Cyclohexanol CAS 108-93-0: The Nylon Precursor With a Hidden Oxidation Problem That Most Buyers Don't Test For

Cyclohexanol

  A quality manager at a caprolactam plant in Liaoning once told me that the two months she spent tracking down an unexplained increase in cyclohexanediol byproduct in the oxidation step were among the most frustrating of her career. Her plant was running the established cyclohexane liquid-phase air oxidation process — the Dupont/DSM route — which produces cyclohexanol and cyclohexanone as the primary products for eventual conversion to cyclohexanone oxime and then caprolactam. The cyclohexanediol level had crept from the normal 0.3% up to 0.9% over about three weeks, which didn’t sound alarming until it started affecting the Beckmann rearrangement selectivity downstream. Diol contamination at that level in the oxime feed shifts the acid-catalyzed rearrangement toward unwanted ring-opening byproducts, and suddenly the amide yield numbers they’d been hitting for two years were off by nearly four percentage points.

  The oxidation conditions hadn’t changed. The cyclohexane feedstock supplier was the same. The culprit, eventually, was a valve seal replacement earlier that month that had introduced trace moisture into the cyclohexane feed header, which altered the peroxide intermediate distribution in the oxidation cascade and increased the proportion going through the diol pathway rather than the intended KA oil pathway. Once they identified it and purged the system, the diol levels came back down within a week. But those two months had cost real money in off-spec caprolactam that had to be downgraded or reworked.
  Cyclohexanol (CAS 108-93-0) is a water-white to very slightly yellow liquid, molecular weight 100.16 g/mol, boiling point 160–161°C, melting point 23–25°C. It solidifies at room temperature in winter climates, which affects unloading and metering procedures for cold-weather receiving facilities — a practical point that cyclohexanol buyers in northern manufacturing regions find out the first time they try to pump a frozen drum. The compound is produced industrially by two main routes: hydrogenation of phenol, which gives high purity with minimal cyclohexanone contamination, and the cyclohexane oxidation route that gives KA oil (a ketone-alcohol mixture), from which the cyclohexanol fraction is separated. The route matters for specification because the impurity profile differs: phenol-hydrogenation cyclohexanol typically has very low cyclohexanone content and negligible diol, while KA oil cyclohexanol may carry residual cyclohexanone that needs to be specified separately if the downstream chemistry is sensitive to it.
  For the largest industrial application — nylon 6 and nylon 6,6 precursor chains — cyclohexanol goes through oxidation to cyclohexanone, then either through the Beckmann rearrangement to caprolactam (for nylon 6) or oxidation further to adipic acid (for nylon 6,6). In both cases, the cyclohexanone-to-cyclohexanol ratio coming out of the oxidation step is a key process parameter, and cyclohexanol purity is the starting point that determines how predictably that ratio lands. High-purity cyclohexanol at ≥99% GC with controlled cyclohexanone and cyclohexane residuals gives the most stable oxidation behavior.
Cyclohexanol
  Solvent applications represent the second major demand category. Cyclohexanol is a plasticizer solvent for cellulose esters and a component in metalworking cutting fluids where its combination of lubricity, moderate volatility, and biodegradability is useful. In this application, the specification priority shifts away from chemical purity toward color stability (Gardner 1930 ≤1 is typical), low acidity, and absence of peroxide formation tendency on aging.
  A third demand stream comes from ester synthesis: cyclohexanol is the alcohol component in cyclohexyl acetate, cyclohexyl acrylate, and various phthalate plasticizer replacements. Ester synthesis is relatively tolerant of minor cyclohexanone contamination, but sensitive to free acid content in the cyclohexanol feed because acid contamination deactivates the esterification catalyst over time.
  Regulatory position is established across major markets. REACH registration covers cyclohexanol in the EU. TSCA listing in the US is long-standing. GHS classification is moderate: irritant and flammable (flash point 67–70°C), requiring standard chemical handling precautions but no special permitting for routine commercial quantities.
 
Shandong Lookchemical Co., Ltd. supplies cyclohexanol (CAS 108-93-0) with GC purity documentation, cyclohexanone content specified on the CoA, and SDS for international export. Batch-specific testing data is available for qualification. Technical samples are supplied ahead of volume orders.
 

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