Diacetone alcohol

The crude diacetone alcohol is purified by distillation. The 2-1. round-bottom flask is fitted with a three-bulb Glinsky fractionating column and a well-cooled condenser. The flask is heated in an oil bath, the temperature of which is gradually raised to 125°. The temperature of the bath is held at this point until no more acetone distils over, the temperature at the top of the column registering about 70° when the process is complete. The recovered acetone, containing a few per cent of diacetone alcohol, amounts to about 200 g. and can be used to prepare more material. The residual liquid has a sp. gr. of 0.928 (20°) and contains about 95 per cent of diacetone alcohol. It is transferred to a 2-1. Claisen flask and distilled under diminished pressure. A little acetone first comes over and then the diacetone alcohol distils smoothly at 71-740 at 23 mm. The yield is 850 g. (71 per cent of the theory based on the total acetone employed). The entire distillation requires about four hours. 

Almost any form of a Soxhlet extractor and condenser will serve. It is advisable to use as much barium hydroxide as possible and to have the extractor empty as often and as completely as possible. The use of glass wool and care in filling the cups prevents any solid hydroxide from being carried down into the lower flask. 

The use of tartaric acid in the flask has been recommended to neutralize any barium hydroxide that is carried down. This has been found unnecessary. 

If hydrated barium hydroxide [Ba(OH)2 - 8H2O] is used in the thimbles this becomes dehydrated after one run the anhydrous form is just as satisfactory and may be used over and over again. 

The time of refluxing depends on the rapidity with which the liquid boils and on the way in which the Soxhlet extractor empties. Similarly, the point at which the liquid ceases to boil will vary somewhat with the way in which it is heated. The 

Hydrated lime is used as an alkaline catalyst to promote the self-condensation of acetone to form diacetone alcohol (4-hydroxy-4-methyl-2-pentanone) [31.26]. Diacetone alcohol is used as a solvent for natural and synthetic resins. It is also used as an intermediate in the produetion of mesityl oxide, methyl isobutyl ketone and hexylene glycol. 

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McjC = CHCOCH3. Colourless liquid b.p. 129"C, with a strong peppermint-like odour. Prepared by distilling diacetone alcohol in the presence of a trace of iodine. Converted to phorone by heating in propanone with dehydrating agents such as sulphuric acid. It is a solvent For cellulose acetate and ethyl-cellulose and other polymers. 

With concentrated alkali, a resin is formed from repeated aldol condensations between aldol, crotonaldehyde and acetaldehyde. A similar condensation occurs with acetone (b.p. 56°), but the equilibrium mixture contains only a few per cent, of diacetone alcohol (III), b.p. 166° ... 

The residual liquid contains about 95 per cent, of diacetone alcohol and is satisfactory for the preparation of mesityl oxide (Section 111,79). 

Diacetone alcohol partially decomposes when distilled under normal pressure. 

Diacetone alcohol is readily dehydrated by adding a very small quantity of iodine as catalyst and distilling slowly ... 

Fit a 750 ml. round-bottomed flask with a fractionating column attached to a condenser set for downward distillation. Place 500 g. of diacetone alcohol (the crude product is quite satisfactory), 01 g. of iodine and a few fragments of porous porcelain in the flask. Distil slowly. with a small free flame (best in an air bath) and collect the following fractions (a) 56-80° (acetone and a little mesityl oxide) (6) 80-126° (two layers, water and mesityl oxide) and (c) 126-131° (mesityl oxide). Whilst fraction (c) is distilling, separate the water from fraction (6), dry with anhydrous potassium carbonate or anhydrous magnesium sulphate, and fractionate from a small flask collect the mesityl oxide at 126-131°. The yield is about 400 g. 

In the three-step process acetone first undergoes a Uquid-phase alkah-cataly2ed condensation to form diacetone alcohol. Many alkaU metal oxides, metal hydroxides (eg, sodium, barium, potassium, magnesium, and lanthanium), and anion-exchange resins are described in the Uterature as suitable catalysts. The selectivity to diacetone alcohol is typicaUy 90—95 wt % (64). In the second step diacetone alcohol is dehydrated to mesityl oxide over an acid catalyst such as phosphoric or sulfuric acid. The reaction takes place at 95—130°C and selectivity to mesityl oxide is 80—85 wt % (64). A one-step conversion of acetone to mesityl oxide is also possible. 

Figure 2 illustrates the three-step MIBK process employed by Hibernia Scholven (83). This process is designed to permit the intermediate recovery of refined diacetone alcohol and mesityl oxide. In the first step acetone and dilute sodium hydroxide are fed continuously to a reactor at low temperature and with a reactor residence time of approximately one hour. The product is then stabilized with phosphoric acid and stripped of unreacted acetone to yield a cmde diacetone alcohol stream. More phosphoric acid is then added, and the diacetone alcohol dehydrated to mesityl oxide in a distillation column. Mesityl oxide is recovered overhead in this column and fed to a further distillation column where residual acetone is removed and recycled to yield a tails stream containing 98—99% mesityl oxide. The mesityl oxide is then hydrogenated to MIBK in a reactive distillation conducted at atmospheric pressure and 110°C. Simultaneous hydrogenation and rectification are achieved in a column fitted with a palladium catalyst bed, and yields of mesityl oxide to MIBK exceeding 96% are obtained. 

Diacetone Alcohol. Diacetone alcohol (DAA) (4-hydroxy-4-methyl-2-pentanone) is a colorless, mild smelling Hquid which is completely miscible with water and most organic solvents. It is the simplest aldol condensation product of acetone, and because of its keto-alcohol functionahes it has special utility in the coatings industry where it is used to dissolve cellulose acetate to give solutions with high tolerance for water (115). 

Uses. Diacetone alcohol is a widely used solvent in the coatings industry where it finds appHcation in hot lacquers which require high boiling components, and in bmshing lacquers where its mild odor, blush resistance, and flow-out properties are desired. Diacetone alcohol is also a solvent for nitrocellulose, cellulose acetate, and epoxy resins. 

In addition to DAA s use in the production of MIBK, DAA also finds use as a specialty reaction intermediate. Hydrogenation of DAA at 100°C and 30 MPa (83) yields hexylene glycol ( 1.43/kg, October 1994), widely used in castor oil-based hydrauhc brake fluids and as a solvent. Reaction of /)-phenetidine [156-43-4] with DAA synthesizes Monsanto s Santoquin (ethoxyquin) [91-53-2] (149), an antioxidant used in animal feeds and also as a mbber additive. Diacetone alcohol (acetone-free) was available at 1.32/kg as of October 1994. 

Ma.nufa.cture. Mesityl oxide is produced by the Hquid-phase dehydration of diacetone alcohol ia the presence of acidic catalysts at 100—120°C and atmospheric pressure. As a precursor to MIBK, mesityl oxide is prepared ia this manner ia a distillation column ia which acetone is removed overhead and water-saturated mesityl oxide is produced from a side-draw. Suitable catalysts are phosphoric acid (177,178) and sulfuric acid (179,180). The kinetics of the reaction over phosphoric acid have been reported (181). 

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