1,1 - pentanedione

Under special circumstances, serendipitously occurring or produced at will, the production of furfural is accompanied by the formation of diacetyl and 2,3-pentanedione. Used as flavors, these compounds are by-products of enormous value greatly contributing to the profitability of a furfural plant. For this reason, they have been shrouded in secrecy, and what little information on the topic leaked out was erroneous. In volume A 12 on page 123 of the s Edition, ULLMANN S ENCYCLOPEDIA OF INDUSTRIAL CHEMISTRY (VCH Verlagsgesellschaft, Weinheim 1989) presents the following statement on the ROSENLEW process  

The fact that the saleable coproduct is actually not diacetin (glyceryl diacetate) but diacetyl (2,3-butanedione) reveals that the author of the article had somehow misunderstood a word gleaned by poor espionage, and that he had absolutely no idea of the chemical reactions involved in the formation of diacetyl, not to speak of 2,3-pentanedione. 

On account of their two conjugated C=0 double bonds, both diacetyl and 2,3-pentanedione are intensely yellow compounds, and both are strong flavors. At a level of up to 2 mg/kg, diacetyl is the principal flavor and colorant of butter, and for this reason it is added to margarine to give it the taste and look of butter. Diacetyl is also used as a flavor in ice cream and baked goods. By contrast, 2,3-pentanedione is used as aroma in alcoholic and nonalcoholic beverages. 

Diacetyl sells for approximately 14 US /kg, and 2,3-pentanedione commands a whopping price in the order of 300 US /kg. Thus, even if the quantities compared to furfural as the main product are small, the profits which can be derived from these by-products are stunning. 

For a ROSENLEW reactor 2.5 m in diameter, making 350 kg/h of furfural, the ratio of diacetyl production to furfural production is 0.01396, and the ratio of 2,3-pentanedione production to furfural production is 0.00118. Thus, if furfural sells for 1 US per kg, the ratio of the sales value of diacetyl to the sales value of furfural is found to be 

Synonyms Acetylacetone, diacetyl methane, acetyl 2-propanone, 2,4-PD 

Physical Form. Clear liquid with a rancid odor 

Chemical intermediate, metal chelator, and lubricant additive 

Toxicology. 2,4-Pentanedione is moderately irritating to the skin and eyes repeated exposure to high concentrations causes dyspnea, central nervous system damage, and death. 

Information on human exposures is limited. Exposure to levels ranging from 2 to 14 ppm have been reported to produce nausea and headache.  

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Nonanedione, another 1,3-difunctional target molecule, may be obtained from the reaction of hexanoyl chloride with acetonide anion (disconnection 1). The 2,4-dioxo substitution pattern, however, is already present in inexpensive, symmetrical acetylacetone (2,4-pentanedione). Disconnection 2 would therefore offer a tempting alternative. A problem arises because of the acidity of protons at C-3 of acetylacetone. This, however, would probably not be a serious obstacle if one produces the dianion with strong base, since the strongly basic terminal carbanion would be a much more reactive nucleophile than the central one (K.G. Hampton, 1973 see p. 9f.). 

Ethyl-cf-chloroacetoacetate gives 5-carbethoxy-4-methyl-2-thiazole thiol (387), while 3-chloro-2,4-pentanedione affords the 2-mercapto-4-methyl-5-thiazolylmethylketone in good yield (74%) (387). 

Both of these features are apparent m the structure of the enol of 2 4 pentanedione shown in Figure 18 2... 

Learning By Model mg contains molecu lar models of the enolates of acetone and 2 4 pentanedione Compare the two with respect to the dis tribution of negative charge... 

By far the most popular commercial ketone peroxide is methyl ethyl ketone peroxide [1338-23-4]. Smaller quantities of ketone peroxides such as methyl isobutyl ketone peroxide [28056-59-9] cyclohexanone peroxide [12262-58-7] and 2,4-pentanedione peroxide [37187-22-7] are used commercially (47). 

Ketones with labile hydrogen atoms undergo enol acetylation on reaction with ketene. Strong acid catalysis is required. If acetone is used, isoptopenyl acetate [108-22-5] (10) is formed (82—85). Isopropenyl acetate is the starting material for the production of 2,4-pentanedione (acetylacetone) [123-54-6] (11). 

Penta.nedione, 2,4-Pentanedione [123-54-6] (acetylacetone) is the lowest member of the aUphatic 1,3-diketones and is a colorless Hquid with a mild ketone-like odor. It is completely miscible with organic solvents other physical properties ate shown in Table 1. 

The industrial precursor to 2,4-pentanedione is isopropenyl acetate, produced from acetone and ketene (307,308). The diketone is formed by the high temperature isomerization of isopropenyl acetate over a metal catalyst (309—311). 

Pentanedione can also be produced by the condensation of acetone with ethyl acetate (312—317), or by the condensation of ethyl acetoacetate and ketene (318—321). Other methods are known (322,323). 

Pentanedione is widely used in extraction processes for the separation and purification of metals because of its abiUty to form covalent metal chelates. It is also used as an intermediate in the production of heterocycHc substances and dyes, as a fuel additive (324), and in metal plating and resin modification. 

The toxicity of 2,4-pentanedione is shown in Tables 3 and 11 to be similar to mesityl oxide, and greater than most other 1,2- or 1,4-diketones or monoketones. Inhalation of low levels of 2,4-pentanedione can cause nausea, eye contact can induce stinging, and recurrent exposure to high concentrations (300—400 ppm) can adversely affect the central nervous system and immune system (325). 

Ligand-Modified Rhodium Process. The triphenylphosphine-modified rhodium oxo process, termed the LP Oxo process, is the industry standard for the hydroformylation of ethylene and propylene as of this writing (ca 1995). It employs a triphenylphosphine [603-35-0] (TPP) (1) modified rhodium catalyst. The process operates at low (0.7—3 MPa (100—450 psi)) pressures and low (80—120°C) temperatures. Suitable sources of rhodium are the alkanoate, 2,4-pentanedionate, or nitrate. A low (60—80 kPa (8.7—11.6 psi)) CO partial pressure and high (10—12%) TPP concentration are critical to obtaining a high (eg, 10 1) normal-to-branched aldehyde ratio. The process, first commercialized in 1976 by Union Carbide Corporation in Ponce, Puerto Rico, has been ficensed worldwide by Union Carbide Corporation and Davy Process Technology. 

The di(hydroxyaLkyl) peroxide (2) from cyclohexanone is a soHd which is produced commercially. The di(hydroxyaLkyl) peroxide (2) from 2,4-pentanedione (11, n = 1 X = OH) is a water-soluble soHd which is also produced commercially (see Table 5). Both these peroxides are used for curing cobalt-promoted unsaturated polyester resins. Because these peroxides are susceptible to promoted decomposition with cobalt, they must exist in solution as equihbrium mixtures with hydroperoxide stmctures (122,149). 

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