Abstract
Acid-catalyzed oligomerization of glycerol was investigated by direct infusion electrospray ionization mass spectrometry in the positive ion mode, i.e. ESI(+)-MS. The ESI(+)-MS data revealed that at 280 oC and in acidic medium (pH 2), glycerol undergoes successive intermolecular condensations to produce oligomeric species, i.e. [(glycerol)n - (n - 1) H2O] (n = 2-5). These ESI(+)-MS data, in association with the information provided by IR, 1H and 13C NMR analyses, indicated that these oligomers undergo intramolecular dehydrations to form miscellaneous products comprised mainly by cyclic compounds as well as alkenes and carbonylic derivatives (aldehydes and ketones).
Highlights
Vegetable and animal oil trans-esterification has been widely studied in recent years.[1,2,3,4,5,6,7,8,9] Glycerol is the most important byproduct of biodiesel and approximately 200 million liters per year are estimated to be produced only in Brazil by 2013
The presence of an intense ion of m/z 93 is clearly noticeable indicating the subsistence of glycerol in the reaction medium even after 2 h reaction
These ions probably arises from in-source dehydrations of [glycerol + H]+ as they are distinguishable in the ESI(+)-MS of an aqueous solution of pure glycerol at pH 2
Summary
Vegetable and animal oil trans-esterification (synthesis of biodiesel) has been widely studied in recent years.[1,2,3,4,5,6,7,8,9] Glycerol is the most important byproduct of biodiesel and approximately 200 million liters per year are estimated to be produced only in Brazil by 2013. This condensation can occur via the primary or secondary hydroxyl groups at the glycerol molecule to yield linear (a,a-diglycerol) and branched (a,b-diglycerol; b,b-diglycerol) isomers, as displayed in Scheme 1. Primary Oligomers (m/z of the protonated forms) diglycerol (167) triglycerol (241)
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