Sustainable Aviation Fuel (SAF) Scale-up: From Lab to Commercial Aviation

Aviation accounts for approximately 2-3% of global CO2 emissions. Sustainable Aviation Fuel (SAF) represents a critical pathway to decarbonise the sector and achieve net-zero targets by 2050. SAF is a drop-in replacement for conventional jet fuel (Jet A-1) produced from sustainable feedstocks including waste oils, agricultural residues, and synthetic pathways.


Key Concepts


SAF can be produced through multiple pathways: HEFA (Hydroprocessed Esters and Fatty Acids), ATJ (Alcohol-to-Jet), and Power-to-Liquids (PtL). Each pathway involves different feedstock-to-fuel conversion chemistry with varying maturity levels. HEFA technology is the most commercially mature, while ATJ and PtL remain in pilot and early-commercial phases.

HEFA Technology: The HEFA process hydroprocesses used cooking oils and other lipids, removing oxygen and producing hydrocarbons equivalent to conventional jet fuel. This pathway can reduce lifecycle greenhouse gas (GHG) emissions by 50-80% compared to fossil jet fuel.

ATJ Technology: Alcohol-to-Jet converts ethanol (from biomass or bio-based routes) via dehydration, oligomerisation, and hydrogenation. The process offers flexibility in feedstock sourcing but requires careful control of intermediate product quality.

Power-to-Liquids: Synthetic pathways combining hydrogen (from renewable electricity) and CO2 (from capture or biomass) to produce SAF. This pathway shows promise for hard-to-abate sectors but faces scaling challenges.


Policy & Market: Global SAF demand is expected to reach 6-10 million tonnes annually by 2030, driven by regulatory mandates (ICAO's Carbon Offsetting and Reduction Scheme for International Aviation) and corporate net-zero commitments. SAF currently costs 2-3x more than conventional jet fuel, requiring investment in scale and R&D.


Applications & Research Frontiers 


Co-processing SAF production within existing refinery infrastructure offers capital efficiency advantages but requires compatibility assessments with existing hydrotreating units.


Advanced sustainability metrics beyond GHG accounting: Life cycle assessment (LCA) frameworks increasingly incorporate water stress, biodiversity impact, and social criteria for feedstock sourcing.


Engine performance and compatibility testing remains critical—SAF blends up to 50% are already approved, with research ongoing to achieve higher concentrations and improve lubricity characteristics.


Feedstock diversification strategies are essential: advanced feedstocks (algae, synthetic biology routes) under development to reduce pressure on traditional biomass supplies.


Conclusion


SAF represents a tangible near-term solution for aviation decarbonisation, with HEFA established and ATJ/PtL emerging. Success requires integrated efforts across policy, infrastructure investment, and feedstock development.


Keywords: Sustainable Aviation Fuel, SAF, HEFA, Alcohol-to-Jet, aviation decarbonisation, net-zero, renewable fuels, biofuels, lifecycle assessment

The Wurtz Reaction: Coupling Alkyl Halides to Form C-C Bonds

Introduction

The Wurtz reaction is a fundamental organic transformation that enables the formation of new carbon-carbon bonds through the coupling of alkyl halides with sodium metal. This classical reaction, discovered by Charles-Adolphe Wurtz in 1855, remains an important tool in synthetic organic chemistry, particularly for the synthesis of alkanes and the construction of larger carbon frameworks.

Definition and Overview

The Wurtz reaction is defined as the coupling of two alkyl halides mediated by sodium metal:

$$2 \text{R-X} + 2 \text{Na} \rightarrow \text{R-R} + 2 \text{NaX}$$

Where:

  • R = alkyl group
  • X = halogen (Cl, Br, or I)
  • Na = sodium metal

Mechanism

The Wurtz reaction proceeds through a radical mechanism involving two main steps:

Step 1: Formation of Alkyl Radical

Sodium metal transfers an electron to the alkyl halide:

$$\text{R-X} + \text{Na} \rightarrow \text{R}^{\bullet} + \text{Na}^{+}\text{X}^{-}$$

