Amines react with carbonyl compounds

The ketone carbonyl group of pyruvic acid (or 2-oxopropanoic acid) has a stretching frequency of a typical ketone, 1710 cm 1. When hydroxylamine is added to a solution of pyruvic acid, this stretching frequency slowly disappears. Later, a new IR absorption appears at 1400 cm 1. What happens  

you saw a diagram like this in the last chapter when we were discussing kinetic and thermodynamic products (p. 329) and you can probably also apply something of what you now know about the reactivity of carbonyl compounds towards nucleophiles to work out what is happening in this reaction between a carbonyl compound and an amine. The hydroxylamine first adds to the ketone to form an unstable intermediate similar to a hemiacetal. 

Notice that it is the more nucleophilic nitrogen atom, and not the oxygen atom, of hydroxy-lamine that adds to the carbonyl group. Like hemiacetals, these intermediates are unstable and can decompose by loss of water. The product is known as an oxime and it is this compound, with its C=N double bond, that is responsible for the IR absorption at 1400 cm-1. 

We know that the oxime is formed via an intermediate because the 1400 cm-1 absorption hardly appears until after the 1710 cm 1 absorption has almost completely gone. There must really be another curve to show the formation and the decay of the intermediate, the hemiacetal, just like the one in the last chapter (p. 329). The only difference is that the intermediate has no double bond to give an IR absorbance in this region of-the spectrum. We come back to oximes later in the chapter. 

In fact, the oxime formed from a ketone and hydroxylamine is just a special example of an imine. 

We showed you glucose as on p. 137 an example of a stable, cyclic hemiacetal. matic hydrolysis of starch or cellulose, which are themselves polyacetals made 

Glucose can, in fact, react with itself to form an acetal known as maltose, up of a string of glucose units. 

Maltose is a disaccharide (made of two sugar units) produced by the enzy- 

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Secondary amines react with carbonyl compounds to form enamines ... 

As we might expect, amines react with carbonyl compounds by nucleophilic addition. If the amine is primary the initial addition product undergoes dehydration (compare Sec. 19.14) to form a compound containing a carbon-nitrogen... 

Iminium salts. N-Silyl derivatives of secondary amines react with carbonyl compounds afford a-siloxyamines. On further treatment with Me,SiCl, iminium chlorides are obtained. Trimethylsilyl triflate is superior to Me SiCl since it can induce the transformation in the cases of enolizable aldehydes. a-Chloro ethers are more reactive than carbonyl compounds, enabling the preparation of vinylogous Viehe salts. 

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