Ketones to Alkanes or Alkenes

6 Ketones to Alkanes or Alkenes 4.6.1 Wolff-Kishner Reduction 

The Wolff-Kishner reaction is a classical reduction method of ketones to alkanes. This method involves converting the ketone to its corresponding hydrazine treatment of the resulting hydrazine with base affords the alkane and nitrogen gas. Because elevated temperatures ( 200 °C) and strong base are required, this method is harsh when sensitive functionality is present. However, milder methods have been developed including the Myers modification where the reaction temperatures are much lower (s 100 °C). 

A mixture of the indolone (1.04 g, 4.2 mmol) and hydrazine monohydrate (1.12 mL, 22.4 mmol) in diethylene glycol (20 mL) was stirred at 80 °C for 1 h and then refluxed for 1 h. The resulting mixture was cooled to room temperature, treated with a solution of KOH (1.2 g, 21.4 mmol) in water (5 mL), and refluxed for 2 h. The resulting mixture was poured into water (100 mL), and the precipitate was filtered off, washed with water (5 x 50 mL), and dried to deliver 0.84 g (86%) of the indole as a greenish solid. 

Raney Nickel (nickel-aluminium alloy) is an effective catalyst for the conversion of thioketals to alkanes. Ultimately, a ketone is converted to the alkane with this mild method through a thioketal. Review Pettit, G. R. van Tamelen, E. E. Org. React. 1962,12, 356-529. 

To a solution containing the dithiane (0.6 g, 1.5 mmol) in absolute ethanol (100 mL) was added Raney nickel (2 g). The suspension was heated at reflux for 4 h, cooled to room temperature, and filtered through Celite with ethanol (200 mL). The solid was recrystallized from EtOAc to give 0.46 g (93%) of the reduced product as a white solid. 

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By-Products. Almost all commercial manufacture of pyridine compounds involves the concomitant manufacture of various side products. Liquid- and vapor-phase synthesis of pyridines from ammonia and aldehydes or ketones produces pyridine or an alkylated pyridine as a primary product, as well as isomeric aLkylpyridines and higher substituted aLkylpyridines, along with their isomers. Furthermore, self-condensation of aldehydes and ketones can produce substituted ben2enes. Condensation of ammonia with the aldehydes can produce certain alkyl or unsaturated nitrile side products. Lasdy, self-condensation of the aldehydes and ketones, perhaps with reduction, can lead to alkanes and alkenes. 

In catalysis, 16 showed very good activity for the hydrogenation of alkynes and alkenes to alkanes or ketones to alcohols (cf. Section 6.2). 

In general, peroxomonosulfates have fewer uses in organic chemistry than peroxodisulfates. However, the triple salt is used for oxidizing ketones (qv) to dioxiranes (7) (71,72), which in turn are useful oxidants in organic chemistry. Acetone in water is oxidized by triple salt to dimethyldioxirane, which in turn oxidizes alkenes to epoxides, polycycHc aromatic hydrocarbons to oxides and diones, amines to nitro compounds, sulfides to sulfoxides, phosphines to phosphine oxides, and alkanes to alcohols or carbonyl compounds. 

Raw Material and Energy Aspects to Pyridine Manufacture. The majority of pyridine and pyridine derivatives are based on raw materials like aldehydes or ketones. These are petroleum-derived starting materials and their manufacture entails cracking and distillation of alkanes and alkenes, and oxidation of alkanes, alkenes, or alcohols. Ammonia is usually the source of the nitrogen atom in pyridine compounds. Gas-phase synthesis of pyridines requires high temperatures (350—550°C) and is therefore somewhat energy intensive. 

In organic chemistry, reduction is defined as a reaction in which a carbon atom forms fewer bonds to oxygen, O, or more bonds to hydrogen, H. Often, a C=0 bond or C=C bond is reduced to a single bond by reduction. A reduction that transforms double C=C or C=0 bonds to single bonds may also be classified as an addition reaction. Aldehydes, ketones, and carboxylic acids can be reduced to become alcohols. Alkenes and alkynes can be reduced by the addition of H2 to become alkanes. 

The reactions of hydrogen peroxide with vanadate have been of interest for many years. Much of the early work was concerned with the function of peroxovanadates as oxygen transfer agents. Alkenes and similar compounds such as allyl alcohols can be hydroxylated or epoxidized. Even alkanes can be hydroxylated, whereas alcohols can be oxidized to aldehydes or ketones and thiols oxidized to sulphones or sulphoxides. Aromatic molecules, including benzene, can be hydroxylated. The rich chemistry associated with the peroxovanadates has, therefore, led to extensive studies of their reaction chemistry. To this end, x-ray diffraction studies have successfully provided details of a number of peroxovanadate structures. 

A carbonyl group dramatically increases the acidity of the protons on the a carbon atom because deprotonation gives a resonance-stabilized enolate ion. Most of the enolate ion s negative charge resides on the electronegative oxygen atom. The pKa for removal of an a proton from a typical ketone or aldehyde is about 20, showing that a typical ketone or aldehyde is much more acidic than an alkane or an alkene (pKa > 40), or even an alkyne (pKa = 25). Still, a ketone or aldehyde is less acidic than water (pKa = 15.7) or an alcohol (pA a = 16 to 18). When a simple ketone or aldehyde is treated with hydroxide ion or an alkoxide ion, the equilibrium mixture contains only a small fraction of the deprotonated, enolate form. 

Also developed by Hill is a (diotochemical system (equations 41 to 48) based on a polyoxoacid, H3PWi2O40 (P)> The excited state of the acid probably oxidizes the alkane in the first step. The radical can then either attack the solvent to give an iminium radical, wiiich leads to ketone on hydrolysis, or it can be oxidized to the caifaonium ion, in wdiich case attack on the solvent leads instead to the -alkyl-acetamide. If the substrate has two adjacent tertiary C—bonds, then alkenes tend to be formed, llie Barton reaction, normally kmwn as an intramolecular C—activation, can give some intermolecular reaction in some examples. Thus, vdien n-octyl nitrite is rf)otolyzed in heptane, some nitrosoheptane is observed. ... 

Further interesting examples of C-S bond formation involve the reaction of previously prepared (or in situ anodically generated) thianthrene or phenothiazine radical cations with alkenes or alkynes, to give l,2-bis(hetaryl) alkanes (or the respective alkenes) [82]. With cyclooctene a 1 1 adduct is obtained instead. Another valuable application is the smooth reaction with ketones (Scheme 26). The thian-threnium salts (40) now obtained are readily deprotonated to the corresponding ylides (41) [83]. The latter compounds are directly obtained when yff-dicarbonyls are used. 

Determination of the residual antioxidant content in polymers by HPLC and MAE is one way to determine the amoimt needed for reasonable stabilization of a material, and also to compare different antioxidants and their individual efficiencies. During ageing and oxidation of PE, carboxyhc acids, dicarboxylic acids, alcohols, ketones, aldehydes, n-alkanes and 1-alkenes are formed [86-89]. The carboxyhc acids are formed as a result of various reactions of alkoxy or peroxy radicals [90]. The oxidation of polyolefins is generally monitored by various analytical techniques. GC-MS analysis in combination with a selective extraction method is used to determine degradation products in plastics. ETIR enables the increase in carbonyls on a polymer chain, from carboxylic acids, dicarboxyhc acids, aldehydes, and ketones, to be monitored. It is regarded as one of the most definite spectroscopic methods for the quantification and identification of oxidation in materials, and it is used to quantify the oxidation of polymers [91-95]. Mechanical testing is a way to determine properties such as strength, stiffness and strain at break of polymeric materials. 

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