Phenol and cyclohexanone are important chemical intermediates, which are produced at large scales using different technologies. Co-production of phenol and cyclohexanone via cyclohexylbenzene (CHB) oxidation is of commercial interest. The CHB-based process comprises three major reaction steps: 1) benzene hydroalkylation to CHB; 2) CHB oxidation to cyclohexylbenzene hydroperoxide (CHBHP); and 3) CHBHP cleavage to phenol and cyclohexanone. Sulfuric acid, which is used in the commercial Hock process for cumene hydroperoxide cleavage, is investigated as catalyst for CHBHP cleavage. When the CHB oxidation effluent (containing ~75% CHB and ~ 25% CHBHP + other oxygenates) is used directly in the cleavage reaction, high concentration of H2SO4 (&gt;1000 ppm) is needed to achieve acceptable rates; but the yields to phenol and cyclohexanone are unsatisfactory (&lt;90%). Byproducts are largely formed from β-scission derived from CHBHP and oxidation of cyclohexanone by CHBHP. When the CHB concentration is held constant (80%, balanced with a mixture of phenol and cyclohexanone), cleavage rate increases exponentially with phenol concentration, clearly indicating the apparent activation energy is lowered by phenol. Additionally, cleavage rate can be modulated by addition of water, which also suppresses β-scission. To help understand these effects, we developed a 31P NMR technique to measure the acid strength of H2SO4 in the non-aqueous and reactive cleavage medium using trimethylphosphine oxide (TMPO) as a probe molecule. It was found that the acid strength depends strongly on the cleavage medium; and the CHBHP cleavage rate and selectivity trends correlate with the acid strength – higher acid strength leads to faster reactions and better selectivity. Based on these observations, we conclude that phenol not only enhances the acid strength, it is also involved in the transition state of CHBHP cleavage. With these fundamental understanding, CHBHP cleavage reaction can be significantly improved. For example, with a proper balance of CHB, phenol, cyclohexanone, and water in the medium, side reactions are essentially eliminated; and high yields to phenol (99%) and cyclohexanone (96%) are achieved in the lab with &lt; 100 wt ppm H2SO4.

Sulfuric acid catalyzed cyclohexylbenzene hydroperoxide cleavage: effects of reaction medium and mechanistic implications

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.