Glycerol ketalization

To make ketahzation more economical, it is necessaiy to shift the equilibrium toward the product. This can be done by using either substantial quantities of a dehydrating catalyst or a large exeess of acetone. Glycerol ketalization oeeurred with acceptable yields (-80% for 3 hr according to GLC) with a fourfold excess of acetone at 65-75°C. To obtain a signifiant yield of product, the catalyst to substrate mass ratio must be 1 5. 

Synonyms 6-lsopropyl-9-methyl-1,4-dioxaspiro-[4,5]-decane-2-methanol Menthone 1,2-glycerol ketal... 

Menthone 1,2-glycerol ketal. See Menthone glycerin acetal... 

Mixtures of glycerol with other substances are often named as if they were derivatives of glycerol eg, boroglycetides (also called glyceryl borates) are mixtures of boric acid and glycerol. Derivatives, such as acetals, ketals, chlorohydrins, and ethers, can be prepared but are not made commercially, with the exception of polyglycerols. 

Acetonide formation is the most commonly used protection for 1,2- and 1,3-diols. The acetonide has been used extensively in carbohydrate chemistry to mask selectively the hydroxyls of the many different sugars. In preparing ace-tonides of triols, the 1,2-derivative is generally favored over the 1,3-derivative which in turn is favored over the 1,4-derivative, but the extent to which the 1,2-acetonide is favored is dependent upon the structure of the triol. Note that the 1,2-selectivity for the ketal from 3-pentanone is better than that from acetone. Its greater lipophilicity also improves the isolation of the ketals of small alcohols such as glycerol. ... 

Triglycerides are nontoxic, biodegradable and renewable molecules which are being used as substrate for the synthesis of a variety of useful molecules such as glycerol esters, fatty acid alkyl esters, triacetin, ketals, acetals, glycerol carbonates, etc (Scheme 1). 

The volatile components identified from the reaction of cystine and DMHF in aqueous medium are shown in Table I. 2,4-Hexanedione, 3,5-dimethyl-l,2,4-trithiolanes and thiophenes are the major compounds. The mechanistic relationship of the three thiophenones produced has been postulated (23). The major groups of volatile components identified from the reaction in the glycerol medium are 1,3-dioxolanes and thiazoles (Table II). 1,3-Dioxolanes are formed by the reaction of glycerol and the degraded carbonyls by ketal or acetal formations. Comparison of the reaction of cystine and DMHF in water and in glycerol is outlined in Table III. 

The effect of reaction time on the major components of the reaction of cystine and DMHF in water is shown in Table IV. It is noteworthy that amounts of 2,4-hexanedione, 3,5-dimethyl-l,2,4-trithiolanes and thiophenones were found at a maximum after one hour. It was also found that the amount of 2-acetylthiazole increased with time and that acetol acetate decreased with time as expected. In the glycerol medium, the effect of reaction time on the major components is shown in Table V. Apparently, the 1,3-dioxo-lane, which is a ketal formed from glycerol and acetone, decreased over time. Also, long reaction time favors the formation of cyclic compounds, including 2,5-dimethyl-2-hydroxy-3(2H)-thiophene, cyclo-pentenones and 4,5-dimethyl-l,2-dithiolenone. 

DIOXOLANE 2,2-DIMETHYL-4-OXYMETHYL-U-DIOXOELNE DIOXOLANE pOT) GIE GLYCEROLACETONE GLYCEROL DIMETHYL-KETAL 4-HYDROXYMETH X-2,2-DIMETHYL-l,3-DIOXOLANE ISOPROPYLIDENE GLYCEROL l,2-o-ISOPROPYLIDENE GLYCEROL SOLKETAL... 

Isopropylideneglycerol, a five-membered cyclic hydroxy ketal from acetone and glycerol, is prepared in 90% yield by removing the liberated water by an azeotropic distillation. In another procedure, calcium carbide is added directly to the reaction mixture as a desiccant. Acetaldehyde and benzaldehyde, unlike acetone, react with glycerol to form a mixture of the five- and six-membered cyclic hydroxy acetals. Alkoxy acetals are made by the acetalization of a,/3-olefinic aldehydes in weakly acidic solutions however, the addition of alcohol to the double bond may not go to completion. ... 

Ketalization. Conversion of glycerol into the acetonide was accomplished by refluxing and stirring a mixture of the components and catalyst in 300 ml. of petroleum ether (b.p. 35-55°) for 21-36 hrs. under a water separator. The mixture was neutralized with sodium acetate, filtered, evaporated, and the product distilled. CHjOH CHOH... 

A Carboxylic add dialkylamides B Carboxylic add esters C Monopropyleneglycol esters D Glycerol acetals and ketals E Glycerol esters F Glycerol diethers G Glycerol triethers H Fluorinated glycerol diethers... 

Roldan L, Mallada R, Fraile JM, Mayoral JA, Menendez M. Glycerol upgrading by ketalization in a zeohte membrane reactor. Asia Pacific J Chem Eng 2009 4(3) 279-284. 

These compounds have received considerable attention because of their importance in biosynthetic pathways and as precursors for the synthesis of enantiomeric phospholipids (cf. Sections 7.5 and 11.2). There are several procedures which involve blocking the 5n-3-hydroxyl in 1,2-isopropylidene- n-glycerol with various groups, followed by cleavage of the ketal, reacylation with specific fatty acids and then removal of the blocking group (Jensen, 1972). 

Fig. 96. Application of TLC in the control of the synthesis of radioactively labelled chimyl alcohol (a-hexadecyl glycerol ether) from palmitic acid-1[425]. (see reaction scheme above) Layer silica gel G solvent petrol ether (BP 60—70° C)-diethyl ether-acetic acid (80 - - 20 + 1) time of run 1 h autoradiograph. 1 palmitic acid 2 methyl palmitate 3 crude pahnityl alcohol 4 recrystallised palmityl alcohol 5 filtrate from (3) 6 crude palmityl mesylate 7 recrystallised palmityl mesylate 8 filtrate from 6) 9 crude acetone ketal of chimyl alcohol 10 crude chimyl alcohol 11 recrystallised chimyl alcohol 12 filtrate from 10)...

Mesoporous MCM-type materials incorporating aluminum triflate were also considered for the synthesis of solketal, which is an acid-catalyzed reaction of acetone with glycerol, also known as ketalization reaction (Equation (8.50)) [119]. The selectivity to the desired product (solketal) was total, not being affected on varying the various reaction variables. On these catalysts the reaction does not produce other products such as hemiketal or six-membered cyclic ketal. 

Inclusion of acetaldehyde in the reaction may lead to the formation of 2-deoxyribose (5i). However, the reaction tends to stop when the formaldehyde has been consumed and ends with the production of higher C4-C7 sugars that can form cyclic acetals and ketals. The reaction produces all of the epimers and isomers of the small C2-C6 sugars, some of the Cl ones, and various dendroaldoses and dendroketoses, as well as small molecules such as glycerol and pentaerythritol. 

The Chemical Abstracts nomenclature is used for most of the acetals described in this chapter. The compounds are named either as dialkoxy derivatives or as derivatives of acetals or ketals. Confusion exists in the earlier literature on naming cyclic acetals. For example, the acetals prepared from glycerol and an aldehyde were at one time referred to as 1,2- or 1,3-alkylidene (or arylidene) glycerol however, today they are named as shown below ... 

Mota, C.J.A., Da Silva, C.X.A., Rosenbach Jr., N., Costa, J., Da Silva, F., 2010. Glycerin derivatives as fuel additives the addition of glycerol/acetone ketal (solketal) in gasolines. Energy Fuels 24, 2733—2736. 

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