2-Isopropylnaphthalenes

Isopropylnaphthalenes produced by alkylation of naphthalene with propjdene have gained commercial importance as chemical intermediates, eg, 2-isopropylnaphthalene [2027-17-OJ, and as multipurpose solvents, eg, mixed isopropylnaphthalenes. Alkylation of naphthalene with alkyl haUdes (except methyl hahdes), acid chlorides, and acid anhydrides proceeds in the presence of anhydrous aluminum chloride by Friedel-Crafts reactions (qv). The products are alkylnaphthalenes or alkyl naphthyl ketones, respectively (see Alkylation). 

Isopropylnaphthalenes can be prepared readily by the catalytic alkylation of naphthalene with propjiene. 2-lsopropylnaphthalene [2027-17-0] is an important intermediate used in the manufacture of 2-naphthol (see Naphthalenederivatives). The alkylation of naphthalene with propjiene, preferably in an inert solvent at 40—100°C with an aluminum chloride, hydrogen fluoride, or boron trifluoride—phosphoric acid catalyst, gives 90—95% wt % 2-isopropylnaphthalene however, a considerable amount of polyalkylate also is produced. Preferably, the propylation of naphthalene is carried out in the vapor phase in a continuous manner, over a phosphoric acid on kieselguhr catalyst under pressure at ca 220—250°C. The alkylate, which is low in di- and polyisopropylnaphthalenes, then is isomerized by recycling over the same catalyst at 240°C or by using aluminum chloride catalyst at 80°C. After distillation, a product containing >90 wt % 2-isopropylnaphthalene is obtained (47). 

Another method of manufacture involves the oxidation of 2-isopropylnaphthalene ia the presence of a few percent of 2-isopropylnaphthalene hydroperoxide/i)ti< 2-22-(y as the initiator, some alkaU, and perhaps a transition-metal catalyst, with oxygen or air at ca 90—100°C, to ca 20—40% conversion to the hydroperoxide the oxidation product is cleaved, using a small amount of ca 50 wt % sulfuric acid as the catalyst at ca 60°C to give 2-naphthalenol and acetone in high yield (70). The yields of both 2-naphthalenol and acetone from the hydroperoxide are 90% or better. 

A process variation of the extraction of 2-isopropylnaphthalene hydroperoxide from the cmde oxidation product with an alkylene glycol has been patented (71). The 2-naphthalenol plant of American Cyanamid, which was using the hydroperoxidation process and had a 14 x 10 t /yr capacity (72), ceased production in 1982, leaving the United States without a domestic producer of 2-naphthol. The 2-naphthol capacity in the Western world is approximately 50 x 10 t/yr, with ACNA, Italy and Hoechst AG, Germany operating the largest plants. China produces about 7 x 10 t/yr. Other important producing countries are Poland, Romania, the former Czechoslovakia, and India (35,52). 

CASRN 2027-17-0 molecular formula CisHu FW 170.25 Photolytic. Fukuda et al. (1988) studied the photolysis of 2-isopropylnaphthalene and other polycyclic aromatic hydrocarbons in distilled water using a high pressure mercury lamp. After 96 h of irradiation, a rate constant of 0.031/h with a half-life of 22.3 h was determined. When the experiment was replicated in the presence of various NaCl concentrations, they found that the rate of photolysis increased proportionately to the concentration of NaCl. After 3 h of irradiation, the photolysis rates of 2-isopropylnaphthalene at various aqueous NaCl concentrations are 17.3% at 0.05 M, 35.8% at 0.10 M, 41.7% at 0.15 M, 54.0 at 0.25 M, 62.8 at 0.30 M, 83.2 at 0.40 M, 96.4 at 0.50 M, and 1.00 M. It appeared that the presence of NaCl, the main component in seawater, is the cause for the increased rate of degradation. 

Alkylation. Naphthalene can be easily alkylated, Isopropvlnaphthalenes produced by alkylation of naphthalene with propylene have gained commercial importance as chemical intermediates. e.g., 2-isopropylnaphthalene, and as multipurpose solvents, e.g, mixed isopropylnaphthalenes. 

Several biocatalytic processes for the production of (5)-(+)-naproxen (5) have also been developed (see Chapter 19). Direct isomerization of racemic naproxen (4) by a microorganism catalyst, Exophialia wilhansil, was reported to give the (S)-isomer 5 (92%, 100% ee) (Scheme 6.5).2X A 1-step synthesis of (5)-(+)-naproxen (5) by microbial oxidation of 6-methoxy-2-isopropylnaphthalene (12) was developed by IBIS (Scheme 6.6).29 In both cases, typical bioprocess-related issues such as productivity, product isolation, and biocatalyst production have apparently prevented them from rapid commercialization. 

Autoclave charged with naphthalene (10 mmol), isopropyl alcohol 20 mmol, 0.5 g zeolite H-Beta (Si/Al = 12.5), cyclohexane (100 ml), undecane (10 mmol) as internal standard, 200 °C, 2 MPa N 2. After 1 h the selectivities to 2-isopropylnaphthalene and to the cyclic compound I are 50 and 46 %, respectively, at 19 % naphthalene conversion. 

The latter have been used in the gas phase methylation of naphthalene with methanol [12-14]. Large pore zeolites, such as H-mordenite or H-Y, led to a nonselective methylation of naphthalene, whereas a high p -selectivity was observed with the medium-pore H-ZSM-5. Liquid phase isopropylation of naphthalene with propene [3,15] or isopropylbromide [16] over zeolites was more recently reported. It was found that isopropylation could be carried out efficiently over such catalysts with a good selectivity for the formation of 2-isopropylnaphthalene and 2,6-/2,7-diisopropylnaphthalenes. We especially demonstrated that the use of zeolites modified by silanation of the external surface led to an improvement of the p -selectivity by suppressing the formation of triisopropyl derivatives [16]. 

The isopropylation of 2-isopropylnaphthalene was studied over heteropoly acid catalyst supported on mesoporous material. The physico-chemical state of loaded heteropoly acid was investigated using XRD, nitrogen adsorption measurement and FT-IR techniques. Heteropoly acid was highly dispersed on the wall of mesoporous material, and retained its Bronsted acidity. The conversion and the selectivity for P, p -diisopropylnaphthalene were very high over the mesoporous material with a large loading amount of heteropoly acid. The treatment of heteropoly acid was helpful for the improvement of the acidity of mesoporous material. 

Two routes have gained industrial prominence to produce 2-naphthol, namely alkali fusion of sodium naphthalene-2-sulfonate and the oxidative cleavage of 2-isopropylnaphthalene. 

American Cyanamid operated a plant with a capacity of 14,000 tpa 2-naphthol, for some years prior to 1982 for the oxidation of 2-isopropylnaphthalene. 2-Iso-propylnaphthalene can be obtained from propylene and naphthalene at 150 to 240 °C and 10 bar with a phosphoric acid catalyst using a large excess of naphthalene, followed by isomerization to a mixture of 1- and 2-isopropylnaphthalenes (5 95). The introduction of air (oxygen) at 110 °C produces the a-hydroperoxide of the 2-isomer. The hydroperoxide is cleaved with sulfuric acid, in a manner analogous to the Hock synthesis of phenol the 2-naphthol yield is around 95%. 

Zawadiak et al. [620] studied the retention of three oxidation products of 2-isopropylnaphthalene (IPN), l-(2-naphthyl)ethanone, 2-(2-naphthyI)-2-propanol,... 

---