Addition to ethylenic bonds

Addition of aliphatic hydrocarbons to ethylenic compounds occurs under the influence of catalysts such as sulfuric acid, phosphoric acid, and aluminum chloride.1 For instance, isobutane and propene afford the three isomeric heptanes. This reaction is not of particular importance in laboratory practice. However, addition of aromatic compounds to olefins is often a practicable method of alkylation.2 Thus ethylbenzene is formed from ethylene and benzene under the influence of aluminum chloride or when the hydrocarbon mixture is passed over a silica-alumina catalyst and Brochet3 obtained 2-phenyl-hexane from benzene and 1-hexene. The C-C bond is always formed to the doubly bonded carbon atom carrying the smaller number of hydrogen atoms benzene and propene, for instance, give cumene, which is important as intermediate in the preparation of phenol. Corson and Ipatieff4 report that benzene reacts especially readily with cyclohexene, yielding cyclohexylbenzene  

Adding cyclohexene (164 g) during 2 h, with stirring, to an ice-cold mixture of benzene (400 g) and concentrated sulfuric acid (92 g) affords cyclohexylbenzene (200 g), b.p. 239-245°. When the reaction mixture is worked up, it is important that before distillation the oily layer must be washed twice with cold concentrated sulfuric acid (50-ml portions) and then successively with water, dilute alkali hydroxide solution, and water. 

Under the above conditions allyl chloride converts benzene into co-chloro-cumene, thus providing a key atom in the side chain for further reactions  

Addition of tertiary or secondary carbonium ions to 1,1-dichloroethylene in sulfuric acid at 0-15° leads to substituted acetic acids,5 the yield being considerably increased, when necessary, if the acid contains 8% by weight of boron trifluoride. Olefins, alcohols, chlorides, and esters can be used to provide the cation. 

3-Phenylbutyric acid 6 A mixture of a-methylbenzyl alcohol (122 g) and 1,1-dichloroethylene (291 g) is dropped into 90% sulfuric acid (200 ml) with stirring at 5-7°. Addition and subsequent stirring each occupy 2 h. The mixture is then hydrolysed with ice, and the precipitated product is taken up in ether. The carboxylic acid is purified by dissolution in aqueous sodium hydroxide solution and reprecipitation by dilute hydrochloric acid. This gives a product (85 g,) m.p. 38 10°, b.p. 113-115°/2 mm. 

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Systematic studies of the selectivity of electrophilic bromine addition to ethylenic bonds are almost inexistent whereas the selectivity of electrophilic bromination of aromatic compounds has been extensively investigated (ref. 1). This surprising difference arises probably from particular features of their reaction mechanisms. Aromatic substitution exhibits only regioselectivity, which is determined by the bromine attack itself, i.e. the selectivity- and rate-determining steps are identical. 

Reagent BMC may cause chlorine addition to ethylenic bonds. This does not occur when the steric strain of the product is forbiddingly high as in perchloroethylbenzene (Ballester and Castaner, 1966 Ballester et al., 1961, 1967) and perchlorobibenzyl (Ballester et al., 1967), but it does take place, at least partly, when the steric strain of both the substrate (the ethylene) and the product (the ethane) are comparable. For example, from either styrene [14] or [15], a mixture of 27/-nonachloroethylbenzene and perchlorostyrene is obtained (Ballester and Castaner, 1966 Ballester et al., 1959b, 1961). 

This section will be mainly devoted to intramolecular radical addition to acetylenic bonds. Some studies with radical addition to allenic systems and cyclopropane rings will also be discussed. Compared to the well-known inter-molecular free radical addition to ethylenic bonds, very little is known about free radical additions to acetylenic or allenic bonds, the same is true of intramolecular processes. 

The use of TAG as a curing agent continues to grow for polyolefins and olefin copolymer plastics and mbbers. Examples include polyethylene (109), chlorosulfonated polyethylene (110), polypropylene (111), ethylene—vinyl acetate (112), ethylene—propylene copolymer (113), acrylonitrile copolymers (114), and methylstyrene polymers (115). In ethylene—propylene copolymer mbber compositions. TAG has been used for injection molding of fenders (116). Unsaturated elastomers, such as EPDM, cross link with TAG by hydrogen abstraction and addition to double bonds in the presence of peroxyketal catalysts (117) (see Elastol rs, synthetic). 

Photochemical additions to give four-membered rings are known. Thus, the reactions of imidazoles across the 4,5-bond with benzophenone and acrylonitrile are illustrated by (389—>390) and (391—>392), respectively (80AHC(27)24l). Oxazolin-2-one undergoes acetone-photosensitized photochemical addition to ethylene (80CB1884). 

