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37-398: 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

74-489: 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

111-427: A carbonyl group is often referred to as a carbonyl compound. The term carbonyl can also refer to carbon monoxide as 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

148-401: A specific transformation. The major types are oxidizing agents such as osmium tetroxide , reducing agents such as lithium aluminium hydride , bases such as lithium diisopropylamide and acids such as sulfuric acid . Finally, reactions are also classified by mechanistic class. Commonly these classes are (1) polar, (2) radical, and (3) pericyclic. Polar reactions are characterized by

185-457: 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

222-542: Is governed by the Woodward–Hoffmann rules and that of many elimination reactions by Zaitsev's rule . Organic reactions are important in the production of pharmaceuticals . In a 2006 review, it was estimated that 20% of chemical conversions involved alkylations on nitrogen and oxygen atoms, another 20% involved placement and removal of protective groups , 11% involved formation of new carbon–carbon bond and 10% involved functional group interconversions . There

259-420: Is intended to cover the basic reactions. In condensation reactions a small molecule, usually water, is split off when two reactants combine in a chemical reaction. The opposite reaction, when water is consumed in a reaction, is called hydrolysis . Many polymerization reactions are derived from organic reactions. They are divided into addition polymerizations and step-growth polymerizations . In general

296-422: 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

333-630: Is no limit to the number of possible organic reactions and mechanisms. However, certain general patterns are observed that can be used to describe many common or useful reactions. Each reaction has a stepwise reaction mechanism that explains how it happens, although this detailed description of steps is not always clear from a list of reactants alone. Organic reactions can be organized into several basic types. Some reactions fit into more than one category. For example, some substitution reactions follow an addition-elimination pathway. This overview isn't intended to include every single organic reaction. Rather, it

370-483: Is not necessarily straightforward or clear in all cases. Beyond these classes, transition-metal mediated reactions are often considered to form a fourth category of reactions, although this category encompasses a broad range of elementary organometallic processes, many of which have little in common and very specific. Factors governing organic reactions are essentially the same as that of any chemical reaction . Factors specific to organic reactions are those that determine

407-554: 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

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444-451: 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

481-617: Is the Bingel reaction (1993). When the named reaction is difficult to pronounce or very long as in the Corey–House–Posner–Whitesides reaction it helps to use the abbreviation as in the CBS reduction . The number of reactions hinting at the actual process taking place is much smaller, for example the ene reaction or aldol reaction . Another approach to organic reactions is by type of organic reagent , many of them inorganic , required in

518-567: Is the case in triarylmethane dyes. This is a bench test for aromatic compounds. Organic reaction The oldest organic reactions are combustion of organic fuels and saponification of fats to make soap. Modern organic chemistry starts with the Wöhler synthesis in 1828. In the history of the Nobel Prize in Chemistry awards have been given for the invention of specific organic reactions such as

555-458: The Fries rearrangement the reactant is an ester and the reaction product an alcohol . An overview of functional groups with their preparation and reactivity is presented below: In heterocyclic chemistry , organic reactions are classified by the type of heterocycle formed with respect to ring-size and type of heteroatom. See for instance the chemistry of indoles . Reactions are also categorized by

592-472: 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

629-620: The Grignard reaction in 1912, the Diels–Alder reaction in 1950, the Wittig reaction in 1979 and olefin metathesis in 2005. Organic chemistry has a strong tradition of naming a specific reaction to its inventor or inventors and a long list of so-called named reactions exists, conservatively estimated at 1000. A very old named reaction is the Claisen rearrangement (1912) and a recent named reaction

666-406: 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

703-417: 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

740-416: 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

777-438: 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

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814-422: 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,

851-459: 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

888-402: 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

925-477: The change in the carbon framework. Examples are ring expansion and ring contraction , homologation reactions , polymerization reactions , insertion reactions , ring-opening reactions and ring-closing reactions . Organic reactions can also be classified by the type of bond to carbon with respect to the element involved. More reactions are found in organosilicon chemistry , organosulfur chemistry , organophosphorus chemistry and organofluorine chemistry . With

962-462: 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,

999-471: 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,

1036-399: 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

1073-482: The introduction of carbon-metal bonds the field crosses over to organometallic chemistry . Carbonyl For organic chemistry , a carbonyl group is a functional group with the formula C=O , composed of a carbon atom double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such as aldehydes , ketones and carboxylic acids ), as part of many larger functional groups. A compound containing

1110-415: 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

1147-450: 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

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1184-463: The movement of electron pairs from a well-defined source (a nucleophilic bond or lone pair) to a well-defined sink (an electrophilic center with a low-lying antibonding orbital). Participating atoms undergo changes in charge, both in the formal sense as well as in terms of the actual electron density. The vast majority of organic reactions fall under this category. Radical reactions are characterized by species with unpaired electrons ( radicals ) and

1221-592: The movement of single electrons. Radical reactions are further divided into chain and nonchain processes. Finally, pericyclic reactions involve the redistribution of chemical bonds along a cyclic transition state . Although electron pairs are formally involved, they move around in a cycle without a true source or sink. These reactions require the continuous overlap of participating orbitals and are governed by orbital symmetry considerations . Of course, some chemical processes may involve steps from two (or even all three) of these categories, so this classification scheme

1258-427: 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,

1295-472: The stability of reactants and products such as conjugation , hyperconjugation and aromaticity and the presence and stability of reactive intermediates such as free radicals , carbocations and carbanions . An organic compound may consist of many isomers . Selectivity in terms of regioselectivity , diastereoselectivity and enantioselectivity is therefore an important criterion for many organic reactions. The stereochemistry of pericyclic reactions

1332-434: The stepwise progression of reaction mechanisms can be represented using arrow pushing techniques in which curved arrows are used to track the movement of electrons as starting materials transition to intermediates and products. Organic reactions can be categorized based on the type of functional group involved in the reaction as a reactant and the functional group that is formed as a result of this reaction. For example, in

1369-449: 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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