Hydrolysis 2,2-dimethoxypropane

Epimerization of 50 at C-3 furnished carba-a-DL-allopyranose (60). Stepwise, 0-isopropylidenation of 50 with 2,2-dimethoxypropane afforded compound 56. Ruthenium tetraoxide oxidation of 56 gave the 3-oxo derivative 57, and catalytic hydrogenation over Raney nickel converted 57 into the 3-epimer 58 exclusively. Hydrolysis of 58, and acetylation, provided the pentaacetate 59, which was converted into 60 on hydrolysis. ... 

Dining dehydration of manganese(II) perchlorate [1] or nickel(II) perchlorate [2] with dimethoxypropane, heating above 65°C caused violent explosions, probably involving oxidation by the anion [1] (possibly of the methanol liberated by hydrolysis). Triethyl orthoformate is recommended as a safer dehydrating agent [2] (but methanol would still be liberated). 

Female guinea pigs are immunised by injection of 200 pg of 3/ -hydroxy-5-chole-noyl-thyroglobulin conjugate. Serum extraction, solvolysis and alkaline hydrolysis of BAs are performed according to the method of Ali and Javitt [46] 3.5 ml of 2,2-dimethoxypropane and 0.4 ml of 1 M hydrochloric acid in methanol are added to... 

Addition of 2,2-dimethoxypropane (76) to a solution of 1 in H2O at pH 10 quickly yielded the hydrolysis products (acetone and methanol). To examine the reaction scope, various alkyl acetals and ketals were screened (Table 7.9). The hydrolysis reactions were screened by mild heating (50 °C) of 5 mol.% of 1 with respect to the acetal substrate at pH 10 in H2O. Smaller substrates, which are able to fit into the cavity of 1, are readily hydrolyzed. However, larger substrates, such as 2,2-dimethox-... 

The hydrated chloride, bromide and iodide (Table 9) are soluble in ethanol, butanol and other organic solvents, but in many systems traces of water cause oxidation, hydrolysis or failure to complex with weak donor ligands. Water can be avoided by dissolving the metal in THF, ethanol or diethyl ether through which hydrogen chloride is bubbled.24,74 75 It is also possible to dissolve or suspend in organic solvents the anhydrous acetate or the halides CrX2 (Table 9), and dehydration of the hydrated halides with 2,3-dimethoxypropane in ethanol, followed by vacuum removal of the liquid, produces mixed alcoholates suitable for use in water-free conditions.76 Triethyl orthoformate may be used similarly. 

Although earlier attempts to isolate chromium(II) complexes of various bidentate amines from aqueous solutions produced chromium(III) complexes and hydrogen, the predominantly non-aqueous methods outlined in Scheme 10 provide complexes of ethylenediamine (en), 1,2-diaminopropane (pn), 1,3-diaminopropane (tmd), l,2-diamino-2-methylpropane (dmp), jVjA-dimethylethylenediamine (NNdmn) and N, N -dimethylethylenediamine (NN dmn) (Table 11). In general, ethanol is a suitable solvent but with some amines it is necessary to dehydrate the halide with 2,2-dimethoxypropane (DMP) and dry the ethanol carefully to prevent hydrolysis and oxidation. 

The second example concerns the study of acetonation of o-mannose (see Scheme 8) and allows a clear distinction between the use of 2,2-dimethoxypropane and 2-methoxy-propene. Thus, whereas D-matmose gives 2,3 5,6-di-0-isopropylidene-D-mannofuranose 5 by reaction of the free sugar with acetone [5,6] as well as with 2,2-dimethoxypropane [96], the major compound (more than 85%) obtained with 2-methoxypropene is 4,6-0-isopropylidene-D-mannopyranose 6 [52]. Once again, a confirmation of the better stability of furanoid acetals in this series is given by the selective hydrolysis of the 2,3 4,6-di-O-isopropylidene-D-mannopyranose 7 (by-product of the preceding reaction or quantitatively obtained by action of 2-methoxypropene on acetal 6), witch gives the furanoid monoacetal 8. Actually, the pyranoid monoacetal 9 can be easily prepared as soon as the anomeric hydroxyl group is protected by acetylation [52]. 

Pseudo-cc-DL-allopyranose (61) has been prepared from 54 by epimerization of the C-3 configuration as follows. O-Isopropylidenation of 54 with 2,2-dimethoxypropane gave l,2 4,6-di-0-isopropylidene-pseudo-a-DL-glucopyranose (56). On oxidation with ruthenium tetroxide and sodium metaperiodate, 56 gave the 3-oxo derivative (57), which was converted into l,2 4,6-di-0-isopropylidene-pseudo-a-DL-allopyranose (58) exclusively by catalytic hydrogenation under the presence of Raney nickel. Conven-. tional acetylation of 58 furnished the 3-O-acetyl derivative (59). Hydrolysis of 59 with aqueous acetic acid, followed by acetylation afforded pseudo-a-DL-allopyranose pentaacetate (60), which gave the free pseudo-sugar 61 on usual alkaline hydrolysis [22] (Scheme 13). 

