Sugar-formaldehyde reaction

Representatives of the second type are encountered in the polyhydroxyal- dehydes. They are substantiallj irreversible, and he cose sugar s are apparently the highest membei-s of the group. Reactions wdiich result in the formation of these products are iisuall " regarded as aldol-type condensa tions and will be discussed in connection rith formaldehyde reactions. 

Other methods of production iaclude hydrolysis of glycolonittile [107-16 ] with an acid (eg, H PO or H2SO2) having a piC of about 1.5—2.5 at temperatures between 100—150°C glycolonittile produced by reaction of formaldehyde with hydrogen cyanide recovery from sugar juices and hydrolysis of monohalogenated acetic acid. None of these has been commercially and economically attractive. 

Further indirect evidence for the oxidation of the primary alcohol in 5 and the formation of glycoside 6 during the course of the reaction was obtained by electrospray mass spectrometry. Towards this end, excess formaldehyde was added to the reaction mixture after the oxidation of 5 into 6, and the resulting solution stirred for an additional 30 min at ambient temperature to form the instable intermediate 7 (eq 6). The unnatural sugar 5-hydroxymethyl-a-methylglucoside (8) is spontaneously derived from 7 at ambient temperature via a Cannizzarro-like reaction in the presence of excess formaldehyde (eq. 7). 

The formation of sugars from the reaction of formaldehyde under alkaline conditions was discovered in 1861 and is known as the formose reaction , although it is not understood fully (Figure 8.7). It requires the presence of suitable inorganic catalysts such as Ca(OH)2 or CaCOr, either of which may be found on a prebiotic Earth. The reaction is autocatalytic and produces over 40 different types of sugars, some rings, some long chains. 

Henry reaction of nitro sugar 11 with formaldehyde allowed the introduction of two hydroxymethyl groups at the carbon bearing the nitro group, and hence opened a specific route for the preparation of branched-chain imino sugar 57 and analogues (Scheme 20).44... 

It is of course surprising that amino acids can be obtained via the Strecker synthesis, purines from the condensation of HCN, pyrimidines from the reaction of cyanoacetilene with urea, and sugars from the autocatalytic condensation of formaldehyde. The synthesis of chemical constiments of contemporary organisms by non-enzymatic processes under laboratory conditions does not necessarily imply that they were either essential for the origin of life or available in the primitive environment. However, the significance of prebiotic simulation experiments is... 

Figure 7.4 Schemae of the formose reaction (a) spontaneous, slow formation of glycolaldehyde from formaldehyde (b) after one cycle, one new molecule of glycolaldehyde is produced. The structural isomers of sugars are specified by the carbon skeleton and by the position of the carbonyl group (open circle). (Adapted, with some modifications, from Maynard Smith and SzathmSry, 1995.)...

The scope of the present article comprises syntheses of sugar-type compounds containing four or more carbon atoms, an aldehyde or a ketone group, and a minimum of two hydroxyl groups (or their equivalents, such as amino or thiol groups) at least one of them being bound to a center of chirality. The subject of aldol-type reactions of formaldehyde and two- or three-carbon atom hydroxy aldehydes and hydroxy ketones has been omitted a comprehensive discussion of this topic, including a historical survey, has appeared in this Series.5... 

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