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36-556: Nucleophilic alkylating agents deliver the equivalent of an alkyl anion ( carbanion ). The formal "alkyl anion" attacks an electrophile , forming a new covalent bond between the alkyl group and the electrophile. The counterion, which is a cation such as lithium, can be removed and washed away in the work-up . Examples include the use of organometallic compounds such as Grignard (organomagnesium) , organolithium , organocopper , and organosodium reagents. These compounds typically can add to an electron-deficient carbon atom such as at

72-500: A carbonyl group . Nucleophilic alkylating agents can displace halide substituents on a carbon atom through the SN2 mechanism. With a catalyst , they also alkylate alkyl and aryl halides, as exemplified by Suzuki couplings . The SN2 mechanism is not available for aryl substituents, where the trajectory to attack the carbon atom would be inside the ring. Thus, only reactions catalyzed by organometallic catalysts are possible. C-alkylation

108-447: A trigonal bipyramidal dihydrogen intermediate is followed by cleavage of the H–H bond, due to electron back donation into the H–H σ*-orbital, i.e. a sigma complex . This system is also in chemical equilibrium , with the reverse reaction proceeding by the elimination of hydrogen gas with simultaneous reduction of the metal center. The electron back donation into the H–H σ*-orbital to cleave

144-590: A carbon attached to one, two, three, or four other carbons respectively. The first named alkyl radical was ethyl, named so by Liebig in 1833 from the German word "Äther" (which in turn had been derived from the Greek word " aither " meaning "air", for the substance now known as diethyl ether ) and the Greek word ύλη ( hyle ), meaning "matter". This was followed by methyl ( Dumas and Peligot in 1834, meaning "spirit of wood" ) and amyl ( Auguste Cahours in 1840 ). The word alkyl

180-567: 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-, 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

216-448: A metal center via a radical mechanism, although some details remain controversial. Reactions which are generally accepted to proceed by a radical mechanism are known however. One example was proposed by Lednor and co-workers. Oxidative addition and reductive elimination are invoked in many catalytic processes in homogeneous catalysis , e.g., hydrogenations , hydroformylations , hydrosilylations , etc. Cross-coupling reactions like

252-534: A metal centre. Oxidative addition is often a step in catalytic cycles , in conjunction with its reverse reaction, reductive elimination. For transition metals, oxidative reaction results in the decrease in the d to a configuration with fewer electrons, often 2e fewer. Oxidative addition is favored for metals that are (i) basic and/or (ii) easily oxidized. Metals with a relatively low oxidation state often satisfy one of these requirements, but even high oxidation state metals undergo oxidative addition, as illustrated by

288-401: A mixture of propene and butene ) in the presence of a Brønsted acid catalyst, which can include solid acids (zeolites). The catalyst protonates the alkenes (propene, butene) to produce carbocations , which alkylate isobutane. The product, called "alkylate", is composed of a mixture of high- octane , branched-chain paraffinic hydrocarbons (mostly isoheptane and isooctane ). Alkylate is

324-430: A premium gasoline blending stock because it has exceptional antiknock properties and is clean burning. Alkylate is also a key component of avgas . By combining fluid catalytic cracking , polymerization, and alkylation, refineries can obtain a gasoline yield of 70 percent. The widespread use of sulfuric acid and hydrofluoric acid in refineries poses significant environmental risks. Ionic liquids are used in place of

360-594: 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

396-519: Is intermediate in electrophilicity. 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 . Electrophilic, soluble alkylating agents are often toxic and carcinogenic, due to their tendency to alkylate DNA. This mechanism of toxicity

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432-563: 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 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

468-474: 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. Electrophilic alkylation uses Lewis acids and Brønsted acids , sometimes both. Classically, Lewis acids, e.g., aluminium trichloride , are employed when

504-435: Is similar to the S N 2 type in that it involves the stepwise addition of two distinct ligand fragments. The key difference being that ionic mechanisms involve substrates which are dissociated in solution prior to any interactions with the metal center. An example of ionic oxidative addition is the addition of hydrogen chloride . In addition to undergoing S N 2-type reactions, alkyl halides and similar substrates can add to

540-481: Is the addition of alkyl groups to molecules, often by alkylating agents such as alkyl halides . Alkylating antineoplastic agents are a class of compounds that are used to treat cancer. In such case, the term alkyl is used loosely. For example, nitrogen mustards are well-known alkylating agents, but they are not simple hydrocarbons. In chemistry, alkyl is a group, a substituent, that is attached to other molecular fragments. For example, alkyl lithium reagents have

