Oxidation to aldehydes, the

PDC with acetic anhydride gives a strong but mild, neutral oxidant It is normally used in dichloromethane at room temperature. Under these conditions secondary alcohols are oxidized to ketones in high yield with 0.6 equiv. of PDC and 3 equiv. of acetic anhydride. With only slightly more PDC (0.7 equiv.) primary alcohols are rapidly and selectively oxidized to aldehydes. (The extra oxidant serves to increase... 

The reactions of a-TMS-substituted boranes with aldehydes proceed with eliminadon of the TMS group to give alkenylboranes as in equations (45) and (46). Such products can be hydrolyzed to alkenes or oxidized to aldehydes. The intermediate in the case of the dimesi lborane reaction was directly oxidized to aldehyde in 95% overall yield, a good formyl homologation process. ... 

Although primary alcohols are first oxidized to aldehydes, the aldehydes are further oxidized to carboxylic acids. The ability of chromic acid to oxidize aldehydes but not ketones is taken advantage of in a test that uses chromic acid to distinguish between aldehydes and ketones (see Experiment 52D). Secondary alcohols are oxidized to ketones, but no further. Tertiary alcohols are not oxidized at all by the reagent hence, this test can be used to distinguish primary and secondary alcohols from tertiary alcohols. Unlike the Lucas test, this test can be used with all alcohols regardless of molecular weight and solubility. 

A new variation of the ozone cleavage is performed in the presence of tetracyanoethylene With dimethyl sulfoxide, prim, alcohols can be differentially oxidized to aldehydes The dimethyl sulfoxide-potassium terf-butoxide system has been recommended for Wittig syntheses In the same system, equatorial mesylates can be efficiently hydrolyzed without inversion. Under these conditions, tosylates give predominantly olefins Favorable conditions for acidic hydrolysis of esters, with methanesulfonic acid as catalyst, have been established... 

In some cases where there is a neighboring group participation effect, aldehydes are formed. The a-vinyl group in the / -lactam 29 is mainly oxidized to aldehyde 30[83],... 

Oxidation Reactions. In general, the aldehyde function is easily oxidized to form the corresponding carboxyUc acid. 

Other modifications of the polyamines include limited addition of alkylene oxide to yield the corresponding hydroxyalkyl derivatives (225) and cyanoethylation of DETA or TETA, usuaHy by reaction with acrylonitrile [107-13-1/, to give derivatives providing longer pot Hfe and better wetting of glass (226). Also included are ketimines, made by the reaction of EDA with acetone for example. These derivatives can also be hydrogenated, as in the case of the equimolar adducts of DETA and methyl isobutyl ketone [108-10-1] or methyl isoamyl ketone [110-12-3] (221 or used as is to provide moisture cure performance. Mannich bases prepared from a phenol, formaldehyde and a polyamine are also used, such as the hardener prepared from cresol, DETA, and formaldehyde (228). Other modifications of polyamines for use as epoxy hardeners include reaction with aldehydes (229), epoxidized fatty nitriles (230), aromatic monoisocyanates (231), or propylene sulfide [1072-43-1] (232). 

The use of silver (II) salts, particularly argentic picolinate, as reagents for hydroxyl oxidation has also been disclosed recently. The reaction may be run in acid, neutral or basic media in aqueous or polar organic solvents at room or slightly elevated temperatures. Primary alcohols may be oxidized to aldehydes or acids depending on the conditions used. Amines and trivalent phosphorous compounds are more sensitive to oxidation with this reagent than are hydroxyl groups. 

The carbon skeleton of helminthosporal can be accounted for from three isoprene units (XVI), but they cannot be formed by cyclization of a farnesol precursor, as the three units are not joined head to tail. There is the possibility that the aldehyde carbons were joined in the early stages of biosynthesis to form helminthosporane (XVII, XX) as an intermediate, followed by later oxidation to yield the dialdehydes. As a test of this hypothesis the actively growing fungus was fed mevalonic acid labeled with carbon-14 in the 2-position (mevalonic acid being a precursor of isoprene units) (2). Thus, three units of radioactivity should be incorporated, one being the... 