Pipeline Mixers used as Reactors for Fast C/C Reactions. Taylor (1996) and colleagues (1998) conducted a study to determine scale-up procedures for fast C/C reactions in pipeline mixers. They used the fourth Bourne reaction, which is the acid catalyzed hydrolysis of dimethoxypropane (DMP) to acetone and methanol. This is an extremely rapid reaction when catalyzed by HCl. The competitive reaction scheme, which is a unique one, is one in which NaOH reacts practically instantaneously with the HCl to remove the catalyst for the hydrolysis reaction. A water/ethanol solution of NaOH and DMP was fed as a main stream to a Kenics helical element mixer and an aqueous side stream containing slightly greater (abour 5% greater) than equimolar amount of NaOH was fed as the side stream. The product was analyzed by GC for methanol and acetone. For extremely rapid mixing, essentially no hydrolysis occurred however, for slow mixing, essentially all the DMP is hydrolyzed because acidic conditions cause very rapid hydrolysis of the DMP. 

Figure 10.48. Yield of the Dimethoxypropane Hydrolysis Reaction vs Static Mixer Residence Time for three Kenics Helical Element Mixer...

Chemical hydrolysis or solvolysis is the only method available at present to remove sulfate groups from bile acids. It is known that some colonic bacteria possess a sulfatase which can utilize sulfated bile acids as substrate (H24), but this enzyme has not yet been purified. The position of the sulfate moiety in monosulfated bile acids is nearly always at C-3 and this group is easily removed by acid hydrolysis in ethereal solution after removal of glycine or taurine (VI). This method, however, does not remove sulfate groups from C-7 or C-12 (PI). For complete removal, other methods have been described, including solvolysis in acidified methanol-acetone for 18 hours at 37°C (P6), acidified ethyl acetate-ethanol for 16 hours at 39 C (A6), or acidified 2,2-dimethoxypropane for 12 hours at room temperature (C3). 

The 1,2-0-isopropylidene derivative 100, derived from L-sorbose, was also used for the synthesis of 1-deoxynojirimycin (2) (Scheme 19) It was prepared from L-sorbose by reaction with 2,2-dimethoxypropane in the presence of stannous chloride, followed by acid hydrolysis. Selective sulfonylation of the primary hydroxyl group with 2,4,6-triisopropylbenzenesulfonyl chloride (TIBSCl) in a 1 1 mixture of triethylamine and pyridine followed by nncleophilic displacement with azide ion in DMF afforded the 6-azido-... 

Of particular interest for the determination of water content is the use of a liquid reagent such as 2,2-dimethoxypropane, which yields liquid products (acetone and methanol) during hydrolysis [79—81]. To accelerate the hydrolysis it is conducted on a water-bath with heating in the presence of methylsulphuric acid (catalyst). The hydrolysis lasts 1 min. The method was applied to the determination of water in organic solvents and crystal hydrates of salts. 

S,3 S)-83. In the first approach, the functionalization was achieved by reaction of 85 with Br2 to give a mixture of the diastereoisomeric dibromoketones (4S)-87 and (4R)-87, from which, after repeated equilibration/crystallization, the desired c/s-compound (4R)-87 was isolated in 68% yield. Dehydrobromination of (4R)-87 in pyridine gave the monobromo compound 88 from which the dihydroxy compound 89 was obtained by mild hydrolysis with NaHCOa. By treatment of 89 with 2,2-dimethoxypropane, the desired synthon 86 was obtained in a yield of 41 % referred to 85 Scheme 21). 

The selective hydrolysis of acetyl groups, led in methanol in presence of concentrated sulphuric acid, gives the a,P unsaturated methyl ester 13e. Therefore the two hydroxyls at C-3 and at C-4, in sin position each other, are protected by means of formation of isopropylidene function, doing react the methyl ester 13e with 2,2-dimethoxypropane in acetone in presence of catalytic quantity of strongly acidic resin, so obtain the 3,4-O-isopropylidene derivative 13f. 

Competitive neutralization of sodinm hydroxide and acid hydrolysis of 2,2-dimethoxypropane with hydrochloric acid... 

Fourth Acid hydrolysis of 2,2-dimethoxypropane vs. NaOH (Baldyga et al., 1998)... 

Esterification of Amino Acids. Methyl ester hydrochlorides of amino acids have been prepared in which 2,2-dimethoxypropane has been used as the source of the methoxy group, the reaction solvent, and the reagent for the removal of the water formed by virtue of the hydrolysis of the acetal to methanol and acetone. This procedure has also been used to prepare the methyl esters of fatty acids. ... 

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