Addition of boric acid to O-hydroxy-carbonyl compounds dissolved in concentrated sulphuric acid, except in a few cases, brings about either a marked intensification or a change in colour of the fluorescence exhibited by them in daylight or under the lamp. In a few other cases fluorescence appears for the first time on the addition of boric acid. Since even the simpler O-hydroxy-carbonyl compounds yield these results with boric acid, it appears reasonable to conclude that this reaction will serve as a suitable method for the detection of O-hydroxy-carbonyl group. It must, however, be borne in mind that while the appearance of fluorescence, its intensification or a change in colour indicates the presence of a hydroxyl group ortho to the carbonyl, the non-appearance of the fluorescence effects described does not indicate the absence of this group.
No fluorescence changes are observed with boric acid if the molecule of the compound under investigation does not contain a ketonic group ortho to the hydroxyl, so also in the absence of either of them or when they are present in positions other than ortho to each other.
Sulphonation of the simpler O-hydroxy-carbonyl compounds brings about a marked change in the colour and intensity of the fluorescence; the sulphonic acid group appears to be markedly auxo-floric in character. It is remarkable that nitration or bromination, on the other hand, damps the fluorescence considerably.
From the brilliant fluorescence effects given by resacetophenone, it is expected to develop into a useful reagent for the detection of boric acid on a semi-micro scale.
Further work along these lines is in progress.