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22-398: The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring . Friedel–Crafts reactions are of two main types: alkylation reactions and acylation reactions. Both proceed by electrophilic aromatic substitution . In commercial applications, the alkylating agents are generally alkenes , some of

44-777: A ligand in an inorganic or organometallic complex (a metal carbonyl , e.g. nickel carbonyl ). The remainder of this article concerns itself with the organic chemistry definition of carbonyl, such that carbon and oxygen share a double bond. In organic chemistry, a carbonyl group characterizes the following types of compounds: Other organic carbonyls are urea and the carbamates , the derivatives of acyl chlorides chloroformates and phosgene , carbonate esters , thioesters , lactones , lactams , hydroxamates , and isocyanates . Examples of inorganic carbonyl compounds are carbon dioxide and carbonyl sulfide . A special group of carbonyl compounds are dicarbonyl compounds, which can exhibit special properties. For organic compounds,

66-489: A Brønsted acid catalyst using the anhydride or even the carboxylic acid itself as the acylation agent. If desired, the resulting ketone can be subsequently reduced to the corresponding alkane substituent by either Wolff–Kishner reduction or Clemmensen reduction . The net result is the same as the Friedel–Crafts alkylation except that rearrangement is not possible. Arenes react with certain aldehydes and ketones to form

88-457: Is completed by deprotonation of the arenium ion by AlCl 4 , regenerating the AlCl 3 catalyst. However, in contrast to the truly catalytic alkylation reaction, the formed ketone is a moderate Lewis base, which forms a complex with the strong Lewis acid aluminum trichloride. The formation of this complex is typically irreversible under reaction conditions. Thus, a stochiometric quantity of AlCl 3

110-422: Is needed. The complex is destroyed upon aqueous workup to give the desired ketone. For example, the classical synthesis of deoxybenzoin calls for 1.1 equivalents of AlCl 3 with respect to the limiting reagent, phenylacetyl chloride. In certain cases, generally when the benzene ring is activated, Friedel–Crafts acylation can also be carried out with catalytic amounts of a milder Lewis acid (e.g. Zn(II) salts) or

132-554: Is reacted with succinic anhydride , the subsequent product is then reduced in either a Clemmensen reduction or a Wolff-Kishner reduction . Lastly, a second Friedel-Crafts acylation takes place with addition of acid. The product formed in this reaction is then analogously reduced, followed by a dehydrogenation reaction (with the reagent SeO 2 for example) to extend the aromatic ring system. Reaction of chloroform with aromatic compounds using an aluminium chloride catalyst gives triarylmethanes, which are often brightly colored, as

154-451: Is shown below. Friedel–Crafts alkylations can be reversible . Although this is usually undesirable it can be exploited; for instance by facilitating transalkylation reactions. It also allows alkyl chains to be added reversibly as protecting groups . This approach is used industrially in the synthesis of 4,4'-biphenol via the oxidative coupling and subsequent dealkylation of 2,6-di-tert-butylphenol . Friedel–Crafts acylation involves

176-547: Is the case in triarylmethane dyes. This is a bench test for aromatic compounds. Organic reaction Too Many Requests If you report this error to the Wikimedia System Administrators, please include the details below. Request from 172.68.168.132 via cp1112 cp1112, Varnish XID 389098163 Upstream caches: cp1112 int Error: 429, Too Many Requests at Fri, 29 Nov 2024 05:36:30 GMT Carbonyl The term carbonyl can also refer to carbon monoxide as

198-472: The Gattermann-Koch reaction , accomplished by treating benzene with carbon monoxide and hydrogen chloride under high pressure, catalyzed by a mixture of aluminium chloride and cuprous chloride . Simple ketones that could be obtained by Friedel–Crafts acylation are produced by alternative methods, e.g., oxidation, in industry. The reaction proceeds through generation of an acylium center. The reaction

220-406: The acylation of aromatic rings. Typical acylating agents are acyl chlorides . Acid anhydrides as well as carboxylic acids are also viable. A typical Lewis acid catalyst is aluminium trichloride . Because, however, the product ketone forms a rather stable complex with Lewis acids such as AlCl 3 , a stoichiometric amount or more of the "catalyst" must generally be employed, unlike the case of

