1,1-Cyclohexanediacetic Acid

Pharmaceutical-grade 1,1-cyclohexanediacetic acid, CAS 4355-11-7, is consumed predominantly as the starting diacid for the preparation of 3,3-pentamethylene glutaric anhydride, which is then converted to gabapentin through ammonolysis and Hofmann rearrangement. In a production-scale glass-lined reactor train with 6,300 L working volume, retreat-blade agitation, and overhead azeotropic distillation, the diacid is charged with toluene and acetic anhydride at a molar ratio of 1.0 mol diacid to 1.2 mol acetic anhydride. Ring closure is conducted at 110–115 °C with water removal through a Dean-Stark trap; residual water in the reaction mass is held below 0.05 % w/w before vacuum stripping because incomplete dehydration shifts the anhydride assay below 99.0 % and depresses gabapentin yield after ammonolysis. Excessive dehydration above 8 h produces amber oligomeric impurities, so nitrogen stripping at 0.8 bar is initiated after 6 h and the batch is transferred to an isolator where the anhydride is crystallized, centrifuged, and washed with chilled toluene. The downstream ammonolysis is executed in tetrahydrofuran at 0–5 °C using 1.0–1.1 equivalents of ammonia per anhydride, followed by Hofmann rearrangement with sodium hypochlorite at 8–12 °C and maintenance of the reaction pH between 12.5 and 13.0. Crude gabapentin is crystallized from aqueous methanol and isolated in a centrifuge with 0.5 µm polypropylene filter cloth; batch-to-batch purity variation is typically below 0.3 % when the filter cake is washed with deionized water at 2–5 °C. Compliance for this route is maintained under ICH Q7 Section 7.1 for raw material control, Section 8.1 for critical operations, and Section 12.1 for process validation. Residual solvent testing follows USP <467> with acceptance limits referenced to ICH Q3C(R8) Class 2 values. Equipment readiness is documented under FDA 21 CFR 211.67, and in-process sampling is controlled under 21 CFR 211.110. Terminal products include gabapentin USP active pharmaceutical ingredient, gabapentin hydrochloride, and extended-release oral dosage forms containing 300 mg or 600 mg gabapentin per tablet.

What Limits the Use of 1,1-Cyclohexanediacetic Acid in High-Solids Polyester-Melamine Bake Networks?

In high-solids coil and automotive OEM clearcoat development, 1,1-cyclohexanediacetic acid is incorporated as a cycloaliphatic dibasic acid comonomer during melt polyesterification with neopentyl glycol, trimethylolpropane, and isophthalic acid. The evaluation loading is 8–16 mol% of the total dibasic acid charge, corresponding to 1.2–2.4 wt% of formulated clearcoat solids in a polyester:melamine 70:30 clearcoat. Below 8 mol%, the contribution of the cycloaliphatic unit to indentation hardness is statistically indistinguishable from the control formulation; above 16 mol%, reverse impact resistance and mandrel flexibility require validation because the quaternary ring carbon restricts segmental mobility in the cured network. Polyesterification is performed in a 10 L glass reactor equipped with a partial condenser, thermowell, and vacuum pump capable of <10 mbar; the target final acid value is <5 mg KOH/g, hydroxyl value is 100–140 mg KOH/g, and non-volatile content is 65–70 wt%. Films are applied with a 20 µm wire-wound drawdown bar on Bonderite 1000 CRS panels, flashed for 10 min, and baked at 140 °C for 25 min. Volatile organic compound content is measured by ASTM D2369-20; chemical resistance is assessed by ISO 2812-1:2017; impact is determined by ASTM D2794-19; accelerated weathering is conducted under SAE J2527; and color change is quantified according to ASTM D2244-23. Terminal outputs include automotive OEM clearcoats, coil coating topcoats for architectural metal cladding, and industrial baking enamels for office furniture. Published data for this exact diacid in current automotive OEM monocoats is limited, and OEM-specific validation under SAE J2527 or a 10-year Florida exposure remains necessary before commercial substitution.

