New oxidation pathway of 3,5-di-tert-butyl-4-hydroxytoluene: An ionspray tandem mass spectrometric and gas chromatographic/mass spectrometric study

The autoxidation of 3,5-di-tert-butyl-4-hydroxytoluene (BHT, 1) in bar soap was investigated with ionspray tandem mass spectrometric and on-line gas chromatographic/mass spectrometric methods. The oxidation products of BHT were extracted from the bar soap surface, concentrated, and fractionated with open-column chromatography to remove the impurities. New oxidation products of BHT (BHT phenol-type dimer 7 and others) were identified with the two mass spectrometric methods. The results suggested that oxidation of BHT in bar soap occurred in a way different from that in the previous studies. In the new pathway, oxidation of BHT first generates an excited state of phenol-type dimer 4, and then this species decomposes, due to its high energy, to form dimer 7. The mechanism of oxidation is discussed.