Hydroxyacetones

After cleavage the reaction mass is a mixture of phenol, acetone, and a variety of other products such as cumylphenols, acetophenone, dimethyl-phenylcarbinol, a-methylstyrene, and hydroxyacetone. It may be neutralised with a sodium phenoxide solution (20) or other suitable base or ion-exchange resins. Process water may be added to facilitate removal of any inorganic salts. The product may then go through a separation and a wash stage, or go direcdy to a distillation tower. 

The yield of acetone from the cumene/phenol process is beUeved to average 94%. By-products include significant amounts of a-methylstyrene [98-83-9] and acetophenone [98-86-2] as well as small amounts of hydroxyacetone [116-09-6] and mesityl oxide [141-79-7]. By-product yields vary with the producer. The a-methylstyrene may be hydrogenated to cumene for recycle or recovered for monomer use. Yields of phenol and acetone decline by 3.5—5.5% when the a-methylstyrene is not recycled (21). 

Hydrogenation gives aUyl alcohol [107-18-6] C H O, its isomer propanal [123-38-6] (20), or propanol, C H O [71-23-8] (21). With acidic mercuric salt catalysts, water adds to give acetol, hydroxyacetone, C2H 02 [116-09-6] (22). 

Oxidation of a glycol can lead to a variety of products. Periodic acid quantitatively cleaves 1,2-glycols to aldehydes and is used as an analysis method for glycols (12,13). The oxidation of propylene glycol over Pd/C modified with Pb, Bi, or Te forms a mixture of lactic acid, hydroxyacetone, and pymvic acid (14). Air oxidation of propylene glycol using an electrolytic crystalline silver catalyst yields pymvic aldehyde. 

Biacetyl is produced by the dehydrogenation of 2,3-butanediol with a copper catalyst (290,291). Prior to the availabiUty of 2,3-butanediol, biacetyl was prepared by the nitrosation of methyl ethyl ketone and the hydrolysis of the resultant oxime. Other commercial routes include passing vinylacetylene into a solution of mercuric sulfate in sulfuric acid and decomposing the insoluble product with dilute hydrochloric acid (292), by the reaction of acetal with formaldehyde (293), by the acid-cataly2ed condensation of 1-hydroxyacetone with formaldehyde (294), and by fermentation of lactic acid bacterium (295—297). Acetoin [513-86-0] (3-hydroxy-2-butanone) is also coproduced in lactic acid fermentation. 

Hydroxyl groups are stable to peracids, but oxidation of an allylic alcohol during an attempted epoxidation reaction has been reported." The di-hydroxyacetone side chain is usually protected during the peracid reaction, either by acetylation or by formation of a bismethylenedioxy derivative. To obtain high yields of epoxides it is essential to avoid high reaction temperatures and a strongly acidic medium. The products of epoxidation of enol acetates are especially sensitive to heat or acid and can easily rearrange to keto acetates. 

Similar hydroxylation-oxidations can be carried out using a catalytic amount of osmium tetroxide with A-methylmorpholine oxide-hydrogen peroxide or phenyliodosoacetate." A recent patent describes the use of triethylamine oxide peroxide and osmium tetroxide for the same sequence. Since these reactions are of great importance for the preparation of the di-hydroxyacetone side-chain of corticoids, they will be discussed in a later section. 

Using (31) as the nucleophile, FSA has been shown to accept several aldehydes as acceptor components for preparative synthesis [91]. In addition to (31), it also utilizes hydroxyacetone as an alternative donor to generate 1-deoxysugars such as (66) regioselectively (Figure 10.25). 

Figure 10.25 Inverted approach for aldose synthesis using FruA catalysis, and application ofthe strategy for deoxysugar synthesis based on a phosphorothioate analog synthesis of 1-deoxysugars by FSA catalyzed addition of hydroxyacetone.

Product Acceptors. Many enzyme assays use acceptors, as for instance 2-ethylaminoethanol and other aminated alcohols iihich act as acceptors for the phosphoryl product of the reaction catalyzed by alkaline phosphatase (25) (Fig. 4). Hydroxylamine can act as an acceptor for the hydroxyacetone produced by eno-lase and semicarbazide can act as an acceptor for the pyruvate produced by LD. It is necessary to optimize the concentration of such an acceptor before using it routinely as often what may be a theoretically desirable acceptor is in practice superfluous. 

Ketones such as acetone, hydroxyacetone, and methoxyacetone can be condensed with both aromatic and aliphatic aldehydes.198... 

Alternative reducing agents are still sometimes proposed and evaluated. A detailed comparison of five reducing agents has been reported sodium dithionite, thiourea dioxide, iron(II) chloride/gluconic acid, sodium hydroxymethanesulphinate and hydroxyacetone [123]. Results of fastness tests on black polyester dyeings variously aftertreated are given in Table 12.10. 

Hydroxyacetone (12.48), mentioned in section 12.8.1 in connection with sulphur dyes, is sulphur-free and biodegradable. This compound was originally proposed for use with vat dyes and continues to generate some interest. This agent can be used for the pad-steam application of vat dyes in the presence of high concentrations of sodium hydroxide (about 3.5-4.5 g/1). Hydroxyacetone does not cause over-reduction of indanthrone vat dyes but does give different shades with carbazole dyes, compared with sodium dithionite [218]. 

Typical waste water analyses and relative costings for sodium dithionite and hydroxyacetone are given in Table 12.35. 

Table 12.35 Continuous dyeing of cotton yarn with indigo using sodium dithionite or hydroxyacetone [212]...

Waste water analysis Sodium dithionite Hydroxyacetone... 

COD values for hydroxyacetone are after treatment in a bioreactor such treatment is not possible with dithionite. 

Tests using indigo have shown that reduction with alkaline hydroxyacetone is most reproducible when the concentrations are as follows [237] ... 

Figure 12.23 Rate of reduction of indigo with and without ultrasound [237], 0.1 g/l Indigo, 40 °C 2.5 ml/l hydroxyacetone 5.0 g/l sodium hydroxide, pH 12.7 0.03 g/l anionic dispersing agent...

In spite of the many reducing systems evaluated or proposed (often quite convincingly), sodium dithionite remains the agent almost universally preferred [242] others such as thiourea dioxide, sulphinates and hydroxyacetone are only used for special purposes. The advantages and disadvantages of the most important reducing agents are summarised in Table 12.38. 

Hydroxyacetone In certain applications dithionite can be replaced by hydroxyacetone (e.g. indigo dyeing)... 

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