2.2- Dimethoxypropane, water

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

Methoxypregna-3,5-dien-20-oned A solution of progesterone (0.3 g) dissolved in 5 ml of 2,2-dimethoxypropane-dimethylformamide (1 1) is treated with p-toluenesulfonic acid monohydrate (8 mg) and 0.1 ml of methanol and then heated under reflux for 3.5 hr. The cooled solution is neutralized with 45 mg of sodium bicarbonate, dissolved in 200 ml of ice water, stirred for 0.5 hr and filtered. The enol ether thus obtained (0.29 g, 92%) is purified by crystallization from acetone-methanol containing a trace of pyridine mp 135-160° [a]o —61° (CHCI3). 

A column which has been deactivated with Wc. / may no longer show adequate separation properties. Restoring the activity of the column by pumping a large volume of dry mobile phase through it is slow and costly. Alternatively, reactivation can be accomplished chemically using the acid-catalyzed reaction between water and 2,2-dimethoxypropane, the products of which, acetone and methanol, are easily eluted from the column [259]. 

Tetrahydro-87/-[l,3]oxazino[3,4- ][l,2]oxazin-8-one 389 (R = H) was dihydroxylated with 0s04 in an NMO/ acetone/water system to obtain 386 after protection of the hydroxyl groups with 2,2-dimethoxypropane <1999TL4391>. 

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. 

In several cases it has proved advantageous to remove water from hydrated salts. In the preparation of PrJ SO complexes of lanthanide nitrates" and Bu"SO complexes of lanthanide perchlorates,12 2,2 -dimethoxypropane and triethyl orthoformate respectively were used as reaction media as 50% solutions in ethanol. 

The majority of the complexes are decomposed by water through ligand displacement, although they are not necessarily sensitive to atmospheric moisture. They are generally prepared by direct addition of the amine TV -oxide to solutions of metal salts in organic solvents. Triethyl orthoformate or 2,2 -dimethoxypropane have often been added to the reaction media as desiccants. 

The common method used for preparing complexes of all these ligands has been the direct reaction between a metal salt and the ligand in a non-aqueous solvent such as an alcohol, acetone or halogenated hydrocarbon, selected according to the solubility of the metal salt. Triethyl orthoformate or 2,2 -dimethoxypropane have been added as an internal desiccant where necessary, because water is a competitive ligand in these systems, and where crystallization was not spontaneous it has been induced by addition of hydrocarbons or diethyl ether. 

Shin and Godber (228) used a silica column and a mobile phase composed mainly of isooctane and small amounts of ethyl acetate, acetic acid, and 2,2-dimethoxypropane. The acetic acid component reduced retention times of the late-eluting E vitamers, presumably by competing with water and polar material for binding to silanol groups on the silica surface. 2,2-Dimethoxy-propane reacts with water to form acetone and methanol, and its inclusion stabilized retention times and reduced the need for column regeneration. Chromatograms of vitamin E vitamers in a standard solution and in a saponified rice bran sample are shown in Fig. 13. 

In contrast to the corresponding palladium system, water is not involved as the oxygen source. In fact it is an inhibitor, and the presence of a dehydrating agent such as 2,2-dimethoxypropane speeds up the reaction. 

Acetals such as dimethoxypropane and diethoxypropane with hydrogen chloride in dioxane extract lignin from wood much more rapidly than methanol, acetone, or water. When the extraction is performed in a Soxhlet extractor, unusually high yields of lignin are obtained. 

A recent procedure for the preparation of methyl esters involves refluxing the carboxylic acid with methanol and 2,2-dimethoxypropane in the presence of toluene-p-sulphonic acid as the catalyst (Expt 5.146). The water produced in the esterification process is effectively removed by acid-catalysed reaction with the ketal to give acetone and methanol. 

In a 500-ml single-necked flask containing a magnetic stirrer bar, place 58.5 g (0.4 mol) of adipic acid, 16 g (20 ml, 0.5 mol) of methanol, 83.2 g (0.8 mol) of 2,2-dimethoxypropane and 0.5 g of toluene-p-sulphonic acid. Fit a reflux condenser to the flask and stir the mixture magnetically for 4 hours in a water bath kept at 45 °C. Rearrange the condenser for distillation and distil off acetone (b.p. 56 °C) and methanol (b.p. 64 °C) on the water bath. Distil the residue under reduced pressure (water pump) and collect the dimethyl adipate, b.p. 130°C/25mmHg. The yield is 54.9 g (79%). 

A. 2-( Bromomethyl)- .-( ehloromethyD-1, -dioxane. A 100-mL, round-bottomed flask is equipped with a 10-mL Dean-Stark apparatus and a condenser. The flask is charged with 30.0 g (0.138 mol) of l-bromo-3-chloro-2,2-dimethoxypropane (Note 1), 10.0 mL (0.138 mol) of 1,3-propanediol (Note 2), and 3 drops of concentrated sulfuric acid. The resulting solution is heated (bath temperature 140°C) for 8 hr (Note 3) with distillative removal of methanol (ca. 11 mL). The mixture is allowed to cool to room temperature and the crude product is partitioned in 150 mL of pentane and 40 mL of water. The... 

Similarly, other ethers, such as l-methoxy-2-methylthioethane, 1-methoxypro-pane, 1,2-dimethoxypropane and 1,3-dimethoxypropane, form water-buried inclusion crystals. In these inclusion crystals, the arrangement of 2 molecules is similar to that of 2 DME H20. All of these inclusion crystals are found to form a zerodimensional L-shaped cavity. In these cavities, the size of the guest molecules is restricted. However, tetrahydrofuran did not give rise to the formation of water-buried inclusion crystals, but preferentially formed inclusion crystals whose channel cavity contained no water [16]. 

Camphorsulphonic acid monohydrate (catalytic amount) was added to a stirred solution of [lR-[la,2a,3 3,4a(R),5a,6a)-3-benzyloxy-5,6-epoxy-4-(l-phenylethoxy)cyclohexane-l,2-diol (0.321 g, 0.9 mmol) in 2,2-dimethoxypropane (10 ml) at RT under argon. After 16 h, the mixture was poured into DCM and washed with aqueous sodium bicarbonate solution and water. The aqueous layers were reextracted with DCM and the combined organic extracts dried (MgS04) and evaporated in vacuum column chromatography (50% ether-petrol) of the residue afforded the title epoxy acetonide (0.317 g, 89%) as needles, m.p. 114°-115°C (recrystallized from ether-petrol) [a]D2°+134.1° (c 1.00, CHCI3). 

Azine approach. 8,8a-Dihydro-l-oxo-l//,3//-oxazolo[4,3-c][l,4]thiazines (265) are available from the corresponding l,4-thiazine-3-carboxylic acids and aldehydes or ketones 2,2-dimethoxypropane with acid catalysis yields the 3,3-dimethyl derivative (265 R=Me), and acetaldehyde with a water absorbent yields the monomethyl derivative as a diastereoisomeric mixture (76JCS(P1)584>. 

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