| Rieche formylation | |
|---|---|
| Named after | Alfred Rieche |
| Reaction type | Substitution reaction |
Rieche formylation is a type of formylation reaction. The substrates are electron rich aromatic compounds, such as mesitylene [1] or phenols, [2] with dichloromethyl methyl ether acting as the formyl source. The catalyst is titanium tetrachloride and the workup is acidic. The reaction is named after Alfred Rieche who discovered it in 1960. [3]
An aromatic hydrocarbon or arene is a hydrocarbon with sigma bonds and delocalized pi electrons between carbon atoms forming a circle. In contrast, aliphatic hydrocarbons lack this delocalization. The term "aromatic" was assigned before the physical mechanism determining aromaticity was discovered, and referred simply to the fact that many such compounds have a sweet or pleasant odour; however, not all aromatic compounds have a sweet odour, and not all compounds with a sweet odour are aromatic. The configuration of six carbon atoms in aromatic compounds is called a "benzene ring", after the simplest possible such hydrocarbon, benzene. Aromatic hydrocarbons can be monocyclic (MAH) or polycyclic (PAH).
Ethers are a class of organic compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula R–O–R′, where R and R′ represent the alkyl or aryl groups. Ethers can again be classified into two varieties: if the alkyl groups are the same on both sides of the oxygen atom, then it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers. A typical example of the first group is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether" (CH3–CH2–O–CH2–CH3). Ethers are common in organic chemistry and even more prevalent in biochemistry, as they are common linkages in carbohydrates and lignin.
Demethylation is the chemical process resulting in the removal of a methyl group (CH3) from a molecule. A common way of demethylation is the replacement of a methyl group by a hydrogen atom, resulting in a net loss of one carbon and two hydrogen atoms.
Enols, or more formally, alkenols, are a type of reactive structure or intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond. The terms enol and alkenol are portmanteaus deriving from "-ene"/"alkene" and the "-ol" suffix indicating the hydroxyl group of alcohols, dropping the terminal "-e" of the first term. Generation of enols often involves removal of a hydrogen adjacent (α-) to the carbonyl group—i.e., deprotonation, its removal as a proton, H+. When this proton is not returned at the end of the stepwise process, the result is an anion termed an enolate (see images at right). The enolate structures shown are schematic; a more modern representation considers the molecular orbitals that are formed and occupied by electrons in the enolate. Similarly, generation of the enol often is accompanied by "trapping" or masking of the hydroxy group as an ether, such as a silyl enol ether.
A methoxy group is the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula O–CH3. On a benzene ring, the Hammett equation classifies a methoxy substituent at the para position as an electron-donating group, but as an electron-withdrawing group if at the meta position. At the ortho position, steric effects are likely to cause a significant alteration in the Hammett equation prediction which otherwise follows the same trend as that of the para position.
Anisole, or methoxybenzene, is an organic compound with the formula CH3OC6H5. It is a colorless liquid with a smell reminiscent of anise seed, and in fact many of its derivatives are found in natural and artificial fragrances. The compound is mainly made synthetically and is a precursor to other synthetic compounds. It is an ether.
The Vilsmeier–Haack reaction is the chemical reaction of a substituted amide (1) with phosphorus oxychloride and an electron-rich arene (3) to produce an aryl aldehyde or ketone (5). The reaction is named after Anton Vilsmeier and Albrecht Haack.
The Duff reaction or hexamine aromatic formylation is a formylation reaction used in organic chemistry for the synthesis of benzaldehydes with hexamine as the formyl carbon source. It is named after James Cooper Duff, who was a chemist at the College of Technology, Birmingham, around 1920–1950.
