Aldehydes, 2-hydroxy

Formaldehyde condenses with itself in an aldol-type reaction to yield lower hydroxy aldehydes, hydroxy ketones, and other hydroxy compounds the reaction is autocatalytic and is favored by alkaline conditions. Condensation with various compounds gives methylol (—CH2OH) and methylene (=CH2) derivatives. The former are usually produced under alkaline or neutral conditions, the latter under acidic conditions or in the vapor phase. In the presence of alkahes, aldehydes and ketones containing a-hydrogen atoms undergo aldol reactions with formaldehyde to form mono- and polymethylol derivatives. Acetaldehyde and 4 moles of formaldehyde give pentaerythritol (PE) ... 

Living olefin polymerization allows the synthesis of end-functionalized polyolefins if appropriate initiation and/or quenching methods are used. Doi et al. first showed the utility of living olefin-polymerization catalysts for the preparation of end-functionalized polyolefins. They synthesized iodine-, amine-, aldehyde-, hydroxy-, and metha-cryl-terminated PPs using living V-PP species and appropriate reagents. " " ... 

In a number of early papers only one isomer was said to be formed,146,159,261 but this conclusion was often incorrect and due to inadequate separation procedures. Even keto aldehydes (hydroxy-methylene ketones) tend to give two products in spite of the considerable difference between the carbonyl groups159,262 here again the earlier papers were at fault.263,264 The reactions of hydroxy-methylene acetophenone, which is particularly accessible, with... 

Isolated carbon-carbon multiple bonds are not normally attacked by Jones reagent, but some doublebond isomerization may occur during the preparation of a, -unsaturated aldehydes. Hydroxy-directed epoxidation (presumably via chromate ester formation, followed by oxygen transfer to the double bond) has also been observed in steroidal substrates for axial alcohols (equation 1). Equatorial alcohols undergo oxidation to give the expected enone. 

By other reactions another mono-basic acid may be obtained in which the carboxyl group is at the other end of the chain. This is an aldehyde hydroxy acid known from its relation to glucose as glucuronic acid (P- 253). It is HOOC—(CH0H)4—CHO. With strong oxidizing agents, e.g. concentrated nitric acid, the result is a di-basic acid. 

Gasoline hydrocarbons volatilized to the atmosphere quickly undergo photochemical oxidation. The hydrocarbons are oxidized by reaction with molecular oxygen (which attacks the ring structure of aromatics), ozone (which reacts rapidly with alkenes but slowly with aromatics), and hydroxyl and nitrate radicals (which initiate side-chain oxidation reactions) (Stephens 1973). Alkanes, isoalkanes, and cycloalkanes have half-lives on the order of 1-10 days, whereas alkenes, cycloalkenes, and substituted benzenes have half- lives of less than 1 day (EPA 1979a). Photochemical oxidation products include aldehydes, hydroxy compounds, nitro compounds, and peroxyacyl nitrates (Cupitt 1980 EPA 1979a Stephens 1973). 

There is thus considerable scope for further examination of the reactions of phosgene with a wide variety of alcohols, diols, aldehydes, hydroxy-aldehydes, epoxides, esters, acids and anhydrides to produce the desired range of chlorinated organic materials. The analogous reactions of COFj and of COCIF will be described in Chapters 13 and 16, respectively. 

Besides the extreme complexity of the mixture resulting from the vapor phase catalytic oxidation of various petroleum fractions, there are numerous other difficulties which act as hindrances to the commercial utilization of the products. This is especially true for the utilization of tlie acids that are formed. The acids are of the aldehydic or aldehydic-hydroxy type and are present in a mixture containing aldehydes of variops molecular weights as well as unsaturated compounds. These compounds give a peculiar, objectionable odor to the acids and a brown or yellow color which is only intensified by polymerization and resinification when the acids are saponified with hot caustic solutions. The same difficulties have been encountered in the rather extensive researches being carried out, particularly in Germany, on the liquid phase, catalytic oxidation of hydrocarbon oils to fonn fatty acids. 

Dimethylamino anil des -Pyridins aldehyd hydroxy thylats 81 I 28B. 

Hoesch synthesis A variation of the Gattermann synthesis of hydroxy-aldehydes, this reaction has been widely applied to the synthesis of anthocyanidins. It consists of the condensation of polyhydric phenols with nitriles by the action of hydrochloric acid (with or without ZnCl2 as a catalyst). This gives an iminehydrochloride which on hydrolysis with water gives the hydroxy-ketone. 

Reformatski reaction Aldehydes and ketones react with a-bromo- fatty acid esters in the presence of zinc powder to give -hydroxy-esters which may be dehydrated to give a-, 0-unsaturated esters. a-Chloroesters will react if copper powder is used in conjunction with the zinc. 

The Reformatsky Reaction consists of the interaction of an ester of an a-halogeno-acid with an aldehyde, a ketone or another ester in the presence of zinc. For example, if a mixture of ethyl bromoacetate and benzaldehyde is heated with zinc, the latter undoubtedly first combines with the ethyl bromoacetate to form a Grignard-like reagent (reaction A), which then adds on to the benzaldehyde Just as a Grignard reagent would do (reaction B). The complex so formed, on acidification gives ethyl p-phenyl-p-hydroxy-propionate (reaction C). Note that reaction A could not satisfactorily be carried out using... 

