Fluorescence reactions with boric acid and O-hydroxy-carbonyl compounds, and their application in analytical chemistry

Conclusion

• (1) 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.

• (2) 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.

• (3) 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.

• (4) 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.