A formylation reaction in organic chemistry refers to organic reactions in which an organic compound is functionalized with a formyl group (-CH=O). The reaction is a route to aldehydes (C-CH=O), formamides (N-CH=O), and formate esters (O-CH=O). A reagent that delivers the formyl group is called a formylating agent. A particularly important formylation process is hydroformylation which converts alkenes to the homologated aldehyde. The conversion of benzene to benzaldehyde is the basis of the Gattermann–Koch reaction:
The Reimer–Tiemann reaction is a chemical reaction used for the ortho-formylation of phenols; with the simplest example being the conversion of phenol to salicylaldehyde. The reaction was discovered by Karl Reimer and Ferdinand Tiemann. The Reimer in question was Karl Reimer (1845-1883) not the less known Carl Ludwig Reimer (1856-1921).
The Betti reaction is a chemical addition reaction of aldehydes, primary aromatic amines and phenols producing α-aminobenzylphenols.
The Dakin oxidation is an organic redox reaction in which an ortho- or para-hydroxylated phenyl aldehyde or ketone reacts with hydrogen peroxide in base to form a benzenediol and a carboxylate. Overall, the carbonyl group is oxidized, and the hydrogen peroxide is reduced.
The Gattermann reaction, (also known as the Gattermann formylation and the Gattermann salicylaldehyde synthesis) is a chemical reaction in which aromatic compounds are formylated by a mixture of hydrogen cyanide (HCN) and hydrogen chloride (HCl) in the presence of a Lewis acid catalyst such as AlCl3. It is named for the German chemist Ludwig Gattermann and is similar to the Friedel–Crafts reaction.
The Blanc chloromethylation is the chemical reaction of aromatic rings with formaldehyde and hydrogen chloride catalyzed by zinc chloride or other Lewis acid to form chloromethyl arenes. The reaction was discovered by Gustave Louis Blanc (1872-1927) in 1923. The reaction is performed with care as, like most chloromethylation reactions, it produces highly carcinogenic bis(chloromethyl) ether as a by-product.
[2.2.2.2.2.2]( 1,2,3,4,5,6)Cyclophane or superphane is a 6-fold bridged cyclophane with all arene positions in the benzene dimer taken up by ethylene spacers. The compound has been of some scientific interest as a model for testing aromaticity and was first synthesised by Boekelheide in 1979. Superphane is the base compound for a large group of derivatives with structural variations. The analogs with 2 to 5 bridges are also known compounds. The benzene rings have been replaced by other aromatic units, such as those based on ferrocene or stabilized cyclobutadiene. Numerous derivatives are known with variations in the type and length of the bridging units.
Dichloromethyl methyl ether (HCl2COCH3) is an organic compound that belongs to the class of ethers with a dichloromethyl group and a methyl group. It can be synthesized from methyl formate and a mixture of phosphorus pentachloride and phosphorus oxychloride or by chlorination of chlorodimethyl ether.
The Quelet reaction is an organic coupling reaction in which a phenolic ether reacts with an aliphatic aldehyde to generate an α-chloroalkyl derivative. The Quelet reaction is an example of a larger class of reaction, electrophilic aromatic substitution. The reaction is named after its creator R. Quelet, who first reported the reaction in 1932, and is similar to the Blanc chloromethylation process.
Hexamethylbenzene, also known as mellitene, is a hydrocarbon with the molecular formula C12H18 and the condensed structural formula C6(CH3)6. It is an aromatic compound and a derivative of benzene, where benzene's six hydrogen atoms have each been replaced by a methyl group. In 1929 Kathleen Lonsdale reported the crystal structure of hexamethylbenzene, demonstrating that the central ring is hexagonal and flat and thereby ending an ongoing debate about the physical parameters of the benzene system. This was a historically significant result, both for the field of X-ray crystallography and for understanding aromaticity.
Electrophilic aromatic substitution is an organic reaction in which an atom that is attached to an aromatic system is replaced by an electrophile. Some of the most important electrophilic aromatic substitutions are aromatic nitration, aromatic halogenation, aromatic sulfonation, and alkylation and acylation Friedel–Crafts reaction..
The Danheiser benzannulation is a chemical reaction used in organic chemistry to generate highly substituted phenols in a single step. It is named after Rick Danheiser who developed the reaction.