The only important precaution in this preparation is to ensure an excess of zinc chloride over sodium cyanide. If the latter is in excess, the zinc cyanide generally precipitates as a sticky mass, which is difficult to filter and unsatisfactory for the preparation of hydroxy-aldehydes. 

Acetaldehyde (and other aldehydes containing at least one hydrogen atom in the a position) when treated with a small quantity of dilute sodium hydr oxide solution or other basic catalyst gives a good yield of aldol (p hydroxy-n-but3Taldehyde) (I), which readily loses water, either by heating the isolated aldol alone or with a trace of mineral acid, to form crotonaldehyde (II) ... 

This reaction, applicable only to the preparation of hydroxy-aldehydee, is alternative to the Gattermann aldehyde reaction (or the Adams modification of it) given under 4. The yields are usually smaller, but a large quantity of the phenol may be recovered. The following mechanism is consistent with the known facts ... 

P-Hydroxy-a-naphthaldehyde, Equip a 1 litre three-necked flask with a separatory funnel, a mercury-sealed mechanical stirrer, and a long (double surface) reflux condenser. Place 50 g. of p-naphthol and 150 ml. of rectified spirit in the flask, start the stirrer, and rapidly add a solution of 100 g. of sodium hydroxide in 210 ml. of water. Heat the resulting solution to 70-80° on a water bath, and place 62 g. (42 ml.) of pure chloroform in the separatory funnel. Introduce the chloroform dropwise until reaction commences (indicated by the formation of a deep blue colour), remove the water bath, and continue the addition of the chloroform at such a rate that the mixture refluxes gently (about 1 5 hours). The sodium salt of the phenolic aldehyde separates near the end of the addition. Continue the stirring for a further 1 hour. Distil off the excess of chloroform and alcohol on a water bath use the apparatus shown in Fig. II, 41, 1, but retain the stirrer in the central aperture. Treat the residue, with stirring, dropwise with concentrated hydrochloric acid until... 

The polyhydric alcohols of Solubility Group II are liquids of relatively high boiling point and may be detected inter alia by the reactions already described for Alcohols (see 6). Compounds containing two hydroxyl groups attached to adjacent carbon atoms (1 2-glyeols), a-hydroxy aldehydes and ketones, and 1 2-diketones may be identified by the periodic acid test, given in reaction 9. 

Both aldoses and ketoses reduce Fehling s solution (for details, see under 4). This fact may appear surprising when it is remembered that Fehling s solution is one of the reagents for distinguishing between aldehydes and ketones (see 4). The explanation lies in the fact that a-hydroxyketones are much more readily oxidised than simple ketones, perhaps because the hydroxy ketone allows its isomerisation, in the presence of alkali, into an aldehyde. For example, fructose, a keto-hexose, might Isomerlse thus ... 

Another reaction that is characteristic of a-hydroxy aldehydes or ketones, which has been found of value for the characterisation of sugars, is the formation of osazones with phenylhydrazine. This reagent reacts with either an aldose... 

Analysis The a-hydroxy acid can best be made from an aldehyde and, then we can cany on as usual with a 1,3-dicarbonyl disconnection ... 

Alkylation of aldol type educts, e.g., /3-hydroxy esters, using LDA and alkyl halides leads stereoselectively to erythro substitution. The erythro threo ratio of the products is of the order of 95 5. Allylic and benzylic bromides can also be used. The allyl groups can later be ozonolysed to gjve aldehydes, and many interesting oligofunctional products with two adjacent chiral centres become available from chiral aldol type educts (G. Prater, 1984 D. Seebach, 1984 see also M. Nakatsuka, 1990, p. 5586). 

A more eflicient and general synthetic procedure is the Masamune reaction of aldehydes with boron enolates of chiral a-silyloxy ketones. A double asymmetric induction generates two new chiral centres with enantioselectivities > 99%. It is again explained by a chair-like six-centre transition state. The repulsive interactions of the bulky cyclohexyl group with the vinylic hydrogen and the boron ligands dictate the approach of the enolate to the aldehyde (S. Masamune, 1981 A). The fi-hydroxy-x-methyl ketones obtained are pure threo products (threo = threose- or threonine-like Fischer formula also termed syn" = planar zig-zag chain with substituents on one side), and the reaction has successfully been applied to macrolide syntheses (S. Masamune, 1981 B). Optically pure threo (= syn") 8-hydroxy-a-methyl carboxylic acids are obtained by desilylation and periodate oxidation (S. Masamune, 1981 A). Chiral 0-((S)-trans-2,5-dimethyl-l-borolanyl) ketene thioketals giving pure erythro (= anti ) diastereomers have also been developed by S. Masamune (1986). 

Cram erythro-products" (G.E. Keck, 1984 A, B, C). [3-(Silyloxy)allyl]stannanes and O-pro-tected a- or y -hydroxy aldehydes yield 1,2,3- or 1,2,4-triols with three chiral centres with high regio- and diastereoselectivity (G.E. Keck, 1987). 

Enantiomerically pure tetroses, pentoses, and hexoses have been synthesized by the following reaction sequence (A.W.M. Lee, 1982 S.Y. Ko, 1983), which is useful as a repetitive two-carbon hotnologi-.ation in total syntheses of higher monosaccharides and other polyhydroxy compounds (1) Wittig reaction of a protected hydroxy aldehyde with (triphenylphosphor-... 

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