576-446: Is the key product-releasing step of several reactions that form C–H and C–C bonds. Oxidative additions proceed by diverse pathways that depend on the metal center and the substrates. Oxidative additions of nonpolar substrates such as hydrogen and hydrocarbons appear to proceed via concerted pathways. Such substrates lack π-bonds , consequently a three-centered σ complex is invoked, followed by intramolecular ligand bond cleavage of

612-448: Is the reaction of hydrogen with Vaska's complex , trans -IrCl(CO)[P(C 6 H 5 ) 3 ] 2 . In this transformation, iridium changes its formal oxidation state from +1 to +3. The product is formally bound to three anions: one chloride and two hydride ligands. As shown below, the initial metal complex has 16 valence electrons and a coordination number of four whereas the product is a six-coordinate 18 electron complex. Formation of

648-416: Is viewed as consisting of two parts. First, five atoms comprise the longest straight chain of carbon centers. The parent five-carbon compound is named pentane (highlighted blue). The methyl "substituent" or "group" is highlighted red. According to the usual rules of nomenclature, alkyl groups are included in the name of the molecule before the root, as in methylpentane . This name is, however, ambiguous, as

684-477: The Base Excision Repair (BER) pathway. Several commodity chemicals are produced by alkylation. Included are several fundamental benzene-based feedstocks such as ethylbenzene (precursor to styrene ), cumene (precursor to phenol and acetone ), linear alkylbenzene sulfonates (for detergents). In a conventional oil refinery , isobutane is alkylated with low-molecular-weight alkenes (primarily

720-404: The H–H bond causes electron-rich metals to favor this reaction. The concerted mechanism produces a cis dihydride, while the stereochemistry of the other oxidative addition pathways do not usually produce cis adducts. Some oxidative additions proceed analogously to the well known bimolecular nucleophilic substitution reactions in organic chemistry . Nucleophilic attack by the metal center at

756-645: 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 : Alkylation in biology causes DNA damage . It is the transfer of alkyl groups to the nitrogenous bases . It is caused by alkylating agents such as EMS (Ethyl Methyl Sulphonate). Bifunctional alkyl groups which have two alkyl groups in them cause cross linking in DNA. Alkylation damaged ring nitrogen bases are repaired via

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792-922: The empirical formula Li(alkyl), where alkyl = methyl, ethyl, etc. A dialkyl ether is an ether with two alkyl groups, e.g., diethyl ether O(CH 2 CH 3 ) 2 . In medicinal chemistry , the incorporation of alkyl chains into some chemical compounds increases their lipophilicity . This strategy has been used to increase the antimicrobial activity of flavanones and chalcones . Usually, alkyl groups are attached to other atoms or groups of atoms. Free alkyls occur as neutral radicals, as anions, or as cations. The cations are called carbocations . The anions are called carbanions . The neutral alkyl free radicals have no special name. Such species are usually encountered only as transient intermediates. However, persistent alkyl radicals with half-lives "from seconds to years" have been prepared. Typically alkyl cations are generated using superacids and alkyl anions are observed in

828-530: The formula −C n H 2 n −1 , e.g. cyclopropyl and cyclohexyl. The formula of alkyl radicals are the same as alkyl groups, except the free valence " − " is replaced by the dot "•" and adding "radical" to the name of the alkyl group (e.g. methyl radical •CH 3 ). The naming convention is taken from IUPAC nomenclature : The prefixes taken from IUPAC nomenclature are used to name branched chained structures by their substituent groups, for example 3-methylpentane : The structure of 3-methylpentane

864-431: The general formula of −C n H 2 n +1 . A cycloalkyl group is derived from a cycloalkane by removal of a hydrogen atom from a ring and has the general formula −C n H 2 n −1 . Typically an alkyl is a part of a larger molecule. In structural formulae , the symbol R is used to designate a generic (unspecified) alkyl group. The smallest alkyl group is methyl , with the formula −CH 3 . Alkylation

900-486: The less electronegative atom in the substrate leads to cleavage of the R–X bond, to form an [M–R] species. This step is followed by rapid coordination of the anion to the cationic metal center. For example, reaction of a square planar complex with methyl iodide : This mechanism is often assumed in the addition of polar and electrophilic substrates, such as alkyl halides and halogens . The ionic mechanism of oxidative addition

