Glucose, acetals monohydrate

In a 1-1. round-bottomed flask are placed 66 g. (0.33 mole) of glucose monohydrate (Note 1) and 302 g. of 95 per cent acetic anhydride (280 cc., 2.81 moles). To this mixture three small drops of concentrated sulfuric acid are added from a medicine dropper (Note 2). The glucose is kept in partial suspension by shaking the flask with a swirling motion the reaction starts almost immediately. If the temperature of the mixture approaches the boiling point, the flask is momentarily immersed in a pan of cold water. Within ten to fifteen minutes nearly all the glucose will have dissolved and the temperature of the reaction mixture will ha ve risen nearly to 100°. The flask is loosely stoppered and is healed on a steam bath for two hours. Then about 200 cc. of mixed acetic acid and acetic anhydride is removed by distillation under reduced pressure (Note 3). 

Monohydrate, needles from methanol, mp 268 270 [< ] -100 (0,07 g in 10 ml glacial acetic acid) (< ) -87 (0.05 g in pyridine). Practically insol in water and the usual organic solvents. Sol in nitrobenzene, phenol, aniline, pyridine, coned adds and alkalies. The water of crystn cannot be removed at KXT in vacuo Over P,0. (Merz) may be removed at 138 in high vacuum (Zempldn). Hydrolysis gives 5,7-dihydroxy -4 -methoxyflavone, D-glucose, and L-rhamnose. 

Acetobromo-a-D-glucose D-Glucose monohydrate (0.33 mole) is first acetylated with acetic anhydride (280 ml) containing 3 drops of concentrated H2S04, then 200 ml of an acetic acid-anhydride mixture is distilled off, fresh acetic anhydride (60 ml) is added, and HBr (140-160 g) is led in with cooling in ice. The mixture is kept overnight, then HBr, acetic acid, and acetic anhydride are distilled off from a bath at not more than 60° under diminished pressure and finally in an oil-pump vacuum (less than 5 mm) and the residue is recrystallized from diisopropyl ether. 

Alkyl glucopyranosides (alkyl is C, to C 2) can be prepared by direct acetalization of glucose with the appropriate alcohol under proton catalysis. Thus, in the case of 1-0-octyl glucoside the a-isomer can be easily and almost quantitatively obtained as its monohydrate by crystallization followed by recycling of the other product components. ... 

Raman spectra of monosaccharide-derived acetates are highly sensitive to substrate stereochemistry, and have proven useful in the study of specific conformational properties. The f.t. Raman spectrum of a-D-glucose monohydrate has been recorded for the first time and, by incorporating crystallographic and vibrational spectroscopy data, band assignments have been made. ... 

An improved procedure for the direct synthesis of 1,2-Q-isopropylidene-a-D-glucofuranose has been published treatment of D-glucose monohydrate with acetone in the presence of sulphuric acid gave, after filtration of unreacted starting material and neutralisation with NaOH, a product mixture consisting to 83% of the 1,2-acetonide. The contaminants, mainly a- and -D-glucopyranose, were readily removed by firactional crystallisation. D-Glucose has been converted to the synthetically useful diacetonide dimethyl acetal (1) by exposure to 2,2-dimethoxypropane and sulphuric add in methanol. The transformation of compound (1) to 2-azido-2-deo -D-maimose and hence to neuraminic add is covered in Chapter 16. 

---