On the reaction of ozone with β-carotene, a naturally occurring polyene

Abstract

The reaction of β-carotene with ozone was studied in detail by UV-Vis-NIR spectroscopy. The radical cation of β-carotene was observed during the ozonization of this molecule. Ozonization causes trans-cis isomerization of β-carotene at its 15-15′ site and then a scission to retinal which in its turn is then degraded by further ozonization to unsaturated and conjugated aldehydes and dialdehydes. The antiozonant properties of β-carotene were tested by measuring the viscosity change undergone by an ozonized standard solution of cis-1,4-polybutadiene in the presence of β-carotene and without any protection. Surprisingly it was found that the dienic rubber scavenges the oxygen and protects β-carotene from ozone attack. In these conditions the behaviour of linear and conjugated polyene β-carotene was found fully comparable to the behaviour of the tridimensional weakly cross-conjugated polyene C 60 fullerene. Cis-1,4-polybutadiene ozonized in the presence and without β-carotene was studied by FT-IR spectroscopy.