All chemicals and solvents, such as toluene sulfonic acid (p-TSA), 85% phosphoric acid, cellulose, glucose, cotton were purchased from ChemicalBook. Other feedstocks were obtained from grocery markets, while wheat straw, wood and grass were from farm fields.

Shimadzu LCMS-2050 is a compact single quadrupole mass spectrometer. It has Heated Dual Ion Source (DUIS), combining Electrospray Ionization (ESI) and Atmospheric Pressure Chemical Ionization (APCI) and LabSolutions software. UV detection undergoes at 210 nm and 254 nm. Shimadzu GCMS-QP2020 single quadrupole mass spectrometer.

CEM, The Discover^® 2.0 is the premier microwave reactor; Power: 0 - 300 W, intelligent control; Temperature range: up to 300˚C; Pressure range: up to 20 bar (~290 psi).

HPLC reverse phase column is from Shimadzu, Shim-pack Scepter C18-120/3 μm, 4.6 × 150 mm. Testing condition: Mobil phase is acetonitrile /water gradient from 5/95 to 80/20 in 35 minutes at room. Injection amount is 5.0 µL.

Thin layer chromatography (TLC) was carried out on precoated silica gel 60 F254 thin layer on glass from ChemicalBook.

NMR: ¹H NMR and ¹³C NMR spectra were recorded on Varian VNMR 400 MHz spectrometer (Varian, Inc., Polo Alto, CA, USA).

To 125 mL one neck-round bottom reaction flask with a stirring bar added 6.0 g feedstock, followed by suspended into 15 mL 85% phosphoric acid and 20 mL PEG400 (b.p. > 250˚C). The reaction flask was charged onto the microwave reactor with reducing pressure distillation apparatus. The reaction conditions were set at 30 W power, 150˚C temperature for regular distillation till no water moisture condensing, the collecting flask was changed by another one, temperature was set at 220˚C. vacuum was about 14.5 psi to distill until no more fraction out, it took about 30 minutes.

3.0 g of the raw material was added to a 125 mL microwave-safe single-necked round-bottom reaction flask equipped with an electron stirrer. Then add 0.3 - 0.5 g p-TSA, or 2% - 19% organic sulfonic acid (2% - 19% of the raw material mass), 20 mL of 8 - 10 times the mass of PEG400 (boiling point > 250˚C). Place the reaction flask in a microwave reactor equipped with a vacuum distillation device. Set the reaction conditions to 30 - 60 W power and 150˚C temperature and perform conventional distillation until no water vapor condenses. After replacing the collection flask, set the temperature to 220˚C and the vacuum level to approximately 14.5 psi, and continue direct vacuum distillation until no distillate is precipitated. The entire process takes approximately 30 minutes.

To the prepared crude product LGO above was added 5 mL 30% hydrogen peroxide, 20 methanol, and 5 mL 0. M HCl. The mixture was refluxed till LGO was completely converted to HBO, monitoring by LC/MS. Sodium sulfite solid was then added to adjust the pH of the system to neutral, simultaneously quenching excess hydrogen peroxide. After concentration, the solution was purified by flash column chromatography using a gradient elution with ethyl acetate and methanol as the fluent phases. The volume concentration of ethyl acetate decreased from 100% to 40%, while the volume concentration of methanol increased accordingly from 0% to 60%. The target fraction was collected and concentrated to obtain pure HBO.

[α]^D₂₀ −112.0 (c 0.01, CHCl₃). [(Lit.12 −114.5 (c 0.1, CHCl₃)] ¹H NMR (CDCl₃, 300 MHz): δH 3.25 (s, 1H, H6), 3.79 (dd, 1H, J = 12 and 3.6 Hz, H5a), 3.99 (d, 1H, J = 12 Hz, H5b), 5.17 (m, 1H, H4), 6.20 (dd, 1H, J = 5.7 and 1.8 Hz, H₂), 7.53 (dd, 1H, J = 5.7 and 1.5 Hz, H₃). ¹³C NMR (CDCl₃, 75 MHz): δC 62.2 (t, C1), 84.3 (d, C4), 122.8 (d, C2), 154.0 (d, C3), 173.5 (s, C1) ESI: m/z [M + H]⁺ called for C₅H₆O₃: 114.0395, found: 114.98.

