Sulfuric Acid Catalyzed Cyclohexylbenzene Hydroperoxide Cleavage by forming phenol-solvated protons; and the phenol-solvated proton is involved in and to Phenol and Cyclohexanone: Effects of Reaction Medium and stabilizes the hydroperoxide cleavage transition state. With this fundamental understanding, CHBHP cleavage reaction can be significantly improved. For example, with a proper balance Mechanistic Implications 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 Kun Wang* and Roberto Garcia with < 100 wt ppm H2SO4. Corporate Strategic Research, ExxonMobil Research and Engineering Company 1545 Route 22 East, Annandale, NJ 08801 (USA) *[email protected] Introduction Phenol and cyclohexanone are two important chemical intermediates, which are produced at large scales using different technologies. Co-production of phenol and cyclohexanone via cyclohexylbenzene (CHB) oxidation [1] is of commercial interest [2]. 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 [2]. 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 (a) (b) used directly in the cleavage reaction, high concentration of H2SO4 (>1000 ppm) is needed to achieve acceptable rates; but the yields to phenol and cyclohexanone are unsatisfactory (<90%). Byproducts are largely formed from β-scission derived from CHBHP and oxidation Figure 1. (a) Dependence the apparent activation energy for CHBHP cleavage on the of cyclohexanone by CHBHP. To better understand the yield loss pathways and ultimately concentration of phenol in the cleavage medium. (b) Acid strength for H2SO4 in the non- 31 improve the yield to phenol and cyclohexanone, detailed kinetics study was performed. We aqueous, reactive reaction medium containing CHB/phenol/cyclohexanone as measured by P also developed a technique for acid strength measurement in the non-aqueous, reactive NMR. cleavage medium [3] and found that CHBHP cleavage rate and selectivity trends correlate strongly with the acid strength. Significance Materials and Methods (a) A technique to measure acid strength in non-aqueous, reactive medium is developed. (b) CHBHP cleavage was carried out in a 50-mL jacketed glass reactor equipped with Insights from these fundamental studies led to pilot plant operations where quantitative yields magnetic stirring and circulating silicon oil for temperature control. The reactor was charged to phenol and cyclohexanone are achieved. with a 30-mL mixture containing CHB, CHBHP, phenol, and cyclohexanone and equilibrated at reaction temperatures. Desired amount of sulfuric acid was added and the reaction followed by taking 1-mL aliquots at various times. The samples were rapidly quenched by neutralizing with dihexylamine and analyzed by GC. Acid strength measurement was performed using 31P References NMR employing trimethylphosphine oxide (TMPO) as a probe molecule. 1. (a) Arends, I.W.C.E.; Sasiidharan, M.; Kuhnle, A.; Duda, M.; Jost, C.; Sheldon, R.A. Tetrahedron 2002, 58, 9055; (b) Aoki, Y.; Sakaguchi, S.; Ishii, Y. Tetrahedron 2005, 61, Results and Discussion 5219. When the CHB concentration is held constant (80%, balanced with a mixture of 2. (a) US6037513, US7799956, US8884067, US9115068, assigned to ExxonMobil; (b) phenol and cyclohexanone), cleavage rate increases exponentially with phenol concentration, US8598388, assigned to Polimeri. revealing the apparent activation energy is lowered by phenol (Figure 1(a)). Additionally, 3. US9335285, assigned to ExxonMobil. cleavage rate can be modulated by addition of water, which also suppresses β-scission. It was found that the acid strength depends strongly on the cleavage medium (Figure 1(b)); and the CHBHP cleavage rate and selectivity trends correlate strongly with the acid strength – higher acid strength leads to faster reactions and better selectivity. Based on these results, we conclude the presence of phenol in the cleavage medium increases the strength of sulfuric acid .