Analytical study on the production of a hydroxylactone from catalytic pyrolysis of carbohydrates with nanopowder aluminium titanate

The hydroxylactone (1R,5S)-1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one (LAC) was isolated from the catalytic pyrolysis of cellulose over Lewis acids, such as zinc chloride and more recently nanopowder aluminium titanate (NP AlTi). In this study, the tendency of several carbohydrates to thermally produce LAC without and with NP AlTi was investigated by an analytical procedure employing a heated filament pyrolyser. Products evolved from off-line pyrolysis were collected onto an adsorbent resin (XAD-2), eluted with ethyl acetate and analysed by gas chromatography–mass spectrometry (GC–MS). LAC was detected in the pyrolysates of neat cellulose, starch, lactose, d-glucose, O-methyl-α-d-glucoside, O-methyl-β-d-glucoside, d-mannose and d-galactose. The yields of LAC augmented when pyrolysis was conducted in the presence of 30% NP AlTi, but with significant differences among sugars. Polysaccharides provided the highest yields (5–6%), monosaccharides the lowest (<1%). Low levels of LAC were thermally released from the anhydrosugar levoglucosan (LG) and its 4-O-acetyl derivative (AcLG), but when this latter was pyrolysed with the catalyst produced LAC yields comparable to those of starch and cellulose. Thermogravimetric (TG) and its derivative (DTG) analysis showed a general decrease of decomposition temperatures when the sugar sample was mixed with NP AlTi. The pyrolytic behaviour of the different sugars was rationalized by assuming that ascopyrone P (APP; 1,5-anhydro-4-deoxy-d-glycero-hex-1-en-3-ulose) was the precursor of LAC.