Dipyridiue-chromium(VI) oxide2 was introduced as an oxidant for the conversion of acid-sensitive alcohols to carbonyl compounds by Poos, Arth, Beyler, and Sarett.3 The complex, dispersed in pyridine, smoothly converts secondary alcohols to ketones, but oxidations of primary alcohols to aldehydes are capricious.4 In 1968, Collins, Hess, and Frank found that anhydrous dipyridine-chromium(VI) oxide is moderately soluble in chlorinated hydrocarbons and chose dichloro-methane as the solvent.5 By this modification, primary and secondary alcohols were oxidized to aldehydes and ketones in yields of 87-98%. Subsequently Dauben, Lorber, and Fullerton showed that dichloro-methane solutions of the complex are also useful for accomplishing allylic oxidations.6... 

Another reagent that convert benzylic halides to aldehydes is pyridine followed by /7-nitrosodimethylaniline and then water, called the Krohnke reaction. Primary halides and tosylates have been oxidized to aldehydes by trimethylamine N-oxide, and by pyridine N-oxide with microwave irradiation. ... 

Reactions of partial electrochemical oxidation are of considerable interest in the electrosynthesis of various organic compounds. Thus, at gold electrodes in acidic solutions, olefins can be oxidized to aldehydes, acids, oxides, and other compounds. A good deal of work was invested in the oxidation of aromatic compounds (benzene, anthracene, etc.) to the corresponding quinones. To this end, various mediating redox systems (e.g., the Ce /Ce system) are employed (see Section 13.6). 

Ten Brink et al. (2000) have shown how biphasic systems, sometimes with the sparingly soluble alcohols as one phase and an aqueous phase as the other phase, benefit from the strategy for air oxidation to aldehydes/ketones by using water soluble Pd complex of bathophenanthroline disulphonate. This is a nice example of green technology. 

Hydroxymethylation (formaldehyde) of nitro-imidazole 76 affords 77, which is oxidized to aldehyde 78. To prepare the other fragment for this convergent synthesis, reaction of epichlorohydrin with morpholine leads to the aminoepoxide 79, which is reacted with hydrazine to afford 80. Reaction of this substituted hydrazine with dimethyl carbonate affords oxazolinone 81 by sequential ester interchange reactions. Condensation of 81 with aldehyde 78 affords the antitricho-... 

As demonstrated by Hoffmann and coworkers, hydroformylation can also be combined with an allylboration and a second hydroformylation, which allows the formation of carbocycles and also heterocycles [213]. A good regioselectivity in favor of the linear aldehyde was obtained by use of the biphephos ligand [214]. Reaction of the allylboronate 6/2-76 having an B-configuration with CO/H2 in the presence of catalytic amounts of Rh(CO)2(acac) and biphephos led to the lactol 6/2-80 via 6/2-77-79 (Scheme 6/2.17). In a separate operation, 6/2-80 was oxidized to give the lactone 6/2-81 using tetrabutyl ammonium perruthenate/N-methylmorpholine N-oxide. 

Aldehydes do not co-oxidize alkanes due to a huge difference in the reactivity of these two classes of organic compounds. Alkanes are almost inert to oxidation at room temperature and can be treated as inert solvents toward oxidized aldehydes [35]. Olefins and alkylaromatic hydrocarbons are co-oxidized with aldehydes. The addition of alkylaromatic hydrocarbon (R2H) to benzaldehyde (R1H) retards the rate of the initiated oxidation [36-39]. The rate of co-oxidation obeys the equation [37] ... 

TEMPO 2,2,6,6-Tetramethylpiperidinyl-1-oxy (20 TEMPO) works as a mediator for the oxidation of primary alcohols to aldehydes. The oxidation of secondary alcohols is much slower than that of primary alcohols as exemplified by the oxidation of (19) to (21) (Scheme 7) [48]. Active species is the oxo-ammonium generated from TEMPO. 

You learned earlier that primary alcohols are oxidized to aldehydes, and secondary alcohols are oxidized to ketones. You can think of the reduction of aldehydes and ketones as the reverse of these reactions. Aldehydes can be reduced to produce primary alcohols. Ketones can be reduced to produce secondary alcohols. 

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