Isophorone

Diisobntyl ketone is used as a solvent for nitrocellulose, lacquers, and synthetic resins in organic syntheses. 

Colorless liquid with mild ether-like smell bp 168 C (334.4 F) density 0.8053 at 20 C (68°F), soluble in alcohol, ether, and chloroform, insoluble in water. 

Inhalation of the vapors of diisobutyl ketone can produce irritation of the eyes, nose, and throat. At 25 ppm its odor was unpleasant, but the irritation effect on humans was insignificant. At 50 ppm the irritation was mild. A 7- hour exposure to 125 ppm had no adverse effect on rats however, at 250 ppm, female rats developed increased liver and kidney weights. An 8-hour exposure to 2000 ppm was lethal. Ingestion of this compound can cause the symptoms of headache, dizziness, and dermatitis. 

Combustible flash point (closed cup) 60° C (140°F) vapor density 4.9 vapor pressure 

7 torr fire-extinguishing agent dry chemical, CO2, or alcohol foam a water spray may be used to disperse the vapors and bring the temperature down below the flash point. 

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Isophorone. Isophorone (3,5,5-trimethyl-2-cyclohexen-l-one) is a cycHc a,P-unsaturated ketone derived from the trimeri2ation of acetone. It has a light yellow color and a disagreeable camphoraceous odor. It has the tendency to discolor and form residues on prolonged storage. Isophorone is completely miscible with organic solvents, and other physical properties are Hsted ia Table 1. 

Isophorone usually contains 2—5% of the isomer P-isophorone [471-01-2] (3,5,5-trimethyl-3-cyclohexen-l-one). The term a-isophorone is sometimes used ia referring to the a,P-unsaturated ketone, whereas P-isophorone connotes the unconjugated derivative. P-lsophorone (bp 186°C) is lower boiling than isophorone and can be converted to isophorone by distilling at reduced pressure ia the presence of -toluenesulfonic acid (188). Isophorone can be converted to P-isophorone by treatment with adipic acid (189) or H on(Ill) acetylacetoate (190). P-lsophorone can also be prepared from 4-bromoisophorone by reduction with chromous acetate (191). P-lsophorone can be used as an iatermediate ia the synthesis of carotenoids (192). 

Ma.nufa.cture. Isophorone is produced by aldol condensation of acetone under alkaline conditions. Severe reaction conditions are requited to effect the condensation and partial dehydration of three molecules of acetone, and consequendy raw material iaefftciency to by-products is limited by employing low conversions. Both Hquid- and vapor-phase continuous technologies are practiced (186,193,194). 

A Hquid-phase isophorone process is depicted ia Figure 4 (83). A mixture of acetone, water, and potassium hydroxide (0.1%) are fed to a pressure column which operates at head conditions of 205°C and 3.5 MPa (- 500 psi). Acetone condensation reactions occur on the upper trays, high boiling products move down the column, and unreacted acetone is distilled overhead ia a water—acetone a2eotrope which is recycled to the column as reflux. In the lower section of the column, water and alkaH promote hydrolysis of reaction by-products to produce both isophorone and recyclable acetone. Acetone conversion is typically ia the range 6—10% and about 70% yield of isophorone is obtained. Condensation—hydrolysis technology (195—198), and other Hquid-phase production processes have been reported (199—205). 

Substantial amounts of 3,3,6,8-tetramethyl-l-tetralone [5409-55-2] are also formed, most notably ia the vapor-phase process (216). This tetralone has been synthesized from isophorone and mesityl oxide and it can thus be assumed to be a product of these two materials ia the isophorone process (217,218). 

Some reversion of the over-condensate residues to acetone and isophorone is possible by hydrolysis with 2% sodium hydroxide solution at 175°C and 0.9 MPa (219). 

Economic Aspects. Isophorone was available at 1.87/kg ia October 1994. The sole domestic producer of isophorone is Union Carbide however, Hbls is by far the largest isophorone producer ia the world. Other significant producers are Hsted ia Table 9. Despite the erosion of some of the historical solvent uses of isophorone, the expanding derivatives market for this product appear to sustain its production ia the short term. 

A trend ia the utihty of isophorone is as an important iadustrial building block. Foremost among these developments has been the use of isophorone as a raw material, and isophorone diisocyanate [2855-13-2] (IPDl), for the production of the light-stable polyurethane. The U.S. market for IPDl-based products was 31 million ia 1989, and is estimated to grow to 53 million ia 1994 (230). 

In the multistep production of IPDI, isophorone is first converted to 3-cyano-3,5,5-trknethylcyclohexanone (231—235), then hydrogenated and ammoniated to 3-aminomethyl-3,5,5-trknethyl-l-aminocyclohexane (1) (236,237), also known as isophorone diamine (IPDA). In the final step IPDA is phosgenated to yield IPDI (2) (238). Commercial production of IPDI began in the United States in 1992 with the startup of Olin s 7000 t/yr plant at Lake Charles, Louisiana (239), and the startup of Hbls integrated isophorone derivatives plant in Theodore, Alabama (240). Hbls has a worldwide capacity for IPDA of 40,000 t/yr. 

The catalytic oxidation of isophorone (259—261) or P-isophorone (262,263) to ketoisophorone [1125-21 -9] (2,6,6-trimethyl-2-cyclohexen-l,4-dione) has been reported. Ketoisophorone is a building block for synthesis in terpene chemistry and for producing compounds of the vitamin A and E series. 

Health nd Safety Factors. Isophorone is considered moderately toxic by ingestion and skin contact. Some rat tumor formation evidence has been found (264), but no demonstration as a human carcinogen has been proven. Isophorone is considered an Environmental Protection Agency (EPA) priority pollutant, and has a permissible acute toxicity concentration of 117, 000 ///L to protect freshwater aquatic life, 12, 900 ///L to protect saltwater aquatic life, and 5, 200 ///L to protect human life (265). Isophorone is mildly toxic by inhalation, but because of its low volatiUty it is not a serious vapor hazard. 

Cycloahphatic amine production economics are dominated by raw material charges and process equipment capital costs. Acetone (isophorone), adiponitnle, aniline, and MDA are all large-volume specification organic intermediates bordering on commodity chemicals. They are each cost-effective precursors. 

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