Reaction LXXVI. Addition of Hydroxyl to Ethylenic Bonds. (B., 21, 919 A., 268, 27.)—When compounds containing ethylenic linkages are treated with mild oxidising agents, e.g., bromine and caustic potash, dilute nitric acid and especially very dilute (2%) potassium permanganate solution, addition of hydroxyl at the double bond to form a 1 2-dihydroxy compound occurs. 

There is a dramatic kinetic stabilization by bulky substituents of the three-membered ring products from silylene addition to jr-bonds. Addition of t-Bu2Si to ethylene led to the first silirane with no substituents on its ring carbon atoms as a distillable liquid 164. Interestingly, l,l-di(terf-butyl)silirane does not undergo photochemical or thermal silylene extrusion, but instead polymerizes. A distillable silirane was also reported from addition of t-Bu2Si to 2-methylstyrene165. 

Addition to double bonds may also occur by a free-radical mechanism. Polyethylene can be made in this way from the monomer ethylene. 

Aminothiazole, with acetaldehyde, 42 to 2-mercaptothiazoie, 370 4-Aminothiazole-2,5-diphenyl, to 2,5 di-phenyl-A-2-thiazoline-4-one, 421 Ammothiazoie-A -oxide, 118 2-Aminothiazoles. 12 acidity of, 90 and acrylophenone, 42 acylations of, with acetic acid. 53 with acetic anhydride, 52 with acyl halides, 48 with chloracetyl chloride, 49 with-y-chlorobutyrylchloride, 50 with 0-chloropropionylchloride, 50 with esters, 53 with ethy acrylate, 54 with indoiyl derivatives, 48 with malonic esters, 55 with malonyl chloride, 49 with oxalyl chloride, 50 with sodium acetate, 52 with unsaturated acyl chloride, 49 additions to double bonds, 40 with aldehydes, 98 alkylations, with alcohols, 38 with benzyhydryl chloride, 34 with benzyl chloride, 80 with chloracetic acid, 33 with chloracetic esters, 33 with 2-chloropropionic acid, 32 with dialkylaminoalkyl halides, 33 with dimethylaminoethylchloride, 35 with ethylene oxide, 34, 38... 

It is rather surprising that these calculations show that the activation energ> for a CIU Ti) insertion into a methanc-CH bond is lower(3.H Kcal/molc) than for an addition to ethylene (calculated S.8 Kcal/mule). 

Additions to nonactivated olefins and dienes are important reactions in organic synthesis [1]. Although cycloadditions may be used for additions to double bonds, the most common way to achieve such reactions is to activate the olefins with an electrophilic reagent. Electrophilic activation of the olefin or diene followed by a nucleophilic attack at one of the sp carbon atoms leads to a 1,2- or 1,4-addition. More recently, transition metals have been employed for the electrophilic activation of the double bond [2]. In particular, palladium(II) salts are known to activate carbon-carbon double bonds toward nucleophilic attack [3] and this is the basis for the Wacker process for industrial oxidation of ethylene to acetaldehyde [41. In this process, the key step is the nucleophilic attack by water on a (jt-ethylene)palladium complex. 

Several early attempts at ADMET polymerization were made with classical olefin metathesis catalysts [57-59]. The first successful attempt was the ADMET polymerizations of 1,9-decadiene and 1,5-hexadiene with the WClg/EtAlf l,. catalyst mixture [60]. As mentioned in the introduction, the active catalytic entities in these reactions are ill-defined and not spectroscopically identifiable. Ethylene was trapped from the reaction mixture and identified. In addition to the expected ADMET polymers, intractable materials were observed, which were presumed to be the result of vinyl polymerization of the diene to produce crosslinked polymer. Addition to double bonds is a common side reaction promoted by classical olefin metathesis catalysts. Indeed, reaction of styrene with this catalyst mixture and even wifh WCl, alone led to polystyrene. Years later, classical catalysts were revisited in fhe context of producing tin-containing ADMET polymers wifh tungsten phenoxide catalysts [61], Alkyl tin reagents have long been known to act as co-catalysts in classical metathesis catalyst mixtures, and in this case the tin-containing monomer acted as monomer and cocatalyst [62]. Monomers with less than three methylene spacers between the olefin and tin atoms did not polymerize (Scheme 6.14). 

FIGURE 16. 6-31G transition state structures for the addition of H20 to silaethylene and to ethylene. Bond distances are in A, bond angles in deg. Reproduced by permission of Kluwer Academic Publishers from Ref. 175b. 

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