As we realized, from earlier techniques, the biggest challenges to prepare the titled chiral valued compounds from agricultural products and biomasses are searching for an approach that must be more active catalysts; heating reaction mixture rapidly; setting the temperature as low as possible; making thermos transfer more evenly; pyrolyzing specifically; separating effortlessly; enlargeable quantitively, and solvents, ultimately to pursuit more efficient, economical and ecological friendly approach. This MW method provides an appropriate solution to meet these needs, which has never been reported. LGO then HBO produced directly from these agricultural masses’ pyrolysis described above assists us for further synthesizing nucleotide building blocks.

We take the advantages of MW reaction that can make the thermos transfer almost at the same time from interior and exterior of the mixture, the desired temperature level is able to reach rapidly. It offers a suite of significant compensation for chemical reactions, particularly for energy intensive processes of pyrolysis. The basis reason for these advantages lies in the fundamental difference in how heat is generated: volumetric and selective versus conventional conductive/convective heating.

In contrast to conventional heating, in an MW reactor, the energy interacts directly with the molecules of the material itself. This interaction, primarily through two mechanisms, dipole polarization and ionic conduction, causes molecules to align and collide with each other billions of times per second, generating heat instantaneously and throughout the entire volume of the materials.

Nevertheless, microwave reactors are not just a “faster heater”. They represent a fundamentally different form of energy transfer that enables faster, more efficient, and more selective chemical processing. For pyrolysis, this translates to transformative potential to produce higher-quality bio-oils and chars with greater energy efficiency and better process control, making it a highly promising technology for sustainable waste valorization.

In common manner, pyrolysis is the thermal decomposition of materials at elevated temperatures in an inert atmosphere, the switch from conventional to MW is a game change. However, a challenge still exposes things such as stirring or mixing almost unbearable because of either high heterogenicity or viscosity of the reaction mixtures.

Volumetric and Rapid Heating impacts on pyrolysis, because that conventional way suffers from large temperature gradients, leading to uneven decomposition, while microwave heating ensures the entire biomass or waste feedstock heats uniformly and rapidly. Companying by constant vacuum, this results in a more consistent product distribution and suppresses secondary cracking of the primary vapors. Therefore, selective or specific products may result.

On the other hand, MW also enhanced Quality of Bio-Oil, because the rapid, uniform heating of microwaves favors the cracking of large biomass molecules into volatile vapors quickly, minimizing their residence time at high temperature. This reduces secondary decomposition reactions, leading to a bio-oil with higher quality, lower viscosity and better stability. For this purpose, we adopted vacuum from beginning to end rather than inert gas atmosphere protection to ensure almost all energy is deposited directly into the feedstock. This leads to exceptional energy efficiency compared to heating a massive furnace, and the products are collected soon as created.

To better optimize the preparation process, we considered undergoing solvents or medium in the reaction mixture, PEG with 85% phosphoric acid (PA) with the substances were suspend initially, and kept stirring as vigorously as possible, although the mixture is heterogenies, evenly heating efficiency was much better, no concern of bumping under vacuum. The temperature was set at 220˚C providing predominately the desired product LGO that was distilled out via vacuum, from which further step was needed to convert into HBO as Scheme 1. It certainly is that PEG and PA could react to each other partially to form PEG-phosphoric ester under such circumstances, which was observed by adding alcohol in our experiments, so does p-TSA.

a. PA, or p-TSA, PEG200, vacuum, MW; b. PA, or p-TSA, PEG400, vacuum, MW; c. 0.5 M HCl, MeOH, 30% H₂O₂, reflexing.

Scheme 1. Directly and LGO mediated preparation of HBO.

HBO was also obtained in a synthetic way in our lab following the reported method [14] in four steps from D-(+)-mannitol, as described in Scheme 2, which was a conventional and economical approach. Even though the overall yield is about 40%, it is adoptable in terms of larger scale preparation before a more efficient method emerges.

Scheme 2. Full synthesis of HBO.

Nevertheless, this full synthetic method could be no longer competitive with this developed MW method. Here LGO has been efficiently converted into optically pure HBO using a two-step in-situ involving Baeyer-Villiger oxidation and a lipase catalyzed acid hydrolysis. Baeyer-Villiger oxidation forms an intermediate format, followed by an acid hydrolysis step to give 4-hydroxymethyl butanolide [15]. To simplify this procedure, we struggled just treat LGO by H₂O₂ under acidic conditions in methanol, the process was monitored by GC/MS, shown in Scheme 3, red is during the Baeyer-Villiger oxidation.

