Aldehydes manganese dioxide

Aromatic aldehydes react with the dimedone reagent (Section 111,70,2). All aromatic aldehydes (i) reduce ammoniacal silver nitrate solution and (ii) restore the colour of SchifiF s reagent many react with sodium bisulphite solution. They do not, in general, reduce Fehling s solution or Benedict s solution. Unlike aliphatic aldehydes, they usually undergo the Cannizzaro reaction (see Section IV,123) under the influence of sodium hydroxide solution. For full experimental details of the above tests, see under Ali-phalic Aldehydes, Section 111,70. They are easily oxidised by dilute alkaline permanganate solution at the ordinary temperature after removal of the manganese dioxide by sulphur dioxide or by sodium bisulphite, the acid can be obtained by acidification of the solution. 

Acetaldehyde [75-07-0] (ethanal), CH CHO, was first prepared by Scheele ia 1774, by the action of manganese dioxide [1313-13-9] and sulfuric acid [7664-93-9] on ethanol [64-17-5]. The stmcture of acetaldehyde was estabhshed in 1835 by Liebig from a pure sample prepared by oxidising ethyl alcohol with chromic acid. Liebig named the compound "aldehyde" from the Latin words translated as al(cohol) dehyd(rogenated). The formation of acetaldehyde by the addition of water [7732-18-5] to acetylene [74-86-2] was observed by Kutscherow] in 1881. 

This photoaffinity labelling analogue of all-fraws-retinal, 95b, has been tritium labelled80 by reduction of unlabelled aldehyde 95a with [3H]-NaBH4 and subsequent oxidation of the obtained tritium-labelled retinol with activated manganese dioxide. The product 95b (specific activity 38.3 mCimmol-1) has been isolated by preparative TLC (equation 36). 

The conventional chemical procedure for the oxidation of toluenes to the corresponding aldehydes according to the following equation produces 302 kg MnS04 and uses up to 196 kg of sulfuric acid plus about 20% waste originating from the technical manganese dioxide consumed which in fact is a mixture of Mn(IY) and Mn(III) [145],... 

Aldehyde 244 reacts with manganese dioxide and sodium cyanide in ethanol to give ethyl ester 245 (Scheme 19), while oxidation of alcohol 12 with sodium peroxodisulfate in the presence of a catalytic amount of ruthenium chloride furnishes the carboxylic acid 246 (Scheme 19) <1998CPB287>. 

The pyrimidine synthesis was therefore changed to the alkynyl ketone route as the appropriate precursors could be formed under much milder conditions. Thus, treatment of the chloro aldehyde 1002 with ethynyl Grignards or lithium species at low temperature, followed by mild oxidation with manganese dioxide, gave the desired chloro alkynyl ketones 1003, which could be successfully converted to the pyrimidine products 1004, by condensation with substituted guanidines, without displacement of the chlorine atom <2003X9001, 2005BMC5346>. 

The modified cephalosporin ceftobiprole (31-8), yet another compound that contains a double bond at the ring carbon, though in this case with a rather complex extended side chain, has shown activity in the clinic against some strains of multidrug resistant bacteria. The synthesis starts with the weU-precedented acylation of the cephalosporin (31-2), available in several steps from the commercially available 7-acetoxy cephalosporanic acid, with the activated thiadiazole carboxylic acid (31-1). The hydroxyl group in the product (31-3) is then oxidized with manganese dioxide to afford the corresponding aldehyde (31-4). This product is then condensed with the fcw-pyrrolidyl phosphonium salt (31-5), itself protected with the... 

Benzo[6]thiophene aldehydes have also been prepared by oxidation of the corresponding primary alcohol with fer -butyl chromate,518 nitric acid,518 or manganese dioxide,337,565 and by reaction of the... 

Manganese dioxide very soon became a widely used standard oxidant for the transformation of allylic and benzylic alcohols into aldehydes and ketones.4 It offers very mild conditions and is extremely selective for allylic and benzylic alcohols when it is not employed at a high temperature. On the other hand, the work-up of oxidations with M11O2 is very simple, involving just filtration of suspended solid and elimination of solvent. 

Keywords allylic alcohol, manganese dioxide, barium manganate, aldehyde, ketone... 

Keywords alcohol, manganese dioxide, silica gel, microwave irradiation, ketone, aldehyde... 

Oxidation of hemiacetals.1 Pyridinium dichromate in DMF effects a novel oxidative cyclization of the aldehyde 1 to the macrocyclic lactone verrucarin T (2a). The conversion is believed to involve cyclization to a hemiacetal (2b) followed by oxidation to 2a. Manganese dioxide does not oxidize 1, and a variety of other oxidants attack the dienic ester side chain. 

Because you can easily further oxidize aldehydes to carboxylic acids, you can only employ mild oxidizing agents and conditions in the formation of aldehydes. Typical mild oxidizing agents include manganese dioxide (MnO), Sarett-Collins reagent (CrO,—(CSHSN)2), and pyridinium chlorochromate (PCC),... 

Manganese dioxide at 200° oxidises alcohol to aldehyde and is itself reduced to Mn203 at 250° the Mn303 brings about further oxidation and tho products are acetaldehyde, carbon dioxide, and acetic acid. 

Figure 19.1 Synthetic scheme for example pheromone components. Abbreviations al and a2 = Wittig-Homer condensations with triethyl 2-phosphonopropionate and triethyl 2-phosphonobutyrate, respectively b = reduction of ester with lithium aluminum hydride c = partial oxidation of alcohol with manganese dioxide to aldehyde dl and d2 = Wittig condensations with ethyltriphenylphosphonium bromide and propyltriphenylphosphonium bromide, respectively e = condensation with dimethylhydrazone phosphonate reagent f = hydrolysis under acidic conditions. Compound numbers are as in Table 19.1.

Conjugated—a,/)-unsaturated or aromatic—aldehydes are oxidized by manganese dioxide in the presence of one equivalent of sodium cyanide to give an acyl cyanide (Formula C in Figure 17.18) via an intermediate cyanohydrin (B in Figure 17.18), which is also either an allylic or a benzylic alcohol. Alcohols of this kind can be oxidized by a relatively weak oxi-... 

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