936-461: The ligand (probably by donation of electron pair into the sigma* orbital of the inter ligand bond) to form the oxidized complex. The resulting ligands will be mutually cis , although subsequent isomerization may occur. This mechanism applies to the addition of homonuclear diatomic molecules such as H 2 . Many C–H activation reactions also follow a concerted mechanism through the formation of an M–(C–H) agostic complex . A representative example

972-425: The metal complex have a vacant coordination site. For this reason, oxidative additions are common for four- and five-coordinate complexes. Reductive elimination is the reverse of oxidative addition. Reductive elimination is favored when the newly formed X–Y bond is strong. For reductive elimination to occur the two groups (X and Y) should be mutually adjacent on the metal's coordination sphere . Reductive elimination

1008-510: The methyl branch could be on various carbon atoms. Thus, the name is 3-methylpentane to avoid ambiguity: The 3- is because the methyl is attached to the third of the five carbon atoms. If there is more than one of the same alkyl group attached to a chain, then the prefixes are used on the alkyl groups to indicate multiples (i.e., di, tri, tetra, etc.) This compound is known as 2,3,3-trimethylpentane . Here three identical alkyl groups attached to carbon atoms 2, 3, and 3. The numbers are included in

1044-545: The name to avoid ambiguity about the position of the groups, and "tri" indicates that there are three identical methyl groups. If one of the methyl groups attached to the third carbon atom were instead an ethyl group, then the name would be 3-ethyl-2,3-dimethylpentane. When there are different alkyl groups, they are listed in alphabetical order. In addition, each position on an alkyl chain can be described according to how many other carbon atoms are attached to it. The terms primary , secondary , tertiary , and quaternary refer to

1080-474: The older generation of strong Bronsted acids. Complementing alkylation reactions are the reverse, dealkylations. Prevalent are demethylations , which are prevalent in biology, organic synthesis, and other areas, especially for methyl ethers and methyl amines . Alkyl In organic chemistry , an alkyl group is an alkane missing one hydrogen . The term alkyl is intentionally unspecific to include many possible substitutions. An acyclic alkyl has

1116-561: The order tertiary amine < secondary amine < primary amine. Typical alkylating agents are alkyl halides. Industry often relies on green chemistry methods involving alkylation of amines with alcohols, the byproduct being water. Hydroamination is another green method for N-alkylation. In the Menshutkin reaction , a tertiary amine is converted into a quaternary ammonium salt by reaction with an alkyl halide . Similar reactions occur when tertiary phosphines are treated with alkyl halides,

Alkylation - Misplaced Pages Continue

1152-580: The oxidation of Pt(II) with chlorine: In classical organometallic chemistry , the formal oxidation state of the metal and the electron count of the complex both increase by two. One-electron changes are also possible and in fact some oxidative addition reactions proceed via series of 1e changes. Although oxidative additions can occur with the insertion of a metal into many different substrates, oxidative additions are most commonly seen with H–H, H–X, and C–X bonds because these substrates are most relevant to commercial applications. Oxidative addition requires that

1188-615: The presence of strong bases. Alkyl radicals can be generated by a photochemical reaction or by homolytic cleavage . Alkyls are commonly observed in mass spectrometry of organic compounds . Simple alkyls (especially methyl ) are observed in the interstellar space as well. Alkyl groups form homologous series . The simplest series have the general formula −C n H 2 n +1 . Alkyls include methyl , ( −CH 3 ), ethyl ( −C 2 H 5 ), propyl ( −C 3 H 7 ), butyl ( −C 4 H 9 ), pentyl ( −C 5 H 11 ), and so on. Alkyl groups that contain one ring have

1224-507: 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. More complex alkylation of a alcohols and phenols involve ethoxylation . Ethylene oxide is the alkylating group in this reaction. In the process called oxidative addition , low-valent metals often react with alkylating agents to give metal alkyls. This reaction

1260-526: The products being phosphonium salts. Thiols are readily alkylated to give thioethers via the thiol-ene reaction . The reaction is typically conducted in the presence of a base or using the conjugate base of the thiol. Thioethers undergo alkylation to give sulfonium ions . Alcohols alkylate to give ethers : When the alkylating agent is an alkyl halide, the conversion is called the Williamson ether synthesis . Alcohols are also good alkylating agents in

1296-399: Was introduced by Johannes Wislicenus in or before 1882, based on the German word "Alkoholradikale" and then-common suffix -yl. Oxidative addition Oxidative addition and reductive elimination are two important and related classes of reactions in organometallic chemistry . Oxidative addition is a process that increases both the oxidation state and coordination number of

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