Nef reaction | |
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Named after | John Ulric Nef |
Reaction type | Substitution reaction |
Identifiers | |
Organic Chemistry Portal | nef-reaction |
RSC ontology ID | RXNO:0000157 |
In organic chemistry, the Nef reaction is an organic reaction describing the acid hydrolysis of a salt of a primary or secondary nitroalkane (R−NO2) to an aldehyde (R−CH=O) or a ketone (R2C=O) and nitrous oxide (N2O). The reaction has been the subject of several literature reviews. [1] [2] [3]
The reaction was reported in 1894 by the chemist John Ulric Nef, [4] who treated the sodium salt of nitroethane with sulfuric acid resulting in an 85–89% yield of nitrous oxide and at least 70% yield of acetaldehyde. However, the reaction was pioneered a year earlier in 1893 by Konovalov, [5] who converted the potassium salt of 1-phenylnitroethane with sulfuric acid to acetophenone.
The reaction mechanism starting from the nitronate salt as the resonance structures 1a and 1b is depicted below:
The salt is protonated forming the nitronic acid 2 (in some cases these nitronates have been isolated) and once more to the iminium ion 3. This intermediate is attacked by water in a nucleophilic addition forming 4 which loses a proton and then water to the 1-nitroso-alkanol 5 which is believed to be responsible for the deep-blue color of the reaction mixture in many Nef reactions. This intermediate rearranges to hyponitrous acid 6 (forming nitrous oxide 6c through 6b) and the oxonium ion 7 which loses a proton to form the carbonyl compound.
Note that formation of the nitronate salt from the nitro compound requires an alpha hydrogen atom and therefore the reaction fails with tertiary nitro compounds.
Nef-type reactions are frequently encountered in organic synthesis, because they turn the Henry reaction into a convenient method for functionalization at the β and γ locations. [6] Thus, for example, the reaction is combined with the Michael reaction in the synthesis of the γ-keto-carbonyl methyl 3-acetyl-5-oxohexanoate, itself a cyclopentenone intermediate: [7] [8]
In carbohydrate chemistry, they are a chain-extension method for aldoses, as in the isotope labeling of C14-D‑ mannose and C14-D‑ glucose from D‑ arabinose and C14‑ nitromethane (the first step here is a Henry reaction):
The opposite reaction is the Wohl degradation.
Nef's original protocol, using concentrated sulfuric acid, has been described as "violent". [9] Strong-acid hydrolysis without the intermediate salt stage results in the formation of carboxylic acids and hydroxylamine salts,[ citation needed ] but Lewis acids such as tin(IV) chloride [10] and iron(III) chloride [11] give a clean hydrolysis. Alternatively, strong oxidizing agents, such as oxone, [12] ozone, or permanganates, will cleave the nitronate tautomer at the double bond to form a carbonyl and nitrate. Oxophilic reductants, such as titanium salts, will reduce the nitronate to a hydrolysis-susceptible imine, but less selective reductants give the amine instead. [9]
In organic chemistry, a ketone is an organic compound with the structure R−C(=O)−R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group −C(=O)−. The simplest ketone is acetone, with the formula (CH3)2CO. Many ketones are of great importance in biology and in industry. Examples include many sugars (ketoses), many steroids, and the solvent acetone.
In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (−OH) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, C
6H
5OH. Phenolic compounds are classified as simple phenols or polyphenols based on the number of phenol units in the molecule.
Hydrazones are a class of organic compounds with the structure R1R2C=N−NH2. They are related to ketones and aldehydes by the replacement of the oxygen =O with the =N−NH2 functional group. They are formed usually by the action of hydrazine on ketones or aldehydes.
In organic chemistry, an imine is a functional group or organic compound containing a carbon–nitrogen double bond. The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bonds. Imines are common in synthetic and naturally occurring compounds and they participate in many reactions.
In organic chemistry, an acyl chloride is an organic compound with the functional group −C(=O)Cl. Their formula is usually written R−COCl, where R is a side chain. They are reactive derivatives of carboxylic acids. A specific example of an acyl chloride is acetyl chloride, CH3COCl. Acyl chlorides are the most important subset of acyl halides.