Powder Coating Resin Glass-Transition Control in TGIC-Free Polyesters

Acid-functional powder coating polyesters crosslinked with β-hydroxyalkylamide curing agents use 1,1-cyclohexanediacetic acid to shift glass transition temperature upward without relying on aromatic dibasic acids that can reduce exterior durability. The monomer is charged at 5–12 mol% of total acidic monomers in a two-stage melt polycondensation reactor operating at 230–245 °C under <5 kPa; the pre-polymer is then pre-mixed with curing agent, pigment, and flow control additives before melt dispersion in a co-rotating twin-screw extruder with L/D 40:1, barrel temperature 85–100 °C, and screw speed 250–350 rpm. After cooling on a stainless steel chill roll, the extrudate is crushed and milled in an air classifier mill to a D50 of 30–40 µm. Application to chromated or chromium-free pretreated aluminum profiles uses electrostatic spray at 60–80 kV; cure is conducted at 180 °C for 12–15 min. Glass transition temperature is determined by ASTM D3418-15 at 10 K/min under nitrogen; gel time is measured by ISO 8130-6:2021 at 200 °C; impact resistance is evaluated by ASTM D2794-19; neutral salt spray resistance follows ISO 9227 with 1,000 h scribe creep evaluation; and specular gloss is measured according to ASTM D523-14. Pilot extrusion trials indicate that loading above 12 mol% raises extruder torque by more than 20% relative to the control and shortens gel time below 90 s at 200 °C, producing orange peel and poor edge coverage on complex aluminum extrusions. Moisture uptake above 0.3 % before extrusion increases microgel formation, so the flake is dried at 50 °C for 2 h when relative humidity exceeds 60 %. Terminal products include architectural aluminum extrusions, domestic appliance panels, outdoor furniture, and heat pump cabinets.

Metal-organic framework and coordination polymer synthesis consumes high-purity 1,1-cyclohexanediacetic acid as a flexible dicarboxylate ligand in which the quaternary ring carbon constrains the two carboxylate arms into a bent coordination geometry. The compound is supplied as a free acid with a purity specification of ≥99.0 % by HPLC and <0.5 % monoacid byproduct. Solvothermal batches in 1 L Teflon-lined autoclaves are charged at a metal salt-to-ligand ratio between 1:1 and 1:2.5 in DMF/water 1:1 v/v; ligand concentration is maintained at 0.05–0.20 mmol/mL. The autoclave is heated at 80–120 °C for 24–72 h, and cooling to room temperature is performed at 5 °C/h to control nucleation. After filtration on a 0.22 µm nylon membrane, solvent exchange with anhydrous methanol is conducted over 72 h, and activation is performed at 150 °C under <1 kPa for 12 h. Surface area and pore size are measured according to ISO 9277:2022 and ASTM D3663-20; micropore analysis follows IUPAC 2015 physisorption guidelines. REACH registration obligations apply for shipment into the European Economic Area under Regulation (EC) 1907/2006, Annex VII. Terminal products are MOF powders for gas sorption screening, shaped pellets for carbon dioxide separation, mixed-matrix membrane fillers, and heterogeneous catalyst supports. Published data for continuous MOF manufacturing with this exact ligand remains limited; batch-to-batch BET surface area can vary by 15% if the solvent ratio deviates beyond ±5%.

When the Cyclized Anhydride Is Deployed as a Spiro Imide Intermediate in Fine Chemical Synthesis

1,1-Cyclohexanediacetic anhydride, obtained by intramolecular dehydration of the parent diacid, is used as a spirocyclic electrophile in the preparation of imide and amic acid intermediates for medicinal chemistry and agrochemical discovery. The anhydride is dissolved in dry tetrahydrofuran and treated with primary amines at 25–40 °C using 1.0 mol anhydride to 1.0–1.2 mol amine; the resulting amic acid is either isolated or cyclized in toluene at 140–160 °C with a Dean-Stark trap until water collection ceases. The addition of 1.1 equivalents of triethylamine accelerates imidization but can increase amide epimerization; for base-sensitive amines, the reaction is conducted without tertiary amine catalyst at 160 °C for 12 h. The crude product is washed with 0.1 M hydrochloric acid and brine, dried over magnesium sulfate, and purified by silica gel flash chromatography with ethyl acetate/heptane 1:4. Laboratory and pilot batches follow ISO 9001:2015 Section 8.5.1 for production control; residual solvent limits are set by ICH Q3C(R8) for research and development intermediates; and REACH Annex VII data and Safety Data Sheet compliance apply for industrial shipment. Terminal products include spirocyclic imides, amic acid derivatives, and chiral building blocks used in central nervous system and anti-infective discovery libraries.