Insight into the Chemical Complexity of Soluble Portions from Cornstalk Methanolysis

Cornstalk was subjected to methanolysis in the presence of NaOH at 220–320 °C to afford soluble portions (SPs) 1–5 (SP₁–SP₅) and an inextractable portion (IEP). The maximum total yield (ca. 51%) of SPs was acquired at 300 °C with the same mass of NaOH and cornstalk. Under the same conditions, SP₁ has the highest yield, followed by SP₅ and SP₂. The relatively volatile and less polar species in the resulting SPs and IEP were identified with a gas chromatograph/mass spectrometer (GC/MS). The polar species in SP₁, SP₂, and SP₅ were further analyzed with a negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). The analysis with GC/MS shows that phenolic compounds and alcohols are the dominant group components in SP₁ and SP₂, respectively, while the predominant compounds in esterified SP₃–SP₅ and IEP are esters. According to analysis with FTICRMS, thousands of compounds were detected in SP₁, SP₂, and SP₅. Most of the compounds are <i>O</i>_<i>n</i> (<i>n</i> = 1–10) class species with double bond equivalent (DBE) values of 1–14 and carbon atom numbers of 5–35. The most abundant class species in SP₁, SP₂, and SP₅ are <i>O</i>₃, <i>O</i>₃, and <i>O</i>₈, respectively. SP₁ and SP₂ are rich in <i>O</i>₂–<i>O</i>₄ class species with DBE values of 5–8, which may be attributed to lignin-derived compounds. Different from SP₁ and SP₂, SP₅ has relatively high contents of <i>O</i>₅–<i>O</i>₁₀ class species, corresponding to various acidic species. In addition, <i>N</i>₁<i>O</i>_<i>n</i> (<i>n</i> = 0–8) class species with DBE values of 3–14 were also identified, which should contain a pyrrole ring as the parent structure