose a proton or combine with chloride ion. If it loses a proton, the product is an unsaturated ketone the mechanism is similar to the tetrahedral mechanism of Chapter 10, but with the charges reversed. If it combines with chloride, the product is a (3-halo ketone, which can be isolated, so that the result is addition to the double bond (see 5-34). On the other hand, the p-halo ketone may, under the conditions of the reaction, lose HC1 to give the unsaturated ketone, this time by an addition-elimination mechanism. In the case of unsymmetrical olefins, the attacking ion prefers the position at which there are more hydrogens, following Markovnikov s rule (p. 750). Anhydrides and carboxylic acids (the latter with a proton acid such as anhydrous HF, H2S04, or polyphosphoric acid as a catalyst) are sometimes used instead of acyl halides. With some substrates and catalysts double-bond migrations are occasionally encountered so that, for example, when 1-methylcyclohexene was acylated with acetic anhydride and zinc chloride, the major product was 6-acetyl-l-methylcyclohexene.198... 

So diat charge is conserved, anionic bases upon reaction with a proton give neutral conjugate acids neutral bases upon reaction with a proton give positively charged conjugate acids. Occasionally shared pairs of electrons can be given up to a proton such as when olefins react with acids. In such cases n electrons are die electron pair which forms a bond to the proton. 

Alkylation. Reactions of olefins with isoparaffins require a highly acidic catalyst. Both Friedel-Crafts and protonic acids are used. The protonic acids, sulfuric (96-100%) and hydrofluoric acids, are commonly used. If the... 

Transfer of two hydride ions and one proton would result in DMH. Since the methyl groups could migrate on the chain, DMH s other than 2,5-DMH could be produced. Some t-butyl cations dissociate into isobutylene and protons hence this method could occur during alkylation with olefins other than isobutylene. Reaction N is probably only of minor Importance in most cases, however, since only small concentrations of free isobutylene are thought to occur at the acid-hydrocarbon interface most isobutylene quickly protonates to form t-butyl cations. 

There are many examples of the alkylation of aromatics with olefins to produce alkylbenzene In textbooks, the open literature, and In numerous patents. This reaction Is catalyzed by both proton and Lewis acids In a homogeneous phase and In heterogeneous phases. The latter systems are characterized by both proton (H FO ) and Lewis acids (BF ) on supports and the amorphous and crystalline alumina silicates. And, the reaction has been studied extensively. However, up until the start of this Investigation (1969) there had not been a systematic investigation of the kinetic parameters nor an adequate catalyst aging study on the alkylation of benzene with propylene over a crystalline alumina silicate. 

The processes are the monomolecular reaction through a protonated cyclopropane produced by the abstraction of H" over Lewis acid sites and the bimolecular mechanism where an olefin takes part in the reaction. The olefin is produced over Bronsted acid sites, in the case of butane in the monomolecular mechanism, isobutane is formed through protonated methylcyclopropane with an activation energy of 8.4kcalmoT followed by the formation of the primary isobutyl cation with high energy [134]. 

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