242-417: The acylium ion is stabilized by a resonance structure in which the positive charge is on the oxygen. The viability of the Friedel–Crafts acylation depends on the stability of the acyl chloride reagent. Formyl chloride, for example, is too unstable to be isolated. Thus, synthesis of benzaldehyde through the Friedel–Crafts pathway requires that formyl chloride be synthesized in situ . This is accomplished by

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264-416: The alkylation of an aromatic ring . Traditionally, the alkylating agents are alkyl halides . Many alkylating agents can be used instead of alkyl halides. For example, enones and epoxides can be used in presence of protons. The reaction typically employs a strong Lewis acid , such as aluminium chloride as catalyst, to increase the electrophilicity of the alkylating agent. This reaction suffers from

286-438: The Friedel–Crafts alkylation, in which the catalyst is constantly regenerated. Reaction conditions are similar to the Friedel–Crafts alkylation. This reaction has several advantages over the alkylation reaction. Due to the electron-withdrawing effect of the carbonyl group, the ketone product is always less reactive than the original molecule, so multiple acylations do not occur. Also, there are no carbocation rearrangements, as

308-422: The acidity of any adjacent C-H bonds. Due to the positive charge on carbon and the negative charge on oxygen, carbonyl groups are subject to additions and/or nucleophilic attacks. A variety of nucleophiles attack, breaking the carbon-oxygen double bond , and leading to addition-elimination reactions . Nucleophiliic reactivity is often proportional to the basicity of the nucleophile and as nucleophilicity increases,

330-459: The carbocation-like complex (R---X---AlCl 3 ) will undergo a carbocation rearrangement reaction to give almost exclusively the rearranged product derived from a secondary or tertiary carbocation. Protonation of alkenes generates carbocations , the electrophiles. A laboratory-scale example by the synthesis of neophyl chloride from benzene and methallyl chloride using sulfuric acid catalyst. The general mechanism for primary alkyl halides

352-402: The carbon-oxygen double bond . Interactions between carbonyl groups and other substituents were found in a study of collagen . Substituents can affect carbonyl groups by addition or subtraction of electron density by means of a sigma bond . Δ H σ values are much greater when the substituents on the carbonyl group are more electronegative than carbon. The polarity of C=O bond also enhances

374-462: The disadvantage that the product is more nucleophilic than the reactant because alkyl groups are activators for the Friedel–Crafts reaction . Consequently, overalkylation can occur. However, steric hindrance can be exploited to limit the number of successive alkylation cycles that occur, as in the t -butylation of 1,4-dimethoxybenzene that gives only the product of two alkylation cycles and with only one of three possible isomers of it: Furthermore,

396-399: The hydroxyalkylated products, for example in the reaction of the mesityl derivative of glyoxal with benzene: As usual, the aldehyde group is more reactive electrophile than the phenone . This reaction is related to several classic named reactions: [REDACTED] Friedel–Crafts reactions have been used in the synthesis of several triarylmethane and xanthene dyes . Examples are

418-415: The largest scale reactions practiced in industry. Such alkylations are of major industrial importance, e.g. for the production of ethylbenzene , the precursor to polystyrene, from benzene and ethylene and for the production of cumene from benzene and propene in cumene process : Industrial production typically uses solid acids derived from a zeolite as the catalyst. Friedel–Crafts alkylation involves

440-450: The length of the C-O bond does not vary widely from 120 picometers . Inorganic carbonyls have shorter C-O distances: CO , 113; CO 2 , 116; and COCl 2 , 116 pm. The carbonyl carbon is typically electrophilic . A qualitative order of electrophilicity is RCHO (aldehydes) > R 2 CO (ketones) > RCO 2 R' (esters) > RCONH 2 (amides). A variety of nucleophiles attack, breaking

462-427: The reaction is only useful for primary alkyl halides in an intramolecular sense when a 5- or 6-membered ring is formed. For the intermolecular case, the reaction is limited to tertiary alkylating agents, some secondary alkylating agents (ones for which carbocation rearrangement is degenerate), or alkylating agents that yield stabilized carbocations (e.g., benzylic or allylic ones). In the case of primary alkyl halides,

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484-449: The synthesis of thymolphthalein (a pH indicator) from two equivalents of thymol and phthalic anhydride : A reaction of phthalic anhydride with resorcinol in the presence of zinc chloride gives the fluorophore fluorescein . Replacing resorcinol by N,N-diethylaminophenol in this reaction gives rhodamine B : The Haworth synthesis is a classic method for the synthesis of polycyclic aromatic hydrocarbons. In this reaction, an arene

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