Step 2: Carbon-Carbon Bond Formation

Two alkyl radicals couple to form the new C-C bond:

$$\text{R}^{\bullet} + \text{R}^{\bullet} \rightarrow \text{R-R}$$

Practical Examples

Example 1: Formation of Butane

The coupling of two ethyl bromide molecules:

$$2 \text{CH}_{3}\text{CH}_{2}\text{Br} + 2 \text{Na} \rightarrow \text{CH}_{3}\text{CH}_{2}\text{CH}_{2}\text{CH}_{3} + 2 \text{NaBr}$$

SMILES representation:

  • Reactant (Ethyl bromide): div data-smiles="CCBr"
  • Product (n-Butane): CCCC
  • Reaction Conditions

    • Temperature: Room temperature to mild heating
    • Solvent: Anhydrous ether or other aprotic solvents
    • Reagent: Freshly cut sodium metal
    • Atmosphere: Inert (N₂ or Ar)
    • Time: 2-24 hours

    Advantages

    • Simple and straightforward procedure
    • Good yields for primary alkyl halides
    • Direct carbon-carbon bond formation
    • Classic synthetic method with well-documented protocols

    Limitations

    1. Selectivity issues - Asymmetric couplings produce mixtures
    2. Beta-hydrogen elimination - Produces alkene side products
    3. Steric effects - Bulky groups reduce reactivity
    4. Hazardous - Requires handling reactive sodium metal
    5. Functional group incompatibility - Cannot tolerate polar groups

    Conclusion

    The Wurtz reaction remains a significant milestone in organic chemistry history, exemplifying the principles of radical chemistry and carbon-carbon bond formation. While modern cross-coupling reactions have largely superseded it in practical synthesis, the Wurtz reaction continues to hold educational value for understanding:

    • Radical reaction mechanisms
    • The role of electron transfer in carbon-carbon bond formation
    • Historical development of synthetic organic chemistry
    • Alternative approaches to molecular synthesis

    Keywords: Wurtz reaction, alkyl halide, sodium metal, carbon-carbon coupling, radical mechanism, organic synthesis, classical reactions


    This comprehensive guide covers the Wurtz reaction with chemical equations (LaTeX), molecular structures (SMILES notation), and proper HTML formatting for optimal readability.

    Top 10 Organic Chemistry Breakthroughs of 2025

    Top 10 Organic Chemistry Breakthroughs of 2025

    Organic chemistry laboratory research

    As we approach the end of 2025, the field of organic chemistry has witnessed remarkable advances that are reshaping how we design molecules, synthesize pharmaceuticals, and address global challenges. From revolutionary metal-organic frameworks that earned the Nobel Prize to groundbreaking skeletal editing techniques, this year has been transformative. Here are the top 10 organic chemistry breakthroughs of 2025.


    1. Nobel Prize: Metal-Organic Frameworks Revolution

    The 2025 Nobel Prize in Chemistry recognized Susumu Kitagawa, Richard Robson, and Omar Yaghi for their pioneering work in developing metal-organic frameworks (MOFs). These crystalline materials feature metal ions connected by organic molecules, creating structures with large cavities that can capture and store specific substances.

    💡 Key Innovation

    MOFs can harvest water from desert air, capture carbon dioxide, store toxic gases, and catalyze chemical reactions with unprecedented selectivity.

    In 1998, Yaghi and coworkers demonstrated that a framework based on $\ce{Zn^{II}}$ and 1,4-benzenedicarboxylate displayed permanent microporosity with specific surface areas of approximately 300 m²/g. This breakthrough opened the door to designing porous materials with tailored properties for gas storage, separation, and catalysis.

    Nobel Committee for Chemistry (2025). "Metal-Organic Frameworks." Scientific Background to the Nobel Prize in Chemistry 2025. The Royal Swedish Academy of Sciences.


