C-alkylation C-alkylation is a process for the formation of carbon-carbon bonds. The largest example of this takes place in the
alkylation units of petrochemical plants, which convert low-molecular-weight
alkenes into high octane
gasoline components. Electron-rich species such as
phenols are also commonly alkylated to produce a variety of products; examples include
linear alkylbenzenes used in the production of
surfactants like
LAS, or butylated phenols like
BHT, which are used as
antioxidants. This can be achieved using either acid catalysts like
Amberlyst, or
Lewis acids like aluminium. On a laboratory scale the
Friedel–Crafts reaction uses
alkyl halides, as these are often easier to handle than their corresponding alkenes, which tend to be gasses. The reaction is catalysed by
aluminium trichloride. This approach is rarely used industrially as alkyl halides are more expensive than alkenes.
N-,P-, S- alkylation N-, P-, and S-alkylation are important processes for the formation of carbon-nitrogen, carbon-phosphorus, and carbon-sulfur bonds, Amines are readily alkylated. The rate of alkylation follows the order tertiary amine R-OH + R'-X -> R-O-R' When the alkylating agent is an alkyl halide, the conversion is called the
Williamson ether synthesis. Alcohols are also good alkylating agents in the presence of suitable acid catalysts. For example, most methyl amines are prepared by alkylation of ammonia with methanol. The alkylation of phenols is particularly straightforward since it is subject to fewer competing reactions. :Ph-O- + Me2-SO4 -> Ph-O-Me + Me-SO4- :(with as a
spectator ion) More complex alkylation of a alcohols and phenols involve
ethoxylation.
Ethylene oxide is the alkylating group in this reaction.
Oxidative addition to metals In the process called
oxidative addition, low-valent metals often react with alkylating agents to give metal alkyls. This reaction is one step in the
Cativa process for the synthesis of
acetic acid from
methyl iodide. Many
cross coupling reactions proceed via oxidative addition as well.
Electrophilic alkylating agents is one of the most electrophilic alkylating agents. Electrophilic alkylating agents deliver the equivalent of an alkyl
cation. Alkyl halides are typical alkylating agents.
Trimethyloxonium tetrafluoroborate and
triethyloxonium tetrafluoroborate are particularly strong electrophiles due to their overt positive charge and an inert leaving group (dimethyl or
diethyl ether).
Dimethyl sulfate is intermediate in electrophilicity.
Methylation with diazomethane Diazomethane is a popular
methylating agent in the laboratory, but it is too hazardous (explosive gas with a high acute toxicity) to be employed on an industrial scale without special precautions. Use of diazomethane has been significantly reduced by the introduction of the safer and equivalent reagent
trimethylsilyldiazomethane.
Hazards Electrophilic, soluble alkylating agents are often toxic and carcinogenic, due to their tendency to alkylate DNA. This mechanism of toxicity is relevant to the function of anti-cancer drugs in the form of
alkylating antineoplastic agents. Some
chemical weapons such as
mustard gas (sulfide of dichloroethyl) function as alkylating agents. Alkylated DNA either does not coil or uncoil properly, or cannot be processed by information-decoding enzymes. Without functional DNA, the functioning of the cell ceases, leading to cell death. Thus, these alkylating agents are
cytotoxic.
Catalysts of benzene is often catalyzed by aluminium trichloride. Electrophilic alkylation uses
Lewis acids and
Brønsted acids, sometimes both. Classically, Lewis acids, e.g.,
aluminium trichloride, are employed when the alkyl halide are used. Brønsted acids are used when alkylating with olefins. Typical catalysts are zeolites, i.e. solid acid catalysts, and sulfuric acid.
Silicotungstic acid is used to manufacture
ethyl acetate by the alkylation of
acetic acid by
ethylene: :C2H4 + CH3CO2H -> CH3CO2C2H5 ==In biology==