Isolation and Identification of Six Difunctional Ethyl Esters from Bio-oil and Their Special Mass Spectral Fragmentation Pathways

Abstract

Three difunctional ethyl esters (DFEEs), including ethyl 16-hydroxyhexadecanoate, ethyl (Z)-18-hydroxyoctadec-9-enoate, and diethyl (Z)-octadec-9-ene-1,18-dioate, were isolated as nearly pure compounds from sawdust-derived bio-oil. Their structures were tentatively identified by gas chromatography/mass spectrometry (GC/MS) and high-resolution mass spectrometry (HR-MS). Combination transesterification reaction of DFEEs to difunctional methyl esters (DFMEs) and determination of the GC/MS retention time differences of DFEEs and corresponding DFMEs is a simple method to determine the ester group number of unknown DFEEs. GC/MS results indicate that the fragment ions at mass-to-charge ratios (m/z) of 88 and 98 are typical ions for these DFEEs. The former ion is formed via well-known McLafferty rearrangement, whereas the formation pathway of the ion at m/z 98 is unreported before. HR-MS results show that the fragment ion at m/z 98 should be a cyclohexanone radical ion, which is possibly formed via a novel rearrangement initiated by remote hydrogen rearrangement. Besides long-chain DFEEs, long-chain difunctional carboxylic acids (including dicarboxylic acids, ω-hydroxy acids, diacid monomethyl ester, and diacid monoethyl ester) and DFMEs (including diacid dimethyl ester and ω-hydroxy methyl ester) are also typical of the fragment ion at m/z 98. Hence, it is a common characteristic to form the rearrangement ion at m/z 98 for long-chain difunctional carboxylic acids, DFEEs, and DFMEs, and this special mass spectral rearrangement could facilitate the identification of these classes of compounds. Using this rearrangement rule of DFEEs, three ω-hydroxy ethyl esters, including ethyl 22-hydroxydocosanoate, ethyl 24-hydroxytetracosanoate, and ethyl 26-hydroxyhexacosanoate, were tentatively identified by GC/MS.

Analysis of the Bio-oil Produced by the Hydrothermal Liquefaction of Biomass Using High-Resolution Mass Spectrometry and Isotope Exchange

“…The structural information about individual compounds can also be obtained from MS/MS experiments. Unfortunately, the complexity of the sample does not allow the isolation of individual m / z , and only few experiments with the use of MS/MS to study complex natural mixtures have been reported. − Unfortunately, even if the MS/MS spectrum of the single m / z is obtained, it is not possible to accurately identify the compound, because the size of databases of collision induced dissociation spectra (MzCloud (), Metlin , ) is insufficient (∼25 000 compounds). However, in silico fragmentation software such as MetFrag (uses iterative bond cleavage), CFM-ID, , and SIRIUS 4, , which integrates CSI:FingerID (uses the fragmentation tree), can be used to determine the most likely compounds.…”

Unambiguous Evidence for the Occurrence of Pentamethylphenol in Lignite Methanolysate

“…E 65 was recrystallized and washed with methanol to offer a nearly pure fraction 1 (F 1 ). F 1 was analyzed with GC/ MS, 20 FTIR, 1 H and 13 C NMR, distortionless enhancement by polarization transfer with a proton pulse angle at 135°NMR (DEPT-135), and 2D NMR, including 1 H− 1 H correlation spectroscopy (COSY), heteronuclear single-quantum correlation (HSQC), and heteronuclear multiple-bond correlation (HMBC).…”