    2. Skeletal Editing: The Cut-and-Paste Chemistry Revolution

    Skeletal editing emerged as one of the hottest trends in organic chemistry this year, enabling chemists to insert, delete, or swap single atoms within complex molecular frameworks. This "molecular surgery" allows researchers to fine-tune drug candidates without rebuilding molecules from scratch.

    Mark Levin at the University of Chicago and Richmond Sarpong at UC Berkeley coined the term and pioneered methods for these transformations. In 2025, numerous groups reported breakthroughs in nitrogen insertion, carbon deletion, and atom swapping reactions.

    Impact on Drug Discovery

    Skeletal editing could save weeks of synthetic effort in pharmaceutical development by allowing direct modification of molecular cores to optimize biological activity.

    One notable advance came from Indrajeet Sharma's group at the University of Oklahoma, who published methods for nitrogen and carbon insertion into pyrroles, indoles, and imidazoles. This work is now being applied to DNA-encoded library drug discovery in collaboration with Baylor University.

    Sharma, R., et al. (2025). "Remodelling molecular frameworks via atom-level surgery: recent advances in skeletal editing of (hetero)cycles." Organic Chemistry Frontiers. DOI: 10.1039/D4QO02157F


    3. Copper-Catalyzed C5-H Functionalization of Indoles

    Researchers at Chiba University achieved a major breakthrough in indole chemistry by developing a copper-catalyzed method for selective C5-H alkylation. Led by Associate Professor Shingo Harada, the team achieved yields up to 91% using an affordable copper-silver catalyst system.

    Indole Core Structure

    The reaction uses highly reactive carbenes and operates through a unique C4-C5 rearrangement mechanism:

    $$\ce{Indole + Carbene ->[Cu(OAc)2·H2O/AgSbF6] C5-Alkylated Product}$$

    📝 Significance

    Since 2015, the FDA has approved 14 indole-based drugs for conditions including migraines, infections, and hypertension. This new method provides a cost-effective route to modify these important pharmaceutical scaffolds.

    Isono, T., Harada, S., Yanagawa, M., & Nemoto, T. (2025). "Copper-catalyzed direct regioselective C5–H alkylation reactions of functionalized indoles with α-diazomalonates." Chemical Science, 16(33), 14967. DOI: 10.1039/D5SC03417E


    4. Hypervalent Iodine: Green Chemistry's New Champion

    A comprehensive review by Professors Toshifumi Dohi and Yasuyuki Kita from Ritsumeikan University highlighted the transformative potential of hypervalent iodine-mediated coupling reactions as sustainable alternatives to traditional transition metal catalysis.

    By manipulating the oxidation state of iodine atoms, researchers can generate aryl cation-like species, radicals, and aryne precursors that facilitate selective bond formation without relying on costly rare metal catalysts.

    Traditional Methods

    • Expensive Pd, Pt catalysts
    • Metal waste generation
    • Lower atom economy

    Hypervalent Iodine

    • Earth-abundant iodine
    • Reduced waste
    • High selectivity

    Dohi, T., & Kita, Y. (2025). "Iodoarene Activation: Take a Leap Forward toward Green and Sustainable Transformations." Chemical Reviews, 125(6). DOI: 10.1021/acs.chemrev


    5. Semi-Artificial Leaf: CO₂ to Fuel Conversion

    Cambridge researchers led by Professor Erwin Reisner developed a revolutionary "artificial leaf" that combines organic semiconductors with bacterial enzymes to convert sunlight, water, and $\ce{CO2}$ into formate—a clean fuel for chemical synthesis.

    This biohybrid device represents the first use of organic semiconductors as the light-capturing component in such systems, offering a non-toxic, tunable alternative to traditional photocatalysts.

    The key reactions are:

    $$\ce{2H2O ->[h\nu] 2H2 + O2}$$

    $$\ce{CO2 + 2H+ + 2e- -> HCOO-}$$

    ⚠️ Industrial Impact

    The chemical industry produces approximately 6% of global carbon emissions. This technology could help "de-fossilize" chemical manufacturing.

