Aldehyde- and Ketone-Reactive Chemical Reactions

In the preceding chapter you learned that nucleophilic addition to the carbonyl group IS one of the fundamental reaction types of organic chemistry In addition to its own reactivity a carbonyl group can affect the chemical properties of aldehydes and ketones m other ways Aldehydes and ketones having at least one hydrogen on a carbon next to the carbonyl are m equilibrium with their enol isomers... 

Most classes of VOCs found in indoor environments are sampled onto sorbents by adsorption but highly reactive VOCs like carbonyl compounds are sampled by chemical reactions with the sorbent. Thus aldehydes and ketones are sampled by their reactions with sorbent gels coated with 2,4-dinitro-phenylhydrazine to form stable hydrazones [38-40]. Similarly, formaldehyde has been sampled by its reaction with N-benzylethanolamine to give 3-benzyl-oxazolidine [41,42]. 

Chemical reactivity is another way of testing the purity of a drug substance. Hydralazine hydrochloride is part of a class of compounds called hydrazine derivatives. It is well known that hydrazine derivatives react with aldehydes and ketones to give hydrazones.The test is conducted by taking a standard reaction of hydrazine with benzaldehyde and comparing it to the same reaction of hydralazine with benzaldehyde as in Scheme 4. By using an HPLC procedure, standard solutions of each derivative are injected, and by comparison of the peak responses, the amount of hydrazine is determined. 

Chemical. A large number of chitin and chitosan derivatives have been synthesized through modification of the primary (C-6) and secondary (C-3) hydroxyl groups present on each repeat imit, including amine (C-2) functionality existing on deacetylated imits (31). Reactions typical of hydroxyl and amine groups (such as acylations with acid chlorides and anhydrides) including urethane and urea formation respectively, are feasible with isocyanates. The primary amine can be quatemized by alkyl iodides or converted to an imine with a variety of aldehydes and ketones that can subsequently be reduced to an N-alkylated derivative. Chitin and chitosan are reactive with a variety of alkyl chlorides after treatment with concentrated NaOH. Important derivatives such as carboxymethylated chitin and chitosan are commonly produced in this manner with the addition of sodium chloroacetate. 

The reaction of an amino group with an aldehyde or ketone leads to an imine, which, as we have just seen with aldolase, provides a splendid example of how to bond a carbonyl substrate to an enzyme, and yet maintain its chemical reactivity in terms of enolate anion chemistry. Another type of covalent interaction is quite commonly encountered, and this exploits the thiol group of cysteine. Thiols are more acidic than... 

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