Olefins alkylating agents

Reaction conditions depend on the reactants and usually involve acid or base catalysis. Examples of X include sulfate, acid sulfate, alkane- or arenesulfonate, chloride, bromide, hydroxyl, alkoxide, perchlorate, etc. RX can also be an alkyl orthoformate or alkyl carboxylate. The reaction of cycHc alkylating agents, eg, epoxides and a2iridines, with sodium or potassium salts of alkyl hydroperoxides also promotes formation of dialkyl peroxides (44,66). Olefinic alkylating agents include acycHc and cycHc olefinic hydrocarbons, vinyl and isopropenyl ethers, enamines, A[-vinylamides, vinyl sulfonates, divinyl sulfone, and a, P-unsaturated compounds, eg, methyl acrylate, mesityl oxide, acrylamide, and acrylonitrile (44,66). 

It is obvious that the production of trimethylpentane involves the formation of an equimolar quantity of a low-boiling paraffin corresponding to the olefin alkylating agent. Such was found to be at least semiquantita-tively the case. It will be noted also that 2 moles of isobutane are consumed for each mole of liquid paraffin produced this excessive consumption of the isobutane is usually undesirable in commercial alkylation processes. 

Other catalysts which may be used in the Friedel - Crafts alkylation reaction include ferric chloride, antimony pentachloride, zirconium tetrachloride, boron trifluoride, zinc chloride and hydrogen fluoride but these are generally not so effective in academic laboratories. The alkylating agents include alkyl halides, alcohols and olefines. 

Reagent for Epoxides e.g. trichothecene-mycotoxins [1 — 6] valepotriates [7,17] Olefins, acetylene derivatives [8] 4-Hydroxycumarin, anthraquinone [8] Alkylating agents [9-12] NOz... 

Isobutylene could be dimerized in the presence of an acid catalyst to diisobutylene. The product is a mixture of diisobutylene isomers, which are used as alkylating agents in the plasticizer industry and as a lube oil additive (dimerization of olefins is noted in Chapter 3). 

The first step in alkylation is the generation of a carbocation (carbo-nium ion). When an olefin is the alkylating agent, a carbocation intermediate forms. 

J. H. Kim and J. J. Thomas, Use of 4-(nitrobenzyl)pyridine (4-NBP) to test mutagenic potential of slow-reacting epoxides, their corresponding olefins, and other alkylating agents. Bulletin of Environmental Contamination and Toxicology, 1992, 49(6), 879-885. 

Tosylhydrazones, with methyllithium to give olefins, 51, 69 Trialkyloxonium salts, as alkylating agents, 51,144... 

Shape selectivity was strongly Influenced by the bulkiness of alkylating agents. The alkylation with ethene was nonselectlve. However, the alkylation with higher olefins occurred para-selectively as in the case of propene. These differences in para-selectivlty reflect the sterlc circumstances of transition... 

Olefins are especially good alkylating agents. With respect to them the reaction is addition of ArH to a C=C double bond ... 

Some zeolitic and non-zeolitic molecular sieve catalysts are claimed to be capable for ortho- and para-selective alkylation using olefin as alkylating agent (refs. 1,2). Zeolite catalysts are less active and selective in the methylation of aniline by methanol (refs. 3,4). Reaction is usually carried out with a large excess of methanol since a large fraction of the alcohol decomposes without participating in the alkylation. Numerous N- and C-alkylated aniline derivatives appear in the reaction product. It was found that N-alkylation requires basic sites while C-alkylation occurs mainly on acidic sites (refs. 5-7). 

Dialkylhalonium ions are reactive alkylating agents. The alkylation of Jt-donor (aromatic and olefinic) and w-donor bases with dialkylhalonium ions has been studied.353 Alkylation of aromatics with dialkylhalonium ions was found to be not significantly different from conventional Friedel-Crafts alkylations, showing particular similarities in the case of alkylation with alkyl iodides. Alkylation of w-donor bases with dialkylhalonium salts provides a simple synthetic route to a wide variety of onium ions. 

When olefins are used as alkylating agents, the catalytic activity of Nafion-H slowly decreases, most probably due to some polymerization on the surface, which deactivates the catalytic sites. The activity decreases faster when more reactive branched alkenes are used. The use of alcohols instead of olefins as the alkylating agents improves the lifetime of the catalyst. With alcohols, no ready polymerization takes place, since water formed as byproduct inhibits polymerization of any olefin formed (by dehydration) but does not affect the acidity of the catalyst at the reaction temperatures. 

In these alkylation reactions primary alkyl halides (the bromide for preference) should be used as the alkylating agents, since secondary and tertiary halides undergo extensive olefin-forming elimination reactions in the presence of the strongly basic acetylide ion. A typical synthesis is that of hex-l-yne (Expt 5.26). 

The observation that the metal carbene complex, (CO)5W = C(Ph)2 [22], catalyzed the polymerization of cyclic olefins to ring opened polymers containing the diphenylmethylene unit of the catalyst provided additional evidence that carbenes were involved in the catalytic cycle. The formation of the initiating metal carbenes in the classic systems that consist of transition metal halides and alkylating agents was proposed to involve metal alkylation followed by oc-hydrogen loss, Eq. (6). Methane and propene were detected in the early stages of these reactions [23]. 

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