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I have studied that Fehling's test is given by aldehydes and alpha hydroxy ketones. I read in a book that it is also given by phenylhydroxylamine converting it to nitrosobenzene.
Does it gives the test as it has an alpha hydrogen or any other reason? Are there any more exceptions like this?

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Quoting from "REDUCTION OF AROMATIC NITRO COMPOUNDS TO N-PHENYLHYDROXYLAMINES - A Comparative Study of the Yields Obtained when Aromatic Nitro Compounds are Reduced, under Similar Conditions, to N-Phenylhydroxyiaminee by William Henry James"

N-Phenylhydroxylamine is unstable. It is readily affected by light, especially white light. It is also affected by moist air, being readily oxidized to nitrosobenzene. It has strong reducing power, reducing almost quantitatively Fehling's Reagent to cuprous oxide, and causing the formation of a silver mirror when warmed with an aramoniacal solution of silver oxide.

So, I guess that its instability and its reducing power are the cause of the effect explained.

Reference

  1. James, William Henry. Reduction of aromatic nitro compounds to N-phenylhydroxylamines. Thesis (M.A.), Boston University, 1932. Boston University Libraries OpenBU
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