Ammonia, aldehyde reaction detection

Analysing the products of reaction between alkyl nitrates and hydrazine they detected nitrate and nitrite ions, a corresponding alcohol, alkyl hydrazine, nitrogen oxides, ammonia and traces of aldehyde. If the reaction is performed without solvents in an excess of hydrazine, reduction occurs. In an aqueous solution of alcohol the process of substitution predominates particularly when the concentrations of reagents are low. 

Tollen s test (Section 19.3) a chemical test for detecting aldehydes by treatment with ammonia-cal silver nitrate. A positive test is signaled by formation of a silver mirror on the walls of the reaction vessel. 

Amino acids are quickly deaminated by L-ascorbic acid, leading to browning reactions (66). In the presence of oxygen, iron, and ascorbic acid or DHA, the amino acids gave ammonia, carbon dioxide, and an aldehyde with one carbon less than the original acid (67,68). The aldehydes are isolated as dimedone derivatives and are useful for identification of the amino acids. In the presence of copper and UV light, the deamination is increased. The red color 69-73) formed upon reaction of DHA with amino acids was used for their detection. Recent studies (74-78) of the reaction of DHA with amino acids led to the isolation of a product that changes readily to a novel, stable, free radical species... 

The Hantzsch synthesis, which was developed in 1882, is perhaps the best known of several ways to construct the pyridine ring. The original synthesis involved the three-component reaction mixture of a beta-ketoester, ammonia, and an aldehyde. The product is a dihydropyridine, which is easily oxidized to a pyridine. An example is given in Scheme 9.45. Two intermediate compounds have been detected in... 

An interesting variation of the method was patented by Glaxo Wellcome Inc [146]. Their synthesis was started from 2,4-dichloro-5-fluoropyrimidine (93) (Scheme 38). Reaction of 93 with NaOEt and then - with anion of 2,2-dimethoxyethanol gave pyrimidine derivative 163, which upon detection formed aldehyde 164. Reaction of 164 and 154 led to the formation of 1,3-oxa-thiolane 165, which was acetylated to give 166. Treatment of 166 with TMSOTf resulted in rearrangement leading to 167, which was transformed to racemic 8 (Racivir) by reaction with ammonia. 

This reaction can be used for the detection of aldehydes in the presence of ketones and for the differentiation of aliphatic aldehydes from aromatic ones. In a neutral medium aldehydes produce a black color or a precipitate other transient colors are sometimes formed which, in the case of aromatic aldehydes, last a bit longer. In an acid medium aliphatic aldehydes behave similarly as in a neutral medium, while in the presence of aromatic aldehydes a yellow color is produced first sometimes a precipitate is formed which persists for a certain time. Some other derivatives also react similarly to aide-hydes, such as, for example, cyanohydrins, aldehyde-ammonia adducts, sodium bisulfite addition compounds of aldehydes, and oximes. For modification with detection tubes containing the reagent see (62). 

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