Products, permanganate oxidations

Out first example is 2-hydroxy-2-methyl-3-octanone. 3-Octanone can be purchased, but it would be difficult to differentiate the two activated methylene groups in alkylation and oxidation reactions. Usual syntheses of acyloins are based upon addition of terminal alkynes to ketones (disconnection 1 see p. 52). For syntheses of unsymmetrical 1,2-difunctional compounds it is often advisable to look also for reactive starting materials, which do already contain the right substitution pattern. In the present case it turns out that 3-hydroxy-3-methyl-2-butanone is an inexpensive commercial product. This molecule dictates disconnection 3. Another practical synthesis starts with acetone cyanohydrin and pentylmagnesium bromide (disconnection 2). Many 1,2-difunctional compounds are accessible via oxidation of C—C multiple bonds. In this case the target molecule may be obtained by simple permanganate oxidation of 2-methyl-2-octene, which may be synthesized by Wittig reaction (disconnection 1). 

Oxidation. Benzene can be oxidized to a number of different products. Strong oxidizing agents such as permanganate or dichromate oxidize benzene to carbon dioxide and water under rigorous conditions. Benzene can be selectively oxidized in the vapor phase to maleic anhydride. The reaction occurs in the presence of air with a promoted vanadium pentoxide catalyst (11). Prior to 1986, this process provided most of the world s maleic anhydride [108-31 -6] C4H2O2. Currendy maleic anhydride is manufactured from the air oxidation of / -butane also employing a vanadium pentoxide catalyst. 

Oxidation. Citric acid is easily oxidized by a variety of oxidizing agents such as peroxides, hypochlorite, persulfate, permanganate, periodate, hypobromite, chromate, manganese dioxide, and nitric acid. The products of oxidation are usually acetonedicarboxyhc acid (5), oxaUc acid (6), carbon dioxide, and water, depending on the conditions used (5). 

Chloro-2,2,3-trifluoropropionic acid has been prepared by permanganate oxidation of 3-chloro-2,2,3-trifluoropropanol which is one of the telomerization products of chlorotrifluoroethylene with methanol. The present procedure is a modification of one reported earlier and is undoubtedly the method of choice for making propionic acids containing 2 fluorine atoms, i.e., 2,2,3,3-tetrafluoropropionic acid, 3,3-dichloro-2,2-difluoropropionic acid, and 3-bromo-2,2,3-trifluoropropionic acid. When preparing 2,2,3,3-tetrafluoropropionic acid from tetrafluoroethylene, it is desirable to use an additional 50 ml. of acetonitrile and externally applied heat to initiate the reaction. 

Stemonidine, CjoHajOgN. The base has m.p. 116 , [a]jf° — 7 65 , and yields a hydrochloride, m.p. 260 (dec.), and a methiodide, m.p. 248 . It is a tertiary base and of the five oxygen atoms two are in a lactone group and a third is present as methoxyl the functions of the other two are unknown. The alkaloid is unaffected by hydrogen chloride (25 per cent.) in alcohol or acetic acid. The permanganate oxidation products vary with the conditions of the experiment —... 

Acetylation of a 3,4-dihydro-j8-carboline derivative has been reported. O. Fischer described an A-acetylharmaline which was formulated as 310 since on controlled permanganate oxidation it yielded a neutral product (311), which on hydrolysis gave 7-methoxy-l-oxo-l,2,3,4-tetrahydro-j8-carboline (313) the constitution of 313... 

By oxidation of d- and Z-pinene of high rotatory power, Barbier and Grignard obtained the optically active forms of pinonic acid. Z-pinene from French turpentine oil (boiling-point 155 to 157 , od - 37 2 157 to 160 , tto - 32 3°) was oxidised with permanganate. From the product of oxidation, which (after elimination of the volatile acids and of nopinic acid) boiled at 189 to 195 under 18 mm. pressure, Z-pinonic acid separated out in long crystalline needles, which, after recrystallisation from a mixture of ether and petroleum ether, melted at 67° to 69 . The acid was easily soluble in water and ether, fairly soluble in chloroform, and almost insoluble in petroleum ether. Its specific rotation is [a]o - 90-5 in chloroform solution. Oximation produced two oximes one, laevo-rotatory, melting-point 128 and the other, dextro-rotatory, melting-point 189° to 191°. 

Isosafrol yields piperonal (heliotropine) melting at 37° as the principal product of oxidation when potassium permanganate is used as the oxidising agent. If the oxidation be very energetic piperonylic acid, melting at 228°, is the principal reaction product. 

In acidic solution MnOj is usually the end product, although particularly vigorous reductants, e.g. iodide and oxalate ions, convert permanganate to manganous ions. Mn(III) is stable only in acidic solution or in the form of a complex, e.g. with pyrophosphate ion, and it has seldom been reported as the end product of a permanganate oxidation, e.g. for that of Mn(II) in a phosphate buffer and for those of alcohols and ethers in the presence of fluoride ion. ... 

Ketols are also observed as products of permanganate oxidation of alkenes. The ketols are believed to be formed as a result of oxidation of the cyclic intermediate.35... 

Although CY-diketones are only rarely isolated from aqueous permanganate oxidations there is conclusive proof that they are intermediates in the reaction (16). Of-Diketones are resistant to further oxidation under anhydrous conditions and can thus be isolated in good yields from the phase transfer assisted reactions. Howeverf under aqueous conditions oxidative cleavage takes place rapidly, thus preventing the accumulation of these products. 

The mechanisms of permanganate oxidations have been the subject of a fairly intensive study which has now lasted for almost a century. While many of these studies were carried out in aqueous solutions, much of what was learned is also germane to an understanding of the reactions which occur in phase transfer assisted reactions. Although most of these studies are interrelated they can conveniently be discussed under the following headings products, substituent effects, isotope effects, and solvent effects, with the latter being of particular importance to the phase transfer assisted reactions. 

Figure 10-32 shows one common reagent mixture (the Jones reagent — Cr03/H2S0yacetone). Another common procedure is a two-step reaction where basic potassium permanganate oxidizes the aldehyde to a carboxylate ion and the second step involves the acidification of the product to form the carboxylic acid. 

The strong oxidants Cr(VI) and Mn04 can also be used for oxidative cleavage of double bonds, provided there are no other sensitive groups in the molecule. The permanganate oxidation proceeds first to the diols and ketols, as described earlier (p. 757), and these are then oxidized to carboxylic acids or ketones. Good yields can be obtained provided care is taken to prevent subsequent oxidative degradation of the products. Entries 5 and 6 in Scheme 12.17 are illustrative. 

Bipyridine was first prepared one hundred years ago by the permanganate oxidation of 1,7-phenanthroline (42) to the dicarboxylic acid 43, followed by decarboxylation. Modifications of this method have been used. 2,3 -Bipyridine is among the products obtained from... 

Ozonolysis of alkynes followed by hydrolysis gives similar products to those obtained from permanganate oxidation. This reaction does not require oxidative or reductive work-up. Unsubstituted carbon atoms are oxidized to CO2, and mono-substituted carbon atoms to carboxylic acids. For example, ozonolysis of 1-butyene followed by hydrolysis gives propionic acid and carbon dioxide. 

Precolumn derivatization with a solid-phase derivatizing precolumn has also been reported. Xie et al. (43) applied polymeric permanganate oxidations of alcohols and aldehydes for the production of UV-absorb-ing species. 

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