Phenylhydrazone formation

Condensation with phenylhydrazine results in phenyl-pyrazole 262. The regiospecificity results from intermediate phenylhydrazone formation of the more... 

Phenylhydrazone formation indicates a carbonyl compound. Since the negative Tollens test rules out an aldehyde, (A) must be a ketone. A negative iodoform test rules out the CH,C=0 group, and the reduction product, pentane, establishes the C s to be in a continuous chain. The compound is CHjCHjCOCHjCH,. 

The accuracy and precision of an enzyme assay usually depend on the underlying chemical basis of techniques that are used. For example, if an assay involving reaction of an enzymatically produced aldehyde with phenylhydrazine to yield a phenylhydrazone product is carried out in buffer of the wrong pH, that is, a pH significantly above 6.0, the observed rate of phenylhydrazone formation will not accurately reflect the rate of enzymatically produced aldehyde, but rather the chemical rate of phenylhydrazone formation. The accuracy of an assay is a reflection of... 

It was not until the beginning of the present century ttiat anofrier great impetus eame to the study of the carbohydrates. This new surge was started by Purdie and his collaborators and the tool they used was methylation. As phenylhydrazone formation clarified the constitution of the straight chains in the sugar molecule, so mefliylation threw new light on ring formation and opened a powerful attack on the constitution of the more complex carbohydrates. 

FIGURE 22.30 The small amount of free aldehyde present at equilibrium accounts for phenylhydrazone formation at C(l). 

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