In organic chemistry, an acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group.
In organic chemistry, nitro compounds are organic compounds that contain one or more nitro functional groups. The nitro group is one of the most common explosophores used globally. The nitro group is also strongly electron-withdrawing. Because of this property, C−H bonds alpha (adjacent) to the nitro group can be acidic. For similar reasons, the presence of nitro groups in aromatic compounds retards electrophilic aromatic substitution but facilitates nucleophilic aromatic substitution. Nitro groups are rarely found in nature. They are almost invariably produced by nitration reactions starting with nitric acid.
In organic chemistry a halohydrin is a functional group in which a halogen and a hydroxyl are bonded to adjacent carbon atoms, which otherwise bear only hydrogen or hydrocarbyl groups. The term only applies to saturated motifs, as such compounds like 2-chlorophenol would not normally be considered halohydrins. Megatons of some chlorohydrins, e.g. propylene chlorohydrin, are produced annually as precursors to polymers.
Lawesson's reagent (LR) is a chemical compound used in organic synthesis as a thiation agent. Lawesson's reagent was first made popular by Sven-Olov Lawesson, who did not, however, invent it. Lawesson's reagent was first made in 1956 during a systematic study of the reactions of arenes with P4S10.
o-Phenylenediamine (OPD) is an organic compound with the formula C6H4(NH2)2. This aromatic diamine is an important precursor to many heterocyclic compounds. OPD is a white compound although samples appear darker owing to oxidation by air. It is isomeric with m-phenylenediamine and p-phenylenediamine.
Palladium on carbon, often referred to as Pd/C, is a form of palladium used as a catalyst. The metal is supported on activated carbon to maximize its surface area and activity.
The Dakin oxidation (or Dakin reaction) is an organic redox reaction in which an ortho- or para-hydroxylated phenyl aldehyde (2-hydroxybenzaldehyde or 4-hydroxybenzaldehyde) or ketone reacts with hydrogen peroxide (H2O2) in base to form a benzenediol and a carboxylate. Overall, the carbonyl group is oxidised, whereas the H2O2 is reduced.
Diisopropylamine is a secondary amine with the chemical formula (Me2CH)2NH (Me = methyl). Diisopropylamine is a colorless liquid with an ammonia-like odor. Its lithium derivative, lithium diisopropylamide, known as LDA is a widely used reagent.
The Meerwein arylation is an organic reaction involving the addition of an aryl diazonium salt (ArN2X) to an electron-poor alkene usually supported by a metal salt. The reaction product is an alkylated arene compound. The reaction is named after Hans Meerwein, one of its inventors who first published it in 1939.
The Béchamp reduction is a chemical reaction that converts aromatic nitro compounds to their corresponding anilines using iron as the reductant:
4-Nitroaniline, p-nitroaniline or 1-amino-4-nitrobenzene is an organic compound with the formula C6H6N2O2. A yellow solid, it is one of three isomers of nitroaniline. It is an intermediate in the production of dyes, antioxidants, pharmaceuticals, gasoline, gum inhibitors, poultry medicines, and as a corrosion inhibitor.
Cyclohexenone is an organic compound which is a versatile intermediate used in the synthesis of a variety of chemical products such as pharmaceuticals and fragrances. It is colorless liquid, but commercial samples are often yellow.
Dimethyldioxirane (DMDO) is the organic compound with the formula (CH3)2CO2. It is the dioxirane derived from acetone and can be considered as a monomer of acetone peroxide. It is a powerful selective oxidizing agent that finds some use in organic synthesis. It is known only in the form of a dilute solution, usually in acetone, and hence the properties of the pure material are largely unknown.
In organic chemistry, alkynylation is an addition reaction in which a terminal alkyne is added to a carbonyl group to form an α-alkynyl alcohol.
Xylylene dibromide is an organic compound with the formula C6H4(CH2Br)2. It is an off-white solid that, like other benzyl halides, a strong lachrymator. It is a useful reagent owing to the convenient reactivity of the two C-Br bonds. Two other isomers are known, para- and meta-xylylene dibromide.