    Yeung, C.W.S., et al. (2025). "Semi-artificial leaf interfacing organic semiconductors and enzymes for solar chemical synthesis." Joule. DOI: 10.1016/j.joule.2025.102165


    6. Iron Photocatalysis: Concurrent CO₂ Reduction and Organic Synthesis

    Chinese researchers reported a groundbreaking iron(II) molecular photocatalyst that independently executes $\ce{CO2}$ reduction without requiring separate photosensitizers—a long-standing challenge in the field.

    The polypyridyl iron complex $\ce{FePAbipyBn}$ achieved a turnover number (TON) of 3,558 for CO production with selectivity exceeding 99%. More remarkably, it simultaneously facilitates enamine oxidation and $\ce{CO2}$ reduction, producing indoles and CO as value-added products.

    $$\ce{CO2 + Enamine ->[Fe^{II} Photocatalyst][h\nu] Indole + CO}$$

    First-of-Its-Kind Achievement

    This represents the inaugural instance of a photoredox reaction coupling $\ce{CO2}$ reduction with organic synthesis using a single molecular photocatalyst.

    Guo, K., et al. (2025). "A Highly Efficient Molecular Iron(II) Photocatalyst for Concurrent CO₂ Reduction and Organic Synthesis." Journal of the American Chemical Society, 147(19), 15942-15946. DOI: 10.1021/jacs.5c01698


    7. Transition Metal-Free Coupling Reactions

    The movement toward sustainable organic synthesis accelerated in 2025 with numerous reports of transition metal-free coupling methods. These approaches align with green chemistry principles by minimizing waste, reducing reliance on rare metals, and lowering energy consumption.

    Key advances included:

    • Hypervalent iodine-mediated aryl-aryl couplings
    • Organocatalytic C-H functionalization
    • Photochemical coupling reactions without metal catalysts

    💡 Green Chemistry Metrics

    These methods significantly improve atom economy and reduce E-factors (environmental waste factors) compared to traditional palladium-catalyzed cross-couplings.


    8. MXenes for Ammonia Synthesis from Air

    Researchers explored MXenes—two-dimensional materials—as promising catalysts for transforming air into ammonia for cleaner fertilizers and fuels. These materials offer tunable atomic structures that can be optimized for nitrogen fixation.

    The nitrogen reduction reaction proceeds as:

    $$\ce{N2 + 6H+ + 6e- -> 2NH3}$$

    MXenes provide a more affordable alternative to traditional Haber-Bosch processes and expensive ruthenium catalysts, potentially revolutionizing sustainable ammonia production.

    Science Daily (November 2025). "New 2D Material Transforms Air Into Fuel and Fertilizer."


    9. Photoelectrocatalytic Fluoroalkylation with Iron

    A resource-economic photoelectrocatalysis strategy enabled versatile direct fluoroalkylations catalyzed by earth-abundant iron, paired with the hydrogen evolution reaction (HER). This approach proved amenable to late-stage C-H fluoroalkylations of bio-relevant heterocycles.

    The synergistic combination of photoexcitation with electron transfer by anodic oxidation creates unique potential for novel reaction manifolds that go beyond individual photo- or electrochemistry.

    📝 Advantages

    The method eliminates the need for expensive photocatalysts or stoichiometric chemical oxidants while enabling extreme redox potentials under mild conditions.

    Motornov, V., et al. (2025). "Photoelectrochemical Iron(III) Catalysis for Late-Stage C-H Fluoroalkylations." Angewandte Chemie International Edition, 64(25), e202504143. DOI: 10.1002/anie.202504143


    10. Molecular Antennas for Lanthanide LED Breakthrough

    Cambridge scientists discovered how to electrically power insulating nanoparticles using organic molecules as "molecular antennas." This breakthrough enabled the creation of ultra-pure near-infrared LEDs from lanthanide-doped nanoparticles—previously thought impossible.

    The organic antenna molecules trap charge carriers and harvest "dark" molecular triplet excitons, directing electrical energy into the insulating materials. These LEDs generate extremely pure near-infrared light ideal for medical diagnostics and optical communications.