Scheme 3. GC monitoring the reaction from LGO to HBO.

To our insight, catalyst effects, PA. and p-TSA for example, can remove LG and HMF and a few other derivatives dramatically, not so specific. In the past, some feedstocks need to be pretreated, the usual way was acid washing to remove alkali metals, reducing char and increasing favorable outcomes. While, in our trails, char formed inevitably in the reacted residue, none of feedstocks being pretreated, but some of them offered almost single fraction of LGO accordingly, particularly the p-TSA. When using approaches as previously reported pyrolysis, the procession would be agonized under punitive conditions and are not suitable for large-scale preparation or commercialization.

Carbohydrates are relatively stable chemically under ambient conditions, which predominantly rely on hydrogen bonds intramolecular and intermolecular. Pyrolysis undergoes at acetic, higher temperature and aerobic condition. The mechanism has been studied extensively [16].

In the practices, we found often that the crude products always aggregated or oligomerized soon as basified to pH 7.5 - 9.0 and formed various structures. We hypothesize that the interactions of any type of carbohydrates with sulfonic acid results in the change of the primary system of hydrogen bonds of single sugars and the polymeric saccharides, and the esterification. Combed the above-mentioned factors have a pronounced effect on the thermolysis of cellulosic materials, namely, on the ratio of the main reactions such as depolymerization and dehydration, and, correspondingly, on the composition of volatile products. Our insight into this favorable consequence of LGO is a thermodynamic result under the developed condition other than a new mechanism.

Regarding HBO, previous research had never directly obtained this specific product just via pyrolyzing, particularly for those structural subunits from a wide range of natural resources possess polysaccharides, therefore, to prepare large quantities of LGO even HBO, cellulose has been stared as an ideal feedstock for the reasons of economy and higher composition of glucose units traditionally. To expand the range of feedstocks that may compose the same basic unit and can convert to same or/and compulsory products via pyrolysis, as shown in Table 1, we treated all these biomasses in same manner either in the present of PA. or p-TSA. As desired, among these biomasses, glucose, sugar, starch, cellulose yielded LGO predominately with little amount of HBO, while p-TSA system provided even better, each of them offers crude LGO yielding from 5% to 60% (W/W) approximately, in which, even cotton given a good fraction of HBO, its quantity is too less to undergo next reaction. We investigated the MW reaction in the present of PA. and p-TSA in PEG200/400 under MW, the volatile fractions contain both products, LGO and HBO, from which LGO is obviously preparable by this way, shown as Scheme 4.

Scheme 4. LC PEG200 system: crude LGO and HBO from soluble starch and cotton.

Mobile phase: acetonitrile/water 0.01% - 62% in 34 minutes; Column: Shimadzu, Shim-pack Scepter C18-120/3 μm, 4.6 × 150 mm.

The pyrolysis depends on temperature, microwave power and pressure, allowing the catalytic activity toward secondary decomposition of levoglucosan (LG) into LGO and continually to HBO.

In contrast, the degree of development by dehydration reactions leading to the formation of LGO depends on chemical components of these biomasses, crystalline carbohydrates and the accessibility for the acidic catalyst, and mediated mixture. The ordered carbohydrates favor the formation of LGO whereas celluloses with a higher amount of less ordered regions show also parallel formation of LG as in Scheme 5.

As mentioned above, the key takeaway is that carbohydrate pyrolysis can transform low-value biomass into high-demand chemicals and fuels. Optimizing temperature, catalysts, and feedstock are critical to maximizing economic returns. Integrated biorefineries could combine pyrolysis with fermentation, converting LGO to ethanol for example, for higher profitability. In our effort, we eventually know which of the feedstocks can create LG, LGO and HBO individually for the first time, which can be practicable of fabrication, a few of them created less, shown as Scheme 6 and Table 1.

1. HBO, 2. LGO.

Scheme 5. LC results from PEG + PA. system.

Rt_LGO = 10.67 min. Rt_HBO = 3.88 min.

Scheme 6. LC results from PEG + p-TSA system.

Table 1. PEG200 + PA. system: LGO approximal proportion from feedstocks.

*Total fractions mass versus raw material mass (g/g).