    Versatile Platform

    The fundamental principle allows exploration of countless combinations of organic molecules and insulating nanomaterials, enabling devices with tailored properties for unimagined applications.

    Yu, Z., et al. (2025). "Triplets electrically turn on insulating lanthanide-doped nanoparticles." Nature, 647(8090), 625. DOI: 10.1038/s41586-025-09601-y


    Conclusion: A Transformative Year for Organic Chemistry

    The breakthroughs of 2025 reflect organic chemistry's evolution toward greater sustainability, precision, and interdisciplinary integration. From Nobel Prize-winning MOFs to molecular surgery techniques, earth-abundant metal catalysis to bio-inspired photosynthesis, these advances are laying the groundwork for next-generation pharmaceuticals, clean energy technologies, and sustainable chemical manufacturing.

    💡 Looking Forward

    As we move into 2026, the convergence of artificial intelligence with these synthetic methodologies promises to accelerate discovery even further, potentially revolutionizing how we design and synthesize molecules.

    The field stands at an exciting crossroads where fundamental discoveries in reactivity meet urgent global challenges in sustainability and healthcare. These top 10 breakthroughs exemplify the creativity, innovation, and problem-solving capacity of the organic chemistry community.


    References

    The Nobel Committee for Chemistry. (2025). *Scientific background: Metal-organic frameworks*. The Royal Swedish Academy of Sciences. Sharma, R., Arisawa, M., Takizawa, S., & Salem, M. S. H. (2025). Remodelling molecular frameworks via atom-level surgery: Recent advances in skeletal editing of (hetero)cycles. *Organic Chemistry Frontiers*. https://doi.org/10.1039/D4QO02157F Isono, T., Harada, S., Yanagawa, M., & Nemoto, T. (2025). Copper-catalyzed direct regioselective C5–H alkylation reactions of functionalized indoles with α-diazomalonates. *Chemical Science, 16*(33), 14967. https://doi.org/10.1039/D5SC03417E Dohi, T., & Kita, Y. (2025). Iodoarene activation: Take a leap forward toward green and sustainable transformations. *Chemical Reviews, 125*(6), 3440–3550. https://doi.org/10.1021/acs.chemrev.4c00808[1] Yeung, C. W. S., Liu, Y., Vahey, D. M., et al. (2025). Semi-artificial leaf interfacing organic semiconductors and enzymes for solar chemical synthesis. *Joule*. https://doi.org/10.1016/j.joule.2025.102165 Guo, K., Yang, S., Wang, Y., et al. (2025). A highly efficient molecular iron(II) photocatalyst for concurrent CO₂ reduction and organic synthesis. *Journal of the American Chemical Society, 147*(19), 15942–15946. https://doi.org/10.1021/jacs.5c01698 Motornov, V., Trienes, S., Resta, S., et al. (2025). Photoelectrochemical iron(III) catalysis for late-stage C–H fluoroalkylations. *Angewandte Chemie International Edition, 64*(25), e202504143. https://doi.org/10.1002/anie.202504143 Yu, Z., Deng, Y., Ye, J., et al. (2025). Triplets electrically turn on insulating lanthanide-doped nanoparticles. *Nature, 647*(8090), 625. https://doi.org/10.1038/s41586-025-09601-y Durrani, J. (2025, December 18). AI continues to make waves and structural editing impresses in 2025. *Chemistry World*. Royal Society of Chemistry. https://www.chemistryworld.com/news/ai-continues-to-make-waves-and-structural-editing-impresses-in-2025/4022665.article Barbu, B. (2025). Skeletal editing: How close are we to true cut-and-paste chemistry? *Chemical & Engineering News, 103*(7).

    Keywords: #OrganicChemistry #GreenChemistry #Photocatalysis #SkeletalEditing #MetalOrganicFrameworks #NobelPrize2025 #SustainableChemistry #DrugDiscovery #Catalysis #MolecularDesign